X17 - A new particle? -- Sixty Symbols

6:17 yeah it's been around for a while I think if it's around at all I'd read her read about it I think a couple of 2016 was the first time I came across it this work done by these nuclear physicists in Hungary they were looking at beryllium the the nucleus of beryllium it's got four protons and four neutrons in it you can excite this nucleus we know with atoms and electrons right if you exciter the electrons in an atom they raise up an energy level and then they don't want to stay there we're all lazy really right we want to go back to what we call our ground state and that's how we produce light and so we're all familiar with the consequences of that but in fact you can do with a nucleus as well what they do is they create an excited beryllium nucleus by they have this that with a lithium nucleus and then they attach a proton to it so a very specific energy so here's my lithium nucleus and in comes a proton with a very specific energy it then forms a beryllium nucleus which is already at an excited state so that and that excited state is compared to its natural ground state it doesn't want to stay like this right it and so what actually usually happens is it just disintegrates again it just goes back to the proton goes out and the electrode the lithium but every now and again what actually happens is as it drops back down to its ground state is it emits a virtual photon and that virtual Photon just goes and disappears off on you then every now and again even less likely is the is that it emits the photon and then the photon itself creates a pair of electron an electron-positron pair and a + e- pair now what usually happens is in those situations the photons coming out and so the the two particles the electron and positron pair they're very light particles so when they're created they're almost collinear with it with the outgoing photon it so photons coming out towards you Brady and then the electron-positron pair are created and and so the angle between them this is the crucial thing is you the rain remains small and so as their angle increases that's the number of electron positron pairs that come out at larger and larger angles decreases because it it doesn't want to do it it wants to create come out because of conservation of momentum easier for it to come out straightforward now what these people noticed was that at an angle of about a hundred and forty degrees so let's say this is zero is that 90 and so hundred and forty I mean is is out here they found a bump they found an increase in the number of electron positron pairs coming out and we know from our Higgs this that if you've got an increase in a number of events then some it's it's a potential sign that something's funny going on though you would normally have expected this number coming out as you increase angle just to drop off monotonically but it suddenly it went up what could be causing this one interpretation is it's a particle that's been produced that then declares itself into the E Plus E - and this is the X particle and when they work out given the angle that the eep lossy - pair come out 140 degrees you can work out what the corresponding mass of the particle must be and it's 17 million electron volts 17 MeV and that's where the X 17 comes from it's that it's the the mass of this particle in comes the initial proton comes out in from outside lithium hits the lithium converts it into a beryllium nucleus which has now got four protons and neutrons by fine-tuning the incoming proton energy you can raise the energy level of this nuclei of the beryllium to actually something as eighteen point one six MeV million electron volts and that's an excited state it's not the ground state it then decays as it decays rather than creating the photon which then creates the electron-positron pair it creates this X particle so that's when the X 17mm during the during the relaxation of the excited it creates this but it's a massive particle so it's coming out now with with relatively low momentum that then means that when it when it decays when it doesn't split it does it split create the electron-positron pair they can come out a large angle where as a photon couldn't because of high momentum is going to then want to go directly into the E Plus E - in the same direction so because the x 17 is so sluggish ya and has less momentum yeah it creates this ability to do a wider angle or wider angle it split and so that was the interpretation and they they wrote this up it didn't do a lot for a little for a while it for a few months it sort of led there but I remember reading a paper by and Jonathan Fang and his collaborators at Irvine where they were looking at this experiment and trying to interpret this result in terms of some model and so it was then die I remember reading it and thinking in order to explain this result they're having to do something some twists and turns in the particle physics beyond what you would normally expect from the standard model of particle physics in order to get these it's a this X particle is a bozo and it's got spin 1 and there have been experiments looking for these particles the NA 48 experiment is one at CERN which had been looking for virtual bosons like these and haven't found any and the in fact it wouldn't i evil ii have ruled out this experiment of the beryllium from their own results and in order to sort of make sure the two were compatible fang and collaborators realized that one way of doing it would be to effectively change some of the interactions that the protons were having with this ex particle such that it would be access it would be allowed for the beryllium experiment to do what it was doing but it would account for the fact that the NA forty eight experiment was not seeing anything it's generated a lot of interest i mean i think there's like a hundred and forty papers have been written citing this original work but it was back in 2016 i think the thing that has caused the renewed interest the same group in hungary produced new results this time not using beryllium but using a helium nucleus they did the same sort of experiment and they found that once again they've there was a bump when they were looking at the the creation of the electron-positron pair they found a bump not at 140 degrees which was the result for the beryllium but I think 115 degrees and when they were than work backwards and took into account the fact this was a helium nucleus and not a beryllium nucleus they once again found that the corresponding mass of the particle that if you D understood it as from the decay of a particle was I think it's sixteen point seven million electron volts again comparable to what they had before that sounds like a smoking gun it does sound like a smoking