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-of- flight. 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

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

The first measurements of elliptic flow of π$^{±}$, K$^{±}$, $\textrm{p}+\overline{\textrm{p}}$, ${\textrm{K}}_{\textrm{S}}^0$, $\Lambda +\overline{\Lambda}$, ϕ, ${\Xi}^{-}+{\overline{\Xi}}^{+}$, and ${\varOmega}^{-}+{\overline{\varOmega}}^{+}$ using multiparticle cumulants in Pb–Pb collisions at $\sqrt{s_{\textrm{NN}}}$ = 5.02 TeV are resented. Results obtained with two- (v$_{2}${2}) and four-particle cumulants (v$_{2}${4}) are shown as a function of transverse momentum, p$_{T}$, for various collision centrality intervals. Combining the data for both v$_{2}${2} and v$_{2}${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 p$_{T}$-differential anisotropic flow measurements for identified hadrons with two-particle correlations, namely the mass ordering at low p$_{T}$ and the approximate scaling with the number of constituent quarks at intermediate p$_{T}$, are similarly present in the four-particle correlations and the combinations of v$_{2}${2} and v$_{2}${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 p$_{T}$ range.[graphic not available: see fulltext]The first measurements of elliptic flow of $\pi^\pm$, ${\rm K}^\pm$, p+$\overline{\rm p}$, ${\rm K_{S}^0}$, $\Lambda$+$\overline{\Lambda}$, $\phi$, $\Xi^-$+$\Xi^+$, and $\Omega^-$+$\Omega^+$ using multiparticle cumulants in Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV are presented. Results obtained with two- ($v_2\{2\}$) and four-particle cumulants ($v_2\{4\}$) are shown as a function of transverse momentum, $p_{\rm T}$, for various collision centrality intervals. Combining the data for both $v_2\{2\}$ and $v_2\{4\}$ 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 $p_{\rm T}$-differential anisotropic flow measurements for identified hadrons with two-particle correlations, namely the mass ordering at low $p_{\rm T}$ and the approximate scaling with the number of constituent quarks at intermediate $p_{\rm T}$, are similarly present in the four-particle correlations and the combinations of $v_2\{2\}$ and $v_2\{4\}$. 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 $p_{\rm T}$ range

f0(980){\rm f}_{0}(980) production in inelastic pp collisions at s=5.02\sqrt{s} = 5.02 TeV

International audienceThe measurement of the production of f0(980) in inelastic pp collisions at s=5.02 TeV is presented. This is the first reported measurement of inclusive f0(980) yield at LHC energies. The production is measured at midrapidity, |y|&lt;0.5, in a wide transverse momentum range, 0&lt;pT&lt;16 GeV/c, by reconstructing the resonance in the f0(980)→π+π− hadronic decay channel using the ALICE detector. The pT-differential yields are compared to those of pions, protons and ϕ mesons as well as to predictions from the HERWIG 7.2 QCD-inspired Monte Carlo event generator and calculations from a coalescence model that uses the AMPT model as an input. The ratio of the pT-integrated yield of f0(980) relative to pions is compared to measurements in e+e− and pp collisions at lower energies and predictions from statistical hadronisation models and HERWIG 7.2. A mild collision energy dependence of the f0(980) to pion production is observed in pp collisions from SPS to LHC energies. All considered models underpredict the pT-integrated 2f0(980)/(π+ +π−) ratio. The prediction from the canonical statistical hadronisation model assuming a zero total strangeness content of f0(980) is consistent with the data within 1.9σ and is the closest to the data. The results provide an essential reference for future measurements of the particle yield and nuclear modification in p–Pb and Pb–Pb collisions, which have been proposed to be instrumental to probe the elusive nature and quark composition of the f0(980) scalar meson

Closing in on critical net-baryon fluctuations at LHC energies: Cumulants up to third order in Pb–Pb collisions

International audienceFluctuation measurements are important sources of information on the mechanism of particle production at LHC energies. This article reports the first experimental results on third-order cumulants of the net-proton distributions in Pb–Pb collisions at a center-of-mass energy sNN=5.02 TeV recorded by the ALICE detector. The results on the second-order cumulants of net-proton distributions at sNN=2.76 and 5.02 TeV are also discussed in view of effects due to the global and local baryon number conservation. The results demonstrate the presence of long-range rapidity correlations between protons and antiprotons. Such correlations originate from the early phase of the collision. The experimental results are compared with HIJING and EPOS model calculations, and the dependence of the fluctuation measurements on the phase-space coverage is examined in the context of lattice quantum chromodynamics (LQCD) and hadron resonance gas (HRG) model estimations. The measured third-order cumulants are consistent with zero within experimental uncertainties of about 4% and are described well by LQCD and HRG predictions

First measurement of <math altimg="si1.svg"><msubsup><mrow><mi mathvariant="normal">Ω</mi></mrow><mrow><mi mathvariant="normal">c</mi></mrow><mrow><mn mathvariant="normal">0</mn></mrow></msubsup></math> production in pp collisions at <math altimg="si2.svg"><msqrt><mrow><mi>s</mi></mrow></msqrt><mo linebreak="goodbreak" linebreakstyle="after">=</mo><mn>13</mn></math> TeV

International audienceThe inclusive production of the charm–strange baryon Ωc0 is measured for the first time via its hadronic decay into Ω−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;12GeV/c. The pT dependence of the Ωc0-baryon production relative to the prompt D0-meson and to the prompt Ξc0-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 Ωc0 and prompt Λc+ baryons multiplied by the Ω−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

