joining us.
Laura Baudis: So yeah Thank you I banner for this kind invitation.
Laura Baudis: Yes, so I will, after a brief introduction to neutrinos and to double record decay, also to the field in general, I will I will discuss mostly the latest girder results and then also what we are doing with the next phase, which is legend.
Laura Baudis: Okay, so just very briefly, since you're all particle physicists to see what we what we actually know about neutrinos.
Laura Baudis: So we know that when they propagate over over macroscopic distances, they can change flavor and that's Of course I studied effect in quantum mechanics.
Laura Baudis: And it just means that flavor is not conserved over over macroscopic distances, so we all know that neutrinos are produced the.
Laura Baudis: State of the week interactions but in flight, they can they can oscillate between between flavors so that also means that neutrino states with.
Laura Baudis: With these different flavors mix with States with different masses and that's described here, this is the probability.
Laura Baudis: To find another state, you know, after some after some time or some distance and for a given energy, so the effect of the neutrino mass is to generate this flavor of simulations as a function of distance now.
Laura Baudis: Right So what do we know that from oscillation experiments so in order to to to be able to observe these oscillations, we have to have non zero neutrino masses and also non trivial mixing and you probably all know this guy's here.
Laura Baudis: conchita son and not McDonald who got the Nobel Prize installs 15 for this discovery of neutrino oscillations that showed, of course, that neutrinos have masses, this was, by the way, a picture that I took during the coupling integration two summers ago into.
Laura Baudis: Right so from this isolation experiments, we know the mixing angles or these entries in the in the neutrino mixing matrix that m&s matrix and also.
Laura Baudis: The mask were differences and and these measurements from atmospheric So what are your three knows, but also accelerate or react or and so on a defined these to mask AIDS, however, we still don't know the sign of this.
Laura Baudis: Data n squared a one, three, so we have to possible mass or during the so called normal ordering where we have here the heaviest state other the third state in the heaviest one.
Laura Baudis: And these are men, the other two states or the so called inverted ordering and here we have the sub state as being the lightest one.
Laura Baudis: So, so we have these two possible mastering still and we also don't know the offset here, so we don't really know the actual and neutrino mass scale.
Laura Baudis: So some of the open questions, then in between or physics what art is absolute values of the neutrino masses because we only measure this mass square differences what's the mass ordering.
Laura Baudis: Of course, also what is the nature, this is something real addressing this talk, are they the record my firm yawns what is the region of small neutrino masses So these are here, these are here.
Laura Baudis: The charts leptons and the courts and, as we also know quite where they are much, much heavier than then these states, of course, we don't actually know the values, as I mentioned, but they must be below below 0.5 or so.
Laura Baudis: So, then the other question is, what is the origin of course of this morning to masses and and there are more open questions here in newtonian physics, Sonia three nodes are well known particles in the standard model, but they are a bit special.
Laura Baudis: Now some of these open questions turns out can be addressed with this extremely rare nuclear decay process, and especially as we should see.
Laura Baudis: The three of these first three questions, so what is the absolute.
Laura Baudis: value of the neutrino Mars is the ordering perhaps what is the nature and and we will also see that if neutrinos are my run our participants, then.
Laura Baudis: Then you know, there are theoretical models that can explain your region or small neutrino monsters without yeah fine tuning it by hand and it's very rare nuclear decay is is where this is where the standard model processed the our beta decay so in the standard model.
Laura Baudis: Where you probably all remember this semi empirical mass formula to learn about his undergraduate so we have done this to.
Laura Baudis: parabola here for or even even nuclei and for, for this is, these are them so bars here with even a and are some cases where, for instance.
Laura Baudis: With the minus or better plastic aids are forbidden for instance on energetic grounds, but the so called double better decays are allowed.
Laura Baudis: And this was actually predicted already in 1935 by marissa Meyer in that paper she estimated based on on Fermi fury of week interactions she estimated half lives that are larger than 10 to the 17 years or so, we will also see that the probability for such a decay is very small.
Laura Baudis: And, and because the mean lifetime of a nucleus will be around 10 to the 20 years or even longer and here's a comparison to the to the age of the universe so it's a very rare process, and then a question is, how can you possibly ever observe it.
Laura Baudis: And, of course, you must use a large amount of nuclear I I you know more than 10 to the 20 or so.