gun it's quite intriguing but in the meantime there have been the the initial results and that they they obtained in 2016 has of course got people thinking about this and the experimentalists at CERN have been there's an experiment called I think as na 64 which published its results in 2006 2018 so about a year ago where they went looking for the original X particle right they went looking for her gauge boson which had a mass of about sixteen point seven million electron volts and the way they did it was they used the super proton synchrotron Collider at CERN they had a beam of electrons of about a hundred GeV that's a Giga electron volts they collided it into a target so it's called a beam dump they collided it into a target because if this particle was there what would happen is that electrons that were being stopped as it hit the target could interact with actually Z bosons said vector bosons in the target and they in principle could produce this X particle and then the X particle being with its interactions could actually leave the beam dump and it would then decay further down the chain and in a set of detectors creating the e plus e minus pair and so what they were looking for were these two sort of almost simultaneous events not quite similar areas where the beam dump loses an amount of energy but that same amount of energy is found further down the line and the interpretation would be the electron had as it hit the Z boson would have created this particle which then moved out from the beam dump further down into the dets detector and decayed and they didn't see it they saw no evidence of it and so that has allowed them to rule out regions of the parameter space that the original paper was was exploring but this new results which is with the helium sort of is it sounds like a smoking gun in some way as it is because it's a new nuclei but what it's really really crying out for is another experiment along the same lines as the beryllium one but done by a different team right so what why did we why did people so readily accept the Higgs well though I think there were two major reasons one was mathematically it was expected to be in the ballpark where it was found that's why they built the LHC with the energy they did on the size it did so the mathematics of the standard model and beyond the standard model had suggested there should be something there and then two detectors totally separate detectors found it effectively simultaneously they were finding evidence for the Higgs that's the CMS detector in Atlas we're finding it simultaneously in this case there's one experiment and is found it once it's there's a bit of a track record where they have found events before there that have disappeared found evidence for these bosons of different masses of disappeared they're arguing this is a stronger result but they've found it for beryllium and now for helium that that's positive but what it's really requiring is another experiment along those lines to come along and say yes and confirm it have other teams try - are there other teams around the world who've done similar experiments and said we haven't found that bump at those angles I'm not aware of other experiments doing exactly what the beryllium the Hungarian guys are doing because they're doing a proper nuclear physics experiment and so this is this interesting interface between nuclear physics and actual particle physics that the experience that I'm aware of that are testing this are particle physics experiments colliding electrons at a high energy into a beam dump and looking for a different types of detectors looking for Dark Matter detectors I mean one of the exciting things about this result if it was to hold is that there are Dark Matter models which would have a particle of around 1020 million electron volts these light particles could be there and and these there are models where they're these vector bosons when I talked about that why did we believe the Higgs I said well because the standard model was suggesting and beyond it was suggesting there should be there was in the mathematics one of the things that has had they've had to do in this particular case from the theoretical standpoint is you we've had to do some quite severe twists and turns to the particle physics to make sure we can accommodate this result in terms of a particle whilst also accepting n a 48 didn't find it at CERN it's not an easy fit it's not an easy fit and in fact you've basically had two introduced a new charge that accounts for why this X particle doesn't interact with the proton like it would with the electron and in fact it's it's called prata phobic it doesn't want to interact with the proton it to walk happily now interact with the neutron but not with the proton and that's unusual photons normally will interact with the width with the proton and you're forcing this to do it and so you need to look for examples why this is not happening is there another logical explanation doing the rounds are there other physicists who are saying oh no I can explain those bumps at those angles it could just be you know yeah X Y Zed well I think that if you want it to be it so one possibilities as I said it was one possibilities as a mistake and oh yeah yes so we should should point that out of course right that there that's another reason why you need to do this experiment with another group that there may be they've got their systematics wrong there perhaps this bump is that I mean the I that the word you hear is this is like a 7 Sigma detection well 7 Sigma means it's one one chance in a hundred billion that it's a random event I mean that so but if you've missed some big systemic that that could all go away I'm not aware of any sort of realistic accepted particle physics explanations as to what this is other than people coming in with this idea of a particle or the possibility that it's it's it's actually not there at all we've just got to go and revisit the systematics of the experiment if we imagine the x17 particle is legit it is real right what can you tell me about can you give me an Isaac can you give me an idea on its like how big that is and so it's light so an electron which we actually tend to think of us have been almost massless right is half an MeV so this is 34 times the mass of the electron the proton is roughly a thousand MeV but that you view as usually you've come up with a key question which which is that it's not particularly the prop the particle that's important here and that why is that the particle in particle physics is is symptomatic of the existence of something else it's symptomatic of the existence of a quantum field so when we think of the photon in particle physics The Associated feels the electromagnetic field when we think of the