Ivana Hristova: Welcome
Saskia Charity: Thanks very much and.
Saskia Charity: yeah Thank you very much for inviting me to give the seminar it's.
Saskia Charity: Great to speak about the first results from this experiments and.
Saskia Charity: Okay, so i'll get started with a bit of history, about the T minus two discrepancy before talking about the experiment and so G most to me on experiments.
Saskia Charity: Quite a long history and the most prior to the family lab experiment that previous measurement of the new on G minus two was with the brookhaven.
Saskia Charity: experiments which announced its final results in 2005 and had a famous discrepancy from the standard model prediction at the 3.7 Sigma level.
Saskia Charity: And ever since that measurement came out there's been excitements among the theoretical community and.
Saskia Charity: strongly motivated that repetition of the experiments with reduced statistical uncertainty in order to confirm or deny the discrepancy that they observed.
Saskia Charity: To the size of the brookhaven standard model discrepancy was 2.4 parts per million, and this equated to a 3.7 Sigma and discrepancy with the standard model.
Saskia Charity: And the target eventual target finally with the third lab experiments is equals statistical and systematic areas of 100 parts per billion each and but today's talk is on the ground, one data.
Saskia Charity: Which is a data set of similar size to brookhaven including something around 10 billion neurons.
Saskia Charity: And this plot on the right just shows the precision of the measurement that the family lab results in the context of all of the size measurements that have been made.
Saskia Charity: And so we can see that we're just a bit more precise than the than the brookhaven experiment, and this is very high, precision, particularly for an experiment a collider facility.
Saskia Charity: So a bit of background about what the new on T minus two is so the me one has a magnetic moment that couples to spend via this quantity, called the Joe magnetic ratio.
Saskia Charity: So this is the expression for the magnetic moment, and you can see that it's a vector quantity that's entirely defined by the spin of the Milan.
Saskia Charity: And what happens with a Milan, if you inject if you have a view on in a vertical magnetic fields, the magnetic moment will spin about the direction of the magnetic field vector and the up sorry.
Saskia Charity: yeah, and this is because of the interaction of the magnetic moment with the external magnetic fields and the spin processes at a rate which is determined by this quantity g.
Saskia Charity: But what we actually measuring that you wanted to experiment which i'll go on to talk about is the difference from to of g.
Saskia Charity: Because direct predicted that for a family on G should be exactly two and, but we know that it's not exactly to because what happens is that there are virtual live interactions which change.
Saskia Charity: which change the rate at this precision procession frequency, so the Milan is constantly interacting with virtual particles and because of its mass it can actually interact with nearly all particles that we know about in the standard model and maybe more.
Saskia Charity: So a bit of theory, I think you had a talk from Thomas toy know, last week, is one of the leading standard model theorists in the G minus two.
Saskia Charity: Community, but the standard model prediction of a new is made up from contributions from all different types of standard model interaction so 99.99% of this standard model.
Saskia Charity: prediction of them you on comes from qed terms that are also electroweak terms and hedonic terms which are divided into hydraulic vacuum polarization terms and hedonic like by light interactions.
Saskia Charity: And, and the, although they account for nearly all of the value of a new standard model, the uncertainty of the Community is very low.
Saskia Charity: And the uncertainty for the standard model prediction is almost entirely dominated by the uncertainty of the non competitive term, so the hedonic vacuum polarization terms, so this is where most of the uncertainty on the standard model prediction comes from.
Saskia Charity: But today i'm going to talk about the experiments so let's go to the lab and i'll describe the accelerator contacts and where we get the new ones from a formula, so I mentioned previously, that the.
Saskia Charity: Experiments at brookhaven was where this discrepancy was first measured but the motivation for repeating it.
Saskia Charity: was based on that we needed highest assistance in order to reduce the uncertainty and the best way to achieve that was to move the experiments fermilab.
Saskia Charity: And the reason for that is that formula we can achieve and lower instantaneous rate to larger tone to.
Saskia Charity: me on rate than at brookhaven so we can have fewer neurons propel but a higher a bit more films per second, meaning that we can in total record me mom your arms, but with a less intense beam.
Saskia Charity: So this is just a sort of top down view of the accelerator complex, this is the old tevatron, which is no longer in use.
Saskia Charity: And if we come over here we can see the different parts of me on campus So this is the G man is to experiment which.
Saskia Charity: Is in this building here, this is the meat experiment which will run after G minus two and prior to the gym is to experiment here, you can see, this delivery during so the Needle, on fermilab.
Saskia Charity: Initially start out with protons which are instance on their targets.
Saskia Charity: And, which produces positive pions so that's actually why we use me plus an experiment, rather than B minus because the crocs cross section positive by production is larger, so we can have higher statistics if we use positive meals in the experiments.
Saskia Charity: So after and after bill after arriving at saving the experiment took four years to build so back in May 2013 here's a picture of.
Saskia Charity: This small collaboration at the time at the day of the groundbreaking and then later in that year, the magnets and took his famous journey from brookhaven by barge.
