Okay.
STFC-RAL-CR03 R61: So today, I'm gonna talk about the gravitational studies that we've been conducting using hydrogen atoms. On the outfit experiment.
STFC-RAL-CR03 R61: just for some perspective. This collaboration is relatively small. We have something on order, 60 people and some 18 institutions worldwide. And we're fundamentally interested in performing precision measurements using it, hydrogen out.
STFC-RAL-CR03 R61: And so
STFC-RAL-CR03 R61: we're investigating from very low energy, perspective precision perspective. This issue with anti matter where we sort of expected, we have equal amounts produced at the beginning of the universe. And then, as the universe kind of went forward and things started annihilating, we were kind of left with this situation where? It seemed like there was excess of matter left in the universe.
STFC-RAL-CR03 R61: Okay. And it seems, as far as we can tell, that the matter of excess is basically the observable universe, as far as you can tell.
STFC-RAL-CR03 R61: So there's much more. And this is not important to our expectations. So
STFC-RAL-CR03 R61: what are some possible explanations? So the sorts of things that we're considering in our experiments of things like Cbt. Symmetry, the weak equivalence principle. Lorenz's variance violation. These kind of oddball, new physics, kinds of questions, and swapping matter for anti matter in these systems can in principle make them sort of uniquely sensitive to certain kinds of new physics.
STFC-RAL-CR03 R61: So for this talk for me to focus on gravity and specifically, what we call the free fall, we could equip ones, principle or a kind of Galilean approach to gravity, where, you know, I might drop an apple off the tower pizza, or something like that, and observe that it falls down, and everything that I drop falls down at the same rate, and then I break my laptop and void my warranty, and send them
STFC-RAL-CR03 R61: and you might expect also from symmetry that anti apples and anti-earths behave the same.
STFC-RAL-CR03 R61: but this case historically has had some wibble room
STFC-RAL-CR03 R61: where we consider the gravitational connection between the anti apple and earth. Will it behave as expected? Or will it do something more exotic. Okay? So that this is really what we're trying to investigate with this experiment. It's a really simple mechanical experiment where we're gonna try and actually see the influence of gravity on the trajectories of hydrogen pose.
STFC-RAL-CR03 R61: So just some perspectives on gravity and antimatter. We're doing this, as we'll see within the hydrogen atoms. The question that comes up is, well, hasn't this been tested before? Why hasn't this been tested with charge and antimatter? We've had that around for many, many, many, many decades
STFC-RAL-CR03 R61: and
STFC-RAL-CR03 R61: there have been fire experiments that have been proposed to test on positron and their protons. But the issue is that the gravitational forces quite weak when you compare with, say, for example, straight electric fields. So the kind of electric field strength that you care about. If you want to be doing. A gravity method is something on the order of like 10 to the minus 11
STFC-RAL-CR03 R61: volts per meter. And it turns out it's extremely difficult to achieve that an experiment, much less get your charged particles to behave that way. But nevertheless, in the sixties
STFC-RAL-CR03 R61: there was an experiment that was proposed to measure the gravitational influence on Pathatrons. And there was a a
STFC-RAL-CR03 R61: Professor Fairbanks, who at Stanford built an experiment that was meant to be used as a sort of prototype for a positron experiment, and the basic idea is that you would pulse electrons a low velocity up through a drift. You would measure their reliable, the detector measure time, delay between those 2 2 things and then infer what the gravitational acceleration was
STFC-RAL-CR03 R61: right straightforward. Okay, that assumed that you could get electric fields down below levels in the descriptions. And they thought they had.
STFC-RAL-CR03 R61: okay. But there's some complications.
STFC-RAL-CR03 R61: That are on this right? So the basic idea is you would expect the electrons to go up that way.
STFC-RAL-CR03 R61: But it turns out that after you've controlled for all those electric fields.
STFC-RAL-CR03 R61: the electrons in the drift tube itself sad under the influence of gravity. Okay. so this is actually what the distribution of electrons looks like
STFC-RAL-CR03 R61: in a drip to, and that makes an electric field that points up
STFC-RAL-CR03 R61: and or rather an electric field, an effective force that points up for an electron going up through the drift tube.
STFC-RAL-CR03 R61: And what they actually measured with the experiment is that electrons don't accelerate at all in traffic.
STFC-RAL-CR03 R61: Okay? I mean, really, that's what they that's what they approved with their experiment.
STFC-RAL-CR03 R61: Okay, now, they kind of took this to be a measurement in the sense that eventually there was a theory that predicted what this distribution was, and at least for their experimental data set. They got consistent results with electrons.
STFC-RAL-CR03 R61: But other theorists came along and really started to look at the material
STFC-RAL-CR03 R61: science of
STFC-RAL-CR03 R61: this distribution of charge and materials. And it turns out to be quite complicated. It's material dependent. It's temperature dependent. It's charge sign dependent. And so there's a lot of complicated systematics associated with that
STFC-RAL-CR03 R61: and unfortunately, at the time Fairbanks wasn't able to then continue on with the experiment positron, because in late sixtys there weren't great sources, and no one's really come back to that experiment. Okay.
STFC-RAL-CR03 R61: there was another experiment that proposed a decade or 2 later. Ps 200 that was meant to run or was running it here. That was, gonna do a similar measurement with the anti profiles. So traffic protons from layer cooling down. Send them up to and don't. They really just didn't quite get to making a measurement by the time
STFC-RAL-CR03 R61: leadership down. Okay? And I'm really not going into all of the systematic details that you need to manage these charge fields
STFC-RAL-CR03 R61: that show up in these experiments. But it's
STFC-RAL-CR03 R61: it's significant and to date. In fact, no gravity measurement has made been made on any charged particle. no trajectory kind of based gravitational measure. Okay? So most of the efforts. Now.
