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. Physics performance of the detector are being constantly assessed and optimized as new data comes. Members of UCL are playing a major role in the understanding of the silicon strip tracker and in the maintenance and development of the local reconstruction code.
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 have provided so far useful information for this experimental technique are the silicon strip tracker and the pixel detectors. Identification of low momentum hadrons and detection of new exotic massive long-lived charged particles have all benefited from this experimental method. Members of UCL pioneered this technique in the early LHC times and have been developing the tools for its use and calibration. Since 2010 particle identification with ionization energy loss has been the basis of the CMS inclusive search for new massive long-lived charged particles, which has been providing the most stringent and model-independent limits existing to date on any model of new physics predicting such particles.
External collaborators: CMS collaboration.
FROG is a generic framework dedicated to visualize events produced in particle collisions and detected by particle detectors. It has been written in C++ and use OpenGL cross-platform libraries. It can be used to any particular physics experiment or detector design. The code is very light and very fast and can run on various Operating System. Moreover, FROG is self consistent and does not require installation of ROOT or Experiment software (e.g. CMSSW) libraries on user's computer. It includes a lot of features based on an unique and powerful principle. Some of the functionalities are listed below : 3D and 2D visualization, graphical user interface, mouse interface, configuration files, production of pictures in various format, integration of personal objects. One of the FROG application is to display events for one of the most complex physics experiment : the CMS experiment. But it works as well and even faster with smaller experiment like the Gastof detector. Frog WebSite CMS TWiki Page
The final state containing two Z bosons decaying into a pair of leptons and a pair of neutrinos has been exploited by the CMS experiment at the LHC to produce a number of results related to the Higgs boson, including measurements of related standard model cross sections. Constraints have been set on the total width of the 125 GeV Higgs boson, using its relative on-shell and off-shell production and decay rates to a pair of Z bosons, where one Z boson decays to an electron or muon pair, and the other to an electron, muon, or neutrino pair. The analysis is based on the data collected by the CMS experiment at the LHC in 2011 and 2012. A simultaneous maximum likelihood fit to the measured kinematic distributions near the resonance peak and above the Z-boson pair production threshold leads to an upper limit on the Higgs boson width of < 22 MeV at a 95% confidence level, which is 5.4 times the expected value in the standard model at the measured mass of 125.6 GeV. A search for heavy Higgs bosons in the H → ZZ → 2l2ν decay channel, where l = e or µ, has also been performed using data collected in 2015 and 2016 at the center of mass energy of 13 TeV. No significant excess is observed above the background expectation. The results are interpreted to set exclusion limits on a number of extensions of the standard model scalar sectors: models with an additional electroweak singlet, as well as Type-I and Type-II two-Higgs doublets models.
The Tracker Simulation group is responsible for the Geant-based simulation of the Pixel and Strip Tracker response, material budget and geometry description. Members from CP3 are concentrating on various aspects of the validation with data. We also share the convenership of the group.