A precise measurement of the hypertriton lifetime is presented. In this letter, the mesonic decay modes $\mathrm{{^3_\Lambda}H \rightarrow ^3He + \pi^-}$ and $\mathrm{{^3_\Lambda}H \rightarrow d + p + \pi^-}$ are used to reconstruct the hypertriton from Au+Au collision data collected by the STAR collaboration at RHIC. A minimum $\chi^2$ estimation is used to determine the lifetime of $\tau = 142^{+24}_{-21}\,{\rm (stat.)} {\pm} 31\,{\rm (syst.)}$ ps. This lifetime is about 50\% shorter than the lifetime $\tau = 263\pm2$ ps of a free $\Lambda$, indicating strong hyperon-nucleon interaction in the hypernucleus system. The branching ratios of the mesonic decay channels are also determined to satisfy B.R.$_{(^3{\rm He}+\pi^-)}/$(B.R.$_{(^3{\rm He}+\pi^-)}+$B.R.$_{(d+p+\pi^-)})$ = $0.32\rm{\pm}0.05\,{\rm (stat.)}\pm 0.08\,{\rm (syst.)}$. Our ratio result favors the assignment $J(\mathrm{^{3}_{\Lambda}H})$ = $\frac{1}{2}$ over $J(\mathrm{^{3}_{\Lambda}H})$ = $\frac{3}{2}$. These measurements will help to constrain models of hyperon-baryon interactions.
The hypertriton yield as a function of ~l/βγ for each of the two analyzed decay channels. The redpoints are for 2-body decays in four bins of ~l/βγ. The yields indicate the number of $^3_{\Lambda}$H per million events for each channel, and are already divided by the theoretical branching ratio 24.89% for the 2-body channel. The data points are fitted with the usual radioactive decay function. Using a minimum chisquare estimation.
The hypertriton yield as a function of l/βγ for each of the two analyzed decay channels. The bluesquares are for 3-body decays in four bins of l/βγ. The yield of hypertriton per million events in 3-body correct for theoretical branching ratio 40.06% 3-body channel. The data points are fitted with the usual radioactive decay function. Using a minimum chisquare estimation.
A summary of worldwide $^3_{\Lambda}$H lifetime experimental measurements and theoretical calculations. The two star markers are the STAR collaboration’s measurement published in 2010 and the present analysis. This measurement was based on the 3-body decay channel $^3_{\Lambda}$H→p+d+π−in a nuclear emulsion experiment. The shorter lifetime was attributed to the dissociation of the lightly-bound Λ and deuteron when traveling in a dense medium.
This work presents a new inclusive search for supersymmetry (SUSY) by the ATLAS experiment at the LHC in proton-proton collisions at a center-of-mass energy sqrt(s) = 7 TeV in final states with jets, missing transverse momentum and one or more isolated electrons and/or muons. The search is based on data from the full 2011 data-taking period, corresponding to an integrated luminosity of 4.7 inverse fb. Single- and multi-lepton channels are treated together in one analysis. An increase in sensitivity is obtained by simultaneously fitting the number of events in statistically independent signal regions, and the shapes of distributions within those regions. A dedicated signal region is introduced to be sensitive to decay cascades of SUSY particles with small mass differences ("compressed SUSY"). Background uncertainties are constrained by fitting to the jet multiplicity distribution in background control regions. Observations are consistent with Standard Model expectations, and limits are set or extended on a number of SUSY models.
We report a study of final states containing a W boson and hadronic jets, produced in proton-proton collisions at a center-of-mass energy of 7 TeV. The data were collected with the ATLAS detector at the CERN LHC and comprise the full 2010 data sample of 36 pb^-1. Cross sections are determined using both the electron and muon decay modes of the W boson and are presented as a function of inclusive jet multiplicity, N_jet, for up to five jets. At each multiplicity, cross sections are presented as a function of jet transverse momentum, the scalar sum of the transverse momenta of the charged lepton, missing transverse momentum, and all jets, the invariant mass spectra of jets, and the rapidity distributions of various combinations of leptons and final-state jets. The results, corrected for all detector effects and for all backgrounds such as diboson and top quark pair production, are compared with particle-level predictions from perturbative QCD. Leading-order multiparton event generators, normalized to the NNLO total cross section for inclusive W-boson production, describe the data reasonably well for all measured inclusive jet multiplicities. Next-to-leading-order calculations from MCFM, studied here for N_jet >= 2, and BlackHat-Sherpa, studied here for N_jet >= 4, are found to be mostly in good agreement with the data.
The measured W+jets cross section as a function of the jet multiplicity for jet PT > 30 GeV shown for "Born" leptons and for QED corrected "dressed" leptons.
