New Higgs Results

ATLAS have released a conference note with new results for Higgs decays to ZZ and then two leptons and two neutrinos in the final states. The update uses 2.05/fb compared to 1.04/fb as first shown at the Europhysics conference in July. This is not the most exciting channel for discovery potential because it does not cover the light mass region, but it is good to see new data appearing now. No significant excesses are seen. Here is the main plot.

The note is aimed at the Hadron Collider Physics conference starting 16th November in Paris when we are already expecting to see a full LHC combination of Higgs searches in all channels based on data from the Lepton-Photon meeting.

As the 2011 proton physics run enters its last week, nearly 5/fb have been collected per experiment. That is enough data to give good observation potential at all possible Higgs masses except the crucial 115 GeV – 125 GeV light mass region. We may yet have to wait a few weeks before plots at that amount of data emerge.

Update 23-Oct-2011: Both ATLAS and CMS now have over 5/fb recorded.


48 Responses to New Higgs Results

  1. Claude says:

    Is it correct to conclude that this eliminates a SM Higgs between 305 and 475 GeV?

    • Philip Gibbs says:

      Yes that is correct, although most of this region has already been excluded on the earlier combination plot. It extends the ATLAS exclusion a little at the high mass end I think.

      The precise range the paper claims 95% confidence exclusion for is 310 GeV to 470 GeV

    • Mario E. de Souza says:

      Sorry, guys, but the Higgs is just a chimera because quarks are composite. You may say now ‘come on, we haven’t seen it’, and the truth is that we have seen several indications of it. The first one was found in 1956 by Hofstadter when he determined the charge distributions of both nucleons. (one can see them around p. 450 (depending on edition) of the Berkeley Physics Course, vol. 1 (Mechanics)). We clearly see that both nucleons have two layers of internal constituents. Unfortunately these results were put aside from 1964 on due to the success of the quark model and of QCD later on. From 1985 on we began to see more indications of compositeness, but we were so enthusiastic with the SM that we didn’t pay much attention to them. A partial list of them: 1) in 1983 the European Muon Collaboration (EMC) at CERN found that the quarks of nucleons are slower when the nucleons are inside nuclei; 2) in 1988 the SLAC E143 Collaboration and the Spin Muon Collaboration found that the three quarks of the proton account for only half of its total spin (other subsequent collaborations (EMC in 1989 and Hermes in 2007) have confirmed this result which is called the proton spin puzzle); 3) in 1995 CDF at Fermilab found hard collisions among quarks indicating that they have constituents (this was not published because CDF didn’t reach a final consensus); 4) Gerald Miller at Argonne (Phys. Rev. Lett. 99, 112001 (2007)) found that close to its center the neutron has a negative charge equal to -1/3e (inside the positive region with +1/2e); 5) new measurements of the EMC effect have been carried out by J. Arrington et al. at Jefferson Lab and they have shown that the effect is much stronger than was previously observed; etc. Both papers can be accessed from Google (are at the top on the subjects Weak decays of hadrons, Decays of hadrons and Weak decays) . We have to go back and probe further the nucleons in the low energy scale, and carry on Miller’s experiment with the proton.

  2. Anonymous says:

    Is there something lurking at 600 GeV (or above)? Although the possible signal is weak, it is consistent over broad range of values. Or is it just inaccuracies in the modelling of the background or a few random events causing the signal to appear consisten?

    • Philip Gibbs says:

      ATLAS has a small excess at 600 GeV in the ZZ channels, but the number of events at this energy are small. This new plot adds to the signal but it is still not very significant. CMS has not seen anything.

      If they increase the energy a bit next year we should get a better hold on this end of the range.

      • Mario E. de Souza says:

