STFC-RAL-CR03 R61: Okay, welcome to the seminar. We are very grateful that Mary accepted our invitation. Let me start with a short introduction.
STFC-RAL-CR03 R61: She studied physics with theoretical physics at the University of Manchester, and completed a master's degree in 2021. She did her PhD in particle… in experimental particle physics at the University of Edinburgh.
STFC-RAL-CR03 R61: with the LHCB group, where she was awarded an Institute of Physics IOP Bel-Barnell Scholarship, and completed in 2025. Now she's a postdoc in the high-energy physics group at Cavendish Laboratory.
STFC-RAL-CR03 R61: And is studying rare particle physics, the case with the OHCB detector.
STFC-RAL-CR03 R61: Her research focuses on the studies of decays of B mesoms into a pair of neurons, which allows precise testing of the standard model and sensitivity to beyond the standard model of physics.
STFC-RAL-CR03 R61: Okay, over to you, and let's… well…
STFC-RAL-CR03 R61: Thank you very much for the introduction, it's really nice to be back here. I've been here a couple of times before, so it's nice to be here. So I'm going to be talking about Charmless B2B decays, specifically the decays of B sub S and B0 to 5x5. And if you don't know what that means now, hopefully you'll know what it means soon, and you'll realize why they're interesting.
STFC-RAL-CR03 R61: So I'm going to talk about what these cameras B2B BDKs are, and why we should care about them, which is going to talk about the Standard Model and its shortcomings, CP violation in the Standard Model, and something called the polarization puzzle, which is a bit curious.
STFC-RAL-CR03 R61: To do that, I'm then going to talk about the LHCB experiment, which is best suited for studying these types of decays, and then go on to this specific analysis of B sub S and V0 sub 5 phi.
STFC-RAL-CR03 R61: which is measuring CP by an agent in BS divided by, and also performing a search for B0s of 5x5. So this is a recent result, this is what I spent most of my PhD doing. And then, I'll wrap up with a bit of status and roadmap.
STFC-RAL-CR03 R61: So, probably you've seen this diagram before, but the standard model of particle physics describes the fundamental particles, how they interact with one another, and
STFC-RAL-CR03 R61: On the whole, it works very well to explain a lot of natural phenomena, and it's been probed in exquisite detail for decades. It's some of the biggest experiments, but there are still several things it can't explain.
STFC-RAL-CR03 R61: Those things are that the universe is made entirely of matter, so we believe, but we also believe that they were… that matter and antimatter were produced in equal amounts. So the question is, where did that antimatter go? And the answer is, still something to be understood.
STFC-RAL-CR03 R61: Another thing is, what is dark matter? We know that dark matter must be there from things like studying galactic rotation curves, and another thing is, neutrinos, do they have mass, which is not accounted for in the standard model? And are they myurana particles? Are neutrinos their own antiparticles? So these are some of the big questions
STFC-RAL-CR03 R61: In the standard model. And the one that I care about the most is this asymmetry in matter and antimatter.
STFC-RAL-CR03 R61: So, how is it that we can generate this asymmetry in matter-antimatter? And there are three conditions that were derived by Sakharov, and that we… to generate this matter-antimatter asymmetry, we need baryon number violation.
STFC-RAL-CR03 R61: We need the violation of charge and charge parity symmetries, and we also need for the universe to move away from thermal equilibrium. So, what I'm going to be talking about is, how we get CP violation from the standard model.
STFC-RAL-CR03 R61: So, this is going to be a bit of a scary slide with a matrix on it. But essentially, the CP violation in the standard model comes from this matrix called the CKM matrix.
STFC-RAL-CR03 R61: Where we have the quark, flavor states, so the states of flavor, mixed with each other, because the mass states and the flavor eigenstates are not the same.
STFC-RAL-CR03 R61: So, this CKM matrix connects the different quark flavors. So, you can see here, we've got up, down, charm, strange, top and bottom. Each of these elements, is a number that connects, for this, for example, here, up to down, which is nearly, nearly 1.
STFC-RAL-CR03 R61: And then this is an approximately diagonal matrix, where it's basically one all along here, but we have non-zero contributions here, so you can have swapping between the quiet generations. You can go, connect up with strange, up with bottom, for example, and that's determined by this matrix.
STFC-RAL-CR03 R61: And where we get this charge parity violation in the standard model is that this matrix has the complex phase in it.
STFC-RAL-CR03 R61: So we can study this matrix, so it's a unitary matrix.
STFC-RAL-CR03 R61: And because it's a unitary matrix, you can write what we call the unitarity relations, which are these, sums over these individual elements.
STFC-RAL-CR03 R61: And if you write these relations, you can also represent those as triangles in the complex plane. So here, I've drawn what is commonly referred to as the CKM triangle, but there are multiple triangles depending on which of these elements you choose. So this one has a PUB, BCD,
STFC-RAL-CR03 R61: and VTD, VTB, and then you can see that this is a closed triangle with, 3 angles alpha, gamma, and beta.
STFC-RAL-CR03 R61: So, the CP violation that we've measured in the standard model by probing these triangles is currently not enough to explain what we believe the observed dosymmetry to be. It's not explained by standard model CP violation. So, we want to search for additional sources of CP violation that could be coming from beyond standard model physics.
STFC-RAL-CR03 R61: And our goal is to measure these triangles, and if we can over-constrain the standard model parameters, we can look for an inconsistency that might be coming from very high-scale new physics, that could… might affect one mode and not the other. So, for example, you might have some new physics that looks something like this.
STFC-RAL-CR03 R61: So, how do we measure these triangles? This is the triangle that I'd drawn, before, this, what we call vertices KM triangle, but then we've got this other triangle that doesn't really look like a triangle, but I promise you that it is. This is what we sort of commonly refer to as the B0 triangle, and then this one on the right is the BS triangle.
STFC-RAL-CR03 R61: So this angle beta, we can probe by studying decays of B0 mesins to JXIK short.
STFC-RAL-CR03 R61: we can get this angle gamma, typically in B decays, to charm.
STFC-RAL-CR03 R61: And then on this, BS triangle, we get this angle B to S from decay's BS to JSI Phi. This is what we call one of our golden modes for LHCB.
STFC-RAL-CR03 R61: So, BS to JSI phi, okay, so J psi is a, charm onlyium, so charm anti-charm, and a phi is typically, SS bar.
STFC-RAL-CR03 R61: So, BS to JS side, phi decays, we can measure this CP-violated phase that I'm going to call 5SCC bar S. You're going to understand why I called it that in a moment. But this relates to the BS triangle that I showed on the previous slide, and this angle V to S, and this is, this CP-violated phase is minus 2V to S.
STFC-RAL-CR03 R61: Now, roughly where that comes from is if you consider the Feynman diagrams that describe the process. So, you have, this process of the decay, so this is a decay that happens at what we call tree level.
STFC-RAL-CR03 R61: Meaning there's no loop is in there.
STFC-RAL-CR03 R61: And we get… at this vertex, we've got a B, an anti-B and an anti-charm, so that's a BCB. At this one, we've got a, charm and a stranger, so that's BCS.
STFC-RAL-CR03 R61: Now, the other thing that you can have in neutral mesons is that they can mix with one another.
STFC-RAL-CR03 R61: So, in a BS mechanism, we've got an anti-V quark and an S quark. Now, if you draw this, rather complicated box diagram, you can end up with an anti-S and a B quark, which is basically the antimatter swap.
STFC-RAL-CR03 R61: of what we had before. So this is called mixing. So you have a BS changing into a BS bar, and that happens at some frequency. So you have these oscillations of
STFC-RAL-CR03 R61: These neutral beam essence.