The measured W+jets cross section ratio as a function of jet multiplicity for jet PT > 30 GeV.
The measured W+jets cross section as a function of the pT of the first jet in the event for jet multiplicities >= 1 and jet PT > 30 GeV shown for "Born" leptons and for QED corrected "dressed" leptons.
A search for doubly-charged Higgs bosons decaying to pairs of electrons and/or muons is presented. The search is performed using a data sample corresponding to an integrated luminosity of 4.7 fb-1 of pp collisions at sqrt(s) = 7 TeV collected by the ATLAS detector at the LHC. Pairs of prompt, isolated, high-pT leptons with the same electric charge (ee, emu, mumu) are selected, and their invariant mass distribution is searched for a narrow resonance. No significant excess over Standard Model background expectations is observed, and limits are placed on the cross section times branching ratio for pair production of doubly-charged Higgs bosons. The masses of doubly-charged Higgs bosons are constrained depending on the branching ratio into these leptonic final states. Assuming pair production, coupling to left-handed fermions, and a branching ratio of 100% for each final state, masses below 409 GeV, 375 GeV, and 398 GeV are excluded for ee, emu, mumu, respectively.
The upper mass limit of the doubly charged Higgs boson as a function of its branching ratio to like sign lepton pairs assuming coupling to left-handed fermions. The results are given separately for each of the lepton pair combinations, electron-electron, electon-muon and muon-muon.
The upper mass limit of the doubly charged Higgs boson as a function of its branching ratio to like sign lepton pairs assuming coupling to right-handed fermions. The results are given separately for each of the lepton pair combinations, electron-electron, electon-muon and muon-muon.
The results of a search for pair production of light top squarks are presented, using 4.7 fb^-1 of sqrt(s) = 7 TeV proton-proton collisions collected with the ATLAS detector at the Large Hadron Collider. This search targets top squarks with masses similar to, or lighter than, the top quark mass. Final states containing exclusively one or two leptons (e, mu), large missing transverse momentum, light-jets and b-jets are used to reconstruct the top squark pair system. Global mass scale variables are used to separate the signal from a large ttbar background. No excess over the Standard Model expectations is found. The results are interpreted in the framework of the Minimal Supersymmetric Standard Model, assuming the top squark decays exclusively to a chargino and a b-quark. Light top squarks with masses between 123-167 GeV are excluded for neutralino masses around 55 GeV.
Expected 95 PCT exclusion limit in the M(stop), M(neutralino) plane in gaugino universality scenario.
Observed 95 PCT exclusion limit in the M(stop), M(neutralino) plane in gaugino universality scenario.
Expected 95 PCT exclusion limit in the M(chargino), M(neutralino) plane in the scenario where M(stop) = 180 GEV.
Distributions sensitive to the underlying event are studied in events containing one or more charged-particle jets produced in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector at the Large Hadron Collider (LHC). These measurements reflect 800 inverse microbarns of data taken during 2010. Jets are reconstructed using the antikt algorithm with radius parameter R varying between 0.2 and 1.0. Distributions of the charged-particle multiplicity, the scalar sum of the transverse momentum of charged particles, and the average charged-particle pT are measured as functions of pT^JET in regions transverse to and opposite the leading jet for 4 GeV < pT^JET < 100 GeV. In addition, the R-dependence of the mean values of these observables is studied. In the transverse region, both the multiplicity and the scalar sum of the transverse momentum at fixed pT^JET vary significantly with R, while the average charged-particle transverse momentum has a minimal dependence on R. Predictions from several Monte Carlo tunes have been compared to the data; the predictions from Pythia 6, based on tunes that have been determined using LHC data, show reasonable agreement with the data, including the dependence on R. Comparisons with other generators indicate that additional tuning of soft-QCD parameters is necessary for these generators. The measurements presented here provide a testing ground for further development of the Monte Carlo models.
Mean value of N(C=CHARGED) v jet PT for R=0.2.
Mean value of N(C=CHARGED) v jet PT for R=0.4.
Mean value of N(C=CHARGED) v jet PT for R=0.6.
This letter reports the results of a search for top and bottom squarks from gluino pair production in 4.7 fb^-1 of pp collisions at sqrt(s) = 7 TeV using the ATLAS detector at the LHC. The search is performed in events with large missing transverse momentum and at least three jets identified as originating from a b-quark. Exclusion limits are presented for a variety of gluino-mediated models with gluino masses up to 1 TeV excluded.
Figure 2-a. Observed limit +1sigma-th.
Figure 2-a. Observed limit.
Figure 2-a. Observed limit -1sigma-th.