        Sorry, guys, but the Higgs is just a chimera because quarks are composite. You may say now ‘come on, we haven’t seen it’, and the truth is that we have seen several indications of it. The first one was found in 1956 by Hofstadter when he determined the charge distributions of both nucleons. (one can see them around p. 450 (depending on edition) of the Berkeley Physics Course, vol. 1 (Mechanics)). We clearly see that both nucleons have two layers of internal constituents. Unfortunately these results were put aside from 1964 on due to the success of the quark model and of QCD later on. From 1985 on we began to see more indications of compositeness, but we were so enthusiastic with the SM that we didn’t pay much attention to them. A partial list of them: 1) in 1983 the European Muon Collaboration (EMC) at CERN found that the quarks of nucleons are slower when the nucleons are inside nuclei; 2) in 1988 the SLAC E143 Collaboration and the Spin Muon Collaboration found that the three quarks of the proton account for only half of its total spin (other subsequent collaborations (EMC in 1989 and Hermes in 2007) have confirmed this result which is called the proton spin puzzle); 3) in 1995 CDF at Fermilab found hard collisions among quarks indicating that they have constituents (this was not published because CDF didn’t reach a final consensus); 4) Gerald Miller at Argonne (Phys. Rev. Lett. 99, 112001 (2007)) found that close to its center the neutron has a negative charge equal to -1/3e (inside the positive region with +1/2e); 5) new measurements of the EMC effect have been carried out by J. Arrington et al. at Jefferson Lab and they have shown that the effect is much stronger than was previously observed; etc. The relevant paper on this subject is Weak decays of hadrons reveal compositeness of quarks which can be accessed from Google (it is at the top on the subjects Weak decays of hadrons, Decays of Hadrons and Weak decays)

  3. Breit Width says:

    The potential signal is not modeled reliably at heavy Higgs masses. Before this is understood one cannot read too much from these plots at heavy masses.

  4. anonymous says:

    Private rumor that the 5 fb^-1 analysis of the Higgs signal will be released in early December (in spite of public statements about next spring). I don’t see why they would need to wait several months, so this might be plausible.

    • carla says:

      That quick?

      It took a month working their butts off to analyze 1/fb, so I was expecting summer next year for 5/fb.

      • Philip Gibbs says:

        It should not take much longer to analyse 5/fb than 1/fb. The only question is whether the conclusion is unclear and therefore needs more time to pass review and approval.

  5. Claude says:

    Phil,

    Clara at physicswithoutideology.blogspot.com predicts that, because of the lack of discoveries at the LHC,

    “CERN will not publish the Higgs results for the first 5 inverse femtobarns this year.”

    And that

    “CERN will spread the results (say for 3 fb^-1, then for 4, then for 5) over various months in 2012, to stay in the press, even though the results will be available long before those dates.”

    What is your opinion on this? Do you share her pessimism?

    • Philip Gibbs says:

      I have been quite unsuccessful in attempts to predict when results will be shown, but I can’t believe they would drip feed the results out in that way.

      I think they only thing they may want to avoid is inconclusive results. Ideally they would want to come straight out with a clear 5 sigma signal and claim discovery. I hope that will not mean waiting for the Higgs Combination Group because they are terribly slow LOL.

      in practice I think the anonymous message above that 5/fb results can be expected in December sounds more likely.

    • carla says:

      Nice strategy for publicity – feed the public tit-bits to keep them interested

  6. wl59 says:

    And nobody know what who really do and search, at CERN …

  7. Philip Gibbs says:

    A lot of blog comments are now indicating a Higgs mass of around 120 GeV but the number of rumors heard does not constitute a significant signal over background yet. More data expected soon.

  8. carla says:

    Now that they’ve recorded the incredible mile-stone of 5/fb making this year a resounding success, I hope they use the remaining week purely for 25ns machine development rather than more data collecting which will achieve little.

    • Philip Gibbs says:

      It depends whether they really want to use 25 ns next year. It reduces pile-up but it also reduces luminosity. If ATLAS and CMS can take the pile-up they are better to stick with 50 ns. I am not sure the 25ns tests so far have gone well enough to justify the option.

      We may see them try to push up the bunch intensity instead for the last few days.

      • Bernd says:

        Can you write a bit about the 25ns and other non-standard runs they’ve done in the past week or so?

    • Philip Gibbs says:

      Looks like more 25ns MD today. We will see what the MD reports say about it at the end of the run.

  9. wl59 says:

    No, I think that before the rest time, they should run the LHC with full power to get still the biggest amount of data possible. In order to finish that discusion so concludent as possible. Even if at 119 the significance will not be excellent, it’s to improve it so good as possible. So that now Higgs can be ruled out already with 95%, and the next year is only for affirm that with better weight, and beside of this, to do other things.

