Abstract:
The formation of toponium, a colour-singlet bound state comprising a top and antitop quark was predicted approximately 40 years ago, a few years before the discovery of the top quark. However, the large value of the top mass implies that toponium systems decay instantly and sharp resonance peaks such as those relevant for other quarkonium resonances cannot be observed. In addition, for a top mass larger than 100 GeV, the impact of the toponium states on the total top-antitop production rate is smaller than 1%. These effects have therefore been considered to be experimentally insignificant, and no further detailed investigations were pursued. On the other hand, recent experimental analyses of top-quark pair production at the LHC have revealed significant excesses of events at a top-antitop invariant mass of approximately twice the top mass. Within the Standard Model, this enhancement could be attributed to the formation of toponium states.
In this cross talk, we discuss what toponium effects are and how to include them in conventional Monte Carlo approaches such as those employed in experimental analyses by means of the Green's function of non-relativistic QCD. Moreover, we review the phenomenological consequences of these effects, as well as the recent results announced by the CMS collaboration in the context of a search that could be interpreted as an observation of the formation of the pseudoscalar toponium state.
Bios:
Afiq Anuar (CMS) is an experimentalist. He obtained his PhD from the University of Hamburg, and went on to do two research fellowships at DESY and then CERN. He is presently based at DESY as a short-term postdoctoral researcher. His research interests are top quark and Higgs boson physics, as well as reconstruction algorithms. He is currently serving as the convener of the electron and photon (EGM) group.
Benjamin Fuks is Professor at Sorbonne Université (Paris, France) and member of the Laboratoire de Physique Théorique et Hautes Énergies (LPTHE). He is involved in teaching at the bachelor and master levels, exploring regularly the usage of novel active learning methods. His research activities address the phenomenology of theories beyond the Standard Model (prospective studies at present and future colliders, reinterpretation of existing experimental results), precision calculations for new physics processes (next-to-leading-order corrections in QCD, resummation of radiative corrections), and the development of simulation tools dedicated to collider physics (Monte-Carlo event generators and satellite programs).