STFC-RAL-CR03 R61: our focus on neutrals. And that kind of explains a little bit. Why, we're doing anti hydrogen. We're not alone. Okay? So we're running at Cern. There's 2 other experiments at Cern
STFC-RAL-CR03 R61: Gvar and ages that are doing gravitational measurements using different techniques. New audio. So
STFC-RAL-CR03 R61: as a kind of hybrid matter, anti matter systems also being studied. And there's efforts
STFC-RAL-CR03 R61: that are going forward to look at gravitational trajectories of positron. Okay. But for today, we're gonna focus on anti hydrogen.
STFC-RAL-CR03 R61: Okay, so is just a balance, a positron and antiproton. Okay? In contrast with, you know, a normal hydrogen atom and we piece this together by collecting the ingredients for this atom. In our experiment, we get positrons
STFC-RAL-CR03 R61: from radioactive sources. Okay, relatively straightforward because you can get data plus decay from a lot of different radioactive isotopes. Turns out bananas are a reasonable source of positrons. You get about 15 positrons for something that you have a banana in the breakfast.
STFC-RAL-CR03 R61: but we need like millions of positrons per second, and I don't think we want a big multi-hide of any of this in our experiment.
STFC-RAL-CR03 R61: Low energy and type protons. We get these at Cern. Okay? So
STFC-RAL-CR03 R61: if you're familiar with cern.
STFC-RAL-CR03 R61: The Ps. Sends a bunch of protons that sort of 10 to Gev. To the antiproton decelerator, which is a little ring that decelerates the antiprotons down to a few mev, and then currently those get extracted into another decelerator called Elena. That decelerates them from a few Mev. To about 100 Kv.
STFC-RAL-CR03 R61: and that sends out about
STFC-RAL-CR03 R61: 5 million or so anti protons to the experiments per 100 s or so per skill cycle
STFC-RAL-CR03 R61: and once we receive those, we degrade them and catch them. So we get a few 100,000 per minute in our experiments.
STFC-RAL-CR03 R61: Okay, so this is kind of a schematic that
STFC-RAL-CR03 R61: I'll come back to you in a second of what our experiment looks like. Anti bertrands come in from the left, from the accelerators. Positrons come in the into the right from the puzzle, from accumulator
STFC-RAL-CR03 R61: and then we conduct experiments with these charged particles in the first instance, using penning traps.
STFC-RAL-CR03 R61: Okay, so we have to catch our antiprotons and cool them further, because 100 kev is just way too much.
STFC-RAL-CR03 R61: So what we do is we set the 100 kvm for a thin foil. That degrades the beam, and a small fraction of them, or a reasonable fraction of them can be trapped actively by switching voltages on the penning trap. Okay? And then it can pull into a preloaded
STFC-RAL-CR03 R61: cloud pilotron. So we have a lot of pinning trucks in the experiment. They all kind of look like this. They're hollow metal cylinders that we bias using amplifiers so that provides an electrostatic potential in the sort of longitudinal direction in the trap.
STFC-RAL-CR03 R61: And depending traps all have a sort of solenoidal magnetic field along the axis that will confine the particles radially sort of through the cyclotron motion. For catching end of protons. We typically do this about through Tesla
STFC-RAL-CR03 R61: and then, having done these manipulations, we have a lot of diagnostics that we can use to learn whether plasmus are doing what we want them to do. For example, we can just throw the particles out of the experiment and image them on a microplate with a camera that looks at a phosphor screen. And so for doing a reasonable job, we see things that look like this where we have an electron plasma and our anti plasma essentially as a hollow ring on the outside.
STFC-RAL-CR03 R61: And that's good. So that they should be on top of each other. But our imaging system kind of separates the 2 masses. They actually separate out when they get cold through centrifugal separation, because the plasmids are rotating the magnetic field and the anti protons are heavy. So they go to the outside. And you know that's the that's kind of diagnostic we can use to determine how many particles in the density and the temperatures that we have.
STFC-RAL-CR03 R61: So there are ideal scenarios that we're aiming for for making that to hydrogen.
STFC-RAL-CR03 R61: And so what we do is we kind of prepare the platforms to get the densities and numbers and temperatures that you want. We bring into protons together and positron's together into one track.
STFC-RAL-CR03 R61: And so you have them in what we sometimes call a message potential. So here I have confined positrons, and on the left hand side. Here I have anti-fronts, and then I can kind of do a simple manipulation
STFC-RAL-CR03 R61: that allows the antiproton to kind of string the positron and vice versa. And when that takes place, if you've got the right sorts of parameters, you form it to hydrogen.
STFC-RAL-CR03 R61: and then they just immediately leave the trap, because the penning trap is doing a great job and find our charged particles. But the anti hydrogen atoms are neutral. So they just leave. They hit the walls and they might end
STFC-RAL-CR03 R61: and that's where we kind of start making measurements with anti genetics. So in order to understand what we've been doing
STFC-RAL-CR03 R61: we have annihilation detectors in our experiments. So Alpha one and Alpha 2, use the silicon script detector. So you know, ions from the annihilation fly out, deposit charge and silicon script detector. We do reconstruction. We can find the vertex and we know when the annihilation happens.
STFC-RAL-CR03 R61: and we have an amazing resolution of 6
STFC-RAL-CR03 R61: Yeah, 70 pretty good. But for us this is pretty good. I mean, we don't need micron resolution. Right? We're not trying to, you know, discover the exposure or something like that, right? We just want to know more or less where the annihilation took place.
STFC-RAL-CR03 R61: so that's how we know kind of where annihilations take place. I'll come back to this in a bit.
STFC-RAL-CR03 R61: But in order to do atomic physics measurements. What we and Apple would like to be able to do is crap the anti jams so we can hold onto them and then interrogate them in some way.
STFC-RAL-CR03 R61: So in order to do that, what we use is something called a magnetic minimum trap in our experiments based on an octopol that we superimpose on top of our background solenoid in addition to fields from 2 short solenoids that we call mirrors. And so you get this kind of
STFC-RAL-CR03 R61: effective potential from the fact that anti hydrogen has a little magnetic moment. And you get this kind of funny bathtub shaped thing that's about half a Kelvin deep and sort of energy equivalent units. So not super strong. And just to give you a sense of how big this volume is. It's like.
