Conclusive evidence of neutrino oscillations (muon to electron neutrino)
That neutrinos change ‘flavor’ between the 3 known varieties as they travel I think was pretty well accepted anyway, but this nails it.
As they describe it in the Fermilab newsletter (link is for ‘today’ which is July 22nd if you read it tomorrow )
It’s as if each neutrino is a ball that has the innate ability to be a baseball, a basketball or a football. It chooses which one to be only when it’s caught. Scientists have made machines that pitch tons of these balls in the form of baseballs across long distances. They then catch the balls and study them.
What they had seen up until this point was that not all of the baseballs they were pitching made it to the catcher. This gave them some evidence that the balls were changing types. Now not only have T2K scientists seen baseballs disappearing but they also have caught a significant number of basketballs on the other side.
Decay rate of B-sub-s confirmed to agree with standard model
This is a little esoteric and I don’t think they really give you the full story since apparently this also relates somehow to radioactive decay. But I think the big news is that it shoots more holes in supersymmetry, although doesn’t kill it.
The Standard Model predicts that the particle, called B-sub-s, will decay into two muons very rarely, only three times in every billion decays. However, the Standard Model assumes that the only particles involved in the decay are the ones physicists already know. If other, unknown particles exist, they might interfere, either making the decay happen more frequently than predicted or effectively canceling the decay out.
“This is the place to look for new physics,” said LHCb physicist Sheldon Stone of Syracuse University. “Small deviations from the predicted rate would firmly establish the presence of new forces or particles.”
What scientists found was a decay that followed the Standard Model’s predictions almost to the letter. This spells trouble for several models, including a number of models within the theory of supersymmetry, which predicts that each known particle has an undiscovered partner particle.
Proton radius is definitely smaller than predicted by QED
I have a thread on this that I’ll try to update but I’m putting it here for now.
As if to rub salt into the wound, in January Pohl and colleagues published a new measurement that almost doubles the accuracy of their smaller value of the proton radius. Now, with all traditional avenues of explanation blocked, there seems to be only one route left: physics beyond the current standard model of particle physics.
Neutrinos probably are not their own anti-particle (Majorana fermions)
This another one of those ‘battle of the evidence’ stories. This experiment found no evidence for neutrinoless double beta decay - which would only occur if they were Majorana fermions.
Very cool - thanks for pointing these out. I don’t feel equipped to comment but enjoy reading this stuff.
two baseballs observed at Pt A, then one football observed at Pt B
Wouldn’t that suggest the two baseballs morphed into one football?
No disappearing act required
In the T2k experiment there wasn’t any recombining, just straight flavor changes: baseball -> basketball -> football.
Acoustic Time travel - a musician in residence at the LHC
When Bill Fontana visits a cafe, he’s one of many customers wearing headphones. To a casual observer, he looks like someone in his own private world, cut off from the life around him.
In fact, it’s the opposite: Tiny, sensitive microphones are amplifying the sounds of the cafe—the clatter of dishes in the kitchen, the laughter of the people at the table next to him, the espresso machine hissing and bubbling—and pumping them into his ears.
Fontana devotes his life to capturing and treasuring the music of the moment.
It was in this spirit that he applied for the Prix Ars Electronica Collide@CERN award, for which a digital artist receives a monetary prize and a three-month residency made possible through a collaboration between CERN and international cyberarts organization Ars Electronica with funding from external private donors.
Stony Brook researchers developing new detector at SLAC - ring-image Cherenkov detector.
The detector they brought for testing is known as a ring-imaging Cherenkov detector, or RICH. This type of detector is not new—an early version was used by the DELPHI experiment at CERN’s Large Electron Photon Collider beginning in 1989—but the prototype Dehmelt’s group tested had a few technical improvements that should make the detector more robust.
When a charged particle plows through the gas in a RICH detector—in this case, tetrafluoromethane gas—it disrupts the gas’ electromagnetic field, pulling electrons out of place. As the disturbed electrons relax back into their proper energy levels, they give off their excess energy in the form of Cherenkov radiation, photons that spray out behind the particle in the shape of a cone. The intersection of that cone with the plane of the detector is focused into rings, which is how the detector got its name.
LHCb experiment has discovered a deviation from the standard model with 4.5 sigma confidence . This has to do with the decay of B mesons and approaches the accepted 5 sigma standard. It may even point toward the existence of a new particle, the Z’-boson .