Laura Baudis: so that you can observe it experimentally, and indeed the standard model decay, with two neutrinos in the final state was observed in a number of nuclear I believe 14 or so, and all of these half lives are.
Laura Baudis: are higher than then tend to the 18 years now in terms of the signature so it's very similar So if you measure here the some energy as oversee later of the two electrons.
Laura Baudis: Then, then the signature is simply a very similar to a single better DK right so it's a continuous spectrum because it's to enter these two neutrinos carry away energy.
Laura Baudis: And this is, for example, a very nice measurement by the name experiment of the of the two new three non decay of hundred hundred molybdenum.
Laura Baudis: So, so the decay rate and depends, then on on the on the one hand side on the npr matrix element.
Laura Baudis: but also here on this face face facts are which are which are in this energy spectrum that we have seen, so the face face factor is relatively easy to calculate and independence, then on the.
Laura Baudis: story on the charge of them have the daughter new clothes and new depends here of course i'm firm is constant and on the toolbar you sewing the end you'll get something that.
Laura Baudis: is proportional to the true value to the 11th power and jf to the fourth power and from this alone, you can already you know do a back of the envelope calculation and you will get this very long haul flights of roughly 10 to the 20 years.
Laura Baudis: We will come later to the matrix elements of this comes from the from the hydraulic from the degrees of freedom, and this is, this is simply a number but it's just more difficult to calculate.
Laura Baudis: Sorry, so um yes much more interesting, of course, is the decay without admission of neutrinos.
Laura Baudis: Because, most importantly, this would mean that outlet phone number is violated by two, and here we will see that half lives are larger than roughly 10 to the 24 years.
Laura Baudis: Now the good thing about this decade is this simply from the kinematics here if you don't if you don't admit this to neutrinos that carry energy away, but then you will have sharp peak that we expect at the true value of the decay so very clear signature.
Laura Baudis: So the first time this was discussed was by vendor for in 1939 and already, and this was shortly after it or am I wrong, I had proposed that neutrinos could actually be their own antiparticles.
Laura Baudis: So this is a simple fine on graph of how this would look like and the simplest possible.
Laura Baudis: yeah scenario is that you have a light virtual neutrino exchange here, and if that happens, then the neutrino has to be a myron of field.
Laura Baudis: So, so this is the, this is the charge contracted spinner here, meaning that it will have two degrees of freedom, instead of four degrees of freedom.
Laura Baudis: As we are used to for for dirac spinners okay so for this to happen, also the holy city must change, meaning that, meaning that neutrinos have to have a nonzero a non zero mass.
Laura Baudis: Now, in terms of the in terms of the actual mass the most general lagrange and is actually to have.
Laura Baudis: Both time from your trainer masses, on the one hand side you can write down a direct master.
Laura Baudis: And then, this is generated, just like in case of the other firm ions from Swanton of symmetry breaking but from from your car by interactions.
Laura Baudis: So that depends on on this you cover couplings, but you can also add, by hand basically this my Iran, a term that's a singlet of the standard modern age group.
Laura Baudis: So that's why doesn't violate any of the cemeteries and and can appear here as a bear master right so, then the masses of the physical neutrinos.
Laura Baudis: Will will be turning by the values, you can write this in terms of mass matrix and and in this simple, there are many versions of the seesaw mechanism, but in the simplest one.
Laura Baudis: You can have this this mass scale being with much, much larger than than the direct mass scale, and so you will get this light neutrinos states.
Laura Baudis: And, and the heavier state and that's why this is called a seesaw because you can determine the lighter one based on this m So if you now take the direct master to be of similar sizes for the other firm yarns and and and.
Laura Baudis: Capital m here, for instance, of the gut scale, then this offers a so called yeah natural explanation of the smallness of the of the neutrino masses.
Laura Baudis: Okay, so let's look a little bit yeah in more detail on the journalists who decay so similarly to what we had before, we will have here the the face space.
Laura Baudis: Then we have the matrix element for the nuclear transition now with different with different energy skating walls and here this so called.
Laura Baudis: The so called effective my Iran and neutrino mass, we will look at it closer at it from the electronic part of the matrix alum and.
