ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2017). Measurement of W boson angular distributions in events with high transverse momentum jets at root s=8 TeV using the ATLAS detector. Phys. Lett. B, 765, 132–153.
Abstract: The W boson angular distribution in events with high transverse momentum jets is measured using data collected by the ATLAS experiment from proton-proton collisions at a centre-of-mass energy root s = 8 TeV at the Large Hadron Collider, corresponding to an integrated luminosity of 20.3 fb(-1). The focus is on the contributions to W + jets processes from real W emission, which is achieved by studying events where a muon is observed close to a high transverse momentum jet. At small angular separations, these contributions are expected to be large. Various theoretical models of this process are compared to the data in terms of the absolute cross-section and the angular distributions of the muon from the leptonic W decay.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2017). Search for new resonances decaying to a W or Z boson and a Higgs boson in the l(+)l(-)b(b)over-bar, l nu b(b)over-bar, and nu(nu)over-barb(b)over-bar channels with pp collisions at root s=13 TeV with the ATLAS detector. Phys. Lett. B, 765, 32–52.
Abstract: A search is presented for new resonances decaying to a W or Z boson and a Higgs boson in the l(+)l(-)b (b) over bar, l nu b (b) over bar, and nu(nu) over barb (b) over bar channels in pp collisions at root s = 13 TeV with the ATLAS detector at the Large Hadron Collider using a total integrated luminosity of 3.2 fb(-1). The search is conducted by looking for a localized excess in the WH/ZH invariant or transverse mass distribution. No significant excess is observed, and the results are interpreted in terms of constraints on a simplified model based on a phenomenological Lagrangian of heavy vector triplets.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2017). Search for dark matter in association with a Higgs boson decaying to b-quarks in pp collisions at root s=13 TeV with the ATLAS detector. Phys. Lett. B, 765, 11–31.
Abstract: A search for dark matter pair production in association with a Higgs boson decaying to a pair of bottom quarks is presented, using 3.2 fb(-1) of pp collisions at a centre-of-mass energy of 13 TeV collected by the ATLAS detector at the LHC. The decay of the Higgs boson is reconstructed as a high-momentum b (b) over bar system with either a pair of small-radius jets, or a single large-radius jet with substructure. The observed data are found to be consistent with the expected backgrounds. Results are interpreted using a simplified model with a gauge boson mediating the interaction between dark matter and the Standard Model as well as a two-Higgs-doublet model containing an additional Z' boson which decays to a Standard Model Higgs boson and a new pseudoscalar Higgs boson, the latter decaying into a pair of dark matter particles.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2017). Search for anomalous electroweak production of WW/WZ in association with a high-mass dijet system in pp collisions at root S=8 TeV with the ATLAS detector. Phys. Rev. D, 95(3), 032001–25pp.
Abstract: A search is presented for anomalous quartic gauge boson couplings in vector-boson scattering. The data for the analysis correspond to 20.2 fb(-1) of root S = 8 TeV pp collisions and were collected in 2012 by the ATLAS experiment at the Large Hadron Collider. The search looks for the production ofWW or WZ boson pairs accompanied by a high-mass dijet system, with one W decaying leptonically and a W or Z decaying hadronically. The hadronically decaying W/Z is reconstructed as either two small-radius jets or one largeradius jet using jet substructure techniques. Constraints on the anomalous quartic gauge boson coupling parameters a 4 and a 5 are set by fitting the transverse mass of the diboson system, and the resulting 95% confidence intervals are -0.024 < alpha(4) < 0.030 and -0.028 < alpha(5) < 0.033.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2017). A measurement of the calorimeter response to single hadrons and determination of the jet energy scale uncertainty using LHC Run-1 pp-collision data with the ATLAS detector. Eur. Phys. J. C, 77(1), 26–47pp.
Abstract: A measurement of the calorimeter response to isolated charged hadrons in the ATLAS detector at the LHC is presented. This measurement is performed with 3.2 nb(-1) of proton-proton collision data at root s = 7 TeV from 2010 and 0.1 nb(-1) of data at root s = 8 TeV from 2012. A number of aspects of the calorimeter response to isolated hadrons are explored. After accounting for energy deposited by neutral particles, there is a 5% discrepancy in the modelling, using various sets of GEANT4 hadronic physics models, of the calorimeter response to isolated charged hadrons in the central calorimeter region. The description of the response to anti-protons at low momenta is found to be improved with respect to previous analyses. The electromagnetic and hadronic calorimeters are also examined separately, and the detector simulation is found to describe the response in the hadronic calorimeter well. The jet energy scale uncertainty and correlations in scale between jets of different momenta and pseudorapidity are derived based on these studies. The uncertainty is 2-5% for jets with transverse momenta above 2 TeV, where this method provides the jet energy scale uncertainty for ATLAS.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., et al. (2016). Measurement of the CP-violating phase phi(s) and the B-s(0) meson decay width difference with B-s(0) -> J/psi phi decays in ATLAS. J. High Energy Phys., 08(8), 147–45pp.