Measurements are presented of differential cross-sections for top quark pair production in pp collisions at sqrt(s) = 7 TeV relative to the total inclusive top quark pair production cross-section. A data sample of 2.05/fb recorded by the ATLAS detector at the Large Hadron Collider is used. Relative differential cross-sections are derived as a function of the invariant mass, the transverse momentum and the rapidity of the top quark pair system. Events are selected in the lepton (electron or muon) + jets channel. The background-subtracted differential distributions are corrected for detector effects, normalized to the total inclusive top quark pair production cross-section and compared to theoretical predictions. The measurement uncertainties range typically between 10% and 20% and are generally dominated by systematic effects. No significant deviations from the Standard Model expectations are observed.
Relative differential cross-section (1/SIG)*D(SIG)/DM(ttbar) measured in the e+jets, mu+jets and the combined lepton+jets channel.
Relative differential cross-section (1/SIG)*D(SIG)/DPT(ttbar) measured in the e+jets, mu+jets and the combined lepton+jets channel.
Relative differential cross-section (1/SIG)*D(SIG)/DYRAP(ttbar) measured in the e+jets, mu+jets and the combined lepton+jets channel.
This paper presents a measurement of the W^+W^- production cross section in pp collisions at sqrt{s}=7 TeV. The leptonic decay channels are analyzed using data corresponding to an integrated 4.6 fb-1 collected with the ATLAS detector at the Large Hadron Collider. The W^+W^- production cross section sigma(pp -> W^+W^-+X) is measured to be 51.9 +- 2.0 (stat) +- 3.9 (syst) +- 2.0 (lumi) pb, compatible with the Standard Model prediction of 44.7 +2.1 -1.9 pb. A measurement of the normalized fiducial cross section as a function of the leading lepton transverse momentum is also presented. The reconstructed transverse momentum distribution of the leading lepton is used to extract limits on anomalous WWZ and WWgamma couplings.
The measured fiducial cross section in the three channels . The first systematic (sys) error is the combined systematic uncertainty excluding that of the luminosity. The second (sys) error is the uncertainty on the luminosity.
The measured total cross section in the three channels. The first systematic (sys) error is the combined systematic uncertainty excluding that of the luminosity. The second (sys) error is the uncertainty on the luminosity.
The measured total cross section (combined). The first systematic (sys) error is the combined systematic uncertainty excluding that of the luminosity. The second (sys) error is the uncertainty on the luminosity.
The inclusive jet cross-section has been measured in proton-proton collisions at sqrt(s)=2.76 TeV in a dataset corresponding to an integrated luminosity of 0.20pb-1 collected with the ATLAS detector at the Large Hadron Collider in 2011. Jets are identified using the anti-kt algorithm with two radius parameters of 0.4 and 0.6. The inclusive jet double-differential cross-section is presented as a function of the jet transverse momentum pT and jet rapidity y, covering a range of 20 <= pT < 430 GeV and |y| < 4.4. The ratio of the cross-section to the inclusive jet cross-section measurement at sqrt(s)=7 TeV, published by the ATLAS Collaboration, is calculated as a function of both transverse momentum and the dimensionless quantity xT = 2 pT / sqrt(s), in bins of jet rapidity. The systematic uncertainties on the ratios are significantly reduced due to the cancellation of correlated uncertainties in the two measurements. Results are compared to the prediction from next-to-leading order perturbative QCD calculations corrected for non-perturbative effects, and next-to-leading order Monte Carlo simulation. Furthermore, the ATLAS jet cross-section measurements at sqrt(s)=2.76 TeV and sqrt(s)=7 TeV are analysed within a framework of next-to-leading order perturbative QCD calculations to determine parton distribution functions of the proton, taking into account the correlations between the measurements.
The measured inclusive jet double-differential cross section in the rapidity bin |y| < 0.3 for anti-kt jets with R = 0.4 as a function of the jet PT. The first (sys) error is the combined correlated systematic error and the second the combined uncorrelated systematic error, excluding the luminosity uncertainty. Also shown are the multiplicative non-perturbative corrections, NPcorr.
The measured inclusive jet double-differential cross section in the rapidity bin 0.3 <= |y| < 0.8 for anti-kt jets with R = 0.4 as a function of the jet PT. The first (sys) error is the combined correlated systematic error and the second the combined uncorrelated systematic error, excluding the luminosity uncertainty. Also shown are the multiplicative non-perturbative corrections, NPcorr.
The measured inclusive jet double-differential cross section in the rapidity bin 0.8 <= |y| < 1.2 for anti-kt jets with R = 0.4 as a function of the jet PT. The first (sys) error is the combined correlated systematic error and the second the combined uncorrelated systematic error, excluding the luminosity uncertainty. Also shown are the multiplicative non-perturbative corrections, NPcorr.
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