STFC-RAL-CR03 R61: you know, like a little plastic coke bottle kind of volume in the trap. Okay? So we make it a hydrogen and the end of hydrogen kinetic energy is last less than about half a degree. Kelvin, it will say, in this potential, as long as it's magnetic moment is oriented. So it's a little field seeking safe.
STFC-RAL-CR03 R61: So a little bit of history
STFC-RAL-CR03 R61: or trapping into hydrogen, we need to search for it. We turn on a magnetic trap. We make ends hydrogen, and then we have to get rid of the charge particles. Okay, so we were using positron and anti protons to make me as hydrogen.
STFC-RAL-CR03 R61: Once we made the end of hydrogen. We don't want the product, the remaining ingredients sitting around. So we apply an electric field to push them out.
STFC-RAL-CR03 R61: Then we turn the trap off. Okay, we used to actually, intentionally plans for super conducting magnets to do this. So the shut off what happens. Sort of tens of milliseconds?
STFC-RAL-CR03 R61: and then we detect it annihilation. So you can see that this step was important, because if we had left charge particles around. We might see these annihilations, and they might be charged particles. And that would be a problem. Okay? So then.
STFC-RAL-CR03 R61: what we see in kind of data, get a data set that looks like this. So here we have some nominal events. We have a time cut, and I know when we're showing off the magnets, we have a spatial cut in the trap. So that's in the traffic volume we get rid of. We reject things that look like cosmic rays. We accept events that look like anti-protons. Okay? And and then we're done right.
STFC-RAL-CR03 R61: We've detected independently. Okay. And you can also then go ahead and just check. You can simulate it. So you target Monte Carlo simulations of these atoms if you're trapped throughout the clinch.
STFC-RAL-CR03 R61: and you see, the gray spots are the simulation events. And here's our nominal data. And there's reasonable overlap between the 6 data events I'm showing, and hundreds and hundreds of simulations.
STFC-RAL-CR03 R61: But there's something called mirror trapped and protons. So I tried to push out the charge particles.
STFC-RAL-CR03 R61: But if you've done sort of
STFC-RAL-CR03 R61: cosmophysics or something, some advanced electrodynamics. What you find out is that if I have, you know, in homogeneous magnetic fields, and I have charged particles with significant transverse energy to the field relative to the parallel energy, and they're born in a minimum. They get reflected by the maximum fields back in so that they can get trapped.
STFC-RAL-CR03 R61: And in our experiment. Then what we have is an effective potential when we try and get rid of the charge particles that's created by alert our electrostatic potential. And then an effective potential that comes from the sort of mirror trapping dynamic. Okay, so this is
STFC-RAL-CR03 R61: our electric potential and black. And this sort of mirror. And as a function of how much transverse energy the particles might have like, we don't get rid of this well entirely, so there may be particles that are left over.
STFC-RAL-CR03 R61: and what are those? Look like? Okay? So here's our data. We simulated your traffic prophets.
STFC-RAL-CR03 R61: Okay. they don't play it for that.
STFC-RAL-CR03 R61: But you can actually do control the experiments.
STFC-RAL-CR03 R61: Okay? And so this is what we did originally to prove that we were trapping instead of turning these electric fields off that we were clearing the particles out with. We left them on in the experiment. Okay? And the electric field should deflect the charged particles and not be apps.
STFC-RAL-CR03 R61: And then you simulate and measure this with the protons you make in this case, where they should be trapped. So our original experiment, then would put trapped
STFC-RAL-CR03 R61: antiprotons overlapping the simulated population, and if we push them off to the left, the antiper comes to off left.
STFC-RAL-CR03 R61: If we push them to the right. They enter peripheral and skip to the right. Okay? And and then you can compare
STFC-RAL-CR03 R61: our data for nominally trapped anti hydrogen atoms in these different electric field configurations. So Field, pushing the left field, pushing to the right. And you see that you know, for the population that should have been a prepared clue. You just hit the particles everywhere and reds everywhere and greens everywhere, and nothing is really where
STFC-RAL-CR03 R61: the mirror top particles were gonna go.
STFC-RAL-CR03 R61: So then you're feeling more confident, actually trapped anti-hydrogen. And you're not just seeing anti-protons that you'd left over in the trap
STFC-RAL-CR03 R61: accidentally. Okay.
STFC-RAL-CR03 R61: so this was great, we concluded we were trapping as hydrogen, and then we can start doing physics on these on the particles.
So
STFC-RAL-CR03 R61: one of the things that we did.
STFC-RAL-CR03 R61: This was an experiment by the way, it was focused on trapping information. But one of the things we did with this initial data set is, we investigated charge neutrality and the hydrogen. Okay? So we're looking for crazy new physics. So why shouldn't antihydrogen? You know
STFC-RAL-CR03 R61: the charge unneutral like it probably should be charged neutral. But you can measure that, and you can measure it specifically with the experiment that we were doing. You can ask the question, well, what if the E fields were deflecting the atoms.
STFC-RAL-CR03 R61: Okay?
STFC-RAL-CR03 R61: And you could model this by saying that into hydrogen has some charge anomaly queue. Okay? And if you do that. Then you again you adjust this potential that you see during the bench. With this added term it comes from this charge anomaly.
STFC-RAL-CR03 R61: And so
STFC-RAL-CR03 R61: and then so simulate that. And if you simulate that, what you get is that the sort of distribution of atoms you get if 2 is equal to 0 can be centered around a trap.
STFC-RAL-CR03 R61: And if you're pushing them to the right or to the left, you get shifted populations.
STFC-RAL-CR03 R61: and you can work out.
STFC-RAL-CR03 R61: A relationship between, like the mean offset, between the sort of a measurement of applying fields to push things to left, which is the pushing to the right to calculate what the charge. Okay? So we did an analysis on the data set we had. And basically, you're just taking 2 data sets pushing things to left and the right.
