(Anti-)deuteron production in pp collisions at 1as=13TeV

The study of (anti-)deuteron production in pp collisions has proven to be a powerful tool to investigate the formation mechanism of loosely bound states in high-energy hadronic collisions. In this paper the production of (anti-)deuterons is studied as a function of the charged particle multiplicity in inelastic pp collisions at s=13 TeV using the ALICE experiment. Thanks to the large number of accumulated minimum bias events, it has been possible to measure (anti-)deuteron production in pp collisions up to the same charged particle multiplicity (d Nch/ d \u3b7 3c 26) as measured in p\u2013Pb collisions at similar centre-of-mass energies. Within the uncertainties, the deuteron yield in pp collisions resembles the one in p\u2013Pb interactions, suggesting a common formation mechanism behind the production of light nuclei in hadronic interactions. In this context the measurements are compared with the expectations of coalescence and statistical hadronisation models (SHM)

ϒ production in p–Pb collisions at √sNN=8.16 TeV

ϒ production in p–Pb interactions is studied at the centre-of-mass energy per nucleon–nucleon collision √sNN = 8.16 TeV with the ALICE detector at the CERN LHC. The measurement is performed reconstructing bottomonium resonances via their dimuon decay channel, in the centre-of-mass rapidity intervals 2.03 < ycms < 3.53 and −4.46 < ycms < −2.96, down to zero transverse momentum. In this work, results on the ϒ(1S) production cross section as a function of rapidity and transverse momentum are presented. The corresponding nuclear modification factor shows a suppression of the ϒ(1S) yields with respect to pp collisions, both at forward and backward rapidity. This suppression is stronger in the low transverse momentum region and shows no significant dependence on the centrality of the interactions. Furthermore, the ϒ(2S) nuclear modification factor is evaluated, suggesting a suppression similar to that of the ϒ(1S). A first measurement of the ϒ(3S) has also been performed. Finally, results are compared with previous ALICE measurements in p–Pb collisions at √sNN = 5.02 TeV and with theoretical calculations.publishedVersio

Azimuthal Anisotropy of Heavy-Flavor Decay Electrons in p-Pb Collisions at root s(NN)=5.02 TeV

Angular correlations between heavy-flavor decay electrons and charged particles at midrapidity (|\u3b7|&lt;0.8) are measured in p-Pb collisions at sNN=5.02 TeV. The analysis is carried out for the 0%-20% (high) and 60%-100% (low) multiplicity ranges. The jet contribution in the correlation distribution from high-multiplicity events is removed by subtracting the distribution from low-multiplicity events. An azimuthal modulation remains after removing the jet contribution, similar to previous observations in two-particle angular correlation measurements for light-flavor hadrons. A Fourier decomposition of the modulation results in a positive second-order coefficient (v2) for heavy-flavor decay electrons in the transverse momentum interval 1.5&lt;4 GeV/c in high-multiplicity events, with a significance larger than 5\u3c3. The results are compared with those of charged particles at midrapidity and those of inclusive muons at forward rapidity. The v2 measurement of open heavy-flavor particles at midrapidity in small collision systems could provide crucial information to help interpret the anisotropies observed in such systems

p-p, p-Lambda, and Lambda-Lambda correlations studied via femtoscopy in pp reactions at root s=7 TeV

We report on the first femtoscopic measurement of baryon pairs, such as p-p, p-\u39b, and \u39b-\u39b, measured by ALICE at the Large Hadron Collider (LHC) in proton-proton collisions at s=7TeV. This study demonstrates the feasibility of such measurements in pp collisions at ultrarelativistic energies. The femtoscopy method is employed to constrain the hyperon-nucleon and hyperon-hyperon interactions, which are still rather poorly understood. A new method to evaluate the influence of residual correlations induced by the decays of resonances and experimental impurities is hereby presented. The p-p, p-\u39b, and \u39b-\u39b correlation functions were fitted simultaneously with the help of a new tool developed specifically for the femtoscopy analysis in small colliding systems: Correlation Analysis Tool using the Schr\uf6dinger equation (CATS). Within the assumption that in pp collisions the three particle pairs originate from a common source, its radius is found to be equal to r0=1.125\ub10.018(stat)-0.035+0.058(syst) fm. The sensitivity of the measured p-\u39b correlation is tested against different scattering parameters, which are defined by the interaction among the two particles, but the statistics is not sufficient yet to discriminate among different models. The measurement of the \u39b-\u39b correlation function constrains the phase space spanned by the effective range and scattering length of the strong interaction. Discrepancies between the measured scattering parameters and the resulting correlation functions at LHC and RHIC energies are discussed in the context of various models