the Higgs particle that was discovered why people were so excited was the existence of the Higgs field and what the particles are excitations of those fields very strong excitations the existence of a field means there there's a force between there's an interaction between particles and so what you are finding here is if this particle really exists there's an Associated X field exist and we have a fifth force and the mass of this field is such that this could be a long-range fifth force and and then you've got all sorts of interesting possibilities coming in about why we're not detected it what are what are its subsequent properties and what other influences could it have on the enforces our own nature we're always looking for fifth forces I mean well some people would say it's a sixth force let me which said there's electromagnetism there's the weak interactions the strong interactions gravity the discovery of the Higgs is regarded as some as providing us with another interaction which is the interaction of the Higgs field with particles and but this new interaction has not been detected before or if it's there and it could open the you know there are many searches on for examples of either these long-range interactions with regard to the dark energy drive in the acceleration of the universe with or with regard to their presence of the particles themselves as dark matter candidates there is a big push for these light dark matter candidates at the moment because we're not we haven't seen any evidence of supersymmetry in the Large Hadron Collider which is usually associated with the existence of wimps so the wimp doubt Matter candidate hasn't shown up yet and so people are naturally begin to sort of think well bouts we should need to look further afield could x17 be dark matter well there's one possibility there are dark matter candidates that are in that regime in terms of their mass range now I I don't know enough about the interaction cross-section of this X 17 particle with other particles the people have looked and are looking in this mass range with these were called directed detectors don't direct out matter detectors and they haven't seen anything but whether or not that in this on right yet says anything about these X 17 remains to be seen x17 has no charge like it's not- like an electron or positive like proton no I don't think so because it decays producing an E Plus E - overall electric charges if you told me Brady go and find me an electron I think I know where to look you know if you said Bradley find me a proton or a neutron I know where to look you said find me a photon but they're quite easy to find where are the x7 teens if they exist where are they living so that if they're there and that they're there it turns out that they're not in that decay of the beryllium for example where remember what I said beryllium naturally just two cares back to the lithium it just breaks up again there's then then the next level of decay is via these virtual photons which then themselves they decay into a plus C minus one in a million of them roughly would be the production of the X particle but that's a rare event so you're gonna have to work hard so right now there's no X 17s if they exist right now there's no exception in you yeah I don't that's a good question I don't think I'm any well I often am I'm quite excited I do get I don't know think of an individual Gila I mean I've got helium in me and I don't think I must have some beryllium in me I guess - I don't think it's that that excited energy state that then decays if it does by the way and it's pretty hard to find I think their lifetime is around ten to the minus twelve seconds so it could have found them there they just disappear so if particles are excitations of a field including electrons and protons and things like that how come electrons and protons are so abundant in this room and so long-lived and yet this X 17 which is heavier than an electron and larger than a proton doesn't have this ability to manifest itself and then hang around so that's that's a that's a tough question but so the electron is the so the electromagnetic field is pervading this room and the electrons would be associated with it well the photons would be associated excitations that as would be the electrons which would be electromagnetic interactions the the protons are a bit more unusual that the majority of the mass of the proton is not in the quarks and the majority of the mass of the proton I mean if you if you add up the mass of the quarks each quark is as a rest mass of about three MeV so their total mass is about ten MeV and I've just said the mass of a proton is a thousand MeV so the majority of the mass of the proton is actually in the binding energy of the other of the quarks of the gluons so sorry that are propagating around it all the time so it's not quite as straightforward as sort of turning on the quarks and same as your proton so but so I think it's it's but you it is a case of that the relative of excitation in the field is the thing that determines the underlying and mass of these objects but the proton itself is this combination of the quarks and the gluons which makes it a bit less clear how you going to generate them so the x17 field it exists yeah is one that just doesn't get excited very often in our world I guess that's true I mean it seems to be the product of the decay of and more excited beryllium but you've got me thinking I'm not quite sure because it's it doesn't require a huge amount of energy these are not massive energy scales compared to what you what you get but I think that the issue is it's not just that it does depend on the interaction these the x17 particles have what what type of interactions it has with the other forces are the matter particles and we've seen that in order to explain its existence we have to already do something rather and usually we have to make that interaction one that's proton proto phobic in order which means that it's not interacting like the usual particles are interacting so that could have an impact on how likely it is to be formed out of some excitation of the field are you an ex 17 skeptic or I still remain a little bit of an accepting skeptic yeah I think it does require and a requires more particle physics explanation for why it might be there in a in a coherent framework and and be it above all it needs more experimental evidence coming from a similar type of experiment to verify whether the bump that they're seeing is actual real or not yeah it's absorbed in the air so to measure the x-ray absorption of our compound which is sensitive to the air we need to be able to remove the air and encase it so we use beryllium to make a magic box around our sample that the x-rays can come into