Laura Baudis: Now for the face space integrated, this is now spend only by the two electrons so you will have again this dependency here on the Fermi constant and on the cube value to the fifth power so it's again a second order.
Laura Baudis: process of the week interaction and there is a somewhat is still is still strong dependency here, but not a strong further to nutrient on So what about is effective, my around a neutrino mass.
Laura Baudis: So this is embed all of the dependence on the neutrino quantities, so you can write it out here as a mixture of this of the three months i'm states.
Laura Baudis: And, and these complex entries in the in the PMs matrix and, unlike for the Iraq case, so this is a particular parameter ization of the neutrino mixing matrix.
Laura Baudis: With this with this data CP violating phase, but now you have to add this other tool so called my arena phases, because, basically, you can remove fewer phases, when you when you really find the fields, and these are completely, these are completely unknown.
Laura Baudis: Now you can you can what you can do now, based on what is already known from neutrinos elation experiments and leaving these two very freely, you can now write down this.
Laura Baudis: This effective my Iran and neutrino mass, for example as a function of the of the lightest mass mass state, you know could be one or could be, in three right so, then you get these two.
Laura Baudis: These two regions were actually three regions so first of all, you have this the general region that is still by where the actual.
Laura Baudis: The actual masses are larger than this mass much larger than this mass differences.
Laura Baudis: And then, this is this inverted mass or they're in region that we mentioned before, and finally, this normal mass ordering very principle, you could also have some some cancellations and the bandwidth here are mainly from this from this unknown my on our faces.
Laura Baudis: And yes, we will see your current experiments or somewhere here, and the next generation of detectors.
Laura Baudis: aims to MC pro basically this inverted inverted mass scale and to get to the normal one is even more challenging so in terms of experiments, what are the employed nuclei in the searches so as we already saw these are even even nuclei.
Laura Baudis: And this is, this is a list that table that I made here, these are all new values above to me me to increase to increase this decay rate.
Laura Baudis: And, and these are also the natural abundance is so the natural abundances are all pretty low the last one here of Carson 48 which, however, has a high IQ value so that's an advantage.
Laura Baudis: But except from lauren hundred 30 which has a pretty high natural abundance so usually you don't really need to enrich it, for instance, if you like, the core experiment, if you operate.
Laura Baudis: crystals that contain hundred sarita room.
Laura Baudis: But all these are experiments have to use have to use enriched material.
Laura Baudis: And here on in some calculation so again the decay rate here some calculations of the of the face space so as we have seen this depends on this depends on Z but also the true value so for some elements it's more favorable let's say that for others.
Laura Baudis: Now, much more difficult, is to calculate this matrix elements and there are many different models.
Laura Baudis: That are being used for instance that look, we are sharing model and others and even after many, many decades of.
Laura Baudis: of progress here, these still very depending on the method by a factor of two to three, so this is a pretty recent compilation here by Javier Mendez.
Laura Baudis: And there are also some recent reviews on this, so the bad news here is that you know these go in a square into the decay rate here, meaning that you can have, up to a factor of of nine or so.
Laura Baudis: difference in the in the in the actual, so this is important when you convert to this effective my Iran and your three nomads from the measure of half love I and here again you have a squared so you will have some uncertainty is there, as we will see.
Laura Baudis: and hear just to put this again into perspective, the half lives, the time skills that are involved, so we are all familiar with.
Laura Baudis: Carbon 14 the case or potassium for the also with natural activity that's one of the big large backgrounds in this in this experiment, we already mentioned the age of the universe So these are the half lives.
Laura Baudis: See, we only have a lower limits on the half life and even even longer.
Laura Baudis: Our our our delight well even longer is the lifetime of the proton.
Laura Baudis: So yeah so what i've been experiment, the requirements to observe this extremely rare case so from an experimental point of view, now the half life scales like this, so this is simply the square root here of the of the so called exposure mass times time.
Laura Baudis: divided over background and energy resolution and this is for a nonzero.
Laura Baudis: background experiment, so if you are in zero background mode will look at this later on, then genesis activity will simply scale as as the exposure.
Laura Baudis: So there's some minimal requirements here hi So this is the, this is the isotopic abundance the efficiency to observe the decay.
Laura Baudis: Of course you'd like to have large detector masses either a little background noise and also very good energy resolution because this helps you this helps you to to pick out the peak from from backgrounds.
