STFC-RAL-Pickavance R22: To the special like around lecture given by Professor Kevin Mcfarman
STFC-RAL-Pickavance R22: from Rochester University and the University of Geneva.
STFC-RAL-Pickavance R22: so we'll have 1 h presentation. And then, followed by half an hour of coffee, tea, and questions just outside.
STFC-RAL-Pickavance R22: So Professor Mcfarlane received his Phd. From the University of Chicago in 1994,
STFC-RAL-Pickavance R22: and as a young researcher he followed originals Korea time.
STFC-RAL-Pickavance R22: and received many grants and awards.
STFC-RAL-Pickavance R22: He became a letterman fellowship at Formula.
STFC-RAL-Pickavance R22: Then
STFC-RAL-Pickavance R22: Was promoted to assistant professor in 2,002, and became a professor in 2,005.
STFC-RAL-Pickavance R22: He's a fellow of the American Physical Society since 2,005 again. And currently.
STFC-RAL-Pickavance R22: he's working on the T. 2 K. Experiment at J. Park in Japan and at Icarus, and the dune experiments at formula
STFC-RAL-Pickavance R22: with his T. 2 K. Collaborators. He's a recipient of the breakthrough prize in fundamental physics in 2,015
STFC-RAL-Pickavance R22: his research interests are in the field of experimental high energy physics and his primary study is in the
STFC-RAL-Pickavance R22: field of neutrino properties and weak interactions.
STFC-RAL-Pickavance R22: So today we are pleased to welcome Professor Mcfarland and
STFC-RAL-Pickavance R22: his lecture on looking for electrons in all the wrong places over to you.
STFC-RAL-Pickavance R22: Okay, good. Can you hear me? Well enough? Great.
STFC-RAL-Pickavance R22: Okay. So my purpose today is to tell you a little bit about an experiment that we ran for almost a couple decades, as you'll see at Fermilab, called the Minerva Experiment, and one of the features of this experiment is that it ended up with very high statistics. Neutrino samples. So as a result, one of the things we can do with the data that we have is we can look for processes that are
STFC-RAL-Pickavance R22: very much subleading
STFC-RAL-Pickavance R22: at in in this beam, and try to make sense of them. And so that's the lecture today is is looking for the presence of electrons. So
STFC-RAL-Pickavance R22: very briefly, because I I don't know how many of you work on neutrino physics. I will have a little
STFC-RAL-Pickavance R22: overview. Actually, does everybody here work on neutrino physics? No? Okay? Good.
STFC-RAL-Pickavance R22: Then then it's worthwhile. So the the big purpose, right? The reason we're building a number of neutrino experiments, and that these facilities, like the one that this experiment
STFC-RAL-Pickavance R22: ran at exist. And the reason for these studies fundamentally is, we're trying to do neutrino interferometry. So the idea is that you start with a neutrino of a given flavor so associated with a charge current weak interaction that produces also a muon. You have a muon neutrino.
STFC-RAL-Pickavance R22: that neutrino may or may not be in nature. In fact, we know, is not in nature a single mass. Eigenstate. It's a mixture of mass eigenstates put together. And so when you produce that neutrino, you produce different mass, eigenstates, they evolve
STFC-RAL-Pickavance R22: somewhat differently in space, according to the time dependent Schrodinger equation, and they pick up relative phases for each of the different mass eigenstates, even if produced with the same momentum, because they will all have slightly different energies, so that phenomenon leads to an evolution of the flavor properties. If you project from the mass space back to the flavor space
STFC-RAL-Pickavance R22: of the neutrino beam over time. So you can start with a beam, for example, of electron neutrinos. Sorry, because over the beam of muon neutrinos. In this example it becomes an electron neutrino, and then can oscillate back to a muon neutrino, and so on and so forth.
STFC-RAL-Pickavance R22: And so this allows us the possibility that we can measure how the different mass components make up the flavors, how those are related to each other, and it gives us the possibility that we can measure the masses of the neutrinos. In fact, it's the only non
STFC-RAL-Pickavance R22: 0 result test that that says that neutrinos have any masses associated with them at all.
STFC-RAL-Pickavance R22: So one of the strange things about this field, I'm telling you we're doing experiments at accelerator. But one of the strange things about this field is that because of some number of lucky parameters, we actually made the original discoveries in this field 25 ish years ago.
STFC-RAL-Pickavance R22: using neutrinos from natural sources, so from the sun and from cosmic rays. And it just so happened that the pattern of neutrino masses and mixings were such that those signals were very, very large. In those experiments you could see nearly 50% of the neutrinos changing flavor over some average.
STFC-RAL-Pickavance R22: and so that allowed for what? Well, at the time it didn't feel fast, I can assure you, but it allowed for a relatively quick and a relatively easy discovery of these phenomena.
STFC-RAL-Pickavance R22: So the challenge in front of us is to try to learn more about these phenomena. So we know things like, for example, from those natural source experiments that there's 2 different mass differences, but we don't know the ordering of those masses. There may be 2 light and one heavy, or there may be 2 heavy and one light. For example.
STFC-RAL-Pickavance R22: we know that some of the mixings are large, some of them are somewhat less large, without, say, without going into any detail that's represented by the small bluish fraction of one of the things of jelly beans up there, illustrating the mixtures of
STFC-RAL-Pickavance R22: of flavors inside each mass eigenstate but one of the things that may happen in nature. When you have 3 states, we know in analogy with the Ckm matrix that you can have a Cp violating phase. And so one of the things that's possible is that there's a matter antimatter, asymmetry also
STFC-RAL-Pickavance R22: in the mixing of the Lepton system, and that may in principle be related to matter and human asymmetries that exist in the universe, which, of course, are very large. Otherwise.
STFC-RAL-Pickavance R22: you know, you might get a lecture from Antimatter Kevin, and that would end disastrously, differently, disastrously than this one will end. But, anyway, so what are the measurements that we want to do so the transitions that we want to study precisely in future experiments are few percent flavor transitions. And we want to make measurements. That sort of schematically look like this.
STFC-RAL-Pickavance R22: If we're looking for Cp violation, it's helpful to measure Neutrinos and Antineutrinos separately, and there are 2 main effects, one of which comes from this ordering of the masses, and the way that the neutrinos interact with the matter as they go from the source to the detector in the experiment over a long distance, and that separates the 2 different colors of ellipses here, and then you also want to measure where you are
STFC-RAL-Pickavance R22: on that ellipse, because that gives sensitivity to the Cp violating parameter delta. So the idea is to make some moderately precise measurements of these relatively small mixing parameters, using neutrinos, which are, of course, very difficult to work with, because
STFC-RAL-Pickavance R22: they hardly ever interact. And there are some other challenges that I'll mention in this talk. And if you want to read more about the work of Minerva. It's all about what those challenges are. Essentially
STFC-RAL-Pickavance R22: so. The idea is that we have this tool for discovery. If we can just make these precision measurements of neutrino in neutrino interferometry we can look for Cp violation. In Leptons. We can look for symmetries in the patterns of masses and mixings. And this is a compelling future science program that's making us want to build some big experiments
STFC-RAL-Pickavance R22: and to do that, we have to make these precise measurements of neutrino flavor transitions. So the experiments that are being built look like this. This is one that's called the T to hyperk, or just the hyperk experiment. So the idea is to take the successful T decay experiment, which took a beam of neutrinos from the east coast of Japan to near the west coast of Japan in a big water detector under a mountain
STFC-RAL-Pickavance R22: and scale it up, make a bigger detector run the accelerator hopefully, a little more than it runs now and run it at higher intensity, and basically try to repeat that experiment which has a little bit of a hint of this matter. Antimatter asymmetry and try to do it with overwhelming statistics. So that's 1 of the approaches.
