76 research outputs found
ATLAS search for a heavy gauge boson decaying to a charged lepton and a neutrino in pp collisions at root s=7 TeV
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 4.7 fb(-1). No excess beyond Standard Model expectations is observed. A W' with Sequential Standard Model couplings is excluded at the 95 % credibility level for masses up to 2.55 TeV. Excited chiral bosons (W*) with equivalent coupling strength are excluded for masses up to 2.42 TeV
Search for WZ resonances in the fully leptonic channel using pp collisions at s=8 TeV with the ATLAS detector
A search for resonant WZ production in the ℓνℓ'ℓ' (ℓ,ℓ'=e,μ) decay channel using 20.3 fb-1 of s=8TeV pp collision data collected by the ATLAS experiment at LHC is presented. No significant deviation from the Standard Model prediction is observed and upper limits on the production cross sections of WZ resonances from an extended gauge model W' and from a simplified model of heavy vector triplets are derived. A corresponding observed (expected) lower mass limit of 1.52 (1.49) TeV is derived for the W' at the 95% confidence level.Peer Reviewe
Measurement of the production cross section of prompt J/ψ mesons in association with a W ± boson in pp collisions at √s = 7 TeV with the ATLAS detector
Aad, G. et al.The process pp → W ± J/ψ provides a powerful probe of the production mechanism of charmonium in hadronic collisions, and is also sensitive to multiple parton interactions in the colliding protons. Using the 2011 ATLAS dataset of 4.5 fb−1 of s√ = 7 TeV pp collisions at the LHC, the first observation is made of the production of W ± + prompt J/ψ events in hadronic collisions, using W ± → μν μ and J/ψ → μ + μ −. A yield of 27.4+7.5−6.5 W ± + prompt J/ψ events is observed, with a statistical significance of 5.1σ. The production rate as a ratio to the inclusive W ± boson production rate is measured, and the double parton scattering contribution to the cross section is estimated.We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWF and FWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF, DNSRC and Lundbeck Foundation, Denmark; EPLANET, ERC and NSRF, European Union; IN2P3-CNRS, CEA-DSM/IRFU, France; GNSF, Georgia; BMBF, DFG, HGF, MPG and AvH Foundation, Germany; GSRT and NSRF, Greece; ISF, MINERVA, GIF, DIP and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; FOM and NWO, Netherlands; BRF and RCN, Norway; MNiSW and NCN, Poland; GRICES and FCT, Portugal; MNE/IFA, Romania; MES of Russia and ROSATOM, Russian Federation; JINR; MSTD, Serbia; MSSR, Slovakia; ARRS and MIZˇS, Slovenia; DST/NRF, South Africa; MINECO, Spain; SRC and Wallenberg Foundation, Sweden; SER, SNSF and Cantons of Bern and Geneva, Switzerland; NSC, Taiwan; TAEK, Turkey; STFC, the Royal Society and Leverhulme Trust, United Kingdom; DOE and NSF, United States of America.Peer reviewe
Jet energy measurement with the ATLAS detector in proton-proton collisions at sqrt(s) = 7 TeV
The jet energy scale (JES) and its systematic uncertainty are determined for jets measured with the ATLAS detector at the LHC in proton-proton collision data at a centre-of-mass energy of sqrt(s) = 7 TeV corresponding to an integrated luminosity of 38 inverse pb. Jets are reconstructed with the anti-kt algorithm with distance parameters R=0.4 or R=0.6. Jet energy and angle corrections are determined from Monte Carlo simulations to calibrate jets with transverse momenta pt > 20 GeV and pseudorapidities eta 50 GeV after a dedicated correction for this effect. The JES is validated for jet transverse momenta up to 1 TeV to the level of a few percent using several in situ techniques by comparing a well-known reference such as the recoiling photon pt, the sum of the transverse momenta of tracks associated to the jet, or a system of low-pt jets recoiling against a high-pt jet. More sophisticated jet calibration schemes are presented based on calorimeter cell energy density weighting or hadronic properties of jets, providing an improved jet energy resolution and a reduced flavour dependence of the jet response. The JES systematic uncertainty determined from a combination of in situ techniques are consistent with the one derived from single hadron response measurements over a wide kinematic range. The nominal corrections and uncertainties are derived for isolated jets in an inclusive sample of high-pt jets