STFC-RAL-CR03 R61: So if you consider these two contributions to this, this decay happening, you can, look at the CKM angles that come into it, so these ones I've highlighted in blue, and work out that the,
STFC-RAL-CR03 R61: that this CP violating phase C, by SCC bar S is minus 2 meter S.
STFC-RAL-CR03 R61: Now, what I'm going to do is I'm going to take that charm away.
STFC-RAL-CR03 R61: And now we have, instead of an CC bar, we've got an SS bar, so now we've got two phi's.
STFC-RAL-CR03 R61: So this is, BS550, and this is a decay that can only happen at penguin level. You don't get this tree-level contribution, you have to have a loop in there somewhere, so that's this bit here. And we call it a penguin, because this is a… what we call a penguin diagram.
STFC-RAL-CR03 R61: And there's a way that you can draw this that makes it look a bit like Penguin, but I think that's a little bit far-fetched.
STFC-RAL-CR03 R61: But I'm gonna call it that anyway. Now, if we compare with what we had before, we've got this,
STFC-RAL-CR03 R61: BCB and VCS here.
STFC-RAL-CR03 R61: Now we've got a loop, and primarily you get top barks in these loops.
STFC-RAL-CR03 R61: So we've got VCB and VCS, and then the exact same mixing diagram here. So what we have now is nearly complete cancellation of these elements that end up in these diagrams.
STFC-RAL-CR03 R61: So, this CP violating phase, which is 5SS bar S, we got rid of the charm, is approximately zero in the standard model. This makes it an excellent probe beyond the standard model physics, because any non-zero CP violation here would be
STFC-RAL-CR03 R61: Resulting from beyond SAM model.
STFC-RAL-CR03 R61: So both of these things are what we call mixing-induced CP violation. You can have CP violation in decay, where you measure directly the rates of different processes, for example, if you have a B+, and then a B-. But this is known as indirect CP violation, where you start with some neutral mes on M,
STFC-RAL-CR03 R61: which could decay to final state F, but it could mix to its anti-meson state before it then decays to F.
STFC-RAL-CR03 R61: So, these types of decays, what we need to do is a flavor-tagged, time-dependent analysis. So, what does that mean? Flavor tagging is, depending on which experiment you're on means different things, but in this context, I mean, was it a BS or a BS bulk to start with? What… was that B quark in there? A B quark or an anti-B quark?
STFC-RAL-CR03 R61: We have to do.
STFC-RAL-CR03 R61: a time-dependent analysis here, because this mixing is encoded in the decay time distributions. As the mesons, evolve in time, that's when they swap between their different, M or M-bar. So, in order to probe this CP-violating phase, we need to know about flavor, and we need to do it in a time-dependent way.
STFC-RAL-CR03 R61: The other thing with this is, to get this phenomenon, you need for this final state F to be accessible to both M and M bar.
STFC-RAL-CR03 R61: So, BS5i is just one example of a Chalmers V to BVV decay, where V is a vector meson.
STFC-RAL-CR03 R61: So that… this is a class of decays where you can have a decay of a B meson, any one of these, to a charm-free vector meson. So,
STFC-RAL-CR03 R61: the vector measure on, I think I've got it written on one of these slides, is,
STFC-RAL-CR03 R61: If it's got a spin.
STFC-RAL-CR03 R61: warm.
STFC-RAL-CR03 R61: So there are many of these combinations of decays. There's lots of ways you can make this up. There are quite a lot of, charmos vector liesons.
STFC-RAL-CR03 R61: here, like, the phi, the K star, and the row, this is their, sort of, part composition, but I'm going to focus on my favourite ones, and that is, BS to 5x5 and B0 to 55. So, in BS to 5x5,
STFC-RAL-CR03 R61: We're looking at measuring CP violation and measuring this polarization puzzle that I hinted at earlier. And B0 to 55, we want to measure its branching fraction. It's not been observed yet.
STFC-RAL-CR03 R61: And its branching fraction is actually sensitive to new visits. And then, also, if you can study this, you have a chance of being able to constrain problems with BS55. It's a fully quadronic.
STFC-RAL-CR03 R61: mode, there's no leptons in there, and these modes are particularly difficult for theorists to make predictions of the properties. So, if you can understand these
STFC-RAL-CR03 R61: Together, you might be able to constrain some of those.
STFC-RAL-CR03 R61: So, what does a BS or a B055 decay look like? This is just a cartoon, not to scale. But we study these in the proton-proton collisions at the LHC, which I've demonstrated here, and then you get a B meson, either a BS or a B0,
STFC-RAL-CR03 R61: And one of the properties of these, B mesons and, B haddrons is that they have, a relatively long lifetime.
STFC-RAL-CR03 R61: And so they have what we call a characteristic displaced vertex. So they travel further from the… where they're created than any of the other particles, which helps us to identify them. If you've got a ver… at the point where they decay, that's further away from the interaction point than for most other things, so…
STFC-RAL-CR03 R61: At this point, it will decay into these two phi mesons, which will then very quickly decay each into, form, a pair of k-ons each, a pair of charged kons.
STFC-RAL-CR03 R61: So, in the end, we're reconstructing these, these 4K on tracks.
STFC-RAL-CR03 R61: So, we measure this with the LHCB experiments at CERN. So, LHCB is maybe a little bit different to Atlas and CMS, where you're maybe expecting a frozen proton collide or a 4 pi detector that would cover the full acceptance. LHCB is a bit unusual in that the collision point is actually here.
STFC-RAL-CR03 R61: your proton-bron beams come together, and you have your collision inside what we call our vertex locator. So this is where we measure exactly where the proton-proton collision happened, and then also where, our V mesole may have decayed.
STFC-RAL-CR03 R61: This is a tracking detector.
STFC-RAL-CR03 R61: We then also, further along, we have our particles typically, coming this way, in the sort of forward direction. And this is because the defocks compared to photon collisions are typically produced very forward.
STFC-RAL-CR03 R61: So, after this, we have our rich detectors, ring imaging Cherokee detectors, so as the particles pass through, they will generate these Chiron called rings, which help us identify with a momentum measurement, what that particle was, so it can distinguish pions, kons, protons.
STFC-RAL-CR03 R61: Then we have our T station, so these are another tracker, so we measure the trajectory of the particles through there, and then we get a measurement of its momentum.
STFC-RAL-CR03 R61: We have another rich detector, which targets a slightly different momentum range. And then we have calorimeters, which then measure the particle energies as they've, sort of, come to the very back.
STFC-RAL-CR03 R61: And muons, in any of these decays, any of these, proton-proton collisions, if we get muons, they can traverse the whole detector without, sort of interacting, so they're picked up right at the back in what we call our muon stations.
STFC-RAL-CR03 R61: So you might be thinking, okay, why is this good for looking at these BS55Ks specifically?
STFC-RAL-CR03 R61: So, if we go back to the beginning with this vertex locator, as I said, we can identify these B mesons by using the fact that they have this displaced vertex. So, by looking at the traps in the vertex locator, if it's traveled a certain distance, or is quite far away from the interaction point, we know that that was a B meson.
STFC-RAL-CR03 R61: The rich detectors are needed to identify those kons in the final state as kons, so we know that, we haven't picked up something that wasn't really, this final state before charge kons.
STFC-RAL-CR03 R61: We need RT stations for measuring, track momentum. We also use, parts of the calorimeter information to trigger on these, events, so obviously we collect an awful lot of data, and we need to separate out the bits that we care about from the bits that we don't.
