Yet another LHC Update

The Large Hadron Collider has now entered a Machine-Development/Technical-Stop phase that will last eleven day. That means they have collected all they can for the ICHEP conference in July. The amount delivered is 6.6/fb, just a shade short of the projected figure of 6.8/fb and well over the 5/fb target,  so they have done very well. As usual it was not easy with many problems holding down run efficiency but in the last week they amassed an impressive figure of 1.3/fb to make up for some time lost at the beginning of this run. They have two more runs of similar length to the last so they are well on the way to reaching the 13.3/fb figure that was given as the amount needed to ensure that both experiments can independently discover or rule out the Higgs Boson. They should also have time to complete other priority tasks before the long shutdown next year, such as testing runs with 25ns that will be needed when they restart at 13 TeV.

Now it is over to the experiments to see what they can achieve in time for ICHEP which starts in just 15 days time. ATLAS has recorded 6.23/fb and CMS has 6.15/fb and they have already been beavering away with the first chunk of this data. There is some chance that they can get to the critical 5-sigma level for independent Higgs discoveries (For the (well-meaning) nit-pickers I mean discovery of a neutral boson resonance (probably) consistent with the standard model Higgs, sigh)  Contrary to what some blogs are saying it is no more difficult to combine the 7 TeV and 8 TeV data than it is to combine all the different channels, and whether or not they do this could be largely a political choice depending on how and where they want the discovery announcement to be made. However, time constraints could also be critical. It will be tempting for them to try to use as much of the 6/fb of data as possible for the Higgs search but that will require maximum computing resources. They may have to face a difficult choice between getting discoveries in the Higgs search in time for ICHEP or looking for other searches for more exotic physics. If it comes to that face-off my bet would be on them prioritising the Higgs search, but whatever the outcome it will be an enthralling conference.

I should also mention that LHCb have 0.65/fb added at 8 TeV so good progress there as well.

By the way, viXra Log has made it into the final of this years science blog contests at 3 Quarks Daily. It is up to Sean Carroll to pick the three winners. Now I wish I hadn’t said all those bad things about him, perhaps he didn’t notice, LOL :) .

30 Responses to Yet another LHC Update

  1. dd says:

    It may be worth tempering your enthusiasm about the good results (ATLAS, CMS, and LHCb) being on schedule (or slightly ahead of schedule) with an update about ALICE from the last LHCC:

    http://indico.cern.ch/getFile.py/access?contribId=1&sessionId=0&resId=0&materialId=slides&confId=194183

    While they are nearly 1/3rd of the way toward their target for min-bias events, they are only about 1/20th of the way through their rare trigger goals. As they mention, this is because they can’t resolve the collisions over the beam-gas (vacuum) interaction in nearby LSSs. Thus, they are forced to wait several hours after declaration of STABLE BEAMS before they can take data.

    I have seem some preliminary slides on what they are doing during the MD and TS, and I haven’t seen any mention of mitigation factors for this (yet).

    Also, it may be worth detailing the story about the LBDS configuration flaw that was fixed last week in some detail. The ramifications of not being to (automatically or manually) dump the beams out of the LHC are frightening.

    Personally, I prefer to consider our friends at CERN as doing *exceptionally* well. But it is also true to remember that we’re working on the bleeding edge of what is possible here, and the LHC beams and vacuum people can’t please everyone all the time.

    • Philip Gibbs says:

      I do mention some of the problems e.g. I mentioned the dump problem in the previous update. I try to give the impression that it is not easy but most of the problems are technical details that not very many people are that interested in. I have not really been following the issues with ALICE. Hope the Heavy Ion runs don’t suffer.

  2. Lubos Motl says:

    Thanks for your precise enough calculations as well as common sense concerning the God particle, Phil.

    I won’t vote for you because I suspect my vote could harm you. ;-) It’s not paranoia if they’re really going after you!

  3. publicfundig says:

    How can they claim Higgs boson discovery if LHC cannot tell the spin (scalar or vector)?

    • Maybee says:

      Landau-Yang theorem, maybe?

      • publicfunding says:

        maybe yes, or maybe no. Say, 50% and 50%.

      • Marc says:

        Publicfundig–huh? The Landau-Yang theorem is true. A massive vector can’t decay into two photons. Not 50-50, but 100-0. The only possibilities are spin zero and two. Distinguishing the two possibilities would require angular distributions, which will take a bit longer.

      • Philip Gibbs says:

        I think it is also very unlikely that a spin 2 would decay to two spin half fermions without us seeing where the other spin one went, so decays to bb or tau-tau will strongly suggest that it is a scalar

      • Lubos Motl says:

        Dear Publicfundig, the probability that they have a scalar must be lower than 50% according to your method, mustn’t it?

        50% is the probability that the LHC eats the Earth. See the calculation using the same “say 50% and 50%” at 3:00-3:30 here:

        http://www.thedailyshow.com/watch/thu-april-30-2009/large-hadron-collider

        I recommend you the whole video. ;-)

  4. Tony Smith says:

    How would the LHC be able to tell whether a 125 GeV thing
    is not a pion-type pseudo-scalar thing
    such as exists in Matti Pitkanen’s model (and mine also) ?