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

The interaction of ${\rm{K}^{-}}$ with protons is characterised by the presence of several coupled channels, systems like ${\rm \overline{K}^0}$n and ${\pi\Sigma}$ with a similar mass and the same quantum numbers as the ${\rm{K}^{-}}$ p state. The strengths of these couplings to the ${\rm{K}^{-}}$p system are of crucial importance for the understanding of the nature of the $\Lambda(1405)$ resonance and of the attractive ${\rm{K}^{-}}$ p strong interaction. In this article, we present measurements of the ${\rm{K}^{-}}$p correlation functions in relative momentum space obtained in pp collisions at $\sqrt{s} = 13$~TeV, in p$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$~TeV, and (semi)peripheral Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$~TeV. The emitting source size, composed of a core radius anchored to the ${\rm{K}^{+}}$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 ${\rm \overline{K}^0}$n and ${\pi\Sigma}$ inelastic channels on the measured ${\rm{K}^{-}}$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 $\omega$, 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 ${\rm{K}^{-}}$p interaction indicates that, while the \mbox{${\pi\Sigma}$$-$${\rm{K}^{-}}$p} dynamics is well reproduced by the model, the coupling to the ${\rm \overline{K}^0}$n channel in the model is currently underestimated.The interaction of $\textrm{K}^{-}$with protons is characterised by the presence of several coupled channels, systems like ${\overline{\textrm{K}}}^0$n and \uppi \Sigma with a similar mass and the same quantum numbers as the $\textrm{K}^{-}$p state. The strengths of these couplings to the $\textrm{K}^{-}$p system are of crucial importance for the understanding of the nature of the $\Lambda (1405)$ resonance and of the attractive $\textrm{K}^{-}$p strong interaction. In this article, we present measurements of the $\textrm{K}^{-}$p correlation functions in relative momentum space obtained in pp collisions at $\sqrt{s}~=~13$ Te, in p–Pb collisions at $\sqrt{s_{\textrm{NN}}}~=~5.02$ Te, and (semi)peripheral Pb–Pb collisions at $\sqrt{s_{\textrm{NN}}}~=~5.02$ Te. The emitting source size, composed of a core radius anchored to the $\textrm{K}^{+}$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 ${\overline{\textrm{K}}}^0$n and \uppi \Sigma inelastic channels on the measured $\textrm{K}^{-}$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 $\omega$, 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 $\textrm{K}^{-}$p interaction indicates that, while the \uppi \Sigma –$\textrm{K}^{-}$p dynamics is well reproduced by the model, the coupling to the ${\overline{\textrm{K}}}^0$n channel in the model is currently underestimated.The interaction of $\rm{K}^{-}$ with protons is characterised by the presence of several coupled channels, systems like ${\rm \overline{K}^0}$n and $\pi\Sigma$ with a similar mass and the same quantum numbers as the $\rm{K}^{-}$p state. The strengths of these couplings to the $\rm{K}^{-}$p system are of crucial importance for the understanding of the nature of the $\Lambda(1405)$ resonance and of the attractive $\rm{K}^{-}$p strong interaction. In this article, we present measurements of the $\rm{K}^{-}$p correlation functions in relative momentum space obtained in pp collisions at $\sqrt{s}~=~13$ TeV, in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}~=~5.02$ TeV, and (semi)peripheral Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}~=~5.02$ TeV. The emitting source size, composed of a core radius anchored to the $\rm{K}^{+}$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 ${\rm \overline{K}^0}$n and $\pi\Sigma$ inelastic channels on the measured $\rm{K}^{-}$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 $\omega$, 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 $\rm{K}^{-}$p interaction indicates that, while the $\pi\Sigma-\rm{K}^{-}$p dynamics is well reproduced by the model, the coupling to the ${\rm \overline{K}^0}$n channel in the model is currently underestimated

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

Hadronic 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 to 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 $\Sigma(1385)^{\pm}$ 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 $\Sigma(1385)^{\pm}$ resonance production at midrapidity inPb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}= 5.02$ TeV with the ALICE detector is presented in this Letter. The resonances are reconstructed via their hadronic decay channel, $\Lambda\pi$, as a function of the transverse momentum ($p_{\rm T}$) 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 \Angantyr and EPOS3 coupled to the UrQMD hadronic cascade afterburner. None of the models can describe the data. For $\Sigma(1385)^{\pm}$, a similar behaviour as ${\rm K}^{*} (892)^{0}$ is observed in data unlike the predictions of EPOS3 with afterburner.Hadronic 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 $\Sigma (1385)^{\pm }$ 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 $\Sigma (1385)^{\pm }$ resonance production at midrapidity in Pb–Pb collisions at $\sqrt{s_{\textrm{NN}}}= 5.02$ TeV with the ALICE detector is presented in this Letter. The resonances are reconstructed via their hadronic decay channel, $\Lambda \pi$, as a function of the transverse momentum ($p_\textrm{T}$) 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 $\Sigma (1385)^{\pm }$, a similar behaviour as $\textrm{K}^{*} (892)^{0}$ is observed in data unlike the predictions of EPOS3 with afterburner.Hadronic 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 to 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 $\Sigma(1385)^{\pm}$ 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 $\Sigma(1385)^{\pm}$ resonance production at midrapidity in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}= 5.02$ TeV with the ALICE detector is presented in this Letter. The resonances are reconstructed via their hadronic decay channel, $\Lambda\pi$, as a function of the transverse momentum ($p_{\rm T}$) 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 $\Sigma(1385)^{\pm}$, a similar behaviour as ${\rm K}^{*} (892)^{0}$ is observed in data unlike the predictions of EPOS3 with afterburner