James Smallcombe: There we go. And then I will hand over to jack please take it away.
Jack Wilson: Okay, thanks. So yeah, as, as James stated in his introduction. I think I should start this talk with a with a warning or a caveat that
Jack Wilson: At least by training. I'm not a nuclear physicist smite my day job is working in the Planetary Sciences at JPL.
Jack Wilson: Or I use data from neutron and gamma ray spectrometers on planetary missions.
Jack Wilson: To learn about the surface composition of planets, especially looking at their hydrogen dependencies and where that's what rights on planets.
Jack Wilson: But here I'm going to talk about some work that we've done using data from a couple of planetary neutron spectrometers onboard messenger and you know prospector to measure the free neutron lifetime.
Jack Wilson: So before I get started, properly and go into the nuclear physics applications. I'll say a little bit about planetary nuclear spectroscopy.
Jack Wilson: So this, this cartoon is a simplified illustration of the principles and it's the left hand side that will be interested in this talk, but we're not going to look at galleries.
Jack Wilson: So the idea is the cosmic rays, which are mostly high energy protons are constantly raining down on the surfaces of planets, they collide with nuclei in the soil.
Jack Wilson: Or the atmospheres for planets that have atmospheres costing speciation reactions that end result of which is the creation of large numbers of high energy neutrons.
Jack Wilson: Those neutrons then and Nicole further collisions with nuclei in the soil and atmospheres and their energy is moderated downwards.
Jack Wilson: So some fraction of that neutron population in the goals of sufficient number of questions so that it ends up in thermal equilibrium with soil.
Jack Wilson: And it's these thermal neutrons that will be of interest. Later, due to their relatively low speeds. Typically, if a planetary applications. They're going at a few comments per second.
Jack Wilson: So the net result of all this, all these collisions, is that the flux that emerges from the surface of planets has energy distribution.
Jack Wilson: that's characteristic of the elemental composition of the planets in there are a few sort of typical spectra.
Jack Wilson: And for that reason, several NASA missions. Well, not just NASA several planetary mission so have flown nutrients back promises to learn about what's going on planetary services.
Jack Wilson: Right. So on this slide, I want to very quickly go through a couple of examples of sort of the conventional results of planetary nuclear spectroscopy.
Jack Wilson: Before we go on to the to the nuclear physics homes, all of the thing is on this slide show measured epi thermal neutron flux
Jack Wilson: And in the planetary context epic level neutrons are primarily sensitive to hydrogen, because it's very effective new front moderator, the similarity of any from a proton message.
Jack Wilson: So I can say is
Jack Wilson: Low heart and abundance and LA County is hydrogen
Jack Wilson: On the left our data from Mars Odyssey taken in the southern summer at the top and northern summer at the bottom.
Jack Wilson: That the non polar variation that lol actually variation that you can see it is the result of different dependencies of hydrated minerals. So, as you probably know,
Jack Wilson: During its past, at least for some time Mars had reasonably large mass of liquid water on the surface that led to the creation of hydrated minerals and some of those hydrated minerals is still present today. A few billion years later.
Jack Wilson: The latitude more variation in every thermal flux is due to water ice that's buried beneath the Martian surface as you get closer to the polls, there's an increase in the amount of water ice. And it's closer to the surface.
Jack Wilson: And indeed at the polls themselves. There are water is kept several kilometers thick.
Jack Wilson: The reason for the seasonal variation is deposition of CO2 ISO Mars's atmosphere is most the carbon dioxide.
Jack Wilson: And during the winter it's sufficiently cold that CO2 can condense out of the atmosphere forming take CO2 ice caps and as carbon dioxide is a much less effective moderator neutrons than hydrogen is that leads to an increase in the epic Mr Fox.
Jack Wilson: So in fact that these measurements we use to estimate the thickness of the CO2 ice cap and it was shown that around a third of Mars is atmospheric CO2 passes through the ice caps annually.
Jack Wilson: The right it is the result of some of your prospector measurement showing this the pot show the north and south poles. And what you can see here is that within certain craters. There's an A decrease in heavy thermal flux corresponding to an increase in hydrogen abundance
Jack Wilson: The explanation for that is that the moon has a very low Orbital angular obliquity it's around five degrees. And so there are some craters at both poles us floors are in permanent shadow. They never see sunlight.
Jack Wilson: And a consequence of that, and the very low thermal conductivity of the regular is that the temperature is always beneath 90 Calvin.