Saskia Charity: All the way around Florida up the Mississippi river and it arrived at saving lab a few months later.
Saskia Charity: Having navigated the highways and the tollbooth just outside fermilab the magnetic storage ring arrives at the campus and the building was completed in 2015.
Saskia Charity: So between 2016 and 2017 there was two years of making the magnetic fields, uniform and a process which is called shipping, and so we after its journey you assemble the magnets again and.
Saskia Charity: try and make it as uniform as it was back when I was at brookhaven and this really was a detailed process that took a couple of years in order to really achieve the precision and uniformity quiet on the magnets.
Saskia Charity: And then in 2017 here's a picture of the small party that we had in the control room celebrating the arrival of the first female.
Saskia Charity: and storage right and being able to see it in the detectors and from then there was a large period of tuning and things to get everything ready for production running and the run one data that i'm talking about today.
Saskia Charity: The data taken to that began in February 2018 so here is the magnetic storage ring and its various stages of construction at fermilab so here's the.
Saskia Charity: Bottom parts of the yolks being installed this middle picture shows the superconducting coils which are the parts that came via barge.
Saskia Charity: And these were the things that were this whole magnet was designed for the brookhaven experiment, and it was so successful in achieving its goals that we.
Saskia Charity: The best thing to do, for this one was to definitely reuse the same magnets and here's what the magnet look like when it was finished being assembled before we installed everything else in the experiment.
Saskia Charity: And the original goal for the uniformity of the magnetic field was to achieve the same as what we had at brookhaven.
Saskia Charity: But actually due to some additional Sherman devices that we were able to install we achieved a magnetic field of three times better than this goal so it's an incredibly uniform magnetic field with very few deviations around the ring.
Saskia Charity: OK, so now that we've got our magnets, how do we measure, a million, so the principle of the experiment is to inject a highly polarized beam of neurons.
Saskia Charity: With a low moments and spread into this magnetic storage ring and the Milan, Spain will undergo different types of procession.
Saskia Charity: So what this diagram shows is that the spin procession frequency is actually slightly faster than the Cyclotron frequency of the moon orbits so over time, a difference between these two frequency sees builds up.
Saskia Charity: And the difference between the sprint procession frequency and the Cyclotron frequency, is what we call the anomalous procession frequency.
Saskia Charity: And it turns out that when you combine these terms and do some cancellation the anomalous recession frequency.
Saskia Charity: depends directly on the new on anomaly, a new, as well as the magnetic field strength be so in order to measure, a new to high precision, we need to make to measurements very precisely one is the novelist procession frequency I knew and the other is the measurement of the magnetic field.
Saskia Charity: So to extract a new, we need to know both Omega A and B to high precision, so what we actually do in the experiment is we measure this ratio, which is the ratio of Omega a.
Saskia Charity: To this quantity Omega P, which is effectively just the magnetic field expressed in terms of lava frequency of a.
Saskia Charity: proton in a spherical water sample which is effectively a free proton so we measure the ratio of the anomalous procession frequency to the lower frequency of these protons, which is a quantity, that is effectively the magnetic field and as well we you we.
Saskia Charity: extract a view from knowledge of these other very precisely known quantities from other experiments.
Saskia Charity: And the precision of all of these measurements is much lower than the precision, which, with which is our target of the measurement of this ratio.
Saskia Charity: So, in order to measure ad We just need to measure the ratio of Omega Omega P it's not quite that simple, and so this expression, our first the ratios are.
Saskia Charity: actually has a great number of terms, so it's we can't we can measure Omega a directly, but there are a number of corrections that also needs to be very precisely known.
Saskia Charity: And for the magnetic field part, we need to measure and a calibration factor, and this is to equate the protons in the nfl probes in our experiments to the protons in the measurement standard.
Saskia Charity: We also need to measure the MAC the beam distribution of the museums and.
Saskia Charity: We need to combine that with the measurement of the magnetic field inside the storage ring, so that we can obtain the average magnetic field experienced by all of the neurons so it's not enough just to know the absolute value of the magnetic fields.
Saskia Charity: and be happy with that we have to continuously measure the magnetic field throughout the experiments, we have to continuously measure the beam profile and the beam dynamics throughout the experiments.
Saskia Charity: combine those two things, and there are also corrections due to other operating conditions in the experiment that we need to measure, precisely as well.
Saskia Charity: So i'll start by talking about how we measure and select the beam so this page to show us some of the inside of the ring and here are the tracking detectors which were built in the in the UK, which we use to measure the beam profile.
Saskia Charity: So the beam is injected and been a positive ions which is highly polarized and it comes to us from the accelerator complex and we injected into the storage ring through an influx of magnet.
Saskia Charity: Which is a magnet that shields it from the magnetic fields of of the storage ring in order to inject it into the beam without perturbing the being too much and, at the end of the electromagnet we have.
Saskia Charity: Some scintillating fibers and under scintillating part which measure both the spatial distribution of the injected beam and the time distribution, so this plot here shows the typical time distribution of the injected beam and the beam is 125 90 seconds wide.
