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Update: Higgs search papers submitted for publication
7 February 2012

The results on Standard Model (SM) Higgs searches that ATLAS reported at a CERN seminar on December 13, 2011 have now been submitted for publication in three papers.

The Higgs boson is predicted to decay in several different ways, known as decay channels. Two of the papers report on searches, performed with the full data sample from 2011, in the Higgs decay channels that result in either two photons or four leptons in the final state. These are two of the channels that are presently most sensitive in the low mass range where a SM Higgs is generally expected to appear.

The third paper reports on the combination of the results from these two channels with those from other channels to provide a more sensitive search, extending over a larger mass range. This last paper was submitted simultaneously with a similar paper from the CMS experiment.

The results of the analyses documented in the papers are essentially unchanged from those presented at the seminar, and the overall conclusion also remains the same. If the SM Higgs exists, it is most likely to have a mass in the range 116-131 GeV; moreover, despite tantalizing hints in the region of 126 GeV, more data are needed to resolve whether or not the SM Higgs exists. The requisite data should be available by the end of the 2012 LHC proton-proton run.


More info:
The CMS Collaboration submitted the Higgs boson search results simultaneously.

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Experimental limits from ATLAS on Standard Model (SM) Higgs production in the mass range 110-600 GeV. The solid curve reflects the observed experimental limits, expressed in terms of the ratio (µ) of the observed cross-section to the cross-section predicted by the SM (vertical axis), for the production of Higgs for each possible mass value (horizontal axis). The region for which the solid curve dips below the horizontal line at the value of 1 is excluded with a 95% confidence level (CL). The dashed curve shows the expected limit in the absence of the Higgs boson, based on simulations. The green and yellow bands correspond (respectively) to 68%, and 95% confidence level regions from the expected limits.

For an explanation of this plot, please click here.



ATLAS event containing four muons. This event is consistent with coming from two Z particles decaying: both Z particles decay to two muons each. Such events are produced by Standard Model processes without Higgs particles. They are also a possible signature for Higgs particle production, but many events must be analysed together in order to tell if there is a Higgs signal. This view is a zoom into the central part of the detector. The four muons are picked out as red tracks. Other tracks and deposits of energy in the calorimeters are shown in yellow.
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