One of seven experiments at the Large Hadron Collider (LHC), the LHCb experiment focuses on the physics of B-mesons – those particles containing the bottom (or beauty) quark – produced during proton collisions. One process of great interest is the decay of a B-meson into a kaon (K*) and two muons: B → K*μ+μ–. This is a relatively rare decay and according to the Standard Model it occurs only because of the subtle effects of heavier particles – W and Z bosons – that mediate the weak force. As a result, particles that are not described by the Standard Model may be contributing to the decay and so their effects could be measured by LHCb. Evidence that this decay happens in a manner that the Standard Model cannot explain could point the way to “new physics”
Thanks deltasigma; that’s intriguing.
In the OP I mentioned one item relating to B-sub-s mesons. Today’s Fermlab newsletter gives a little more background on that.
Tommaso Dorigo gives his take on the 4 sigma discrepancy in his blog:
Evidence of New Physics
As usual, he throws some cold water on it. According to the talk he cites, the probability to observe that level of discrepancy with 24 independent measurements is .5% (2.8 sigma). It sounds like more data will be forthcoming at some point, so we can wait and see if it holds up.
The LHC will finally run at full power in 2015 so it is once again time for the proverbial micro-black hole debate . The good news is that you probably don’t need to worry.
Almost all physicists say this scenario is beyond unlikely. As far as we know, black holes form when a massive star collapses on itself in a huge implosion once it burns up all its fuel—not when subatomic particles are slammed together at high speed. But unlikely as it was, the prospect touched all of us—the whole planet. With such high stakes, the concept of risk takes on a whole new meaning. So, physicists studied the apocalyptic hypothesis through a series of three unlikely events: that tiny black holes could form in the first place; that they could last longer than a millisecond; and that they could stick around and swallow everything nearby.
It has just been shown that higher energy neutrinos travel farther between oscillations than lower energy neutrinos.
Neutrino oscillations depend on both energy and distance. Higher-energy neutrinos travel farther before changing flavors than lower-energy neutrinos. It’s as if a neutrino is a person who must change his shirt every time he takes a certain number of steps. The higher-energy neutrinos take longer strides, so they cover greater distances in between wardrobe changes than lower-energy ones.
Scientists on the Daya Bay experiment, which includes more than 200 members from six countries and regions, were able to confirm this by studying the antimatter partners of electron neutrinos. The experiment can detect these particles, but not the other two flavors of neutrinos. So, from the standpoint of a Daya Bay detector, when the electron-flavor neutrinos oscillate to different flavors, they seem to disappear.
More interesting info from Daya Bay at the link
deltasigma - just a note to say thank you for keeping this going; I appreciate seeing these updates.
Thanks Wordman . I wouldn’t normally post these two items. The first is pretty technical and I barely understand it but points to one of those niggling little issues with the standard model. The second doesn’t really reveal much about particle physics per se but a great deal about the art and science of how it’s done. Both happen to be from the past couple Fermilab newsletters.
The first is from yesterday and has to do with top-anti-top quark directional asymmetry.
For several years, CDF and DZero physicists have been studying a puzzle in the production of top quarks at the Tevatron: The outgoing top quarks prefer to travel in the same direction as the incoming protons (forward) and the top antiquarks prefer to go in the opposite direction (backward). The Standard Model predicts a small amount of such “forward-backward asymmetry,” but the observed asymmetry is much larger and raises the question of whether the Standard Model calculation is deficient or something else is going on.
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Using the full CDF run II data set, the first coefficient a1 is measured to be 0.40 ± 0.12, while the Standard Model prediction is 0.15 +0.07/-0.03. This sharpens the search for an explanation of the asymmetry. Some nonstandard theories involving a new heavy partner of the gluon (axigluon) would include such a linear term. Alternatively, any missing ingredient in the Standard Model calculations would need to have this form. There is unfortunately too much uncertainty in the Tevatron measurement to point one way or another, but when applied to the much larger top quark samples at the LHC, this powerful new technique can perhaps provide further clues to the mystery of the top quark asymmetry.
The second is from today and talks about the difficulty in distinguishing particles from collision debris.
Of the six known types of quarks, only two can be distinguished in a typical particle physics experiment. The top quark, once produced, has a dramatic signature involving cascades of decays from heavy particles into lighter ones. The bottom (b) quark also decays into lighter particles, but these are hidden in a spray of additional particles that form along with it, called a jet. A jet is essentially random: random particles moving in nearly random directions. The lighter quarks—charm, strange, up, and down—produce only jets when they decay.
