Λ c + production in pp collisions at√ s=7 TeV and in p-Pb collisions at√ sNN=5.02 TeV

The pT-differential production cross section of prompt Λ c + charmed baryons was measured with the ALICE detector at the Large Hadron Collider (LHC) in pp collisions at s√=7 TeV and in p-Pb collisions at sNN−−−√=5.02 TeV at midrapidity. The Λ c + and Λ¯¯¯¯c¯¯¯ were reconstructed in the hadronic decay modes Λ c +  → pK−π+, Λ c +  → pK S 0 and in the semileptonic channel Λ c +  → e+νeΛ (and charge conjugates). The measured values of the Λ c + /D0 ratio, which is sensitive to the c-quark hadronisation mechanism, and in particular to the production of baryons, are presented and are larger than those measured previously in different colliding systems, centre-of-mass energies, rapidity and pT intervals, where the Λ c + production process may differ. The results are compared with the expectations obtained from perturbative Quantum Chromodynamics calculations and Monte Carlo event generators. Neither perturbative QCD calculations nor Monte Carlo models reproduce the data, indicating that the fragmentation of heavy-flavour baryons is not well understood. The first measurement at the LHC of the Λ c + nuclear modification factor, RpPb, is also presented. The RpPb is found to be consistent with unity and with that of D mesons within the uncertainties, and consistent with a theoretical calculation that includes cold nuclear matter effects and a calculation that includes charm quark interactions with a deconfined medium

First measurement of 0c production in pp collisions at √s=7TeV

The production of the charm-strange baryon 0cis measured for the first time at the LHC via its semileptonic decay into e+−νein ppcollisions at √s=7TeV with the ALICE detector. The transverse momentum (pT) differential cross section multiplied by the branching ratio is presented in the interval 1 <pT<8GeV/cat mid-rapidity, |y| <0.5. The transverse momentum dependence of the 0cbaryon production relative to the D0meson production is compared to predictions of event generators with various tunes of the hadronisation mechanism, which are found to underestimate the measured cross-section ratio

Measurements of e(+)e(-) pairs from open heavy flavor in p plus p and d plus A collisions at root S-NN=200 GeV

We report a measurement of e+e− pairs from semileptonic heavy-flavor decays in p+p collisions at √sNN=200 GeV. The e+e− pair yield from b¯b and c¯c is separated by exploiting a double differential fit done simultaneously in dielectron invariant mass and pT. We used three different event generators, pythia, mc@nlo, and powheg, to simulate the e+e− spectra from c¯c and b¯b production. The data can be well described by all three generators within the detector acceptance. However, when using the generators to extrapolate to 4π, significant differences are observed for the total cross section. These difference are less pronounced for b¯b than for c¯c. The same model dependence was observed in already published d+A data. The p+p data are also directly compared with d+A data in mass and pT, and within the statistical accuracy no nuclear modification is seen

Lévy-stable two-pion Bose-Einstein correlations in √sNN=200 GeV Au+Au collisions

We present a detailed measurement of charged two-pion correlation functions in 0–30% centrality √sNN=200 GeV Au+Au collisions by the PHENIX experiment at the Relativistic Heavy Ion Collider. The data are well described by Bose-Einstein correlation functions stemming from Lévy-stable source distributions. Using a fine transverse momentum binning, we extract the correlation strength parameter λ, the Lévy index of stability α, and the Lévy length scale parameter R as a function of average transverse mass of the pair mT. We find that the positively and the negatively charged pion pairs yield consistent results, and their correlation functions are represented, within uncertainties, by the same Lévy-stable source functions. The λ(mT) measurements indicate a decrease of the strength of the correlations at low mT. The Lévy length scale parameter R(mT) decreases with increasing mT, following a hydrodynamically predicted type of scaling behavior. The values of the Lévy index of stability α are found to be significantly lower than the Gaussian case of α=2, but also significantly larger than the conjectured value that may characterize the critical point of a second-order quark-hadron phase transition

Measurements of double-helicity asymmetries in inclusive J／ψ production in longitudinally polarized p+p collisions at √s=510 GeV