Jack Wilson: And that means that water is stable that even in the vacuum of space and it's accumulated there over a period of billions of years and the exciting thing about this result is that it's a potential future
Jack Wilson: Usable resource for climate emissions and indeed one of the next NASA missions is inspire or just going to explore these deposit
Jack Wilson: OK, so now on to something that's that's a bit more familiar to you, I think, as you all know, three neutrons decayed Ian decayed with mean lifetime around 800 seconds.
Jack Wilson: This is very important decaying as its simplest week decay. There is it sort of forms the prototype for all week decays of leptons and patterns.
Jack Wilson: Additionally, the precise value of the neutral lifetime is an important parameter in several branches of physics, including cosmology and particle physics.
Jack Wilson: Lifetime along with lambda, the ratio of axiom factual coupling Constance, it can be used to determine the UD in the CPM matrix and therefore test the unit guarantee, but the secant matrix.
Jack Wilson: This is one of the most important low energy tested the standard lot of areas.
Jack Wilson: And although at the moment, the most precise determination of the UT is have taken from measurement of the half lives of super loud nuclear beta decay is using the neutron lifetime provides it theoretically clean and measurement
Jack Wilson: And this is particularly important moment, given the recent updates to the universal region correct VT k and the resulting value of the D. Place the CPM matrix and some tension with new charity.
Jack Wilson: Additionally, in in cosmology. The neutron lifetime is very important. It's a key inputs, the calculations of the ratio of protons, neutrons in the universe. And therefore, the amount of helium created during the nuclear synthesis
Jack Wilson: And primordial nuclear synthesis is one of the major lines and evidence that we have for the Big Bang, along with the observed the expansion of the universe and the cosmic microwave background.
Jack Wilson: And in fact, it turns out that uncertainty on neutral lifetime is the dominant source of uncertainty in calculations of primordial human sentence.
Jack Wilson: Okay, so that's why it's important. And there are two techniques that are conventionally been used to measure the neutron lifetime bottle and been experiments.
Jack Wilson: So first off, bottle ones that have the bottle experiments involved storing altar call neutrons that is neutrons that have kinetic energy is that typically less than around 100 nano electron volts, which corresponds to a temperature of less than one another. Calvin.
Jack Wilson: At least barrier energies, it's possible to trap neutrons for long periods, using the potential energy of their interaction with either solid or liquid materials and magnetic fields already the Earth's gravitational fields. If the track is sufficiently tone.
Jack Wilson: So in the bottle methods you count the number of neutrons that remain in the trap as a function of time and then lifetime is determined from the exponential decay function, which means that these experiments are sensitive to nutrient decay by any by any possible channel.
Jack Wilson: And so in theory, of course, this, this all sounds very simple but
Jack Wilson: It requires very accurately measuring or removing all of the last mechanisms from the Boston from the bottle so that they don't
Jack Wilson: Impact your measurement of
Jack Wilson: The most precise current measurement using this bottle technique is from you CN Tower land or this is a combined magnetic gravitational trap.
Jack Wilson: That consists of a this asymmetric callback array that provides a field gradient for magnetic gravitational spin polarized neutrons.
Jack Wilson: And then gravity prevents the optical illusions from from escaping from the top of the track. So you can sort of see the asymmetric played in this cross section nine brand.
Jack Wilson: And the purpose of it is to quickly object cause the bound use the n minus tangential Boston's. So the problem is that otherwise these quasi burn Lucien would be rejected at some point during the measurement period and then would affect the result.
Jack Wilson: As well as being the state of the art bottle measurement. This is for all the most precise measurement athlete from lifetime that we have with a statistical uncertainty point seven seconds and a systematic plus point two minus point four. It's really very impressive results.
Jack Wilson: Okay, now wanted the beam, these, this is the alternative classics, the order to to all of the early experiments will be in experiments and it involves passing a beam of thermal or colder. Ideally,
Jack Wilson: Neutrons through some tracking volume in which the decay products either electrons, protons but in practice at the moment. Usually protons, French, and then after leaving this volume. The neutron beam encounter some sort of absorbing file.
Jack Wilson: From which the rate of reaction product. So if nutrient absorption is measured
Jack Wilson: So with both the production of the key products and the measure greater reaction from absorption products you can use the differential form at the exponential functions find any time.
Jack Wilson: There was developed a whole of the beam experiments is the sex IRL NIST method. You can see the experimental setup of BL to hear and a diagram.
