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LHC Research May Help Explain the Universe's Matter/Antimatter Imbalance 113

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

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  • Kaon decay (Score:5, Informative)

    by tylersoze ( 789256 ) on Friday November 18, 2011 @07:16PM (#38104446)

    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 (Score:5, Informative)

      by torako ( 532270 ) on Friday November 18, 2011 @07:26PM (#38104538) Homepage

      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).

      • Careful: QCD hard! (Score:5, Informative)

        by Roger W Moore ( 538166 ) on Friday November 18, 2011 @08:54PM (#38105150) Journal

        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.

        • Great comment and my semi-learned mind says you are likely to be proven correct. One other thing to point out - eventhough this is reported as 3.5sigma, that does not mean that additional statistics will push it to 5 and in fact, many 3 sigma-ish 'discoveries' end up being background or explained by other parameters/variables.

    • by Skarecrow77 ( 1714214 ) on Friday November 18, 2011 @09:25PM (#38105312)

      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.

  • by 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?

    • the problem is whenever matter and matching antimatter come in contact we get to see what E=MC^2 means (Very Large Bang for the TL;DR crowd). So an Anti-Star would most likely convert to a Black Hole before it could be seen.

      • do you get E=(anti+real)MC^2 or E=(anti*real)MC^2 when that happen ?

        • 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.
          • I tough so, but since my confusing quantum physic class (thought by a confused individual nonetheless) 10years ago, I almost don't have any certainties left about high energy physics....

      • by HiThere ( 15173 ) <> on Saturday November 19, 2011 @03:13PM (#38110038)

        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.)

        • Perhaps this is a naive view, but if matter and antimatter *did* exist in similar quantities, wouldn't they *have* to "chunk"?

          If it didn't, significant quantities of it would annihilate at the boundary, creating an outward force that would tend to keep the two apart, would they not?

          Now, I don't see any reason why there wouldn't still be interactions, and consequently why we wouldn't see the proper gamma rays, so it seems unlikely that that much antimatter does exist, but...

    • by bsane ( 148894 ) on Friday November 18, 2011 @07:35PM (#38104598)

      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...

      • by ackthpt ( 218170 )

        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.

      • by nomel ( 244635 )

        Could a stray bit of antimatter interacting with matter be the cause of some of the gamma-ray bursts?

        Maybe something like a comet []?

        • Re: (Score:2, Interesting)

          by 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

      • Re: (Score:2, Interesting)

        by 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 pe

        • 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.
          • Because a virtual particle pair is created at random from the sea, then annihilates resulting in a gamma, which then disappears into the sea without a trace.

            • Wouldn't the gamma ray sometimes get absorbed by matter, perhaps imparting momentum. Would this maybe be akin to the force of 'dark matter', since it would provide a force 'out of nowhere' on normal matter. So maybe the universe is expanding because of the very nature of the vacuum sea, being rectified / non-symmetric in this way. Kind of delivering something out of nothing, not in a mystical way either.
              • by bsane ( 148894 )

                Like Vacuum Energy [] or Dark Energy []?

              • Learning physics from Slashdot is not recommended. You sound generally interested in this material; go to the library and read some books that can actually explain it consistently.

                Rude translation: I'm not going to figure this shit out for you. Go ask someone who not only knows but cares.

                • I thank you for your wasted time replying. I am not trying to learn serious physics via Slashdot. Like anyone else using social media I'm merely looking for pointers, not a graduate seminar. Your candid and useless answer is appreciated in the spirit with which it was given, and in the same spirit, please investigate the effect of gravity on matter falling off bridges.
  • Observable universe (Score:4, Interesting)

    by Lord Lode ( 1290856 ) on Friday November 18, 2011 @07:39PM (#38104632)

    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.

    • by bmuon ( 1814306 )

      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.

      • 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.

        To quote Wikipedia []

        The current comoving distance to the particles which emitted the CMBR, representing the radius of the visible universe, is calculated to be about 14.0 billion parsecs (about 45.7 billion light years), while the current comoving distance to the edge of the observable universe is calculated to be 14.3 billion parsecs (about 46.6 billion light years),[1] about 2% larger.

        I'm kind of surprised that you don't understand that the universe is larger than our observable universe.

      • by Surt ( 22457 ) on Friday November 18, 2011 @08:54PM (#38105148) Homepage Journal

        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.

        • by Thing 1 ( 178996 )

          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 th

          • by Surt ( 22457 )

            Well I have good news and bad news:
            The good news is, we don't have to worry about ever losing the moon.
            The bad news is that the reason will be the sun puffing up into a red giant, vaporizing both planets, long before the moon would be lost to us.

            • by DrVxD ( 184537 )

              The bad news is that the reason will be the sun puffing up into a red giant, vaporizing both planets, long before the moon would be lost to us.

              The even worse news is that, several billion years before the Sun goes red giant, it will have boiled all the water (and us) off the surface of the Earth.

        • by HiThere ( 15173 )

          Currently the galactic clusters are still gravitationally bound. Unless Dark Energy gets a lot stronger, they will stay visible. If it does, the remaining intelligences will have other problems.

          OTOH, IIUC, by the time Dark Energy gets strong enough to break up the galactic clusters, at it's maximal current rate of strengthening, the Milky Way will have merged with Andromeda, and there effectively won't BE any local galactic cluster. Just a much larger galaxy of MUCH older stars. (Andromeda is already so

          • by Surt ( 22457 )

            Looks like you're right, and it extends as far as the local supercluster being sufficiently gravitationally bound to avoid that doom, at least until after all the stars burn out anyway.

      • 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 s

      • > And where would the unobservable universe be?

        Beyond the horizon where it is too far away for its information to ever reach us in our lifetime due to the lightspeed limit.