STFC-RAL-CR03 R61: And the muon stations are useful here because it allows us to reject any background that comes from muons. If the muon looks a little bit like a K-on at this point, then we can say, oh, well, if it was in here, then it's probably a muon, and that's okay.
STFC-RAL-CR03 R61: So, now I've taught you how we measure these things, how we actually get the physics out of this, so,
STFC-RAL-CR03 R61: Oh, here we go, this is what I was looking for. So, BS mesons, these are called pseudoscalar mesons, so they've got a total spin of 0 and an odd parity. Now, phi mesons, or these vector mesons, have a total spin of 1 and an odd parity, and
STFC-RAL-CR03 R61: What this all boils down to is that, in the end, you have three contributing amplitudes from different, what we call, helicity combinations. So we have CP odd amplitudes and CP even amplitudes.
STFC-RAL-CR03 R61: And this is because we… and we can define this decay in what we call the helicity basis. So, if we look here, we've got a diagram of the decay, so we've got the BS rest frame in the middle, and then the fires back.
STFC-RAL-CR03 R61: And then, if we look at, this, we've got the chaos coming back to back, and what we do is…
STFC-RAL-CR03 R61: we can measure the angles between the K-on and the direction of flight of the phi in the VMS frame, and the… these, K-Ons
STFC-RAL-CR03 R61: each of the five decays forms a plane, and you measure the angle between the two planes, and that can allow you to describe these amplitudes and do a… so what we end up doing is a fit to these angles to extract that CP violating phase that I described earlier.
STFC-RAL-CR03 R61: So, this is a little bit, technical, but essentially, you, you do this, this fit to the angles, you calculate these angles.
STFC-RAL-CR03 R61: when you've reconstructed your decay, and then you can fit for the… essentially, you… you can fit for the magnitude of these different amplitudes, the CP odd and CP even amplitudes, and also, what comes out of this fit is the CP violated base, bias, SS by S. So doing this fit, you get this value
STFC-RAL-CR03 R61: of the CP violating phase, which we're expecting to be zero.
STFC-RAL-CR03 R61: So, this is the latest measurement of bi-SS bar S, and this is coming from LHCP BROM2 data, so this is data that was collected from 2015 to 2018.
STFC-RAL-CR03 R61: So the way that this is done is this is the… we reconstruct those four kons, we calculate their invariant mass when you combine them together, and we look for a peak at the mass of the VS, and that's how we know we've had a VS to start with.
STFC-RAL-CR03 R61: So we use this fit to the max to statistically subtract any background. So they… all the rest of these distributions in this red box are the BS to 55 signal, and these are the distributions of the angles I was talking about just before. So this line shape is fit to these angles.
STFC-RAL-CR03 R61: of what's used to actually extract that value of that CP-violating phase. And this is a four-dimensional fit, where you've got the three angles, and also the decay time. As I said, we need the decay time to be able to encode… get out the encoding that mixing of the two neutral mesons.
STFC-RAL-CR03 R61: So that's the more complicated way of probing CP violation in the S5i. It's quite a complicated measurement, but there's another way of probing Bonsai model CP violation in these decays, and this is using something called triple product asymmetries.
STFC-RAL-CR03 R61: So, these angles that I just defined earlier.
STFC-RAL-CR03 R61: there's a way that you can combine them, so you can make these variables u and v, where you take the sine and cosine of these angles, multiply them together, and these just give you a quantity that is, T odd, so times, odd. So if something… if you… if you believe CPT symmetry.
STFC-RAL-CR03 R61: the CPT theorem, then if you've got a T… a non-zero T odd.
STFC-RAL-CR03 R61: scalable product, that means you've got a non-zero CP, asymmetric.
STFC-RAL-CR03 R61: So you calculate these asymmetries by basically counting. If you measured the angles.
STFC-RAL-CR03 R61: and then calculate these numbers. If you have an asymmetry in these numbers, so if you've got more greater than zero than you have less than zero, then you've got a non-zero asymmetry. And this is zero in the standard model, and this would be a smoking bone for beyond standard model of physics.
STFC-RAL-CR03 R61: Now, the benefit of doing a measurement like this is you just have to calculate the angles, and then count how many events you have one side or the other of zero. So you don't have to do this complicated fit to the angles or the decay time, you essentially just count how many there are, but that doesn't give you access to this CP-violating phase from the CKM matrix.
STFC-RAL-CR03 R61: The other thing I alluded to earlier is this thing called the polarization puzzle. So, for B2B data case, there are these three polarization amplitudes I mentioned earlier. So, this is the CP odd and the CPEM amplitudes.
STFC-RAL-CR03 R61: Now, one of these we call the longitudinal polarization, and because these decays are what we call felicity suppressed.
STFC-RAL-CR03 R61: We expect from theory that this longitudinal polarization should be very dominant, so one of these amplitudes should be close to 1.
STFC-RAL-CR03 R61: Now, if you look in tree-level B2BDKs, like the B2C sci-Fi that I showed earlier, that is the case the longitudinal polarization does dominate. But if you then have these decays where your penguin
STFC-RAL-CR03 R61: level, there are sizeable, contributions from the other polarisations, and this is really not quite understood. We really do expect that they're going to be
STFC-RAL-CR03 R61: primarily this one amplitude, but we get quite a lot of the other amplitudes in these loop-level B2B occurs. So, that's something that's a bit complex and not understood, and we're still trying to figure out.
STFC-RAL-CR03 R61: So here's a bit of history of these measurements. So I've shown you the LHV12 measurement, but actually this started at the Temetron era at CDF, so this was a proton-antiproton collider at Fermilab, where the first evidence for this DS55K
STFC-RAL-CR03 R61: Was seen, and then this also was the first measurement of this branching fraction, the polarization amplitudes, the product asymmetry.
STFC-RAL-CR03 R61: Then moving on to LHCP from 1, again, there's measurements of these triple product asymmetries, but it was the first time we were able to make measurements of this CP-violating phase by S, and this was the first time we searched for B0 to Phi Phi as well.
STFC-RAL-CR03 R61: As we've gone through the years, and LHEB has collected more data, we've updated our value of IS again and again, and kept searching for this mode, B055.
STFC-RAL-CR03 R61: So, this is a summary of the values by SSS bar S, so far. So, we've got the first one at the bottom, and then going… more and more data were going up, but slowly but surely, we're improving the value of 5SS bar S with more of this data, and so far, it's consistent with the standard model.
STFC-RAL-CR03 R61: But what else can we prove? So I've hinted at this a lot, and that's searching for B0 to 5x5.
STFC-RAL-CR03 R61: So, this has an even more complicated diagram that I've simplified to just showing you a dot. So this is an example of what we call a BD to SS bar annihilation. This is very, very suppressed in the standard model. So, it's got commibo suppression, this means you've got,
STFC-RAL-CR03 R61: quarks from different families swapping over, you're crossing over, between the two… between multiple generations of the quarks, so that adds a suppression. You get suppression from the fact that you've got loops in this Feynman diagram, and you've also got suppression from something called the, OZ or OZI rule.
STFC-RAL-CR03 R61: Now, this rule is, if you can draw a refinement diagram, where at any point in time, you only have gluons, so you could cut the gluon lines and have two disconnected diagrams, that is a suppressed mode.
STFC-RAL-CR03 R61: So, this mode, B059, has all of these things, so it's really not looking good for having many of those.
