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LHC and experiments give round-up of first three years

Highlights included sensitive searches for new physics, the decay of a Bs meson, quark-gluon plasma and insights on the structure of the proton


Representatives of the Large Hadron Collider (LHC) and five of its experiments delivered a round-up report to the CERN Council this morning. The ATLAS and CMS experiments presented a wide range of results, including sensitive searches for new physics. The highlight from the LHCb experiment was a measurement of one of the rarest processes so far observed in particle physics, the decay of a Bs (pronounced B-sub-s) meson into two muons. Measurements of rare decays provide important tests of the Standard Model of particle physics, and are good places to look for new physics beyond the Standard Model. The highlights from the ALICE experiment’s first three years are detailed studies of the quark-gluon plasma, QGP, the matter of the primordial universe. Measurements from the TOTEM experiment give insights on the structure of the proton and provide input to the analyses of the other LHC experiments. All the experiments congratulated the LHC on its exemplary performance over its first full three years of running.

With the Milner Foundation’s Fundamental Physics Prize being awarded to seven scientists from ATLAS, CMS and the LHC earlier in the week for the discovery of a Higgs-like particle, all eyes were on CMS and ATLAS. Each experiment reported that the significance of its observation now stands close to the 7 sigma level, well beyond the 5 required for a discovery, and that the new particle’s properties appear to be consistent with those of a Standard Model Higgs boson. They are both careful to say, however, that further analysis of the data, and a probable combination of both experiments’ data next year, will be required before some key properties of the new particle, such as its spin, can be determined conclusively.  The focus of the analysis is now moved from discovery to measurement of the new particle in its individual decay channels.

The measurements reported by both experiments show that the new Higgs-like particle is in good health with a mass of around 125 GeV, but much further analysis is needed to reveal the full details of its identity. The next update is scheduled for the spring 2013 conferences, but for the final word before the LHC resumes running in 2015, we’ll probably have to wait some time longer.