Jack Wilson: Of the principle behind the operation.
Jack Wilson: So in this experiment, you have a well coordinated been called neutrons passing through this cause the pending trends that consists of 16 annual electrode segments.
Jack Wilson: During trapping the mirror and door electrodes which is shown in in red and green hair have the hell that plus 800 volts, which traps all of the recall protons produced by beatification inside the volume.
Jack Wilson: And then after some period, the door voltage is closed and the protons of flush towards the silicon detector with a small rank potential
Jack Wilson: Then this process is repeated to improve statistics.
Jack Wilson: So BL to is the latest generation of this this sort of bottling beam experiment.
Jack Wilson: The results to do any day now. And I think possibly if it weren't for the current situation, we might even have them already.
Jack Wilson: And with expected uncertainties below one second.
Jack Wilson: Edition BL three is being planned.
Jack Wilson: And it would have uncertainties beneath point three seconds on statistical and systematic
Jack Wilson: In addition to these there's another ongoing beam experiment at a park. If the running since 2016 they published some results in 2018 but I'm not sure when the final results from that experiment, but you are
Jack Wilson: Okay, so this plot shows where we are at the moment it's it has the result of some at least most I think the recent
Jack Wilson: Experiments of both classes, along with the mean and standard error for each class of measurement, the open circles.
Jack Wilson: The open center console results that have either been retracted or succeeded in some way.
Jack Wilson: And the problem is, I think, clear from this plot right you can see that the two techniques produce substantially different values of the neutron lifetime.
Jack Wilson: Means different by around nine seconds, which is all for sigma and this disagreement has been present for at least the last 15 years since 2005
Jack Wilson: Now the most likely explanation for this.
Jack Wilson: Discrepancy is as ever. But there's an uncorrected or
Jack Wilson: On accounted for systematic error in one of potentially both classes of experiment.
Jack Wilson: And indeed losses from the bottle, which are the most likely systematic in those experiments would have to pull the lifetime measurement down. And similarly,
Jack Wilson: The most likely systematics on the beam measurement app to push it up. So the disagreement is in the direction that you'd expect if that were the explanation.
Jack Wilson: For this discrepancy
Jack Wilson: Because the disagreement so significant. And it's been president now for a reasonably long time people have started to look for physical explanations for it, or at least considered
Jack Wilson: One of these is decay of the neutron outside of the standard model into into the dark sector.
Jack Wilson: This was proposed by funnel and grinstein in 2018. So in this scenario, while the beam experiments measured just the branch and ratio.
Jack Wilson: For the proton decay channel Peter decay, the bottle experiments and measuring the overall neutron lifetime, which is of course necessarily smaller because nutrients. I go into the key more often interprets omens or something else and they are just into protons.
Jack Wilson: Now it seems that decays that involve a dark matter particle and Standard Model count counterparts like photons or electron positron has a rule that experimentally.
Jack Wilson: And basically, like the one that's shown here to a dark matter firmly on the scalable is on
Jack Wilson: Me the gospel, although there are strong constraints from neutron star equations of state and there are other theoretical considerations that suggested perhaps unlikely, but it's an interesting possibility, unless
Jack Wilson: So that's the state of Oregon, and I think you can probably see that having a third technique with independent systematics could at least potentially be invaluable in breaking this impasse.
Jack Wilson: And that's where space based measurement of neutron lifetime potentially steps in
Jack Wilson: So this was first suggested 30 years ago now. In a paper published by Bill Feldman this referenced on the slight bill was instrumental in websites in the field of energy nuclear spectroscopy.
Jack Wilson: And it's our connection with him that true, or center best work really
Jack Wilson: The reason that this technique can work is that at the Earth and Venus the surface, the surface time of flight of a neutron is if the order to neutral lifetime.
Jack Wilson: And also for spacecraft that are a few hundred to a few thousand kilometers above the surface of any planet, the time of flight of a thermal neutron is avoided the neutron lifetime.
Jack Wilson: So it's clear that when you're detecting these neutrons. The precise value of the neutron lifetime has
Jack Wilson: An effect, at least on the neutron calibrate that you're detecting
Jack Wilson: One point to make here is that while in theory, a model independent measurement of new from lifetime is possible. Usually space based techniques. If you could measure
Jack Wilson: Both the Angular and energy distribution of what would going and download going neutrons, then you can simply calculate the neutron lifetime, because the propagation is just Newtonian mechanics.