Measurement of the cross-section for W boson production in association with b-jets in pp collisions at root s=7 TeV with the ATLAS detector
This paper reports a measurement of the W+b-jets (W+b+X and W+b (b) over bar +X) production cross-section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC. These results are based on data corresponding to an integrated luminosity of 4.6 fb(-1), collected with the ATLAS detector. Cross-sections are presented as a function of jet multiplicity and of the transverse momentum of the leading b-jet for both the muon and electron decay modes of the W boson. The W+b-jets cross-section, corrected for all known detector effects, is quoted in a limited kinematic range. Combining the muon and electron channels, the fiducial cross-section for W+b-jets is measured to be 7.1 +/- 0.5 (stat) +/- 1.4 (syst) pb, consistent with the next-to-leading order QCD prediction, corrected for non-perturbative and double-parton interactions (DPI) contributions, of 4.70 +/- 0.09 (stat) (+0.60)(-0.49) (scale) +/- 0.06 (PDF) +/- 0.16 (non-pert) (+0.52)(-0.38) (DPI) pb
Dynamics of isolated-photon plus jet production in pp collisions at root s=7 TeV with the ATLAS detector
The dynamics of isolated-photon plus jet production in pp collisions at a centre-of-mass energy of 7 TeV has been studied with the ATLAS detector at the LHC using an integrated luminosity of 37 pb(-1). Measurements of isolated-photon plus jet bin-averaged cross sections are presented as functions of photon transverse energy, jet transverse momentum and jet rapidity. In addition, the bin-averaged cross sections as functions of the difference between the azimuthal angles of the photon and the jet, the photon jet invariant mass and the scattering angle in the photon jet centre-of-mass frame have been measured. Next-to-leading-order QCD calculations are compared to the measurements and provide a good description of the data, except for the case of the azimuthal opening angle
Charged-particle multiplicities in pp interactions at root s=900 GeV measured with the ATLAS detector at the LHC
22 páginas, 4 figuras, 1 tabla.-- et al.(ATLAS Collaboration).-- arXiv:1003.3124v2The first measurements from proton-proton collisions recorded with the ATLAS detector at the LHC are presented. Data were collected in December 2009 using a minimum-bias trigger during collisions at a centre-of-mass energy of 900 GeV. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity. and the relationship between mean transverse momentum and charged-particle multiplicity are measured for events with at least one charged particle in the kinematic range vertical bar eta vertical bar 500 MeV. The measurements are compared to Monte Carlo models of proton-proton collisions and to results from other experiments at the same centre-of-mass energy. The charged-particle multiplicity per event and unit of pseudorapidity eta = 0 is measured to be 1.333 +/- 0.003(stat.) +/- 0.040(syst.), which is 5-15% higher than the Monte Carlo models predict.We are greatly indebted to all CERN’s departments and to the LHC
project for their immense efforts not only in building the LHC, but also
for their direct contributions to the construction and installation of the ATLAS
detector and its infrastructure. All our congratulations go to the LHC
operation team for the superb performance during this initial data-taking period. We acknowledge equally warmly all our technical colleagues in the
collaborating Institutions without whom the ATLAS detector could not have
been built. Furthermore we are grateful to all the funding agencies which
supported generously the construction and the commissioning of the ATLAS
detector and also provided the computing infrastructure.
The ATLAS detector design and construction has taken about fifteen
years, and our thoughts are with all our colleagues who sadly could not see
its final realisation.
