Search for collectivity with azimuthal J/psi-hadron correlations in high multiplicity p-Pb collisions at ,root s(NN)=5.02 and 8.16 TeV

We present a measurement of azimuthal correlations between inclusive J/psi and charged hadrons in p-Pb collisions recorded with the ALICE detector at the CERN LHC. The J/psi are reconstructed at forward (p-going, 2.03 <y <3.53) and backward (Pb-going, -4.46 <y <-2.96) rapidity via their mu(+)mu(-) decay channel, while the charged hadrons are reconstructed at mid-rapidity (vertical bar eta vertical bar <1.8). The correlations are expressed in terms of associated charged-hadron yields per W . trigger. A rapidity gap of at least 1.5 units is required between the trigger J/psi 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 high-multiplicity collisions. After the subtraction, we observe a strong indication of remaining symmetric structures at Delta phi approximate to 0 and Delta phi approximate to pi), similar to those previously found in two-particle correlations at middle and forward rapidity. The corresponding second-order Fourier coefficient (v(2) ) in the transverse momentum interval between 3 and 6 GeV/c is found to be positive with a significance of about 5 sigma. The obtained results are similar to the J/psi v(2) coefficients measured in Pb-Pb collisions at root s(NN) = 5.02 TeV, suggesting a common mechanism at the origin of the J/psi v(2) . (C) 2018 The Author. Published by Elsevier B.V.Peer reviewe

Multiplicity dependence of jet-like two-particle correlation structures in p-Pb collisions at 1asNN=5.02 TeV

Two-particle angular correlations between unidentified charged trigger and associated particles are measured by the ALICE detector in p\u2013Pb collisions at a nucleon\u2013nucleon centre-of-mass energy of 5.02 TeV. The transverse-momentum range 0.7 < pT,assoc < pT,trig < 5.0 GeV/c is examined, to include correlations induced by jets originating from low momentum-transfer scatterings (minijets). The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range |\u3b7| < 0.9. The near-side long-range pseudorapidity correlations observed in high-multiplicity p\u2013Pb collisions are subtracted from both near-side short-range and away-side correlations in order to remove the non-jet-like components. The yields in the jet-like peaks are found to be invariant with event multiplicity with the exception of events with low multiplicity. This invariance is consistent with the particles being produced via the incoherent fragmentation of multiple parton\u2013parton scatterings, while the yield related to the previously observed ridge structures is not jet-related. The number of uncorrelated sources of particle production is found to increase linearly with multiplicity, suggesting no saturation of the number of multi-parton interactions even in the highest multiplicity p\u2013Pb collisions. Further, the number scales only in the intermediate multiplicity region with the number of binary nucleon\u2013nucleon collisions estimated with a Glauber Monte-Carlo simulation

Two-particle differential transverse momentum and number density correlations in p-Pb collisions at 5.02 TeV and Pb-Pb collisions at 2.76 TeV at the CERN Large Hadron Collider

We present measurements of two-particle differential number correlation functions R2 and transverse momentum correlation functions P2, obtained from p-Pb collisions at 5.02 TeV and Pb-Pb collisions at 2.76 TeV. The results are obtained by using charged particles in the pseudorapidity range |\u3b7|<1.0 and transverse momentum range 0.2<2.0 GeV/c as a function of pair separation in pseudorapidity, |\u394\u3b7|, azimuthal angle \u394\u3c6, and for several charged-particle multiplicity classes. Measurements are carried out for like-sign and unlike-sign charged-particle pairs separately and combined to obtain charge-independent and charge-dependent correlation functions. We study the evolution of the width of the near-side peak of these correlation functions with collision centrality. Additionally, we study Fourier decompositions of the correlators in \u394\u3c6 as a function of pair separation |\u394\u3b7|. Significant differences in the dependence of their harmonic coefficients on multiplicity classes are found. These differences can be exploited, in theoretical models, to obtain further insight into charged-particle production and transport in heavy-ion collisions. Moreover, an upper limit of nonflow contributions to flow coefficients vn measured in Pb-Pb collisions based on the relative strength of Fourier coefficients measured in p-Pb interactions is estimated

Systematic studies of correlations between different order flow harmonics in Pb-Pb collisions at root s(NN)=2.76 TeV

The correlations between event-by-event fluctuations of anisotropic flow harmonic amplitudes have been measured in Pb-Pb collisions at root s(NN) = 2.76 TeV with the ALICE detector at the Large Hadron Collider. The results are reported in terms of multiparticle correlation observables dubbed symmetric cumulants. These observables are robust against biases originating from nonflow effects. The centrality dependence of correlations between the higher order harmonics (the quadrangular v(4) and pentagonal v(5) flow) and the lower order harmonics (the elliptic v(2) and triangular v(3) flow) is presented. The transverse momentum dependences of correlations between v(3) and v(2) and between v(4) and v(2) are also reported. The results are compared to calculations from viscous hydrodynamics and a multiphase transport (AMPT) model calculations. The comparisons to viscous hydrodynamic models demonstrate that the different order harmonic correlations respond differently to the initial conditions and the temperature dependence of the ratio of shear viscosity to entropy density (eta/s). Asmall average value of eta/s is favored independent of the specific choice of initial conditions in the models. The calculations with the AMPT initial conditions yield results closest to the measurements. Correlations among the magnitudes of v(2), v(3), and v(4) show moderate p(T) dependence in midcentral collisions. This might be an indication of possible viscous corrections to the equilibrium distribution at hadronic freeze-out, which might help to understand the possible contribution of bulk viscosity in the hadronic phase of the system. Together with existing measurements of individual flow harmonics, the presented results provide further constraints on the initial conditions and the transport properties of the system produced in heavy-ion collisions

