The prompt production of the charm baryon $\rm \Lambda_{c}^{+}$ and the $\rm \Lambda_{c}^{+}/\mathrm {D^0}$ production ratios were measured at midrapidity with the ALICE detector in pp and p-Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$TeV. These new measurements show a clear decrease of the $\rm \Lambda_{c}^{+}/\mathrm {D^0}$ ratio with increasing transverse momentum ($p_{\rm T}$) in both collision systems in the range $2<p_{\rm T}<12$ GeV/$c$, exhibiting similarities with the light-flavour baryon-to-meson ratios ${\rm p}/\pi$ and $\Lambda/\mathrm {K^0_S}$. At low $p_{\rm T}$, predictions that include additional colour-reconnection mechanisms beyond the leading-colour approximation; assume the existence of additional higher-mass charm-baryon states; or include hadronisation via coalescence can describe the data, while predictions driven by charm-quark fragmentation processes measured in $\mathrm {e^+e^-}$ and $\mathrm {e^-p}$ 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.
Prompt $\Lambda_{\rm {c}}^{+}$ baryon $p_{\rm {T}}$-differential cross section in pp collisions at $\sqrt{s} = 5.02$ TeV in the rapidity interval $|y|<0.5$.
Prompt $\Lambda_{\rm {c}}^{+}$ baryon $p_{\rm {T}}$-differential cross section in p-Pb collisions at $\sqrt{s_{\rm {NN}}} = 5.02$ TeV in the rapidity interval $-0.96 \lt y \lt 0.04$.
The nuclear modification factor $R_\mathrm{pPb}$ of prompt $\Lambda_{\rm {c}}^{+}$ baryons in p-Pb collisions at $\sqrt{s_{\rm {NN}}} = 5.02$ TeV in the rapidity interval $ -0.96\lt y \lt 0.04$.
The ALICE experiment at the LHC has studied J/psi production at mid-rapidity in pp collisions at sqrt{s}=7 TeV through its electron pair decay on a data sample corresponding to an integrated luminosity L_int = 5.6nb-1. The fraction of J/psi from the decay of long-lived beauty hadrons was determined for J/psi candidates with transverse momentum p_t>1.3 GeV/c and rapidity |y|<0.9. The cross section for prompt J/psi mesons, i.e. directly produced J/psi and prompt decays of heavier charmonium states such as the Psi(2S) and Csi_c resonances, is sigma_prompt-J/psi(pt > 1.3 GeV/c, |y| < 0.9) = 8.3 +- 0.8(stat.) +- 1.1(syst.) + 1.5 - 1.4(syst. pol.) micro barn. The cross section for the production of b-hadrons decaying to J/psi with p_t>1.3 GeV/c and |y|<0.9 is sigma_{J/psi<-h_B} = 1.46 +- 0.38(stat.) + 0.26 -0.32(syst.) micro barn. The results are compared to QCD model predictions. The shape of the p_t and y distributions of b-quarks predicted by perturbative QCD model calculations are used to extrapolate the measured cross section to derive the b-bbar pair total cross section and dsigma/dy at mid-rapidity.
The cross section for b-bbar production in the |y| region < 0.9 integrated over PT. The the second (sys) error is the extrapolation systematic error.
The cross section for b-bbar production integrated over PT and rapidity. The the second (sys) error is the extrapolation systematic error.
Charged-particle production was studied in proton-proton collisions collected at the LHC with the ALICE detector at centre-of-mass energies 0.9 TeV and 2.36 TeV in the pseudorapidity range |$\eta$| < 1.4. In the central region (|$\eta$| < 0.5), at 0.9 TeV, we measure charged-particle pseudorapidity density dNch/deta = 3.02 $\pm$ 0.01 (stat.) $^{+0.08}_{-0.05}$ (syst.) for inelastic interactions, and dNch/deta = 3.58 $\pm$ 0.01 (stat.) $^{+0.12}_{-0.12}$ (syst.) for non-single-diffractive interactions. At 2.36 TeV, we find dNch/deta = 3.77 $\pm$ 0.01 (stat.) $^{+0.25}_{-0.12}$ (syst.) for inelastic, and dNch/deta = 4.43 $\pm$ 0.01 (stat.) $^{+0.17}_{-0.12}$ (syst.) for non-single-diffractive collisions. The relative increase in charged-particle multiplicity from the lower to higher energy is 24.7% $\pm$ 0.5% (stat.) $^{+5.7}_{-2.8}$% (syst.) for inelastic and 23.7% $\pm$ 0.5% (stat.) $^{+4.6}_{-1.1}$% (syst.) for non-single-diffractive interactions. This increase is consistent with that reported by the CMS collaboration for non-single-diffractive events and larger than that found by a number of commonly used models. The multiplicity distribution was measured in different pseudorapidity intervals and studied in terms of KNO variables at both energies. The results are compared to proton-antiproton data and to model predictions.