STFC-RAL-Pickavance R22: A different approach is the dune experiment which is being built in the Us. The source is a new beam at Fermilab. The detector is a new detector underground in a mine in South Dakota. This is actually a smaller detector than a hyperk detector, which is a somewhat unusual choice. But the reason for doing that is to build a detector that is very precisely sensitive to all the ionization for neutrino interactions
STFC-RAL-Pickavance R22: and to give it more capabilities to resolve things like the energy and the flavor of the neutrinos. So that's the those are the 2 main
STFC-RAL-Pickavance R22: main ideas. And just to make the point about what it is that you're measuring up here. Well, I guess it's on both sides, isn't it? I was going to say on my right, your left. But you can take your pick is a plot of the dune neutrino spectrum, and superimposed in it, for some different choices of parameters are the probabilities for neutrino oscillations. Actually do. I have a pointer?
STFC-RAL-Pickavance R22: Don't know if there's 1 here. Maybe I don't really need one. It'll be fun. So you can see different curves there. And one of the things to notice is that the oscillations, the flavor transitions occur actually different energies. So it isn't just a simple counting experiment the way I made it look in that original slide. It's actually measuring transition probability as a function of energy. Okay.
STFC-RAL-Pickavance R22: So these experiments, as I mentioned before, are done, taking a beam of muon neutrinos and looking for them, appearing as electron neutrinos. And remember, this is a seminar about electrons, if you can remember, back all the way to my title slide. So the idea is we have to make some number of measurements of electron neutrinos, but we have a problem in doing so.
STFC-RAL-Pickavance R22: So the accelerator experiments that we build that make the Gev energy beams that allow us to study. These oscillations are almost entirely muon neutrino beams. That's good in a sense, because it means that if we're looking for electron neutrinos. There's not a big background. But it's bad because it doesn't actually let us study the interactions of electron neutrinos. And you might say, okay.
STFC-RAL-Pickavance R22: flavor, universality standard model. What am I actually worrying about? It turns out I'm worried about a couple things great. It's that. Okay.
STFC-RAL-Pickavance R22: wonderful. I'm worried about a couple of things. So one of them is that the muon on the scale of a gev neutrino is actually a fairly massive object. And so what that means is that if you look, for example, in a space of
STFC-RAL-Pickavance R22: yeah.
STFC-RAL-Pickavance R22: well, okay, if you look in a space of momentum and energy transfer, there's simply a bunch of space that isn't there
STFC-RAL-Pickavance R22: for the muon neutrinos, that is, for the electron neutrinos. So if all you study are the muon neutrinos, you never have access to that, and you never get a clean measurement. And so you're doing some sort of theoretical extrapolation in the rates. There are other things that come in there are potentially different nuclear effects exacerbated by this problem.
STFC-RAL-Pickavance R22: And there are radiative corrections that are different because the Lepton masses are very different. So all those things come into effect. And you're basically relying on theory unless you can make a measurement.
STFC-RAL-Pickavance R22: So part of the idea of this is to ask, what sorts of measurements can we do in an experiment like Minerva?
STFC-RAL-Pickavance R22: So I should tell you about the Minerva experiment that I've alluded to, and and what it is that it was about and what we were trying to do.
STFC-RAL-Pickavance R22: So Minerva was an interaction experiment. So it was designed to study neutrino interactions, not neutrino interferometry, not neutrino oscillations, and it ran for about a decade at Fermilab, mostly in the 2,010 s. And the design was fairly simple it was, build a relatively capable cheap detector. Put it as close as possible to the world's highest rate. Gev neutrino source and
STFC-RAL-Pickavance R22: just measure a lot of interactions and a couple of other features that aren't so important for this talk are that we actually put several different nuclei, several different nuclear targets in the experiment, so we could measure the nuclear effects that disrupt things like energy reconstruction, and so on. But that again, not the point of today's story.
STFC-RAL-Pickavance R22: So one signature of the experiment that is important for today's story is that because we were relatively large, I mean not by neutrino experiment standards, but many tons of target material experiment, and because we were so close to the source we had enormous, we have enormous neutrino samples to work with many millions of events, and that is unusual in neutrino experiments.
STFC-RAL-Pickavance R22: Okay.
STFC-RAL-Pickavance R22: so I don't mean to discourage any of the younger people in the audience, but but sometimes it takes a while to do these experiments. And there's a couple of reasons that I want to make a point about the history. So this, this.
STFC-RAL-Pickavance R22: yeah, I appreciated the reference to my young career, I guess, in my young career, which probably isn't anymore. One of the things I did is, I wrote the expression of interest for what eventually became this experiment. I wrote it in 2,002, and this timeline goes out a couple of decades before we get to the peak of publishing the bulk of our data.
STFC-RAL-Pickavance R22: and it took us a while to build the experiment. Neutrinos take a long time to accumulate a detector like this, and so on and so forth. So there was a lot going on.
STFC-RAL-Pickavance R22: One of the things that happened along the way is a lot happened in neutrino science in interferometry, and then that helped us to set and understand our goals. So at the time we designed this experiment, we didn't actually think that a precision new Mu to New E experiment was all that important? Necessarily, I mean, maybe it would be. But we didn't know
STFC-RAL-Pickavance R22: we didn't know what experiments would become important, but because of work beyond the original discovery. Phase, like work from the Minos experiment, T decay nova, the reactor measurement of the theta, 1 3 mixing angles, so on and so forth. The importance and the goals became far more clear in the experiment, so that in the end we were able to.
STFC-RAL-Pickavance R22: You know, as as these goals became more and more clear sort of tune, what our objectives were, and that's what what led to this work just on a personal note. Lots of other things happened over a decade. So this is my youngest child, my daughter, at the time of the Eli, and she's now a music teacher in an elementary school in the Washington DC area. So you know, stuff happens.
STFC-RAL-Pickavance R22: Okay, so what's the cheap detector that we built that we put so close to the beam. It's basically a big chunk of scintillator with some calorimetry on the outside, and some of the calorimetry will become important later, so I'll mention it. Calorimetry is very simple. It was
STFC-RAL-Pickavance R22: just lead sheets in between planes of scintillator. And it's it's a relatively simple scintillator. Bar. It's read out with vacuum photo multipliers. We kind of missed the solid State revolution by about a year, as we were doing the construction planning, but
STFC-RAL-Pickavance R22: is what it is, and you know just a very straightforward detector design, but again fairly big and sitting close to this very intense beam, remember, in a neutrino experiment. You're trying to capture everything you can get. The interactions just occur anywhere inside this detector. So we're focusing on events that have electrons in their final state. A lot of them are
STFC-RAL-Pickavance R22: fairly in the forward direction. And so we're looking for the interactions of those electrons in the scintillator which then spill into the electromagnetic calorimeter. If you knew where the interaction was. This isn't the detector that you would build, of course, to build, to measure an electromagnetic final state. But you need the target material mixed in. So it's a somewhat suboptimal detector in the, you know. If you're doing a collider experiment, you wouldn't design this. Let's put it that way.
STFC-RAL-Pickavance R22: Okay, that detector, as I say, ran until 2019. It's it's mostly in trash cans. Hopefully, it ends up. It's mostly polystyrene. So hopefully. It ended up in takeout food containers and lawn furniture and things like that. Some of it got recycled for tests for the dune experiment.