STFC-RAL-CR03 R61: However, the branching fraction can be enhanced in a few scenarios, so we might get more than these than we're expecting if we have something like R-parallel parity violated supersymmetry, so this is just a model of supersymmetry. Models of omega-phi mixing, so omega is another one of these mesons, and it's possible that the omega and the phi can mix in the same way that neutral B mesons can.
STFC-RAL-CR03 R61: And if that's possible, then that can enhance this branching fraction.
STFC-RAL-CR03 R61: The other thing is rescattering, so if it decays into something, and then the final state particles re-scatter to give you the same final state as B055, that can also enhance the process.
STFC-RAL-CR03 R61: So, there's a lot of interesting things that we could probe by looking at how often this process occurs.
STFC-RAL-CR03 R61: Now, the problem is the theory predictions for these branching fractions are very different, and vary by optimal order of magnitude. So, that's shown in this plot on the right. So, we've got the branching fraction in times 10 to the minus 8.
STFC-RAL-CR03 R61: Along the bottom, and this blue point here is at about, 0.2, 0.3, and then this point over here is more than 4. So…
STFC-RAL-CR03 R61: there's quite a big range of predictions for this. They vary depending on how they were calculated, for example.
STFC-RAL-CR03 R61: And also, they are quite difficult to calculate, but let's see if LHCB has anything to say on this. So, the previous best limit from LHCB was dated from, up to 2016, and so a limit at 2.7 times 10 to the minus 8, so that's this pink region,
STFC-RAL-CR03 R61: Towards the right.
STFC-RAL-CR03 R61: So, how do you search for a mode like this at LHCB? So, as I said before, these fires duplicate into two charged kaons, so that's a nice final state to reconstruct their charge tracks, so they do trajectory in our trackers, and our rich detectors are able to identify them as KOs quite cleanly.
STFC-RAL-CR03 R61: So, what we do is we reconstruct these peons. We require… we reconstruct this, phi, and we require that the phi mesons and the four peons are consistent with coming from an identified, bee.
STFC-RAL-CR03 R61: And what you need to do is look for the B0 to 55 by looking for a significant peak at the B0 mass when you calculate the invariant mass of those 4K-ons. So, this is in this sketch on the right, so if you get all of the data from LHCB, and you find
STFC-RAL-CR03 R61: pairs of 4K-ons, you would expect a peak at the BS mass, where you've got BS to 55. This has a branching fraction at about 10 to the minus 5, and then you'd also have one at B0s… at the B0 mass, with a branching fraction of
STFC-RAL-CR03 R61: Who knows?
STFC-RAL-CR03 R61: Now, this looks quite, nice and straightforward, and in a perfect world, this is what we would have.
STFC-RAL-CR03 R61: But, it's not so simple in reality, and that's because we have lots of backgrounds that can limit how sensitive you are for looking for these things. We can't do everything perfectly.
STFC-RAL-CR03 R61: So you get events in this… in this distribution, you're not just going to have these two peaks, you're going to have events coming from lots of different things that are not signal, but look sufficiently like signal that it passes your selections.
STFC-RAL-CR03 R61: So, one of these things is misidentified backgrounds. If a particle is given the wrong label, so that it looks like you've got 4 kons, but you didn't really, you might have had 3 kons and a pion, 3 kons and a proton.
STFC-RAL-CR03 R61: combinatorial background, this is where you've just shoved 4K odds together and hoped for the best, and it doesn't actually come from anything. In particular, you've just found 4K odds that look, look…
STFC-RAL-CR03 R61: Looked like they could have come from a bin.
STFC-RAL-CR03 R61: And then also you get partially reconstructed background, so you might have had 4 real ca-ons and then missed something else.
STFC-RAL-CR03 R61: Another background is the BS to Bifi itself, and…
STFC-RAL-CR03 R61: The S&P 500 is what we call our normalization mode. It's the sort of benchmark that we can compare any V0 or signal to. So, why is that a background? Well, it's because there's a limit of precision on the momentum.
STFC-RAL-CR03 R61: So when we calculate the invariant mass of these four kaons, these peaks are spread out by the fact that we don't know the momentum perfectly well.
STFC-RAL-CR03 R61: And this means that the B0 divided by distribution and the BS divided by distribution overlap.
STFC-RAL-CR03 R61: So, we want to limit this overlap as much as possible to allow us to have more sensitivity to any peak that is at the zero mass. And the main culprit for this are actually, if you have a KON, maybe S255, that has a decay in flight.
STFC-RAL-CR03 R61: Or it interacts hedronically within the detector, that gives you a really poor momentum reconstruction.
STFC-RAL-CR03 R61: So, I'm gonna call these K-on interactions, that means interaction… hydraulic interaction or a decay in flight, but… but,
STFC-RAL-CR03 R61: Not having to write that every time. So, at the top, we've got a cartoon of a KL that hasn't interacted, it's got a nice straight track, you can see where it came from, you can see where it's going, and you can measure its momentum. But if, something happened here, some sort of kale interaction, you end up with a kinked track, it's not continuous, it's got a sort of break in it.
STFC-RAL-CR03 R61: And if this happens before the trajectory that's been measured in our tracking stations, you get a poorer track reconstruction, and as a result, a poorer momentum measurement, which then has its impact on the VMAS. So, this is seen again here, so…
STFC-RAL-CR03 R61: you can imagine this is a KON that's got a nice trajectory through the trackers. We've got hits in all of these trackers that we can join together. Obviously, this is a bit, we don't actually join the dots, there's a combination bit that goes into this. But essentially what we see is these series of hits that detects that… the track reconstruction doesn't know the track…
STFC-RAL-CR03 R61: So, it does a pretty poor job of reconstructing what the initial momentum of that K-On was. So…
STFC-RAL-CR03 R61: This is a problem.
STFC-RAL-CR03 R61: So what I'm showing here is… this is LHGB simulation, where I've, on the left, I've decided, let's only look at the invariant mass distribution, where we've got payoffs that have stayed completely intact the whole way through.
STFC-RAL-CR03 R61: And this is a nice, narrow peak. It's got a RMS value of about 18.5.
STFC-RAL-CR03 R61: Now, if we compare this, to the plot on the right, so, the Y scale is, is, truncated because there are a few of these, but the x-axis is, is exactly the same range.
STFC-RAL-CR03 R61: This is where I've said, of those four pa-ons, if at least one of them has had one of these hydronic interactions, or because it's like, show me what the invariant mass of that looks like. And this is very broad with large tails, it's got an RMS of nearly 80. So.
STFC-RAL-CR03 R61: To show you where the B0 mass is, it's about here. So you can see we've got a lot of events from BS55 where you've got these, dodgy chaons populating here. Now, I showed you on the previous plot, the branching fraction for BS to 5xi is at the level of 10 to the minus 5.
STFC-RAL-CR03 R61: So, if we expect that there'd be 0 to 5 bias at 10 to the minus 8, you don't have to have very many of these for this to completely swarm any signal that you have.
STFC-RAL-CR03 R61: So how do we deal with this? Well, at the time that I was doing it, the option is to remove them. And the way we did that is training a boosted decision tree classifier. So this is a machine learning technique, and this classifier was able to distinguish those interactive k-ons
STFC-RAL-CR03 R61: From the stable ones, despite the fact that we don't know anything more than, sort of, really where the track… where the hits were in the tracker.
STFC-RAL-CR03 R61: So…
STFC-RAL-CR03 R61: This BDT was trained on some discriminating variables, and these variables that are good at telling these types of chaos apart are the quality of the track fit, so if the track had a 4 fit, a 4 pi squared, we… that's an indication that it had one of these events.
