Search for single production of a vector-like T quark decaying to a top quark and a neutral scalar boson in the lepton+jets final state in proton-proton collisions at $ \sqrt{s}=13 $ TeV

C Sturm for the KaoS Collaboration, A. Hayrapetyan, V Makarenko, A Tumasyan, W. Adam, J. W. Andrejkovic, L. Benato, T Bergauer, M G Dragicevic, C. Giordano, P. S. Hussain, M. Jeitler, N Krammer, An Li, D. Liko, M N Matthewman, I Mikulec, Schieck, R. Schöfbeck, D Schwarz, M. Shooshtari, M. Sonawane, W. Waltenberger, C.-E. Wulz, T. Janssen, H Kwon, D. Ocampo Henao, T. Van Laer, P Van Mechelen, J. Bierkens, N. Breugelmans, J D'hondt, S. Dansana, A F Moor, M Delcourt, F. Heyen, Y. Hong, P. Kashko, S R J Lowette, I V Makarenko, D. Müller, J. Song, S Tavernier, M G Tytgat, G P Van onsem, S Van putte, D. Vannerom, B. Bilin, B Clerbaux, A Das, I. De Bruyn, G W P De lentdecker, H. Evard, L Favart, P. Gianneios, A. Khalilzadeh, F. A. Khan, A. Malara, M. A. Shahzad, L Thomas, M. Vanden Bemden, C. Vander Velde, P Vanlaer, F Zhang, M. De Coen, D. Dobur, G. Gokbulut, J. Knolle, D. Marckx, K Skovpen, A. M. Tomaru, N. Van Den Bossche, J Van der linden, J. Vandenbroeck, L. Wezenbeek, S L Bein, A Benecke, A. Bethani, G. Bruno, A. Cappati, J. De Favereau De Jeneret, C Delaere, A Giammanco, A. O. Guzel, V Lemaître, J. Lidrych, P. Malek, P. Mastrapasqua, S. Turkcapar, Alves GA, M. Barroso Ferreira Filho, E. Coelho, C. Hensel, T. Menezes De Oliveira, C. Mora Herrera, P. Rebello Teles, M. Soeiro, E. J. Tonelli Manganote, A. Vilela Pereira, W. L. Aldá Júnior

A search for single production of a vector-like T quark with charge 2e/3, decaying to a top quark and a neutral scalar boson is presented. The boson can be a standard model Higgs boson (H) or a new scalar boson (ϕ). In the first case, a branching fraction of 25% is assumed for the decay T → tH, while in the second case the T quark is assumed to decay exclusively to tϕ. The top quark is identified via its lepton+jets decay, and the neutral boson via its decay into a bottom quark-antiquark pair. Final states with Lorentz-boosted topologies are considered and machine-learning techniques are exploited for optimal event classification. The analysis uses data collected by the CMS experiment in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb$^{−1}$ recorded at the CERN LHC in 2016–2018. Upper limits at 95% confidence level are set on the product of cross section and branching fraction for a T quark in a narrow-width approximation. They vary between 14.7 and 0.1 fb, for T quark masses in the range 1.3–3.0 TeV and ϕ boson masses in the range 25–250 GeV. These are the first exclusion limits set on the production of a single T quark decaying into a top quark and a new neutral scalar boson. For the decay channel into a top quark and a standard model Higgs boson, the results provide the best limits on production cross sections to date, for T quark masses above 2 TeV.