Hot and Cold QCD White Paper from ALICE-USA: Input for 2023 U.S. Long Range Plan for Nuclear Science

The ALICE-USA collaboration presents its plans for the 2023 U.S. Long Range Plan for Nuclear Science

Production of inclusive gamma(1S) and gamma(2S) in p-Pb collisions at, root S-NN=5.02 TeV

We report on the production of inclusive gamma(1S) and gamma(2S) in p-Pb collisions at root S-NN = 5.02 TeV at the LHC. The measurement is performed with the ALICE detector at backward (-4.46 &lt; ycms &lt; 2.96) and forward (2.03 &lt; ycms &lt;3.53) rapidity down to zero transverse momentum. The production cross sections of the gamma(1S) and gamma(2S) are presented, as well as the nuclear modification factor and the ratio of the forward to backward yields of gamma(1S). A suppression of the inclusive gamma(1S) yield in p-Pb collisions with respect to the yield from pp collisions scaled by the number of binary nucleon-nucleon collisions is observed at forward rapidity but not at backward rapidity. The results are compared to theoretical model calculations including nuclear shadowing or partonic energy loss effects. (C) 2014 The Authors. Published by Elsevier B.V

Measurement of dielectron production in central Pb-Pb collisions at root S-NN=2.76 TeV

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&lt;3.5GeV/c2. The ratio of data and the cocktail of hadronic contributions without vacuum ρ0 is measured in the invariant-mass range 0.15&lt;0.7GeV/c2, 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&lt;1GeV/c2 is consistent with the predictions from two theoretical model calculations that include thermal dielectron production from both partonic and hadronic phases with in-medium broadened ρ0 meson. The fraction of direct virtual photons over inclusive virtual photons is extracted for dielectron pairs with invariant mass 0.1&lt;0.3GeV/c2 and in the transverse-momentum intervals 1&lt;2GeV/c and 2&lt;4GeV/c. The measured fraction of virtual direct photons is consistent with the measurement of real direct photons by ALICE and with the expectations from previous dielectron measurements at RHIC within the experimental uncertainties

Neutral pion and eta meson production in p-Pb collisions at root S-NN=5.02 TeV

Neutral pion and \u3b7 meson invariant differential yields were measured in non-single diffractive p\u2013Pb colli- sions at 1asNN = 5.02 TeV with the ALICE experiment at the CERN LHC. The analysis combines results from three complementary photon measurements, utilizing the PHOS and EMCal calorimeters and the Photon Conversion Method. The invariant differential yields of \u3c00 and \u3b7 meson inclu- sive production are measured near mid-rapidity in a broad transverse momentum range of 0.3 4 GeV/c at 0.483 \ub1 0.015stat \ub1 0.015sys . A deviation from m T scaling is observed for pT < 2 GeV/c. The measured \u3b7/\u3c00 ratio is consistent with previous measurements from proton-nucleus and pp collisions over the full pT range. The measured \u3b7/\u3c00 ratio at high pT also agrees within uncertainties with measure- ments from nucleus\u2013nucleus collisions. The \u3c0 0 and \u3b7 yields in p\u2013Pb relative to the scaled pp interpolated reference, RpPb, arepresentedfor0.3< pT <20GeV/cand0.7< pT <20 GeV/c, respectively. The results are compared with theoreti- cal model calculations. The values of RpPb are consistent with unity for transverse momenta above 2 GeV/c. These results support the interpretation that the suppressed yield of neutral mesons measured in Pb\u2013Pb collisions at LHC energies is due to parton energy loss in the hot QCD medium

Charged-particle production as a function of multiplicity and transverse spherocity in pp collisions at root s=5.02 and 13 TeV

We present a study of the inclusive charged-particle transverse momentum (p(T)) spectra as a function of charged-particle multiplicity density at mid-pseudorapidity, dNch/d., in pp collisions at root s = 5.02 and 13TeV covering the kinematic range vertical bar eta vertical bar &lt; 0.8 and 0.15 &lt; p(T) &lt; 20GeV/c. The results are presented for events with at least one charged particle in vertical bar eta vertical bar &lt; 1 (INEL&gt; 0). The p(T) spectra are reported for two multiplicity estimators covering different pseudorapidity regions. The p(T) spectra normalized to that for INEL&gt; 0 show little energy dependence. Moreover, the high-p(T) yields of charged particles increase faster than the charged-particle multiplicity density. The average p(T) as a function of multiplicity and transverse spherocity is reported for p(T) collisions at root s = 13TeV. For low- (high-) spherocity events, corresponding to jet-like (isotropic) events, the average pT is higher (smaller) than that measured in INEL&gt; 0 pp collisions. Within uncertainties, the functional form of &lt; p(T)&gt; (N-ch) is not affected by the spherocity selection. While EPOSLHCgives a good description ofmany features of data, PYTHIA overestimates the average p(T) in jet-like events