We report the double-helicity asymmetry, AJ/ψLL, in inclusive J/ψ production at forward rapidity as a function of transverse momentum pT and rapidity |y|. The data analyzed were taken during √s=510  GeV longitudinally polarized p+p collisions at the Relativistic Heavy Ion Collider in the 2013 run using the PHENIX detector. At this collision energy, J/ψ particles are predominantly produced through gluon-gluon scatterings, thus AJ/ψLL is sensitive to the gluon polarization inside the proton. We measured AJ/ψLL by detecting the decay daughter muon pairs μ+μ− within the PHENIX muon spectrometers in the rapidity range 1.2<|y|<2.2. In this kinematic range, we measured the AJ/ψLL to be 0.012±0.010 (stat) ±0.003 (syst). The AJ/ψLL can be expressed to be proportional to the product of the gluon polarization distributions at two distinct ranges of Bjorken x: one at moderate range x≈5×10−2 where recent data of jet and π0 double helicity spin asymmetries have shown evidence for significant gluon polarization, and the other one covering the poorly known small-x region x≈2×10−3. Thus our new results could be used to further constrain the gluon polarization for x<5×10−2

J/ψ Elliptic Flow in Pb-Pb Collisions at √sNN=5.02 TeV

We report a precise measurement of the J/ψ elliptic flow in Pb-Pb collisions at √sNN=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 v2 of the J/ψ is studied as a function of the transverse momentum and centrality. A positive v2 is observed in the transverse momentum range 2<pT<8  GeV/c in the three centrality classes studied and confirms with higher statistics our earlier results at √sNN=2.76  TeV in semicentral collisions. At midrapidity, the J/ψ  v2 is investigated as a function of the transverse momentum in semicentral collisions and found to be in agreement with the measurements at forward rapidity. These results are compared to transport model calculations. The comparison supports the idea that at low pT the elliptic flow of the J/ψ originates from the thermalization of charm quarks in the deconfined medium but suggests that additional mechanisms might be missing in the models

Prompt and non-prompt J/ψ production and nuclear modification at mid-rapidity in p–Pb collisions at √sNN=5.02 TeV

A measurement of beauty hadron production at mid-rapidity in proton-lead collisions at a nucleon–nucleon centre-of-mass energy sNN−−−√=5.02 TeV is presented. The semi-inclusive decay channel of beauty hadrons into J/ψ is considered, where the J/ψ mesons are reconstructed in the dielectron decay channel at mid-rapidity down to transverse momenta of 1.3 GeV/c. The bb¯ production cross section at mid-rapidity, dσbb¯/dy, and the total cross section extrapolated over full phase space, σbb¯, are obtained. This measurement is combined with results on inclusive J/ψ production to determine the prompt J/ψ cross sections. The results in p–Pb collisions are then scaled to expectations from pp collisions at the same centre-of-mass energy to derive the nuclear modification factor RpPb, and compared to models to study possible nuclear modifications of the production induced by cold nuclear matter effects. RpPb is found to be smaller than unity at low pT for both J/ψ coming from beauty hadron decays and prompt J/ψ

Measuring K 0 S K ± interactions using Pb–Pb collisions at √sNN = 2 . 76 TeV

We present the first ever measurements of femtoscopic correlations between the Kos and K± particles. The analysis was performed on the data from Pb–Pb collisions at √sNN=2.76 TeV measured by the ALICE experiment. The observed femtoscopic correlations are consistent with final-state interactions proceeding via the a0(980) resonance. The extracted kaon source radius and correlation strength parameters for K os K- are found to be equal within the experimental uncertainties to those for K os K+ . Comparing the results of the present study with those from published identical-kaon femtoscopic studies by ALICE, mass and coupling parameters for the ao resonance are tested. Our results are also compatible with the interpretation of the ao having a tetraquark structure instead of that of a diquark

Charged-particle multiplicity distributions over a wide pseudorapidity range in proton-proton collisions at s√= 0.9, 7, and 8 TeV

We present the charged-particle multiplicity distributions over a wide pseudorapidity range (−3.4<η<5.0) for pp collisions at s√=0.9,7, and 8 TeV at the LHC. Results are based on information from the Silicon Pixel Detector and the Forward Multiplicity Detector of ALICE, extending the pseudorapidity coverage of the earlier publications and the high-multiplicity reach. The measurements are compared to results from the CMS experiment and to PYTHIA, PHOJET and EPOS LHC event generators, as well as IP-Glasma calculations