Laura Baudis: And then, apart from these minimum requirements or some other tools that help you to distinguish a signal from background like event apology.
Laura Baudis: We will look at this in detail for for for gerda positive discrimination and also party like the meaning that you can distinguish, for instance between beta gamma Alpha and you know other possible backgrounds so very roughly speaking, there are different ways to yeah to.
Laura Baudis: categorize these types of experiments, but one is in terms of source detector so in this case the source is not a detector so we have a source here are the thing foil.
Laura Baudis: Like, for instance in this name I experiment and then you detect these electrons with with different type of party protectors, so the good thing is here that you have the event apology, possibly, you can.
Laura Baudis: reconstruct the tracks and then also the the vertex here of the decay.
Laura Baudis: About in general, you have low resolution and also low detection, efficiency and actually also lot mass because this boy is have to be very, very thin because you don't want the electrons to lose.
Laura Baudis: Energy wise scattering in the fluids, then we have this other approach that most of the detectors use, namely calorie matters so you're basically measure of the some energy of these two electrons so here, you have the signature that I showed before this clear peek at the Q value.
Laura Baudis: So the advantages are high energy resolution detection efficiency, however, you don't really have an event topology.
Laura Baudis: And if you if you have if you combine these two coloring mentor plus plus topology, namely plus tracker, for instance, like in a high pressure gas detector high pressure tpc here, in this case, it turned on.
Laura Baudis: Then, yes, then you can also have means to identify to identify these two these two electrons these two betas here, you can see here this brag peak and to reconstruct reconstruct the tracks and also the the vertex the origin of the decay.
Laura Baudis: And that's yet another another way to.
Laura Baudis: You know, to look at these detectors naming in terms of what they actually measure so, for instance, heat or phone on this would this is for the fourth quarter detectors installation light is our large ventilators with.
Laura Baudis: doped with with some yeah with either accept or not, the law room in this case or ionization and some of these experiments also measure.
Laura Baudis: For instance, heat and light, this is the case for the for the future cupid experiments that allows them, for instance, to get rid of some alpha background or or light in charge, such as for.
Laura Baudis: example on time protection chambers and, in addition, this next this next and also been like three they plan to use high pressure X and on where they, in addition, see see his tracks so that's a very broad overview is not actually a complete list of experiments.
Laura Baudis: Okay So what are the main experiment of challenges to see to to actually observe the decay.
Laura Baudis: So the largest one maybe it's the resolution of why because the ultimate background is actually from the two neutrino from the standard model decay that you can't really suppress.
Laura Baudis: And this is, this is a these are some sketches here, showing the effect if you have the relative resolution here at the one seat.
Laura Baudis: You know 2.5% 0.5 and 0.1% you can see why that is makes actually makes a very, very big difference so with this sort of energy resolution here you don't really have to worry at all about about this.
Laura Baudis: These two neutrino background, however, we are not quite there yet they still have other backgrounds to deal with from cosmic rays, and actually also customer journey in situ episodic activation on the ground for the activity of detector materials.
Laura Baudis: yeah human made human made nuclei and and also neutrinos it in the end, so, for instance I bought neutrinos sonar is born neutrinos will also give you yeah elastic neutrino electron scatters in this region of interest, however, they won't generate a peek so it will be a flat background.
Laura Baudis: At some point, you know depending where the peak is this background could, however, be you know higher than your signal.
Laura Baudis: So what are the background reduction strategies, or at least some of them so for the cosmic background and especially also for.
Laura Baudis: The voice in situ production of some of these nuclei, we have to go deep on the ground that's from that's from a review of the of the team pink lab in China here, you can see.
Laura Baudis: what's shown is the moon flux as a function of the Covenant depth in in kilometer what a given and so all of these labs.
Laura Baudis: yeah are different that's different backgrounds and, and this is the snow lap here and the deepest one is actually this distant being lab in China.
Laura Baudis: So we have to avoid cosmic activation of materials why they're above ground for instance of you know, high energy cosmic rays can produce all kinds of stuff and then sometimes some of these.
Laura Baudis: Some of these elements, like 60 Colbert, and so our then Long live tweet don't want or relatively long leaves you don't have time.
