1,088,108 research outputs found
Standard Model Higgs boson searches with the ATLAS detector at the Large Hadron Collider
The investigation of the mechanism responsible for electroweak symmetry
breaking is one of the most important tasks of the scientific program of the
Large Hadron Collider. The experimental results on the search of the Standard
Model Higgs boson with 1 to 2 fb^-1 of proton proton collision data at sqrt s=7
TeV recorded by the ATLAS detector are presented and discussed. No significant
excess of events is found with respect to the expectations from Standard Model
processes, and the production of a Higgs boson is excluded at 95% Confidence
Level for the mass regions 144-232, 256-282 and 296-466 GeV.Comment: Proceedings of the Lepton Photon 2011 Conference, to appear in
"Pramana - journal of phsyics". 11 pages, 13 figure
Search for pair production of Higgs bosons in the final state using proton--proton collisions at TeV with the ATLAS detector
A search for Higgs-boson pair production in the final
state is carried out with 3.2 fb of proton--proton collision data
collected at TeV with the ATLAS detector. The data are
consistent with the estimated background and are used to set upper limits on
the production cross section of Higgs-boson pairs times branching ratio to
for both nonresonant and resonant production. In the case of
resonant production of Kaluza--Klein gravitons within the Randall--Sundrum
model, upper limits in the 24 to 91 fb range are obtained for masses between
600 and 3000 GeV, at the 95% confidence level. The production cross section
times branching ratio for nonresonant Higgs-boson pairs is also constrained to
be less than 1.22 pb, at the 95% confidence level.Comment: 25 pages plus author list + cover pages (43 pages total), 10 figures,
7 tables, published in Phys. Rev. D, All figures including auxiliary figures
are available at
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/EXOT-2015-1
Study of the rare decays of and into muon pairs from data collected during the LHC Run 1 with the ATLAS detector
A study of the decays and has been
performed using data corresponding to an integrated luminosity of
fb of TeV and TeV proton--proton collisions collected with the
ATLAS detector during the LHC Run 1. For , an upper limit on the branching
fraction is set at at
confidence level. For , the branching fraction is measured.
The results are consistent with the Standard Model expectation with a -value
of , corresponding to standard deviations.Comment: Comments: 29 pages plus author list + cover pages (46 pages total), 9
figures, 5 tables, submitted to Eur. Phys. J. C., regular article. All
figures including auxiliary figures are available at
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/BPHY-2012-01
Properties of jets measured from tracks in proton-proton collisions at center-of-mass energy sqrt(s) = 7 TeV with the ATLAS detector
Jets are identified and their properties studied in center-of-mass energy
sqrt(s) = 7 TeV proton-proton collisions at the Large Hadron Collider using
charged particles measured by the ATLAS inner detector. Events are selected
using a minimum bias trigger, allowing jets at very low transverse momentum to
be observed and their characteristics in the transition to high-momentum fully
perturbative jets to be studied. Jets are reconstructed using the anti-kt
algorithm applied to charged particles with two radius parameter choices, 0.4
and 0.6. An inclusive charged jet transverse momentum cross section measurement
from 4 GeV to 100 GeV is shown for four ranges in rapidity extending to 1.9 and
corrected to charged particle-level truth jets. The transverse momenta and
longitudinal momentum fractions of charged particles within jets are measured,
along with the charged particle multiplicity and the particle density as a
function of radial distance from the jet axis. Comparison of the data with the
theoretical models implemented in existing tunings of Monte Carlo event
generators indicates reasonable overall agreement between data and Monte Carlo.
These comparisons are sensitive to Monte Carlo parton showering, hadronization,
and soft physics models.Comment: 15 pages plus author list (27 pages total), 6 figures, 3 tables,
final version published in Physical Review
Recent Heavy Ion Results with the ATLAS Detector at the LHC
Results are presented from the ATLAS collaboration from the 2010 LHC heavy
ion run, during which nearly 10 inverse microbarns of luminosity were
delivered. Soft physics results include charged particle multiplicities and
collective flow. The charged particle multiplicity, which tracks initial state
entropy production, increases by a factor of two relative to the top RHIC
energy, with a centrality dependence very similar to that already measured at
RHIC. Measurements of elliptic flow out to large transverse momentum also show
similar results to what was measured at RHIC, but no significant pseudorapidity
dependence. Extensions of these measurements to higher harmonics have also been
made, and can be used to explain structures in the two-particle correlation
functions that had long been attributed to jet-medium interactions. New hard
probe measurements include single muons, jets and high hadrons. Single
muons at high momentum are used to extract the yield of bosons and
are found to be consistent within statistical uncertainties with binary
collision scaling. Conversely, jets are found to be suppressed in central
events by a factor of two relative to peripheral events, with no significant
dependence on the jet energy. Fragmentation functions are also found to be the
same in central and peripheral events. Finally, charged hadrons have been
measured out to 30 GeV, and their centrality dependence relative to peripheral
events is similar to that found for jets.Comment: 9 pages, 9 figures, proceedings for Quark Matter 2011, Annecy,
France, May 23-28, 201
Measurement of long-range pseudorapidity correlations and azimuthal harmonics in = 5.02 TeV proton-lead collisions with the ATLAS detector
Measurements of two-particle correlation functions and the first five
azimuthal harmonics, to , are presented, using 28
of +Pb collisions at a nucleon-nucleon center-of-mass energy of
TeV measured with the ATLAS detector at the LHC.
Significant long-range ``ridge-like'' correlations are observed for pairs with
small relative azimuthal angle () and back-to-back pairs
() over the transverse momentum range
GeV and in different intervals of event activity. The event activity is defined
by either the number of reconstructed tracks or the total transverse energy on
the Pb-fragmentation side. The azimuthal structure of such long-range
correlations is Fourier decomposed to obtain the harmonics as a function
of and event activity. The extracted values for to
decrease with . The and values are found to be positive in the
measured range. The is also measured as a function of and is observed to change sign around GeV and
then increase to about 0.1 for GeV. The ,
and are compared to the coefficients in
Pb+Pb collisions at TeV with similar event
multiplicities. Reasonable agreement is observed after accounting for the
difference in the average of particles produced in the two
collision systems.Comment: 21 pages plus author list + cover pages (34 pages total), 16 figures,
submitted to Phys. Rev. C., All figures including auxiliary figures can be
found at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2013-04
Search for the Standard Model Higgs boson in the diphoton decay channel with 4.9 fb-1 of pp collisions at sqrt(s) = 7 TeV with ATLAS
A search for the Standard Model Higgs boson is performed in the diphoton
decay channel. The data used corresponds to an integrated luminosity of 4.9
fb-1 collected with the ATLAS detector at the Large Hadron Collider in
proton-proton collisions at a center-of-mass energy of sqrt(s) = 7 TeV. In the
diphoton mass range 110-150 GeV, the largest excess with respect to the
background-only hypothesis is observed at 126.5 GeV, with a local significance
of 2.8 standard deviations. Taking the look-elsewhere effect into account in
the range 110-150 GeV, this significance becomes 1.5 standard deviations. The
Standard Model Higgs boson is excluded at 95% confidence level in the mass
ranges of 113-115 GeV and 134.5-136 GeV.Comment: 6 pages plus author list (19 pages total), 4 figures, 3 tables,
matches published version in Physical Review Letter
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