Other Collider News

End of the OPERA Story

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In case you haven’t yet heard (check my previous post from this morning), neutrinos traveling 730 kilometers from the CERN laboratory to the Gran Sasso laboratory do arrive at the time Einstein’s special relativity predicts they would. Of course (as the press mostly seems to forget) we knew that.  We knew it because ICARUS already made … Read more

Guess What?! Neutrinos Travel Just Below the Speed of Light

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Five out of five experiments agree: neutrinos do not travel faster than the speed limit. Or more precisely: to within the uncertainties of current measurements, neutrino speed, for neutrinos with energies far larger than their masses, is experimentally indistinguishable from the speed of light in vacuum.  This is just as expected in standard Einsteinian special … Read more

A Violation of Lepton Universality?

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A brief mention today of a new measurement from the BABAR experimental collaboration, which tests lepton universality (to be explained below) and finds it wanting.

The Basic Story (Slightly Oversimplified)

Within the Standard Model of particle physics (the equations that describe and predict the behavior of all of the known particles and forces), the effects of the weak nuclear force on the three leptons — the electron, the muon and the tau — are all expected to be identical. This called “lepton universality”.

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OPERA’s Timing Issue Confirmed? Yes!

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[QUICK UPDATE April 2: I’ve now finished an article giving more details of how OPERA, with LVD’s help, solved the mystery.]

[UPDATE March 31 2 a.m.: following study of the slides from a mini-workshop recording the results of investigations by OPERA and LVD, I now have the information to remove all the guesswork from my original post; you’ll see outdated information crossed out and newer and more precise information written in orange.  I’ve also added figures from the talks.]

March 30 5:30 p.m. Two main scientists at OPERA, one leading the OPERA team as a whole and the other leading the neutrino speed measurement, resigned their leadership positions today.  The suggestion from the press is that this is due to personal and scientific conflicts within the OPERA experiment, rather than due directly to the errors made in the neutrino speed experiment; but of course the way the measurement was publicized by OPERA caused serious internal conflicts at the time and are surely part of the issue.    [Oh, and meanwhile, back over at the CERN lab, some good news: collisions at the Large Hadron Collider with 8 TeV of energy per collision were achieved this afternoon.]

The mystery surrounding OPERA, the Gran Sasso experiment which (apparently through a technical problem) measured that neutrinos sent from the CERN lab to the Gran Sasso lab in Italy arrived earlier than expected by 60 nanoseconds, seems to be on the verge of being is resolved.  Statements made by an OPERA scientist in the Italian language press, pointed out to me by commenters (Titus and A.K.), seem to imply that OPERA has more or less confirmed that the problematic fiber optic cable (along with the clock problem, to a lesser extent) was responsible for a 60 nanosecond (billionth-of-a-second) shift in the timing, creating the false result.  We do not yet have official information from OPERA about this, but talks given at a mini-workshop a couple of days ago make clear that this is the case.

The way this was done if I/we understand the Italian correctly is something like is the following  with all details still very uncertain.

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Taking Stock: Where is the Higgs Search Now?

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Today, we got new information at the Moriond conference on the search for the Higgs particle (in particular, Phase 1 of the search, which involves the search for the simplest possible Higgs particle, called the “Standard Model Higgs”) from the Tevatron and the Large Hadron Collider [LHC], the Tevatron’s successor.  With those results in hand, and … Read more

Higgs Results from The First Week of the Moriond Conference

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[UPDATE: Tevatron results start a few paragraphs down; LHC results will appear soon] [2nd UPDATE: ATLAS  new results added: the big unexpected news.   As far as I can tell CMS, which got its results out much earlier in the year, didn’t add anything very new in its talk today.] [3rd UPDATE: some figures from … Read more

Awaiting Higgs News from the Tevatron Experiments

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The search for the Higgs particle has been dominated recently by the new kids on the block, the ATLAS and CMS experiments at the Large Hadron Collider [LHC], who benefit from the LHC’s record high energy per collision. But at its predecessor, the now-closed Tevatron, the CDF and DZero experiments still have a few tricks up their sleeves. Though the energy per collision in recent years at the Tevatron was 3.5 times smaller than was the LHC’s  in 2011,  CDF and DZero have twice as much data as do ATLAS and CMS right now. And there’s one more thing going for them. In contrast to the LHC, where protons collide with protons, at the Tevatron protons collided with antiprotons. That gives the Tevatron a little edge in one particular search mode for the Higgs. It won’t be enough to beat the LHC at the game for which it was designed, but it’s enough that the Tevatron experiments can at least play. And we’ll see results from the two experiments tomorrow (Wednesday) — with a preview already publicly available, as you’ll see below.

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Welcome 2012

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Well, 2011 was certainly an interesting and exciting year for particle physics. And 2012 promises to be even better.

LHC and the Higgs search

At the Large Hadron Collider [LHC], the accelerator physics team did a fantastic job of assuring the collider worked effectively, and provided significantly more proton-proton collisions than were originally expected. Meanwhile the experimental teams found clever ways to dig more information out of the collision data than was initially anticipated. And thanks to this, the search for the Higgs particle (or Higgs particles, or whatever replaces the Higgs particle) is  most of the way through Phase 1 — the search for the simplest possible form of Higgs particle, known as the “Standard Model Higgs”. We started 2011 knowing that the mass of the Standard Model Higgs particle might lie almost anywhere between 115 GeV/c2 and 800 GeV/c2 (where GeV, a measure of energy, is described here, and c is the speed of light, as in E = m c2.) The exception was a narrow gap around 160-170, excluded by the Tevatron experiments.  We ended the year, thanks to the great work at the ATLAS and CMS experiments, with the Standard Model Higgs excluded everywhere except above 600 GeV/c2 (where it is disfavored for other reasons) and in a window between 115 and about 128 GeV/c2. Even more exciting, there is a serious hint of a Higgs particle signal at around 124–126 GeV/c2.

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