STFC-RAL-CR03 R61: how likely it is that the track is a ghost. So, a ghost track is where you, randomly combine hits in the tracker because they look like they could be a trajectory. So, it turns out that we, it looks more like a ghost if it's had one of these, interactions.
STFC-RAL-CR03 R61: The number of hits that the track leaves in the tracker is actually useful for separating these things, and also the kinematics of the track, so what its momentum was and its pseudo-rapidity. So pseudo-rapidity is essentially a measure of how close it is to the beamline.
STFC-RAL-CR03 R61: So, I trained this cutterfire, and there's a lot of plots on here, so I'm going to go step by step. So, on the left, we've got the response of this cutifier. So, what happens is you give
STFC-RAL-CR03 R61: give this classifier your data, and you say, give it a score based on how likely you think it is to have been stable or not stable. So you get a value between 1 and minus 1, where 1 is… I think this K on was, perfect, and minus 1 is… I have no doubt in my mind that this was a terrible K-on.
STFC-RAL-CR03 R61: So, you can see in this inset plot, where we've got these red and blue, distributions. So, this was trained on simulation, so we know that the events in blue were the ones that had an interaction, and we know that the events in red
STFC-RAL-CR03 R61: Did not, and you can see that this classifier gives really good separation, so the non-interactive k-ons have peaked at 1, and the interactive ones have peaked at minus 1.
STFC-RAL-CR03 R61: Perfect, it's got really good separation between these two things.
STFC-RAL-CR03 R61: The other thing we want to check is, because we don't know that it's done missing data, because we don't have the true information that we have in simulation, we want to check that does this classifier do what we expect it to on real data?
STFC-RAL-CR03 R61: And the way we do that is we look at B plus subjects, like K-clusterKs.
STFC-RAL-CR03 R61: And we look at when a JB side decays, it primarily decays to a pair of muons.
STFC-RAL-CR03 R61: Now, I looked at what this classifier did when you gave it a muon. So, as I told you before, these muons make it all the way to the end of LHCB, we collect them in the muon stations. They shouldn't have a kinked track or a bent track, because they make it all the way through.
STFC-RAL-CR03 R61: And that's exactly what we see here. We see that the… so this is actually truncated at the cut point, but, believe me when I say there weren't any at minus 1.
STFC-RAL-CR03 R61: And the other thing we want to check is, this behaves in the same way whether you look at the real data or the simulation. So the classifier works pretty much consistently, regardless of whether it's simulated data or real data.
STFC-RAL-CR03 R61: So that's great, we can separate these interactive K1s From the non-interactive ones.
STFC-RAL-CR03 R61: Now, if we look at this spot on the right, this is, again, the BS55 invariant mass distribution in simulation. So what I was doing before is I was looking at the simulation, the information there, to decide which ones were interactive and which ones weren't. Now I'm just requiring that we have this score greater than minus 0.4, I think it is where I picked it.
STFC-RAL-CR03 R61: So if you apply this classifier.
STFC-RAL-CR03 R61: you see that the distribution, we've got the dark pink is after the requirement, and the light pink is before. So you can see this bit here, which is where the B0 mass, this tail is reduced hugely, which is exactly where we want to be most sensitive.
STFC-RAL-CR03 R61: So that's great.
STFC-RAL-CR03 R61: That was my mistake.
STFC-RAL-CR03 R61: But that wasn't the only background.
STFC-RAL-CR03 R61: As I mentioned before, we have these combinatorial backgrounds. This is where you get randomly combined tracks to form a final state of four peons.
STFC-RAL-CR03 R61: But, some combinatorial is, less randomly than others, so something that we get a lot of in these proton-proton collisions, and especially at LHCB, is DS nissons. So this is a charm and an anti-strange, or the other way around.
STFC-RAL-CR03 R61: And we get these both prompts, so actually in the proton-proton collision itself, and also in the decays from BS. So BS decays to DS quite… quite a lot. So that means we get tons of these DS plus mesons.
STFC-RAL-CR03 R61: So it turns out that when a GS plus decays, about 15% of the time, it has a 5 in the decay.
STFC-RAL-CR03 R61: So, the question is, is were we combining five mesons that were actually coming from DS, because we have so many of them, that it's really likely that we get two independent phi mesons in an event? And it turns out the answer is yes.
STFC-RAL-CR03 R61: So, we can check for these in a data-driven way. So, we take our BS to 5x5 data, so this is the data that we've selected as being consistent with being a BS to 5x5 decay, and we look at the side bands of the data, so away from where the peak is, where it just looks like junk.
STFC-RAL-CR03 R61: We take that data set, and then we look… we take one of the mesons, the bi-mezzons from there, and we look and see if there was another trap nearby. So in this case, we look for a charged ion.
STFC-RAL-CR03 R61: Sorry, that sidebands in the BS, maps. Yeah, so it would be, what?
STFC-RAL-CR03 R61: here onwards, sort of from maybe 5500 this way, because we know that this actual signal isn't there.
STFC-RAL-CR03 R61: So…
STFC-RAL-CR03 R61: We take that sideband data, we take one of the five mesons, we look to see if there was a charge pione, and then what we do is we reconstruct, we calculate the invariant mass of the two pions plus the pion.
STFC-RAL-CR03 R61: Because that would give you the DS mass, if it really, truly came from a DS.
STFC-RAL-CR03 R61: And if you look at this, sample, okay, there's a lot of combinatorial background there as well, because this isn't all of it, but there's a very, very clear peak at the DSMAS. So, a lot of this event in our BS55 data that we'd already selected, we've got a very clear signal for this, for this particular background.
STFC-RAL-CR03 R61: So, one thing I will say as well is this is just the case where we look for a pion. There are lots of other options where you could get a DS to apply something else, and a lot of those are the case where you have a neutrino in it, which we can't reconstruct, and therefore we can't get this neat peak.
STFC-RAL-CR03 R61: So, doing this method, we can only really get the ones with a charge for ion.
STFC-RAL-CR03 R61: So… what would you know? I've trained another BDT, so I can identify these as well. So.
STFC-RAL-CR03 R61: what we do is we can veto the ones where there was a tyrant. We knew it had a massive DS mass.
STFC-RAL-CR03 R61: But then we can also use those events to train another classifier. We…
STFC-RAL-CR03 R61: presumed that a lot of the properties of those events would be very similar to the ones where we couldn't reconstruct that extra track and reconstruct the maps properly. So, we trained a BDT that would target any event that looked like it was consistent with a DS going to a 5, and then you missing that extra track.
STFC-RAL-CR03 R61: Now, so, we've got a classified that can get rid of those, and then we also took away the ones that we know for sure, were gone.
STFC-RAL-CR03 R61: But that's not all of the combinatorial. You can get 4K on from lots of different places.
STFC-RAL-CR03 R61: And so we also train another MBA that targets those more general combinatorial backgrounds, and it turns out that if you do this sort of staged approach, where you've got… you're targeting slightly different criteria, you get a much better reduction of the background by targeting them separately, instead of trying to get them all in one go.
STFC-RAL-CR03 R61: And when we sort of worked out what we should… what requirements we should place on these classifiers, we did this optimization altogether, so we used,
STFC-RAL-CR03 R61: Particle identification variables, which come from the rich, and we used these two classifiers, and we optimized that selection in a sort of multi-dimensional way to ensure that we got the best sensitivity we could using a combination of techniques.
STFC-RAL-CR03 R61: Now, the very last backgrounds we've got are what I call these misID backgrounds. So this is where we could think we've got 4K-ons, but we didn't really. So one of these is decays of lambda B. So lambda B is a B pharyon.