STFC-RAL-Pickavance R22: The beam that we sat in is a conventional neutrino beam, meaning it's produced by protons striking a target, making primarily pions which decay to muon neutrinos. That's why it's predominantly a muon neutrino source. And we ran in a couple of different beams with different focusing configurations to give us different energies, so that another useful thing about the experiment.
STFC-RAL-Pickavance R22: Okay? So I promised to talk about electrons. Actually, is there a clock clock? Okay? Fantastic.
STFC-RAL-Pickavance R22: So I promise to talk about electrons. So what gives you electrons in a primarily muon neutrino beam? Well, it's either the beam or the target right? So the target, of course, has electrons. The problem with the reaction on the target electrons is that it has a very small cross section. It's about a part in 10 to the 4 compared to the cross section on the carbon nuclei in the scintillator. So
STFC-RAL-Pickavance R22: fine. That's that's 1 thing that you could look for. But you have to have the expectation that it will be a rare reaction.
STFC-RAL-Pickavance R22: The other thing that's true is that that beam when it produces neutrinos, muon neutrinos from pion decay. It also produces muons in that pion decay, and those Muons themselves can decay, and they make a roughly 1% component of the neutrino beam at low energies. There are other processes that dominate at high energies
STFC-RAL-Pickavance R22: think about the lower energies of the beam.
STFC-RAL-Pickavance R22: And so we get also electrons from that source
STFC-RAL-Pickavance R22: right? So here. Sorry I didn't need to go back. So here, in fact, is the spectrum of electrons from that source. So it's sitting here at a little bit lower energy than the dominant muon neutrinos. By the way, I should add, this beam was run in 2 configurations, either focusing positive or negative pions, therefore giving you neutrinos or Antineutrinos, and we chose between the 2, and took a lot of statistics in both.
STFC-RAL-Pickavance R22: Now, of course, because this is relatively rare, you could imagine that there might be other things that are going on. People have imagined there might be other things going on. So if you made electrons or photons, generally speaking, you would find them in these samples, even if they were made by exotic processes. And there are ideas about how that might be useful. Remember, we're taking an enormous number of protons.
STFC-RAL-Pickavance R22: slamming them into a target. We could be making all sorts of things. The conventional mesons that are made could decay into exotic things, and so on and so forth.
STFC-RAL-Pickavance R22: So maybe this is a fruitful place to go looking for things like that.
STFC-RAL-Pickavance R22: Okay, so if we're looking for electrons, how do we go about doing that? So electron showers which have slightly obscured in this diagram, which is perhaps not optimal. Anyway, electron showers basically look like a cone of energy that's not consistent with a minimum ionizing particle.
STFC-RAL-Pickavance R22: leaving a single head as it goes. So they spread out a little bit in the plastic. Those same showers will, of course, tick up when they get to the electromagnetic calorimeter and start leaving more and more energy. And so it basically just looks like a splashy, wide, fat track.
STFC-RAL-Pickavance R22: but very easy to distinguish from a muon. That's not a big challenge for the experiment. What's more of a challenge is that you produce a lot more neutral pions than you do. Electrons in a neutrino beam like this, made from muon neutrinos. And so those neutral pions, of course, also decay to photons which look very similar to electrons, and you have to have some way to separate them.
STFC-RAL-Pickavance R22: You separate them by looking at the energy deposit right at the start of the shower. If it's a single electron, you'd expect a peak if it's from a pair conversion you expect a peak at roughly twice that energy. So in principle, that's relatively straightforward, there are a couple of complications, actually, 3 of which I want to point out on this plot. So one is that the electrons here in orange in this simulation
STFC-RAL-Pickavance R22: spill over from the peak over to here. That happens because the electrons start showering
STFC-RAL-Pickavance R22: right. And so if it starts showering, it's going to have more energy deposit near its start. And that just happens sometimes. That's how nature is. Another thing that happens is you have photons sitting here that end up under the electron peak. Why does that happen? Photon goes to E plus e minus pair sometimes. That can be a very asymmetric pair. All the energy can go to an electron or a positron.
STFC-RAL-Pickavance R22: almost all. And so you get this happening. And again, there's nothing you can do about that. Every detector has that's trying to do. This sort of experiment has this problem to one degree or another.
STFC-RAL-Pickavance R22: So so we always have to deal with the backgrounds. Then the other thing you might notice about this plot, which is a little bit weird, is here's data. There are error bars on this data. But I told you Minerva had overwhelming statistics. And here's our simulation prediction sort of out of the box. And they're in terrible agreement. Okay, so that was one of our early mysteries as we started doing this. And I'll come back to that that mystery. Actually, I'll come back to it very quickly.
STFC-RAL-Pickavance R22: so so here's the the way that we do the separation. And you can see again. You know, it's it's not even close. So what's going on? It turns out that there were some processes which are essentially, it's a very weird process. It's a, it's a
STFC-RAL-Pickavance R22: process that's either coherent on nuclei or can happen on protons. It's effectively a diffractive like production where the neutrino comes in, it emits a W. Boson. In this case this is the charge current, but in a neutral current it would be a z boson, that boson, that weak boson in the field of whatever the target is without disrupting that thing
STFC-RAL-Pickavance R22: converts itself into a quark antiquark pair which appears as a high energy pion
STFC-RAL-Pickavance R22: it. I usually use the analogy that it's like shooting a bullet at a bubble, and it turns into a flower or something like that. Right? The kinematics seem very weird, but it's actually comparable in rate, especially at high energies to the electron producing processes. So which might be surprising. But it turns out that's the way nature is.
STFC-RAL-Pickavance R22: And what was going on in our original attempts to measure. This was essentially that we had a terrible model for that process, and so we struggled for a while as an experiment to understand what was going on, and as I'll come back to the end, if there's time, it turns out that this process just was not well modeled at high energies at all. So we had to go and basically measure it and and try to figure out how to account for that.
STFC-RAL-Pickavance R22: Okay, so what I want to run through are a series of measurements in some degree of detail, one of which is is completely new, actually have not shown this to any audience at all. It's in preliminary form. So the lucky few in the audience will get to be the 1st and very much interested in feedback, because there's some weird stuff.
STFC-RAL-Pickavance R22: all right. So neutrino electron elastic scattering. So this is something that one of my students decided on a lark to go try to do I, as a terrible advisor, tried very much to dissuade him from doing this, and failed, and it turned out to be a great measurement.
STFC-RAL-Pickavance R22: So what's the idea. The idea is that if you measure neutrino electron elastic scattering, it gives you a unique window into the flux of neutrinos in your experiment, because you know what the reaction is, you can calculate it in the standard model. It's 2 fundamental fermions scattering off of each other. There's nothing really unknown. It's predicted to a fraction of a percent.
STFC-RAL-Pickavance R22: But what is not known are the number of neutrinos that create that reaction. So by measuring it, the concept is that you can measure the flux of neutrinos.
STFC-RAL-Pickavance R22: And so the way that this analysis goes is fairly simple. It's 1 of these fat tracks from an electromagnetic shower that you have. That looks something like this, except because of the kinematics. It has to be going dead forward. There's not much chance to exchange a lot of momentum with that electron.
STFC-RAL-Pickavance R22: right? And so because it's going dead forward, it's much easier to to deal with the backgrounds. When we started looking at this I I again thought this was completely hopeless, but these are the final results
STFC-RAL-Pickavance R22: for the experiment. The signal process is in the red and also the light blue here, depending on the flavor of neutrino, the type of neutrino that's creating the reaction. And you see, if we just look in this angle variable. Yes, there are some backgrounds. But there's a huge peak
STFC-RAL-Pickavance R22: of this process. And so we demonstrated that this was actually a viable technique for constraining, for constraining the flux. Here's the same picture now in this variable Ddx that I described before, same one as before, and you can see the
STFC-RAL-Pickavance R22: of the Photon peak cleanly separated from the electron peak. This one is going to look a little nicer than when I start looking more inclusively at electrons being produced. But but you get the idea.
