Production of charged pions, kaons, and (anti-)protons in Pb-Pb and inelastic pp collisions at √sNN=5.02 TeV

Midrapidity production of π±, K±, and (¯p)p measured by the ALICE experiment at the CERN Large Hadron Collider, in Pb-Pb and inelastic pp collisions at √sNN=5.02 TeV, is presented. The invariant yields are measured over a wide transverse momentum (pT) range from hundreds of MeV/c up to 20 GeV/c. The results in Pb-Pb collisions are presented as a function of the collision centrality, in the range 0–90%. The comparison of the pT-integrated particle ratios, i.e., proton-to-pion (p/π) and kaon-to-pion (K/π) ratios, with similar measurements in Pb-Pb collisions at √sNN=2.76 TeV show no significant energy dependence. Blast-wave fits of the pT spectra indicate that in the most central collisions radial flow is slightly larger at 5.02 TeV with respect to 2.76 TeV. Particle ratios (p/π, K/π) as a function of pT show pronounced maxima at pT≈3 GeV/c in central Pb-Pb collisions. At high pT, particle ratios at 5.02 TeV are similar to those measured in pp collisions at the same energy and in Pb-Pb collisions at √sNN=2.76 TeV. Using the pp reference spectra measured at the same collision energy of 5.02 TeV, the nuclear modification factors for the different particle species are derived. Within uncertainties, the nuclear modification factor is particle species independent for high pT and compatible with measurements at √sNN=2.76 TeV. The results are compared to state-of-the-art model calculations, which are found to describe the observed trends satisfactorily.publishedVersio

J/ψ production as a function of charged-particle multiplicity in p-Pb collisions at √sNN = 8.16 TeV

Inclusive J/ψ yields and average transverse momenta in p-Pb collisions at a center-of-mass energy per nucleon pair sNN−−−√ = 8.16 TeV are measured as a function of the charged-particle pseudorapidity density with ALICE. The J/ψ mesons are reconstructed at forward (2.03 < ycms < 3.53) and backward (−4.46 < ycms < −2.96) center-of-mass rapidity in their dimuon decay channel while the charged-particle pseudorapidity density is measured around midrapidity. The J/ψ yields at forward and backward rapidity normalized to their respective average values increase with the normalized charged-particle pseudorapidity density, the former showing a weaker increase than the latter. The normalized average transverse momenta at forward and backward rapidity manifest a steady increase from low to high charged-particle pseudorapidity density with a saturation beyond the average value.publishedVersio

Multiplicity dependence of light (anti-)nuclei production in p–Pb collisions at √sNN=5.02 TeV

The measurement of the deuteron and anti-deuteron production in the rapidity range −1 < y < 0 as a function of transverse momentum and event multiplicity in p–Pb collisions at √sNN = 5.02 TeV is presented. (Anti-)deuterons are identified via their specific energy loss dE/dx and via their time-offlight. Their production in p–Pb collisions is compared to pp and Pb–Pb collisions and is discussed within the context of thermal and coalescence models. The ratio of integrated yields of deuterons to protons (d/p) shows a significant increase as a function of the charged-particle multiplicity of the event starting from values similar to those observed in pp collisions at low multiplicities and approaching those observed in Pb–Pb collisions at high multiplicities. The mean transverse particle momenta are extracted from the deuteron spectra and the values are similar to those obtained for p and particles. Thus, deuteron spectra do not follow mass ordering. This behaviour is in contrast to the trend observed for non-composite particles in p–Pb collisions. In addition, the production of the rare 3He and 3He nuclei has been studied. The spectrum corresponding to all non-single diffractive p-Pb collisions is obtained in the rapidity window −1 < y < 0 and the pT-integrated yield dN/dy is extracted. It is found that the yields of protons, deuterons, and 3He, normalised by the spin degeneracy factor, follow an exponential decrease with mass number.publishedVersio

Measurement of strange baryon–antibaryon interactions with femtoscopic correlations

Two-particle correlation functions were measured for pp, p, p, and pairs in Pb–Pb collisions at √sNN = 2.76 TeV and √sNN = 5.02 TeV recorded by the ALICE detector. From a simultaneous fit to all obtained correlation functions, real and imaginary components of the scattering lengths, as well as the effective ranges, were extracted for combined p and p pairs and, for the first time, for pairs. Effective averaged scattering parameters for heavier baryon–antibaryon pairs, not measured directly, are also provided. The results reveal similarly strong interaction between measured baryon–antibaryon pairs, suggesting that they all annihilate in the same manner at the same pair relative momentum k∗. Moreover, the reported significant non-zero imaginary part and negative real part of the scattering length provide motivation for future baryon–antibaryon bound state searches.publishedVersio