Measured pseudorapidity dependence of DN/DETARAP for INEL collisions at a centre-of-mass energy of 900 GeV.
Measured pseudorapidity dependence of DN/DETARAP for NSD collisions at a centre-of-mass energy of 900 GeV.
Measured pseudorapidity dependence of DN/DETARAP for INEL collisions at a centre-of-mass energy of 2360 GeV.
In our Galaxy, light antinuclei composed of antiprotons and antineutrons can be produced through high-energy cosmic-ray collisions with the interstellar medium or could also originate from the annihilation of dark-matter particles that have not yet been discovered. On Earth, the only way to produce and study antinuclei with high precision is to create them at high-energy particle accelerators. Although the properties of elementary antiparticles have been studied in detail, the knowledge of the interaction of light antinuclei with matter is limited. We determine the disappearance probability of $^{3}\overline{\rm He}$ when it encounters matter particles and annihilates or disintegrates within the ALICE detector at the Large Hadron Collider. We extract the inelastic interaction cross section, which is then used as input to calculations of the transparency of our Galaxy to the propagation of $^{3}\overline{\rm He}$ stemming from dark-matter annihilation and cosmic-ray interactions within the interstellar medium. For a specific dark-matter profile, we estimate a transparency of about 50%, whereas it varies with increasing $^{3}\overline{\rm He}$ momentum from 25% to 90% for cosmic-ray sources. The results indicate that $^{3}\overline{\rm He}$ nuclei can travel long distances in the Galaxy, and can be used to study cosmic-ray interactions and dark-matter annihilation.
Raw primary antihelium3-to-helium3 ratio as a function of the momentum p_primary.
Raw primary antihelium3-to-helium3 ratio from Geant4-based MC simulations as a function of the momentum p_primary with default sigma_inel(3Hebar).
Raw primary antihelium3-to-helium3 ratio from Geant4-based MC simulations as a function of the momentum p_primary with sigma_inel(3Hebar)x0.5.
Measurements of charge dependent azimuthal correlations with the ALICE detector at the LHC are reported for Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV. Two- and three-particle charge-dependent azimuthal correlations in the pseudo-rapidity range $|\eta| < 0.8$ are presented as a function of the collision centrality, particle separation in pseudo-rapidity, and transverse momentum. A clear signal compatible with a charge-dependent separation relative to the reaction plane is observed, which shows little or no collision energy dependence when compared to measurements at RHIC energies. This provides a new insight for understanding the nature of the charge dependent azimuthal correlations observed at RHIC and LHC energies.
The centrality dependence of the three-particle charge-dependent correlator MEAN(COS(PHI(A)+COS(PHI(B)-2*PHI(RP)) measured with the cumulant method.
The centrality dependence of the correlator three-particle charge-dependent MEAN(COS(PHI(A)+COS(PHI(B)-2*PHI(RP)) measured from correlations with the reaction plane (RP) estimated using the TPC detector.
The centrality dependence of the correlator three-particle charge-dependent MEAN(COS(PHI(A)+COS(PHI(B)-2*PHI(RP)) measured from correlations with the reaction plane (RP) estimated using the VZERO detector.
We report the first measurement of the net-charge fluctuations in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV, measured with the ALICE detector at the CERN Large Hadron Collider. The dynamical fluctuations per unit entropy are observed to decrease when going from peripheral to central collisions. An additional reduction in the amount of fluctuations is seen in comparison to the results from lower energies. We examine the dependence of fluctuations on the pseudorapidity interval, which may account for the dilution of fluctuations during the evolution of the system. We find that the fluctuations at LHC are smaller compared to the measurements at the Relativistic heavy Ion Collider (RHIC), and as such, closer to what has been theoretically predicted for the formation of Quark-Gluon Plasma (QGP).
The measured NU(+-DYN) as a function of the centrality of the collisions, expressed as the number of participating nucleons, for two values of midrapidity range.