Laura Baudis: To wait until the UK, you need to use active shields, this is here just me on the veto shield of the guard I experiment So you see here the water thing when he was open, and this is just this is the crowd start with this.
Laura Baudis: With this reflective foil surrounding it, and then there's a lot, a lot of work to to select low productivity materials.
Laura Baudis: So very brief status of the field before we go to a hospital germanium experiments.
Laura Baudis: So yeah there's no observation of these decay, but so far best lower limits on this main elements here on this 336 sign on 76 germanium and research that l'oreal moderate level of.
Laura Baudis: Here 10 to the 26 years on the few times that will 25 years and this translates then into this upper limits in this this range of upper limits on this effective my Iran and Israel mass and again the range comes.
Laura Baudis: From these uncertainties in the matrix the matrix element, and this is hero selection of running and also upcoming experiment.
Laura Baudis: Okay, so we arrived at germanium experiments, where we look for this decade to medium i'm going to selenium plus plus two electrons and.
Laura Baudis: yeah, so why are these yeah, why is this a good technology.
Laura Baudis: So, in general we use a high purity germanium detectors that are mph in 76 Romanian, for example, 87% or in the meantime to also help them more than 90%.
Laura Baudis: So again, the sources that detector so you have a very high detection efficiency of this of this double beta decay.
Laura Baudis: You can produce very, very high purity material, so you basically don't have any intrinsic backgrounds, we have only upper limits in terms of you know, Dan of backers for uranium authorial.
Laura Baudis: In in the in the back of the detectors so because it's a semiconductor you know the energy revolution is at the level of premier here for full behalf maximum.
Laura Baudis: So that's yeah that's quite favorable to look for the two volume sorry for the for the speak, which is a huge value of.
Laura Baudis: Around 240 TV and because of the high stopping power these these metals are also absorbed within within one millimeter that's more of a disadvantage because, as I said, you don't have tracks.
Laura Baudis: But, but on the other hand, so this is a schematic of such a detect or so you have this debate it came and so called a single side so very, very localized.
Laura Baudis: Then gamma rays, they tend to constant scatter so you will have multiple interactions and, as we will see on you can also have.
Laura Baudis: fit case on the surface, for instance here that the plus electrode or or or beta decays and we will we will be able to distinguish these from signal like events, based on the based on the pile shapes.
Laura Baudis: So recent recent germanium experiments are a worm my Iran in the US at serve underlying us as well, so my Iran, I had a total, you can see here, these detectors.
Laura Baudis: The so called PPC point contact detectors they operated about 30 kilograms and reach to 88% in in 76 or germanium they achieved actually the best resolution.
Laura Baudis: Someone better than gerda, namely 2.5 kb for with half maximum and and their final exposure, or at least the published exposure let's say was around 26 kilogram years and it is then here to lower limit on the half life.
Laura Baudis: So for gerda we will go in a bit more detail, but the summary about 40 kilograms of enriched detectors in in an active shield of off leak in Oregon in Ross haskell.
Laura Baudis: With this resolution, and the final the final exposure, the way the final resigned from from the total exposure was just published last year.
Laura Baudis: And so very small excursion because yeah i've been working in this field for quite some time now actually already as a PhD student here on the.
Laura Baudis: Famous or infamous Heidelberg Moscow experiment, perhaps some of you remember it, but we had then five and reached.
Laura Baudis: germanium 7060 titers later this detectors actually made it into into her now with his total mass, and this was this was the reside, at least, that I got before I left.
Laura Baudis: Afterwards, there was also claim of a detection, though, though I wasn't involved in that and and back then, however, we already also started to.
Laura Baudis: to study this concept to operate to operate bear germanium crystals in a crowded it Likud.
Laura Baudis: So, back then, it was called genius and and now we're later it was called Third and finally we are moving, we are moving to legend.
Laura Baudis: yeah but what I wanted to say here is that, back then, we had you know 1.6 times 725 as as as lower limit, so it took as you can see here more than 20 years for for this factor and improvement in the in the half life sensitivity.
Laura Baudis: Okay, so burn down gorillas operated in or was operated in this whole a hassle with a shield of about 303,600 meter what a given and.
Laura Baudis: In, so this is this water to drink of sheer, then we have the liquid arm cryostat here with a large amount about 64 cubic meter so the arbonne served.