STFC-RAL-CR03 R61: And most… it can decay into a proton, the charge decon, and a phi, where that phi is, again.
STFC-RAL-CR03 R61: Two charged kaons, so this is three charged kons and a proton.
STFC-RAL-CR03 R61: But, sometimes that proton gets misidentified as a K-on, and you can see how this can sort of very clear… quickly look like what we're looking for.
STFC-RAL-CR03 R61: But we can get rid of this, because if you, calculate this invariant mass where you think this one was a Klon, if you… if you require that that mass is close to the thigh mass, which is what we actually want in our signal, then, we get rid of most of this.
STFC-RAL-CR03 R61: So that's good.
STFC-RAL-CR03 R61: The other one is B05K star. This is another, interesting decay, because it's another one of these Chalmers B2B decays, but, I don't care about these ones, so I'm going to throw them away.
STFC-RAL-CR03 R61: And what we have here is we've got 3 carbations and then a pion. And, this one's a little bit trickier, to get rid of, but essentially you look at the invariant mass of the,
STFC-RAL-CR03 R61: K in the pi, you give the track that looks most like a pion, you say, okay, let's pretend this one's the pion, look at the invariant mass. If it's close to the K star mass, we'll get rid of it.
STFC-RAL-CR03 R61: And then we also look at the… if we… if we pretend that the one that's most pion-like is, is a pion, we get… calculate that invariant mass. If that's close to the B0 mass, then we'll just tighten our… tighten our selections a bit more on those ones, and that gets rid of a lot of this.
STFC-RAL-CR03 R61: as well.
STFC-RAL-CR03 R61: So, that's a lot of studying what could be going wrong, getting rid of the stuff that we don't want, so we've developed these selections to clean up the data as much as possible, while also maintaining the signal as much as possible. And like I say, I optimized this using what's called a Bonsai Figure merit, which optimizes for your signal significance.
STFC-RAL-CR03 R61: After you've done that, you then model what contributions are left over. You model what the shapes look like in the ovarian mass distribution. We get yields of the background… we get estimates of the background yields using both data-driven methods, and also using the simulation.
STFC-RAL-CR03 R61: And then right at the end, we're fitting our data to the 4K invariant mass distribution and looking for that peak in the weed zero mass.
STFC-RAL-CR03 R61: So, when I show you this, it splits into two plots, and the reason for that is that there are differences in the data-taking conditions between run 1 and Run 2 in LHCB. So.
STFC-RAL-CR03 R61: The shapes are very slightly different, so we fit them simultaneously, so the yield of our signal is something that's shared in both of the fits, but we have the data split up for better sensitivity.
STFC-RAL-CR03 R61: So, these are the final fits after all of that work.
STFC-RAL-CR03 R61: This is also a log plot. I wish I put it in the backup, but I forgot. There are plots at the linear scale, and you can see just how much background we got rid of. It's very, very small.
STFC-RAL-CR03 R61: So, what we've got here is this big blue peak is the BS5 pi signal, where we've got, like, very good control over these tails.
STFC-RAL-CR03 R61: These shaded regions are all these various backgrounds, so this sort of big purple shoulder is, lambda B, we've got this sort of more bluey-coloured one peeking right in the middle, that's the 0 to 5K star, and then we've got this partially reconstructed stuff at lower masses.
STFC-RAL-CR03 R61: And then this sort of gold-yellow peak is the fitted value of the V0 to 5i signal.
STFC-RAL-CR03 R61: So in the end, in run 1, there's 2.6 plus or minus 1.5, and in run 2, 10.5 plus or minus 6.3, which is a significance of 1.9 sigma, which means we did not find anything. But all is not lost, because we've got actually the new best upper limit on searching for this mode.
STFC-RAL-CR03 R61: So, we do this using what's called the CLS method.
STFC-RAL-CR03 R61: Which is the statistical method to tell you what the, sort of, 90% and 95% limit on the branching fraction is based on what, what you saw, and also what you would expect in a null test.
STFC-RAL-CR03 R61: And we set our limit at 1.3 times 10 to the minus 8 at 90% confidence level. So, this plot on the right, shows you… it was the same plot we had before, but with my new limit. And you can see that quite a lot of these are getting, sort of.
STFC-RAL-CR03 R61: slowly but surely, ruled out, so I think this one's probably wrong, actually. But this improved… this limit is improved by a factor of 2 on the previous LHCB limit.
STFC-RAL-CR03 R61: Now, you expect that, the expected limit, so this… the actual limit comes from this solid line. This is what we actually saw in the data.
STFC-RAL-CR03 R61: But the expected limit, that's this dashed line. That's what we expected based on if we sort of saw nothing, and where that dashed line is actually improved by a factor of 2.5 on the previous analysis, because we've got an awkward fluctuation.
STFC-RAL-CR03 R61: Now, that expected limit, improving by a factor of 2.5, you get a factor of 1.4 from increased statistics. We used extra bits of the dataset. As I said, the first one was up to 2016. We've included data from 2017 and 2018.
STFC-RAL-CR03 R61: So that's a factor of 1.4. But that means we get a factor of 1.8 improvement from doing all of this stuff with the BDTs. So we haven't just added more data, we've been smarter about what the background is to really push it even further, to the point where
STFC-RAL-CR03 R61: We might like to see, when… what on earth the value actually is.
STFC-RAL-CR03 R61: So that was a really nice result.
STFC-RAL-CR03 R61: So, what's coming next? I think it's safe to say I squeezed everything that I could out of Run 1 and Run 2, but luckily for us, LHCB Run 3 has collected a record amount of data. It's, really incredible. So, this plot on the right is our, recorded integrated luminosity, so how much data we collected.
STFC-RAL-CR03 R61: This is, run 1, this is run 2, and then this is run 3. We've got a total of 37 inverse center bars, the result I just showed you was with 9.
STFC-RAL-CR03 R61: Now, BS255 and other Hadronic modes benefit in an additional way, and that is because when we upgraded our detector to do around 3, so when we collected all this data, not only are we collecting more data, we've also upgraded our trigger solution so that it's fully software.
STFC-RAL-CR03 R61: Now, what this means is, before, we had very harsh momentum codes from our hardware trigger, and they are gone. And now we have an efficiency on these hedronic modes that is improved by up to a factor of 2,
STFC-RAL-CR03 R61: per inverse vector bar. So, not only do we have more inverse vector bar, we're also getting twice as much in each of those inverse center bars as we were before. So, more data, more…
STFC-RAL-CR03 R61: BS to 5 phi per data, and so if you assume similar performance as run 1 and RUM2, you get a really good sensitivity on this PHYS phase, so 23 milliv is the sensitivity that we might gain. And RUM1 and RUM2, it was 69, so this is a huge improvement.
STFC-RAL-CR03 R61: This slide's a bit sad, actually, because, on a…
STFC-RAL-CR03 R61: what was it? Monday, I found out that actually we're not getting this from the UK, but…
STFC-RAL-CR03 R61: that's fine. We'll go on anyway. But let's be optimistic. LHCB is going to be upgraded again before the Luminosity LHC project for LHCB Upgrade 2. So this upgrade is designed to fully exploit
STFC-RAL-CR03 R61: that high luminosity LHC to get as much data as we can. So, if you look at the previous slide, like.
STFC-RAL-CR03 R61: This… this looks like insane gates in our… in our base ticket, but that is just this little block here. It looks miniscule compared to what we could have with LHCD Upgrade 2.
