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Scientific Objectives Of The U.S. CMS Operations Program

A fundamental mystery of elementary particle physics relates to the understanding of the mechanism that generates the masses of the W and Z gauge bosons and of quarks and leptons. Current experimental results and theoretical analysis points to the mass and energy range between 100 and 1000 GeV (1 TeV) for this mechanism. The Large Hadron Collider currently nearing completion at CERN, near Geneva, Switzerland, will collide protons against protons every 25 ns with a center-of-mass energy of 14 TeV and a design luminosity of 1034 cm-2 s-1. The LHC provides the collisions whose study will enable high energy physicists to confront this puzzle and to solve it.

The US CMS Collaboration participates in the operation of the Compact Muon Solenoid (CMS) experiment, one of two large experiments designed to study this problem at the LHC. To enable studies of rare phenomena at the TeV scale, CMS is designed to operate at the full luminosity of 1034 cm-2 s-1 provided by the LHC. The physics program includes the study of electroweak symmetry breaking, investigation of the properties of the top quark, searches for new heavy gauge bosons, probing quark and lepton substructure, looking for supersymmetry, and exploring for other new phenomena.

The detector was designed to fully utilize the high luminosity so that detailed studies of rare phenomena can be carried out. While the primary goal of the experiment is to determine the mechanism of electroweak symmetry breaking via the detection of Higgs bosons, the new energy regime will also offer new opportunities. The detector was designed to be sufficiently versatile to detect and identify the final state products from a great variety of processes. In particular, it is capable of reconstructing the momenta and directions of quarks and gluons (hadronic jets, tagged by their flavors where possible), taus, photons, electrons, and muons and is sensitive to energy carried off by weakly interacting particles such as neutrinos that cannot be directly detected.

Technical Requirements of CMS

The CMS detector is designed to perform a comprehensive study of the source of electroweak symmetry breaking. It is expected to operate for twenty or more years, with appropriate upgrades, at the CERN LHC, observing collisions of protons, and recording more than 109 events per year. The critical objectives to achieve these goals are:

  • Excellent muon identification capability and momentum resolution.
  • Efficient tagging of b-decays and t-jets.
  • Excellent photon and electron identification capability, as well as energy and directional resolution.
  • Hermetic calorimetry coverage to allow accurate measurement of direction and magnitude of energy flow, and excellent reconstruction of missing transverse momentum.
  • Efficient charged particle track reconstruction and good momentum resolution.
  • Well-understood trigger and data acquisition systems to go from 1 GHz raw interaction rate to ~100 Hz readout rate without significant loss of interesting signals.
  • Massive amounts of computing.
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