We acknowledge the support of ANPCyT, Argentina; Yerevan Physics
Institute, Armenia; ARC and DEST, Australia; Bundesministerium für Wissenschaft
und Forschung, Austria; National Academy of Sciences of Azerbaijan;
State Committee on Science & Technologies of the Republic of Belarus;
CNPq and FINEP, Brazil; NSERC, NRC, and CFI, Canada; CERN; CONICYT,
Chile; NSFC, China; COLCIENCIAS, Colombia; Ministry of Education,
Youth and Sports of the Czech Republic, Ministry of Industry and
Trade of the Czech Republic, and Committee for Collaboration of the Czech
Republic with CERN; Danish Natural Science Research Council and the
Lundbeck Foundation; European Commission, through the ARTEMIS Research
Training Network; IN2P3-CNRS and Dapnia-CEA, France; Georgian
Academy of Sciences; BMBF, HGF, DFG and MPG, Germany; Ministry of
Education and Religion, through the EPEAEK program PYTHAGORAS II
and GSRT, Greece; ISF, MINERVA, GIF, DIP, and Benoziyo Center, Israel;
INFN, Italy; MEXT, Japan; CNRST, Morocco; FOM and NWO, Netherlands;
The Research Council of Norway; Ministry of Science and Higher
Education, Poland; GRICES and FCT, Portugal; Ministry of Education and
Research, Romania; Ministry of Education and Science of the Russian Federation
and State Atomic Energy Corporation “Rosatom”; JINR; Ministry
of Science, Serbia; Department of International Science and Technology Cooperation,
Ministry of Education of the Slovak Republic; Slovenian Research
Agency, Ministry of Higher Education, Science and Technology, Slovenia;
Ministerio de Educación y Ciencia, Spain; The Swedish Research Council,
The Knut and Alice Wallenberg Foundation, Sweden; State Secretariat for
Education and Science, Swiss National Science Foundation, and Cantons of
Bern and Geneva, Switzerland; National Science Council, Taiwan; TAEK,
Turkey; The Science and Technology Facilities Council and The Leverhulme
Trust, United Kingdom; DOE and NSF, United States of America.Peer reviewe
Search for dark matter candidates and large extra dimensions in events with a jet and missing transverse momentum with the ATLAS detector
A search for new phenomena in events with a high-energy jet and large missing transverse momentum is performed using data from proton-proton collisions at root s = 7 TeV with the ATLAS experiment at the Large flatiron Collider. Four kinematic regions are explored using a dataset corresponding to an integrated luminosity of 4.7 fb(-1). No excess of events beyond expectations from Standard Model processes is observed, and limits are set on large extra dimensions and the pair production of dark matter particles
ATLAS search for new phenomena in dijet mass and angular distributions using pp collisions at root s=7 TeV
Mass and angular distributions of dijets produced in LHC proton-proton collisions at a centre-of-mass energy root s = 7TeV have been studied with the ATLAS detector using the full 2011 data set with an integrated luminosity of 4.8 fb(-1). Dijet masses up to similar to 4.0TeV have been probed. No resonance-like features have been observed in the dijet mass spectrum, and all angular distributions are consistent with the predictions of QCD. Exclusion limits on six hypotheses of new phenomena have been set at 95% CL in terms of mass or energy scale, as appropriate. These hypotheses include excited quarks below 2.83 TeV, colour octet scalars below 1.86TeV, heavy W bosons below 1.68 TeV, string resonances below 3.61 TeV, quantum black holes with six extra space-time dimensions for quantum gravity scales below 4.11 TeV, and quark contact interactions below a compositeness scale of 7.6 TeV in a destructive interference scenario
Triggers for displaced decays of long-lived neutral particles in the ATLAS detector
A set of three dedicated triggers designed to detect long-lived neutral particles decaying throughout the ATLAS detector to a pair of hadronic jets is described. The efficiencies of the triggers for selecting displaced decays as a function of the decay position are presented for simulated events. The effect of pile-up interactions on the trigger efficiencies and the dependence of the trigger rate on instantaneous luminosity during the 2012 data-taking period at the LHC are discussed
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