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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. (2018). Combination of the Searches for Pair-Produced Vectorlike Partners of the Third-Generation Quarks at root s=13 TeV with the ATLAS Detector. Phys. Rev. Lett., 121(21), 211801–20pp.
Abstract: A combination of the searches for pair-produced vectorlike partners of the top and bottom quarks in various decay channels (T -> Zt/Wb/Ht, B -> Zb/Wt/Hb) is performed using 36.1 fb(-1) of pp collision data at root s = 13 TeV with the ATLAS detector at the Large Hadron Collider. The observed data are found to be in good agreement with the standard model background prediction in all individual searches. Therefore, combined 95% confidence-level upper limits are set on the production cross section for a range of vectorlike quark scenarios, significantly improving upon the reach of the individual searches. Model-independent limits are set assuming the vectorlike quarks decay to standard model particles. A singlet T is excluded for masses below 1.31 TeV and a singlet B is excluded for masses below 1.22 TeV. Assuming a weak isospin (T, B) doublet and vertical bar V-Tb vertical bar << vertical bar V-tB vertical bar, T and B masses below 1.37 TeV are excluded.
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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. (2019). Measurements of W and Z boson production in pp collisions at root s=5.02 TeV with the ATLAS detector. Eur. Phys. J. C, 79(2), 128–29pp.
Abstract: Measurements of fiducial integrated and differential cross sections for inclusive W +, W -and Z boson production are reported. They are based on 25.0 +/- 0.5 pb -1 of pp collision data at v s = 5.02 TeV collected with the ATLAS detector at the CERN Large Hadron Collider. Electron and muon decay channels are analysed, and the combined W +, W -and Z integrated cross sections are found to be sW+ = 2266 +/- 9 (stat) +/- 29 (syst) +/- 43 (lumi) pb, sW-= 1401 +/- 7 (stat) +/- 18 (syst) +/- 27 (lumi) pb, and sZ = 374.5 +/- 3.4 (stat)+/- 3.6 (syst)+/- 7.0 (lumi) pb, in good agreement with next-to-next-to-leading-order QCD crosssection calculations. Thesemeasurements serve as references for Pb+ Pb interactions at the LHC at v sNN = 5.02 TeV.
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MoEDAL Collaboration(Acharya, B. et al), Bernabeu, J., Mamuzic, J., Mitsou, V. A., Papavassiliou, J., Ruiz de Austri, R., et al. (2019). Magnetic Monopole Search with the Full MoEDAL Trapping Detector in 13 TeV pp Collisions Interpreted in Photon-Fusion and Drell-Yan Production. Phys. Rev. Lett., 123(2), 021802–7pp.
Abstract: MoEDAL is designed to identify new physics in the form of stable or pseudostable highly ionizing particles produced in high-energy Large Hadron Collider (LHC) collisions. Here we update our previous search for magnetic monopoles in Run 2 using the full trapping detector with almost four times more material and almost twice more integrated luminosity. For the first time at the LHC, the data were interpreted in terms of photon-fusion monopole direct production in addition to the Drell-Yan-like mechanism. The MoEDAL trapping detector, consisting of 794 kg of aluminum samples installed in the forward and lateral regions, was exposed to 4.0 fb(-1) of 13 TeV proton-proton collisions at the LHCb interaction point and analyzed by searching for induced persistent currents after passage through a superconducting magnetometer. Magnetic charges equal to or above the Dirac charge are excluded in all samples. Monopole spins 0, 1/2, and 1 are considered and both velocity-independent and-dependent couplings are assumed. This search provides the best current laboratory constraints for monopoles with magnetic charges ranging from two to five times the Dirac charge.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Castillo, F. L., et al. (2020). Measurement of the azimuthal anisotropy of charged-particle production in Xe plus Xe collisions at root S-NN=5.44 TeV with the ATLAS detector. Phys. Rev. C, 101(2), 024906–35pp.
Abstract: This paper describes the measurements of flow harmonics v(2)-v(6) in 3 μb(-1) of Xe Xe collisions at root S-NN = 5.44 TeV performed using the ATLAS detector at the Large Hadron Collider (LHC). Measurements of the centrality, multiplicity, and p(T) dependence of the v(n) obtained using two-particle correlations and the scalar product technique are presented. The measurements are also performed using a template-fit procedure, which was developed to remove nonflow correlations in small collision systems. This nonflow removal is shown to have a significant influence on the measured v(n) at high p(T), especially in peripheral events. Comparisons of the measured v(n) with measurements in Pb + Pb collisions and p + Pb collisions at root S-NN = 5.02 TeV are also presented. The v(n) values in Xe + Xe collisions are observed to be larger than those in Pb + Pb collisions for n = 2, 3, and 4 in the most central events. However, with decreasing centrality or increasing harmonic order n, the v(n) values in Xe + Xe collisions become smaller than those in Pb + Pb collisions. The v(n) in Xe + Xe and Pb + Pb collisions are also compared as a function of the mean number of participating nucleons, < N-part >, and the measured charged-particle multiplicity in the detector. The v(3) values in Xe + Xe and Pb + Pb collisions are observed to be similar at the same < N-part > or multiplicity, but the other harmonics are significantly different. The ratios of the measured v(n) in Xe + Xe and Pb + Pb collisions, as a function of centrality, are also compared to theoretical calculations.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Castillo, F. L., et al. (2020). Measurement of differential cross sections for single diffractive dissociation in root s=8 TeV pp collisions using the ATLAS ALFA spectrometer. J. High Energy Phys., 02(2), 42–37pp.
Abstract: A dedicated sample of Large Hadron Collider proton-proton collision data at centre-of-mass energy s= 8 TeV is used to study inclusive single diffractive dissociation, pp -> X p. The intact final-state proton is reconstructed in the ATLAS ALFA forward spectrometer, while charged particles from the dissociated system X are measured in the central detector components. The fiducial range of the measurement is -4.0 < log(10)xi < -1.6 and 0.016 < |t| < 0.43 GeV2, where xi is the proton fractional energy loss and t is the squared four-momentum transfer. The total cross section integrated across the fiducial range is 1.59 +/- 0.13 mb. Cross sections are also measured differentially as functions of xi, t, and increment eta, a variable that characterises the rapidity gap separating the proton and the system X . The data are consistent with an exponential t dependence, d sigma/dt proportional to e(Bt) with slope parameter B = 7.65 +/- 0.34 GeV-2. Interpreted in the framework of triple Regge phenomenology, the xi dependence leads to a pomeron intercept of alpha(0) = 1.07 +/- 0.09.
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