10,970 research outputs found
Search for a heavy gauge boson decaying to a charged lepton and a neutrino in 1 fb^(â1) of pp collisions at âs = 7 TeV using the ATLAS detector
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^(â1). 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 Te
Discriminating Minimal SUGRA and Minimal Gauge Mediation Models at the Early LHC
Among various supersymmetric (SUSY) standard models, the gravity mediation
model with a neutralino LSP and the gauge mediation model with a very light
gravitino are attractive from the cosmological view point. These models have
different scales of SUSY breaking and their underlying physics in high energy
is quite different. However, if the sparticles' decay into the gravitino is
prompt in the latter case, their collider signatures can be similar: multiple
jets and missing transverse momentum. In this paper, we study the
discrimination between these models in minimal cases at the LHC based on the
method using the significance variables in several different modes and show the
discrimination is possible at a very early stage after the discovery.Comment: 29 pages, 3 figures, captions improved, typos corrected, appendix
added, version published in JHE
Anomalously interacting new extra vector bosons and their first LHC constraints
In this review phenomenological consequences of the Standard Model extension
by means of new spin-1 chiral fields with the internal quantum numbers of the
electroweak Higgs doublets are summarized. The prospects for resonance
production and detection of the chiral vector and bosons at
the LHC energies are considered. The boson can be observed as a
Breit-Wigner resonance peak in the invariant dilepton mass distributions in the
same way as the well-known extra gauge bosons. However, the bosons
have unique signatures in transverse momentum, angular and pseudorapidity
distributions of the final leptons, which allow one to distinguish them from
other heavy neutral resonances. In 2010, with 40 pb of the LHC
proton-proton data at the energy 7 TeV, the ATLAS detector was used to search
for narrow resonances in the invariant mass spectrum of and
final states and high-mass charged states decaying to a charged
lepton and a neutrino. No statistically significant excess above the Standard
Model expectation was observed. The exclusion mass limits of 1.15 TeV and
1.35 TeV were obtained for the chiral neutral and charged
bosons, respectively. These are the first direct limits on the and
boson production. For almost all currently considered exotic models the
relevant signal is expected in the central dijet rapidity region. On the
contrary, the chiral bosons do not contribute to this region but produce an
excess of dijet events far away from it. For these bosons the appropriate
kinematic restrictions lead to a dip in the centrality ratio distribution over
the dijet invariant mass instead of a bump expected in the most exotic models.Comment: 24 pages, 34 figure, based on talk given by V.A.Bednyakov at 15th
Lomonosov conference, 22.08.201
Study of LHC Searches for a Lepton and Many Jets
Searches for new physics in high-multiplicity events with little or no
missing energy are an important component of the LHC program, complementary to
analyses that rely on missing energy. We consider the potential reach of
searches for events with a lepton and six or more jets, and show they can
provide increased sensitivity to many supersymmetric and exotic models that
would not be detected through standard missing-energy analyses. Among these are
supersymmetric models with gauge mediation, R-parity violation, and light
hidden sectors. Moreover, ATLAS and CMS measurements suggest the primary
background in this channel is from t-tbar, rather than W+jets or QCD, which
reduces the complexity of background modeling necessary for such a search. We
also comment on related searches where the lepton is replaced with another
visible object, such as a Z boson.Comment: 23 pages, 12 figures, 1 tabl
Quarkonia production at forward rapidity in Pb+Pb collisions at TeV with the ALICE detector
The study of formation of heavy quarkonia in relativistic heavy ion
collisions provides important insight into the properties of the produced high
density QCD medium. Lattice QCD studies show sequential suppression of
quarkonia states with increasing temperature; which affirms that a full
spectroscopy, can provide us a thermometer for the matter produced under
extreme conditions in relativistic heavy ion collisions and one of the most
direct probes of de-confinement. Muons from the decay of charmonium resonances
are detected in ALICE Experiment in p+p and Pb+Pb collisions with a muon
spectrometer, covering the forward rapidity region(). The analysis of
the inclusive J/ production in the first Pb+Pb data collected in the fall
2010 at a center of mass energy of TeV is discussed.