Laura Baudis: As a cooling medium and a passive sheared for the phase one that for the face to experiment, it was upgraded to an active shield, which was quite important, and this is also Is it also ultrapure it purely get our lawn.
Laura Baudis: So the concept here and was also to surround the detectors with a minimal amount of material to reduce this especially this uranium thorium and also potassium.
Laura Baudis: A background from materials, so the data taking period phase one phase two altogether was until the end of under the end of 2019 when all of this infrastructure was basically handed over to to the new collaboration, which is now legend.
Laura Baudis: Yes, so so in the end we had this seven strings with with for the detectors so Simon but 30 Of these, we will come back to these the so called broad energy germanium detectors.
Laura Baudis: Seven coaxial these were from the previous hide that Moscow and I didn't experiments and then three natural detectors and later, these were this was a central string later it was replaced with this new type of detectors that we're also using now in legend the so called invert the coaxial.
Laura Baudis: And the liquid arlen for phase two was a kid here with this optical fibers that are read out by silicon pm, and also there were these two arrays of three inch Laura activity mts so this serve that this liquid Armand veto.
Laura Baudis: yeah so I already mentioned that there's the three type of detectors in.
Laura Baudis: In garner so the broad energy to medium detectors these these older type of coaxial so this had higher masses, but, as we will see later this bullshit discrimination.
Laura Baudis: capabilities are much nicer for the so called point contact detectors and then, finally, this new thing so called inverted coaxial detectors they combine.
Laura Baudis: They combine the the large mass, on the one hand side of the box here with this feature of the point contact here and and.
Laura Baudis: yeah I will show you later some plots but basically depending on.
Laura Baudis: The device shape the final one doesn't depend so much on the on the position of the interaction, but it's quite distinct from from single scatters vs vs this mighty precisely bands.
Laura Baudis: Now the detector holders are also other ultrapure materials silicon plates here copper PDF fee, and this has to be, however, still improved for the next phase.
Laura Baudis: So the several hammers to to.
Laura Baudis: to suppress the backgrounds are the topology that I already mentioned, also the anti coincidence between detector so obviously, if you have.
Laura Baudis: If you have interactions and more more sorry that yeah interactions in more than one crystal, then you can reject those.
Laura Baudis: Positive discrimination, we will come to that, and also the coincidence, or the anti coincidence, with the legal argument veto so again if a constant scattered at the positive energy energy manual and then in the surrounding veto that won't be adopted by that okay.
Laura Baudis: Before I move on just the word on the energy calibration so you know, given that we have all these detectors and that we take data for over several years it's quite important.
Laura Baudis: To preserve that with any additional resolution for the you know, especially also for the final analysis, when you sum up all the.
Laura Baudis: All the data from all the detectors and so on, so, so we have the three loan neutron a mission sources that they produce, together we PSI here in Switzerland and also source insertion system.
Laura Baudis: So we have three we had three of these systems in order that were deployed once a week.
Laura Baudis: Yes, and in the end picture we have now pretty recent publication on this in the end, these are the, this is a spectrum so respect right here for the street type of detectors for a calibration with this.
Laura Baudis: To a forum source, but again, these are better solutions that were that were achieved, so the good news is that what is much larger detectors then BG is you can still you can still preserve preserve the quote on energy resolution.
Laura Baudis: So what about the background, however, so this is this is yeah, this is a big overview of the some spectrum here, where you have similar detector events or events only in one germanium detector.
Laura Baudis: that's for a certain explorer, and this would be for the some spectrum and to detect or, but if we.
Laura Baudis: yeah if you concentrate on this one here.
Laura Baudis: What do we see here so at low energy is well, first of all, we have our 39 in our own.
Laura Baudis: That has that has a lot to value so it's not so important for the neutrino establish beta decay, but it's important if you want to do other searches like low energy searches in this type of experiment.
Laura Baudis: Then we have here the two neutrino events, then this region here was blinded so plus minus 25 K be around the two value.
Laura Baudis: Then we have events also from the naked Armand.
Laura Baudis: From from Oregon for the tool, so you can see here are over 42 decades to potassium for it to there's a line but they're also betas that end up in your region of interest and then there's also crypto 95 but, again, that has that has a lot to value and then, finally, we have.