Measurement of electrons from heavy-flavour hadron decays as a function of multiplicity in p-Pb collisions at √sNN = 5.02 TeV

The multiplicity dependence of electron production from heavy-flavour hadron decays as a function of transverse momentum was measured in p-Pb collisions at √sNN = 5.02 TeV using the ALICE detector at the LHC. The measurement was performed in the centre-of-mass rapidity interval −1.07 < ycms< 0.14 and transverse momentum interval 2 < pT< 16 GeV/c. The multiplicity dependence of the production of electrons from heavy-flavour hadron decays was studied by comparing the pT spectra measured for different multiplicity classes with those measured in pp collisions (QpPb) and in peripheral p-Pb collisions (Qcp). The QpPb results obtained are consistent with unity within uncertainties in the measured pT interval and event classes. This indicates that heavy-flavour decay electron production is consistent with binary scaling and independent of the geometry of the collision system. Additionally, the results suggest that cold nuclear matter effects are negligible within uncertainties, in the production of heavy-flavour decay electrons at midrapidity in p-Pb collisions.publishedVersio

Elliptic and triangular flow of (anti)deuterons in Pb-Pb collisions at √sNN=5.02 TeV

The measurements of the (anti)deuteron elliptic flow (v2) and the first measurements of triangular flow (v3) in Pb-Pb collisions at a center-of-mass energy per nucleon-nucleon collision √sNN = 5.02 TeV are presented. A mass ordering at low transverse momentum (pT) is observed when comparing these measurements with those of other identified hadrons, as expected from relativistic hydrodynamics. The measured (anti)deuteron v2 lies between the predictions from the simple coalescence and blast-wave models, which provide a good description of the data only for more peripheral and for more central collisions, respectively. The mass number scaling, which is violated for v2, is approximately valid for the (anti)deuterons v3. The measured v2 and v3 are also compared with the predictions from a coalescence approach with phase-space distributions of nucleons generated by iebe-vishnu with ampt initial conditions coupled with urqmd, and from a dynamical model based on relativistic hydrodynamics coupled to the hadronic afterburner smash. The model predictions are consistent with the data within the uncertainties in midcentral collisions, while a deviation is observed in the most central collisions.publishedVersio

Jet-hadron correlations measured relative to the second order event plane in Pb-Pb collisions at sNN\sqrt{s_{NN}} =2.76 TeV

The quark gluon plasma produced in ultrarelativistic heavy-ion collisions at the Large Hadron Collider (LHC) can be studied by measuring the modifications of jets formed by hard scattered partons which interact with the medium. We studied these modifications via angular correlations of jets with charged hadrons for jets with momenta 20<p jet T<40 GeV/c as a function of the associated particle momentum. The reaction plane fit method is used in this analysis to remove the flow modulated background. The analysis of angular correlations for different orientations of the jet relative to the second order event plane allows for the study of the path length dependence of medium modifications to jets. We present the dependence of azimuthal angular correlations of charged hadrons with respect to the angle of the axis of a reconstructed jet relative to the event plane in Pb-Pb collisions at √sNN = 2.76 TeV. The dependence of particle yields associated with jets on the angle of the jet with respect to the event plane is presented. Correlations at different angles relative to the event plane are compared through ratios and differences of the yield. No dependence of the results on the angle of the jet with respect to the event plane is observed within uncertainties, which is consistent with no significant path length dependence of the medium modifications for this observable.publishedVersio

