Abstract
A search is performed for the pair production of spin-3/2 excited top quarks, each decaying to a top quark and a gluon. The search uses the data collected with the CMS detector from proton–proton collisions at a center-of-mass energy of 13TeV, corresponding to an integrated luminosity of 35.9 fb−1. Events are selected by requiring an isolated muon or electron, an imbalance in the transverse momentum, and at least six jets of which exactly two must be compatible with originating from the fragmentation of a bottom quark. No significant excess over the standard model predictions is found. A lower limit of 1.2TeV is set at 95% confidence level on the mass of the spin-3/2 excited top quark in an extension of the Randall–Sundrum model, assuming a 100% branching fraction of its decay into a top quark and a gluon. These are the best limits to date in a search for excited top quarks and the first at 13TeV.
Highlights
The standard model (SM) of particle physics provides a successful description of the properties of the elementary particles and their interactions
Event reconstruction is based on the CMS particle-flow (PF) algorithm [30], which takes into account information from all subdetectors, including measurements from the tracking system, energy deposits in the electromagnetic calorimeter (ECAL) and hadron calorimeter (HCAL), and tracks reconstructed in the muon detectors
A search has been conducted for pair production of spin-3/2 excited top quarks t∗ in proton–proton interactions, with each t∗ decaying exclusively to a standard model top quark and a gluon
Summary
The standard model (SM) of particle physics provides a successful description of the properties of the elementary particles and their interactions. In string realizations of the Randall–Sundrum (RS) model [10,11], the right-handed t∗ quark is expected to be the lightest spin-3/2 excited state [12]. In the RS model, the spin-3/2 t∗ quark is expected to have a√pair production cross section of the order of a few picobarns at s = 13 TeV, for a t∗ of mass mt∗ = 1 TeV [1,14,15], which dominates over single t∗ production for most of the parameter space in the model [12]. A search for pair-produced √t∗ quarks was previously performed by CMS using pp collisions at s = 8 TeV [17]. This Letter presents a more sensitive search because of the higher collision energy and larger signal cross sections, and the larger data sample, which is nearly twice the size. The simulation has been improved by explicitly including the Rarita–Schwinger Lagrangian in the generator, resulting in the correct spin correlations for the signal
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