Channel: Sixty Symbols

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Keywords: sixtysymbols

Id: 8k6dKfmOufI

Length: 23min 3sec (1383 seconds)

Published: Sun Jan 26 2020

Reddit Comments

[u/jazzwhiz]

Note that NA64 ruled out most of the available parameter space in December. They can probably cover the last of it given time. https://arxiv.org/abs/1912.11389

(The money plot is fig. 5.)

[u/jose_russo_cassignol]

It's always great to see sixty symbols is still uploading after so many years. It would be incredible if X17 turns to be part of what we know as dark matter.

[u/mobibig]

Ah shit, here we go again

[u/EmperorDalek91011]

Am I the only one who thinks this looks like a Nintendo DS game?

[u/ComaVN]

How come the original berillium result was years ago, yet no other experimental group has replicated that result? Is anyone working on that?

[u/sdwvit]

How come it is 7 sigma, but there is a chance for systematic error?

[u/stupidreddithandle91]

So does a more energetic photon produce a pair that is separated by a wider angle? The energy in excess of the rest energy of the particles is converted to kinetic energy of the particles moving away from each other? Is that what accounts for the differences in the angles of the pairs produced? If so, why wouldn’t they assume a more energetic photon was the particle that produced the more energetic pair?

[u/SpiritOfCharizard]

I've been following this!

[u/sagittariusnefarious]

I didn't expect much, all the X17 signals were from the same place. It's alright, "old physics" or new there's still a lot to discover and explore. Higgs boson decay seems more likely place to look for new stuff.