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 \u3c10 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\ub10.28(stat.)\ub10.08(syst.)\ub10.27(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 \u3c10 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

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 &lt; y &lt; 4.0) in Pb-Pb collisions at sNN=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) &lt; vn(D0) &lt; vn(h\ub1) (n = 2, 3) at low and intermediate pT up to 6 GeV/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

Charged jet cross section and fragmentation in proton-proton collisions at root S=7 TeV

We report the differential charged jet cross section and jet fragmentation distributions measured with the ALICE detector in proton-proton collisions at a center-of-mass energy s=7 TeV. Jets with pseudorapidity |\u3b7|&lt;0.5 are reconstructed from charged particles using the anti-kT jet-finding algorithm with a resolution parameter R=0.4. The jet cross section is measured in the transverse momentum interval 5 64pTch jet&lt;100 GeV/c. Jet fragmentation is studied measuring the scaled transverse momentum spectra of the charged constituents of jets in four intervals of jet transverse momentum between 5 and 30 GeV/c. The measurements are compared to calculations from the pythia model as well as next-to-leading-order perturbative QCD calculations with powheg+pythia8. The charged jet cross section is well described by powheg for the entire measured range of pTch jet. For pTch jet&gt;40 GeV/c, the pythia calculations also agree with the measured charged jet cross section. pythia6 simulations describe the fragmentation distributions to 15%. Larger discrepancies are observed for pythia8

Dielectron and heavy-quark production in inelastic and high-multiplicity proton-proton collisions at root s=13 TeV

The measurement of dielectron production is presented as a function of invariant mass and transverse momentum (pT) at midrapidity (|ye|&lt;0.8) in proton\u2013proton (pp) collisions at a centre-of-mass energy of 1as=13 TeV. The contributions from light-hadron decays are calculated from their measured cross sections in pp collisions at 1as=7 TeV or 13 TeV. The remaining continuum stems from correlated semileptonic decays of heavy-flavour hadrons. Fitting the data with templates from two different MC event generators, PYTHIA and POWHEG, the charm and beauty cross sections at midrapidity are extracted for the first time at this collision energy: d\u3c3cc\uaf/dy|y=0=974\ub1138(stat.)\ub1140(syst.)\ub1214(BR)\u3bcb and d\u3c3bb\uaf/dy|y=0=79\ub114(stat.)\ub111(syst.)\ub15(BR)\u3bcb using PYTHIA simulations and d\u3c3cc\uaf/dy|y=0=1417\ub1184(stat.)\ub1204(syst.)\ub1312(BR)\u3bcb and d\u3c3bb\uaf/dy|y=0=48\ub114(stat.)\ub17(syst.)\ub13(BR)\u3bcb for POWHEG. These values, whose uncertainties are fully correlated between the two generators, are consistent with extrapolations from lower energies. The different results obtained with POWHEG and PYTHIA imply different kinematic correlations of the heavy-quark pairs in these two generators. Furthermore, comparisons of dielectron spectra in inelastic events and in events collected with a trigger on high charged-particle multiplicities are presented in various pT intervals. The differences are consistent with the already measured scaling of light-hadron and open-charm production at high charged-particle multiplicity as a function of pT. Upper limits for the contribution of virtual direct photons are extracted at 90% confidence level and found to be in agreement with pQCD calculations