The CMS silicon strip tracker is the largest device of its type ever built. There are 24244 single-sided micro-strip sensors covering an active area of 198m2. While first data from collisions are coming in, the physics performances of the detector are being assessed and optimized. Members of UCL are playing a major role in the understanding of the silicon strip tracker and in the finalization of all tools needed for its configuration, control, monitoring and calibration. We are sharing the convener-ship of the tracker detector performance group (DPG).
External collaborators: CMS tracker collaboration.
The CMS detector at the LHC can be used to identify particles via the measurement of their ionization energy loss. The sub-detectors that are expected to provide useful information for this experimental technique are the silicon strip tracker, the pixel detectors and the electromagnetic calorimeter. Identification of low momentum hadrons, improvement of electron identification and detection of new exotic heavy stable charged particles can all benefit from this experimental method. Members of UCL have explored for the first time this technique and have developed the tools for calibrating and measuring the ionization energy loss with the silicon strip tracker. Particle identification with ionization energy loss was commissioned on cosmic rays and on first LHC collisions: it has proved to perform extremely well allowing protons, kaons, as well as light resonances decaying into kaons and protons to be cleanly identified. This technique has also allowed the first search for new heavy stable charged particles. The pixel and electromagnetic calorimeter detectors are planned to be also used in order to further improve the current performance.
External collaborators: CMS collaboration.
The CMS detector at the LHC is used to search for yet unobserved heavy (mass >100 GeV/c$^2$), quasi-stable (lifetime > 1 ns), electrically charged particles, called generically HSCPs. HSCPs can be distinguished from Standard Model particles by exploiting their unique signature: very high momentum and low velocity, due to their mass and the available LHC collision energy. Two experimental techniques are used to measure the velocity of such particles. They make use of the Silicon Tracker and of the Barrel Muon Drift Tube detectors. UCL members lead the analysis since 2010, when the first HSCP paper was one of the first published LHC search papers. Updated results, using the 2011 dataset, were produced and submitted for publication. The analysis, which is extremely model-independent and inclusive, doesn't find evidence of HSCP. It currently excludes the existence of stable gluinos, predicted by split supersymmetry, with a mass lower than about 1.1 TeV. This limit is the most stringent to date.
