LHC Research May Help Explain the Universe's Matter/Antimatter Imbalance

suraj.sun sends this excerpt from the BBC: "Particles called D-mesons seem to decay slightly differently from their antiparticles, LHCb physicist Matthew Charles told the HCP 2011 meeting on Monday. The result may help explain why we see so much more matter than antimatter. The team stresses that further analysis will be needed to shore up the result. At the moment, they are claiming a statistical certainty of '3.5 sigma' — suggesting that there is less than a 0.05% chance that the result they see is down to chance. The team has nearly double the amount of data that they have analyzed so far, so time will tell whether the result reaches the 'five-sigma' level that qualifies it for a formal discovery."

Comments

Kaon decay

[tylersoze]

CP violation in weak interactions has been known for some time, specifically in neutral Kaon decay. If I'm understanding this results correctly, the surprise here seems to be the magnitude of the CP violation in this case.

Re:Kaon decay

[torako]

CP violation in Kaon decays can be explained by the Standard Model, but if the magnitude of CP violation they have claimed exists in the D system can not. It would be the first actual hint of physics beyond the Standard Model at the LHC. That would be some very exciting news (especially because everybody expected the big "discovery" detectors ATLAS and CMS to actually find something new first, i.e. the Higgs or Supersymmetry).

Re:Kaon decay

[Skarecrow77]

I've spent too much time at encyclopedia dramatica recently, because I'm reading your statement way differently than I assume you mean it, based on my understanding of the meaning of the letters CP.

How do we know matter is more common?

[Anonymous Coward]

A star made of antimatter would look exactly the same as one made of matter, wouldn't it? What if half of what we can see in the universe is antimatter?

Re:How do we know matter is more common?

[bsane]

The assumption is- if the universe had a fair amount of both, we'd see the gamma radiation leftovers from collisions, and we don't...

Re:How do we know matter is more common?

[ackthpt]

The assumption is- if the universe had a fair amount of both, we'd see the gamma radiation leftovers from collisions, and we don't...

May as well theorize the equal and opposite reaction to the Big Bang was one of Antimatter in an inverse universe. Not saying there's anti Cowboy Neal or anyone else in that universe, it's doing its own thing.

Re:How do we know matter is more common?

[Anonymous Coward]

The assumption is- if the universe had a fair amount of both, we'd see the gamma radiation leftovers from collisions, and we don't...

That's not a great assumption. Contrary to popular belief, when random matter and antimatter collide, they don't always create gamma radiation. Anything is possible that still is consistent with a conservation of energy, momentum, and quantum number(s). Although the most likely result of a electron/positron collision is 2 gamma ray photons, it is not impossible that there is some other "light-weight" particle is formed (say like a neutrino/anti-neutrino or some unknown ligher particle or even whatever people might be calling dark matter that is not easily detectible). It may be that there is some unknown field/symmetry that favors the create of something else on the "lightweight" side instead of a photon. Or perhaps there is something that somehow segregates matter from antimatter (like dark energy with negative pressure) to prevent large scale production of gamma radiation.

However, the current wisdom is that antimatter just doesn't exist in large quantities in the universe because the cosmic radiation which is detected in our neck of the woods is mostly of matter origin (high energy protons, electron), and not of the anti-matter origin. If there were large amounts of anti-matter galaxies, and such, there probably wouldn't be this type of bias in cosmic radiation...

Re:How do we know matter is more common?

[Walt Dismal]

I've never understood why the vacuum sea doesn't equally create as much anti-matter as it does matter. If it does, then why don't we observe constant energy bursts from collisions of antiparticles with normal particles? If doesn't, why would the vacuum sea be unsymmetrical? Either way, it doesn't seem to be reasonable.

Re:How do we know matter is more common?

[Anonymous Coward]

Posting anonymously because I've moderated in this discussion, but the quick answer is no, probably not - we know the signatures of matter/anti-matter annihilations very well, and they simply don't describe gamma ray bursts well enough.

Interestingly off-topic but I once entertained myself in an astronomy project filling in a cloudy night by calcuating if gamma ray bursts could possibly be accounted for by tightly-collimated electron/positron annihilations. My conclusion was that if they *weren't* collimated, it would involve almost as many electrons as seem likely to be in the universe, while if they were collimated it was possible... but you'd have issues with the red- or blue-shifting.

Now, I wouldn't actually *trust* those results since I did them in my second year of university, but they were interesting nonetheless. From people I'd actually trust who do this, it doesn't seem too likely that gamma ray bursts are caused by matter/anti-matter annihilations. But hell, it's physics, you never actually know.

Re:How do we know matter is more common?

[CtownNighrider]

I believe it would be the sum of the masses. The anti matter is converted to energy plus the regular matter is converted to energy.

Re:How do we know matter is more common?

[HiThere]

Black hole? Something's wrong with your physics model.

