[HN Gopher] Majorana, the search for the most elusive neutrino o...
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Majorana, the search for the most elusive neutrino of all (2012)
Author : bilsbie
Score : 109 points
Date : 2024-05-25 20:35 UTC (1 days ago)
(HTM) web link (newscenter.lbl.gov)
(TXT) w3m dump (newscenter.lbl.gov)
| mmastrac wrote:
| The article takes about 66% of its content before it actually
| explains why "Majorana" -- from the theoretician Ettore Majorana:
|
| > So far the only known particles that are their own
| antiparticles are all bosons, particles that often carry force or
| mediate interactions, such as the photon, the pi-zero, or the Z.
| Ettore Majorana, a brilliant Italian theoretician who had a brief
| career in the 1920s and 30s but vanished mysteriously at the age
| of 32, was the first to propose that some fermions, particles of
| matter, might also be their own antiparticles.
|
| https://en.wikipedia.org/wiki/Ettore_Majorana
| omgJustTest wrote:
| As is typical of LBL, they don't also note the leading theories
| place majorana characteristics in a very small probability
| regime (particles are more and more demonstrating Dirac
| characteristics).
|
| Demonstration of neutrino less double beta decay would prove
| majorana conjectures and point to fractures in the "standard
| model of physics" meaning new fundamental particles would be
| needed.
|
| In my opinion whoever measures the CvB (cosmic neutrino
| background) will be more compelling because it isn't a
| nullification result, it's a result that would tell us far more
| about the Big Bang than we know now.
|
| Neutrinos are hard to measure, have been the source of a lot of
| Nobel prizes!
|
| Disclaimer: I use to work at lbl
| jessriedel wrote:
| The CvB is the holy grail. But it is an insanely challenging
| detection problem. I think the (multidecade?) PTOLEMY
| experiment is the only serious proposal, and particle
| physicists I knew were pretty skeptical it could actually
| pull it off for SM neutrinos.
|
| https://arxiv.org/abs/1902.05508
| initramfs wrote:
| Interesting, I read about neutrinos a while back
| https://arxiv.org/pdf/2304.14995
|
| https://www.universetoday.com/13052/do-advanced-
| civilization... (I was reminded of this recently after
| watching the Three Body Problem - Tencent's version,
| interstellar quantum communication)
| SaberTail wrote:
| I used to work in neutrino physics, and I will consider
| myself lucky if I see a detection of the cosmic neutrino
| background in my lifetime (roughly the next 50 years).
| dphidt wrote:
| If there's a prior in the community, my impression (as a
| neutrino physicist) is that if anything it's more toward
| Majorana than not, in the absence of evidence either way. It
| is surely nicer from a theory perspective, with a (seesaw)
| mechanism to help explain the very light neutrino masses, and
| lepton number violation that helps in the case for
| leptogenesis as an explanation for the universe's matter-
| antimatter asymmetry, etc. One way I think about it is that
| it's pretty interesting either way: Majorana demands physics
| beyond the Standard Model, while Dirac would seem to suggest
| that lepton number is more than an accidental symmetry of the
| Standard Model, implying some unknown quantum number.
| Meanwhile, many experimental searches for neutrinoless double
| beta decay go on, with many new/clever ideas to carve through
| the quite large allowed parameter space.
| SaberTail wrote:
| 2012. They released their final results last year:
| https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.13...
| i_k_k wrote:
| LEGEND is the follow-on project. https://legend-exp.org/
| EdwardDiego wrote:
| So... no luck this time? But they know how to look better next
| time? I think? I'm bad at reading science papers.
| SaberTail wrote:
| Yeah, they didn't observe the decay, but set lower limits on
| the half life of the decay, which translates into upper
| limits on a neutrino mass. Next time will mostly involve
| getting more germanium 76, but also improving the techniques
| they use to beat down backgrounds.
| dphidt wrote:
| Just to add for reference, the strongest bounds (for any NLDBD
| candidate isotope) are from KamLAND-Zen using Xenon-136, also
| last year: https://journals.aps.org/prl/abstract/10.1103/PhysRe
| vLett.13....
| aaronblohowiak wrote:
| One step closer to synthetic astrophage
| smokel wrote:
| An interesting story in this context is that a research group in
| Delft thought they observed the Majorana particle (2018), but
| then it turned out they didn't (2021).
|
| https://delta.tudelft.nl/en/article/majorana-not-fraud-confi...
| SaberTail wrote:
| The more interesting one was the Klapdor-Kleingrothaus claim of
| observing neutrinoless double beta decay in germanium 76 in the
| early 2000s. That was a major impetus for the generation of
| double beta decay experiments like this that ran in the 2010s.
| The MAJORANA experiment used the same isotope and was
| significantly more sensitive, and pretty thoroughly excluded
| the half life Klapdor-Kleingrothaus claimed.
| YakBizzarro wrote:
| Despite the similar name, in Delft they were not looking at
| fundamental particles, but at quasiparticles in a solid state
| system. So, similar equations, but completly different physics
| antirez wrote:
| Thanks to the authors for remembering in a highlighted section
| the disturbed genius of Ettore Majorana. He was from Catania,
| Sicily, where I live: if not for a few schools with his name he
| is hardly remembered by young generations.
| fch42 wrote:
| What I'm missing in the article is actually the crucial point:
|
| How do you _distinguish_ between the "ordinary if rare"
| conventional double-beta (that has reproducibly been observed for
| Ge76 -> Se76 + 2b + 2 anti-n) and the hypothetical neutrino-less
| one ?
|
| In "ordinary" beta decay, the (anti)neutrino takes part of the
| decay energy and hence the energy spectrum of the electron
| emitted is "blurry". "ordinary double beta" would imply the same,
| both of the (seen) emitted electrons should show an energy
| spectrum. If at least some of these double-betas were
| neutrinoless, the two electrons would take the entire decay
| energy. If you observe a lot of double-beta, you should therefore
| see the "smooth" ordinary (non-neutrinoless) spectrum ... with an
| excess at the top end (neutrinoless).
|
| Is that correct? I.e. we're basically trying to measure enough
| double beta to get an energy distribution spectrum, and then
| hope/expect to see a "majorana peak" at the top end?
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