Abstract: A measurement of the B-s(0) decay parameters in the B-s(0) -> J/psi/phi channel using an integrated luminosity of 14.3 fb(-1) collected by the ATLAS detector from 8TeV pp collisions at the LHC is presented. The measured parameters include the CP-violating phase phi(s), the decay width Gamma(s) and the width di ff erence between the mass eigenstates Delta Gamma(s). The values measured for the physical parameters are statistically combined with those from 4.9 fb-1 of 7TeV data, leading to the following: phi(s) = -0.090 +/- 0.078 (stat.) +/- 0.041 (syst.) rad Delta Gamma s = 0.085 +/- 0.011 (stat.) +/- 0.007 (syst.) ps(-1) Gamma(s) = 0.675 +/- 0.003 (stat.) +/- 0.003 (syst:) ps(-1). In the analysis the parameter Delta Gamma(s) is constrained to be positive. Results for phi(s) and Delta Gamma(s) are also presented as 68% and 95% likelihood contours in the phi(s)-Delta Gamma(s) plane. Also measured in this decay channel are the transversity amplitudes and corresponding strong phases. All measurements are in agreement with the Standard Model predictions.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Measurement of the double-differential high-mass Drell-Yan cross section in pp collisions at root s=8 TeV with the ATLAS detector. J. High Energy Phys., 08(8), 009–61pp.
Abstract: This paper presents a measurement of the double-differential cross section for the Drell-Yan Z/gamma* -> l(+)l(-) and photon-induced gamma gamma -> l(+)l(-) processes where l is an electron or muon. The measurement is performed for invariant masses of the lepton pairs, m(ll), between 116 GeV and 1500 GeV using a sample of 20.3 fb(-1) of pp collisions data at centre-of-mass energy of root s = 8TeV collected by the ATLAS detector at the LHC in 2012. The data are presented double differentially in invariant mass and absolute dilepton rapidity as well as in invariant mass and absolute pseudorapidity separation of the lepton pair. The single-differential cross section as a function of m(ll) is also reported. The electron and muon channel measurements are combined and a total experimental precision of better than 1% is achieved at low m(ll). A comparison to next-to-next-to-leading order perturbative QCD predictions using several recent parton distribution functions and including next-to-leading order electroweak effects indicates the potential of the data to constrain parton distribution functions. In particular, a large impact of the data on the photon PDF is demonstrated.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Dark matter interpretations of ATLAS searches for the electroweak production of supersymmetric particles in root s=8 TeV proton-proton collisions. J. High Energy Phys., 09(9), 175–44pp.
Abstract: A selection of searches by the ATLAS experiment at the LHC for the electroweak production of SUSY particles are used to study their impact on the constraints on dark matter candidates. The searches use 20 fb(-1) of proton-proton collision data at root s = 8 TeV. A likelihood-driven scan of a five-dimensional effective model focusing on the gaugino-higgsino and Higgs sector of the phenomenological minimal supersymmetric Standard Model is performed. This scan uses data from direct dark matter detection experiments, the relic dark matter density and precision flavour physics results. Further constraints from the ATLAS Higgs mass measurement and SUSY searches at LEP are also applied. A subset of models selected from this scan are used to assess the impact of the selected ATLAS searches in this five-dimensional parameter space. These ATLAS searches substantially impact those models for which the mass m((chi) over tilde (0)(1)) of the lightest neutralino is less than 65 GeV, excluding 86% of such models. The searches have limited impact on models with larger m((chi) over tilde (0)(1)) due to either heavy electroweakinos or compressed mass spectra where the mass splittings between the produced particles and the lightest supersymmetric particle is small.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Search for gluinos in events with an isolated lepton, jets and missing transverse momentum at root s=13 TeV with the ATLAS detector. Eur. Phys. J. C, 76(10), 565–29pp.
Abstract: The results of a search for gluinos in final states with an isolated electron or muon, multiple jets and large missing transverse momentum using proton-proton collision data at a centre-of-mass energy of root s = 13 TeV are presented. The dataset used was recorded in 2015 by the ATLAS experiment at the Large Hadron Collider and corresponds to an integrated luminosity of 3.2 fb(-1). Six signal selections are defined that best exploit the signal characteristics. The data agree with the Standard Model background expectation in all six signal selections, and the largest deviation is a 2.1 standard deviation excess. The results are interpreted in a simplified model where pair-produced gluinos decay via the lightest chargino to the lightest neutralino. In this model, gluinos are excluded up to masses of approximately 1.6 TeV depending on the mass spectrum of the simplified model, thus surpassing the limits of previous searches.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Measurement of the Inelastic Proton-Proton Cross Section at root s=13 TeV with the ATLAS Detector at the LHC. Phys. Rev. Lett., 117(18), 182002–19pp.
Abstract: This Letter presents a measurement of the inelastic proton-proton cross section using 60 μb(-1) of pp collisions at a center-of-mass energy root s of 13 TeV with the ATLAS detector at the LHC. Inelastic interactions are selected using rings of plastic scintillators in the forward region (2.07 <vertical bar eta vertical bar < 3.86) of the detector. A cross section of 68.1 +/- 1.4 mb is measured in the fiducial region. xi = M-X(2) > s > 10(-6), where M-X is the larger invariant mass of the two hadronic systems separated by the largest rapidity gap in the event. In this xi range the scintillators are highly efficient. For diffractive events this corresponds to cases where at least one proton dissociates to a system with M-X > 13 GeV. The measured cross section is compared with a range of theoretical predictions. When extrapolated to the full phase space, a cross section of 78.1 +/- 2.9 mb is measured, consistent with the inelastic cross section increasing with center-of-mass energy.
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