Week 9: Lecture 45: Unexplored paths involving neutrino detector ideas

In this lecture we will talk about uh a couple of ideas uh about detecting uh neutrinos from the sun and also from the supernova explosions. These detectors have not yet been made. Uh so right now they are ideas but uh they have certain a certain uh attractiveness about them. Uh and that is why I will talk about this. Okay. So I will first talk about an indium based detector for solar neutrinos and then about a dutrated liquid cintillator uh for both solar as well as supernova neutrinos. We have seen uh the solar neutrino detection by a detector that was especially built to look at berillium 7 nutrinos. uh and we saw that the uh you know the spectrum uh could be understood in terms of bidium 7 nutrinos and then also other contributions uh including when they refined their analysis uh they found that uh there is a contribution from the CNO nutrinos uh in the solar neutino spectrum. Uh however you would have noticed that the uh a moneretic nutrino gives a Comptonlike spectrum uh because it is after all based on neutrino electron scattering and since we are not detecting the scattered nutrino uh you get a Compton-like spectrum. Uh however this Indian based detector will actually detect the uh electrons uh through a charge current interaction. So there is a onetoone correspondence between the energy that you detect and the energy that the uh of the nutrino that came in and so this is a sort of calorimetric kind of detector for the nutrino rather than a compton scattered kind of response for the nutrinos. So that is one. So we'll talk first about that but then we'll also talk about a duty liquid cintillator which uh has the advantage that it can because it provides a neutron target and a proton target. So you can detect uh through the charge current interaction uh the uh electron type of neutrinos as well as the anti-electron neutrinos. But in addition because the dutron is a loosely bound object it has a binding energy of just 2.2 me or so. Uh therefore uh you can have a inelastic scattering of any type of neutron whether it's electron type neon type or uh the tow type and it can give rise to uh breakup which can then be measured in this liquid cintilator. So uh this is of course if you remember the D2O detector uh a pure heavy water detector actually solved the solar neutrino problem. And so this is probably you might think of it as if this is ever built this would be a kind of build on that idea and perhaps uh you might uh say that you know this can give further uh uh measurements which might be interesting for from the supernova point of view and also from the solar neutino as we shall see. Okay. So let's first talk about the Indian detector for solar neutinos. Now, Ragavan in 1976 proposed a realtime detector for solar neutrinos. Uh this was a fizerev paper in 1976 and he had many ideas of building such a detector. the last one uh in fact there was something called the lens collaboration and uh they uh focused on a possible uh segmented 8% indo loaded 125 ton liquid cintillator detector which would have a so-called photon latis with the liquid cintillator subdivided into 3-in size cubical units uh that is uh because you have a random background and we'll come to of the betas that come out of 115 indium decay natural 115 indium decay beta decay. Uh so this segmentation is necessary to hu to reduce the huge random coincidence background and a 3 in by 3 in by 3 in kind of segmentation was uh I mean the simulation showed that this segmentation was enough to reduce that huge random background. If the timing resolution which of course uh for a liquid cintillator is good uh then this could reduce that background. In 1987, Booth uh in Oxford explored the possibility of measuring quasi particles in a superconducting indium uh which is part of an indium junction and so indium aluminum junction. So uh the proposal was that you he he could show that this indeed worked in very small uh sizes but his idea was that you could build a much larger detector of the order of a few tons uh in order to uh look at uh the solar neutrinos with a cryogenic bome cryogenic device which measured the quasi particles. So what are the quasi particles? When a uh when a anazing particle falls in in a on a superconductor then it uh there's a band gap which is uh which happens when you uh take a material below the superconducting transition temperature and these quasi particles can then be actually transported and that can lead to a current or a charge and that can be measured. That was his idea. Uh the other possibility is that can one make a cryogenic bometer of indium uh metal or a suitable compound or even perhaps a scintillator of of course indium cannot form a cintilator but it might have compounds of indium which can be scintillating or you can form a 35 or uh 26 combination such that you get a semiconductor and then you can have electron whole pairs which are measured. So these are the various possibilities for Indium. So let's look at what is it about the level diagram which makes Indium so interesting and uh this was first pointed out by as I said Raon in 1976. So this is the ground state of India. It's a 9 half plus state and it decays by you know L forbidden transition uh to indium uh tin 115. You can see the large spin difference 9 half plus and uh half plus. So this is uh G9 half single particle state of the odd particle in this which is of course the proton you have an odd number of protons and this is the odd neutron which is a half plus so it's a S half state in India in 10 115 anyway so this is hindered and that's what leads to to a very large half-life of 4.4 4 10^ the 14 years. Now the beauty of this is that there are excited states in tin 115. There's one at lowest uh excited state is the 497 uh KV state and above that is