Search results for "Heavy-ion"
showing 10 items of 119 documents
Measuring the non-linear hydrodynamic response of higher flow harmonics in Pb-Pb at sqrt(s_NN)=2.76 TeV
2017
Ultrarelativistisissa raskasionitörmäyksissä syntyvän kvarkki-gluoniplasman (QGP) dynamiikkaa on relativistisella hydrodynamiikalla kuvattu erittäin vakuuttavasti. Teorian vapaa parametri, keskimääräinen viskositeetti-entropiasuhde, on kuitenkin vielä tarkasti määrittämättä. Alustamalla törmäyksen alkutila teoreettisesti sekä soveltamalla relativistista hydrodynamiikkaa QGP:n evoluution mallintamiseen, saadaan viskositeettia tarkastelemalla käsitys QGP:n rakennesosien välisten vuorovaikutusten vahvuuksista, minkä lisäksi voidaan ymmärtää plasman evoluutioon vaikuttavia tekijöitä. Tavanomaisesti QGP:n viskositeetti määritetään vertailemalla teoreettisen alkutilan eksentrisyyden lineaarista s…
Exploration of jet substructure using iterative declustering in pp and Pb–Pb collisions at LHC energies
2020
The ALICE collaboration at the CERN LHC reports novel measurements of jet substructure in pp collisions at $\sqrt{s}$= 7 TeV and central Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 2.76 TeV. Jet substructure of track-based jets is explored via iterative declustering and grooming techniques. We present the measurement of the momentum sharing of two-prong substructure exposed via grooming, the $z_{\rm{g}}$, and its dependence on the opening angle, in both pp and Pb-Pb collisions. We also present the first measurement of the distribution of the number of branches obtained in the iterative declustering of the jet, which is interpreted as the number of its hard splittings. In Pb-Pb collisions, we…
Freeze-out radii extracted from three-pion cumulants in pp, p–Pb and Pb–Pb collisions at the LHC
2014
In high-energy collisions, the spatio-temporal size of the particle production region can be measured using the Bose-Einstein correlations of identical bosons at low relative momentum. The source radii are typically extracted using two-pion correlations, and characterize the system at the last stage of interaction, called kinetic freeze-out. In low-multiplicity collisions, unlike in high-multiplicity collisions, two-pion correlations are substantially altered by background correlations, e.g. mini-jets. Such correlations can be suppressed using three-pion cumulant correlations. We present the first measurements of the size of the system at freeze-out extracted from three-pion cumulant correl…
ϕ meson production in p+Al, p+Au, d+Au, and 3He+Au collisions at √sNN = 200 GeV
2022
Small nuclear collisions are mainly sensitive to cold-nuclear-matter effects; however, the collective behavior observed in these collisions shows a hint of hot-nuclear-matter effects. The identified-particle spectra, especially the ϕ mesons which contain strange and antistrange quarks and have a relatively small hadronic-interaction cross section, are a good tool to study these effects. The PHENIX experiment has measured ϕ mesons in a specific set of small collision systems p+Al, p+Au, and 3He+Au, as well as d+Au [Adare et al., Phys. Rev. C 83, 024909 (2011)], at √sNN=200 GeV. The transverse-momentum spectra and nuclear-modification factors are presented and compared to theoretical-model pr…
Heavy ions at the Future Circular Collider
2016
The Future Circular Collider (FCC) Study is aimed at assessing the physics potential and the technical feasibility of a new collider with centre-of-mass energies, in the hadron-hadron collision mode, seven times larger than the nominal LHC energies. Operating such machine with heavy ions is an option that is being considered in the accelerator design studies. It would provide, for example, Pb-Pb and p-Pb collisions at sqrt{s_NN} = 39 and 63 TeV, respectively, per nucleon-nucleon collision, with integrated luminosities above 30 nb^-1 per month for Pb-Pb. This is a report by the working group on heavy-ion physics of the FCC Study. First ideas on the physics opportunities with heavy ions at th…
Investigations of Anisotropic Flow Using Multiparticle Azimuthal Correlations in pp, p-Pb, Xe-Xe, and Pb-Pb Collisions at the LHC
2019
Measurements of anisotropic flow coefficients ($v_n$) and their cross-correlations using two- and multi-particle cumulant methods are reported in collisions of pp at $\sqrt{s} = 13$ TeV, p-Pb at $\sqrt{s_{_{\rm NN}}} = 5.02$ TeV, Xe-Xe at $\sqrt{s_{_{\rm NN}}} = 5.44$ TeV, and Pb-Pb at $\sqrt{s_{_{\rm NN}}} = 5.02$ TeV recorded with the ALICE detector. The multiplicity dependence of $v_n$ is studied in a very wide range from 20 to 3000 particles produced in the mid-rapidity region $|��|<0.8$ for the transverse momentum range $0.2 < p_{\rm T} < 3.0$ GeV/$c$. An ordering of the coefficients $v_2 > v_3 > v_4$ is found in pp and p-Pb collisions, similar to that seen in large coll…
First measurement of quarkonium polarization in nuclear collisions at the LHC
2021
The polarization of inclusive J/$\psi$ and $\Upsilon(1{\rm S})$ produced in Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}=5.02$ TeV at the LHC is measured with the ALICE detector. The study is carried out by reconstructing the quarkonium through its decay to muon pairs in the rapidity region $2.5<y<4$ and measuring the polar and azimuthal angular distributions of the muons. The polarization parameters $\lambda_{\theta}$, $\lambda_{\phi}$ and $\lambda_{\theta\phi}$ are measured in the helicity and Collins-Soper reference frames, in the transverse momentum interval $2<p_{\rm T}<10$ GeV/$c$ and $p_{\rm T}<15$ GeV/$c$ for the J/$\psi$ and $\Upsilon(1{\rm S})$, respectively. The polarization parameter…
Performance of the ALICE experiment at the CERN LHC
2014
ALICE is the heavy-ion experiment at the CERN Large Hadron Collider. The experiment continuously took data during the first physics campaign of the machine from fall 2009 until early 2013, using proton and lead-ion beams. In this paper we describe the running environment and the data handling procedures, and discuss the performance of the ALICE detectors and analysis methods for various physics observables.
Nucleon dissociation and incoherent J/ψ photoproduction on nuclei in ion ultraperipheral collisions at the CERN Large Hadron Collider
2019
Using the general notion of cross section fluctuations in hadron-nucleus scattering at high energies, we derive an expression for the cross section of incoherent J / ψ photoproduction on heavy nuclei d σ γ A → J / ψ Y / d t , which includes both elastic d σ γ p → J / ψ p / d t and proton-dissociation d σ γ p → J / ψ Y / d t photoproduction on target nucleons. We find that, with good accuracy, d σ γ A → J / ψ Y / d t can be expressed as a product of the sum of the d σ γ p → J / ψ p / d t and d σ γ p → J / ψ Y / d t cross sections, which have been measured at HERA, and the common nuclear shadowing factor, which is calculated using the leading twist nuclear shadowing model. Our prediction for …
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…