STFC-RAL-CR03 R61: Imagine their average distance. which is nearly compatible with 0,
STFC-RAL-CR03 R61: and that relates to a chart anomaly limit on the order of sort of 10 to the minus 8. Okay, so so that's nice.
STFC-RAL-CR03 R61: and
STFC-RAL-CR03 R61: what have we learned from doing this? Okay, so fine neutrality is great. But this was the kind of start of a sort of investigation that we were doing now with our experiment, where we were considering the behavior of the atoms under the influence of your potentials.
STFC-RAL-CR03 R61: Okay, by comparing our data with these Tommy Monte Carlo slots. So what does this do for gravitation? So I'm coming back to gravitation now in this original machine. We also looked at whether or not we could observe
STFC-RAL-CR03 R61: the influence of gravity. So you cook up a new potential. So now we're considering why the vertical direction and some scalar half on top of the sort of normal gravitational potential that the atom would experience. Okay?
STFC-RAL-CR03 R61: And you look at what this effective potential does over the course of our magnetic shutdown. So at 0 ms in the vertical direction. The experiment. You see a potential that looks kind of like this. This is just governed by the shape of the octopole field plus the background solenoid. Okay? And as the trap gets shallower and shall work while the depth of the well drops. But more importantly, like the minimum of the trap moves to the left.
STFC-RAL-CR03 R61: Okay? And it's in this is, calculated for an example where app is equal to 100 to really sort of show this effect. Okay? And so what you expect should happen
STFC-RAL-CR03 R61: is that if for some reason, anti hydrogen was gravitating down in this case
STFC-RAL-CR03 R61: at a hundred times, the effect of mass
STFC-RAL-CR03 R61: of hydrogen, you would see over the course of the quench
STFC-RAL-CR03 R61: more things annihilating towards the bottom of the track which we were able to resolve, using our silicon Vertex detector. Okay, so this thing should move to the left in time. And then you're effectively measuring this
STFC-RAL-CR03 R61: potential across the track. Okay.
STFC-RAL-CR03 R61: so
STFC-RAL-CR03 R61: what does data like that look like? So here we projected the sort of Y coordinates of
STFC-RAL-CR03 R61: our events, both data and simulation. Okay? And the black curve shows the results for this sort of that I've shown. So you see, there's an extreme group when you kind of do a cumulative at running cumulative average of this
STFC-RAL-CR03 R61: of this annihilation. Y-coordinate as function time.
STFC-RAL-CR03 R61: Okay? And then what you're gonna do is compare the data that you have against a bunch of different experiments to rule out different models. Okay? So the different models are giving you sort of confidence intervals of
STFC-RAL-CR03 R61: different effective gravitational forces. Okay? And so data has to be outside these constants intervals to rule them out.
STFC-RAL-CR03 R61: And what we concluded is that
STFC-RAL-CR03 R61: you know, F is somewhere between minus 65 and plus 110. Okay. which is not super precise.
STFC-RAL-CR03 R61: Okay? Turns out it'll hydrogen
STFC-RAL-CR03 R61: crazy, heavy or crazy light.
STFC-RAL-CR03 R61: But this experiment's not very precise. Okay, this experiment has a short distance. I didn't really talk about it, but our trap is about 40 tall.
STFC-RAL-CR03 R61: Okay, it's very hot in the scheme of things and hot in the sense that, for example, if I took one of these into hydrogen atoms that's in my distribution and just let it go.
STFC-RAL-CR03 R61: Okay.
STFC-RAL-CR03 R61: on the surface of the earth, it would fly up like 200 meters or so before gravity would turn it around. Okay. So really, it's really quite hot, all right. And of sort of figure merit you can calculate is what this effective change in potential
STFC-RAL-CR03 R61: energy that you get at sort of Fc. The one or normal gravity is about 10 to the minus 3 milli kelvin per millimeter, and we have per atoms that are starting at sort of 500 milli. Kelvin. Okay, so
STFC-RAL-CR03 R61: this is not a great experiment for making this measurement, however, the idea of the experiment then kind of moved forward, and we planned
STFC-RAL-CR03 R61: a real experiment dedicated to this, which is Alpha G. So here's a picture about the G. After we installed it. I'll show you in a little bit more detail. But up here is a large, superconducting, solid provides uniform field for the pinning trap. It's about 2 meters tall, and inside is our atom trap, and it's all sitting on top of a bee line. A lot of these components were designed
STFC-RAL-CR03 R61: and actually manufactured here at Raoul by the the technology group, and it was a big effort to get installed. But it's all working great. So I'm going to show you a short video, that kind of walks in a cartoon way
STFC-RAL-CR03 R61: through how this gravity experiment actually kind of works. So
STFC-RAL-CR03 R61: here we are just assembling the ad, all at certain everything's flying into space. This happens by the way, and then our experiments gonna cut in half in awkward way. And you see this side, this is where positive funds come from. Over here we have a
STFC-RAL-CR03 R61: radioactive source and a positron accumulator, which is just yet another pending trap. And it sends a bunch of positrons, which we then guide them
STFC-RAL-CR03 R61: up into this Alpha G experiment, where we trap them using penning trap electrodes here and in parallel. We're collecting anti protons from the ad in our ketching trap, penning trap, and then we send bunches along our green line. And send them up
STFC-RAL-CR03 R61: also into Alpha. G, okay. And so within this kind of trap. Now we do the manipulations that we're gonna do to cool and prepare the particles and the right densities make anti hydrogen.
And
STFC-RAL-CR03 R61: we energize the atom trap, which you can tell because these 2 cylinders are glowing alright
STFC-RAL-CR03 R61: and we bring the process together, and predominantly. We expect we get 3 body recombination where we have this witness polytron, that carries away the momentum from this reaction, and then, for the most part the anti hydrogen that we made leaves and a night. So we can mention that with our detectors. But some of them will remain trapped. Okay?