STFC-RAL-Pickavance R22: So we were able to measure the spectrum of these electrons. That gives us a very significant flux constraint, and in the end, what we were able to do was to take our uncertainties in our flux and reduce them quite significantly through these measurements. So these were the a priori uncertainties in the antineutrino beam.
STFC-RAL-Pickavance R22: Here it is after significantly reduced. Similarly, in the neutrino beam to the point where these measurements are giving us a sort of 4 to 5% constraint on the number of neutrinos. They also told us something that we weren't expecting, but is probably consistent with the uncertainties with which we could predict our flux a priori, which is that the flux is about 10% lower than we thought it should be
STFC-RAL-Pickavance R22: 10 to 15.
STFC-RAL-Pickavance R22: So that was not necessarily something that we expected to come out of this. So this technique is very useful for high energy neutrino experiments generally. So it actually turns out that it's part of the backbone of the way that dune will understand its flux is by making exactly this measurement, and we've thought about what the statistics are which will be yet again higher in the future dune experiment. And so it ends up being very valuable.
STFC-RAL-Pickavance R22: And so this was one of these little engineering things that we did. But it was our 1st foray into electrons.
STFC-RAL-Pickavance R22: So okay, so then, you know, like, like always happens, you have some moderate success. And you think, Oh, I'll just keep going, and this is how we, you know, get
STFC-RAL-Pickavance R22: Oh, I'll pick a random example, you know. Rock bands from the seventies continuing to perform today. So but anyway, so we went on, and we thought, well, if we can do this, probably we can do more general interactions of the electron neutrinos. And maybe we can do it fairly. Precisely so. The next story I'll tell you is about doing those measurements.
STFC-RAL-Pickavance R22: Let me sorry. Skip ahead there. So again, a reminder, we're looking at about a 1% flux component. And so the idea is that you use these same algorithms that I talked about to identify the electrons. You look at the backgrounds the best you can with sidebands you have. I didn't emphasize it, but you have a little component of Antineutrinos in the neutrino beam and neutrinos in the Antineutrino beam that you have to deal with.
STFC-RAL-Pickavance R22: but you can use the measurement of one beam to subtract that component in the other, based on the prediction. So you do that you can then measure the cross sections of those electron neutrinos, and importantly.
STFC-RAL-Pickavance R22: because you're trying to ask the question, is it the same as the muon neutrino? Can I shed any light on this problem I mentioned before you want to take the ratio, but you want to do that accounting for the different fluxes. So this is the physics fairly ambitious physics program that we set out to do. And I'll
STFC-RAL-Pickavance R22: give you some highlights from that program. So again, fundamentally, the background subtraction comes about because you're looking for this separation in Ddx
STFC-RAL-Pickavance R22: and the photon backgrounds kind of fall into 2 categories. One would be ones where a bunch of other things are produced in association with the pi 0. But the others are from these diffractive or coherent processes that I mentioned before, and so the idea was to separate them
STFC-RAL-Pickavance R22: and to use that predictive power.
STFC-RAL-Pickavance R22: So what's shown here is a function of the transverse momentum of the electron, because now it's not just going dead forward, it can have some some scattering angles and transverse momentum.
STFC-RAL-Pickavance R22: And this is in one of our beams are different sidebands, different regions before any tuning is done, and I already telegraphed the reason that this agreement is terrible is that we have a bad prediction effectively for the coherent and diffractive processes off of hydrogen and carbon.
STFC-RAL-Pickavance R22: So these are 2 selections for the hydrogen and carbon, and then this is the incoherent production. The signal component, by the way, is the orange shown here, so the signal component continues also to be a complication.
STFC-RAL-Pickavance R22: But basically, we use these sidebands to tune the background. You can see that the the agreement was absolutely terrible. We were having to increase things. This this green component we ended up having to increase by about a factor of 4 or 5, because the model was just completely wrong about the production. But you can see that we were able to get a good description of the sideband data with essentially tuning the reactions to to what we observe.
STFC-RAL-Pickavance R22: And so this is the signal. It's certainly not background free. It's sort of one to one in the neutrino sample, and maybe 2 to one in the Antineutrino sample, but because of those sidebands we can get a fairly reasonable prediction for the backgrounds. Okay.
STFC-RAL-Pickavance R22: I mentioned the wrong species problem. So the neutrino beam has this little bit of Antineutrinos. The Antineutrino beam has a larger bit of neutrinos. Again, because we measure in the 2 beams simultaneously. We can just
STFC-RAL-Pickavance R22: effectively convolve those 2 together, based on the flux prediction and make the separation.
STFC-RAL-Pickavance R22: And so here are the details of that which I I won't run through.
STFC-RAL-Pickavance R22: So in the end we're able to make the measurement. This is on a log Y scale here, as a function of
STFC-RAL-Pickavance R22: how much other visible energy there is in the detector so things like protons and pions that are produced, we measure as a function of that visible energy in different bins of the transverse momentum. So this is getting a little wonky. But the point is, we're trying to probe the space of interactions, visible momentum. You see that we're able to measure a cross section with some fairly decent precision. Here.
STFC-RAL-Pickavance R22: One of the features of this cross section is has a peak at 0.
STFC-RAL-Pickavance R22: That peak at 0 in the antineutrino beam is because one of the dominant reactions is antineutrino comes in, takes a proton either in the hydrogen in the target or the carbon in the target turns it into a neutron. And you get an electron in the final state. So that has 0 energy other than the electron, and therefore gives you this peak here. And you can see relative to this model that's been tuned on muon neutrinos.
STFC-RAL-Pickavance R22: It is at least in reasonable qualitative agreement, and we did the same thing in our neutrino beam that doesn't have this peak at 0. So not shown on a log scale. So you get an idea of how well we can do this.
STFC-RAL-Pickavance R22: Okay, the important thing to do from here, as I said, is, we want to know the question, is there any difference that we can see in the muon neutrino and electron neutrino cross sections? So the logical thing is to take the ratio to the well measured, very high statistics, muon neutrino cross sections, but easier said than done because the fluxes are somewhat different of the 2. And so you have to decide how you're going to account for that.
STFC-RAL-Pickavance R22: So here is the ratio of the electron neutrino flux to the muon neutrino flux as a function of energy, and you can see it has a highly non-trivial shape here. It averages at about 1%. The peak of the beam is here.
STFC-RAL-Pickavance R22: but on the tails, you get a proportionately larger electron component. So this presents some challenges. Right? If you're going to try to correct for this in particular energy smearing. You know you don't perfectly measure the neutrino energy. That's kind of one of the points of our experiment is that you don't
STFC-RAL-Pickavance R22: perfectly measured neutrino energy, certainly not in a model, independent way. And you can see these slopes are actually quite large. The advantage is we're making a measurement that integrates all over all the flux. So some of these effects become a little bit more manageable.
STFC-RAL-Pickavance R22: But we realized pretty quickly, because this has some model dependence. We were going to have to take 2 different approaches, so one of which is to just try it and accept the fact that we have a little bit of model dependence. And the other thing to do is to just not correct the ratios for the flux, and just show flux integrated ratios to different fluxes, so that becomes a little more difficult to interpret in a raw way. You have to do some
STFC-RAL-Pickavance R22: some more work to understand what the data is telling you but we ended up doing both. And I I'll
STFC-RAL-Pickavance R22: I I think it's probably best if I just gloss over some of the details and show the results.