the 7 half plus state which is the 63 KV state and this has a lifetime of about 3.3 microsconds. Of course there is a higher state 11 half minus and that is a long half life also 159 but the ones of interest are this uh if you connect this these two uh then because 9 half to 7 half plus this is a allowed uh transition uh is a gamotella transition allowed and this matrix element by the way an estimate has also been made through the PN reaction and so on. [snorts] So the idea is that a new e falls on indium 115 and gives you 115 tin in an excited state here and an electron and the electron energy is related to the neutrino energy via the Q value. The Q value is as low as 114 uh minus 114 KV. So it requires a minimum energy of the nutrino of 114 KV. But if you notice the PP neutrinos go from 0 to 420 KV or so. So this will capture most of the uh PP neutrinos okay or a sizable fraction more than 50% of them and of course if you can lower the threshold uh for detecting these electrons then of course you gain that much in uh getting the PP signal. Uh the berillium 7 nutrinos of course give you two lines and they would be rather easily visible with such a detector. So the big advantage of this detector is that it has a low Q value. So you can detect low energy nutrinos and that this transition uh you you get a onetoone correspondence between the detected electron and the incident nutrino energy. The downside is of course that there's this radioactivity. So uh okay so this is we will discuss that also in the next uh or subsequent slides. However, I just want to point out that what would be the signal for a solar neutrino detection. So you would get an electron. So a inverse beta decay electron. Then you have a delayed 116 KV gamma ray because this is a half-life. And of course there is a cascade. So in this you is partly converted of roughly the same number of conversion electrons and gamma rays both of which of course would be detected and that would constitute the delayed signal. But the 497 KV gamma would also be delayed because and this would be in fast coincidence with the 116 KV gammaray. So this cascade is in fast coincidence and overall with respect to this electron it's a delayed. So there are two delayed uh you know energy signals. So this is the signature of this uh uh so-called charge current interaction of the solar neutrino for example with indium 115. Okay. So this has been simulated and if you uh have uh you know a situation where you can uh reduce this background. So the uh delayed coincidence tag uh uh reduces the background uh in if you because you this is the signal and this is the background in terms of time. What is plotted here is events uh versus in some time bin versus the delta t the the time correlation between the uh electron and the uh the other uh two gamma rays or converging electron gamma ray and this is the background this random background and this is the signal in time. Okay. uh if you were to do the segmentation of the detector suitably and so on and if the signal to noise ratio is about a factor of three then the solar neutrino spectrum that you would observe in such a detector detector would be like this. So this is from the PP nutrinos. This is from the Indian background. Uh and then of course if you go to higher energies this is uh very clear the seven bilium is a line. So you would see it very nicely. This is a continuum of course. So it gives rise to a broader kind of peak like structure. And then if there are CNO neutrinos you would see them somewhere here. So in this simulation which is for five years and for a 10 ton liquid cintilator uh you don't uh see this but if you have improved uh systems you would perhaps see it and similarly you would see a certainly a signal for the pep nutrinos. Okay. Uh so this is a plot from 0 to about 1.6 me. This is taken from Ragawan's physics colloquium uh in Mumbai in 2010. So the idea would be that you measure this Espectrum energy spectrum of PP 7 berillium and PP neutrinos from about 50 to 1500 KV in real time. Uh you can also measure the core temperature of the sun directly via the Doppler broadening of the seven berillium nutrinos. Okay. As well as the PP nutrinos and we'll come to that that is in a subsequent slide. You could also of course search for possible sterile neutrino uh electron neutrino mixing using a radioactive source or you can create radioactivity with a high current proton or dutarium target beam on a suitable target. Uh six is probably out of place because this is for some paper. So in any case you you could in principles do such a thing. Uh similarly you could look for dark matter decay or analation and look at a unidentified peak in the neutrino spectrum because as I said the you you get actually the nutrino spectrum and not a continuum which you have to unfold to get uh to get the nutrino spectrum. Okay. So Ragavan had actually built a small device about 2 ft by 2 ft by 2 ft in a uh and put it in a Kimbleton mine which is close to Virginia Tech. And so this was part of the lens collaboration effort and he had made this latis as I said 3 in x 3 in by 3 in for xyz localization. So if there is some source of light then you see this in all three dimensions right one face on the other face and on this top face in principle you will see it for the o on the opposite side as well. Okay. And in principle from both the timing information and from this uh uh you know which one lights up you can localize this perhaps even a little better than 3 in by 3 in by 3 in. Okay. So this is again the same spectrum shown on the left hand side but compare this to what has been seen by the uh borax detector. Uh so this is the uh early paper which showed PP and 7 berium nutrinos and this is the paper which shows the CNO nutrinos. Okay so the CNO nutrinos are somewhere here and of course this is for a 300 