Search results for " collisions"
showing 10 items of 516 documents
Λc+ production in Pb–Pb collisions at √sNN = 5.02 TeV
2019
A measurement of the production of prompt Λc+ baryons in Pb–Pb collisions at √sNN = 5.02 TeV with the ALICE detector at the LHC is reported. The Λc+ and Λ‾c− were reconstructed at midrapidity (|y|<0.5) via the hadronic decay channel Λc+ → pKS0 (and charge conjugate) in the transverse momentum and centrality intervals 6<pT <12 GeV/c and 0–80%. The Λc+/D0 ratio, which is sensitive to the charm quark hadronisation mechanisms in the medium, is measured and found to be larger than the ratio measured in minimum-bias pp collisions at √s = 7 TeV and in p–Pb collisions at √sNN = 5.02 TeV. In particular, the values in p–Pb and Pb–Pb collisions differ by about two standard deviations of the combined s…
Measurement of the cross section for top-quark pair production in pp collisions at √s = 7TeV with the ATLAS detector using final states with two high…
2012
A measurement is reported of the production cross section of top-quark pairs (tt¯) in proton-proton collisions at a center-of-mass energy of 7 TeV recorded with the ATLAS detector at the LHC. Candidate events have a signature consistent with containing two isolated leptons, large missing transverse momentum, and at least two jets. Using a data sample corresponding to an integrated luminosity of 0.70 fb−1, a tt¯ production cross section σtt¯=176±5(stat.)+14−11(syst.)±8(lum.) pb is measured for an assumed top-quark mass of mt = 172.5 GeV. This measurement is in good agreement with Standard Model predictions.
Search for charged Higgs bosons through the violation of lepton universality in t(t)over-bar events using pp collision data at root s=7 TeV with the …
2013
In several extensions of the Standard Model, the top quark can decay into a bottom quark and a light charged Higgs boson H [superscript +], t → bH [superscript +], in addition to the Standard Model decay t → bW. Since W bosons decay to the three lepton generations equally, while H [superscript +] may predominantly decay into τν, charged Higgs bosons can be searched for using the violation of lepton universality in top quark decays. The analysis in this paper is based on 4.6 fb[superscript −1] of proton-proton collision data at √s = 7 TeV collected by the ATLAS experiment at the Large Hadron Collider. Signatures containing leptons (e or μ) and/or a hadronically decaying τ (τ [subscript had])…
Azimuthal harmonics of color fields in a high energy nucleus
2015
Recent experimental results have revealed a surprisingly rich structure of multiparticle azimuthal correlations in high energy proton-nucleus collisions. Final state collective effects can be responsible for many of the observed effects, but it has recently been argued that a part of these correlations are present already in the wavefunctions of the colliding particles. We evaluate the momentum space 2-particle cumulant azimuthal anisotropy coefficients v_n{2}, n=2,3,4 from fundamental representation Wilson line distributions describing the high energy nucleus. These would correspond to the flow coefficients in very forward proton nucleus scattering. We find significant differences beteen W…
Transverse momentum spectra and nuclear modification factors of charged particles in Xe–Xe collisions at √sNN = 5.44 TeV
2019
Transverse momentum (pT) spectra of charged particles at mid-pseudorapidity in Xe–Xe collisions at √sNN = 5.44 TeV measured with the ALICE apparatus at the Large Hadron Collider are reported. The kinematic range 0.15 10 GeV/c. The centrality dependence of the ratio of the average transverse momentum (pT) in Xe–Xe collisions over Pb–Pb collision at √s = 5.02 TeV is compared to hydrodynamical model calculations. peerReviewed
Measurement of Z0-boson production at large rapidities in Pb–Pb collisions at √sNN = 5.02 TeV
2018
The production of Z0 bosons at large rapidities in Pb–Pb collisions at √sNN=5.02TeV is reported. Z0 candidates are reconstructed in the dimuon decay channel (Z0→μ+μ−), based on muons selected with pseudo-rapidity −4.020GeV/c. The invariant yield and the nuclear modification factor, RAA, are presented as a function of rapidity and collision centrality. The value of RAA for the 0–20% central Pb–Pb collisions is 0.67±0.11(stat.)±0.03(syst.)±0.06(corr. syst.), exhibiting a deviation of 2.6σ from unity. The results are well-described by calculations that include nuclear modifications of the parton distribution functions, while the predictions using vacuum PDFs deviate from data by 2.3σ in the 0–…
Direct photon production at low transverse momentum in proton-proton collisions at √s = 2.76 and 8 TeV
2019
Measurements of inclusive and direct photon production at midrapidity in pp collisions at √s=2.76 and 8 TeV are presented by the ALICE experiment at the LHC. The results are reported in transverse momentum ranges of 0.47 GeV/c is at least one σ above unity and consistent with expectations from next-to-leading order pQCD calculations. peerReviewed
Multiplicity dependence of light-flavor hadron production in pp collisions at √s = 7 TeV
2019
Comprehensive results on the production of unidentified charged particles, π±, K±, K0S, K∗(892)0, p, ¯p, ϕ(1020), Λ, ¯¯¯Λ, Ξ−, ¯¯¯Ξ+, Ω−, and ¯¯¯Ω+ hadrons in proton-proton (pp) collisions at √s=7 TeV at midrapidity (|y|<0.5) as a function of charged-particle multiplicity density are presented. In order to avoid autocorrelation biases, the actual transverse momentum (pT) spectra of the particles under study and the event activity are measured in different rapidity windows. In the highest multiplicity class, the charged-particle density reaches about 3.5 times the value measured in inelastic collisions. While the yield of protons normalized to pions remains approximately constant as a functi…
Measurement of dielectron production in central Pb-Pb collisions at √sNN = 2.76 TeV
2019
The first measurement of dielectron ( e + e − ) production in central ( 0 – 10 % ) Pb–Pb collisions at √ s NN = 2.76 TeV at the LHC is presented. The dielectron invariant-mass spectrum is compared to the expected contributions from hadron decays in the invariant-mass range 0 < m ee < 3.5 GeV / c 2 . The ratio of data and the cocktail of hadronic contributions without vacuum ρ 0 is measured in the invariant-mass range 0.15 < m ee < 0.7 GeV / c 2 , where an excess of dielectrons is observed in other experiments, and its value is 1.40 ± 0.28 ( stat . ) ± 0.08 ( syst . ) ± 0.27 ( cocktail ) . The dielectron spectrum measured in the invariant mass range 0 < m ee < 1 GeV / c 2 is consistent with …
Suppression of Λ(1520) resonance production in central Pb-Pb collisions at √sNN = 2.76 TeV
2019
The production yield of the Λ(1520) baryon resonance is measured at midrapidity in Pb-Pb collisions at √sNN = 2.76 TeV with the ALICE detector at the Large Hadron Collider (LHC). The measurement is performed in the Λ(1520)→ pK− (and charge conjugate) hadronic decay channel as a function of the transverse momentum (pT) and collision centrality. The ratio of the pT-integrated production of Λ(1520) baryons relative to Λ baryons in central collisions is suppressed by about a factor of 2 with respect to peripheral collisions. This is the first observation of the suppression of a baryonic resonance at the LHC and the first 3σ evidence of Λ(1520) suppression within a single collision system. The m…