EPS Early Posters showing up to 1.21/fb from ATLAS

The Europhysics HEP conference (EPS) starts in earnest tomorrow with a good chance that some very strong results on Higgs searches will be revealed. There is likely to be either a plausible signal or an extensive exclusion, and maybe both.

The conference will include hundreds of talks during parallel sessions followed by the plenary talks. In addition there will be some posters which traditionally display some less important results on one poster-size page so that anyone interested can go and talk to the authors about them.

The LHC collaborations are being careful not to reveal their best results in advance of the big show, but some posters have already been made available and some are not so unimportant. Already five of them are showing plots using up to 1.21/fb of recorded data from ATLAS. Here are some brief summaries.

ttbar resonance searches in ATLAS by Reina Camacho: reports a search for heavy particles decaying into t-tbar pairs with 200/pb worth of data. At least some of these results were shown at PLHC last month but nice colourful plots are always worth looking at again.

Measurement of the top quark pair production cross section in dilepton final states with ATLAS by Hovhannes Khandanyan: measures the top quark cross-section using 0.7/fb.

The answer is 176 ± 6 (stat) ± 10 (syst) ± 6 (lum) pb

This poster refers to an ATLAS conference note number 117 whereas the latest note available is number 94. This gives an indication of just how many new results are being held back to release in the next few days.

First measurements of jet substructure in ATLAS by David Miller: is a technical note about how to squeeze more information out of QCD jets. The poster includes this plot using 0.6/fb

Search for high mass dimuon resonances in ATLAS by Simon Viel: ATLAS must be congratulated for showing plots using almost all the data recorded before the conference, 1.21/fb no less.

Search for high mass dielectron resonances at ATLAS by Sarah Heim: is doing the same thing using electrons instead of muons. 1.08/fb is searched for dielectron resonances.

Both these last two posters report that no new resonances are found and new limits are set on Z’ and Randall-Sundrum gravitons

If any more posters with new LHC data turn up today I will update this post.

24 Responses to EPS Early Posters showing up to 1.21/fb from ATLAS

  1. Luboš Motl says:

    Refreshing graphs with big numbers – still in the “nothing to see here” category.

    For a moment, I was scared by the limited reach of the dimuon and dielectron. Then I realized that they have only reached 3 TeV with dijets which have much higher a cross section – because jets may come from gluons, quarks, and they have many flavors and colors and not just 1 like electrons and muons.

    The dijets are among the things I also eagerly expect near 1/fb. Among many other things, of course.

    • Philip Gibbs says:

      Ben watching a film, just catching up now.

      • Luboš Motl says:

        The most urgent thing to focus your attention to is the Mott’s slide:


        Looking in the right lower corner, “results and limits”, do you agree that in the MU box (muons), Mr Mott is reporting a 15-sigma excess? 😉 What should one think about this stuff?

      • Philip Gibbs says:

        Well it must be a typo mustn’t it?

        An expected number of events can’t be 0.51 +- 0.20 . That does not make sense.

        And he is only using 36/pb despite the abstract promising 2011 data. Very odd.

      • Philip Gibbs says:

        Anduaga is also using 36/pb despite 2011 data mentioned in the abstract. I hope there are not too many more similar disappointments.

      • Luboš Motl says:

        Right, just to be sure, for Poisson distibution, if the average number if N, the standard deviation is simply sqrt(N), exactly. For N=0.51, the standard deviation is 0.71, so he may have been surprised that it’s formally 0.51 +- 0.71, which goes to negative numbers, so he interpreted 0.71 as the upper limit, counting the difference as 0.20. However, this mis-counting doesn’t work for the other two boxes haha.

  2. Francis Bursa says:


    It’s a Poisson distribution – if the mean is indeed 0.51, the probability of getting 3 events, assuming there is only background, is 0.013, which is more like 2 sigma. If the mean is up by one sigma at 0.71 it is 0.03. Nothing to get excited about…

    • Luboš Motl says:

      Right, I had already calculated this Poisson numerics, too. Still, it’s bizarre why the error is written as 0.2 only. It should be higher, right?

    • Philip Gibbs says:

      That’s what I though. Saying that an integer is expected to be between 0.31 and 0.71 does not sound possible for any kind of distribution.

      • piscator says:

        If the 0.2 is a theory/systematics error then it makes perfect sense. There are in principle two sources of uncertainty, first how well is the cross-section for the relavent process known, the second what is the Poisson fluctuation for a given integrated luminosity. A value of 0.5 \pm 0.2 could perfectly well be assigned to the first type.

  3. Philip Gibbs says:

    A couple of good ATLAS slide presentations for tomorrow setting limits on exotics with 1/fb

    Gibson – http://indico.in2p3.fr/contributionDisplay.py?contribId=323&sessionId=6&confId=5116

    Mariotti – http://indico.in2p3.fr/contributionDisplay.py?contribId=846&sessionId=6&confId=5116

  4. ervin goldfain says:

    For those interested, look up the session entitled “Higgs and New Physics” and click on the pdf presentation by Margarete MUEHLLEITNER.



    • Philip Gibbs says:

      It’s a good background talk, but just theory with no new results I think.

      • ervin goldfain says:

        I agree. The reason I cited it is that it gives a comprehensive review on Higgs searches for future reference.

  5. Walter says:

    The Dzero Higgs mass limits for the EPS meeting are here:

    Note not all channels are updated using 8.1 fb^-1, which might be the reason the low mass Higgs limit is not as good as expected…

    • Philip Gibbs says:

      Thanks for that pointer. If it could be combined from a similar result from CDF it should make a good advance. We should see the CDF result first thing tomorrow but we are not expecting the combination.

  6. paolo says:

    Atlas conf notes is full of new papers with almost or over 1fmb-1 data analysed. what they have in common is this phrase “These measurements are in good
    agreement with Standard Model predictions”
    Shouldn’t Your new blog entry be titled ” is high energy physics dead or still dying?”.

    • Philip Gibbs says:

      There are only seven new notes so far today, but we expect at least three times that number and more from CMS.

    • Luboš Motl says:

      Paolo, this is a truly loaded statement. The Standard Model is a key part of particle physics, so its confirmation may also be interpreted by the sentence “particle physics is thriving and overtaking ever greater realms of phenomena”.

      • paolo says:

        Too much time with VKlaus or/ and other politicians ?

      • Luboš Motl says:

        Well, I spent some hours with them, and so should you.

        However, I have spent many more hours with David Gross, Frank Wilczek, Sheldon Glashow, Steven Weinberg, and a few others. You may be denying their existence but they do exist, believe me, I have touched all of them. 😉

  7. ervin goldfain says:

    Quite the contrary, particle physics is alive and well. These are truly exciting times for hep-th. Regardless of what we’ll learn from EPS and future symposia, there is now a large dataset available from both Tevatron and LHC. Nature is beginning to tell us where to go next.

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