Abstract
A search for the production of a heavy B quark, having electric charge -1/3 and vector couplings to W, Z, and H bosons, is carried out using proton-proton collision data recorded at the CERN LHC by the CMS experiment, corresponding to an integrated luminosity of 19.7 inverse femtobarns. The B quark is assumed to be pair produced and to decay in one of three ways: to tW, bZ, or bH. The search is carried out in final states with one, two, and more than two charged leptons, as well as in fully hadronic final states. Each of the channels in the exclusive final-state topologies is designed to be sensitive to specific combinations of the B quark-antiquark pair decays. The observed event yields are found to be consistent with the standard model expectations in all the final states studied. A statistical combination of these results is performed and upper limits are set on the cross section of the strongly produced B quark-antiquark pairs as a function of the B quark mass. Lower limits on the B quark mass between 740 and 900 GeV are set at a 95% confidence level, depending on the values of the branching fractions of the B quark to tW, bZ, and bH. Overall, these limits are the most stringent to date.
Highlights
The discovery of a Higgs boson [1,2,3] has intensified the search for physics beyond the standard model (SM)
This paper describes the search for a vectorlike B quark of electric charge −1=3, using data recorded by the CMS experiment from proton-proton collisions at a center-ofmass energy of 8 TeV at the CERN LHC in 2012
A search for pair production of the B quark with vectorlike couplings to W, Z, and Higgs bosons has been performed, using data recorded by the CMS experiment from proton-proton collisions at a center-of-mass energy of 8 TeV at the CERN LHC in 2012
Summary
The discovery of a Higgs boson [1,2,3] has intensified the search for physics beyond the standard model (SM). In several beyond the standard model scenarios, vectorlike quarks are considered partners of the top and bottom quarks [16] Both the charged-current [17] and the flavor changing neutral current (FCNC) [18,19] decay processes are allowed. We search for an excess of events over the backgrounds in mutually exclusive final states and set limits on the pair-production cross section for all values of the B quark branching fractions with the constraint BðB → tWÞ þ BðB → bZÞ þ BðB → bHÞ 1⁄4 1. The ATLAS Collaboration set lower limits on the B quark mass ranging from 575 to 813 GeV, for different combinations of the B quark branching fractions [22].
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