Search results for "Collisions"
showing 10 items of 558 documents
Highly occupied gauge theories in 2 + 1 dimensions : a self-similar attractor
2019
Motivated by the boost-invariant Glasma state in the initial stages in heavy-ion collisions, we perform classical-statistical simulations of SU(2) gauge theory in 2+1 dimensional space-time both with and without a scalar field in the adjoint representation. We show that irrespective of the details of the initial condition, the far-from-equilibrium evolution of these highly occupied systems approaches a unique universal attractor at high momenta that is the same for the gauge and scalar sectors. We extract the scaling exponents and the form of the distribution function close to this non-thermal fixed point. We find that the dynamics are governed by an energy cascade to higher momenta with sc…
Minijet initial state of heavy-ion collisions from next-to-leading order perturbative QCD
2014
A Monte Carlo simulation for the elastic energy loss of high-energy partons in a strongly interacting medium
2012
Jet fragmentation transverse momentum distributions in pp and p-Pb collisions at √s, √sNN = 5.02 TeV
2021
Jet fragmentation transverse momentum (jT) distributions are measured in proton-proton (pp) and proton-lead (p-Pb) collisions at √sNN = 5.02 TeV with the ALICE experiment at the LHC. Jets are reconstructed with the ALICE tracking detectors and electromagnetic calorimeter using the anti-kT algorithm with resolution parameter R = 0.4 in the pseudorapidity range |η| < 0.25. The jT values are calculated for charged particles inside a fixed cone with a radius R = 0.4 around the reconstructed jet axis. The measured jT distributions are compared with a variety of parton-shower models. Herwig and Pythia 8 based models describe the data well for the higher jT region, while they underestimate the low…
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…
Heavy quarkonium suppression in a fireball
2018
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…