STFC-RAL-CR03 R61: To do this, LHQB needs to be able to cope with the large number of interactions happening per bunch crossing. These events are highly, really messy. And you can see this in this plot on the bottom. So this is the bellow, our vertex locator. So on the left, this is a proton-proton, interaction in this sort of,
STFC-RAL-CR03 R61: this is just one proton-proton collision. I mean, I don't know about you, but I would have absolutely no hope of disintending what's going on in here.
STFC-RAL-CR03 R61: But if you add timing to the Velo, and you can look at this in a 20 picosecond window, all of a sudden this becomes much more manageable.
STFC-RAL-CR03 R61: So, if you did introduce timing to the detectors to do, hand-waverly or 4D reconstruction, it means that we could collect a dataset up to 300 inverse fib arms.
STFC-RAL-CR03 R61: Which would give us the statistics we really, to see a really good, measurement of these things, and, you know, potentially say something about Bonsai model physics.
STFC-RAL-CR03 R61: So, I think that's, me, pretty much perfectly on time. Brilliant. So hopefully I've convinced you that there's a lot of interesting things you can study with these U to BDD decays. I just showed you V0 and VS to 5x5, but of course, if you swap the 5s for something else, you get
STFC-RAL-CR03 R61: even more interesting physics there. So these B2B decodes, especially in upgrade 1, so Run 3 of LHEV, these are really one's watch.
STFC-RAL-CR03 R61: The BS and the B0s provide these excellent tests of the standard model, so non-zero phiS, non-zero triple product asymmetry, B0 smoking gun for the Understandable physics, and also there's something really curious going on with this polarization puzzle that's not fully understood.
STFC-RAL-CR03 R61: The branching fraction of this V0 to 5x mode is enhanced in many scenarios, and it's very complex, and it puts theory, really, to the test, and LHCB might be… it might be one of these cases where LHCB can say something.
STFC-RAL-CR03 R61: say something first, but all of these measurements are limited by load statistics. These are rare modes, and we don't have the huge data sets. Well, we didn't, and now we're getting more. But that means that these modes are really targets for the unbook and the LHCB upgrades, because getting more data will get you better measurements.
STFC-RAL-CR03 R61: And if these errors apply phi, if the branching fraction is at the lower end of those theory predictions, we really might be able to see it in run 3. So, stay tuned!
STFC-RAL-CR03 R61: Thank you very much.
STFC-RAL-CR03 R61: Okay.
STFC-RAL-CR03 R61: Very nice bunk, so let's… Questions.
STFC-RAL-CR03 R61: Yes. Sorry, I realize I'm a bit ignorant about pi's, but, if you were looking for a decay that involved D, you'd be worried about a D star emitting a pi zero decaying to a D, and you lose the pi zero.
STFC-RAL-CR03 R61: Is there no case where a BS would go to a phi in an excited phi state, and then you lose a pi zero?
STFC-RAL-CR03 R61: Oh, so that would reflect into your region.
STFC-RAL-CR03 R61: So… I mean, it would be at the lower masses.
STFC-RAL-CR03 R61: I actually don't know what that would…
STFC-RAL-CR03 R61: what that would be. That's sort of the excited buy, so I think I'm sure…
STFC-RAL-CR03 R61: Must be able to go to higher ed. There must… there must be. So I think these probably, these will have been accounted for when we… so we studied,
STFC-RAL-CR03 R61: It pays to, sort of, other,
STFC-RAL-CR03 R61: sort of light, what we call light, unflavoured, vexed miseons.
STFC-RAL-CR03 R61: And,
STFC-RAL-CR03 R61: You essentially look at what they look like if you miss that… that pion, and they… they sort of really get pushed to these lower,
STFC-RAL-CR03 R61: Really, it's fine too far left to worry, Ellis. Sorry? Maybe it's fine too far left to worry. I think so. I think, and there are probably… I'm trying to imagine, I think there are probably other cuts that might get that as well, like, if you… like, requiring that they're consistent with coming for a food.
STFC-RAL-CR03 R61: If you miss, I guess if you miss, No, it's crazy.
STFC-RAL-CR03 R61: If you've got…
STFC-RAL-CR03 R61: I'm trying to imagine if you've got the fine, it might not point back quite right as well, so that… I imagine that that would probably catch it as well, but yeah, you're right, I mean, in principle, any of these things where you miss a track and you've still got…
STFC-RAL-CR03 R61: something that's consistent with the phi. And the other problem with the phi is, it's, what we call close to threshold. So those two k-ons are… the invariant mass of the two k-ons is very close to the, breadth mass of the phi, so you don't get very much of an opening angle.
STFC-RAL-CR03 R61: When they decay, so the vertex of the… the decay vertex of the fire… oh, well, that's because it decays finally, so it's basically the same thing, but you don't get very good pointing back to that anyway, so there are things we have to do to deal with that that will bleed.
STFC-RAL-CR03 R61: maybe capture as well.
STFC-RAL-CR03 R61: Just like, are you saying a state where you could have two phi's, but one of the phi's a higher resonance PHY, became down to a phi? But then, I guess, wasn't that…
STFC-RAL-CR03 R61: Both have a really low branch.
STFC-RAL-CR03 R61: Feynman diagram would be the same, right? So the branch should fraction. No, that's BS, and the BS is… I see you. Yeah. Yeah.
STFC-RAL-CR03 R61: But yeah, you're right, that… that's… that's something that would… we would reconstruct as having 4K arms that would be insistent with having a B. So yeah, I think it would be… I'd have to… I'd have to check, but yeah, it would be quite…
STFC-RAL-CR03 R61: That comfortably.
STFC-RAL-CR03 R61: Captured by all of the selections that look for similar topologies.
STFC-RAL-CR03 R61: I still think it probably had a quiet or branching thread. I think so. I'll have to look at what it was, yeah.
STFC-RAL-CR03 R61: Yes. So you had a specific rejection of the DS plus peak?
STFC-RAL-CR03 R61: Which… but you also showed a D0 plus peak in the same… the same plot, and you didn't mention it, and it looked like it was almost as… not almost as deep, but… Yeah, so that's just another D, meson, so, but why not remove those as well?
STFC-RAL-CR03 R61: Well… we do, I think… The method is pretty agnostic as to what that was.
STFC-RAL-CR03 R61: the reason I've sort of explained it in the way that I have is, because they're the sort of most clear, example of where you've got
STFC-RAL-CR03 R61: you get more DS from BS, but yeah, it's… there's no reason… the properties don't rely on… The approach will catch both, you say. Exactly, yeah, so the… that… that peak is just used to select a clean signal that you can then use to train the NVA that catches the other one. So,
STFC-RAL-CR03 R61: it has to be, sort of, agnostic of Macs, otherwise you bias things, so, it's,
STFC-RAL-CR03 R61: Yeah, it caches those other ones as well.
STFC-RAL-CR03 R61: The first PD you talked about was for catching the King's tracks, having interactions.
STFC-RAL-CR03 R61: Okay, looked like it worked really well, but I was kind of surprised you didn't use the phi peak as a… you know, you could tighten your cuts on the finance to check that the K-on was correctly constructed.
STFC-RAL-CR03 R61: So… the… the five… So, yes, and this is something that we sort of discussed, but it doesn't really…
STFC-RAL-CR03 R61: help you so much. So the PHY is… defines, a broader resonance.
