Distribution of the four-lepton reconstructed mass for the sum of the 4e, 4μ, and 2e2μ channels. Points represent the data, shaded histograms represent the background and un-shaded histogram the signal expectations. The distributions are presented as stacked histograms. The measurements are presented for the sum of the data collected at centre-of-mass energies of 7 TeV and 8 TeV.
This week the Complex Muon Solenoid ( CMS) collaboration is presenting a range of new results at the annual winter conference, Rencontres de Moriond. The results are based on the full dataset collected by the experiment during 2012, and include measurements of the Higgs candidate discovered last Summer. Perhaps the biggest question in particle physics at present is whether the new boson behaves as predicted by the Standard Model. Although more data will be required before we have a full answer to this question, the latest results represent important steps along this road.
By looking at its decays into pairs of Z bosons, the mass of the new particle has been measured to be 125.8 GeV (as shown below). Another important measurement, also using decays to Z pairs, is the spin-parity of the new particle. CMS finds this to be consistent with 0+, the value predicted by the Standard Model. Since the discovery, one eagerly awaited result has been the observation of decays to tau pairs. CMS reports a signal in this channel with a significance of 2.8 sigma, not quite enough to claim an "observation", but interesting since the rate of these events is another indicator that the new particle behaves like a Standard Model Higgs boson. University of Bristol researchers are searching for rare decays of the new boson, that would indicate physics beyond the Standard Model, and hope to present results later this year.
As well as performing measurements of the Higgs candidate, CMS has been busy searching for physics beyond the Standard Model. New results presented include searches for Supersymmetry and long-lived particles - two areas in which Bristol played a leading role. Unfortunately no sign of either has yet been observed, but these searches will be of great interest when the LHC starts up in 2015 with energy increased to 13 TeV. Lastly, the LHC provides an opportunity to study the top quark in large numbers. This, the heaviest known particle, is also the least well measured (or it was prior to the 2012 discovery!). CMS presents new precision measurements of it's mass and decays to other particles, this week.
More information on the new results from CMS can be found here: http://cms.web.cern.ch/news/new-cms-results-moriond-electroweak-2013