STFC-RAL-CR03 R61: And then we just kind of keep repeating this process. So we keep the atoms that we made in this magnetic trap. And then we keep sending bunches in. And we do this sort of for for this experiment. We did this about
STFC-RAL-CR03 R61: 50 times, and so
STFC-RAL-CR03 R61: we would have maybe a hundred atoms per experimental cycle that we would then use
STFC-RAL-CR03 R61: to conduct an experiment. And the experiment that we're going to conduct to be basically
STFC-RAL-CR03 R61: ramp down these magnets in a very controlled way. Okay, so we, rather than quenching the trap, we slowly ramp down these fields. So if
STFC-RAL-CR03 R61: if the fields at the top and the bottom are exactly equal, and we start turning them off.
STFC-RAL-CR03 R61: Things will slowly start coming down and going up, and we can see where they're coming out where, by looking at where the ocean start with our detector.
STFC-RAL-CR03 R61: and what we sort of expect should happen in our experiment is about 80% or so
STFC-RAL-CR03 R61: we'll annihilate down, and 10% or 20% or so will annihilate in the upward direction.
STFC-RAL-CR03 R61: Okay? And that's the experiment. So that's kind of the hypothesis that we're testing.
STFC-RAL-CR03 R61: Okay?
STFC-RAL-CR03 R61: So why?
STFC-RAL-CR03 R61: Why does it do this? Well, we have a sort of thermal population of atoms in our trap.
STFC-RAL-CR03 R61: And then we have magnetic potentials which in principle are equal.
STFC-RAL-CR03 R61: And there's a background potential that has to do with gravity, presumably. And so, if I have these 2 equally strength magnetic fields that I ran down.
STFC-RAL-CR03 R61: You can see that
STFC-RAL-CR03 R61: which atoms go where is kind of dependent on the trajectories the atoms happen to be in and kind of a complicated way. And the fact that they have some thermal distribution. But you expect some distribution's gonna go down. Some's gonna go up.
STFC-RAL-CR03 R61: Okay? And
STFC-RAL-CR03 R61: you can consider them controlling this as a parameter experiment.
STFC-RAL-CR03 R61: So this red curve here is the so-called uncompensated version of the experiment where the magnetic potentials equal. Okay? But we assume we have a gravitational potential.
STFC-RAL-CR03 R61: We can balance gravity by making one of the magnets a little bit stronger, in which case you might expect half go up and half go down, and then you can over compensate. So you can have the lower potential be much stronger than the upper potential and push particles up intentionally.
STFC-RAL-CR03 R61: Okay? And so the systematic measurement we're gonna make is by varying this feature that we call the bias of the experiment.
STFC-RAL-CR03 R61: Okay? So to get a sense of where these fields are in this experiment, you can take a look at a picture like this.
STFC-RAL-CR03 R61: So these are our pinning trap electrodes. That we're making it to hydrogen width in the middle. And then the trapping potential in the vertical directions generated in this experiment by
STFC-RAL-CR03 R61: 2 magnets we call Mirror A and G, they're separated by about 25 or 26 cm. Okay? And that's where this is gonna take place.
STFC-RAL-CR03 R61: Okay.
STFC-RAL-CR03 R61: looking at the onion going outwards, we have our detector volume, which runs the entire length of the experiment. And then our outer solid.
STFC-RAL-CR03 R61: So the detector for Alpha D is a radial time projection chamber and the barrel scintillator that wraps around it to help Vito Cosmix. And our resolution is a little worse. Okay. Now, now talk to sinks and sorry. 2 cm, and we really don't have much in the way up
STFC-RAL-CR03 R61: as a loophole resolution. Okay, but you'll notice that 2 cm is a lot smaller than the separation between the top and the bottom of the trap, which is 25 cm, so we should at least be able to see if stuff is going up or down out of the experiment.
STFC-RAL-CR03 R61: And then I kind of glossed over the magnets. So the measurement we're doing here involves 2 magnets on this side, and we have an octopole in blue that's wound on this side. But Alpha G over all is very complicated. Magnetic design, which I'll talk about later.
STFC-RAL-CR03 R61: There's an additional precision measurement region that we didn't use for this measurement. And then there's a reflective copy of the experiment on the top. And for the
STFC-RAL-CR03 R61: multiple, we have strong multiples at the top and the bottom, and then something that we call the long octopole that runs the entire length, the experiment. So in principle, if we make it to hydrogen, we can shuffle around in the region. But for the purposes of this experiment, we're just working in this bottom region. Okay, with this 25.6 cm and some numbers to kind of keep in the back of your head if you're interested is
STFC-RAL-CR03 R61: what we call this magnetic bias, and it's sort of defined as the kind of ratio between magnetic potential energy and gravitational potential energy across the front. Okay? And for this particular geometry.
STFC-RAL-CR03 R61: The field difference between the top and the bottom, corresponding with one g. Of gravitational potential energy, is about 4 and a half gallons.
STFC-RAL-CR03 R61: and the connective energy associated with that is about 300.
STFC-RAL-CR03 R61: Remembering that we still have sort of 500 ishmili, kelvin and to hydrogen.
STFC-RAL-CR03 R61: And just look at this bias in a little bit more detail. So if I consider the fields that A and B
STFC-RAL-CR03 R61: if I'm recording on the bias, can I really reporting on strength of the maximum, the magnetic field in those regions and the actual geometric distance between those 2 things. Okay? And so you can pull this out, either by modeling the magnets for measuring. And we'll talk about that in a second
STFC-RAL-CR03 R61: so magnetic. The magnet construction is obviously very important. The superconducting magnets we use for this atom trap are manufactured at Brookhaven and the goal here is to try and make the magnets identical
STFC-RAL-CR03 R61: final, 1% level. Okay? And this involves rather complicated manufacturing. So we sort of optically monitor each magnet layer as it gets found, and we compensate for errors and winding along the way, and then, so doing, have hopefully made relatively accurate magnets. And ultimately what we do then, is measure field differences which we then can compensate with currents.
