ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., Castillo, F. L., et al. (2022). Constraints on Higgs boson properties using WW*(-> e nu μnu)jj production in 36.1 fb(-1) of root s=13 TeV pp collisions with the ATLAS detector. Eur. Phys. J. C, 82(7), 622–33pp.
Abstract: This article presents the results of two studies of Higgs boson properties using the WW*(-> e nu μnu)jj final state, based on a dataset corresponding to 36.1fb(-1) of root s = 13 TeV proton-proton collisions recorded by the ATLAS experiment at the Large Hadron Collider. The first study targets Higgs boson production via gluon-gluon fusion and constrains the CP properties of the effective Higgs-gluon interaction. Using angular distributions and the overall rate, a value of tan (alpha) = 0.0 +/- 0.4(stat.) +/- 0.3(syst.) is obtained for the tangent of the mixing angle for CP-even and CP-odd contributions. The second study exploits the vector-boson fusion production mechanism to probe the Higgs boson couplings to longitudinally and transversely polarised W and Z bosons in both the production and the decay of the Higgs boson; these couplings have not been directly constrained previously. The polarisation-dependent coupling-strength scale factors are defined as the ratios of the measured polarisation-dependent coupling strengths to those predicted by the Standard Model, and are determined using rate and kinematic information to be a(L) = 0.91(-0.18)(+0.10)(stat.)(-0.17)(+0.09)(syst.) and a(T) = 1.2 +/- 0.4(stat.)(-0.3)(+0.2)(syst.). These coupling strengths are translated into pseudo-observables, resulting in kappa(VV) = 0.91(-0.18)(+0.10)(stat.)(-0.17)(+0.09)(syst.) and epsilon(VV) = 0.13(-0.20)(+0.28)(stat.)(-0.10)(+0.08)(syst.). All results are consistent with the Standard Model predictions.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., Castillo, F. L., et al. (2021). Determination of the parton distribution functions of the proton from ATLAS measurements of differential W-+/- and Z boson production in association with jets. J. High Energy Phys., 07(7), 223–44pp.
Abstract: This article presents a new set of proton parton distribution functions, AT-LASepWZVjet20, produced in an analysis at next-to-next-to-leading order in QCD. The new data sets considered are the measurements of W+ and W- boson and Z boson production in association with jets in pp collisions at root s = 8 TeV performed by the ATLAS experiment at the LHC with integrated luminosities of 20.2 fb(-1) and 19.9 fb(-1), respectively. The analysis also considers the ATLAS measurements of differential W-+/- and Z boson production at root s = 7 TeV with an integrated luminosity of 4.6 fb(-1) and deep-inelastic-scattering data from e(+/-) p collisions at the HERA accelerator. An improved determination of the sea-quark densities at high Bjorken x is shown, while confirming a strange-quark density similar in size to the up- and down-sea-quark densities in the range x less than or similar to 0.02 found by previous ATLAS analyses.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., Castillo, F. L., et al. (2021). Muon reconstruction and identification efficiency in ATLAS using the full Run 2 pp collision data set at root s = 13 TeV. Eur. Phys. J. C, 81(7), 578–44pp.
Abstract: This article documents the muon reconstruction and identification efficiency obtained by the ATLAS experiment for 139 fb-1 of pp collision data at <mml:msqrt>s</mml:msqrt>=13 TeV collected between 2015 and 2018 during Run 2 of the LHC. The increased instantaneous luminosity delivered by the LHC over this period required a reoptimisation of the criteria for the identification of prompt muons. Improved and newly developed algorithms were deployed to preserve high muon identification efficiency with a low misidentification rate and good momentum resolution. The availability of large samples of Z -> μμand J/psi -> μμdecays, and the minimisation of systematic uncertainties, allows the efficiencies of criteria for muon identification, primary vertex association, and isolation to be measured with an accuracy at the per-mille level in the bulk of the phase space, and up to the percent level in complex kinematic configurations. Excellent performance is achieved over a range of transverse momenta from 3 GeV to several hundred GeV, and across the full muon detector acceptance of |eta|<2.7.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., Castillo, F. L., et al. (2021). Medium-Induced Modification of Z-Tagged Charged Particle Yields in Pb plus Pb Collisions at 5.02 TeV with the ATLAS Detector. Phys. Rev. Lett., 126(7), 072301–20pp.
Abstract: The yield of charged particles opposite to a Z boson with large transverse momentum (p(T)) is measured in 260 pb(-1) of pp and 1.7 nb(-1) of Pb + Pb collision data at 5.02 TeV per nucleon pair recorded with the ATLAS detector at the Large Hadron Collider. The Z boson tag is used to select hard-scattered partons with specific kinematics, and to observe how their showers are modified as they propagate through the quarkgluon plasma created in Pb + Pb collisions. Compared with pp collisions, charged-particle yields in Pb + Pb collisions show significant modifications as a function of charged-particle p(T) in a way that depends on event centrality and Z boson p(T). The data are compared with a variety of theoretical calculations and provide new information about the medium-induced energy loss of partons in a p(T) regime difficult to measure through other channels.
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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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