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ATLAS and CMS Collaborations(Aaboud, M. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., et al. (2019). Combinations of single-top-quark production cross-section measurements and vertical bar f(LV)V(tb)vertical bar determinations at root s=7 and 8 TeV with the ATLAS and CMS experiments. J. High Energy Phys., 05(5), 088–81pp.
Abstract: This paper presents the combinations of single-top-quark production cross-section measurements by the ATLAS and CMS Collaborations, using data from LHC proton-proton collisions at = 7 and 8 TeV corresponding to integrated luminosities of 1.17 to 5.1 fb(-1) at = 7 TeV and 12.2 to 20.3 fb(-1) at = 8 TeV. These combinations are performed per centre-of-mass energy and for each production mode: t-channel, tW, and s-channel. The combined t-channel cross-sections are 67.5 +/- 5.7 pb and 87.7 +/- 5.8 pb at = 7 and 8 TeV respectively. The combined tW cross-sections are 16.3 +/- 4.1 pb and 23.1 +/- 3.6 pb at = 7 and 8 TeV respectively. For the s-channel cross-section, the combination yields 4.9 +/- 1.4 pb at = 8 TeV. The square of the magnitude of the CKM matrix element V-tb multiplied by a form factor f(LV) is determined for each production mode and centre-of-mass energy, using the ratio of the measured cross-section to its theoretical prediction. It is assumed that the top-quark-related CKM matrix elements obey the relation |V-td|, |V-ts| << |V-tb|. All the |f(LV)V(tb)|(2) determinations, extracted from individual ratios at = 7 and 8 TeV, are combined, resulting in |f(LV)V(tb)| = 1.02 +/- 0.04 (meas.) +/- 0.02 (theo.). All combined measurements are consistent with their corresponding Standard Model predictions.
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ATLAS and CMS Collaborations(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Castillo, F. L., Castillo Gimenez, V., et al. (2020). Combination of the W boson polarization measurements in top quark decays using ATLAS and CMS data at root s=8 TeV. J. High Energy Phys., 08(8), 051–67pp.
Abstract: The combination of measurements of the W boson polarization in top quark decays performed by the ATLAS and CMS collaborations is presented. The measurements are based on proton-proton collision data produced at the LHC at a centre-of-mass energy of 8 TeV, and corresponding to an integrated luminosity of about 20 fb(-1)for each experiment. The measurements used events containing one lepton and having different jet multiplicities in the final state. The results are quoted as fractions of W bosons with longitudinal (F-0), left-handed (F-L), or right-handed (F-R) polarizations. The resulting combined measurements of the polarization fractions are F-0= 0.693 +/- 0.014 and F-L= 0.315 +/- 0.011. The fractionF(R)is calculated from the unitarity constraint to be F-R=-0.008 +/- 0.007. These results are in agreement with the standard model predictions at next-to-next-to-leading order in perturbative quantum chromodynamics and represent an improvement in precision of 25 (29)% for F-0(F-L) with respect to the most precise single measurement. A limit on anomalous right-handed vector (V-R), and left- and right-handed tensor (g(L), g(R)) tWb couplings is set while fixing all others to their standard model values. The allowed regions are [-0.11,0.16] for V-R, [-0.08,0.05] for g(L), and [-0.04,0.02] for g(R), at 95% confidence level. Limits on the corresponding Wilson coefficients are also derived.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., et al. (2023). Measurement of the inclusive t(t)over-bar production cross section in the lepton plus jets channel in pp collisions at √s=7 TeV with the ATLAS detector using support vector machines. Phys. Rev. D, 108(3), 032014–34pp.
Abstract: A measurement of the top quark pair-production cross section in the lepton + jets decay channel is presented. It is based on 4.6 fb(-1) of root s = 7 TeV pp collision data collected during 2011 by the ATLAS experiment at the CERN Large Hadron Collider. A three-class, multidimensional event classifier based on support vector machines is used to differentiate t (T) over bar events from backgrounds. The tt production cross section is found to be sigma(t (t) over bar) = 168.5 +/- 0.7(stat)(-5.9)(+6.2) (syst)(-3.2)(+3.4) (lumi) pb. The result is consistent with the Standard Model prediction based on QCD calculations at next-to-next-to-leading order.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., et al. (2021). Measurement of the relative B-c(+/-)/B-+/- production cross section with the ATLAS detector at root s=8 TeV. Phys. Rev. D, 104(1), 012010–26pp.
Abstract: The total cross section and differential cross sections for the production of B-c(+/-) mesons, times their branching fraction to J/psi pi(+/-), are measured relative to those for the production of B-+/- mesons, times their branching fraction to J/psi K-+/-. The data used for this study correspond to an integrated luminosity of 20.3 fb(-1) of pp collisions recorded by the ATLAS detector at the Large Hadron Collider in 2012 at a center-of-mass energy of root s = 8 TeV. The measurement is performed differentially in bins of transverse momentum p(T) for 13 GeV < p(T)(B-c(+/-)) < 22 GeV and p(T)(B-c(+/-)) > 22 GeV and in bins of rapidity y for vertical bar y vertical bar < 0.75 and 0.75 < vertical bar y vertical bar < 2.3. The relative cross section times branching fraction for the full range p(T) > 13 GeV and vertical bar y vertical bar < 2.3 is (0.34 +/- 0.04(stat) (+0.06)(-0.02 sys) +/- 0.01(lifetime))%. The differential measurements suggest that the production cross section of the B-c(+/-) decreases faster with p(T) than the production cross section of the B-+/-, while no significant dependence on rapidity is observed.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., et al. (2021). Measurement of the associated production of a Higgs boson decaying into b-quarks with a vector boson at high transverse momentum in pp collisions at root s=13 TeV with the ATLAS detector. Phys. Lett. B, 816, 136204–28pp.
Abstract: The associated production of a Higgs boson with a W or Z boson decaying into leptons and where the Higgs boson decays to a b (b) over bar pair is measured in the high vector-boson transverse momentum regime, above 250 GeV, with the ATLAS detector. The analysed data, corresponding to an integrated luminosity of 139 fb(-1), were collected in proton-proton collisions at the Large Hadron Collider between 2015 and 2018 at a centre-of-mass energy of root s = 13 TeV. The measured signal strength, defined as the ratio of the measured signal yield to that predicted by the Standard Model, is 0.72(-0.36)(+0.39) corresponding to an observed (expected) significance of 2.1 (2.7) standard deviations. Cross-sections of associated production of a Higgs boson decaying into b quark pairs with a W or Z gauge boson, decaying into leptons, are measured in two exclusive vector boson transverse momentum regions, 250-400 GeV and above 400 GeV, and interpreted as constraints on anomalous couplings in the framework of a Standard Model effective field theory.
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