CMS has a new search for supersymmetry out today. This one looks for events with b jets and four W bosons in the final state. Jets made by b quarks can be identified because their decays will be displaced from the original vertex position. The lifetime of a b quark is actually long enough for it to often travel a measurable distance before decaying. Lifetimes of particles including b quarks are typically of order 1 ps, so a 100 GeV particle with a b quark (with a mass around 5-10 GeV) can travel up to a few millimeters from the vertex. The preprint uses 19.5 fb-1 of data at an 8 TeV center of mass energy.
Final states with b jets and W bosons are interesting because top quarks – the heaviest known elementary particles – decay almost exclusively to b quarks and W bosons. So, this paper is really focusing on new particles that decay into final states involving top quarks. It looks at two models in particular:
- gluino (supersymmetric gluon) pair production leading to two top-antitop pairs in the final state; and
- bottom squark (supersymmetric bottom quark) pair production leading to a top-antitop pair and two charginos (supersymmetric W or charged Higgs bosons) with the charginos decaying into W bosons and lightest supersymmetric particles (LSPs – typically neutralinos, which are supersymmetric equivalents of photons, Z bosons or neutral Higgs bosons).
In the first case, the measured energy depends on the decays of the W bosons. In some modes, the full energy is attainable, while in others large amounts are carried off by neutrinos leaving missing energy. In the second case, the LSPs carry off a significant fraction of the energy regardless of the W decay modes. The paper organizes the different modes by the number and types of leptons in the final state and combines the results from analyzing several different categories of final states.
As expected, no real evidence for SUSY is found. Instead, limits are recorded for various benchmark SUSY models. The shapes of the limit contours allow CMS to place limits on the masses of gluinos and bottom squarks.