STFC-RAL-Pickavance R22: So here is the flux, corrected ratio, where we've taken our prediction for the electron and muon neutrinos. And we've made that correction. So the answer should be very close to one. The Monte Carlo is incredibly confident that the answer should be one. If you look at the air bars here with very tiny errors.
STFC-RAL-Pickavance R22: we have fairly small uncertainties. There's some significant. There's some significant
STFC-RAL-Pickavance R22: excuse me, systematics to worry about. But you can see that we're actually in the realm of probing this at the few percent level, which is great, and the agreement, again, is qualitatively good. There are, you know, some little things you might
STFC-RAL-Pickavance R22: look at carefully. Is there anything going on here? Is there anything going on here? But it's it's not dramatically far off, right? So you might think that that maybe we've we've basically confirmed that the 2 cross sections are similar.
STFC-RAL-Pickavance R22: We've done the same thing with the unweighted result that I told you about here. Of course, the the flux ratio is about 1%. So the value comes in at 1%. What happens here is that you get much smaller experimental uncertainties, because you're not building in these model dependent effects. But again, it's a little bit harder to interpret, and I'll leave the data to speak for itself as to whether there's anything that isn't consistent with the simulation. Not evidently, anyway.
STFC-RAL-Pickavance R22: And again, we did the same thing for Antineutrinos with very similar results, although here there's something a little bit different. So we're calling the Antineutrinos. The cross section is much higher, near 0, visible energy. These points here. And so you get larger uncertainties just from statistics out here. But one of the features is that, especially at this low momentum, there's actually a little starting to be a little bit of a hint of a discrepancy here.
STFC-RAL-Pickavance R22: and that would be much easier to see in the Antineutrinos than it would be in the Neutrinos. So I think it's the sort of thing that once this data is published, we'll go back with models. We'll try to see if any of the ways that the cross sections could be different might be consistent with the little hints that we're seeing.
STFC-RAL-Pickavance R22: Another thing you might notice about this, though, by the way, is that on average, these are maybe just a little bit higher than one than you might have expected.
STFC-RAL-Pickavance R22: So and I'll come back to that point in just a minute.
STFC-RAL-Pickavance R22: All right. So that's essentially the the bread and butter physics that we wanted to do. And then again, you know, is that that rock star that started in the seventies was maybe still going okay through the nineties. Gets up to the 2,010 s. Wants to keep going, you think? Oh, what else could we do with this sample?
STFC-RAL-Pickavance R22: What else could you do with this sample?
STFC-RAL-Pickavance R22: If you had a lot of electron neutrinos, a lot of muon neutrinos, and a prediction of what they are. Hmm!
STFC-RAL-Pickavance R22: Well, you could go looking for neutrino oscillations, couldn't you? But unfortunately, neutrino Minerva is a single detector experiment. Right? So in a typical neutrino oscillation experiment, you take your neutrino beam, you measure it in a new detector, you let it oscillate, and you look for the oscillations between the 2 detectors.
STFC-RAL-Pickavance R22: We don't have anything like that, right? So
STFC-RAL-Pickavance R22: the working title of our paper for this, by the way, is why you should never do a 1 detector oscillation experiment. We'll see if the editors of Prl like that.
STFC-RAL-Pickavance R22: Okay, so what's the what's the idea? Well, the idea is to take the same data that I just described, and to look at it as a function of energy. If that's all we were doing, that would actually be a little bit boring. So let me explain why it's not completely crazy to try to do this, maybe only moderately crazy.
STFC-RAL-Pickavance R22: We have a bunch of samples that I've shown you that are actually kind of interesting for this measurement. So one of them is, you have a sample of neutrino electron scattering events, right, which have really no interaction uncertainties. So they're purely sensitive to the flux.
STFC-RAL-Pickavance R22: We also can make very high statistics, samples, certainly, compared to competitor experiments, millions of events, of the tens of millions actually of the muon neutrinos, and
STFC-RAL-Pickavance R22: many tens of thousands of the electron neutrinos. And so so we end up with very high statistics. But one of the things you can do is, you can actually.
STFC-RAL-Pickavance R22: you know, consider the ratio of those 2 things.
STFC-RAL-Pickavance R22: So that would be. Another way to get away from uncertainties and neutrino interactions is to take that ratio. So what would oscillations do in an experiment like Minerva? Well, if you had new mu to new E flavor transition in nature. It would make a much bigger impact on the very small electron sample than it would on the very large Muon sample, and then it would do something in between for the neutrino electron scattering sample.
STFC-RAL-Pickavance R22: If your neutrinos were disappearing into some sterile state, you know. Then you just see disappearance in your samples, at whatever level nature tells you.
STFC-RAL-Pickavance R22: And there's sort of a funny thing we're actually sensitive to oscillations, to tau neutrinos. And that's because tau neutrinos appear in this neutrino electron scattering cross section. But we're not very sensitive to tau neutrinos, because we only have a couple 1,000 of those neutrino electron scattering events. But that's sort of a weird curiosity.
STFC-RAL-Pickavance R22: So I probably shouldn't bore you with this. But maybe maybe just to show this. So one of the things, I'll explain it. So one of the things that is true about the electrons and the Muons is they're actually not produced at the same point in the beam line.
STFC-RAL-Pickavance R22: So picture of the beam line
STFC-RAL-Pickavance R22: here, right is pions are produced here. They're focused. There's a long decay pipe the pions predominantly decay here near the beginning.
STFC-RAL-Pickavance R22: The Muons, of course, are very long lived. They predominantly end up in the beam dump and don't decay, but the ones that do decay that make neutrinos that you see are coming from the downstream part.
STFC-RAL-Pickavance R22: so the distance that they travel and the oscillation effects go as L over E, the distance that they travel is actually different. So one of the slightly weird things about this experiment, if you do it as an oscillation experiment. And, let's say, take a look at this one for Delta M squared, of 10 electron volts, squared the muon neutrino oscillations and the electron neutrino oscillations are just completely different.
STFC-RAL-Pickavance R22: By the way, one thing to notice about this, there is wiggly oscillation behavior here, but it's kind of muted. And one reason that it's muted in this prediction is that the neutrinos are being produced all along this beam line. So it's a range of different l's, so that's sort of the nature of what we can do on the experiment.
STFC-RAL-Pickavance R22: The analysis proceeds in very much the same way as what I just described. We, you know, use Ddx to to separate them. The other thing that we do is to get away from interaction systematics. We restrict the sample
STFC-RAL-Pickavance R22: to a relatively small amount of other things in the neutrino interaction. So we're looking for the events that look pretty elastic because their cross sections are better known.
STFC-RAL-Pickavance R22: And then we want to get rid of the neutrino electron scattering thing that I just crowed about right? Because that makes a background. So we require some transverse momentum. And really, that's the only cuts in the experiment.
STFC-RAL-Pickavance R22: So here are the D Dx curves
STFC-RAL-Pickavance R22: in this oscillation search. They look very much like what you've seen before. They have a little bit now of the pre-tuning baked into them, but not much, and so you can see the 2 samples, the forward and the neutrino dominant, and the anti-neutrino dominant samples. The electrons are sitting here so backgrounds, but not uncontrollable backgrounds, and we use again the same technique
STFC-RAL-Pickavance R22: of the Dedx to to control it.
STFC-RAL-Pickavance R22: So here's what this looks like as the 1st time for the 1st time as a function of energy.
STFC-RAL-Pickavance R22: So what's shown here are the different samples for different energies. Now this is very low energy. This is where we don't really expect to see very many events at all. Certainly. No.
