Search results for "Collisions."
showing 10 items of 533 documents
Cross section for bb¯ production via dielectrons in d + Au collisions at √sNN = 200 GeV
2015
We report a measurement of e+e− pairs from semileptonic heavy-flavor decays in d + Au collisions at √sNN = 200 GeV. By exploring the mass and transverse-momentum dependence of the yield, the bottom decay contribution can be isolated from charm, and quantified by comparison to PYTHIA and MC@NLO simulations. The resulting bb¯-production cross section is σdAu bb¯ = 1.37 ± 0.28 (stat) ± 0.46 (syst) mb, which is equivalent to a nucleon-nucleon cross section of σ NN bb = 3.4 ± 0.8 (stat) ± 1.1 (syst) μb. peerReviewed
Charged jet cross sections and properties in proton-proton collisions at $\sqrt{s}=7$ TeV
2015
The differential charged jet cross sections, jet fragmentation distributions, and jet shapes are measured in minimum bias proton-proton collisions at centre-of-mass energy $\sqrt{s}=7$ TeV using the ALICE detector at the LHC. Jets are reconstructed from charged particle momenta in the mid-rapidity region using the sequential recombination $k_{\rm T}$ and anti-$k_{\rm T}$ as well as the SISCone jet finding algorithms with several resolution parameters in the range $R=0.2$ to $0.6$. Differential jet production cross sections measured with the three jet finders are in agreement in the transverse momentum ($p_{\rm T}$) interval $20<p_{\rm T}^{\rm jet,ch}<100$ GeV/$c$. They are also consistent w…
Measurement of transverse energy at midrapidity in Pb-Pb collisions at √sNN = 2.76 TeV
2016
We report the transverse energy (ET) measured with ALICE at midrapidity in Pb-Pb collisions at √sNN = 2.76 TeV as a function of centrality. The transverse energy was measured using identified single-particle tracks. The measurement was cross checked using the electromagnetic calorimeters and the transverse momentum distributions of identified particles previously reported by ALICE. The results are compared to theoretical models as well as to results from other experiments. The mean ET per unit pseudorapidity (η), dET/dη , in 0%–5% central collisions is 1737 ± 6(stat.) ± 97(sys.) GeV. We find a similar centrality dependence of the shape of dET/dη as a function of the number of participating …
Realization of time-resolved two-vacuum-ultraviolet-photon ionization
2009
International audience; Ultrafast dynamics of excited molecules is studied through time-resolved two-vacuum-ultraviolet (vuv)- photon ionization using a nonlinear volume autocorrelator unit. The two-vuv-photon process is induced by the intense fifth harmonic radiation of a femtosecond Ti:sapphire laser. In a proof-of-principle experiment, ultrafast dynamics of excited ethylene and oxygen molecules are investigated. Molecular decay times are deduced by comparing the experimental data with the results of a numerical model that accounts for the spatial and temporal characteristics of the harmonic field. The present experiments pave a convenient way for time domain investigations in the vuv-xuv s…
On the friction/tangential restitution problem: Independent friction-restitution modeling of sphere rebound with arbitrary spin
2023
Most descriptions of collision events introduce coefficients of friction and tangential restitution which vary significantly with the impact angle, in contrast with the independence of the normal coefficient of restitution with this parameter. A redefinition of the coefficients of friction and tangential restitution based on the idea that friction and restitution effects can be treated as being mutually independent, provides a satisfactory description of experimental data using a ‘constant’ restitution coefficient independent on the impact angle. This independent friction-restitution modeling is developed here for the rebound of a homogeneous sphere having an arbitrary spin on a rough massi…
Measurement of the top quark charge in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector
2013
A measurement of the top quark electric charge is carried out in the ATLAS experiment at the Large Hadron Collider using 2.05 fb[superscript −1] of data at a centre-of-mass energy of 7 TeV. In units of the elementary electric charge, the top quark charge is determined to be 0.64 ± 0.02 (stat.) ± 0.08 (syst.) from the charges of the top quark decay products in single lepton t[¯ over t] candidate events. This excludes models that propose a heavy quark of electric charge −4/3, instead of the Standard Model top quark, with a significance of more than 8σ.
Search for photonic signatures of gauge-mediated supersymmetry in 8TeV pp collisions with the ATLAS detector
2015
A search is presented for photonic signatures motivated by generalized models of gauge-mediated supersymmetry breaking. This search makes use of 20.3 fb[superscript −1] of proton-proton collision data at √s = 8 TeV recorded by the ATLAS detector at the LHC, and explores models dominated by both strong and electroweak production of supersymmetric partner states. Four experimental signatures incorporating an isolated photon and significant missing transverse momentum are explored. These signatures include events with an additional photon, lepton, b-quark jet, or jet activity not associated with any specific underlying quark flavor. No significant excess of events is observed above the Stand…
Nuclear Dependence of the Transverse-Single-Spin Asymmetry for Forward Neutron Production in Polarized p+A Collisions at √sNN = 200 GeV
2018
During 2015, the Relativistic Heavy Ion Collider (RHIC) provided collisions of transversely polarized protons with Au and Al nuclei for the first time, enabling the exploration of transverse-single-spin asymmetries with heavy nuclei. Large single-spin asymmetries in very forward neutron production have been previously observed in transversely polarized p + p collisions at RHIC, and the existing theoretical framework that was successful in describing the single-spin asymmetry in p + p collisions predicts only a moderate atomic-mass-number ( A ) dependence. In contrast, the asymmetries observed at RHIC in p + A collisions showed a surprisingly strong A dependence in inclusive forward neutron …
Forward-central two-particle correlations in p–Pb collisions at √sNN = 5.02 TeV
2016
Two-particle angular correlations between trigger particles in the forward pseudorapidity range (2.5 2 GeV/c. peerReviewed
Measurement of dielectron production in central Pb-Pb collisions at √sNN = 2.76 TeV
2019
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. The first measurement of dielectron (e + e −) production in central (0 – 10 %) Pb – Pb collisions at √sNN=2.76TeV 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 < mee < 3.5 GeV / c2. The ratio of data and the cocktail of hadronic contributions without vacuum ρ0 is measured in the invariant-mass range 0.15 < mee < 0.7 GeV / c2, w…