OTOH, as stars emit gas, and so do galaxies, you'd expect to detect a lot of matter-antimatter annihilation going on. This is a particular energy range of gamma radiation that we just aren't seeing, so we believe that there's no sizable amount of antimatter in the universe. This isn't entirely certain, as glaxy clusters are much more separated than individual galaxies, but if there is a significant amount of antimatter it's at the galactic cluster range of size, and it's really hard to explain why it would chunk in that way. (OTOH, I'm not a cosmologist. I could be wrong. But in this case I'd make a reasonable bet that I wasn't.)

Observable universe

[Lord Lode]

What we see is just the observable universe. What if all this missing antimatter happens to be in a non-observable part? You'll never be able to see that! Unless those faster than light particles end the theory of observable universe of course.

Re:Observable universe

[bmuon]

And where would the unobservable universe be? Unless you're thinking about antimatter being coiled up in extra spatial dimensions, everything points to there being a process by which the symmetry is broken.

Re:Observable universe

[Surt]

The unobservable universe is the infinite portion beyond the light speed horizon.
If you really want to be depressed, think about future civilizations in our galaxy for whom all other galaxies will have retreated beyond the light speed horizon. They will have a much harder time figuring out how the universe works.

Now realize that we may already be one of those future civilizations from the perspective of the lucky folks who got to see the universe early on.

Re:Observable universe

[Roger W Moore]

And where would the unobservable universe be?

So far away that light from it has not yet had a chance to reach us, and thanks to the accelerating expansion, never will. I vaguely remember seeing some discussion of this in relation to inflation - we end up in a region which is matter dominated and another region is antimatter dominated with the two regions being causally separated by inflation.

However I believe that these theories have problems because you'd expect to be able to see gamma rays from the edges of each region...unless we happen to be strangely right in the centre of a massive matter-dominated region and cannot see the edge. Plus, since CP violation does exist it we do know that there is a matter/anti-matter asymmetry so it seems strange that, given this, there would be a completely unrelated mechanism to cause an imbalance.

Re:Observable universe

[Thing 1]

Similarly, the moon is receding from the Earth at a rate of 1.5 inches per year. At some point, it's going to "fly off into space". Imagine if we hadn't developed intelligence and telescopes until after that happened? We wouldn't be able to describe our origin!

I read a short story a while ago in which there were astronomers wondering at the significance of the six stars in their sky. As they were debating this, one of the stars winked out, and they were left with only five visible stars. Really neat thought experiment.

Re:Observable universe

[izomiac]

As I understand it, the theory is that anything galaxy-sized or smaller must be almost completely composed of either matter or antimatter since otherwise it'd destroy itself. But, if you had antimatter galaxies then you'd expect to see gamma particles created when they interacted with matter galaxies.

That hasn't been observed, so the prevailing theory is that the whole universe is almost exclusively comprised of matter, thus there must be some preference in the laws of physics for matter. Personally, I suspect we'll discover an alternate explanation for the missing gamma rays that doesn't require an asymmetry in physics, such as your idea, but I'm certainly not an expert on the topic ("neophyte" would be generous).

Re:More importantly....

[ackthpt]

Is such an imbalance dangerous for a universe this age? Does our universe need medical treatment?

Further, don't expect a balanced universe amendment any time soon.

Re:sigma?

[Anonymous Coward]

No, this is not MBA-speak, sigma is standard statistical terminology for "standard deviation":

In some fields, for example nuclear and particle physics, it is common to express statistical significance in units of the standard deviation of a normal distribution.

Re:...the fuck?

[Anonymous Coward]

Ok, here we go again:

LHCb sees where the antimatter's gone

ALICE looks at collisions of lead ions

CMS and ATLAS are two of a kind

They're looking for whatever new particles they can find.

The LHC accelerates the protons and the lead

And the things that it discovers will rock you in the head.

Re:What are the odds?

[ShakaUVM]

>>>>At the moment, they are claiming a statistical certainty of '3.5 sigma' Ã" suggesting that there is less than a 0.05% chance that the result they see is down to chance.
>>Seems legit. I mean how many times would one need to take the chance of the results being down to chance for that chance having a chance of happening?

My plan for runs on the LHC is to run 1000 experiments and then pick the result that most supports some media-attention-grabbing theory that I'll just make up on the spot. /sacrasm off

In all honestly, a sigma of 0.05 isn't especially good for experiments like this. You don't have the confounding effects that make social "science" so hard to trust.

Re:More importantly....

[GrpA]

Any medical treatment given the universe would most certainly not be good for sub-microscopic lifeforms living on planets...

GrpA

Re:sigma?

[Theovon]

Sounds like he had a brain-fart. RIgth now, he's smacking his forehead and calling himself an idiot because he didn't put together this sigma with the sigma he knows about as the standard deviation.

This sort of thing happens to me all the time. (Sometimes I feel really old.) I hate it when it makes me look stupid in front of someone. Like the day I was in the office of a Linguistics professor and asked a really stupid question about the fridge magnet letters that just happened to be IPA characters. I know IPA like the back of my hand, so I don't know what I was thinking.