STFC-RAL-Pickavance R22: we don't have neutrinos here, basically. And so you see, nice, pretty well described photon contributions. But none of the orange electron contributions. As you march up in energy. You start to see more and more of the electron contributions, and then at high energies, electrons completely dominate because you don't make very many pi zeros.
STFC-RAL-Pickavance R22: So as we vary in energy. One kind of undesirable feature. If you're doing an oscillation experiment is that the signal? The background changes a lot, right? So something we have to be conscious of when we do our measurement.
STFC-RAL-Pickavance R22: Okay?
STFC-RAL-Pickavance R22: So again, a reminder of the samples, neutrino electron scattering. And then these 2 samples, the very high statistics, muon neutrinos, and the electron neutrinos that we could consider in a ratio that we're going to use.
STFC-RAL-Pickavance R22: All right. So you are the 1st audience to see this. Here's what we see.
STFC-RAL-Pickavance R22: So here's our neutrino electron scattering sample
STFC-RAL-Pickavance R22: this is our muon neutrino sample. That exponent is 10 to the 6. So we have, as I said, a lot of neutrinos here.
STFC-RAL-Pickavance R22: Here. Sorry muon neutrino sample. Here's the electron neutrino sample, and here's the ratio of the muon to electron neutrinos, and I'm deliberately not showing you things in ratio plots between the data and simulation. Yet there are ratio plots here, but they're actually the Antineutrino to neutrino dominant beam. And then the flavor ratios shown over here.
STFC-RAL-Pickavance R22: Okay. So if you stared at that, you could start to see some things that don't look like awesome agreements. I can highlight them for you if you don't like the eye test. So one of them is that there is sort of a level disagreement here, and a little bit of something that looks kind of like wiggliness in the muon neutrinos.
STFC-RAL-Pickavance R22: So that is there.
STFC-RAL-Pickavance R22: The electron neutrinos are kind of interesting. So look at the prediction of the simulation here, and look at the data.
STFC-RAL-Pickavance R22: and there's a very, you know, good agreement here. But at the lower energies there's actually quite a large excess on this falling edge.
STFC-RAL-Pickavance R22: Everyone should be very suspicious of an excess and a falling edge. Right?
STFC-RAL-Pickavance R22: But it's there in the data. Can't really deny that. And then, if you take the ratios here which have different falling edges for the muon and electron neutrinos. Again, something to be aware of. This ratio is the new mu over nu e. You can see now this excess gets transformed into a deficit, because this is in the denominator, and it really is there in the ratio. It's not, doesn't go away.
STFC-RAL-Pickavance R22: So what do the systematics look like? So things like the difference in the level here have very large systematics associated with them, the Neutrinos, the Antineutrinos, and the Muons.
STFC-RAL-Pickavance R22: and similarly here. But these flavor ratios that I showed you actually have quite small systematics, particularly at the lower energy. And that's because there are cancellations both in the flux and the interaction uncertainties and one of the other things is that the double ratio here has particularly low systematics
STFC-RAL-Pickavance R22: for what it's worth.
STFC-RAL-Pickavance R22: Okay?
STFC-RAL-Pickavance R22: So I should finish within like 5, 10 min at most. Yeah.
STFC-RAL-Pickavance R22: so this is the point where one should emphasize that we've been careful. Okay, so what are the sorts of things that you were worried about your systematic uncertainties. Well, certainly, Flux, we better have treated that correctly. If we're doing an oscillation experiment, the electron identification, we probably should figure out a way to test that. And then the electromagnetic okay, magnetic energy scale. We probably better get that right because we're looking at an excess and a falling edge.
STFC-RAL-Pickavance R22: So this is to assure you that we've we've done our homework, and I'll go a little bit quickly.
STFC-RAL-Pickavance R22: So one of the reasons that we look at the flavor ratios so carefully is that the way that you produce the muon neutrinos and the way you produce the electron neutrinos are very closely related to each other.
STFC-RAL-Pickavance R22: This pion makes a muon of a certain energy right and a neutrino of a certain energy, and then you get the 3 body muon decay.
STFC-RAL-Pickavance R22: These are very similar energies for the muon and electron neutrino on average. So it's really the same particles that are producing those neutrinos.
STFC-RAL-Pickavance R22: And that's why, if you look at all the ensembles, we use a multi-universe method for our flux estimation. It's not worth detailing, but you get very large uncertainties in the raw fluxes. But then, in this ratio of new mu to New E, the uncertainties collapse very significantly because of these correlations.
STFC-RAL-Pickavance R22: so as far as we can tell that should be pretty solid.
STFC-RAL-Pickavance R22: You might worry a lot about this subtraction. So, for example, how do I know that the photons that are asymmetric pair production to give you low Dedx are accurately predicted. It turns out to be really difficult, even despite what they told you about the rareness to find an electron free sample to do this on that doesn't also have other particles on top of your neutral pion.
STFC-RAL-Pickavance R22: So the sample that we found are very weird events. They have very high angle muons, they produce a pi 0, and almost nothing else.
STFC-RAL-Pickavance R22: That's not a super common topology. If you're looking for multi gev pi zeros. Right?
STFC-RAL-Pickavance R22: So we did go looking for those. And fortunately Minerva has, as I've said before, overwhelming statistics. So here's our sample. The red is the background we're looking for. The electrons are the orange and the blue. These are things that are neither. They're not electromagnetic. They're typically pi pluses that shower in the detector and then give you neutral pions in the shower right? But
STFC-RAL-Pickavance R22: bye.
STFC-RAL-Pickavance R22: so so here's that sample. And if you look at the Ddx spectrum. It's fine, right, and within our within our systematic uncertainties this is a perfectly good description.
STFC-RAL-Pickavance R22: The one thing about this is that it's a better test at lower energies. So this is up to 5 gev. Say, than it is at higher energies. Because you just run out of these events. They're very, very rare to produce a high energy pi 0, and nothing else in a charge. Current event with a wide angle just doesn't happen.
STFC-RAL-Pickavance R22: But this is where the backgrounds are biggest.
STFC-RAL-Pickavance R22: So you know, we, we evaluate ourselves as having passed that test.
STFC-RAL-Pickavance R22: Then the last thing is the electromagnetic energy scale. So one of the things we see is that we're wrong on a falling edge. If we had the energy scale wrong, we just shift the prediction done no problem.
STFC-RAL-Pickavance R22: So fortunately, we have a lot of neutral pions, and we can form the 2 photon invariant mass peak from where we resolve both photons in the Pi 0 decay.
STFC-RAL-Pickavance R22: So here's sort of what you might think that Mask Peak would look like. Here's what it actually looks like, and there's a couple of reasons why it looks like this. So this terrible long tail is mostly because it turns out that plastic doesn't make a very good electromagnetic calorimeter.
STFC-RAL-Pickavance R22: right or plastic. Then followed by plastic interspersed plastic scintillator with lead or traditional calorimeter. It gives you all sorts of horrible nonlinearities. It's not really optimal for measuring it. And your resolutions aren't good. So that's just how it is. But if you look in the data and simulation on this high end tail and near the peak, it's actually very good.
STFC-RAL-Pickavance R22: This is a different matter. So the agreement here is not perfect. But actually, what's going on here are 2 things. If you produce the pi 0 at a very large angle, which is a physics model dependent question.
STFC-RAL-Pickavance R22: Then the photons go out the side of the detector sometimes and aren't cleanly captured
STFC-RAL-Pickavance R22: the other thing that happens. And again, it's correlated with the kinematics of the pi. 0 is that sometimes you swap energy from one photon to another, and if you do that, you ship the mass peak lower.
