The prompt production of the charm baryon Λ+c and the Λ+c/D0 production ratios were measured at midrapidity with the ALICE detector in pp and p-Pb collisions at √sNN=5.02 TeV. These new measurements ...show a clear decrease of the Λ+c/D0 ratio with increasing transverse momentum (pT) in both collision systems in the range 2<pT<12 GeV/c, exhibiting similarities with the light-flavor baryon-to-meson ratios p/π and Λ/K0S. At low pT, predictions that include additional color-reconnection mechanisms beyond the leading-color approximation, assume the existence of additional higher-mass charm-baryon states, or include hadronization via coalescence can describe the data, while predictions driven by charm-quark fragmentation processes measured in e+e− and e−p collisions significantly underestimate the data. The results presented in this Letter provide significant evidence that the established assumption of universality (colliding-system independence) of parton-to-hadron fragmentation is not sufficient to describe charm-baryon production in hadronic collisions at LHC energies.
The production cross section of prompt Λc+ charm baryons was measured with the ALICE detector at the LHC at midrapidity in proton-proton (pp) and proton-lead (p-Pb) collisions at a center-of-mass ...energy per nucleon pair of sNN=5.02TeV. The Λc+ and Λ¯c- baryons were reconstructed in the hadronic decay channels Λc+→pK-π+ and Λc+→pKS0 and respective charge conjugates. The measured differential cross sections as a function of transverse momentum (pT) and the pT-integrated Λc+ production cross section in pp and in p-Pb collisions are presented. The Λc+ nuclear modification factor (RpPb), calculated from the cross sections in pp and in p-Pb collisions, is presented and compared with the RpPb of D mesons. The Λc+/D0 ratio is also presented and compared with the light-flavor baryon-to-meson ratios p/π and Λ/KS0, and measurements from other LHC experiments. The results are compared to predictions from model calculations and Monte Carlo event generators.
The study of nuclei and antinuclei production has proven to be a powerful tool to investigate the formation mechanism of loosely bound states in high-energy hadronic collisions. The first measurement ...of the production of HΛ3 in p-Pb collisions at sNN=5.02 TeV is presented in this Letter. Its production yield measured in the rapidity interval -1
The first measurement of the ϒ(1S) elliptic flow coefficient (v2) is performed at forward rapidity (2.5 < y < 4) in Pb–Pb collisions at √sNN=5.02 TeV with the ALICE detector at the LHC. The results ...are obtained with the scalar product method and are reported as a function of transverse momentum (pT) up to 15 GeV/c in the 5%–60% centrality interval. The measured ϒ(1S)v2 is consistent with 0 and with the small positive values predicted by transport models within uncertainties. The v2 coefficient in 2 < pT < 15 GeV/c is lower than that of inclusive J/ψ mesons in the same pT interval by 2.6 standard deviations. These results, combined with earlier suppression measurements, are in agreement with a scenario in which the ϒ(1S) production in Pb–Pb collisions at LHC energies is dominated by dissociation limited to the early stage of the collision, whereas in the J/ψ case there is substantial experimental evidence of an additional regeneration component.
The measurement of the production of f0(980) in inelastic pp collisions at $\sqrt{s}$ = 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| < 0.5, in a wide transverse momentum range, 0 < pT < 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.
The inclusive production of the charm–strange baryon $Ω^0_c$ is measured for the first time via its hadronic decay into Ω–π+ at midrapidity(|y| < 0.5) in proton–proton (pp) collisions at the ...centre-of-mass energy $\sqrt{s}=$ 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 < pT < 12 GeV/c. The pT dependence of the $Ω^0_c$-baryon production relative to the prompt D0-meson and to the prompt $Ξ^0_c$-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 $Ω^0_c$ and prompt $Λ^+_c$ 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.
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