Jack Wilson: Know, none of the Quran data have this information have sufficient information to do that. So all of the reports that I'll show here a based on a comparison of the measured neutron counts to predictions of models to include neutron production.
Jack Wilson: Following cosmic ray exploration transport multitude, and then detection at the spacecraft
Jack Wilson: Okay, so first stop is mercury with messenger, and then I'll move on to the prospect to later.
Jack Wilson: Messenger was an API master plan for science missions mercury X Factor first spacecraft to orbit Mercury, which you did between 2011 or 2015 on it the way that it performed to flybys of Venus as part of a gravitational assist me that
Jack Wilson: And during the second of Venus Venus flybys the neutral spectrometer was not simply to check that it was working. He wasn't intended to do any science that. But it turns out that it's it's the data that was collected jerkiness flyby, they were critical for making the lifetime measurement
Jack Wilson: There were also to five miles of mercury as part of additional complexity assists and we use the data for one of those supermodel normalization.
Jack Wilson: Okay so messenger of course wasn't designed to measure the neutron month time. It's a planetary science mission you have planetary science goals and those involve measuring surface composition
Jack Wilson: Particularly looking at water at polls and it which successfully found it was also designed to learn about Mercury's geological history. So it's my heater sphere and the size and state of its core among several other things.
Jack Wilson: In order to achieve those goals. It carried a whole host of instruments, which you can see in this in this cartoon, only one of which very interested in here, this this tiny thing that's bolted to the back of the spacecraft, which is the neutron spectrometer.
Jack Wilson: Okay so Mercury's NS consisted of three optically isolated centimeters with separate photo multiply achieve readouts. There were two within blessed plates hundred square centimeter area four millimeters thick and they sandwiched a braided plastic cube.
Jack Wilson: The idea behind the sensor design was was to make use of the Doppler filter technique to obtain a course energy spectrum of neutrons. So the thing here is that the principle is that when the spacecraft velocity is parallel to the outward normal on of these lithium class plates.
Jack Wilson: The plates see a boosted count rate driven by a boost in thermal neutron counts because the spacecraft is essentially ramming into those thermal neutrons both the thermal neutrons and spacecraft have philosophy that's a few kilometers per second.
Jack Wilson: And conversely, when the spacecraft velocity is anti parallel to the outward normal UCF a suppressed neutron count because you're you're out running those thermals
Jack Wilson: Father flybys of both Venus and Mercury.
Jack Wilson: The geometry search that spacecraft velocity was mostly parallel with the out with not more pointed philosophy class plates and those are the detectives that are used for them for measurement here.
Jack Wilson: So this is where the the mercury data came from the model counts are determined by integrating over
Jack Wilson: Protecting you from energy and direction, the product of the Ns response with the neutron flux and altitude and an additional factor factor, accounting for the relative motion of the spacecraft and you from field.
Jack Wilson: So we derive the surface originating neutron flux within MTM px simulation of both of the planets other planets and taken to be circle and they're illuminated with a
Jack Wilson: Representative galactic cosmic respect that has the correct spectral shape for GC ours but doesn't take into account the absolute number. And that's why the additional mercury data required in a top of on top of the Venus measurements that we're using.
Jack Wilson: The mercury model that we're using is very simple. Mercury has no atmosphere and here it's modeled incorrectly as a sphere of uniform composition
Jack Wilson: So the fact that we move model mercury as a uniform sphere is because there are large uncertainties in the composition of variation and now turns out to be one of the largest systematic uncertainties on our result.
Jack Wilson: Venus has a very thick atmosphere and it's modeled as a set of 50 concentric spheres with pressure and density profiles that are appropriate for its atmosphere which has been measured by several to send probes that have gotten into the news.
Jack Wilson: So example output spectra shown in this figure for a couple of different compositions for both the planets.
Jack Wilson: And the transformation of the surface flux that we get from MCS out books to the flux altitude. It's just a matter of combining Newtonian mechanics and we've asked them.
Jack Wilson: At the mass of all the planets very well known. So like this doesn't introduce any additional uncertainty.
Jack Wilson: Additionally, we get the Ns response from MTN px simulation, but this time of the entire spacecraft and including the detector which we eliminate with more energetic incomes various energies from the various instruments and more similar to get response function.
Jack Wilson: OK, so the plot here shows both the measured and model count rates during messengers second fly by Venus with different lifetimes in the models.