NU(+-DYN), corrected for charge conservation and finite acceptance effects, as a function of the centrality of the collisions, expressed as the number of participating nucleons, for two values of midrapidity range.
The measured and corrected NU(+-DYN) in P P collisions for two values of midrapidity range.
The charged-particle pseudorapidity density measured over 4 units of pseudorapidity in non-single-diffractive (NSD) p-Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}} = 5.02$ TeV is presented. The average value at midrapidity is measured to be $16.81 \pm 0.71$ (syst.), which corresponds to $2.14 \pm 0.17$ (syst.) per participating nucleon. This is 16% lower than in NSD pp collisions interpolated to the same collision energy, and 84% higher than in d-Au collisions at $\sqrt{s_{\rm NN}} = 0.2$ TeV. The measured pseudorapidity density in p-Pb collisions is compared to model predictions, and provides new constraints on the description of particle production in high-energy nuclear collisions.
The pseudorapidity density of charged particles in the lab. frame.
The ALICE collaboration at the CERN Large Hadron Collider reports the first measurement of the inclusive differential jet cross section at mid-rapidity in pp collisions at $\sqrt{s} = 2.76$ TeV, with integrated luminosity of 13.6 nb$^{-1}$. Jets are measured over the transverse momentum range 20 to 125 GeV/c and are corrected to the particle level. Calculations based on Next-to-Leading Order perturbative QCD are in good agreement with the measurements. The ratio of inclusive jet cross sections for jet radii $R = 0.2$ and $R = 0.4$ is reported, and is also well reproduced by a Next-to-Leading Order perturbative QCD calculation when hadronization effects are included.
Inclusive differential jet cross section for R=0.2 and R=0.4.
Ratio of the inclusive differential jet cross section for R=0.2 and R=0.4.
Two-particle transverse momentum differential correlators, recently measured in Pb--Pb collisions at energies available at the CERN Large Hadron Collider (LHC), provide an additional tool to gain insights into particle production mechanisms and infer transport properties, such as the ratio of shear viscosity to entropy density, of the medium created in Pb-Pb collisions. The longitudinal long-range correlations and the large azimuthal anisotropy measured at low transverse momenta in small collision systems, namely pp and p-Pb, at LHC energies resemble manifestations of collective behaviour. This suggests that locally equilibrated matter may be produced in these small collision systems, similar to what is observed in Pb-Pb collisions. In this work, the same two-particle transverse momentum differential correlators are exploited in pp and p-Pb collisions at $\sqrt{s} = 7$ TeV and $\sqrt{s_{\rm NN}} = 5.02$ TeV, respectively, to seek evidence for viscous effects. Specifically, the strength and shape of the correlators are studied as a function of the produced particle multiplicity to identify evidence for longitudinal broadening that might reveal the presence of viscous effects in these smaller systems. The measured correlators and their evolution from pp and p--Pb to Pb--Pb collisions are additionally compared to predictions from Monte Carlo event generators, and the potential presence of viscous effects is discussed.
Two-particle transverse momentum correlation $G_{2}^{\rm CD}$ for 0$-$5% multiplicity class pp collisions at $\sqrt{s}=7\;\text{TeV}$.
Two-particle transverse momentum correlation $G_{2}^{\rm CD}$ for 30$-$40% multiplicity class pp collisions at $\sqrt{s}=7\;\text{TeV}$.
Two-particle transverse momentum correlation $G_{2}^{\rm CD}$ for 70$-$80% multiplicity class pp collisions at $\sqrt{s}=7\;\text{TeV}$.
The fractions of non-prompt (i.e. originating from beauty-hadron decays) D$^0$ and D$^+$ mesons with respect to the inclusive yield are measured as a function of the charged-particle multiplicity in proton$-$proton collisions at a centre-of-mass energy of $\sqrt{s} = 13$ TeV with the ALICE detector at the LHC. The results are reported in intervals of transverse momentum ($p_{\rm T}$) and integrated in the range $1 < p_{\rm T} < 24$ GeV/$c$. The fraction of non-prompt D$^0$ and D$^+$ mesons is found to increase slightly as a function of $p_{\rm T}$ in all the measured multiplicity intervals, while no significant dependence on the charged-particle multiplicity is observed. In order to investigate the production and hadronisation mechanisms of charm and beauty quarks, the results are compared to PYTHIA 8 as well as EPOS 3 and EPOS 4 Monte Carlo simulations, and to calculations based on the colour glass condensate including three-pomeron fusion.
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