Rencontres de Moriond QCD 2012: Clearing up for the Higgs

Taking a hint from the name of the conference, Thursday’s sessions focused on QCD studies. Among the many analyses presented were new measurements that may improve background in Higgs events.


ATLAS and CMS data is compared with theoretical predictions for a variety of di-boson decays.

The LHC and Tevatron experiments began the morning with updates to their measurements of boson (W and Z) and di-boson (WW, WZ and ZZ) decays. These decays need to be understood with a high degree of precision, as they appear in typical searches for the Standard Model Higgs and new physics. Results presented by LHC experiments were all in agreement with the Standard Model (as shown for di-bosons decays in the image). Among the new results presented was the world’s first measurement by CMS of the branching ratio of the Z → 4l process, which is an important background process in the Higgs search.

ATLAS and CMS also presented a wide range of results that looked at the characteristics of particle jets, including new, detailed measurements of jet and di-jet cross-sections. A high precision understanding of these jets is essential, as they form the basis for most of the measurements made by the experiments.

The QCD sessions continued into the afternoon, with experiments presenting their measurements of various decays into photons. These are used to better understand the gluon distribution function in the proton, which can also help with searches for new physics. ATLAS presented a new measurement (published that same day, in fact) of the cross-section of an isolated photon in association with jets, which was in good agreement with theory.

One of the more niche talks of the day reviewed a new measurement of the strong coupling, αS, by the JADE experiment. If you haven’t heard of JADE, you certainly aren’t the only one! The experiment went offline back in 1986, but improvements to theory and data models encouraged a re-examination of its data. The result was consistent with measurements by other, newer experiments – evidence that analysing old data can still deliver new results.

by Katarina Anthony