133 research outputs found

    Multiplicity dependence of inclusive J/psi production at midrapidity in pp collisions at root s=13 TeV

    Get PDF
    Measurements of the inclusive J/psi yield as a function of charged-particle pseudorapidity density dN(ch)/d eta in pp collisions at root s = 13 TeV with ALICE at the LHC are reported. The J/psi meson yield is measured at midrapidity (vertical bar y vertical bar <0.9) in the dielectron channel, for events selected based on the charged-particle multiplicity at midrapidity (vertical bar eta vertical bar <1) and at forward rapidity (-3.7 <eta <-1.7 and 2.8 <eta <5.1); both observables are normalized to their corresponding averages in minimum bias events. The increase of the normalized J/psi yield with normalized dN(ch)/d eta is significantly stronger than linear and dependent on the transverse momentum. The data are compared to theoretical predictions, which describe the observed trends well, albeit not always quantitatively. (C) 2020 European Organization for Nuclear Research. Published by Elsevier B.V.Peer reviewe

    First measurement of Ωc0 production in pp collisions at s=13 TeV

    Get PDF
    The inclusive production of the charm–strange baryon 0 c is measured for the first time via its hadronic √ decay into −π+ at midrapidity (|y| &lt;0.5) in proton–proton (pp) collisions at the centre-of-mass energy s =13 TeV with the ALICE detector at the LHC. The transverse momentum (pT) differential cross section multiplied by the branching ratio is presented in the interval 2 &lt; pT &lt; 12 GeV/c. The pT dependence of the 0 c-baryon production relative to the prompt D0-meson and to the prompt 0 c-baryon production is compared to various models that take different hadronisation mechanisms into consideration. In the measured pT interval, the ratio of the pT-integrated cross sections of 0 c and prompt + c baryons multiplied by the −π+ branching ratio is found to be larger by a factor of about 20 with a significance of about 4σ when compared to e+e− collisions

    Elliptic flow of charged particles at midrapidity relative to the spectator plane in Pb–Pb and Xe–Xe collisions

    Get PDF
    Measurements of the elliptic flow coefficient relative to the collision plane defined by the spectator neutrons v2{ SP} in collisions of Pb ions at center-of-mass energy per nucleon–nucleon pair √ 2.76 TeV and Xe ions at √ sNN = sNN =5.44 TeV are reported. The results are presented for charged particles produced at midrapidity as a function of centrality and transverse momentum for the 5–70% and 0.2–6 GeV/c ranges, respectively. The ratio between v2{ SP} and the elliptic flow coefficient relative to the participant plane v2{4}, estimated using four-particle correlations, deviates by up to 20% from unity depending on centrality. This observation differs strongly from the magnitude of the corresponding eccentricity ratios predicted by the TRENTo and the elliptic power models of initial state fluctuations that are tuned to describe the participant plane anisotropies. The differences can be interpreted as a decorrelation of the neutron spectator plane and the reaction plane because of fragmentation of the remnants from the colliding nuclei, which points to an incompleteness of current models describing the initial state fluctuations. A significant transverse momentum dependence of the ratio v2{ SP}/v2{4} is observed in all but the most central collisions, which may help to understand whether momentum anisotropies at low and intermediate transverse momentum have a common origin in initial state f luctuations. The ratios of v2{ SP} and v2{4} to the corresponding initial state eccentricities for Xe–Xe and Pb–Pb collisions at similar initial entropy density show a difference of (7.0 ±0.9)%with an additional variation of +1.8% when including RHIC data in the TRENTo parameter extraction. These observations provide new experimental constraints for viscous effects in the hydrodynamic modeling of the expanding quark–gluon plasma produced in heavy-ion collisions at the LHC

    Constraining the KN{\overline{\textrm{K}}}{\textrm{N}} coupled channel dynamics using femtoscopic correlations at the LHC