Inclusive quarkonium production in pp collisions at √s = 5.02 TeV

This article reports on the inclusive production cross section of several quarkonium states, $\textrm{J}/\psi$, $\psi \mathrm{(2S)}$, $\Upsilon \mathrm (1S)$, $\Upsilon \mathrm{(2S)}$, and $\Upsilon \mathrm{(3S)}$, measured with the ALICE detector at the LHC, in pp collisions at $\sqrt{s} = 5.02$ TeV. The analysis is performed in the dimuon decay channel at forward rapidity ($2.5< y < 4$). The integrated cross sections and transverse-momentum ($p_{\textrm{T}}$) and rapidity ($y$) differential cross sections for $\textrm{J}/\psi$, $\psi \mathrm{(2S)}$, $\Upsilon \mathrm (1S)$, and the $\psi \mathrm{(2S)}$-to-$\textrm{J}/\psi$ cross section ratios are presented. The integrated cross sections, assuming unpolarized quarkonia, are: $\sigma _{\textrm{J}/\psi }$ ($p_{\textrm{T}} <20$ GeV/c) = 5.88 ± 0.03 ± 0.34$~\mu$b, $\sigma _{\psi \mathrm{(2S)}}$ ($p_{\textrm{T}} <12$ GeV/c) = 0.87 ± 0.06 ± 0.10$~\mu$b, $\sigma _{\Upsilon \mathrm (1S)}$ ($p_{\textrm{T}} <15$ GeV/c) = 45.5 ± 3.9 ± 3.5 nb, $\sigma _{\Upsilon \mathrm{(2S)}}$ ($p_{\textrm{T}} <15$ GeV/c) = 22.4 ± 3.2 ± 2.7 nb, and $\sigma _{\Upsilon \mathrm{(3S)}}$ ($p_{\textrm{T}} <15$ GeV/c) = 4.9 ± 2.2 ± 1.0 nb, where the first (second) uncertainty is the statistical (systematic) one. For the first time, the cross sections of the three $\Upsilon$ states, as well as the $\psi \mathrm{(2S)}$ one as a function of $p_{\textrm{T}}$ and $y$, are measured at $\sqrt{s} = 5.02$ TeV at forward rapidity. These measurements also significantly extend the $\textrm{J}/\psi$ $p_{\textrm{T}}$ reach and supersede previously published results. A comparison with ALICE measurements in pp collisions at $\sqrt{s} = 2.76$, 7, 8, and 13 TeV is presented and the energy dependence of quarkonium production cross sections is discussed. Finally, the results are compared with the predictions from several production models.publishedVersio

Investigation of the p–Σ0 interaction via femtoscopy in pp collisions

This Letter presents the first direct investigation of the p–Σ0 interaction, using the femtoscopy technique in high-multiplicity pp collisions at √s = 13 TeV measured by the ALICE detector. The Σ0 is reconstructed via the decay channel to Λγ , and the subsequent decay of Λ to pπ−. The photon is detected via the conversion in material to e+e− pairs exploiting the capability of the ALICE detector to measure electrons at low transverse momenta. The measured p–Σ0 correlation indicates a shallow strong interaction. The comparison of the data to several theoretical predictions obtained employing the Correlation Analysis Tool using the Schrödinger Equation (CATS) and the Lednický–Lyuboshits approach shows that the current experimental precision does not yet allow to discriminate between different models, as it is the case for the available scattering and hypernuclei data. Nevertheless, the p–Σ0 correlation function is found to be sensitive to the strong interaction, and driven by the interplay of the different spin and isospin channels. This pioneering study demonstrates the feasibility of a femtoscopic measurement in the p–Σ0 channel and with the expected larger data samples in LHC Run 3 and Run 4, the p–Σ0 interaction will be constrained with high precision.publishedVersio

Inclusive J/ψ production at midrapidity in pp collisions at √s=13 TeV

We report on the inclusive $\text {J}/\psi$ production cross section measured at the CERN Large Hadron Collider in proton–proton collisions at a center-of-mass energy $\sqrt{s}~=~13$ TeV. The $\text {J}/\psi$ mesons are reconstructed in the $\text {e}^{+}\text {e}^{-}$ decay channel and the measurements are performed at midrapidity ($|y|<0.9$) in the transverse-momentum interval $0<p_{\mathrm{T}} <40$ GeV/$c$, using a minimum-bias data sample corresponding to an integrated luminosity $L_{\text {int}} = 32.2~\text {nb}^{-1}$ and an Electromagnetic Calorimeter triggered data sample with $L_{\text {int}} = 8.3~\mathrm {pb}^{-1}$. The $p_{\mathrm{T}}$-integrated $\text {J}/\psi$ production cross section at midrapidity, computed using the minimum-bias data sample, is $\text {d}\sigma /\text {d}y|_{y=0} = 8.97\pm 0.24~(\text {stat})\pm 0.48~(\text {syst})\pm 0.15~(\text {lumi})~\mu \text {b}$. An approximate logarithmic dependence with the collision energy is suggested by these results and available world data, in agreement with model predictions. The integrated and $p_{\mathrm{T}}$-differential measurements are compared with measurements in pp collisions at lower energies and with several recent phenomenological calculations based on the non-relativistic QCD and Color Evaporation models.publishedVersio