Jack Wilson: And you can see from the x axis that there's only around 45 minutes worth of data taken at Venus in addition to those later. As I said, we make use of them around 30 minutes worth of data, taking train the first mercury find by certainly absolutely normalization.
Jack Wilson: During both of those pipelines think ECR conditions were very similar as measured by satellites and on earth. It's just that this is a reasonable thing to do.
Jack Wilson: So ideally, for a given but messenger spent four years in orbit around mercury, you know, the elliptical orbit, we use those data to measure the neutron lifetime.
Jack Wilson: And but that's proved very difficult to to the uncertainties in mercury surface composition and so if it has made about a dozen or so elements that are present insignificant quantities.
Jack Wilson: And they all vary across the surface and other mobile at the moment we just can't model that accurately enough in order to drive new for my time.
Jack Wilson: However, unlike mercury. So because Venus is atmosphere is very simple. It contains only two major species.
Jack Wilson: Carbon dioxide, which makes it around 95% and nitrogen, which is most of the remainder of other species, including by oxide, a President that sort of 100 parts per million level and lower, but they have no substantial effect on the different flux around the planet.
Jack Wilson: And it's also spatially uniform. There's no point and shoot more variation composition and temperature because the atmosphere is well mixed and very rapidly rotating
Jack Wilson: There's also little latitude more variation in temperature and variation in temperature density without students well understood and included in the model.
Jack Wilson: So, that being the case, our models of need from production at Venus involve only two or three parameters, there's
Jack Wilson: Nitrogen abundance and lifetime. Why not jump on that's, of course, it's critical because nitrogen. So relatively strong so neutron absorber. So in effect, but then when you translate that you get a land beans.
Jack Wilson: Okay, so let to make the measurement we ran a set of models with different values for the nitrogen abundance and Venus's atmosphere and the new lifetime and this plot shows a comparison of those models to the data where each of the pixels is a separate model.
Jack Wilson: You can see that there's this degeneracy how long the semi major emphasis of the ISO kind squared ellipses. And this is a result of using the mercury data.
Jack Wilson: To set the normalization. So the consequence of that is the measurement ends up being sensitive to the total number of neutrons measured around Venus or modeled around penis and
Jack Wilson: The total number increases with increased my time and decreases with increasing natural abundance
Jack Wilson: So there's this this line in which the toggle doesn't change and. However, the fact that these controls are closed. There isn't complete degeneracy shows that it is possible to simultaneously measure nitrogen abundance and lifetime. The reason for that is that
Jack Wilson: Although they both affect the total number of neutrons their effect on the current rate profile the current rate with altitude profile that I showed a couple of slides. Go is slightly different.
Jack Wilson: So within update or and we have just enough fear that you can simultaneously medical my lifetime.
Jack Wilson: Now, I realized this is this is a new music seminar. So you're not necessarily terribly interested in how much nitrogen areas in in Venus's atmosphere.
Jack Wilson: Although it turns out that this is the most accurate measurement of the nitrogen abundance and Venus has an atmosphere, it wasn't a motivation for doing it. We were trying to work up a neutral lifetime.
Jack Wilson: But if you take the PG value for neutral lifetime and read off our abundance, the value that you get is the most precise one that we have
Jack Wilson: But anyway, yes, that's, that's an aside, I know you're not here to learn about Venus has not been done, so we can be and get rid of that parameter, bye bye marginalizing it out and then we do that, we find that the lifetime is 790 seconds with 60 seconds testicle uncertainty.
Jack Wilson: I won't go into the details on the calculation of the systematics but they're comparable in magnitude to the systematic to this mystical uncertainty.
Jack Wilson: The largest of the systematics is due to the uncertainty and notary service composition and the consequent uncertainty and modern normalization, and the effect of that pants on, on my time. But the final result is good talent is 790
Jack Wilson: With 60 seconds is for internal DNS 72nd systematic uncertainty.
Jack Wilson: This is one on a bit sigma away from the PD G around you. But obviously, the uncertainty is very large and we've only used a smaller data information that wasn't designed to make this measurement, but nonetheless thing they stand as a proof of principle.
Jack Wilson: For measuring you need from lifetime from space.
Jack Wilson: Okay, so next stop is the moon, the best available from data that we have from the moon was taken by a unit prospector prospector
Jack Wilson: entered orbit around the moon at the start of January 1998 and it's been 18 months there we the prospectors neutron spectrometer consists of two human three cats proportional counters. You can see it sticking out on the boom, the right hand edge of this figure.