    No full text
    International audienceThe interaction of K\textrm{K}^{-}with protons is characterised by the presence of several coupled channels, systems like K0{\overline{\textrm{K}}}^0n and \uppi \Sigma with a similar mass and the same quantum numbers as the K\textrm{K}^{-}p state. The strengths of these couplings to the K\textrm{K}^{-}p system are of crucial importance for the understanding of the nature of the Λ(1405)\Lambda (1405) resonance and of the attractive K\textrm{K}^{-}p strong interaction. In this article, we present measurements of the K\textrm{K}^{-}p correlation functions in relative momentum space obtained in pp collisions at s = 13\sqrt{s}~=~13 Te, in p–Pb collisions at sNN = 5.02\sqrt{s_{\textrm{NN}}}~=~5.02 Te, and (semi)peripheral Pb–Pb collisions at sNN = 5.02\sqrt{s_{\textrm{NN}}}~=~5.02 Te. The emitting source size, composed of a core radius anchored to the K+\textrm{K}^{+}p correlation and of a resonance halo specific to each particle pair, varies between 1 and 2 fm in these collision systems. The strength and the effects of the K0{\overline{\textrm{K}}}^0n and \uppi \Sigma inelastic channels on the measured K\textrm{K}^{-}p correlation function are investigated in the different colliding systems by comparing the data with state-of-the-art models of chiral potentials. A novel approach to determine the conversion weights ω\omega , necessary to quantify the amount of produced inelastic channels in the correlation function, is presented. In this method, particle yields are estimated from thermal model predictions, and their kinematic distribution from blast-wave fits to measured data. The comparison of chiral potentials to the measured K\textrm{K}^{-}p interaction indicates that, while the \uppi \Sigma K\textrm{K}^{-}p dynamics is well reproduced by the model, the coupling to the K0{\overline{\textrm{K}}}^0n channel in the model is currently underestimated

    Production of pions, kaons, and protons as a function of the relative transverse activity classifier in pp collisions at s \sqrt{s} = 13 TeV

    No full text
    International audienceThe production of π±^{±}, K±^{±}, and (p)p \left(\overline{\textrm{p}}\right)\textrm{p} is measured in pp collisions at s \sqrt{s} = 13 TeV in different topological regions of the events. Particle transverse momentum (pT_{T}) spectra are measured in the “toward”, “transverse”, and “away” angular regions defined with respect to the direction of the leading particle in the event. While the toward and away regions contain the fragmentation products of the near-side and away-side jets, respectively, the transverse region is dominated by particles from the Underlying Event (UE). The relative transverse activity classifier, RT_{T} = NT_{T}/〈NT_{T}〉, is used to group events according to their UE activity, where NT_{T} is the measured charged-particle multiplicity per event in the transverse region and 〈NT_{T}〉 is the mean value over all the analysed events. The first measurements of identified particle pT_{T} spectra as a function of RT_{T} in the three topological regions are reported. It is found that the yield of high transverse momentum particles relative to the RT_{T}-integrated measurement decreases with increasing RT_{T} in both the toward and the away regions, indicating that the softer UE dominates particle production as RT_{T} increases and validating that RT_{T} can be used to control the magnitude of the UE. Conversely, the spectral shapes in the transverse region harden significantly with increasing RT_{T}. This hardening follows a mass ordering, being more significant for heavier particles. Finally, it is observed that the pT_{T}-differential particle ratios \left(\textrm{p}+\overline{\textrm{p}}\right)/\left({\uppi}^{+}+{\uppi}^{-}\right) and (K+^{+} + K^{−})/(π+^{+} + π^{−}) in the low UE limit (RT_{T} → 0) approach expectations from Monte Carlo generators such as PYTHIA 8 with Monash 2013 tune and EPOS LHC, where the jet-fragmentation models have been tuned to reproduce e+^{+}e^{−} results.[graphic not available: see fulltext

    Anisotropic flow and flow fluctuations of identified hadrons in Pb–Pb collisions at sNN \sqrt{s_{\textrm{NN}}} = 5.02 TeV

    Get PDF
    International audienceThe first measurements of elliptic flow of π±^{±}, K±^{±}, p+p \textrm{p}+\overline{\textrm{p}} , KS0 {\textrm{K}}_{\textrm{S}}^0 , Λ+Λ \Lambda +\overline{\Lambda} , ϕ, Ξ+Ξ+ {\Xi}^{-}+{\overline{\Xi}}^{+} , and Ω+Ω+ {\varOmega}^{-}+{\overline{\varOmega}}^{+} using multiparticle cumulants in Pb–Pb collisions at sNN \sqrt{s_{\textrm{NN}}} = 5.02 TeV are resented. Results obtained with two- (v2_{2}{2}) and four-particle cumulants (v2_{2}{4}) are shown as a function of transverse momentum, pT_{T}, for various collision centrality intervals. Combining the data for both v2_{2}{2} and v2_{2}{4} also allows us to report the first measurements of the mean elliptic flow, elliptic flow fluctuations, and relative elliptic flow fluctuations for various hadron species. These observables probe the event-by-event eccentricity fluctuations in the initial state and the contributions from the dynamic evolution of the expanding quark–gluon plasma. The characteristic features observed in previous pT_{T}-differential anisotropic flow measurements for identified hadrons with two-particle correlations, namely the mass ordering at low pT_{T} and the approximate scaling with the number of constituent quarks at intermediate pT_{T}, are similarly present in the four-particle correlations and the combinations of v2_{2}{2} and v2_{2}{4}. In addition, a particle species dependence of flow fluctuations is observed that could indicate a significant contribution from final state hadronic interactions. The comparison between experimental measurements and CoLBT model calculations, which combine the various physics processes of hydrodynamics, quark coalescence, and jet fragmentation, illustrates their importance over a wide pT_{T} range.[graphic not available: see fulltext