STFC-RAL-Pickavance R22: So if we look within our systematic uncertainties, we believe these little differences here are pretty well explained, and this is the one that's reliable. And in, you know, really a probe of detector resolution.
STFC-RAL-Pickavance R22: So as far as we can tell, it works. We've divided the sample up in energy the best we can. We run out of statistics at high energy again. And you know the data, Monte Carlo agreement between the true Pi 0 Mass Peak, and where our peak sits. I mean, there are some nonlinearities here, but they're well modeled by the Monte Carlo as far as we can tell.
STFC-RAL-Pickavance R22: And then the last part of this is that we have these 2 parts of the detector, the plastic tracker, and the calorimeter, and we have to check that. The energy scale is the same in the different parts of the detector, and we actually found we made a mistake here. We miscalibrated it.
STFC-RAL-Pickavance R22: but we miscalibrated it in data in Monte Carlo in exactly the same way. So here is a fraction of the tracker energy. The data in Monte Carlo, and they're not at one. It's not flat, but they sit on top of each other, so we're not going to go back and correct it. But it looks okay.
STFC-RAL-Pickavance R22: And the sorts of uncertainties that we're applying right now are 2% on what I've shown you. These blue bars are 1% scale uncertainties for these 2 effects, the overall uncertainty, and then the extra uncertainty in the calorimeter.
STFC-RAL-Pickavance R22: everything's covered. I mean, this, this doesn't seem to be a problem.
STFC-RAL-Pickavance R22: So so the next thing you might ask is, I've shown you these little hints.
STFC-RAL-Pickavance R22: and I'll wrap up quickly. Is any of this evidence of short baseline oscillations.
STFC-RAL-Pickavance R22: We don't think it is
STFC-RAL-Pickavance R22: so. Here's what the data looks like once you remove. So we, the way we actually do this is, we parameterize our flux uncertainties, and we actually do a fit. We profile over those uncertainties. And then we have the remainder of the uncertainties due to interactions and detector energy scale and things like that.
STFC-RAL-Pickavance R22: So here are the muon neutrino events, the the electron neutrino electron scattering with no uncertainties now, because we profiled out. The flux are here.
STFC-RAL-Pickavance R22: These are fine. Now, you notice, of course, there's a big difference in the level here between the neutrinos and the bars disappeared. Oh, well, between the Neutrinos and the Antineutrinos that are here. But that's completely consistent with the interaction uncertainties. There's no problem at all with that.
STFC-RAL-Pickavance R22: But here's this persistent effect that remains a little bit outside the air bar. Well, quite a bit outside the air bar, actually, of these extra low energy electron neutrinos. So these are the muon to electron neutrino ratio, and you can see low energy is here. High energy is here that this is a low energy effect. Now, when you try to fit it with oscillations in a standard picture where they should have an L over E dependence
STFC-RAL-Pickavance R22: they don't fit. It doesn't look like it has a 1 over E dependence at all.
STFC-RAL-Pickavance R22: so this would be the best fit to oscillations. It's very low, Delta M squared and crazily large mixing angles. But it still doesn't really improve the description of the data.
STFC-RAL-Pickavance R22: So there's no evidence that we can see that we're seeing oscillations. But we also have no idea what this is.
STFC-RAL-Pickavance R22: this low energy excess of electron neutrinos.
STFC-RAL-Pickavance R22: So you can go through the usual step of setting limits. I won't spend a lot of time boring you with those. I'll note one thing. Our limits in some cases are a little bit better than you would expect, and one of the reasons is that this excess of electron neutrinos means that you significantly favor a disfavor, a disappearance of electron neutrinos because you have some extra ones.
STFC-RAL-Pickavance R22: So our sensitivity and our limits don't match perfectly at all values of Delta M squared. But that's how it is when you have a little unexplained fluctuation in your data. So this is in different panels. We're sensitive to all sorts of mixing angles.
STFC-RAL-Pickavance R22: In a 3 plus one scenario. Different panels of Mu Mu 4 is our limit shown here in Ue 4 space versus delta M squared, and then another way to show it in our limits. The blue Whoa! I need to say one thing about this. So this curve is actually a new limit from the Catrine experiments. I don't know if anybody saw this paper it appeared within maybe the last couple of months
STFC-RAL-Pickavance R22: but but the limit curve that we put here we weren't quite sure which of their curves to use. They have one that assumes that the there is no
STFC-RAL-Pickavance R22: primary effect from the Catherine experiment, which is looking for a neutrino mass and beta decay. And that's the curve we picked. Probably the one we should pick is the one that's a little more ecumenical about what might be causing it, because oscillations would cause a cancellation that actually makes this lobe sitting here go away. For the most part it kind of just
STFC-RAL-Pickavance R22: fades off in that direction. So Catherine will absolutely win at high Delta M squared. But we have a region where we actually do a pretty nice job of ruling out some parameter space, probably all to ourselves. Here's the same thing in some fixed slices of Delta M squared. Now it's the electron mixing angle and the muon mixing angle. This, by the way, for comparison is a recent measurement by microburn, so high statistics are helpful.
STFC-RAL-Pickavance R22: All right.
STFC-RAL-Pickavance R22: I don't have time for my last topic, although I've referred to it, so I'll skip to it and just come to my conclusions. So we've measured a bunch of processes, kind of had fun doing it with electrons in the final state where really you shouldn't expect a lot of electrons from a mu one neutrino beam.
STFC-RAL-Pickavance R22: We've prototyped this flux constraint method with neutrino electron scattering for dune, and I think, been quite successful. We have some interesting results. When we compare electron neutrinos to muon neutrinos.
STFC-RAL-Pickavance R22: we interpret it 1st as a cross section measurement, and that's something that should appear in publication fairly soon. And it's really the 1st precise measurement anybody has done. And then I led you down a little garden path that we've gone on thinking about some nonstandard explanations, and whether there's anything in our data
STFC-RAL-Pickavance R22: and hit the low energies, we find something we don't understand.
STFC-RAL-Pickavance R22: And then finally, I've talked a little bit about these interesting backgrounds that we had. There's actually some physics there to explore that I'll put in the slides. If you end up posting them. We don't have time to go through them today, but that's been an interesting adventure as well, so I hope you've enjoyed our little trip through electromagnetic final states where you shouldn't have any electromagnetic final states. Thanks for your attention.
STFC-RAL-Pickavance R22: Thank you very much for fascinating talk. We? Now open the floor for any questions here in the room or on zoom? We are. Please ask your questions in the question, and answer.
STFC-RAL-Pickavance R22: or raise your hand, Johnson. Yes, still be there.
STFC-RAL-Pickavance R22: A fascinating talk. I'm a mudslinging peasant when it comes to this. Yeah sling, please. That's why I'm showing you this? No, no. So for separating, is it possible to use time of flight measurements for separating?
STFC-RAL-Pickavance R22: electron immune neutrinos, just so that you know
STFC-RAL-Pickavance R22: there's a clear distinction. Yeah. So the the masses involved are far too small, unfortunately, in fact,
STFC-RAL-Pickavance R22: if if well, okay. So so 1st of all, that it would be decomposition into different mass. Eigenstates would give you the the different propagation speeds. And what would actually happen? I showed you this picture of the coherent
STFC-RAL-Pickavance R22: you know, staying as one wave packet, the phase separation. If you actually had a time of flight difference and they spatially separated, then obviously that interference effect would just go away. You'd be looking at pure mass, eigenstates. Now you would see a change in flavor
STFC-RAL-Pickavance R22: from that. So if if if the masses are actually high enough.
