The Nagoya (Japan) conference in celebration of the Inauguration of the Kobayashi-Maskawa Institute has come to a close this morning. There was a pleasant little ceremony yesterday in which Kobayashi and Maskawa took up shovels to place dirt around a newly-planted tiny apple tree outside the institute — an apple tree descended directly from “Newton’s apple tree” at Trinity College, Cambridge (you know the one, the tree whose apple is said to have inspired Newton’s theory of gravity — as though he’d never seen a dropped fork before.)
Meanwhile, back indoors there were numerous talks on a wide variety of research topics. Several of these addressed Japan’s broad experimental particle physics program, which covers neutrinos, bottom quarks, dark matter, cosmic rays, and the development of new experimental devices. Here are a few tidbits I heard about yesterday.
First, the one you all want to know: there was some very good news from the OPERA experiment (the one with the speedy neutrinos,) in which Nagoya is a participant. A key problem with the experimental method used in that measurement (one that I and many others expressed concerns about immediately) is that the pulses of neutrinos that were sent from CERN to OPERA were 10,000 nanoseconds long, while the effect observed by OPERA involved a shift of only 60 nanoseconds; the measurement therefore required precise knowledge of the neutrino pulse shape, but this had to be inferred from the shape of the pulse of protons that leads to the pulse of neutrinos. (Recall how you make a neutrino beam.) There have been widespread concerns that a very small error in that inference could potentially cause a fake shift. So the obvious thing to do instead is to have CERN send a series of short pulses — a couple of nanoseconds long, with big gaps between them. It’s like sending a series of loud and isolated clicks instead of a long blast on a horn; in the latter case you have to figure out exactly when the horn starts and stops, but in the former you just hear each click and then it’s already over. In other words, with the short pulses you don’t need to know the pulse shape, just the pulse time. And you also don’t need to measure thousands of neutrinos in order to reproduce the pulse shape, getting the leading and trailing edges just right; you just need a small number — maybe even as few as 10 or so — to check the timing of just those few pulses for which a neutrino makes a splash in OPERA (recall how you detect neutrinos). OPERA didn’t want to do this because it comes at the cost of a large reduction in the sheer number of neutrinos, and this affects OPERA’s main research program (which involves neutrino oscillations). But apparently the concerns raised by the community have been strong enough to prompt OPERA to request that the CERN neutrino beam operators (remember OPERA is not part of CERN, despite press reports to the contrary) send them short pulses. This process has already begun, as of last week, and according to the speaker, Nagoya’s own Professor Mitsuhiro Nakamura, it will be a matter of only a few weeks before OPERA will have enough neutrinos to make this important cross check. So this is very good news.
Meanwhile, I personally am still quite confused about what the Minos experiment [which measures similar neutrinos, at only slightly lower energies, traveling from Fermilab (near Chicago) to a mine in Minnesota — just about the same distance as from CERN to OPERA] can and can’t do to check the OPERA measurement. I have not run into a Minos expert and have heard conflicting information. So please set me straight if what I now say is wrong. What I was told yesterday is that Minos does not need to take any new data in order to check the OPERA measurement; the data is fine. All that is needed is to calibrate the clocks, which can be done in relatively short time: months, not years. So that too would be good news… though I did not hear what the expected level of precision would be. [UPDATE — see a statement and a link from a more knowledgeable person in the comments below.]
There were many other talks, and here are just a few I enjoyed hearing about.
- There was a very nice talk that included a description of the Super-KEK B-factory (a machine for making bottom quark/antiquark pairs in a controlled environment, at a rate 100 times higher than its predecessor machines.). [Why make so many bottom quarks? The decays of hadrons that contain bottom quarks are a well-known opportunity for high-precision tests of the equations that describe the known particles and forces, tests that are often complementary to what can be done at a very high-energy machine such as the Large Hadron Collider.]
- Nagoya University, which has a long and distinguished history in experimental high-energy physics, is involved in the development of innovative very high-precision devices for detecting particle tracks. These have several potential important applications to particle experiments. A previous generation of these devices was used in the OPERA experiment.
- There was a presentation of this summer’s result from the T2K neutrino oscillation experiment (which sends neutrinos from one Japanese laboratory to another — Tokai to Kamiokande [hence “T2K”]). This very important result, which still has rather low statistical significance and therefore is potentially subject to considerable change, suggests that the oscillation of muon neutrinos into electron neutrinos might be just below what was excluded by previous experiments. If this is true, it will not only be important in and of itself, it will also mean that other interesting neutrino-oscillation measurements will be easier than feared. (By the way — because they use rather low-energy neutrinos and because of certain timing uncertainties at Kamiokande, it appears they are unlikely to be competitive in checking the OPERA result on neutrino speeds.)
- A very nice talk mainly focused on the Fermi/LAT satellite’s results covered many interesting topics. One that caught my eye included a very interesting limit (i.e. no signal was observed) on collisions of dark-matter particles (in which they are converted to known particles, which are then observable.) Specifically, none were seen occurring in dwarf galaxies near the Milky Way, a good place to look because backgrounds from astrophysical sources are small in dwarf galaxies. And another result that was quite striking put a very powerful limit on the possibility that high-energy photons travel at a different speed from lower-energy photons — confirming to a new level of precision that the speed of light does not vary with the energy of the photons that make up the light.
- There were interesting presentations on “lattice gauge theory” (computer simulations of the physical behavior of forces like the strong nuclear force, involving particles such as quarks, antiquarks and gluons) as applied to hypothetical worlds in which the number of types of lightweight quarks (lighter than the proton) is larger than we have in nature. Such studies might be relevant for understanding the Higgs field itself. (The buzzword here is a speculation for the origin of the Higgs field called “technicolor”. ) Personally I find this very interesting, as I’ve been part of a community of theorists who for well over a decade have been urging lattice gauge theory experts to do these studies. Computer power seems to be reaching the point where useful results on the tougher cases are possible.
- One of the world’s experts on technicolor (Professor Elizabeth Simmons) talked about a [relatively!] simple version of technicolor, called topcolor-assisted-technicolor, and presented evidence that current LHC data (from the search for the Higgs) already essentially excludes this possibility. This means a more complex version of this class of models (such as top-seesaw-assisted technicolor) is needed.