STFC-RAL-CR03 R61: so in order to make the magnetic field. Of course, you energize magnets. Burns. Okay, we need to control this field difference between these 2 coils. Very precisely, which means you need to control currents very precisely in the face of noise. And the important thing for us is the difference current between the 2 coils. Okay? And so to avoid a lot of issues that you might have with
STFC-RAL-CR03 R61: sort of noise on the relatively large excitation current you need, in the first place, sort of on this order of 70 amps.
STFC-RAL-CR03 R61: we control the differential current with a table supply that runs in parallel to the main current across one of the coils. Okay. So we use this table current with a small current that we can precisely control to compensate for construction differences and then impose this bias as we
STFC-RAL-CR03 R61: modulate the current in these experiments. And so what we're gonna basically do is in a very simple way. You apply the tickle at some given bias. And then you ramp down this name, feel, and the whole thing will just kind of drop while you're maintaining this, bias and variables will come out.
STFC-RAL-CR03 R61: Okay? And so then.
STFC-RAL-CR03 R61: what does this look like? Sort of in practice? We have different biases. So
STFC-RAL-CR03 R61: the red curve here shows this no bias case that I had talked about another curve to any way. That's when you've got no magnetic field. Sorry you have the same magnetic field in region A and G, okay? And then what we consider to be a positive bias is one that will act like.
STFC-RAL-CR03 R61: you know, positive, extra gravitational force pushing down. Okay, so up is in this direction. So a plus 10 G bias here has a stronger magnetic field on the top side will tend to push anti hydrogen atoms down.
STFC-RAL-CR03 R61: Okay.
STFC-RAL-CR03 R61: so that's all. Well and good. We built all these magnets and have this wonderful control system. So how do we measure whether or not magnetic fields are actually doing what they want them to do.
STFC-RAL-CR03 R61: You're like hall pros or Nmr. Prose.
STFC-RAL-CR03 R61: and we have hall prose and and Pros. The problem is that whole prose and and Nmr. Probes tend to be stuff
STFC-RAL-CR03 R61: and stuff tends to annihilate with antimatter.
STFC-RAL-CR03 R61: and you can't put those probes where you want to measure the field. Okay? So we have a lot of sort of
STFC-RAL-CR03 R61: probes like this to just kind of generally monitor what's going on with the experiment. But to actually measure what the fields are in the trap.
STFC-RAL-CR03 R61: So-called trap field magnetometry for us is quite tricky. Okay, and so we use a number of techniques.
STFC-RAL-CR03 R61: the main workforce is something that we call ecr, which is electron cyclotron resonance. Okay? So if I have an electron in a magnetic field, and I illuminate it with microwave radiation, which is resonant with the cyclotron frequency of the particle. I can excite cyclotron motion. If I have a little plasma.
STFC-RAL-CR03 R61: What I do is heat that population of particles up. I can measure the temperature. Okay. And if I pick the resonance, I see the temperature. My plasma has gone up. So we do a lot of measurements where we load successive little plasmas into our trap. We illuminate each plasma with a different microwave frequency
STFC-RAL-CR03 R61: and measure the temperature after we've done the illumination. And so we got these spectra that look like this. Okay, where the peak is the typically the main ecr resonances where the resonances. These sidebands or bounce resonances and other structures have to do with how the plasma actually sits in our specific potentials. Okay? So there's
STFC-RAL-CR03 R61: systematics. And how we interpret these things. Okay, but we can kind of measure the fields to about a Ppm ish level. If they're uniform, it becomes much more complicated to measure the non uniform fields. Okay.
STFC-RAL-CR03 R61: but we, we use this as a work course to measure it. Throughout the course of the experiment.
STFC-RAL-CR03 R61: and we do this by extracting little bunches. So we load
STFC-RAL-CR03 R61: kind of relatively big source plasma, and we can pull out little tiny scoops of particles that frankly, are less like plasmas, more like scoops. We can move them around in our pending traps, different places and switch them. And so we can get sort of a millimeter
STFC-RAL-CR03 R61: by millimeter, by millimeter ish volume in the trap that we can measure the field at, and you can move that plasma around. So you can kind of pretty easily map out the magnetic field along the axis of the trap. Okay.
STFC-RAL-CR03 R61: so then, to carry out the gravity experiment with all of these things in mind. We make a trap and stack anti hydrogen for 50 s. That takes about 3 or 4 h. Okay, we ran down this long mark to pull
STFC-RAL-CR03 R61: and then we measure the magnetic fields at these full trapping currents, using Ecr, okay? And then we slowly ramp
STFC-RAL-CR03 R61: these 2 potentials down to kind of the tense Gauss level. So that trap depth we're left with at the end about 10 ish milk, Kelvin deep, or something like that. We do that over about 18 s while maintaining this constant magnetic jump.
STFC-RAL-CR03 R61: Okay? And then.
STFC-RAL-CR03 R61: while this is happening, we're identifying the annihilation. They go up and down. Okay? And then we measure the magnetic field at the end to check the bias. And we repeat this for many magnetic biases and accumulate statistics. So we have about 300 h per events for bias. Okay.
STFC-RAL-CR03 R61: what does this look like?
STFC-RAL-CR03 R61: So a controlled experiment is like, I do this. But II just like, don't shut off.
STFC-RAL-CR03 R61: II like, leave one magnet entirely, energize, push everything down versus up to identify events that look like stuff going down and up. Okay, they're not quite symmetric because the mechanical structures and the tramp weren't symmetric. Okay? But you get data sets that look something like this. Okay, so these are annihilations that went down and annihilations that went up. Compared with our simulations that don't include detectors hearing. That's if I just do a real extreme version of this.
STFC-RAL-CR03 R61: Okay. But the actual experiment is, I'm going to vary this bias
STFC-RAL-CR03 R61: in this case, minus 10 g plus 10 g. And remember, plus 10 g. It means that the magnets are adding to normal gravity and pushing anti hydrogen down minus 10 g. Is pushing things up in this direction. Okay? And so, as I kind of go through these biases, I can see the population shifting from one side to the other, and the sort of region of interest is kind of in the bit.