Saskia Charity: So, once this beam has been injected after it's gone around a quarter of a turn.
Saskia Charity: The objective neurons are 77 meters millimeters away from the ideal orbit radius because it's not practical to inject them exactly on the desired radius.
Saskia Charity: And so what we need to do is to apply a fast break your magnetic pulse, in order to kick the murals on to their correct orbit path so this plot and.
Saskia Charity: Show us in the dotted line, this is the time profile of one of the injected pulses.
Saskia Charity: And in black overlaid here is the kicker pulse, so this is what we would how we measure the radio magnetic field applied.
Saskia Charity: And this is what that pulse would look like so obviously in an ideal world, you would have all of your radio pulse applied to the millions on the first turn to avoid kicking them again and applying for the pulse.
Saskia Charity: And i'm consecutive turns so each of these blue lines is the Cyclotron period so in an ideal world you'd have all of this field applied in the first term.
Saskia Charity: But it's quite difficult to design a kick and madness that applies such a large field in such a short time, and so we have a slight effect which needs to be corrected, for which is that there's some amount of.
Saskia Charity: kick a field which has felt by some of them, he wants in a subsequent turn, so this is one of the corrections that i've talked about a bit later and.
Saskia Charity: The other thing is that if you had a slightly if you're not able to apply a kick strength as high as you would like you won't kick your neurons up to the exactly ideal orbit.
Saskia Charity: And so, in the run one data you'll see that the beam is slightly off Center, and this is because in run one we weren't kicking it the full ideal strength.
Saskia Charity: In the subsequent data, we are, but in run one we weren't so this also introduces a correction that we need to apply for the fact that the neurons are all on their central or bit.
Saskia Charity: So the next thing you have to do is focus the beam so the objective beam has got some vertical spreads.
Saskia Charity: And if we didn't apply electric fields in some parts of the ring you would slowly lose your beam through the top and bottom and because you weren't focusing the beam vertically.
Saskia Charity: And so we have electrostatic quadruples to do that, and these plates cover 43% of the total circumference of the ring.
Saskia Charity: So, now that we're storing the beam, we need to detect it, so the positive me on circulating around work decayed positrons which are detected by suites of 24 electromagnetic kind of remixes which furnish the inside of the ring.
Saskia Charity: And this is a similar detection principles what was used in the brookhaven experiments.
Saskia Charity: But one of the main improvements is that the new kind of segmented so we have spatial information about where the cables or trump's came from, so that each detector is an array of six by nine lead fluoride crystals.
Saskia Charity: Which got very high time resolution, so that we can be counting the cables or trans very, very quickly.
Saskia Charity: The next set of detectors is the tracking detectors which I flashed a picture of before.
Saskia Charity: And so, there are two stations of tracking detectors one at around 180 degrees and one at around 270 degrees and each of these detectors consists of eight.
Saskia Charity: modules and one module contains four rows of 32 straws, so there are 128 gasfield stores, but module and these in further decay positions.
Saskia Charity: or info me on being profile by extrapolating the tracks of the decay positrons so the cake was transmitted through the tracking detectors.
Saskia Charity: We work out there trajectories and from that we can determine the beam profile in the storage ring, so these were all the tracking detectors were provided by the UK for the experiment.
Saskia Charity: So, now that we've got our captors, how do we actually measure, a mega a.
Saskia Charity: So in the wanda Kay the cables are trying is preferentially admitted in the direction of the neon spin and this correlation between the spin direction of the momentum direction is strongest for high energy milan's so.
Saskia Charity: If we look at this animation you can see that there's an oscillation in the number of detected decay positrons above a threshold energy.
Saskia Charity: And as a function of time, so when the view on spin is aligned with its momentum your detective will see more to cables have tons.
Saskia Charity: Of when this bonus points away from the detector you'll see fewer the cables problems.
Saskia Charity: And this modulation and the number is exactly equivalent to that anomaly frequency Omega a so symmetric a mega a We simply have to count the number of the cables of sean's above a threshold energy as a function of time.
Saskia Charity: So here's, what are the case signal or a measurement signal looks like in just one hour of data, so this plot shows this isolation of this weekend plot accumulating just over one hour, so there are a number of features here, the first, you can see the.
Saskia Charity: exponential decay of the neurons with the boosted lifetime of 64 microseconds so over this time and the millions of the cave away, and then the next of this feature here is this sign aside or oscillation.
Saskia Charity: And so, this all you have to do is count the number of this is just the number of positions versus time you can't remember positrons versus time fits the sine wave to it and extract your Omega a frequency.
Saskia Charity: And that is not the end of the story, because of real world considerations to do with how we actually.
Saskia Charity: store and measure the beam mean that we have to apply some corrections that I mentioned, so the expression for Omega a I said dependence just on the anomaly, a new and the field.
Saskia Charity: But these two terms represent two productions, so the first of these is what we call the airfield correction and it's.
Saskia Charity: This term would completely cancel out if all of your murals were able to have the momentum of 3.1 gv so.
Saskia Charity: You wouldn't have this direction at all at all of if you have no momentum spread of your beam and it will all the new ones, have the same.