    • by izomiac ( 815208 ) on Friday November 18, 2011 @09:40PM (#38105386) Homepage
      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).
      • We couldn't live in a universe with both matter and antimatter since they destroy each other. So it's obvious that a place where life appears and we get born to ask that question, has only one of them.

        • We couldn't live in a universe with both matter and antimatte.

          Yes, we could: due to inflation, there could be pockets of matter/antimatter which won't ever causally interact again. I dont know enough about Lambda-CDM to know if this is consistent with the cosmological standard model, but it's at least theoretically possible...

  • Is this sigma terminology coming from some discipline? I've taken plenty of grad statistics and we've always called them alpha-significance levels.

    From wikipedia:

    The term Six Sigma originated from terminology associated with manufacturing, specifically terms associated with statistical modeling of manufacturing processes

    So...the MBAs went and redefined some terms? And we're using them to summarize an empirical physics paper's results...why?

    • by EvanED ( 569694 )

      s this sigma terminology coming from some discipline? I've taken plenty of grad statistics and we've always called them alpha-significance levels.

      Surely if you've taken plenty of grad statistics, you've seen sigma used for the standard deviation.

      They're saying something like the observed difference is 3.5 times sigma. That corresponds to an alpha=0.05% (or is it 99.95%?); they're not saying that sigma itself is 0.05%.

    • Re:sigma? (Score:5, Informative)

      by Anonymous Coward on Friday November 18, 2011 @07:52PM (#38104742)
      • They are averaging the results of many collisions, which are presumed to be independent and identically distributed of finite variance. Thus the central limit theorem dictates that the measured average is normally distributed about the mean of the true distribution of the statistics of a single collision. As they repeat the experiment n times the variance of the mean reduces at order n (hence std dev. the square root of the variance reduces at order sqrt(n)) Once they have repeated the experiment suffici

    • Funny that you mention alpha, since Wikipedia says: [] "In some fields, for example nuclear and particle physics, it is common to express statistical significance in units of the standard deviation Ïf of a normal distribution."
    • How in the world do you take even ONE grad class and never hear of sigma or standard deviation? This is like the intro to the intro to statistics class and everything builds on it. You would have seen sigma dozens of times in each class...

      • by Theovon ( 109752 )

        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 k

        • by ThorGod ( 456163 )

          Oh, I knew they were trying to refer to the second parameter of a normal distribution. But, whatever symbol we *use* for the variance (std dev) is just a symbol. We could call it: "a", "alpha", "sigma", "theta", all with various subscripts, and so on and so forth. Ever heard of six-theta_2 ? Six-theta_2 refers to 6 times the standard deviation of an estimated, normal curve. The term six-theta_2 only makes sense because we filled in the crucial parts (that shouldn't be left out).

          Saying "sigma" without any qu

    • by Rich0 ( 548339 )

      Well, the MBAs apply Six Sigma to all kinds of stuff that it really doesn't fit. However, the definition of six sigma is pretty straightforward:

      A six sigma process is one whose specification limits are at least six standard deviations away from the mean.

      So, if a space shuttle part needs to be 1 meter long, and if bad things happen if it is more than one cm off, then a six sigma process would need to produce parts that are 1 meter long with a standard deviation of 1/6th of a centimeter (and a normal distrib

  • Identifying an a real-world mismatch of our models' predictions does not "explain" anything but that our models are incomplete.

    When spheres, and spheres on spheres, don't explain planetary motion, let's try another model: the ellipse.

    When "classical" mechanics can't explain why "orbiting" electrons don't fall into the nucleus of an atom due to electrostatic attraction, let's come up with a new model (while confusingly calling them "orbitals"): shells and quantum exclusion effects.

    When whatever synthesis of

  • All these experiments occured on earth in the vicinity of a lot of matter. How do we know that if we performed the experiments on a anti-earth we would not get an opposite result?
    • Because we did the experiment here, and these are the results we got. Feel free to doubt, but unless you are willing to create an experiment to falsify their findings, your claim has as much validity as young earth creationist.

    • by osu-neko ( 2604 )

      All these experiments occured on earth in the vicinity of a lot of matter. How do we know that if we performed the experiments on a anti-earth we would not get an opposite result?

      All these experiments occurred within 5000 years of 1AD. How do we know that if we performed the experiments before 5000 BC or after 5000 AD we would not get an opposite result?

      The answer to both your question and mine is: we don't, but unless we have evidence that we would see an opposite result, it would be silly to believe we would in the absence of any good reason for it. Waving your hands and saying "maybe all the matter around influences things" is silly unless you have evidence to support that clai

  • The radiation of an antimatter star would be the exact same as a matter star. There is no way of knowing that our visible Universe is mainly matter. That the Universe is made mostly of matter is a myth not really backed up.

    • by Surt ( 22457 ) on Friday November 18, 2011 @09:48PM (#38105422) Homepage Journal

      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.

      • by Hentes ( 2461350 )

        We have good reason to believe that the Universe expanded from a much smaller initial state. Thus, the homogenous matter/antimatter regions that were created early could become very big, maybe bigger than our visible Universe. But even if not, galaxies very rarely collide, and even when they do, it's only a "collision" in a gravitational sense, it's very unlikely that two stars actually hit each other.

        • by Surt ( 22457 )

          Stars don't need to hit each other. The dust getting sucked into stars is plenty.

    • by Old Wolf ( 56093 )

      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 Interga

  • A bit off topic but this is very interesting find, just a few weeks after the 'Faster than light neutrinos'. Why can't we put money into projects like these instead of killing people in other countries. Err correction: Bringing democracy to other people.
    • by Anonymous Coward

      you need energy to run experiments

  • Significance (Score:5, Informative)

    by kievit ( 303920 ) on Saturday November 19, 2011 @07:12AM (#38107598) Journal

    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.

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