  10. wl59 says:

    The integrated luminousity increased during the last run by 0.2 . If they continue like this, they will pass 7 before the rest time …

  11. ondra says:

    25ns MD today and there is further high pile-up MD scheduled before end of 2011 proton run this Saturday. So i would say 5 fb-1 are considered enough, next is MD period with TS and ion setup and run before Xmas stop.
    Last time 25 ns MD also acted as “scrubbing” and they could go to 1.45e11 buch intensity after that, although there seem to be some instability issue with such a high intensity.

  12. ohwilleke says:

    This data isn’t too relevant to a single light Higgs scenario, because, as you note, it doesn’t address the critical 115-125 GeV range or even really the somewhat less likely 140-145 GeV range. But, I would think that it could be quite a bit more relevant in excluding theories with multiple Higgs doublets, such as SUSY models, where there is one light Higgs, and then a couple of heavier ones (or more).

    Also, shouldn’t the searches for H–>ZZ–>llvv also add significance to exclusions of all electrically neutral unstable particles in that mass range (e.g. Z’, neutralinos, etc.)?

    • Philip Gibbs says:

      Good, point, I agree that there is plenty of interest in doublets and they could show up at these masses.

      The decay of Higgs, Z’ and neutralinos will be different because they have different spin (0, 1, half respectively). Of course the neutrinos are not seen so there could be more of them and a candidate event for one decay can also be a candidate event for something very different. They will run a different analysis with different cuts etc to produce a different plot.

      This plot could show signs of any other weakly interacting neutral scalar or pseudoscalar boson

    • carla says:

      “The LHC performed over 5x what was expected at the start of the year” – has a nice ring to it, don’t you think?

      I hope they now trash the machine a bit more to see what unexpected wonders it’s capable of for next year

  13. Philip Gibbs says:

    They are still planning 2 or 3 more days of physics runs so they may get near 6/fb delivered. Intensity has been pushed up but has not yet had much impact on peak luminosity. If they get some clean runs we could see some good luminosity records before the end.

    • They are doing high pile up tests now. Maybe they are aiming for both 25ns and high intensity?

    • Philip Gibbs says:

      It’s really a case of one or the other. With 25ns spacing the present injection setup cannot deliver such high intensity bunches. This is because the bunches need to be split one more time in the PS to get 25ns trains. The cryogenics in the LHC may not be able to cope with it either.

      If the experiments find that they can deal with the high pile-up they may stick with 50ns and go for higher luminosity with higher intensity bunches.

  14. ondra says:

    Does the separation test in high pile-up MD suggest possible lumi leveling in Atlas and CMS?

    • Philip Gibbs says:

      I dont think that is something they need to test. They all ready do leveling regularly for LHCb so it is already established. In any case they should not have to use leveling yet.

      I am not sure why they were doing that for CMS, possibly they just wanted to compare different levels of pile-up.

  15. Tony Smith says:

    http://physics.lbl.gov/AnalysisJamboree-2011/htdocs/index.html

    says
    “… The Lawrence Berkeley National Laboratory will host an Analysis Jamboree on October 24-26, 2011 … to … discuss plans for the full 2011 dataset and brainstorm analysis issues.
    For the first two days of the jamboree, we will have ATLAS-only sessions …
    An open session with theorists and experimentalists is scheduled during the last day of the jamboree …”.

    Does that mean that the 2011 data collection is substantially over (with Machine Development etc only for the last few days)
    and that analysis has already begun ?

    Will the open session presentations (tomorrow Thursday 26 October 2011) be downloadable or even watchable on the web ?

    Tony

    • Philip Gibbs says:

      It will soon be over but they still have a few days of physics scheduled. They are setting up for more now.

      Hopefully they will determine a schedule for the analysis at that meeting. Last data taking will be on the 30th, then the analysis can begin.

    • Philip Gibbs says:

      I am hearing that Higgs results from the full dataset will be submitted for approval in December. There are not many conferences at that time and people will be taking end of year breaks so it is not sure that they will be public before January.

      However we can expect some further minor updates at 2/fb within days

  16. Tony Smith says:

    As to “… results from the full will be submitted for approval in December … there are not many conferences at that time …”:

    If the results show clear evidence (3 sigma) or discovery (5 sigma) then maybe CERN will organize a special event announcement as a Christmas Present.

    If the results are not so clear then maybe CERN will wait for the Winter Conferences 2012 and release the ambiguous stuff
    in which case the Winter Conferences will be as inconclusive as were EPSHEP 2011 and Lepton-Photon 2011.