Saskia Charity: have this magic momentum which cancels out this term, but in practice, there is a momentum spreads so some of the not all of them, the ones will have this term cancel out, so we have to measure and.
Saskia Charity: We have to measure how to.
Saskia Charity: account for this correction because of this momentum spread and the other correction is what's called the pitch correction, and this has to do with the fact that the.
Saskia Charity: beam has got some vertical spread and that some of the big ones will have a vertical momentum component which is aligned with the vertical magnetic field, so if you're the one has got some vertical momentum in the same direction as the be field.
Saskia Charity: This will reduce the measured Omega a for those neurons so we have a correction to account for the meal ones with some vertical angle as well.
Saskia Charity: As the both of these corrections depends on your experiment settings so the strength that which you're running your.
Saskia Charity: electrostatic quadruples and they both less than not one five ppm in terms of the size of the correction i'll talk a bit more about all the productions and their sizes and uncertainties, at the end.
Saskia Charity: OK, so now that we've talked about the tracking detectors measuring the beam.
Saskia Charity: So, in order to quantify those corrections I just mentioned it's crucial to measure the beam profile as a function of time.
Saskia Charity: In order to understand how many of these neurons and which means will not be in this ideal orbits and which means will have a larger correction.
Saskia Charity: So we use the tracking detectors to measure the decay positrons and infer that the key positions so these videos show the new on being this is data.
Saskia Charity: That shows the meal on beam oscillating throughout one fill.
Saskia Charity: So the top plot here shows the mean radio position of the beam as a function of time in the fill.
Saskia Charity: And the bottom plot shows and oscillation in the rms of the beam so the spread of the beam as a function of time throughout the phil, and so there are clear oscillations in both of these.
Saskia Charity: and actually there's also i'm just showing the radio oscillations here but there's also an effective vertically, which is less big in terms of amplitude but still significant when we come to correct our data, so this is.
Saskia Charity: That yeah what data from the trackers and showing the radial oscillation in both the mean and the width.
Saskia Charity: And you can see, and the plot on the right here, this is a 2d plot showing the radio position as a function of time and this just illustrates as well this oscillation So you can see, and.
Saskia Charity: Firstly, we have an oscillation in the position and then you can also see the beam bunching up this high momentum so this higher and radio position, so this, you can see both the oscillation in the position and the oscillation the way.
Saskia Charity: Okay, so I mentioned that we just fit our sine wave and extract the frequency, in order to measure, a new.
Saskia Charity: But if we just fit the if we just fit our data with the simple expression and and take the residuals from the date of the fit and fit with that simple expression, we have a number of terms which are apparent in the fit of those residuals.
Saskia Charity: And so, all of these different terms correspond to different frequencies to do with different oscillations that we measured with the tracking detectors.
Saskia Charity: And so there are oscillations in the vertical with the vertical position the.
Saskia Charity: Radio with the radio position and combinations of all of those as well, so there are a large number of terms that appear in our 50s that we need to make sure we're accounting for an outfitting function.
Saskia Charity: So that we get a good fit to the data, so there are additional terms included in the final fit function which actually has a total of 24 parameters and, in addition to just the five.
Saskia Charity: OK, so now we've measured our Omega a term and we've talked about how we measure them you on been profile the.
Saskia Charity: Another sort of half of the measurement really is to measure the magnetic fields and throughout as a function of time throughout the experiment so that's what i'll talk about now.
Saskia Charity: Okay, so measuring the magnetic field.
Saskia Charity: So here's a diagram with the Cross section of our storage ring magnets which has a number of features so.
Saskia Charity: The meal on storage region is in the middle of these two Paul pieces have, and this is the region in which we try and keep the magnetic field incredibly uniform across this this me on region.
Saskia Charity: And so, in an ideal world your magnetic field would be perfect uniform everywhere, but in practice that's difficult to obtain.
Saskia Charity: So what we have to do is continuously measure the magnetic field, so that we understand the changes in the field over time and over the space of whether be on circulate, so we have two different measurement.
Saskia Charity: tools, much to do that, one of which is the fixed probes which are a suite of Mr graves installed above and below the new on storage region, and these continuously track changes in the field over time.
Saskia Charity: But it's not those they give you quite enough measurement because they cannot imagine the field inside the me on storage region so every around three days we actually have to stop the beam for three hours in order to drive this.
Saskia Charity: trolley around the whole ring and it takes about three hours to go, it has to go around and then come back to measure the fields.
Saskia Charity: And it's got 17 animal groups on it as well, so this is where the trials mapping fields and above and below the fixed price which are continuously tracking the changes.
Saskia Charity: So what does the field look like inside the storage ring so from a typical trolley run these at the crosses represent the trolley and Mr probes.
Saskia Charity: And you can combine the frequencies, which are measured by these Mr probes in order to obtain a sort of 2d map of the field in the beyond storage region so.
Saskia Charity: Ideally, this contour plot would just be one color everywhere.
Saskia Charity: But we try and tune all of our streaming devices and as well as the shipping devices that we changed at the very start of the installation, we have.
