Abstract
A search for baryon number violation (BNV) in top-quark decays is performed using pp collisions produced by the LHC at s=8 TeV. The top-quark decay considered in this search results in one light lepton (muon or electron), two jets, but no neutrino in the final state. Data used for the analysis were collected by the CMS detector and correspond to an integrated luminosity of 19.5 fb−1. The event selection is optimized for top quarks produced in pairs, with one undergoing the BNV decay and the other the standard model hadronic decay to three jets. No significant excess of events over the expected yield from standard model processes is observed. The upper limits at 95% confidence level on the branching fraction of the BNV top-quark decay are calculated to be 0.0016 and 0.0017 for the muon and the electron channels, respectively. Assuming lepton universality, an upper limit of 0.0015 results from the combination of the two channels. These limits are the first that have been obtained on a BNV process involving the top quark.
Highlights
In the standard model (SM) of particle physics [1,2,3], baryon number is a conserved quantity as a consequence of an accidental symmetry of the Lagrangian
The required ttcross section is the prediction at next-to-next-to-leading order (NNLO) that includes soft-gluon resummation at next-to-next-to-leading log (NNLL) [38]
Top: distributions for the basic selection; because of the normalization to data, the integrals of the two distributions are equal; overflowing entries are included in the last bins of the distributions
Summary
In the standard model (SM) of particle physics [1,2,3], baryon number is a conserved quantity as a consequence of an accidental symmetry of the Lagrangian. Search for 0.49 fb−1 evidence of such BNV to√p-quark deof pp collision data at s = 8 TeV, collected in 2012 with the Compact Muon Solenoid (CMS) detector [20] at the Large Hadron Collider (LHC) These decays are referred to as “BNV decays” in the following, as opposed to the SM decay of the top quark into a W boson and a down-type quark, the latter being a bottom quark in about 99.8% of the cases. One for the muon and one for the electron channel, are defined and optimized for such a process In both cases the final state consists of a lepton, five quarks, and no neutrino
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