Search results for " collision"
showing 10 items of 629 documents
Event-by-event fluctuations in a perturbative QCD + saturation + hydrodynamics model: Determining QCD matter shear viscosity in ultrarelativistic hea…
2016
We introduce an event-by-event perturbative-QCD + saturation + hydro (“EKRT”) framework for ultrarelativistic heavy-ion collisions, where we compute the produced fluctuating QCD-matter energy densities from next-to-leading-order perturbative QCD using a saturation conjecture to control soft-particle production and describe the space-time evolution of the QCD matter with dissipative fluid dynamics, event by event. We perform a simultaneous comparison of the centrality dependence of hadronic multiplicities, transverse momentum spectra, and flow coefficients of the azimuth-angle asymmetries against the LHC and RHIC measurements. We compare also the computed event-by-event probability distribut…
Neutron skin and centrality classification in high-energy heavy-ion collisions at the LHC
2015
The concept of centrality in high-energy nuclear collisions has recently become a subject of an active debate. In particular, the experimental methods to determine the centrality that have given reasonable results for many observables in high-energy lead-lead collisions at the LHC have led to surprising behaviour in the case of proton-lead collisions. In this letter, we discuss the possibility to calibrate the experimental determination of centrality by asymmetries caused by mutually different spatial distributions of protons and neutrons inside the nuclei --- a well-known phenomenon in nuclear physics known as the neutron-skin effect.
Temperature dependence of sodium and ionized calcium resonance lines perturbed by helium
2014
International audience; Traces of heavy metals in cool DZ white dwarf stars may be attributed to the accretion of circumstellar dust thought to originate from tidal disruption of rocky parent bodies. Spectra of such stars therefore provide a unique opportunity to study the composition of extrasolar planetary systems. The determination of metal abundances from stellar spectra depends on stellar atmospheric parameters and an accurate prior knowledge of the collision broadening of the line profiles by the most common constituents of the stellar atmosphere. For this purpose, we present theoretical absorption spectra of Na and Ca+ broadened by He for the conditions prevailing in cool white dwarf…
Sapphire-bearing magmatic rocks trace the boundary between paleo-continents: A case study of Ilmenogorsky alkaline complex, Uralian collision zone of…
2021
Abstract Metamorphic gem corundum (mainly ruby) deposits are robust indicators of continent-continent collision processes. However, a systematic link of primary magmatic blue sapphire occurrences to orogenic belts is less understood. An example is the Ilmenogorsky alkaline complex, within the Ilmen Mountains region and part of the Uralian orogenic belt. The mobile belt is a product of the collision among Kazakhstania, Laurussia, and Siberia continents prior to the closure of the Paleo-Uralian ocean and formation of the Laurasia supercontinent (330–250 Ma). It is believed that the alkaline complex became inсluded into the separate Sysertsk-Ilmenogorsk microcontinent with unconstrained border…
Forward J/ψ production at high energy: Centrality dependence and mean transverse momentum
2016
Forward rapidity J=ψ meson production in proton-nucleus collisions can be an important constraint of descriptions of the small-x nuclear wave function. In an earlier work we studied this process using a dipole cross section satisfying the Balitsky-Kovchegov equation, fit to HERA inclusive data and consistently extrapolated to the nuclear case using a standard Woods-Saxon distribution. In this paper we present further calculations of these cross sections, studying the mean transverse momentum of the meson and the dependence on collision centrality. We also extend the calculation to backward rapidities using nuclear parton distribution functions. We show that the parametrization is overall ra…
Inclusive J/ψ production in Xe–Xe collisions at √sNN = 5.44 TeV
2018
Inclusive J/ψ production is studied in Xe–Xe interactions at a centre-of-mass energy per nucleon pair of √sNN = 5.44 TeV, using the ALICE detector at the CERN LHC. The J/ψ meson is reconstructed via its decay into a muon pair, in the centre-of-mass rapidity interval 2.5 < y < 4 and down to zero transverse momentum. In this Letter, the nuclear modification factors RAA for inclusive J/ψ, measured in the centrality range 0–90% as well as in the centrality intervals 0–20% and 20–90% are presented. The RAA values are compared to previously published results for Pb–Pb collisions at √sNN = 5.02 TeV and to the calculation of a transport model. A good agreement is found between Xe–Xe and Pb–Pb resul…
J/ψ Elliptic Flow in Pb-Pb Collisions at √sNN = 5.02 TeV
2017
We report a precise measurement of the J / ψ elliptic flow in Pb-Pb collisions at √ s N N = 5.02 TeV with the ALICE detector at the LHC. The J / ψ mesons are reconstructed at midrapidity ( | y | < 0.9 ) in the dielectron decay channel and at forward rapidity ( 2.5 < y < 4.0 ) in the dimuon channel, both down to zero transverse momentum. At forward rapidity, the elliptic flow v 2 of the J / ψ is studied as a function of the transverse momentum and centrality. A positive v 2 is observed in the transverse momentum range 2 < p T < 8 GeV / c in the three centrality classes studied and confirms with higher statistics our earlier results at √ s N N = 2.76 TeV in semicentral collisions.…
J/ψ suppression at forward rapidity in Pb–Pb collisions at √sNN = 5.02 TeV
2017
The inclusive J/ψ production has been studied in Pb–Pb and pp collisions at the centre-of-mass energy per nucleon pair √sNN = 5.02 TeV, using the ALICE detector at the CERN LHC. The J/ψ meson is reconstructed, in the centre-of-mass rapidity interval 2.5 < y < 4 and in the transverse-momentum range pT < 12 GeV/c, via its decay to a muon pair. In this Letter, we present results on the inclusive J/ψ cross section in pp collisions at √s = 5.02 TeV and on the nuclear modification factor RAA. The latter is presented as a function of the centrality of the collision and, for central collisions, as a function of the transverse momentum pT of the J/ψ. The measured RAA values indicate a suppression of…
Forward J/ψ production in U+U collisions at √sNN = 193 GeV
2016
The invariant yields, dN/dy, for J/ψ production at forward rapidity (1.2 < |y| < 2.2) in U + U collisions at √sNN = 193 GeV have been measured as a function of collision centrality. The invariant yields and nuclearmodification factor RAA are presented and compared with those from Au + Au collisions in the same rapidity range. Additionally, the direct ratio of the invariant yields from U + U and Au + Au collisions within the same centrality class is presented, and used to investigate the role of cc¯ coalescence. Two different parametrizations of the deformed Woods-Saxon distribution were used in Glauber calculations to determine the values of the number of nucleon-nucleon collisions in each …
Search for collectivity with azimuthal J/ψ -hadron correlations in high multiplicity p–Pb collisions at √sNN = 5.02 and 8.16 TeV
2018
We present a measurement of azimuthal correlations between inclusive J/ψ and charged hadrons in p–Pb collisions recorded with the ALICE detector at the CERN LHC. The J/ψ are reconstructed at forward (p-going, ) and backward (Pb-going, ) rapidity via their decay channel, while the charged hadrons are reconstructed at mid-rapidity (). The correlations are expressed in terms of associated charged-hadron yields per J/ψ trigger. A rapidity gap of at least 1.5 units is required between the trigger J/ψ and the associated charged hadrons. Possible correlations due to collective effects are assessed by subtracting the associated per-trigger yields in the low-multiplicity collisions from those in the…