    Jet-like correlations with respect to KS0^{0}_{\rm S} and Λ\Lambda (Λˉ\bar{\Lambda}) in pp and Pb-Pb collisions at sNN\mathbf{\it\sqrt{s_\mathrm{NN}}} = 5.02 TeV

    No full text
    International audienceTwo-particle correlations with KS0\textrm{K}^{0}_\mathrm{{S}}, Λ\Lambda /Λ\overline{\Lambda }, and charged hadrons as trigger particles in the transverse momentum range 8{3 GeV/cc as expected from strong in-medium energy loss, while an enhancement develops at low pT,assocp_{{\textrm{T}},{\textrm{assoc}}} on both the near and away sides, reaching IAA1.8I_{\textrm{AA}}\approx 1.8 and 2.7 respectively. These findings are in good agreement with previous ALICE measurements from two-particle correlations triggered by neutral pions (π0\pi ^{0}–h) and charged hadrons (h–h) in Pb–Pb collisions at sNN = 2.76\sqrt{s_{\textrm{NN}}}~=~2.76 TeV. Moreover, the correlations with KS0\textrm{K}^{0}_\mathrm{{S}} mesons and Λ\Lambda /Λ\overline{\Lambda } baryons as trigger particles are compared to those of inclusive charged hadrons. The results are compared with the predictions of Monte Carlo models

    Σ(1385)±\Sigma (1385)^{\pm } resonance production in Pb–Pb collisions at sNN = 5.02\sqrt{s_{\textrm{NN}}}~=~5.02 TeV

    No full text
    International audienceHadronic resonances are used to probe the hadron gas produced in the late stage of heavy-ion collisions since they decay on the same timescale, of the order of 1–10 fm/c, as the decoupling time of the system. In the hadron gas, (pseudo)elastic scatterings among the products of resonances that decayed before the kinetic freeze-out and regeneration processes counteract each other, the net effect depending on the resonance lifetime, the duration of the hadronic phase, and the hadronic cross sections at play. In this context, the Σ(1385)±\Sigma (1385)^{\pm } particle is of particular interest as models predict that regeneration dominates over rescattering despite its relatively short lifetime of about 5.5 fm/c. The first measurement of the Σ(1385)±\Sigma (1385)^{\pm } resonance production at midrapidity in Pb–Pb collisions at sNN=5.02\sqrt{s_{\textrm{NN}}}= 5.02 TeV with the ALICE detector is presented in this Letter. The resonances are reconstructed via their hadronic decay channel, Λπ\Lambda \pi , as a function of the transverse momentum (pTp_\textrm{T}) and the collision centrality. The results are discussed in comparison with the measured yield of pions and with expectations from the statistical hadronization model as well as commonly employed event generators, including PYTHIA8/Angantyr and EPOS3 coupled to the UrQMD hadronic cascade afterburner. None of the models can describe the data. For Σ(1385)±\Sigma (1385)^{\pm }, a similar behaviour as K(892)0\textrm{K}^{*} (892)^{0} is observed in data unlike the predictions of EPOS3 with afterburner

    J/ψ\psi production at midrapidity in p-Pb collisions at sNN=8.16\sqrt{s_{\rm NN}} = 8.16 TeV

    No full text
    International audienceThe production of inclusive, prompt and non-prompt J/ψ was studied for the first time at midrapidity (−1.37 2 GeV/c. The study of the J/ψ mesons in the dielectron channel used for the first time in ALICE online single-electron triggers from the Transition Radiation Detector, providing a data sample corresponding to an integrated luminosity of 689 ± 13 μb1^{−1}. The proton-proton reference cross section for inclusive J/ψ was obtained based on interpolations of measured data at different centre-of-mass energies and a universal function describing the pT_{T}-differential J/ψ production cross sections. The pT_{T}-differential nuclear modification factors RpPb_{pPb} of inclusive, prompt, and non-prompt J/ψ are consistent with unity and described by theoretical models implementing only nuclear shadowing.[graphic not available: see fulltext
    corecore