Saskia Charity: Active shipping, where we can apply small currents across the me on beam across the me on storage region and to try and cancel out some of these gradients.
Saskia Charity: But in run one we weren't able to fully cancel out all of these terms that we had some shapes here in the field map, so this is why we have to measure it all the time in order to really understand what this field looks like.
Saskia Charity: So the 2d spatial magnetic field console map can be described in terms of multiple expansion of the field in terms of our theater.
Saskia Charity: And so, if we took this field map here, the point is this slide is just to show that these are the different shapes which we can extract if you performed a two dimensional fit to this contour plot so each of these terms is a different.
Saskia Charity: terminus expansion, so we use this function to fit this console plots and extract all of these different shapes and the trolley is sensitive to a very high order in this expansion, so the trolley can men can measure.
Saskia Charity: field shapes even higher than the order i've shown here and but with the fixed probes the way that we.
Saskia Charity: extract these beam these field shapes is from a geometrical combination of each of the probes so we're only sensitive to the first the dipole tampers the first three.
Saskia Charity: field shapes with the fixed groups, so we have to measure the trolley to make sure that we're capturing all of the shapes in the field, and then we track the changes in the first enemy significant terms, using the.
Saskia Charity: Fixed probes in between trolley runs so just explain about this expression.
Saskia Charity: The Omega P measurement the field measurement we have a calibration we have the magnetic field spatial distribution weighted by the spatial distribution of me on beam.
Saskia Charity: And the corrections, so the measurement the crucial things that we need to measure the spatial distribution of field components everywhere in the storage region.
Saskia Charity: track changes over time and wait this by the me on intensity and distribution in order to obtain the average field of experienced by the millions.
Saskia Charity: So this truly is a cylindrical Shell which houses 17 and Mr probes and, as I said, every three days it's going to drive around and take.
Saskia Charity: measurements of all of these slices and it measures of between eight and 9000 slices and each Troy Brown.
Saskia Charity: And, and from a typical trolley run we extract these terms in this beam shapes that I showed on a couple of slides ago So if you plotted each of these terms as a function of azimuth, this is what you'd see for a typical trolley run.
Saskia Charity: So if we just had trolley runs we would only have measurements every few days, so this plot the top left shows the time of the run one data and so you'd have this is just showing the dipole term, which is the bicycle term.
Saskia Charity: The most important one, and this shows just the variation in that term move time throughout run one.
Saskia Charity: But we what we're interested in is the field that means actually seeing, so we have to track changes in the field.
Saskia Charity: and fill it in with fixed prob data, so you can see that the fixed probes do still track changes which we wouldn't know about if we didn't have them so it's crucial to have these fixed probes and measurable that these changes.
Saskia Charity: But they only contract changes not absolute fields, so we have to calibrate the fixed price measurements using the trolley measurements and it's not enough just to do that, once because the calibration drifts over time.
Saskia Charity: Due to the fact that the fixed price sensitive to all high orders and expansion of the field, so we have to regularly have truly runs to make sure that.
Saskia Charity: This calibration drift here, so this plot shows the fixed prob data, which has been calibrated with Charlie brown here and then three days later, you can see, this is how much it's drifted away from its calibrated value so we recalibrate all the data using the second trolley run.
Saskia Charity: Okay, so the next part of the magnetic field measurement procedure is to calibrate the and Mr probes.
Saskia Charity: And this procedure is done so that we can relate the protons in the nfl probes and experiments which are in a petroleum jelly medium.
Saskia Charity: And we have to relate those to a spherical water sample, which is the sort of measurement standards, so this expression just shows the magnetic field expressed in terms of the.
Saskia Charity: protons in the spherical water sample, and the reason we chose that is because the ratio in this expression has been measured to very high precision so that's why that's our measurement standard that we're using.
Saskia Charity: For the magnetic field measurement so the way that we do the calibration is in two parts, the first of which is absolute calibration where we have a calibration probe containing a water sign ball.
Saskia Charity: And we have to make sure that that's measuring the absolute field correctly, so we cross check the measurements of the calibration probe alongside two very different.
Saskia Charity: probes for measuring the field in this 1.4 or five tesla Mr i'm at argonne national lab.
Saskia Charity: So the first prove that the US is a spherical water sample which has actually improved that's been used the p&l as well as enough number of other experiments and it's a very high fidelity prototypes very well understood to measure absolute fields exactly.
Saskia Charity: And we have very good agreement between the spherical waterproof and the cylindrical waterproof and but the systematics on this part of the measurements are highly dependent on things like.
Saskia Charity: shape and also the phase of the sample you're using so for this experiment a novel helium three sample was developed as an additional cross check which has got entirely different systematics.
Saskia Charity: And there's very good agreement between all three of those absolute probes.
Saskia Charity: The next step of the calibration procedure is to take your absolute calibration probe and transfer these calibrations to the trolley probes.
Saskia Charity: which contain protons and petroleum jelly, so this is a procedure that we do during the summer shutdowns easily and it's performed sort of at least once sometimes twice per.
