Measuring (KSK +/-)-K-0 interactions using pp collisions at root s=7 TeV

We present the first measurements of femtoscopic correlations between the K-S(0) and K-+/- particles in pp collisions at root s = 7 TeV measured by the ALICE experiment. The observed femtoscopic correlations are consistent with final-state interactions proceeding solely via the a(0)(980) resonance. The extracted kaon source radius and correlation strength parameters for (KSK-)-K-0 are found to be equal within the experimental uncertainties to those for (KSK+)-K-0. Results of the present study are compared with those from identical-kaon femtoscopic studies also performed with pp collisions at root s = 7 TeV by ALICE and with a (KSK +/-)-K-0 measurement in Pb-Pb collisions at root s(NN) = 2.76 TeV. Combined with the Pb-Pb results, our pp analysis is found to be compatible with the interpretation of the a (980) having a tetraquark structure instead of that of a diquark. (C) 2018 Published by Elsevier B.V.Peer reviewe

Multiplicity dependence of light-flavor hadron production in pp collisions at s =7 TeV

Comprehensive results on the production of unidentified charged particles, π±, K±, KS0, K∗(892)0, p, p, φ(1020), Λ, Λ, Ξ-, Ξ+, Ω-, and Ω+ hadrons in proton-proton (pp) collisions at s=7 TeV at midrapidity (|y|<0.5) as a function of charged-particle multiplicity density are presented. In order to avoid autocorrelation biases, the actual transverse momentum (pT) spectra of the particles under study and the event activity are measured in different rapidity windows. In the highest multiplicity class, the charged-particle density reaches about 3.5 times the value measured in inelastic collisions. While the yield of protons normalized to pions remains approximately constant as a function of multiplicity, the corresponding ratios of strange hadrons to pions show a significant enhancement that increases with increasing strangeness content. Furthermore, all identified particle-to-pion ratios are shown to depend solely on charged-particle multiplicity density, regardless of system type and collision energy. The evolution of the spectral shapes with multiplicity and hadron mass shows patterns that are similar to those observed in p-Pb and Pb-Pb collisions at Large Hadron Collider energies. The obtained pT distributions and yields are compared to expectations from QCD-based pp event generators as well as to predictions from thermal and hydrodynamic models. These comparisons indicate that traces of a collective, equilibrated system are already present in high-multiplicity pp collisions

Multiplicity dependence of light-flavor hadron production in pp collisions at root s=7 TeV

Comprehensive results on the production of unidentified charged particles, \u3c0\ub1, K\ub1, KS0, K 17(892)0, p, p, \u3c6(1020), and Omega+ hadrons in proton-proton (pp) collisions at 1as = 7 TeV at midrapidity (|y| < 0.5) as a function of charged-particle multiplicity density are presented. In order to avoid autocorrelation biases, the actual transverse momentum (pT) spectra of the particles under study and the event activity are measured in different rapidity windows. In the highest multiplicity class, the charged-particle density reaches about 3.5 times the value measured in inelastic collisions. While the yield of protons normalized to pions remains approximately constant as a function of multiplicity, the corresponding ratios of strange hadrons to pions show a significant enhancement that increases with increasing strangeness content. Furthermore, all identified particle- to-pion ratios are shown to depend solely on charged-particle multiplicity density, regardless of system type and collision energy. The evolution of the spectral shapes with multiplicity and hadron mass shows patterns that are similar to those observed in p-Pb and Pb-Pb collisions at Large Hadron Collider energies. The obtained pT distributions and yields are compared to expectations from QCD-based pp event generators as well as to predictions from thermal and hydrodynamic models. These comparisons indicate that traces of a collective, equilibrated system are already present in high-multiplicity pp collisions

Study of J/psi azimuthal anisotropy at forward rapidity in Pb-Pb collisions at root s(NN)=5.02 TeV

The second (v2) and third (v3) flow harmonic coefficients of J/\u3c8 mesons are measured at forward rapidity (2.5 < y < 4.0) in Pb-Pb collisions at 1asNN = 5.02 TeV with the ALICE detector at the LHC. Results are obtained with the scalar product method and reported as a function of transverse momentum, pT, for various collision centralities. A positive value of J/\u3c8 v3 is observed with 3.7\u3c3 significance. The measurements, compared to those of prompt D0 mesons and charged particles at mid-rapidity, indicate an ordering with vn(J/\u3c8) < vn(D0) < vn(h\ub1) (n = 2, 3) at low and intermediate pT up to 6GeV/c and a convergence with v2(J/\u3c8) 48 v2(D0) 48 v2(h\ub1) at high pT above 6\u20138 GeV/c. In semi- central collisions (5\u201340% and 10\u201350% centrality intervals) at intermediate pT between 2 and 6 GeV/c, the ratio v3/v2 of J/\u3c8 mesons is found to be significantly lower (4.6\u3c3) with respect to that of charged particles. In addition, the comparison to the prompt D0-meson ratio in the same pT interval suggests an ordering similar to that of the v2 and v3 coefficients. The J/\u3c8 v2 coefficient is further studied using the Event Shape Engineering technique. The obtained results are found to be compatible with the expected variations of the eccentricity of the initial-state geometry

Event-Shape Engineering for the D-meson elliptic flow in mid-central Pb-Pb collisions at sNN=5.02 TeV

The production yield of prompt D mesons and their elliptic flow coefficient v2 were measured with the Event-Shape Engineering (ESE) technique applied to mid-central (10\u201330% and 30\u201350% centrality classes) Pb-Pb collisions at the centre-of-mass energy per nucleon pair 1asNN = 5.02 TeV, with the ALICE detector at the LHC. The ESE technique allows the classification of events, belonging to the same centrality, according to the az- imuthal anisotropy of soft particle production in the collision. The reported measurements give the opportunity to investigate the dynamics of charm quarks in the Quark-Gluon Plasma and provide information on their participation in the collective expansion of the medium. D mesons were reconstructed via their hadronic decays at mid-rapidity, |\u3b7| < 0.8, in the transverse momentum interval 1 < pT < 24GeV/c. The v2 coefficient is found to be sensitive to the event-shape selection confirming a correlation between the D-meson azimuthal anisotropy and the collective expansion of the bulk matter, while the per-event D-meson yields do not show any significant modification within the current uncertainties

Event-Shape Engineering for the D-meson elliptic flow in mid-central Pb-Pb collisions at √sNN = 5.02 TeV

The production yield of prompt D mesons and their elliptic flow coefficient v2 were measured with the Event-Shape Engineering (ESE) technique applied to mid-central (10–30% and 30–50% centrality classes) Pb-Pb collisions at the centre-of-mass energy per nucleon pair √sNN = 5.02 TeV, with the ALICE detector at the LHC. The ESE technique allows the classification of events, belonging to the same centrality, according to the az- imuthal anisotropy of soft particle production in the collision. The reported measurements give the opportunity to investigate the dynamics of charm quarks in the Quark-Gluon Plasma and provide information on their participation in the collective expansion of the medium. D mesons were reconstructed via their hadronic decays at mid-rapidity, |η| < 0.8, in the transverse momentum interval 1 < pT < 24GeV/c. The v2 coefficient is found to be sensitive to the event-shape selection confirming a correlation between the D-meson azimuthal anisotropy and the collective expansion of the bulk matter, while the per-event D-meson yields do not show any significant modification within the current uncertainties