    Tony

    • Leo Vuyk says:

      Hi Tony,
      I like your statement and I am interested in your ideas, please give me the url.
      Perhaps you are also interested in my microscopic 3D geometry alternative see:
      http://vixra.org/pdf/1112.0065v2.pdf
      LHC signals between 121-130 GeV interpreted with non Standard Model
      Quantum-FFF theory.

    • Philip Gibbs says:

      I think it is an interesting question Tony. Photons are CP-even so if the Higgs is CP-odd the decay would be CP violating. I’m not sure if that is consistent with other observations but in any case a defintive test is likely to require a lot of data and perhaps an ILC

    • D R Lunsford says:

      Hey Tony, good to see you,

      What implications for your model does this light Higgs have? Composite? tia

      -drl

  5. Ervin Goldfain says:

    Phil,

    Your point above about H decays to b-b or tau-tau is well taken. Could it be possible that these decays involve also emission of a single low-energy photon, as in gamma-b-b or gamma-tau-tau? These channels would be somewhat similar to gamma – (lepton +) – ( lepton – ) but with the photon being quickly absorbed in the detector. What would forbid these channels?

    • Philip Gibbs says:

      We know it is not charged so the decay involving a photon (if it is spin two) would have to involve loops and would therefore be much less than other decays. I am not sure what mechanism would make the photon always soft.

      It is always going to be possible to contrive processes that would make somehting else look like a Higgs, but if something is swimming on a pond and quacking like a duck then the chances are it is a duck, especially if you thought there was likely to be a duck there to start with.

      The question that is becoming interesting now is whether the Higgs production rates and decay rates match the SM predictions. If they dont it could mean the presence of other particles that enhance or suppress the rates. The Higgs is a good window onto such particles because it should couple to anything with mass.

      • Ervin Goldfain says:

        I think the really intriguing question is what if the Higgs production and decay rates deviate from SM predictions BUT no new particles are found. This can either indicate some sort of estimation artifact or systematic uncertainty or that the Higgs signal is someting else.
        Somehow these deviations (if they continue to persist) remind me of the magnetic moment anomaly of charged leptons and of the CDF and PAMELA excesses seen in the past.

    • Marc says:

      Phil—couldn’t the decay of a spin-2 particle into b-b or tau-tau be allowed if it is p-wave, i.e. the final fermions have one unit of angular momentum? Admittedly unlikely, though. I like your duck analogy.

  6. Guest says:

    Here are the slides presented at Kyoto neutrino conference, 8. june 2012, concerning all the neutrinos measurements done by Opera, Borexino, Icarus, LVD, CNGS etc:

    https://docs.google.com/file/d/0B9tJ2lLf2TgobUdpTk1qOHFWQ1E/edit

  7. Guest says:

    I meant “all the neutrino speed measurements”

  8. Neil Bates says:

    For a humorous interlude, here’s my offering of what Dirty Higgsy had to say about all this:

    I know what you’re thinking: “Did we find five sigma, or only four?” Well, to tell you the truth, in all this excitement, I’ve kinda lost track myself. But being this is the LHC, the most powerful collider in the world, and would blow your mind clean off, you’ve got to ask yourself one question: “Do I feel lucky?” Well do you, punk?

  9. Tony Smith says:

    As to Higgs being CP-even or CP-odd, there is an interesting paper at arxiv hep-ph/980930 by Gunion and Pliszaka that says:
    “… We demonstrate that the relative size of the CP-even and CP-odd couplings of a Higgs boson to t tbar can be determined at the LHC at a level that is very useful in discriminating between models, provided that a Higgs signal can be observed at a reasonable S/sqrt(B) level in the t tbar h (with h to gamma-gamma or b bbar) channels. In particular,
    the CP-even nature of a SM-like Higgs boson’s coupling to t tbar can be confirmed with very substantial statistical significance
    using the t tbar h (h to gamma-gamma) production/decay mode. …”.

    Do you think that the data so far will allow determination of whether or not the thing at 125 GeV is CP-even (as is the plain vanilla SM Higgs) ?

    Tony

    PS – to D R Lunsford – As to the thing around 125 GeV in my model, it is more like a K-meson or a B-meson (mixed generation meson) than a pion (first generation only) meson, so it is likely to be CP-violating and (as Phil indicated) maybe experimentally distinguishable from a purely CP-even SM Higgs.
    However, my Higgs is a TTbar condensate with 3 mass states (each with lower cross section than a single SM Higgs).

    • Philip Gibbs says:

      I think this means they need to look at the production of the Higgs in association with two top quarks. That requires much more data than they currently have.

  10. carla says:

    Do you know if there’s a link to the LMC meeting on Wednesday 27th June?

    The MD went very well and it’s mentioned in the news they can increase PPB from 1.5×10^11 further this year, where they discuss this and other stuff in the meeting in detail.

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