Physicists measure rare top quark-photon collisions with new precision
Researchers at CERN have completed the most detailed analysis yet of top quarks produced alongside photons in particle collisions. The findings validate theoretical predictions and refine our understanding of fundamental forces—knowledge essential for designing next-generation particle detectors and improving physics-based industrial applications.
Originaltitel: Inclusive and differential measurements of the $$ \textrm{t}\overline{\textrm{t}}\upgamma $$ cross section and the $$ \textrm{t}\overline{\textrm{t}}\upgamma /\textrm{t}\overline{\textrm{t}} $$ cross section ratio in proton-proton collisions at $$ \sqrt{s}=13 $$ TeV
A bstract Inclusive and differential cross section measurements of top quark pair ( $$ \textrm{t}\overline{\textrm{t}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>t</mml:mi> <mml:mover> <mml:mi>t</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> ) production in association with a photon (γ) are performed as a function of lepton, photon, top quark, and $$ \textrm{t}\overline{\textrm{t}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>t</mml:mi> <mml:mover> <mml:mi>t</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> kinematic observables, using data from proton-proton collisions at $$ \sqrt{s}=13 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> <mml:mo>=</mml:mo> <mml:mn>13</mml:mn> </mml:math> TeV, corresponding to an integrated luminosity of 138 fb − 1 , collected at the CERN LHC with the CMS detector. Events containing two leptons (electrons or muons) and a photon in the final state are considered. The fiducial cross section of $$ \textrm{t}\overline{\textrm{t}}\upgamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>t</mml:mi> <mml:mover> <mml:mi>t</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>γ</mml:mi> </mml:math> is measured to be 137 ± 8 fb, in a phase space including events with a high momentum, isolated photon. The fiducial cross section of $$ \textrm{t}\overline{\textrm{t}}\upgamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>t</mml:mi> <mml:mover> <mml:mi>t</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>γ</mml:mi> </mml:math> is also measured to be 56 ± 5 fb when considering only events where the photon is emitted in the production part of the process. Both measurements are in agreement with the theoretical predictions, of 126 ± 19 fb and 57 ± 5 fb, respectively. Differential measurements are performed at the particle and parton levels. Additionally, inclusive and differential ratios between the cross sections of $$ \textrm{t}\overline{\textrm{t}}\upgamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>t</mml:mi> <mml:mover> <mml:mi>t</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>γ</mml:mi> </mml:math> and $$ \textrm{t}\overline{\textrm{t}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>t</mml:mi> <mml:mover> <mml:mi>t</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> production are measured. The inclusive ratio is found to be 0.0133 ± 0.0005, in agreement with the standard model prediction of 0.0127 ± 0.0008. The top quark charge asymmetry in $$ \textrm{t}\overline{\textrm{t}}\upgamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>t</mml:mi> <mml:mover> <mml:mi>t</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>γ</mml:mi> </mml:math> production is also measured to be −0.012 ± 0.042, compatible with both the standard model prediction and with no asymmetry.