Observation of a pseudoscalar excess at the top quark pair production threshold

(CMS Collaboration) Hayrapetyan, Aram ; ... ; Godinović, Nikola ; Lelas, Damir ; Šćulac, Ana ; Kovač, Marko ; Petković, Andro ; Šćulac, Toni ; Bargassa, Pedrame ; Brigljević, Vuko ; Chitroda, Bhakti Kanulal ; Ferenček, Dinko ; Jakovčić, Krešimir ; Starodumov, Andrey ; Šuša, Tatjana ; ... ; Mishra, Saswat ; ... ; Roguljić, Matej ; ... ; Sosnov, Dmitry (2025) Observation of a pseudoscalar excess at the top quark pair production threshold. Reports on Progress in Physics, 88 (8). ISSN 1361-6633

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Abstract

A search for resonances in top quark pair ( tt & horbar;) production in final states with two charged leptons and multiple jets is presented, based on proton-proton collision data collected by the CMS experiment at the CERN LHC at s=13TeV, corresponding to 138 fb-1. The analysis explores the invariant mass of the tt & horbar; system and two angular observables that provide direct access to the correlation of top quark and antiquark spins. A significant excess of events is observed near the kinematic tt & horbar; threshold compared to the non-resonant production predicted by fixed-order perturbative quantum chromodynamics (pQCD). The observed enhancement is consistent with the production of a color-singlet pseudoscalar ( 1S0[1] ) quasi-bound toponium state, as predicted by non-relativistic quantum chromodynamics. Using a simplified model for 1S0[1] toponium, the cross section of the excess above the pQCD prediction is measured to be 8.8-1.4+1.2pb.

Item Type:	Article
Uncontrolled Keywords:	High energy physics ; Experimental particle physics ; LHC ; CMS ; top ; pseudoscalar ; scalar ; toponium
Subjects:	NATURAL SCIENCES > Physics > Physics of Elementary Particles and Fields
Divisions:	Centre for detectors, sensors and electronics Division of Experimental Physics
Depositing User:	Lorena Palameta
Date Deposited:	22 Jan 2026 11:36
URI:	http://fulir.irb.hr/id/eprint/11052
DOI:	10.1088/1361-6633/adf7d3

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