Laura Baudis: We have co by 16 potassium 44 uranium and so on in the detector materials, and we also have some to 10 polonium on the thing plus contact.
Laura Baudis: That gives you is of a certain energy, but some of these alphas can lose energy, so we have what we call them degraded if as and again a potentially they can they could give you some some events here in your region of interest.
Laura Baudis: So all of this background, all of this background, has to be reduced for for this next phase, as we will see for legend 200 and even more so for the thorns good experiment.
Laura Baudis: So what about this policy discrimination so for the for the big detector it's actually a very simple card.
Laura Baudis: Namely it's based on one parameter the so called what we call the a over he so we have here the we have here the current pies and we have the charge poses.
Laura Baudis: So, roughly speaking for the single site events, the current class looks like this and then, if you have more than one sketch, or what we call it my decisive and then you would have this.
Laura Baudis: These two peaks in your current pies and then, if you this is a normalized here a Wer E.
Laura Baudis: as a function of energy, so, if you look at this, then you will have here this this is single site events, this is again the blind and region, this was from an older publication, but it's still valid.
Laura Baudis: Then we have here this alpha events that are on the on the thing plus contact and, and here the so called multi site events so by by selecting here are caught in a over he we can we can reject a large part, large part of this background.
Laura Baudis: And the other, yet the other method that I mentioned was this anti coincident with the liquid argon so it signals in the pmt is and and in the silicon pm, so this would be the amplitude and the germanium So if you have something in the pmt in the silicon pm, then.
Laura Baudis: This can be rejected, and you can see here now, the background here that prior to this liquid arbonne veto, this is the one that's coincident with a liquid are going to be taught and and you can see here also this potassium 42 peak.
Laura Baudis: Because the case happen in the liquid argon white here to happen on some materials and, finally, this is the actual the two neutrino beta decay spectrum after after this liquid Oregon veto cut.
Laura Baudis: And the acceptance is is pretty high.
Laura Baudis: So these are, this is already the all the data, so the final resides here.
Laura Baudis: So yeah again, you can see the spectrum here before cards and then in red is what is left after this liquid Oregon Vito and after the palace shape discrimination cuts.
Laura Baudis: Again, you see the two neutrino spectrum, you see here some i'm fast and you also see some events that come from from her yeah radioactivity and finally.
Laura Baudis: This region, here and now, if we zoom if you zoom into that region, this would be this here so around this would be here around the value of the decay again.
Laura Baudis: This is a spectrum prior to the analysis cuts and then the what what remains here is after after cuts, so of course we can determine the half life of the tune your three not decay.
Laura Baudis: We can also determine the background level now in a bit larger energy window to to to have more statistics so 230 TV around the to value and that's actually the lowest background.
Laura Baudis: That was ever measured for a for a new journalist i'm a big advocate sperm and and that would be here the peak of a signal that would correspond to this half life and clearly there's there's no peak there.
Laura Baudis: And this is, then, so this resides on the half life translates here into this range of.
Laura Baudis: Your upper limits on the on the effective my on your screen on mass, this is a bit of historical plot for governor So this was the first result from phase one and then and then.
Laura Baudis: Subsequent resides This is basically the sensitivity that was predicted for no signal and then depending on the backlog background fluctuations, that your actual limit can be you know above or below and this this was this reside from 2020 that I mentioned.
Laura Baudis: Okay So what about the future so legend that that means large and rich germanium experiment for nutritional establish beta decay so new collaboration formed.
Laura Baudis: From from all the garden Members, my original members in the US and also quite a few new groups and this experiment is.
Laura Baudis: Yes, plan to proceed in two phases, so the first phase to operate 200 kilograms of enrich detectors in the existing but upgraded infrastructure of God, I will show you in a minute, with a background goal.
Laura Baudis: Of this, so in Garda we had about three if you translate the background that I showed before into events are full with have maximum torn year we had three events in gerda.
Laura Baudis: And we must reduce this to about 0.6 in legend 200 and then legend 1000 this would be a sketch so yeah the baseline scenario is that it would be a snow lab and and, however, it could also be hosted in France so so, but here the baseline you can see, you can see, on yeah.
Laura Baudis: sketch of it, how it would look like the snow leopard so it's a it's a stage approach as well with for for individual modules here that would each contain 250 kilograms of often rich detectors so of these arrays and the background go there is much lower than than for legend 200.