STFC-RAL-Pickavance R22: you could see such a thing. But the problem is, we have a gev many gev neutrino beam, so those masses would have to be
STFC-RAL-Pickavance R22: many tens or more of a of Mega electron volts, not probably a a
STFC-RAL-Pickavance R22: parameter space that we're so interested in. But I will tell you it is something that we've thought about, and the beam has a little Rf structure, and you can actually go look to see if anything fills in that Rf structure that suggests something might be going a little bit slowly. That would probably be the most
STFC-RAL-Pickavance R22: That would be the stronger test.
STFC-RAL-Pickavance R22: Wish we had another army of people to work on the Minerva data, we might get that one.
STFC-RAL-Pickavance R22: Yeah, thank you for the talk. This was lovely.
STFC-RAL-Pickavance R22: this is perhaps quite an ignorant question on regards to the the nutrient oscillation stuff, because you're right in the sense of doing it with one detector seems but the new Me beam has quite a few detectors in it. Is there any way that you can use some of the other detectors to improve your measurement.
STFC-RAL-Pickavance R22: Yeah, it's it's a good question. So
STFC-RAL-Pickavance R22: I and I haven't thought very hard about that. So the way in which you would do that is, you'd look at detectors that are different angles, right? So you might try to compare electron neutrino rates at Minerva and Nova, and even Icarus, which is very far off, Axis, and try to do something with that.
STFC-RAL-Pickavance R22: I think it's a really intriguing idea. I I haven't thought through how that would work. Certainly the precision cancellations that we have would not be a thing in in that type of analysis. But if you're looking for a large effect.
STFC-RAL-Pickavance R22: you you might be able to find it with something like that. It's really it's a good idea, and we should try to figure out some way to do that seems hard. And one thing we'll do with this data is we'll release it in the rawest form we can, you know. Here's our prediction of the flux. Here are all our uncertainties. Here's all the data. Have fun with it, and it would be great if somebody picked up a project like that. Because I agree, that's a, that's a really interesting test.
STFC-RAL-Pickavance R22: Cool? Thank you. Yeah.
STFC-RAL-Pickavance R22: Yeah. So you coming to your electron excess, low energy, the one of the things you were testing was the Ddx Yup, and I was just left wondering whether there could be processes involving a muon and a proton
STFC-RAL-Pickavance R22: didn't appear to be in your your diagram.
STFC-RAL-Pickavance R22: Say say more right. Muon and proton and
STFC-RAL-Pickavance R22: neon and proton are not very much else. I mean, you can take a proton. Oh, well, we have. That's our dominant reaction. Right? We we have, we have many, many of those events. The proton is very unlikely to look like an energetic well, a couple of things. So 1st of all, the the spectrum of those knocked out protons
STFC-RAL-Pickavance R22: is fairly low energy, the the kinetic energies that you get sort of end because the form factor falls off at maybe 500. Mev, they're they're basically gone. And we're looking for many Gev
STFC-RAL-Pickavance R22: products. So at at those energies. If you're if it's some hadron, it's doesn't really matter what, Hadron. It is. Any strongly interacting thing that's a Gev can make a neutral pion along the way as it goes through our detector, right doesn't really matter. It's any any particle. And so when I showed
STFC-RAL-Pickavance R22: the predictions for that sample that looked like
STFC-RAL-Pickavance R22: basically everybody, everything went to sleep.
STFC-RAL-Pickavance R22: Yeah.
STFC-RAL-Pickavance R22: So so I showed this this sample here. This was the test, the Dedx, that black background, right? So that's all things. It's mostly pi pluses, but it could as well be protons contributing all things that produce a pi 0 and some secondary interaction end up there, and the Ddx is confused sometimes because it's something that's not ionizing very much. And then it produces this pi 0. Sometimes there's a gap.
STFC-RAL-Pickavance R22: Yeah, so it doesn't. It doesn't do a great job of reconstructing those. So you know, that's that's probably the biggest caveat. And I was being directly confusing the proton for yeah, but we just don't that. The way that we would do it is is to go through the production of Pi 0, or just have some showery thing. Maybe it could be shower a mini pi
STFC-RAL-Pickavance R22: many pi pluses and minuses produced as well it it it just. We don't produce single high energy particles that would easily be confused except by that mechanism of making the pi zeros.
STFC-RAL-Pickavance R22: Because we're we're, you know, we're looking at multi Gv things
STFC-RAL-Pickavance R22: okay and sorry, since since I've got the microphone, the next slide where you were trying to argue that the the pi 0 energy resolution energy calibration was good. I didn't really understand you. You demonstrate that the low energy tail is not well reconstructed. And is that a problem for your low energy?
STFC-RAL-Pickavance R22: Again, we don't. We don't think so. So. The thing I don't have on this is a clear demonstration of what the systematic uncertainty effects are. But what dominates that tale for the for the most part is as I said.
STFC-RAL-Pickavance R22: You know things where where energy goes out the side, and that's not
STFC-RAL-Pickavance R22: what we're seeing in these events, because we force them to be in the detector. But it's a good point, right? We could just take a know nothing approach and say, what if that
STFC-RAL-Pickavance R22: right? What if? What if we had a tail? We weren't modeling? It looked exactly like that. Throw it in as a systematic. It's actually, it's a really good idea. We should probably just do it. We're quite confident it's not gonna matter. But we should just do it.
STFC-RAL-Pickavance R22: It's a good idea. Thank you.
STFC-RAL-Pickavance R22: I'm obviously workshopping this. This was all a bit of a surprise when we started looking at it a couple of months ago.
STFC-RAL-Pickavance R22: Any questions.
STFC-RAL-Pickavance R22: Okay? Yeah, we are short on time, maybe just one last question. So yeah, we are curious what your reviewers would comment as well. And sorry for dinner. Is there a success? So you found some interesting.
STFC-RAL-Pickavance R22: is there a successor? Yeah. So there's a couple of ways to answer that question. So all this data that I showed you is from one of the 2, the higher energy beam. At Minerva we have a lower statistics, but not low statistics sample of lower energy neutrinos. So we are absolutely going to. And we're in the process of reproducing this analysis with that beam.
STFC-RAL-Pickavance R22: And so we'll see that being peaks in exactly the region of our low energy excess.
STFC-RAL-Pickavance R22: I don't, I don't. We haven't looked. We don't know. I don't know what it looks like. But clearly, that's a study we should do
STFC-RAL-Pickavance R22: you know. So so dune can definitely do this
STFC-RAL-Pickavance R22: right? It can look for these electron neutrinos. See if there's any distortion of the spectrum. And importantly, it can kind of do the study that we were just discussing right? It can look at the detector in different locations, because one of the dune strategies is to move its detector, its near detector off axis and change the spectrum. So that's a that's probably the best test I can think of of what this is, and then finally, the the
STFC-RAL-Pickavance R22: the the bnd, the booster neutrino beam beam line at Fermilab
STFC-RAL-Pickavance R22: has made measurements of this will continue to make measurements of this.
STFC-RAL-Pickavance R22: I will point out that I didn't invent the term. Low energy excess in this field that's often used to describe the result of the Miniboon experiment. In fact, I started using low energy excess for our stuff basically to tease my graduate students when this result appeared.
STFC-RAL-Pickavance R22: So I I guess maybe the experiments already been done
STFC-RAL-Pickavance R22: so. But but Dune should be able to knock this out of the park. I mean that that really would be a great test.
STFC-RAL-Pickavance R22: Okay, thank you very much, for everyone joined the send the lecture today. Let's close now, thank you.