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Register a new userHadron production in pp and p-Pb collisions: A mass dependent phenomenon
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The mass dependence plays a significant role in the yield enhancement or suppression of hadrons in pp and p-Pb collisions at the LHC energies. This has been observed by parameterizing the variation of yield ratios between any two hadrons with event charged-particle multiplicity using a single empirical function. We notice that this variation is independent of all quantum numbers and solely depends on masses of hadrons and masses of their valence quarks. The function shows that the amount of quark deconfinement increases with event multiplicity, and the quark coalescence favours more the production of heavier hadrons compared to lighter ones.
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Recent results for high multiplicity pp and p-Pb collisions have revealed that they exhibit heavy-ion-like behaviors. To understand the origin(s) of these unexpected phenomena, event shape observables such as transverse spherocity ($S_{rm 0}^{p_{rm T} = 1}$) and the relative transverse activity classifier ($R_{rm{T}}$) can be exploited as a powerful tools to disentangle soft (non-perturbative) and hard (perturbative) particle production. Here, the production of light-flavor hadrons is shown for various $S_{rm 0}^{p_{rm T} = 1}$ classes in pp collisions at $sqrt{s}$ = 13 $textrm{TeV}$ measured with the ALICE detector at the LHC are presented. The evolution of average transverse momentum ($langle p_{rm T}rangle$) with charged-particle multiplicity, and identified particle ratios as a function of $p_{rm T}$ for different $S_{rm 0}^{p_{rm T} = 1}$ are also presented. In addition, the system size dependence of charged-particle production in pp, p-Pb, and Pb-Pb collisions at $sqrt{s_{rm NN}}$ = 5.02 TeV is presented. The evolution of $langle p_{rm T}rangle$ in different topological regions as a function of $R_{rm{T}}$ are presented. Finally, using the same approach, we present a search for jet quenching behavior in small collision systems.
It has been observed that the yields of strange and multi-strange hadrons relative to pion increase significantly with the event charged-particle multiplicity. We notice from experimental data that yield ratios between non-strange hadrons, like p/$pi$ or hadrons of same strange content, like $Lambda$/K$_s^0$, show similar enhancement. We have studied this behavior within the ambit of a parton model (EPOS3) and A Multi-Phase Transport (AMPT) model in pp and p-Pb collisions at LHC energies. We investigate model predictions of yields and yield ratios of different identified hadron productions as a function of charged-particle multiplicity and compare them with published ALICE results. The string melti
We study charm production in Pb+Pb collisions at $sqrt{s_{rm NN}}=$2.76 TeV in the Parton-Hadron-String-Dynamics transport approach and the charm dynamics in the partonic and hadronic medium. The charm quarks are produced through initial binary nucleon-nucleon collisions by using the PYTHIA event generator taking into account the (anti-)shadowing incorporated in the EPS09 package. The produced charm quarks interact with off-shell massive partons in the quark-gluon plasma and are hadronized into $D$ mesons through coalescence or fragmentation close to the critical energy density, and then interact with hadrons in the final hadronic stage with scattering cross sections calculated in an effective Lagrangian approach with heavy-quark spin symmetry. The PHSD results show a reasonable $R_{rm AA}$ and elliptic flow of $D$ mesons in comparison to the experimental data for Pb+Pb collisions at $sqrt{s_{NN}}$ = 2.76 TeV from the ALICE Collaboration. We also study the effect of temperature-dependent off-shell charm quarks in relativistic heavy-ion collisions. We find that the scattering cross sections are only moderately affected by off-shell charm degrees of freedom. However, the position of the peak of $R_{rm AA}$ for $D$ mesons depends on the strength of the scalar partonic forces which also have an impact on the $D$ meson elliptic flow. The comparison with experimental data on the $R_{rm AA}$ suggests that the repulsive force is weaker for off-shell charm quarks as compared to that for light quarks. Furthermore, the effects from radiative charm energy loss appear to be low compared to the collisional energy loss up to transverse momenta of $sim$ 15 GeV/c.
Measurements made by the ALICE Collaboration of single- and two-particle distributions in high-energy pp and p-Pb collisions are used to characterize the interactions in small collision systems, tune models of particle production in QCD, and serve as a baseline for heavy-ion observables. The measurements of charged-particle multiplicity density, $langle dN_{ch}/detarangle$, and multiplicity distributions are shown in pp and p-Pb collisions, including data from the top center-of-mass energy achieved at the Large Hadron Collider (LHC), $sqrt{s}$ = 13 TeV. Two-particle angular correlations in p-Pb collisions are studied in detail to investigate long-range correlations in pseudorapidity which are reminiscent of structures previously thought unique to heavy-ion collisions.
Recent measurements of various charm-hadron ratios in $pp$, $p$-Pb and Pb-Pb collisions at the LHC have posed challenges to the theoretical understanding of heavy-quark hadronization. The $Lambda_c/D^0$ ratio in $pp$ and $p$-Pb collisions shows larger values than those found in $e^+e^-$ and $ep$ collisions and predicted by Monte-Carlo event generators based on string fragmentation, at both low and intermediate transverse momenta ($p_T$). In AA collisions, the $D_s/D$ ratio is significantly enhanced over its values in $pp$, while the $Lambda_c/D^0$ data indicates a further enhancement at intermediate $p_T$. Here, we report on our recent developments for a comprehensive description of the charm hadrochemistry and transport in $pp$ and $AA$ collisions. For $pp$ collisions we find that the discrepancy between the $Lambda_c/D^0$ data and model predictions is much reduced by using a statistical hadronization model augmented by a large set of missing states in the charm-baryon spectrum, contributing to the $Lambda_c$ via decay feeddown. For $AA$ collisions, we develop a 4-momentum conserving resonance recombination model for charm-baryon formation implemented via event-by-event simulations that account for space-momentum correlations (SMCs) in transported charm- and thermal light-quark distributions. The SMCs, together with the augmented charm-baryon states, are found to play an important role in describing the baryon-to-meson enhancement at intermediate momenta. We emphasize the importance of satisfying the correct (relative) chemical equilibrium limit when computing the charm hadrochemistry and its momentum dependence with coalescence models.
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