Search results for "Collision"
showing 10 items of 908 documents
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–…
Observation of Collisional De-Excitation Phenomena in Plutonium
2022
Proceedings for the "virtual Workshop on the Atomic Structure of Actinides & Related Topics" conference submitted to the special issue of Atoms "Atomic Structure of the Heaviest Elements". A program of research towards the high-resolution optical spectroscopy of actinide elements for the study of fundamental nuclear structure is currently ongoing at the IGISOL facility of the University of Jyväskylä. One aspect of this work is the development of a gas-cell-based actinide laser ion source using filament-based dispensers of long-lived actinide isotopes. We have observed prominent phenomena in the resonant laser ionization process specific to the gaseous envir…
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…
Neutral pion and η meson production at midrapidity in Pb-Pb collisions at √sNN = 2.76 TeV
2018
Neutral pion and η meson production in the transverse momentum range 1 < p T < 20 GeV / c have been measured at midrapidity by the ALICE experiment at the Large Hadron Collider (LHC) in central and semicentral Pb-Pb collisions at √ s NN = 2.76 TeV. These results were obtained using the photon conversion method as well as the Photon Spectrometer (PHOS) and Electromagnetic Calorimeter detectors. The results extend the upper p T reach of the previous ALICE π 0 measurements from 12 to 20 GeV / c and present the first measurement of η meson production in heavy-ion collisions at the LHC. The η / π 0 ratio is similar for the two centralities and reaches at high p T a plateau value of 0.457 ± 0 . 0…