Lighting up the top quark: New tt+photon measurements at CMS

by Dr Beatriz Lopes (CERN)

Thursday 10 Jul 2025, 15:00 → 16:30 Europe/Lisbon

LIP-Lisboa/3-311 - Sala de Seminários (LIP Lisboa)

Top quark physics is at the center of the CERN LHC program. Being the heaviest of the standard model (SM) particles and the only quark to decay before hadronization, the top quark is a unique test ground for the SM predictions.

At the LHC, top quark pairs are produced abundantly and measured with high precision, with more than a million top quark pairs ($t\bar{t}$) produced in the Run 2 alone. Top quark production in association with an energetic photon ($t\bar{t}\gamma$) is a much rarer process, with about 1% of the cross section of $t\bar{t}$, but it gives us direct access to the top-photon coupling, and allows to constrain various beyond the SM physics scenarios.

New results from the CMS Collaboration on $t\bar{t}\gamma$ production will be shown, including differential cross section measurements, and the first-ever measurement of the cross section ratio between the $t\bar{t}\gamma$ and $t\bar{t}$ processes at the LHC. The measurements are compared with predictions obtained with different simulation techniques, as well as with fixed-order calculations at NLO in QCD. A measurement of the top quark charge asymmetry in $t\bar{t}\gamma$ events is also presented.