    Therefore, if we do not hear anything by mid-December,
    my guess is that Winter Conference results will be inconclusive and that nothing conclusive will come out until the end of the 2012 run which might give 5 + 10 = 15/fb total.

    Then, if things are still inconclusive,
    you have 2013 for work on the machine
    so maybe the end of 2014 for enough data that might get something conclusive.

    Tony

    • Anonymous says:

      They have previously stated that by summer 2012 they have enough data to either discover Higgs or prove that it does not exist.

      Even with 5/fb of data they should be able to exclude very large range of possible Higgs masses, if nothing else.

  17. Tony Smith says:

    As to “… with 5/fb of data they should be able to exclude very large range of possible Higgs masses …”
    are you sure ???

    See for example slide 14 of the EPS 2011 Grenoble presentation by Andrey Korytov about CMS combined search based on 1.1/fb of data that shows
    “… Excluded at 95 percent CL (GeV)
    [149-206] … [300-440
    and 3 short segments in between …”

    but

    shows much less exclusion at 99 percent CL.

    Since even 99 per cent CL has 1 out of 100 chance of error
    which
    is much too large an error for a serious claim of real exclusion

    I have doubts about the LHC being able to seriously exclude anything outside around 150-180 GeV with 5/fb of data.

    Tony

    • Philip Gibbs says:

      This was referring to the usual 2-sigma confidence level standard for exclusions. Some people are now asking for 5 sigma for exclusion. In practice it will be more of case of looking at different channels for a consistent picture of where the Higgs is and is not. I am sure we will know it when we see it.

  18. Clara says:

    Phil,

    did the conference this week (14 to 16 november 2011) publish any new results on the Higgs search?

    • Tony Smith says:

      There is a talk for Friday 18 November
      Higgs Status (Tevatron+LHC) and combination
      Speaker: G. Rolandi (CERN/CMS)
      that might announce some new combinations.

      Tony

    • ondra says:

      Clara, there were only 2or 3 channels, nothing saying channels, updated with 2 fb-1 and they were not even included in shown Atlas only combination! So there is basically nothing new.

    • Philip Gibbs says:

      It is disappointing that they have not released more, but not unexpected. As I have been saying, they appear to be holding stuff back for now. I can only assume that this is because someone high up has told them to be more cautious until a clear signal appears, or perhaps they don’t want to release anything significant until a full combination is ready for the same data.

      • kevin says:

        In one of the atlas talks, they confirm the disclosure of a preliminary analysis of the full data set in december. A refined analysis and combination will then be released in march.

      • Philip Gibbs says:

        I know they have said that they will have plots ready in December but will they disclose internally only or will they make them public?

      • Did some talk addressed the topic of the top-antitop asymmetry. I am inrigued about setting these q=4/3 scalars inside the SSM, that should mean whole new symmetries in the scalar sector. Which should be good, even if, as Mitchell hinted, it runs the philosophy of my own model.

  19. I forgot the question mark :-) So, Did some talk addressed the topic of the top-antitop asymmetry?

  20. Tony Smith says:

    There are two listings for Thursday (17 November 2011)

    ———————————-

    Measurement of the Charge Asymmetry in Top Quark Pair Production with the CMS Experiment
    Speaker: Christian Boser (Karlsruhe)

    The Boser poster says
    “… Results …
    Ac(eta) = -0.016 +/- 0.030(stat.) +0.010 -0.019(syst.)
    Ac(y) = -0.013 +/- 0.026(stat.) +0.026 -0.021(syst.)

    are in good agreement with the Standard Model predictions …
    Ac(eta) = 0.013 +/- 0.001
    Ac(y) = 0.011 +/- 0.001
    … arXiv: hep-ph/1109.6830 …

    Used data: 1.09/fb …
    Published in Physics Analysis Summary CMS-PAS-11-014 …”.

    ———————–

    The measurement of the charge asymmetry in top-antitop production using data at sqrt (s) = 7 TeV collected by the ATLAS detector
    Speaker: Rachik Soualah (Udine)

    The Soualah poster says
    “… Asymmetry … Ac = -0.024 +/- 0.016(stat)+/-0.023(syst)
    … using … 0.70/fb …
    Both results in the electron and muon channels are compatible
    with the SM predictions (from MC@NLO) of Ac = 0.006 …”.

    ————————–

    Tony

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