Jack Wilson: One of those healing friendships was covered by cadmium to block the neutrons and the other Lawson. And then the third one, you can count rate. It's just him in from the difference between those two tubes.
Jack Wilson: And it's the thermal new friends again that will use for the measurement huge there, whereas relatively low velocity
Jack Wilson: So,
Jack Wilson: Luna prospector for most of the mentioned was in a circular orbit either 100 kilometers from the surface or later in the mission 30 kilometers, but just after it was captured into orbit around the moon it executed a set of highly elliptical orbits.
Jack Wilson: And it's these that will use to examine
Jack Wilson: How the cap rate changes with altitude in both the data and models, you know, to determine the neutron lifetime and the other panelists bigger shows out is food for those elliptical orbit. So on the camera angle.
Jack Wilson: Okay, so
Jack Wilson: Unlike Venus. The means that surface composition is is complex and specialty area and that has an effect on the thermal neutron flux above
Jack Wilson: This plot here shows the thermal different counts as measured by hiring a prospector during its low altitude, that is 30 kilometers circular orbital phase.
Jack Wilson: And sort of orient you hear the low thermal here from camps that you see in blue around zero degrees.
Jack Wilson: These are the lunar Marissa so so it goes a bit, but when you look at the moon, they appear dark. The reason for that is that they're they're high in iron that flood batons that contain iron
Jack Wilson: In addition to some rare earth elements like snowmen gotten any so they have quite a long lunch thermal neutron microscopic absorption cross section, which means to lower them on each uncountable.
Jack Wilson: However, an important thing about them is that unlike mercury it service composition is very well understood. That's because tracking multiple machines to the moon and indeed multiple samples returned from the room from the locations that are shown in this pot.
Jack Wilson: A consequence of that is that we can include this non uniformity in composition in our models of neutron production.
Jack Wilson: So in the models, what we do is we've defined five regions that correspond to the major compositional terrains on on Mercury surface and that's shown and this figure here so you can see the other Marissa ones that are that are highlighted on the previous slide. In addition to that,
Jack Wilson: There's a terrain is known as South Pole eight convincing that's around 180 degrees in the South. So this thing here.
Jack Wilson: It's a, it's an ancient impact basin, but excavated part of the aluminum mental, which is why it's composition, the distinct from the surroundings and then to the north of that.
Jack Wilson: We have
Jack Wilson: Original thought in the highlands, which is thought to be a remnant of the primordial crossed
Jack Wilson: So when the moon formed the meaning it's believed was formed by Johnny and pence between the earth and Mr size body.
Jack Wilson: That when it formed it had a completely molten surface and then during crystallization surface crystallized our first bits of that we're particularly iron port and this region is thought to be a room number five.
Jack Wilson: Okay. OK, so
Jack Wilson: Again we have taken it from lifetime by comparing
Jack Wilson: The results of the modeling with the data, both of which are shown here are the models in the top panel.
Jack Wilson: Some neutron countering that's been measured finding prospects, with all kind of with the contours of the different competition regions.
Jack Wilson: And now, as we have a lot more data available for leave a prospector. There are a few days worth rather than just 45 minutes in the quantum the messenger.
Jack Wilson: Or able to normalize the model.
James Smallcombe: Sorry, Jeff, it was just me, but I lost your audio for like 20 seconds there so
Jack Wilson: Oh, okay.
James Smallcombe: Your previous few sentences.
Jack Wilson: Sure. So all I
Jack Wilson: Said about this slide was that
Jack Wilson: And the way we obtained the lifetime was a comparison of the models to the data, the model shown on top the data on the bottom.
Jack Wilson: And unlike for the messenger analysis.
Jack Wilson: At for the lead prospector because we have considerably more data or able to directly normalize the models to to the data and that avoids what was a very large systematic error in the previous analysis.
Jack Wilson: Okay, so this top here on the left shows a comparison of the model counts to the magic data for a set of different lifetimes. And you can see the result is that the new from lifetime as measured by Lena prospector is 900 plus 40 minus 50 seconds statistical or
Jack Wilson: The histogram of the residuals for the best fit in model shown on the right you can see those residuals are very close to, but not identical to
Jack Wilson: A standard normal suggesting that we've included at least most of the physics in our modeling. If the calories and I think you see on the on the previous slide that at least qualitatively, and he quantitatively, the agreement between the data and the model is good.