ton detector and this is something that is done I think for the 10 ton detector. So in any case uh these are the counts per 20 maybe per 10 ton. uh you could scale this up by you know make it a 100 ton and you would get of course more counts and so on. So this is taken from again this Raguan's colloquium and this is so you can see that there is a I mean it's much more easy to identify the seven berillium but also the PP neutrinos and the PP neutrinos uh as compared to what you would get uh in borexino okay so that's the advantage but of course there is this background and that uh background means that you have to segment this uh detector okay so this is a 25 ton uh 8% indium loaded liquid centrator and uh so the raw rate is like this the background event is 10^ the 12 but if you do spatial cuts it reduces this by more than seven orders of magnitude you demand three hits because of course you have three uh you have two gamma rays or converg electron gamma ray and uh the electron then this reduces by another order of magnitude. If you put a some energy cut then this reduces it by another couple of orders of magnitude and from the topology you would get another background reduction. So you would the background events per year per ton of indium is of the order of 13 some error bar. Okay. So the science goals of such a indium loaded liquid cintillator as I said of the order of 100 tons or so that would and with 8% loading in the liquid cintilator you would measure the energy spectrum directly and in real time you would measure the core temperature of the sun directly via doppler broadening of these neutrinos as well as pp nutrinos you could also as I said search for possible sterile neutrino mixing uh antiutrino neutrino oscillations search for dark matter events so This is just a recap of the earlier slide. Okay. So the gre and aan wrote this paper in 2007 where they pointed out that if you uh you could also in principle measure the uh shift as well as the broadening and from there you can actually get a measure of the temperature of the plasma uh in that region. So, so anyway, these are the Q values and this is the mean energy shift for the PP uh here in KV and uh this is the precision attainable the delta E is the precision attainable. Okay, because you can measure the peak position with a precision better than the width of that peak. Okay, this is one way of doing it. In principle, you could make a cryogenic indium detector. And cryogenics has the uh potentially a big advantage in that you have excellent energy resolution of the order of a few KV. In fact, at about 7800 KV or few hundred KV. So of course there is a downside to it. You would have to operate this at 10 ml. But as we have seen uh almost a ton uh of uh toum oxide has been cooled down and so with advances in technology perhaps we could take over you could take that to a few five to 10 tons even. [snorts] Uh so now instead of a indium loading you have indium itself uh as the detector and you uh the way this works anyway is that you have you have automatically segmentation involved. So you could have between 1 to 3 cm dimension in XY Z and the volume would be very compact because of course Indium has a density of the order of 7 to 8 whereas the liquid cintilator has a density of order one and then you're only putting 8% of that in terms of indium. So this would be much more compact but of course the volume would be dominated by the cryogenics. uh you could make let's say a ton detector and have five to 10 modules each with its own shielding and in of course in view of the internal uh indium uh 115 indium radioactivity the shielding could be placed outside the cryost you don't need internal shielding because of course the indium itself is a radioactive source albeit a weak radioactive source but because if you go to tons then that causes a sizable uh background [snorts] of course The other thing that would be needed is that you need a timing of the order of half a microcond or so half to one microcond. And the neutron transmutation doped germinium thermometers are slow with response times of the order of 100 milliseconds or so. Whereas the transition sensor is much faster. They have response times of less than a microcond. But there is another uh difficulty involved. Unless you are able to show that you detect the so-called fast phonons before they thermalize uh this method may not work. Okay. Uh the other possibility is measuring quasi cu particles broken you know cooper pairs of electrons and boo showed that that was a possibility in very small devices. Now whether that can be carried over to larger much larger volumes and masses that we there is no demonstrator of that uh yet. One uh experiment which was done is that if you take let's say a nobium bar single crystal and you have these uh you know detectors of phonons on either side uh then in this 15 mm uh sized object you can actually get resolutions of the order of a you know a few centimeters 1 to 2 millm and that is shown by this. If you have some event occurring here then this is the response this is the response and so on. So these are the uh the time differences in these signals because you can take the time difference between this and this as I said these if they are made out of transition uh you know devices then they are extremely fast and you can certainly measure such uh you know responses in time. So this is taken from a reference here in 1996 Booth Cabrera and Fiorini and uh this was done by putting a alpha source in this and then measuring this phonon detection using these uh array of superconducting tunnel junction uh detectors. Okay. Now we'll talk about a a very different kind of uh possibility namely a a dutrated liquid simulator. Now as you remember the a one ton pure heavy water detector was used in the Sbury neutrino observatory and it measured