K. Perez

Measurement of the inelastic proton–proton cross-section at √s=7 TeV with the ATLAS detector

The dependence of the rate of proton–proton interactions on the centre-of-mass collision energy, √s, is of fundamental importance for both hadron collider physics and particle astrophysics. The dependence cannot yet be calculated from first principles; therefore, experimental measurements are needed. Here we present the first measurement of the inelastic proton–proton interaction cross-section at a centre-of-mass energy, √s, of 7 TeV using the ATLAS detector at the Large Hadron Collider. Events are selected by requiring hits on scintillation counters mounted in the forward region of the detector. An inelastic cross-section of 60.3±2.1 mb is measured for ξ>5×10−6, where ξ is calculated from the invariant mass, MX, of hadrons selected using the largest rapidity gap in the event. For diffractive events, this corresponds to requiring at least one of the dissociation masses to be larger than 15.7 GeV.

Study of jet shapes in inclusive jet production in pp collisions at √s = 7 TeV using the ATLAS detector

Jet shapes have been measured in inclusive jet production in proton-proton collisions at √ s = 7 TeV using 3 pb of data recorded by the ATLAS experiment at the LHC. Jets are reconstructed using the anti-kt algorithm with transverse momentum 30 GeV < pT < 600 GeV and rapidity in the region |y| < 2.8. The data are corrected for detector effects and compared to several leadingorder QCD matrix elements plus parton shower Monte Carlo predictions, including different sets of parameters tuned to model fragmentation processes and underlying event contributions in the final state. The measured jets become narrower with increasing jet transverse momentum and the jet shapes present a moderate jet rapidity dependence. Within QCD, the data test a variety of perturbative and non-perturbative effects. In particular, the data show sensitivity to the details of the parton shower, fragmentation, and underlying event models in the Monte Carlo generators. For an appropriate choice of the parameters used in these models, the data are well described.

Measurement of tt production with a veto on additional central jet activity in pp collisions at √s = 7 TeV using the ATLAS detector

A measurement of the jet activity in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}

Search for a Standard Model Higgs boson in the H -> ZZ -> l + l - vv − decay channel with the ATLAS detector

t\bar{t}

Measurement of the top quark-pair production cross section with ATLAS in pp collisions at √s = 7 TeV

\end{document} events produced in proton–proton collisions at a centre-of-mass energy of 7 TeV is presented, using 2.05 fb−1 of integrated luminosity collected by the ATLAS detector at the Large Hadron Collider. The \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}

Measurement of the charge asymmetry in top quark pairproduction in pp collisions at √s = 7 TeV using the ATLASdetector

t\bar{t}

Measurement of the W →τν_τ cross section in pp collisions at√s = 7 TeV with the ATLAS experiment

\end{document} events are selected in the dilepton decay channel with two identified b-jets from the top quark decays. Events are vetoed if they contain an additional jet with transverse momentum above a threshold in a central rapidity interval. The fraction of events surviving the jet veto is presented as a function of this threshold for four different central rapidity interval definitions. An alternate measurement is also performed, in which events are vetoed if the scalar transverse momentum sum of the additional jets in each rapidity interval is above a threshold. In both measurements, the data are corrected for detector effects and compared to the theoretical models implemented in MC@NLO, Powheg, Alpgen and Sherpa. The experimental uncertainties are often smaller than the spread of theoretical predictions, allowing deviations between data and theory to be observed in some regions of phase space.A measurement of the jet activity in tt̄ events produced in proton-proton collisions at a centre-ofmass energy of 7 TeV is presented, using 2.05 fb of integrated luminosity collected by the ATLAS detector at the Large Hadron Collider. The tt̄ events are selected in the dilepton decay channel with two identified b-jets from the top quark decays. Events are vetoed if they contain an additional jet with transverse momentum above a threshold in a central rapidity interval. The fraction of events surviving the jet veto is presented as a function of this threshold for four different central rapidity interval definitions. An alternate measurement is also performed, in which events are vetoed if the scalar transverse momentum sum of the additional jets in each rapidity interval is above a threshold. In both measurements, the data are corrected for detector effects and compared to the theoretical models implemented in MC@NLO, Powheg, Alpgen and Sherpa. The experimental uncertainties are often smaller than the spread of theoretical predictions, allowing deviations between data and theory to be observed in some regions of phase space. Eur. Phys. J. C manuscript No. (will be inserted by the editor) Measurement of tt̄ production with a veto on additional central jet activity in pp collisions at √ s = 7 TeV using the ATLAS detector The ATLAS Collaboration CERN, 1211 Geneva 23, Switzerland

Search for the Higgs Boson in the H → WW^((*))→ l^+ vl^-v Decay Channel in pp Collisions at √s = 7 TeV with the ATLAS Detector

A search for a heavy Standard Model Higgs boson decaying via H → ZZ → llνν̄, where l = e, μ, is presented. It is based on proton-proton collision data at √ s = 7 TeV, collected by the ATLAS experiment at the LHC in the first half of 2011 and corresponding to an integrated luminosity of 1.04 fb. The data are compared to the expected Standard Model backgrounds. The data and the background expectations are found to be in agreement and upper limits are placed on the Higgs boson production cross section over the entire mass window considered; in particular the production of a Standard Model Higgs boson is excluded in the region 340 < mH < 450 GeV at the 95% confidence level.