STFC-RAL-CR03 R61: Okay? So if we focus in on that.
STFC-RAL-CR03 R61: what we get is a data set that looks like this. So from this data set, we calculate for a given bias the probability that the atoms going down. Okay, it's just sort of an arbitrary choice we've made. Okay. So if I have a strong bias.
STFC-RAL-CR03 R61: I expect stuff is gonna mostly go down. Okay. So I should be at 100% on this side. If I have a negative bias, I expect things should mostly go up. So I'm at a low probability this side. Okay? And if they're totally balanced.
STFC-RAL-CR03 R61: But, thanks to my bias, balance is gravity.
STFC-RAL-CR03 R61: I would expect normal gravity to be biased at minus one GA base of magnets are pushing up at one Gd, gravity's pushing down with one G, and then I kind of expect something like 50% of the atoms to come out.
STFC-RAL-CR03 R61: Okay, the blood crosses are the data.
STFC-RAL-CR03 R61: Okay, with various errors in statistics and systematics, and the orange curve is a simulation for what we expect. The anti hydrogen atoms in this experiment to do under these conditions. Okay? And it has an error bar that has to do with systematics in the simulation. Okay?
STFC-RAL-CR03 R61: And
STFC-RAL-CR03 R61: we can compare this to other simulations.
STFC-RAL-CR03 R61: So here's our data.
STFC-RAL-CR03 R61: Here's G is equal to one. And here's some exotic things. This purple curve is repulsive gravity or so-called anti-gravity. So this is for some reason anti-matter just behaves at exactly the opposite way of normal matter, and just goes up with an acceleration of G on Earth.
STFC-RAL-CR03 R61: And I think we've definitively ruled that model out with our days. So anti-gravity totally ruled out. Okay, the green curve is just that our particles were entirely unaffected by gravity in the experiment.
STFC-RAL-CR03 R61: Okay? And that is also largely rolled out to pretty high significance by the experiment.
STFC-RAL-CR03 R61: But of course, like just rolling up models is never enough. People want a number. Okay, who who doesn't want number. So you can come up with a number by then simulating sort of the distribution of effective G-values, and then do sort of best fit between model and data. And what you get as a number is that G bar or the gravitational acceleration of anti hydrogen, anyway, is point 7 5
STFC-RAL-CR03 R61: plus or minus 1 3 plus or minus 0 point 1 6 g. Okay. And these
STFC-RAL-CR03 R61: our
STFC-RAL-CR03 R61: errors coming from measurement, and then errors coming from our ability to simulate these are alright.
STFC-RAL-CR03 R61: so great.
STFC-RAL-CR03 R61: largely consistent with one right?
STFC-RAL-CR03 R61: Broadly speaking. so what are the limits
STFC-RAL-CR03 R61: to this experiment? Where are these errors coming from?
STFC-RAL-CR03 R61: So
STFC-RAL-CR03 R61: the the primary era that we have is in our ability to measure? Okay. so we need to model and control the currents
STFC-RAL-CR03 R61: and persistent currents. Okay? So it was super conducting
STFC-RAL-CR03 R61: magnet. In addition to just the current to put in. You get persistent currents that get created when you have changing flux around superconducting materials that create flux
STFC-RAL-CR03 R61: lines that get pinned and they look like effective current loops. And those create field errors in superconducting magnets. Okay?
STFC-RAL-CR03 R61: And to get a scale for the idea in this experiment. Persisting currents that we measure we have when we ramp these magnets down is about 10 Gauss on axis.
STFC-RAL-CR03 R61: Okay? And one G is 4 and a half dous. And we need to control this precision than 4 and a half desk. So how does that work out?
STFC-RAL-CR03 R61: And so so so it starts the long magnetometry campaign? Okay, where you characterize persistent currents in the experiment, and you measure what happens to these currents when you ramp down in the 2 locations of interest
STFC-RAL-CR03 R61: and persistent current decay. And this is a known feature. Persistent currents which are. I don't know, somewhere between phenomenologically modeled and voodoo. Okay, but they decay and thankfully
STFC-RAL-CR03 R61: within our experiment. They decay at the same rate under mirrors A and G. So even though we don't necessarily hit or have the exact absolute magnet magnet feel every time during a ramp down that we want.
STFC-RAL-CR03 R61: When this current decays, they decay, and they maintain the bias that we've set on them.
STFC-RAL-CR03 R61: Okay? So when evaluating the sort of systematic error on this, we include an error which is the largest observable persistent current difference. In these locations. Okay? And this turns out to be a relatively small error. Actually, because these 2 things decay rather closely to one another.
STFC-RAL-CR03 R61: But that's a static measurement
STFC-RAL-CR03 R61: that we do at the end of the experiment.
STFC-RAL-CR03 R61: Okay, these persistent currents are dynamical things that happen when you change plus
STFC-RAL-CR03 R61: and we're ramping the magnets data which is changing bugs. So what we actually need to do is magnetometry throughout the course of the rant down with pretty high precision.
STFC-RAL-CR03 R61: And we're able to do that with the technique we developed. That involves not the cyclotron residence, but observing the magnetron procession of our plasmas in the trap. And we can kind of get sort of
STFC-RAL-CR03 R61: one hundred-ish microsecond resolution on the magnetic field over the course of the ramp, and we could measure
STFC-RAL-CR03 R61: the size of these persistent currents which, also listly turn out to be pretty well balanced between the top and the bottom. Okay, so dynamical field effects are also important. This experiment, but so far not on the level that you care so much.
STFC-RAL-CR03 R61: Okay. so now
STFC-RAL-CR03 R61: comes all the complexity. I showed you this plot here, where I have
STFC-RAL-CR03 R61: bias on the X-axis and some data.
STFC-RAL-CR03 R61: But, in fact, the bias I actually have over the course of the experiment that I actually run after you measure all the effects of these persistent currents, and take into account the fact. These are not cartoon magnets, and they have different physical sizes. Is a bit more complicated. So as I kind of basically maintain what is effectively a constant current bias.
