Experimental Nuclear and Subnuclear Physics: CMS
CMS - Compact Muon Solenoid - is one of the five experiments installed at the Large Hadron Collider – LHC - at CERN (Geneva). LHC is the most powerful particle collider ever built for elementary particle physics researches, designed to accelerate proton beams up to 7 TeV. CMS is the outcome of a big collaboration involving more than four thousand people from Universities and Research Agencies all over the world. Collaboration goals are comprehensive of several items, such as the validation of the electroweak unification theory, the physics of the heavy quarks bottom and top and of the tau lepton, the search for dark matter and supersymmetric and exotic particles. The experiment has already given an important contribution to the recent achievements of the whole scientific community. Worth mentioning, the Higgs boson discovery, of which the existence had already been required by the theory in the sixties, was confirmed on the 14th of March 2017 during the Moriond conference.
The Pavia CMS group, with the support of the Sezione INFN, is currently working on several items :
Muon System:
- Resistive Plate Chambers: • CMS Pavia has been involved from the very beginning in the development and construction of the RPCs for the muon detection system of CMS. Currently the group participates in the system maintenance and in the detector irradiation tests, concerning the longevity in relation with the strong increase of the luminosity foreseen during the operation of the future High Luminosity LHC;
- Gas Electron Multiplier: • The CMS experiment, in the last three years, begun to study the detector modifications needed to insure the opportunities of research and discovery in the arising in difficulty operating conditions foreseen with the collider upgrade. We are planning intervention on the existing instrumentation as well as new detectors installation. The CMS Pavia group is involved in the upgrade of the muon detection system concerning the realization of new detectors based on GEM (Gas Electron Multipliers) technology to be installed in the region nearest the beam line. During January 2017 the group has worked on the installation and operation of a GEM demonstrator and is currently involved in the operating conditions check. Throughout the next few years, the activity of the group will be mainly on the production and characterization of the new detectors with the high particle fluxes foreseen in the region where these detectors will operate. Specifically the detectors response will be studied with high photons and neutrons fluxes in the devoted CERN facilities.
Simulation studies for the Upgrade: The group has strong competences in the diffused background simulation in the CMS cavern. The background is mainly composed of neutrons, photons, electrons and positrons and it gives spurious signals inside the detectors. Since long the group, using the GEANT4 simulation software, has been studying the signals in GEM chambers due to this kind of particles. In this field, the contribution has aimed as well to develop a background simulation strategy that has been adopted by all the muon detectors of CMS. The activity has also supported the R&D and the tests beam on the detector for the experiment upgrade with specific simulations. Recently some of us joined the CMS trigger group for the study of a trigger system dedicated to all new GEM stations proposed for the CMS upgrade in 2023.
Data analysis: Before the start of LHC operation, our group in CMS had already been involved in the search for the Higgs boson, analysing Monte Carlo samples in order to estimate the observation opportunities for several production and decay channels and to evaluate particle reconstruction algorithms performances. Some of the discussed topics were the Higgs production associated with a couple of top quarks, the production through vector boson fusion and the Higgs’ decay in a couple of tau leptons. The group is currently active both on physics behind the Standard Model, with an analysis aimed to localize the presence of charged Higgs boson, and on precision measurements of SM parameters, as the study of the electroweak boson W.
Staff: Alessandro Braghieri, Paolo Montagna, Cristina Riccardi, Paola Salvini, Paolo Vitulo