Saskia Charity: year long run, a few months run, and so this procedure takes many hours but prob because what we do is take the calibration probe.
Saskia Charity: And we move it to the exact position of the trolley probe and then it's mounted on a translation stage, so we can rapidly swap the positions of the calibration prob with the trolley probes.
Saskia Charity: and know that we're measuring the same field with both of them and then we use those measurements to calibrate the trolley which, in turn, get transferred to the calibration of the fixed permit measurements.
Saskia Charity: So that's how we go from an absolute measurement as a field to the measurements of the field that we're making the experiments.
Saskia Charity: So, now that we've got our field measurement and we understand how it relates to free protons.
Saskia Charity: And we need to wait, the magnetic field distribution in the ring by the measured been distribution, so we end up doing a mathematical combination combination between the beam shape and the field contours.
Saskia Charity: And, as well as waiting with the shape of the beam we measured by the number of yours is function of time, so you can imagine if your field changed slightly.
Saskia Charity: And that was a time when you, for some reason had more neurons in your ring and you.
Saskia Charity: You have to wait to make sure that you're getting the average over the number of neurons in the brain, as well as the space through distribution of the neurons in the brain.
Saskia Charity: And this plot on the right, shows the effect of the mirror and waiting so if you just have the dipole contribution that's what's shown in orange for different.
Saskia Charity: periods of time during one one, and then the weighted field after you have wide the full weight and procedure is 120 parts per billion smaller than the unweighted dipole field.
Saskia Charity: And this shift is almost entirely dominated by the size size of the largest field gradients.
Saskia Charity: So if I just flip back to this one, I mentioned that there's some you can see a shape gradient in the magnetic field and it's this shape which drives the size of the shift when you apply the form you're waiting to your dipole term.
Saskia Charity: So it's nearly the end of the story for the magnetic field but there's two more corrections which needs to be applies.
Saskia Charity: And these arise because of the post systems and experiments, so I mentioned before, that were to post system thing experiment that it used to beam storage the kickers and the quads.
Saskia Charity: And that pulsing introduces transient magnetic fields which happened during the meal on storage times, so we need to have a good understanding of what those fields were.
Saskia Charity: In order, so that we can apply the right direction for the fact that those fields weren't happening.
Saskia Charity: All of the elements that there's additional fields were happening, which can't be measured by our usual magnetic field measuring devices so that's why we need to have a dedicated measurement campaign to quantify these transiting corrections.
Saskia Charity: The first of these is the kicker transients So this is the plot I showed before showing the kicker pulse relative to the different Cyclotron periods.
Saskia Charity: And so the kicker pulse of 22 minute tesla is applied in the radio direction 459 seconds at the time of the meal injection so the peak this post is 20 minutes tesla.
Saskia Charity: And the fixed probes do not see this because they're sitting in.
Saskia Charity: Their embedded in the elements from above and below the storage ring so there's significant shielding, which means that they don't see the same effect that the neurons in the storage ring would see.
Saskia Charity: And so, this is what happens in our dedicated measurement campaign, we have a laser magnetometer which measures, the kicker pulse, for a long, long time after the initial hundred and 50 nanoseconds.
Saskia Charity: And the residual pulses at the micro tesla level during the meal on storage time, so this Gray shaded region shows the fit.
Saskia Charity: During the meal story times, which are 30 to 700 microseconds so after all of this measurement campaign we end up with a correction which is minus 27.
Saskia Charity: parts per billion, with an uncertainty of 37 parts per billion to the magnetic field part of measurement.
Saskia Charity: And the uncertainties dominated by our knowledge of the baseline and we anticipate reduction in the uncertainty for this correction in future data sets with a longer measurement campaign at this affect.
Saskia Charity: The other transient field that we have to correct for the experiment is the quad transients, so this is a diagram showing the electrostatic quadrupled plates.
Saskia Charity: And when you post them they oscillate radio Lee and the top and bottom plates obsolete vertically and the motion causes a field perturbation so we actually did notice this in the fixed prob measurements, when we were able to.
Saskia Charity: Post the fixed probes at the same time as the new on trigger we noticed isolation and the fixed probes.
Saskia Charity: However, we don't see the full effect, and so, because of this Alan minium shielding so the clocks here on the right.
Saskia Charity: And the orange a data shows the fixed prob data, so this is the oscillation that you observed in the fixed probes and the experiments.
Saskia Charity: And the blue data is the measurement of using our dedicated measuring device for this effect, which is.
Saskia Charity: An enema probe inside a peak, which is a type of plastic Shell that doesn't have the same shielding effect that we insert inside the quad region to measure this effect.
Saskia Charity: And so, this is the combination that that's how large it is compared to what we see in the fixed proofs, but if you take account of the shielding with the known skin depth of the LM onion and you can reproduce the APP the fixed proteins.
Saskia Charity: Very well, so if you take the method and isolation from your dedicated pete pro and apply the skin depth correction you recover what you would measure in the p probes so the relationship between these things is understood quite well.