In practice, this means that it’s almost impossible to distinguish an up-quark from a down-quark
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Jets from b-quarks are a little different in a lot of ways. Since b-quarks fly a small distance before they decay (about 5 millimeters), some particle trajectories trace back to this decay rather than the collision point. Jets with a b-quark are slightly narrower with slightly fewer charged particles and are more likely to include an electron or muon. No one characteristic is enough to tell us, “This is certainly a b-jet and that is not,” but the confidence adds up with each additional clue, and physicists are able to assign a probability that a given jet is a b-jet. In a recent paper , CMS scientists presented the state of their art: For an 80 percent probability of identifying a real b-jet, they have a 10 percent probability of misidentifying a non-b-jet. . .
From the OP:
Heh. I remember about 8 or 9 years ago, I was presenting some research involving neutrinos at a talk. Our results were different for Majorana or Dirac neutrinos, and we didn’t want to take sides on the issue, so we just presented both sets of results. One of the audience members was quite upset that we had done this, because the evidence was so overwhelmingly in favor of Majorana that it was absurd to even consider Dirac neutrinos.
Personally, my take has always been that it would be quite peculiar for lepton number to be conserved as well as it is, if it doesn’t even exist.
And on the last post, isn’t it quite easy to distinguish between an up and a down quark, just based on their charge? I assume that the tracks are in an external magnetic field that causes them to curve.
Pasta
August 24, 2013, 10:53pm
18
Chronos:
From the OP:
Heh. I remember about 8 or 9 years ago, I was presenting some research involving neutrinos at a talk. Our results were different for Majorana or Dirac neutrinos, and we didn’t want to take sides on the issue, so we just presented both sets of results. One of the audience members was quite upset that we had done this, because the evidence was so overwhelmingly in favor of Majorana that it was absurd to even consider Dirac neutrinos.
That audience member is kooky. The evidence is so overwhelmingly non-informative.
With the neutrinoless double beta decay technique in the OP, the ability to see the process given Majorana neutrinos depends on the mass of the lightest neutrino, the neutrino mass ordering (i.e. , which one is the lightest one), and on a particular algebraic combination of the masses that in turn depends on how the neutrino flavors are mixed. Based on what we know about all these things, it would have been unexpected to see this process with the current round of experiments. This new result is the first to have enough sensitivity to rule out an earlier positive result that nobody believed.
And on the last post, isn’t it quite easy to distinguish between an up and a down quark, just based on their charge? I assume that the tracks are in an external magnetic field that causes them to curve.
As you know, the outgoing quarks cannot be bare and instead will “hadronize” into various mesons. At the energies in the experiments referred to by that article, this hadronization process results in a large spew (termed a “jet”) of mesons, with the original quark lost among the flurry of newly born quarks and antiquarks. The jet, which can have anywhere from a few to scores of (mostly) pions and kaons in it, will have a fairly generic appearance in the detector. At much lower collision energies (on the order of a few times the pion mass), the outgoing up or down quark can sometimes be identified in a magnetized detector, but still not every time since both up and down quarks will hadronize into neutral pions about half the time.
It’s amazing to me that they are still milking data from the old Tevatron. In today’s Fermilab newsletter , another report of evidence for a real-life 4-quark hadron.
In recent years, there have been several observations and hints of this kind: a class of particle that appears to stretch our comprehension of the way that quarks interact. We currently know of only two ways that quarks combine into composite particles, either in quark-antiquark pairs (“mesons”) or in threesomes (“baryons”) like the proton. The “new” particles behave like mesons, but their properties show that there must be some other quarks inside as well: We could be seeing four-quark states for the first time! These unexpected particles are so mysterious that they are called simply X, Y or Z states in the official listings, and scientists are working hard to understand and identify them more fully.
Inspired by one of these hints from the CDF collaboration, a new search at the DZero experiment looks for the snappily named X(4140) state decaying into a charm-anticharm meson and a strange-antistrange meson. The analyzers indeed see an excess of possible signal events, sharply peaked in mass, consistent with this fledgling state, with less than a 0.3 percent chance that it is a natural fluctuation of background events.
Google street view takes you under the LHC and gives you a tour of its facilities and detectors.
Visitors all over the world can now explore CERN’s massive detectors and 1200 meters of the Large Hadron Collider tunnel with Google Street View—a Google product that links a series of panoramic photos into a virtual tour.
In 2011, members of Google’s Zurich team joined forces with CERN and spent two full weeks photographing the subterranean experiments and portions of the LHC, as well as the interiors of surface buildings at the laboratory. Compiling the imagery and coordinating the GPS locations took an additional two years, according to CERN photographer Max Brice.