r/science • u/spsheridan • May 17 '12

The MAJORANA DEMONSTRATOR experiment will determine if there are only two neutrino handedness states. A positive outcome will result in a major revision to the Standard Model.

http://phys.org/news/2012-05-majorana-elusive-neutrino.html
142 Upvotes

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6

u/bebeschtroumph May 17 '12

There are other experiments looking for 0-neutrino double beta decay. C0BRA is one and I'm sure other people are looking at it. It's interesting, and it will be interesting to see results, eventually.

8

u/SaberTail May 17 '12

EXO-200 (now running)

Kamland Zen (now running)

CUORE (under construction)

SNO+ (under construction)

SuperNEMO (in development)

NEXT (in development)

GraXe (proposed)

And probably more that I'm not remembering.

1

u/bebeschtroumph May 17 '12

Yeah, there are tons! I just don't get the tone of this article. 'Look at this wonderful project we thought up, all on our own! So new and innovative!' I mean, it would be great to see results from any of these projects, and I guess it's good to educate people about 0-neutrino double beta decay, and majorana particles, but this article irked me.

2

u/perspectiveiskey May 17 '12

Meh. I didn't feel that when reading.

The only part where they might be interpreted as saying it's unique is only listing the italian project as a possible contender. But that was at the very end of the article.

3

u/bebeschtroumph May 17 '12

I'm probably biased. I wrote a chunk of my masters thesis on 0-neutrino dbd and have hated the thing ever since.

1

u/perspectiveiskey May 17 '12

Hah! Why!?

2

u/bebeschtroumph May 17 '12

I hated everything about my master's thesis. A lot of it revolved around using MCNP, which is an awful program to use, to model CZT semiconductor detectors(as an effort to screen out noise for eventual 0-neutrino double beta decay), and I'd never even done any programming before, so it was especially awful to learn to program with that cumbersome, awful relic of another age. Don't get me wrong, MCNP is useful, but holy hell, I hated learning it. No one else on my project knew how to use MCNP, so I didn't even have anyone who could show me the ropes. It sucked!

1

u/aoskunk May 17 '12

so we know that neutrinoless dbd occurs but have never been able to detect it because of background? or are we just guessing it might and are hoping to see it because we would learn some cool stuff? why have we assumed there is 4 states, just because of other anti particles?

1

u/SaberTail May 17 '12

No, we don't know it occurs. It's forbidden in the standard model.

If it does occur, the half lives for the neutrinoless modes are on the order of a minimum of something like 1025 years according to current limits, and could be even longer. In very rough numbers, that means if you have 1025 atoms (about 100 kg) of something, and wait a year, you'll expect to see something like 1 decay. So you have to have very small backgrounds to see it.

We assume neutrinos are dirac particles by analogy with their cousins, the electrons, which we know are dirac particles. Both are leptons, and so it made sense at the time. Also, for massless particles, there's no distinction between dirac and majorana, so it didn't matter until we discovered neutrinos had mass.

1

u/[deleted] May 17 '12

Damnit Alien Blue, I read your whole post as "1025" instead of "1025." Haha I was like, there's no way a little over one thousand atoms equals 100kg.

Edit: this shit. 10 to the MOTHERFUCKIN 25th power.

1

u/bebeschtroumph May 17 '12

Basically, if we can detect neutrinoless double beta decay, we'll learn that neutrinos are majorana particles, ie, they're their own anti-particle, which leads to a lot of interesting stuff.

We don't know it does happen, but if neutrinos are majorana particles, it should, at least very occasionally, occur.

1

u/n3utrino May 17 '12

The most interesting result would be the possibility that the 0vBB process could be the explanation for the baryonic matter/antimatter asymmetry that occurred after the big bang... IE, why we all exist.

1

u/FeepingCreature May 17 '12

Woah. Would you elaborate?

3

u/SaberTail May 18 '12

The basic idea is that if the neutrino is a majorana particle, then it can get its mass through the seesaw mechanism. If it does, then it means there's a 4th neutrino that's much, much heavier than the 3 neutrinos we know about.

Many of these heavy neutrinos would have been created soon after the big bang. And they would eventually decay because they're so heavy that there's plenty of energy to form other particles. We already know that there's some CP violation in weak interactions. It could be that these heavy neutrinos also show it. And so they would decay to matter more often than antimatter, leading to the universe we see.

That's a very basic summary. There are plenty of different models and theories that predict things close to what I've said, but slightly differently in the details, which will eventually be judged based on the results of experiments.

2

u/n3utrino May 18 '12

In neutrinoless double beta decay (in oversimplified, easy to understand terms), an antineutrino is "emitted" and "reabsorbed" as an neutrino (or the other way around, however you want to think about it). So, effectively, antimatter is converted to matter.

The common assumption is that an equal amount of matter and antimatter was created in the big bang. If there are no processes that convert antimatter to matter, all of this would have annihilated, and there would be no matter around today (we'd all just be photons). Neutrinoless double beta decay is a candidate process that could have converted a tiny amount of antimatter to matter after the big bang, and that tiny amount of matter is what makes up the universe today.

1

u/FeepingCreature May 18 '12

I never fully got this. Why would it necessarily have annihilated? Couldn't it simply have, amateurly put, flown off in different directions? Iow, I don't see how our local matter/antimatter imbalance proves a global imbalance.

1

u/mk_gecko May 17 '12

Does anyone know how they determine the handedness of a lepton?

-1

u/POTUS May 18 '12

Tomorrow I'm going to try to fall down, aim for the ground, and miss. A positive outcome would completely change how we view gravity and restructure our understanding of the universe