Saskia Charity: However, it's still further complicated by the fact that the effect is a different size, depending on where inside the quiet place you are.
Saskia Charity: So I mentioned that we have 43% coverage of the ring with these templates and, if you take your peak probe and step along one of the quad plates you see a different.
Saskia Charity: Relative field change depending on if you're at the place where the quiet place anchored or whether you're in the middle, so this is a very long dedicated measurement campaigns understand this isolation.
Saskia Charity: And, and the plots on the right here to show the isolation overlaid with me on storage times like in the previous plot So if you these green lights here i'll show you when the new ones are in the ring.
Saskia Charity: And if you zoomed in on one of them, you see that there's quite a significant field change over the time when the new ones are there so that's why we really have to map this out very well.
Saskia Charity: And for run one the correction here is minus 17 parts per billion, with an uncertainty of 92 parts per billion, and the reason that the uncertainty so large compared to the measurement there is because we were only able to do this mapping.
Saskia Charity: Of the quotes for one cloud section and because, by the time we realized this effect is happening, and it was.
Saskia Charity: Quite a significant amount of time later, and there have been changes with how the courts, whereas we have put the experiment back the way it was in order to understand how much this effect was so very conservative.
Saskia Charity: Uncertainty was applied to this quantity but in the future data sets and we're.
Saskia Charity: very confident this will be very significantly reduced and with much further and detailed mapping of this effect.
Saskia Charity: So nearly at the end of the story for our ratio and there are further sets of corrections which needs to be applied due to beam dynamics.
Saskia Charity: Effects so i'll talk about a few of these now, so the first of these corrections is the electric field correction, so this is to do with the fact that the beam has got the momentum spread.
Saskia Charity: Which means that be across the storage ring all of your meals not have the same momentum we can't inject a beam with completely uniform momentum so this cartoon in the middle here shows a top down view of the storage ring.
Saskia Charity: And it shows the change all the different momentum of the new ones at the different radio positions in the ring.
Saskia Charity: So that our new ones, have the highest momentum and the enemy ones, have the lowest momentum just because if you have a high momentum particle in the same field, it will orbits at a high radius so that's where the.
Saskia Charity: Radio distribution of the momentum spread comes from, however, that will see in a second, that the what the new ones at the lower radius will have a shorter.
Saskia Charity: orbit so they will actually complete one ton of the rain faster than the ones.
Saskia Charity: At the outside of the ring So if I play this animation We can see this effect was, which is what we call D bunching So you can see that the nuance of the lower radius.
Saskia Charity: of completing that orbit faster than the neurons at the outer radius so the beam although it's injected it's narrow and timing is injected they all.
Saskia Charity: orbit at different times so you have this the bunching effect.
Saskia Charity: So the plot on the right here shows data from an individual color perimeter and you can see, to oscillations of President here, so the slower one is the anomaly frequency.
Saskia Charity: And this rapid oscillation is what we call the fast rotation frequency and so this is the Cyclotron frequency for all of the neurons and.
Saskia Charity: The amplitude in the measured Cyclotron frequency is decreasing over time, because an individual detector sees the effect most strongly after the debunking has happened.
Saskia Charity: So all of that is to say that you use the we use the color amateurs which have got very fine time resolution to understand the.
Saskia Charity: How quickly the beam is the bunching and then we can perform a threat analysis to that in order to obtain the.
Saskia Charity: equilibrium radius of all of the Milan, so this shows, so if all of your real ones were in the Center of the ring.
Saskia Charity: And then you would you want your equilibrium radius to be zero the equilibrium radius being the orbit about which they're having all these radios radio oscillations so you would like your equilibrium radius be zero.
Saskia Charity: Because I mentioned the kicker in run one was not at its full strength we actually have a slightly higher equilibrium radius and.
Saskia Charity: And because of that that means that this correction that we apply for the fact that not all of them can have this emotional electric bill term cancel the hell is quite a large correction in one.
Saskia Charity: The next been dynamics correction is what's called the pitch correction, so this is to do with the fact that the new on beam has got a vertical spread.
Saskia Charity: So the reduced possession there's a reduced precession frequency measured for museums, with momentum component which is parallel to the be fields.
Saskia Charity: So what's happening to these nuances there in the ring is that they've got some vertical momentum and as they go around their pitching up and down.
Saskia Charity: And anything which has got a vertical momentum component is going to be in have some component of that in the same direction as magnetic field which is going to reduce its anomalous procession frequency, which you can measure.
Saskia Charity: So we use the tracking detectors to measure the vertical decay position, distribution and this expression on the bottom here shows that the.
Saskia Charity: pitch correction is directly dependent on the vertical position of the beam so we have trucking detectors which can very precisely measure the vertical position of being.
Saskia Charity: They only do that in two locations, but we can extrapolate that around the ring, and then we can use the measured vertical being with to quantify the correction.
Saskia Charity: So now we've got all the pieces, and so I talked about mainly the pitch and either your corrections, because those most significant and they're irreducible corrections which will be.
Saskia Charity: Well, not irreducible they'll still be present and strongly in the run two and three data, although the electric field correction will.
