ATLAS reports an 8+ sigma excess in ttbar production near threshold, consistent with NRQCD quasi-bound states and measuring 9.3 pb.
Measurements of the production cross-section for a $Z$ boson in association with $b$- or $c$-jets in proton-proton collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector
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abstract
This paper presents a measurement of the production cross-section of a $Z$ boson in association with $b$- or $c$-jets, in proton-proton collisions at $\sqrt{s} = 13$ TeV with the ATLAS experiment at the Large Hadron Collider using data corresponding to an integrated luminosity of 140 fb$^{-1}$. Inclusive and differential cross-sections are measured for events containing a $Z$ boson decaying into electrons or muons and produced in association with at least one $b$-jet, at least one $c$-jet, or at least two $b$-jets with transverse momentum $p_\textrm{T} > 20$ GeV and rapidity $|y| < 2.5$. Predictions from several Monte Carlo generators based on next-to-leading-order matrix elements interfaced with a parton-shower simulation, with different choices of flavour schemes for initial-state partons, are compared with the measured cross-sections. The results are also compared with novel predictions, based on infrared and collinear safe jet flavour dressing algorithms. Selected $Z + \ge 1 c$-jet observables, optimized for sensitivity to intrinsic-charm, are compared with benchmark models with different intrinsic-charm fractions.
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The GN2 b-jet tagger is calibrated in 56 fb⁻¹ of 13.6 TeV pp data using dileptonic tt̄ events, yielding data-to-simulation scale factors of 0.9–1.3 with ~1% uncertainty in the best bins.
Fiducial cross-section for W+b-jets at 13 TeV measured as 16.6±1.9 pb, consistent with NLO QCD prediction of 16.8±2.3 pb with twice the previous precision.
No excess above Standard Model background is observed; 95% CL limits are set on couplings of the U1 vector leptoquark model for masses 1.5-3.0 TeV.
citing papers explorer
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Observation of a cross-section enhancement near the $t\bar{t}$ production threshold in $\sqrt{s}=13$ TeV $pp$ collisions with the ATLAS detector
ATLAS reports an 8+ sigma excess in ttbar production near threshold, consistent with NRQCD quasi-bound states and measuring 9.3 pb.
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Measurement of the $b$-jet identification efficiency in dileptonic $t\bar{t}$ events using proton-proton collision data at $\sqrt{s}=13.6$ TeV collected with the ATLAS detector
The GN2 b-jet tagger is calibrated in 56 fb⁻¹ of 13.6 TeV pp data using dileptonic tt̄ events, yielding data-to-simulation scale factors of 0.9–1.3 with ~1% uncertainty in the best bins.
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Measurement of the cross-section for the production of a $W$ boson in association with $b$-jets in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector
Fiducial cross-section for W+b-jets at 13 TeV measured as 16.6±1.9 pb, consistent with NLO QCD prediction of 16.8±2.3 pb with twice the previous precision.
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Search for a leptoquark in events with a hadronically decaying $\tau$-lepton and missing transverse momentum using $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector
No excess above Standard Model background is observed; 95% CL limits are set on couplings of the U1 vector leptoquark model for masses 1.5-3.0 TeV.