Giacomo Bruno

The CMS experiment is used to study the di-muon invariant mass spectrum. These spectra allow searches for high-mass unstable particles (resonances) to be performed in a yet unexplored high mass range.

High-mass resonances decaying into muon pairs are predicted in a number of models beyond the Standard Model of the fundamental interactions. Notable examples are heavy neutral gauge bosons predicted by grand unification theories, as well as gravitons arising in the Randall-Sundrum model of extra dimensions.

The first search for high mass resonances was published in JHEP by CMS using the data acquired in 2010. Updated results were produced using part of the 2011 dataset in Summer 2011. By combining di-electron and di-muon data, CMS excluded the existence of resonances predicted by a number of theoretical models with masses below about 2 TeV. These limits are the most stringent to date.
The UCL CP3 group contributed to these two early CMS publications by being one of the three teams of the CMS Collaboration that regularly analyzed new data, optimising the muon isolation criteria and conducting a full study of a mild excess observed in the low-mass region (at ~120 GeV) in both the di-electron and the di-muon channels.

Since 2012 the activity of the UCL-CP3 group is limited to the exploration of a matrix-element approach to this search. Preliminary results show that the exploitation of the full kinematical information of the di-muon events can give some sizable improvements over the classical one that uses just the di-muon invariant mass. In addition, the group develops a new algorithm for measuring the energy of TeV-muons (for details, please read the dedicated project). This algorithm is expected to bring improvements in both the di-muon and single muon+missing energy searches starting from 2014.