Saskia Charity: be much smaller due to the optimized strength, there are further couple of.
Saskia Charity: Corrections to beam which were more significant, for one, we have the magnetic field measurement which has got all the detailed calibration campaign, combined with me on the profile and I talked about the corrections to the magnetic field measurement as well.
Saskia Charity: So let's talk about all of these corrections, so this plot here shows in purple all of the measurements uncertainties and corrections associated with the Omega P measurements.
Saskia Charity: and yellow you can see the measurements and corrections and uncertainties that make a measurement and the green.
Saskia Charity: lines just show you the cumulative value and uncertainty as you add in all of these pieces of the puzzle.
Saskia Charity: So the first thing to notice here is that the statistical uncertainty is.
Saskia Charity: By far the greatest uncertainty here, so the best prospect, we have for reducing the precision or improving the precision of our measurement is to take more data.
Saskia Charity: And you can see that the electric field correction, as well as quite a large collection of around 450 parts per billion and, as I said, this is going to be reduced.
Saskia Charity: And so This just shows how all of these different measurements and corrections combined in order to achieve our final measured value and and the statistical uncertainty dominates the total uncertainty.
Saskia Charity: So here's the results, and so the analysis of the run Monday to use result of 60 billion precision.
Saskia Charity: And when you combine our measurement which isn't very good agreement with the brookhaven measurements, if you combine those two results which are based statistically limited.
Saskia Charity: Then we get a deviation from the theory initiative recommended standard model prediction at the 4.2 Sigma level of significance, and so this yeah this is, this is the famous result that was announced a couple of months ago.
Saskia Charity: and
Saskia Charity: yeah okay So how do we interpret this result, I know you had a talk from Thomas so don't talk too much about the different theoretical theoretical.
Saskia Charity: treatments and things, but the short answer from the experimental side is that more precision is needed in order to really determine the significance of this discrepancy, so this plot on the left, shows the me on T minus two in blue, these are the experimental.
Saskia Charity: measurements and in yellow, these are the standard model predictions and uncertainties for a wide range of different.
Saskia Charity: Current discrepancies in the to do with flavor in the laptop sector, so you can see that the T minus two uncertainty on the experiment is comparable to the uncertainty on the theoretical treatments.
Saskia Charity: So obviously there's been a lot of interest in this result this plot shows the citations and the brookhaven experiment over time.
Saskia Charity: And just one week after announcement we'd already been side 69 times so there was, it was a highly anticipated result there's a whole host of different papers on the archive talking about different.
Saskia Charity: Explanations perhaps this discrepancy, and this plot on the bottom just shows one potential.
Saskia Charity: The potential sensitivity of the G minus two discrepancy to new physics, so this shows that for low mass low matt said PRIMES and we have sensitivity that could be seen with.
Saskia Charity: neutrino experiments so it's not just the it's not just beyond the standard model extensions, which could be found at the lsc that we're sensitive to.
Saskia Charity: There are other extensions, which could be seen in future neutrino experiments which could accommodate an anomaly, the size of the GMOs to discrepancy.
Saskia Charity: So where do we go from here, so this plot on the right shows how much data we've taken already So this was the raw.
Saskia Charity: Data taken and run one which covers what I talked about today we're already it's.
Saskia Charity: A lot more depth, and this is close from April and we're still running now it's running today, so the data is still coming in, we have at least one more experimental run.
Saskia Charity: Next year, so we hope to get you know really up to I think if we got to 20 times the brookhaven data set in terms of statistics we would.
Saskia Charity: be confident of having our era was small enough to take the discrepancy to very significant levels, assuming this theoretical collection stayed the same.
Saskia Charity: So the main hope for improvement for our results is to take is to analyze all of the States Have you taken and continue to take more data.
Saskia Charity: But there are other improvements that will reduce the systematics in the future analyses, so there are reduced being dynamic systematics due to the fact that we're operating the kicker its intended voltage.
Saskia Charity: So we can put the neurons in its central orbit and reduce this electric field correction.
Saskia Charity: We can take more detailed measurements of the two transients corrections in order to reduce the uncertainty on the magnetic field parts of the measurements.
Saskia Charity: And there will be additional improvement on magnetic field parts because of reduced or improved.
Saskia Charity: temperature control inside the experimental so we're now insulating the magnet so.
Saskia Charity: The changes in the magnetic field, at a time are driven by temperature corrections which can expand and contract magnet gap.
Saskia Charity: And we're now controlling the temperature better, so there are fewer variations in the magnetic field, meaning, we can track it better so there's less uncertainty in the magnetic field part of measurement.
Saskia Charity: But as I said, more data, and so we expect approximately a factor of two times better precision with the run two and three datasets.
Saskia Charity: Okay, so that's everything, and thank you very much, listening it's a pleasure to give this seminar.
Ivana Hristova: Thanks very much Saskia for this very nice talk and thanks for focusing on the experimental side that's complimentary to the theory talk, we had last week that was very interesting.
Ivana Hristova: Thank you again.
Ivana Hristova: Let me stop the recording.