Rencontres de Moriond QCD 2012: Uncertain signals from the Higgs boson

Some of the most recent analyses of the Higgs searches were presented on 11 March at the Moriond QCD conference, together with other Standard Model measurements relevant to the Higgs.


The new measurements of the W boson mass by Tevatron's experiments have improved the world average (the solid blue circle is the new average, the dotted blue circle is the previous average). Indirect measurements of the Higgs mass due to this new average is shown overlapping with the Higgs mass-range yet to be excluded by experimental results (light blue band).

The main results of the Higgs searches conducted by the LHC experiments are that they continue to narrow in on the Standard Model Higgs, if it exists, by excluding wider ranges of masses. This now leaves only a small window in the region between 115 and 130 GeV.

Tevatron’s experiments presented the refined measurement of the mass of the W boson announced 2 March. This allowed an improved prediction of the Higgs mass: mH = 94 +29-24 GeV. “The W mass plays an important role in determining the consistency of the Standard Model,” said Rafael Lopes de Sá, from Stony Brook University. In other words, even after the Higgs is measured, it will have to correlate with the mass of the W in order to fit with the Standard Model.

This talk was followed by reports on the most recent analyses of the Higgs searches by the CMS and ATLAS experiments that use the complete 2011 data sets. CMS is now analysing data across 11 channels and ATLAS across 12 channels; some were presented for the first time yesterday. Both experiments showed an excess of events compatible with a Standard Model Higgs. Also, the window still left by the direct Higgs searches is compatible with the prediction that comes from the new W mass measurement presented at moriond by the Tevatron's experiments.

However, as pointed out in Guido Altarelli’s presentation, some issues remain to be addressed. For example, three H→ ZZ→ 4l CMS events gave a mass measurement at 119.5 GeV (2.5σ)*. Also, ATLAS does not observe an excess of events in the WW channel while CMS data is compatible with such an excess.

Further studies are clearly needed, and the whole community is looking forward to the 2012 LHC run planned to begin this week.

(*) All the σ are calculated locally. They refer to analyses that do not include the “Look Elsewhere” effect.

You can access all the Moriond QCD presentations here.

by Katarina Anthony