Laura Baudis: So what about the status of legend 200 So yes, after after gerda ended at the end of 2019 we had a so called PTT the postcard tests, you can see here some pictures, so we tested about 20.
Laura Baudis: detectors in total from from gerda from my Iran and also this new inverted coaxial detectors so that was quite successful this is this is again a sketch of the legend 200 immigrants so So this is the yeah the Garda cryo start.
Laura Baudis: And, and the new, these are the new inner strings of detectors this is or wavelength shifting deflector here around it, to increase the efficiency of the naked arm and Vito and here.
Laura Baudis: Our group, together with the ministry institute the position here of the wavelength shifter so the liquid are on.
Laura Baudis: The simulation light of hundred 28 nanometers indicated Oregon has to be shifted into the visible wait for instance with stp be you can see here to have my students and i'll be aligned Yannick when they were in cancer, so this was in December actually of last year.
Laura Baudis: Here are also the new calibration systems that were built for.
Laura Baudis: For legend actually we have for now for 200, and these will also be installed in the next weeks, but in total, in total, we already had 70 kilograms from these two experiments and then later new detectors were produced from from yeah for a total of.
Laura Baudis: 30 kilograms.
Laura Baudis: And the goal is actually to start either later either later this year or early early next year, of course, we had also some delays, because of.
Laura Baudis: yeah because we couldn't travel so much as in the past, and also the lab was not quite as accessible as as before 2020.
Laura Baudis: So what is the expected sensitivity so again, this is, these are the background goals, of course, assuming we can reach these goals, and we have we have.
Laura Baudis: At least good strategies in place, how to do so, and this is what I mentioned at the beginning, so this is the sensitivity here as a function of exposure and this would be this linear increase.
Laura Baudis: If you would have a background free experiment and then this other this other curves, as I mentioned it bends then on the square root of the exporter, but it depending on the background rate.
Laura Baudis: So, if in legend we can reach the 0.0 to five events, then yeah it would be this curve here wherefore legend one time for version 200 we plan to go to this tend to the 27 years with this rate and, basically, this is the prediction here for the.
Laura Baudis: If he would have an effective myron and neutrino mass of around 17 million electron void.
Laura Baudis: Now to put this into perspective, this is yeah This is again this muscle observable.
Laura Baudis: But not only as a function here of the lightest neutrino mass but also a function of the some of the three mass It states that can be probed by cosmology and have this effective electron neutrino mass that can be proved directly by experiments.
Laura Baudis: Such as katrine so actually Kathleen recently they publish the 0.5 sorry 0.8 electron void and and their aim is 0.2 electron void.
Laura Baudis: So this, this is a bit older plot, so it sort of updated so this is where we are now with gerda and and, basically, as I mentioned, we want to cover this.
Laura Baudis: With legend this inverted inverted piracy scenario, and of course we are already probing this degenerate region here, which is still, which is still allowed by the data.
Laura Baudis: So I arrived already at the summary yeah so, as you know, was we have now yeah 90 years that firm he postulated his silly child and see coordinator three now and it's still quite exciting and there are many open questions in in your trainer physics.
Laura Baudis: I hope that I convinced you that neutrinos double beta decay, is an excellent tool and maybe the only practical approach to test this let the number of violation.
Laura Baudis: and also the nature of neutrinos experiments.
Laura Baudis: yeah existing experiments prop half lives up to up to 1.8 times 10 to the 26 years, and this is roughly scaling here how this how this half life depends depends on the on the neutrino mass scale.
Laura Baudis: it's also clear that we need on scale experiments legend 1000 is one was one example.
Laura Baudis: To cover to cover these so called inverted mass ordering scenario, and there are indeed several technology is moving into this direction, also using yet aluminum.
Laura Baudis: sign on and so on, but much larger experiments, probably at the 10 point scale or beyond will be required to probe to prove the normal math ordering, so I will stop here.
Hristova, Ivana (STFC,RAL,PPD): Thank you, thank you very much, allow for this very interesting and.
Hristova, Ivana (STFC,RAL,PPD): and very nice overview of the status of the devil beta decay physics.
Hristova, Ivana (STFC,RAL,PPD): Let me stop the recording.