ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Escobar, C., et al. (2011). Search for stable hadronising squarks and gluinos with the ATLAS experiment at the LHC. Phys. Lett. B, 701(1), 1–19.
Abstract: Hitherto unobserved long-lived massive particles with electric and/or colour charge are predicted by a range of theories which extend the Standard Model. In this Letter a search is performed at the ATLAS experiment for slow-moving charged particles produced in proton-proton collisions at 7 TeV centre-of-mass energy at the LHC, using a data-set corresponding to an integrated luminosity of 34 pb(-1). No deviations from Standard Model expectations are found. This result is interpreted in a framework of supersymmetry models in which coloured sparticles can hadronise into long-lived bound hadronic states, termed R-hadrons, and 95% CL limits are set on the production cross-sections of squarks and gluinos. The influence of R-hadron interactions in matter was studied using a number of different models, and lower mass limits for stable sbottoms and stops are found to be 294 and 309 GeV respectively. The lower mass limit for a stable gluino lies in the range from 562 to 586 GeV depending on the model assumed. Each of these constraints is the most stringent to date.
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ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Escobar, C., et al. (2011). Measurement of the W charge asymmetry in the W -> mu nu decay mode in pp collisions at sqrt(s)=7 TeV with the ATLAS detector. Phys. Lett. B, 701(1), 31–49.
Abstract: This Letter reports a measurement of the muon charge asymmetry from W bosons produced in proton-proton collisions at a centre-of-mass energy of 7 TeV with the ATLAS experiment at the LHC. The asymmetry is measured in the W -> μnu decay mode as a function of the muon pseudorapidity using a data sample corresponding to a total integrated luminosity of 31 pb(-1). The results are compared to predictions based on next-to-leading order calculations with various parton distribution functions. This measurement provides information on the u and d quark momentum fractions in the proton.
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ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Escobar, C., et al. (2011). Search for high-mass states with one lepton plus missing transverse momentum in proton-proton collisions sqrt(s)=7 TeV with the ATLAS detector. Phys. Lett. B, 701(1), 50–69.
Abstract: The ATLAS detector is used to search for high-mass states, such as heavy charged gauge bosons (W'. W*), decaying to a charged lepton (electron or muon) and a neutrino. Results are presented based on the analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 36 pb(-1). No excess beyond standard model expectations is observed. A W' with sequential standard model couplings is excluded at 95% confidence level for masses below 1.49 TeV, and a W* (charged chiral boson) for masses below 1.35 TeV.
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ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Escobar, C., et al. (2011). Search for a heavy gauge boson decaying to a charged lepton and a neutrino in 1 fb(-1) of pp collisions at sqrt(s)=7 TeV using the ATLAS detector ATLAS Collaboration. Phys. Lett. B, 705(1-2), 28–46.
Abstract: The ATLAS detector at the LHC is used to search for high-mass states, such as heavy charged gauge bosons (W '), decaying to a charged lepton (electron or muon) and a neutrino. Results are presented based on the analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 1.04 fb(-1). No excess above Standard Model expectations is observed. A W ' with Sequential Standard Model couplings is excluded at the 95% confidence level for masses up to 2.15 TeV.
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ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Escobar, C., et al. (2011). Measurement of the gamma(1S) production cross-section in pp collisions at sqrt(s)=7 TeV in ATLAS ATLAS Collaboration. Phys. Lett. B, 705(1-2), 9–27.
Abstract: A measurement of the cross-section for gamma(1S) -> mu(+)mu(-) production in proton-proton collisions at centre of mass energy of 7 TeV is presented. The cross-section is measured as a function of the gamma(1S) transverse momentum in two bins of rapidity, vertical bar y(gamma(1S))vertical bar < 1.2 and 1.2 < vertical bar y(gamma(1S))vertical bar < 2.4. The measurement requires that both muons have transverse momentum p(T)(mu) > 4 GeV and pseuclorapidity vertical bar eta(mu)vertical bar < 2.5 in order to reduce theoretical uncertainties on the acceptance, which depend on the poorly known polarisation. The results are based on an integrated luminosity of 1.13 pb(-1), collected with the ATLAS detector at the Large Hadron Collider. The cross-section measurement is compared to theoretical predictions: it agrees to within a factor of two with a prediction based on the NRQCD model including colour-singlet and colour-octet matrix elements as implemented in PYTHIA while it disagrees by up to a factor of ten with the next-to-leading order prediction based on the colour-singlet model.
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