STFC-RAL-CR03 R61: is itself… it depends who you ask whether or not phi is a broad resonance, actually. It's a… anyway, if you ask a theorist, it's a very narrow resonance, but it's actually broad enough that the phi itself has a width that's at the same level as the momentum, and you sort of get momentum effects and actual width effects, so, I mean, one of the things that,
STFC-RAL-CR03 R61: we thought about was, fitting the fire mass as well, but because you get… it just doesn't help you, really. I guess maybe you've placed a threshold with decay on it. Yeah, and, and as well, we make quite tight cuts on that mass window anyway,
STFC-RAL-CR03 R61: But, yeah, it doesn't help you, fortunately, but…
STFC-RAL-CR03 R61: But it helps work with things.
STFC-RAL-CR03 R61: Yeah, this is coming from someone who's really unfamiliar with… I don't know how to see it, but…
STFC-RAL-CR03 R61: Especially going into the, sort of, high stats here at Pionumi, are there any areas where you, like, heavily rely on simulation, so specific models?
STFC-RAL-CR03 R61: Where, sort of, changing that model might massively change the result, similar to the sort of issues we're dealing with going into fast dance and neutrino analyses, where, you know, you switch a model out in simulation, your result can change massively, and we're really worried about that, going forward. So, don't see any of that in the, sort of, AIC analyses?
STFC-RAL-CR03 R61: I mean, we do… we do see these things in LHP analysis, a lot of… especially… I mean, these ones will always be statistically limited, I think. And especially in these searches, like, you basically don't really rely
STFC-RAL-CR03 R61: on, simulation being a specific, decay model, or whatever for, for that. I think, and Phi Phi, the sort of CKMM, like, with it being very close to zero, I think as well, that, that's not super reliable. Like I said, they will probably always be, statistically limited.
STFC-RAL-CR03 R61: But we do see this in LHCB, right? Like, you have these very high stats, charm modes, like, we get tons of charm, and a lot of those are having to do, basically, data-driven
STFC-RAL-CR03 R61: everything, and you just can't generate enough, like, even just generating enough simulation… like, you've got bigger samples of data than you could ever hope to have simulated anyway. So, yeah, we have, sort of, problems with, some nodes. But then,
STFC-RAL-CR03 R61: I mean, you're right as well in, sort of, the model that you use for the decay. I mean, these always come into systematics with these analyses, so you might generate,
STFC-RAL-CR03 R61: generate simulation under a different, different decay model, with different, different, sort of, hypothesis about what your CP violation is, how they decay, the altitudes, things like that. So, but they would come into, sort of, doing systematics check.
STFC-RAL-CR03 R61: Yeah, for this, B0, to 5x5, not at all. The S to 5x5, it definitely comes into a systematic, but then yes.
STFC-RAL-CR03 R61: Okay, good question.
STFC-RAL-CR03 R61: not a physi, more of a data. So when the proton…
STFC-RAL-CR03 R61: And we'll get a lot of drag.
STFC-RAL-CR03 R61: How do we detect the angle, the triangle, using the machine learning, or through the encryption?
STFC-RAL-CR03 R61: So you mean, the… the sort of…
STFC-RAL-CR03 R61: the angles that we used to calculate the CP violation thing when I showed the sort of planes. Yeah, I mean, you have… Yeah, so that… that will be… they're calculated from, you know, the trajectories of the… the tracks, so you… you measure where the tracks went, and then you sort of reconstruct them back.
STFC-RAL-CR03 R61: And then, calculate the angles between the vectors, as he claims. So, because you have
STFC-RAL-CR03 R61: I mean, you get a lot of background as well that you try and reduce as best you can, but when you know you've got a pure signal, you just use the tracks that you reconstructed to sort of work back and
STFC-RAL-CR03 R61: sort of work out where that vertex was and what the angles between them were, at the point of…
STFC-RAL-CR03 R61: At the point that they would produce.
STFC-RAL-CR03 R61: Nope.
STFC-RAL-CR03 R61: Let's see…
STFC-RAL-CR03 R61: Any questions?
STFC-RAL-CR03 R61: I don't even know what the question is, but I noticed it on page 26. Can you go about that? Oh my goodness.
STFC-RAL-CR03 R61: Awesome, yeah, yeah, fantastic.
STFC-RAL-CR03 R61: 26. Yeah. Yeah.
STFC-RAL-CR03 R61: Yeah, right. The Feynman diagram, you talk about the OZXI suppression, but if I wanted to fill in something for that dot, I would start with a loop of two parts and two W's. Yeah, have I got this in the back of…
STFC-RAL-CR03 R61: That's not it.
STFC-RAL-CR03 R61: No. Okay, so I haven't got it, but you… You end up with… Let's get back.
STFC-RAL-CR03 R61: So… you have…
STFC-RAL-CR03 R61: You end up with a top loop, and then the top radiates another gluon.
STFC-RAL-CR03 R61: So you have this view on coming from here, But then… No, it's not hot.
STFC-RAL-CR03 R61: It's BD bar, so it's got some part number that's got to carry through.
STFC-RAL-CR03 R61: Or W. Yeah. But maybe the same thing applies if you have a W there, as well as a blue. Yeah, you have… you have the W's for the blade changing, and then…
STFC-RAL-CR03 R61: there's a…
STFC-RAL-CR03 R61: Yes, you have the W's, and then they have top loops in them, and then it's the tops that are radiating the blue ones, and then the blue ones are…
STFC-RAL-CR03 R61: it's just the blue ones, and then you get the SS bar, and then there's a sort of consideration of color, but I can't remember the argument for why just having… there's a reason why you shouldn't have just two blue ones, but it's fine.
STFC-RAL-CR03 R61: In this, I have to look at it. Yeah, the BD had to be a different color, but you take as your own officer, so yeah, they're not the same color. Goodbye.
STFC-RAL-CR03 R61: Yeah, it's in my thesis, but I should put it in the, in the, in the backup. That's probably what pushes it to be… I've remembered it now. So you have…
STFC-RAL-CR03 R61: you have the W sort of coming back down, and then you have… so you have… Okay.
STFC-RAL-CR03 R61: So you have… pretty sure You have something like…
STFC-RAL-CR03 R61: None.
STFC-RAL-CR03 R61: That. It's something like that.
STFC-RAL-CR03 R61: But you get this sort of thing changing the top, radiating the blue ones, and then the other ones going to SFR check code. Thank you. Yeah, that's much simpler than I was thinking, yeah. It's just a bit gross. And all the theorists sort of look at it like this, because you've got,
STFC-RAL-CR03 R61: Because you sort of look at, whether you can sort of factorise the diagrams or not, and,
STFC-RAL-CR03 R61: Essentially, you end up with
STFC-RAL-CR03 R61: if you forget about the box, you end up with these diagrams being higher-order corrections to the BS version as well, which is why this… if you actually saw this and could, you know, marry some theory prediction with what you've observed, you might then have a better idea of what these higher-order corrections in the S55
STFC-RAL-CR03 R61: we're doing. I mean, if we saw a sort of large enhancement from the CP violation, for example, like, there'd probably be, some
STFC-RAL-CR03 R61: consideration for whether that's theory of factors that they're solved, and then…
STFC-RAL-CR03 R61: This would then become useful to understand if that high-level approach can do that.
STFC-RAL-CR03 R61: Excellent.
STFC-RAL-CR03 R61: Megan.
STFC-RAL-CR03 R61: Okay, so shall we close? If I don't leave there, no more questions.
STFC-RAL-CR03 R61: I think we can, thank, Mary again.
STFC-RAL-CR03 R61: And we're going for lunch.
STFC-RAL-CR03 R61: Thanks for joining us.
STFC-RAL-CR03 R61: Thank you.
STFC-RAL-CR03 R61: On Zoom?