Date: Friday, April 2nd, 2021, 15:00-19:00 (KST/JST)

TOPIC: Multi-lepton anomalies at the LHC

Venue: Offline (Room 1503, KIAS), Online (Zoom)

Programs:

1.

Time: 15:00 - 16:00 (KST/JST)

Speaker: Prof. Kaoru Hagiwara (KEK) and Prof. Benjamin Fuks (LPTHE and Inst. U. de France)

Title: Signatures of toponium formation in LHC run 2 data

Abstract: We study reported deviations between observations and theoretical predictions associated with the production of a pair of di-leptonically decaying top quarks at the LHC, and we examine the possibility that they reflect a signal of toponium formation. We investigate the production by gluon fusion of a color-singlet spin-0 toponium bound state of a top and anti-top quark, that then decays di-leptonically. We find strong correlations favoring the production of di-lepton systems featuring a small angular separation in azimuth and a small invariant mass. Although toponium production only contributes to 0.8% of the total top-quark pair-production cross section at the 13 TeV LHC, there is a possibility that it can account for observed excesses in the narrow edges of phase space. We propose a method to discover toponium formation by `reconstructing' both its top and anti-top quark constituents in the di-lepton channel.

2.

Time: 16:00 - 17:00 (KST/JST)

Speaker: Prof. Bruce Mellado (University of the Witwatersrand & iThemba LABS)

Title: The anatomy of the multi-lepton anomalies at the LHC

Abstract: In this presentation an account of the multi-lepton (electrons and muons) anomalies at the LHC will be given. These include the excess production of opposite sign leptons with and without b-quarks, including a corner of the phase-space with a full hadronic jet veto; same sign leptons with and without b-quarks; three leptons with and without b-quarks, including also the presence of a Z. Excesses emerge in corners of the phase space where a range of SM processes dominate, indicating that the potential mismodeling of a particular SM process is unlikely to explain them. A procedure is implemented that avoids parameter tuning or scanning the phase-space in order to nullify potential look-else-where effects or selection biases. The internal consistency of these anomalies and their interpretation in the framework of a simplified model will be presented. Implications on the SM Higgs boson measurements, the muon g-2 and astrophysics will also be briefly discussed.

3.

Time: 17:00 - 19:00 (KST/JST)

Discussions