Preliminary results on the nuclear modification factor () and the
central to peripheral nuclear modification factor () are presented.Comment: 2 figures. Proceedings for XXV International Symposium on Lepton
Photon Interactions at High Energies, 22-27th August 2011, Mumbai, Indi
Measurement of the ΄ (1S) production cross-section in pp collisions at âs = 7 TeV in ATLAS
A measurement of the cross-section for ΄ (1S)âÎŒ^+ÎŒ^â production in protonâproton collisions at centre of mass energy of 7 TeV is presented. The cross-section is measured as a function of the ΄ (1S) transverse momentum in two bins of rapidity, |y^(΄(1S))| 4 GeV and pseudorapidity |η^ÎŒ| < 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^(â1), 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
Search for a Heavy Particle Decaying into an Electron and a Muon with the ATLAS Detector in âs = 7 TeV pp collisions at the LHC
This Letter presents the first search for a heavy particle decaying into an e^±Ό^â final state in âs=7ââTeV pp collisions at the LHC. The data were recorded by the ATLAS detector during 2010 and correspond to a total integrated luminosity of 35ââpb^(-1). No excess above the standard model background expectation is observed. Exclusions at 95% confidence level are placed on two representative models. In an R-parity violating supersymmetric model, tau sneutrinos with a mass below 0.75 TeV are excluded, assuming all R-parity violating couplings are zero except λ'_(311)=0.11 and λ_(312)=0.07. In a lepton flavor violating model, a ZâČ-like vector boson with masses of 0.70â1.00 TeV and corresponding cross sections times branching ratios of 0.175â0.183 pb is excluded. These results extend to higher mass R-parity violating sneutrinos and lepton flavor violating Zâs than previous constraints from the Tevatron
Search for direct top quark pair production in final states with one isolated lepton, jets, and missing transverse momentum in âs=7ââTeV pp collisions using 4.7ââfb-1 of ATLAS data
A search is presented for direct top squark pair production in final states with one isolated electron or muon, jets, and missing transverse momentum in proton-proton collisions at âs=7ââTeV. The measurement is based on 4.7ââfb-1 of data collected with the ATLAS detector at the LHC. Each top squark is assumed to decay to a top quark and the lightest supersymmetric particle (LSP). The data are found to be consistent with standard model expectations. Top squark masses between 230 GeV and 440 GeV are excluded with 95% confidence for massless LSPs, and top squark masses around 400 GeV are excluded for LSP masses up to 125 GeV
Search for pair production of first or second generation leptoquarks in proton-proton collisions at âs = 7 TeV using the ATLAS detector at the LHC
This paper describes searches for the pair production of first or second generation scalar leptoquarks using 35ââpb^(-1) of proton-proton collision data recorded by the ATLAS detector at âs=7ââTeV. Leptoquarks are searched in events with two oppositely-charged muons or electrons and at least two jets, and in events with one muon or electron, missing transverse momentum and at least two jets. After event selection, the observed yields are consistent with the predicted backgrounds. Leptoquark production is excluded at the 95% CL for masses M_(LQ)<376 (319) GeV and M_(LQ)<422 (362) GeV for first and second generation scalar leptoquarks, respectively, when assuming the branching fraction of a leptoquark to a charged lepton is equal to 1.0 (0.5)
Limits on the production of the standard model Higgs boson in pp collisions at âs = 7 TeV with the ATLAS detector
A search for the Standard Model Higgs boson at the Large Hadron Collider (LHC) running at a centre-of-mass energy of 7 TeV is reported, based on a total integrated luminosity of up to 40 pb^(â1) collected by the ATLAS detector in 2010. Several Higgs boson decay channels: Hâγγ, HâZZ^((â))âââââ, HâZZâââΜΜ, HâZZâââqq, HâWW^((â))ââÎœâÎœ and HâWWââÎœqq (â is e, ÎŒ) are combined in a mass range from 110 GeV to 600 GeV. The highest sensitivity is achieved in the mass range between 160 GeV and 170 GeV, where the expected 95% CL exclusion sensitivity is at Higgs boson production cross sections 2.3 times the Standard Model prediction. Upper limits on the cross section for its production are determined. Models with a fourth generation of heavy leptons and quarks with Standard Model-like couplings to the Higgs boson are also investigated and are excluded at 95% CL for a Higgs boson mass in the range from 140 GeV to 185 GeV
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