solar neutrinos via the cherankov light and basically they solved the solar neutino problem. The threshold of that detector was about 5 me. If one were to make a dutrated liquid cintilator where the hydrogens's in the liquid in the cintil you may first of all you have to make a cintilator and then you have to have all or most of the hydrogens's replaced by dutarium. If you were to do that you can get a much lower threshold and possibly a few hundred kilo electron volts. The other advantage is that of course you can measure nutrinos and anti-utrinos of the electron type via the charge current interaction and all types of nutrinos via the neutral current interaction. So these are the interactions that you would use charge current neutral current charge current plus neutral current in the case of new and neutral current in the case of mutow nutrinos. So these of course have zero thresholds. uh the threshold for the uh anti-utrino on dutron is about 1.44 44 me whereas the new E on D is about 4 M so it's higher uh uh so for instance this you could use as a detector for reactor antiutinos and uh you could use this for solar neutrons with a higher threshold okay so let me see okay so this is for the uh you know so any case you could go down to a almost like whatever is the threshold that you can get of the order of hundreds of KV and you can measure uh certainly uh charge current and neutral current interactions on electrons. Okay. Okay. So what is the science that this 1 kilot ton dls this has been explored in this paper uh in 2021 that you could for instance look at the survival probability of the electron neutrino coming from the sun and the data points that we have are these so they have fairly large error bars. So this this is the theoretical curve on the basis of the Wolfenstein and uh Smeirnoff uh so the MSW uh you know you know paradigm uh and this is what you expect but were you to measure this for instance the PP neutrinos and uh then you could distinguish if you have sufficient accuracy uh between uh the MSW mechanism and a non-standard interaction mechanism. Okay. Uh and even the PP nutrinos uh uh if you had the Indian experiment, you could improve on that and so on also. So you could look for the dayight effect for instance which has been seen at the one sigma 2 sigma level. Uh you could do that better with a dutrated liquid cintilator. Of course supernovas don't occur in our galaxy or near our galaxy very often. They probably occur once in 50 to 100 years. We don't know. Uh there is a uncertainty there. The last one we saw was in 1987 so-called SN1987A. But where you to build such a detector, it can detect both neutrinos and anti-utrinos of all flavors. This uh uh will also tell you about uh multi this will also add to our understanding of multime messenger astronomy and the so-called super nova nutrino watch. Uh there are also effects of neutrino mass ordering on such a supernova neutrino signal and also nonlinear uh new new interactions taking place in the while the core is collapsing. Okay. So this has if you were to observe a supernova through such a detector we would have a lot of information because it as I said it detects all kinds of it would detect all kinds of neutral loss. Okay. So this is just a picture of the supernova that exploded in 1987. Okay. Now why are we talking about this? India is the largest producer of the heavy water in the world. The heavy water board uh which is part of the department of atomic energy has the capability of manufacturing a 1 kiloton uh dutrated liquid cintillator once the R&D is carried out by research groups in India or elsewhere. The possible phases for such a DLS detector uh would be that you first start out with pure D2O and you have nowadays PMTs with quantum efficiency which is about double of uh what you had in the earlier days when for instance snow was getting set up and so this would immediately lower the threshold from about 4 and a half to about 2 2.2 2me if you can develop a heavy water soluble liquid cintilator let's say you have 95% D2O and you dissolve say 2 to 5% of uh a hydrogen-based liquid cintilator then you could lower the threshold by another factor of two or three okay so you would go into the subme range of course if you could make a greater than 90% duterrated liquid cintilator and that cintilator could be based on lab which is the linear alkyle benzene or xylene or toluine based uh then you would of course go all the way and you could have probably 100 kV threshold ideally uh this is of course challenging but not impossible uh for instance such a 90% dutrated uh organic substance uh the dutration has been done with greater than 90% using of course very expensive catalysts which involve platinum and roodium Now if you want to do this on a kiloton scale of course uh this has been done as I said on a millie liter scale that means a few cc if you want to do it on the level of tons or even 100 tons kiloton then of course you require cheaper catalyst and so there is a lot of R&D involved whether it is uh whether it is possible or not only once you do the R&D you can tell okay so so these are the three kinds of steps in which one could go this step already would be make it very interesting. Uh this step would be also interesting no doubt and uh so this is the possible uh methodology which you could adopt on the way to building a fully dutrated liquid centilator if if any. Okay. So in summary we have discussed the possibility of an indium based detector based primarily for solar neutinos. We've also discussed the possibility of a dutrated liquid cintilator and its use for solar neutrinos precision measurements of solar neutrinos including disentangling the uh MSW paradigm as well as non-standard interaction that theorists propose and also its use in detecting supernova nutrinos. Thank you. >> [music] [music]