STFC-RAL-CR03 R61: the bias I actually get by measuring the field train, the top and the bottom and subtracting them out. Varies as a function of time. Okay, so this is an example for what actually happens to the measured bias, taking into account all of these different things
STFC-RAL-CR03 R61: as a bunch of time in the rampant, and you can see it varies quite a bit
STFC-RAL-CR03 R61: over the course of the RAM sound. But most of our data this is showing where the events are coming out is is happening towards the end of the ramp, at which point the bias is relatively fixed. Okay, and so what we do to evaluate a bias is, we kind of take a weighted average between the bias that we measure. And when data comes out.
STFC-RAL-CR03 R61: okay, so this is kind of more like a a label for something that's like a bias distribution. If you will. But at the end of the day, when we're comparing data to simulation, what we're doing is we're simulating the behavior of the fields.
STFC-RAL-CR03 R61: not the behavior, necessarily the currents. And we're comparing them the simulation to the distributions that we measure from the experiments.
STFC-RAL-CR03 R61: Okay? And then you can go. Look at our paper and see all the uncertainty tables. But the one I want to call your attention to is the single largest uncertainty of point 1 6 g. And it comes in from modeling of the magnetic fields specifically off axis. So we're very good doing on the axis of the experiments in both space and time. We know very little of the fields off axis, and we have these very unhomogeneous opticals
STFC-RAL-CR03 R61: that also have persistent currents that we can try and model. But we're never going to find until we measure. Okay. So at the moment, this measurement specifically is limited by our uncertainty in the magnetic field, and that comes both into play as a systematic and measurement, as well as the systematic in our, in our simulation, because we can only simulate the fields as well as we can actually measure what they are.
STFC-RAL-CR03 R61: Okay. So that's a summary of the gravity measurement to date.
STFC-RAL-CR03 R61: Where are we going? So we'd like to kind of head towards 1% measurements.
STFC-RAL-CR03 R61: And what we need to do to achieve that is make these curves that I was showing simulated curves steeper. Okay? So this red curve shows the kind of slope as a function of bias for this probability measurement. For the sort of experiment we conducted, and the 1% measurement supposed to be a much steeper curve. Okay, so we have a plan.
STFC-RAL-CR03 R61: We're going from here to there. So what does that plan involve? Okay? And it involves this so called precision region. So we did a, we did a measurement down here.
STFC-RAL-CR03 R61: Okay. And it's we was the first place we could do the measurement. We made the hydrogen there.
STFC-RAL-CR03 R61: And we can do that. But we designed the experiment to move the anti hydrogen into the so-called precision region. And the thing that makes this region precise is a few things. One is that the octopole is weaker, and therefore you have less influence of persistent currents in the octople itself.
STFC-RAL-CR03 R61: The superconducting wire that we use has less superconducting material spoils. So they have or should have less persistent currents. And then the field effects of these other magnets will be coupled. They'll be canceling each other geometrically, because
STFC-RAL-CR03 R61: the idea is to be able to run these magnets symmetrically. So you kind of get a match to the resus. It cancels the effect out in the middle of the experiment. Okay. So doing this much should improve.
STFC-RAL-CR03 R61: This applied bias potential. But these analysis foils are not just simple solvites. Okay, you also have to correct for the geometry of the field
STFC-RAL-CR03 R61: when you go off. Access right? Like the field, is not just like a flat wall. I solid. So normally, the field goes up and down, rather down and up. And what I actually want to have at the top of the bottom is a flat potential and so there's additional correct records
STFC-RAL-CR03 R61: that flatten out this effective potential that the atoms see at the top on the bottom of the trap.
STFC-RAL-CR03 R61: There's a match octopol that helps the optical influence on that as well.
STFC-RAL-CR03 R61: Okay? And so, bringing these 2 things into play
STFC-RAL-CR03 R61: are also intended to flatten the curve.
STFC-RAL-CR03 R61: And one more thing. Okay.
STFC-RAL-CR03 R61: we are at 500 milli, kelvin anti-hydrogen in the experiment at the moment. But we'd be doing a lot better if our hydrogen was told.
STFC-RAL-CR03 R61: and we've also demonstrated in Alpha that we can, in fact, use doppler laser cooling to reduce the temperature of our hydrogen atoms to about tense. 10 ish, millish. Millical.
STFC-RAL-CR03 R61: Okay? And so of course, it's still quite a lot more than this. 300 micro pop. And it's a distribution, though we can throw away particles we don't want.
STFC-RAL-CR03 R61: Okay.
STFC-RAL-CR03 R61: but significantly, better than 500 bills.
STFC-RAL-CR03 R61: Okay, so this should be a significant improvement for us as well.
STFC-RAL-CR03 R61: And that's the kind of story of where we're going at the 1% level. So developing these techniques and improving our magnetometry and bringing into operation the rest of our trap.
STFC-RAL-CR03 R61: So beyond the 1% level, you have to do something else. Okay, so antimatter interferometry for gravity measurements.
STFC-RAL-CR03 R61: If you're in a situation where you've got colder atoms. you can set up sort of
STFC-RAL-CR03 R61: atomic interferometers in the vertical direction, and you can probe effective gravity, gravitational potentials along one arm of your interferometer.
STFC-RAL-CR03 R61: this involves
STFC-RAL-CR03 R61: challenging layers of different geometry. Okay, but it's starting to be something that we're now thinking about more seriously in Alpha, since well, for reasons that are not presented here, we're getting better, laser cooling. We're getting better, producing it to hydrogen. And so we have a larger population of atoms over with.
STFC-RAL-CR03 R61: okay. so thanks for your attention. And
STFC-RAL-CR03 R61: I hope I've convinced you that I probably have to retire.
STFC-RAL-CR03 R61: My dad cartoon, at least for the most part. It seems like the anti atom is more or less falling down.
STFC-RAL-CR03 R61: Any questions. Thank you.