A search for t¯t resonances in the lepton plus jets final state with ATLAS using 4.7 fb−1 of pp collisions at √s = 7 TeV

Aad, G. and Abajyan, T. and Abbott, B. and Abdallah, J. and Khalek, S. A. and Abdelalim, A. A. and Abdinov, O. and Aben, R. and Abi, B. and Abolins, M. and AbouZeid, O. S. and Abramowicz, H. and Abreu, H. and Abulaiti, Y. and Acharya, B. S. and Adamczyk, L. and Adams, D. L. and Addy, T. N. and Adelman, J. and Adomeit, S. and Adragna, P. and Adye, T. and Aefsky, S. and Aguilar-Saavedra, J. A. and Agustoni, M. and Ahlen, S. P. and Ahles, F. and Ahmad, A. and Ahsan, M. and Aielli, G. and Krasznahorkay, Attila and Nagai, Yoshikazu and Pásztor, Gabriella and Tóth, József (2013) A search for t¯t resonances in the lepton plus jets final state with ATLAS using 4.7 fb−1 of pp collisions at √s = 7 TeV. PHYSICAL REVIEW D, 88 (1). ISSN 2470-0010

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Abstract

A search for new particles that decay into top quark pairs (t¯t) is performed with the ATLAS ex- periment at the LHC using an integrated luminosity of 4.7 fb−1 of proton–proton (pp) collision data collected at a center-of-mass energy √s = 7 TeV. In the t¯t → W bW b decay, the lepton plus jets final state is used, where one W boson decays leptonically and the other hadronically. The t¯t system is reconstructed using both small-radius and large-radius jets, the latter being supplemented by a jet substructure analysis. A search for local excesses in the number of data events compared to the Standard Model expectation in the t¯t invariant mass spectrum is performed. No evidence for a t¯t resonance is found and 95% credibility-level limits on the production rate are determined for massive states predicted in two benchmark models. The upper limits on the cross section times branching ratio of a narrow Z′ resonance range from 5.1 pb for a boson mass of 0.5 TeV to 0.03 pb for a mass of 3 TeV. A narrow leptophobic topcolor Z′ resonance with a mass below 1.74 TeV is excluded. Limits are also derived for a broad color-octet resonance with Γ/m = 15.3%. A Kaluza–Klein excitation of the gluon in a Randall–Sundrum model is excluded for masses below 2.07 TeV.

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