Physicists Measure Rare Top Quark Collisions with New Precision
Scientists at CERN have precisely measured how often top quarks pair with charm quarks in particle collisions, using a novel detection technique. The findings validate physics simulation models critical for understanding fundamental particle interactions and could refine calculations used in high-energy physics research and detector design.
Originaltitel: Measurement of top-quark pair production in association with charm quarks in proton-proton collisions at √s=13 TeV with the ATLAS detector
<p>Inclusive cross-sections for top-quark pair production in association with charm quarks are measured with proton-proton collision data at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 140 fb<sup>-1</sup>, collected with the ATLAS experiment at the LHC between 2015 and 2018. The measurements are performed by requiring one or two charged leptons (electrons and muons), two <em>b</em>-tagged jets, and at least one additional jet in the final state. A custom flavor-tagging algorithm is employed for the simultaneous identification of <em>b</em>-jets and <em>c</em>-jets. In a fiducial phase space that replicates the acceptance of the ATLAS detector, the cross-sections for tt<over bar> ≥ 2c and tt<over bar> + 1c production are measured to be 1.28<sub>-0.24</sub><sup>+0.27</sup> pb and 6.4<sub>-0.9</sub><sup>+1.0</sup> pb, respectively. The measurements are primarily limited by uncertainties in the modeling of inclusive tt<over bar> and tt<over bar> + bb<over bar> production, in the calibration of the flavor-tagging algorithm, and by data statistics. Cross-section predictions from various tt<over bar> simulations are largely consistent with the measured cross-section values, though all underpredict the observed values by 0.5 to 2.0 standard deviations. In a phase-space volume without requirements on the tt<over bar> decay products and the jet multiplicity, the cross-section ratios of tt<over bar> + ≥ 2c and tt<over bar> + 1c to total tt<over bar> + jets production are determined to be (1.23 ± 0.25)% and (8.8 ± 1.3)%.</p>