I do other things that make me look stupider than I really am. Recently, I did a doozie in a slashdot comment. But this time, I was just being lazy. They were talking about Bulldozer, and I said a bunch of things that were wrong, mostly because I had forgotten, and I didn't take the time to look it up. I'm getting a Ph.D. specializing in computer architecture, but my lazyness made me look like a total idiot.

Fortunately, my dissertation committee won't be looking at my slashdot comments. :)

Careful: QCD hard!

[Roger W Moore]

CP violation in Kaon decays can be explained by the Standard Model, but if the magnitude of CP violation they have claimed exists in the D system can not.

The calculations required to predict the amount of CP violation in meson systems are extremely hard to do. When I worked on the NA48 experiment, which measured direct CPV in the kaon system, the theorists were initially adamant that there was no way the parameter we measured (espilon-prime over epsilon) could be above 0.001 in the Standard Model. Several year later after both NA48 and KTeV had published results putting the parameter at well above that I saw a theory talk saying that these results were in perfect agreement with the Standard Model!

Now the discrepancy seems a lot larger here but, nevertheless, even if the result holds I'd give the theorists time to think about this and see whether they find problems in the calculations. I have a huge amount of respect for my theory colleagues but QCD calculations like this are fantastically hard so it is not at all uncommon for the results to change.

Re:We don't "see" much more matter

[Surt]

We know what annihilation looks like. If there were anti-stars in our galaxy, we'd see some substantial annihilation signatures in the mixing in nebulae for example. Even if whole galaxies were anit-matter, we'd see some signature where the galaxies mix. The smallest unit of mass that could be anti matter unnoticeably is probably the supercluster. Even then, doubtful that we couldn't see annihilation signatures along the great walls, for example.

Re:More importantly....

[BergZ]

How many more galaxies must suffer before we build a universal healthcare system?!?

Re:We don't "see" much more matter

[Old Wolf]

Firstly,it might not, as Nature respects neither C-symmetry (swapping matter for antimatter) nor CP-symmetry (swapping matter for antimatter and taking a reflection), as shown by TFA. So antimatter stars might behave differently or not even exist.

Secondly,if there were large amounts of antimatter in the observable universe, there would be huge amounts of radiation produced along the bounday between it and the bits that are made of matter. ('Empty space' isn't empty; look up Interstellar medium and Intergalactic medium).

Re:More importantly....

[mangu]

Supernovas are universal antibiotics.

Significance

[kievit]

Being a physicist myself I am very happy that this topic makes it into the news. But it is important to keep cool and skeptical. The statement that a statistical fluke has a probability of 0.05% implies that it is bound to happen if you let 2000 students do data analyses on independent data sets. There are indeed literally thousands of PhD students doing such analyses LHC data, trying to address hundreds of specific research questions that each require different data selections. So it is very likely that some of them will find a result several standard deviations away from the expectation. Actually 3.5 sigma deviations happen very often, because of all sorts of mistakes and inaccuracies in the analyses, but most of the time these mistakes are scrutinzed away before loud public announcements are made. After all scrutiny a few genuine statistical flukes should still remain, and recognized as such.

(For the xkcd inclined: green jellybeans linked to acne.)

More caveats:

• On slide 14 and 15 you see a summary of the estimated systematic errors and the final result: the deviation of the observed value from the expected value is 0.82 ± 0.21(stat.) ± 0.11(sys.) %. Estimating and combining systematic errors is almost by definition dark magic. It looks like the "3.5 sigma" was obtained by adding the statistical and systematic error in quadrature, which yields a total error of 0.237, and 0.82/0.237=3.5.
• The statement that the probability of this 3.5 sigma deviation is 0.05% is based on the assumption that if you repeat this analysis several times on more data with exactly the same experimental setup, the deviations from expectation are distributed like a Gaussian (bell curve) with a sigma equal to the total error mentioned in the previous bullet point. That is a major idealization, it could be distributed in many other ways, and then the relation between the deviation (in units of sigma, which is also defined for non-Gaussian distributions) and "the fraction of events with such a deviations or larger" can be quite different. Furthermore, when repeating the identical experiment the systematical errors do *not* fluctuate (that is one of the aspects in which they differ from statistical errors), so aforementioned idealized Gaussian would have an arbitrary offset with a magnitude of the order of the estimated systematic error (0.11), in either direction, and a width of the actual statistical error, 0.21. Depending on what this systematic error really is, the true statistical significance is much larger or much smaller than the quoted 3.5 sigma.

So this is a very interesting result, but more study is needed and in my experience such flukes almost always evaporate in the light of more data and scrutiny. Still, it's not completely excluded that this was indeed the first hint of a real discovery (otherwise no researcher would ever do all that work).

OK, enough for now. Sorry for misinterpretations and other errors I might have made.

Re:What are the odds?

[Lawrence_Bird]

I noted in a reply further up that 3sigma events many times end up going away as more statistics are taken. Google "3 sigma bump" for examples.

Re:sigma?

[Dragonslicer]

units of the standard deviation Ïf of a normal distribution

Now how'd that get in there?

Pair production? Maybe now there's an anti-Ïf floating around somewhere.