Of Particular Significance

At a CERN Workshop

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 07/13/2012

Today I’m attending the start of a several day workshop at the CERN laboratory (host of the Large Hadron Collider [LHC]).  This is bringing LHC experimentalists and theoretical particle physicists together to hear about and discuss not only results from the (successful) search for the Higgs particle but also from many other searches (so far unsuccessful, but still important and instructive for our understanding of nature) for other new particles and/or forces, as well as relatively high-precision tests of the Standard Model itself.  This should help those of us who were distracted for the past week by the discovery of the Higgs-like particle to catch up with everything else that the experiments reported at the ICHEP conference.  Will update today or over the next few days if anything striking is presented.

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5 Responses

  1. Prof. Strassler: Are here credible hints of a stop squark in this article?

    “Search for direct top squark pair production in final states with one isolated lepton, jets, and missing transverse momentum in √s = 7 TeV pp collisions using 4.7 fb−1of ATLAS data”

    Notorious is the result of “Search Region E” (ETmiss>275 Gev), where the expected number of events (with 95% confidence limits) was 1.8 ± 0.7. ATLAS got 5 events, not only well above the 95% confidence interval but is not too far from the simulation results of the benchmark point 1 (Mstop=400 GeV, 7.1 events) and even slishtly more than the simulation results of bechmark point 2 (Mstop=500 Gev, 4.5 events). In the exclusion zone graphs, figure 3, this is called an “excess”: “Note that in SR E there is no observed exclusion limit due to an excess in data.”

    What is more likely, that this is a hint of stops or that is just a statistical fluctuation?

    1. Your question isn’t well posed: “What is more likely, that this is a hint of stops or that is just a statistical fluctuation?” You can’t determine which is more likely unless ask about a very particular model.

      However, I would generally guess this is a fluke. Seeing 5 events where 1.8 +- 0.7 is expected is pretty unimpressive. Remember ATLAS is making dozens of measurements. If you make 20 measurements, the chance that one of them will come out above 95% confidence is very high. We have seen excesses this large several times at the LHC (in fact we have seen more impressive excesses in the multi-lepton search from last year, all of which went away.)

  2. Prof. Strassler: In a July 6th response to Thilo, you wrote that you would eventually discuss “rho mesons are to photons as massive spin-2 particles are to gravitons” and the differences between rho mesons and W particles. Have you done this already … I might have missed it.

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