Jack Wilson: Okay, I'm onto my final slide now. So what I've shown here is the TO space based new phone lifetime measurements in comparison to the set of laboratory measurements that I showed earlier.
Jack Wilson: And the gray region shows a one segment on that era around the mean of the combined space based measurements and you can see the result that is that the lifetime is 870 seconds with a 42nd uncertainty.
Jack Wilson: Obviously this is still very launch compared to the laboratory measurements, but
Jack Wilson: Again, it's based on a relatively small amount of data permissions that weren't designed to make this this measurement. I mean, nobody ever considered doing this one the
Jack Wilson: Instruments and spacecraft operations were being designed and but despite the slides, or is it still a proof of principle of the feasibility of making a measurement of any from lifetime from space. And ultimately, potentially, at least resolving the scheme from lifetime problem.
Jack Wilson: So looking to the future there. There are a few other things that we can try and there are a couple of other dates sense that can be made you saw
Jack Wilson: That mas mas Odyssey is one and Dawn is another donde was a mission to invest in series that are those are two of the largest bodies in the asteroid belt.
Jack Wilson: It's also possible that a more sophisticated analysis of the mercury orbital data could sidestep the uncertainty associated with composition and produce a more precise question.
Jack Wilson: But I think making real progress with this technique would require
Jack Wilson: A dedicated mission and we've started to think
Jack Wilson: About what the requirements on a mission like that will be both detected size and mission duration in order to get good statistical uncertainties and what the major systematics would be that we have to overcome to get really precise measurement
Jack Wilson: Okay, so with that I'll thank you for listening and invite any questions.
James Smallcombe: Okay, can I just say that I particularly appreciate your little data points just that.
Jack Wilson: Little moon planet. Yes, question. So
James Smallcombe: We've got these little claps, please. So if you want to ask question. If you're going to participants when you use the raise hand icon or type in the chat. We've already got one off the bat jack Henderson. Please go ahead.
Jack Henderson: Hello, I'm
Jack Henderson: naive question or foolish question. Is there a reason or is it possible to perform
Jack Henderson: I mean you have to go to extraterrestrial planet or could, in principle, would you do it on the Earth's atmosphere or are there additional complications, because you both.
Jack Wilson: Yeah, so that's that's that's a good question. And that's the question that we've been asking as well. And because obviously one issue is kind of emissions is that they can be very expensive.
Jack Wilson: And getting into low Earth orbit is much cheaper. So the answer is that, yeah, you can make this measurement from the earth.
Jack Wilson: In the original proposal was to do this at the Earth, the paper that the 19 90,000 and our paper that I referenced suggested doing this at the Earth.
Jack Wilson: With a rotating detector in a circular orbit that would measure the angular dependence of the neutron flux
Jack Wilson: But there are a couple of issues associated with an Earth observation. One is the Earth has has this
Jack Wilson: As a very strong magnetosphere, and a radiation environment that makes measuring the neutron flux in orbit noisy. It also introduces an additional systematic because the the Galactic rain.
Jack Wilson: Flux changes with a function of latitude because of the magnetic field.
Jack Wilson: The other factor is that the atmosphere is mostly nitrogen. Nitrogen is a pretty good strong priests from the front absorber. So you can see here that the earth.
Jack Wilson: Flux sees that there's a model flux is for the earth Moon and Venus and you can see that the earth is substantially lower
Jack Wilson: And that's just because there are fewer thermal neutrons around the earth because of all that nitrogen. So if you did want to do this experiment at the Earth, you'd have to spend a lot longer doing it.
Jack Wilson: It turns out that the best place to do is actually Venus, because the large mass of the planet, it's comparable to the earth means that
Jack Wilson: The rate of change of them neutrons without without today is quite steep and also the five of us very little nitrogen and lots of carbon dioxide means you get a lot of thermal neutrons.
Jack Wilson: And yeah, so the earth is is a possibility but money being no object. It's not the ideal place to do
Jack Henderson: Okay, thank you very much for the very good, thanks.
James Smallcombe: Okay, we've got another question. Philip. Please go ahead.
Philip Adsley: Hello. Can you hear me.
Philip Adsley: I can. Great. And so I have, in fact, two questions. One of them is, you mentioned the traps systematics
Philip Adsley: If you, if you were losing more nutrients than you expect. It would make the lifetime of a shorter, and then you said the beam systematics would like to make the lifetime longer, but unless I missed it. I don't think you said what they were. And I was wondering what
Jack Wilson: Yes, sorry. I think they're couple
Jack Wilson: One is the, you have to end the beam measurement
Jack Wilson: Precisely mentioned the absolute
Jack Wilson: Flux in the beam which is done at the end. But I think that's a major systematic that people are concerned about the other is potentially and I'm not sure this is
Jack Wilson: Is a big problem in practice and losses from the trap. If you were so at least new transferring the tramp, then you'd fit in for a higher lifetime, because we syndicate products.
Yeah.
Philip Adsley: And so the other question I have is usually said something about marginalizing out which I I'm just not familiar with what is meant by that. So it's probably very basic, but
Jack Wilson: Okay. And so let's see. I think
Philip Adsley: It was the neutron composition with the
Jack Wilson: Yes, the Venus one. Yeah. So it's this. This is a part of chi square right and you can convert if you're shooting yesterday six accounts. The and you can convert chi square to likely voters rights, it's easy to the minus chi square icon to
Jack Wilson: And to get a probability density. So we have essentially a probability density of nitrogen abundance and buying time
Jack Wilson: And what you can do is you can integrate all the nitrogen abundance there in order to just ask what the in the lifetime is right. So if we carry out that integration, when we sort of get a we get a measurement of lifetime that's blind. So the 1900s.
Jack Wilson: That's what I mean by that.
Philip Adsley: Okay, thanks.
Philip Adsley: Okay. Do we have any other questions from the
Audience
James Smallcombe: While I'm thinking I did have one. So you mentioned that one of the possibilities might be to use the most. You can use the mercury data. If you can, their
James Smallcombe: Account your problems there. So if I understood rightly the having, having this change in altitude is good for you but majority of the measurement. So with the mercury data was in particularly eccentric orbit or is it just the flybys that you would be able to use
Jack Wilson: Yeah, so the reason that we initially went to using messenger data was precisely that it is in a very eccentric of it.
Jack Wilson: And it varies between I thought I had it written on this fight. I don't. It varies between. I think it's a few hundred kilometers and about eight or 10,000 during a single out of it. So it's incredibly eccentric. The reason for that is that
Jack Wilson: you're carrying a lot of angular momentum and you go into orbit around mercury, so it's it's not ideal, from time to science point of view, but actually for me for like, time management point of view, it's quite good thing.
Jack Wilson: So, yeah.
James Smallcombe: All right, do we have any other questions.
James Smallcombe: I do also, you said this point if for whatever reason you don't have a raised hand button. You are welcome to just unmute yourself and don't have to go question.
James Smallcombe: But I don't see anything. So I think we'll call it there and so
Andy Briscoe: Sorry, James. I had a quick question. I did raise
Andy Briscoe: My hand in the
James Smallcombe: Scientist. Go ahead.
No worries.
Andy Briscoe: That was really nice talk. I really enjoyed it. I just wanted to ask one quick question.
Andy Briscoe: And and it was about when you mentioned people talking about dark matter in relation to the disparity between the two measurements and
Andy Briscoe: I wondered if if you're if their space based measurement was consistent with either of the two bottle or being measurements, would that say anything about the claims that the dark matter could be involved in
Andy Briscoe: In this
Andy Briscoe: Case, do you think
Jack Wilson: Yeah words that that's a, that's a really good point. So,
Jack Wilson: The reason that the reason for the difference if it's dark matter is that a bottle measurement. It's just measuring measuring neutrons to came to anything. And he was measuring your foster gained programs.
Jack Wilson: The space based methods are measuring neutron sticking to anything for it because you're measuring powder.
Jack Wilson: Flux significant changes with altitude but altitudes, the proxy for time, so they should agree with the bottle measurements, if they agree with the beam measurements, then that rules out new physics being aliens.
Andy Briscoe: Yeah, but that'd be nice. Thanks very much for talking on the answers as well. Thanks.
Andy Briscoe: Okay, good.
James Smallcombe: Do we have any other questions, apparently need to shout out because my screen didn't update show on defense. So, real quickly out. Okay, so we will call that time. So thank you very much jack and thank you all for joining us. That was a great talk.
James Smallcombe: I hope that you're able to join us for our next off on Monday, which is again three. Same time 3pm PST we've got Skylar dang called
James Smallcombe: I think I'm saying that right, I have to learn for introducing my Monday, who will be talking to us about search for permanent dipole moment. So thank you again jack. That was very interesting. Have a good weekend, everybody. Bye.
Jack Wilson: Bye.