No Arabic abstract
Results for high multiplicity pp and p-Pb collisions at the LHC have revealed that these small collision systems exhibit features of collectivity. To understand the origin of these unexpected phenomena, the relative transverse activity classifier ($R_{rm{T}}$) can be exploited as a tool to disentangle soft and hard particle production, by studying the yield of charged particles in different topological regions associated with transverse momentum trigger particles. This allows to study system size dependence of charged particle production of different origins and in particular search for jet-quenching effects. Here, results on the system size and $R_{rm{T}}$ dependence of charged particle production in pp, p-Pb and Pb-Pb collisions at $sqrt{s_{rm NN}}$ = 5.02 TeV are presented.
In these proceedings, measurements of angular correlations between hadron pairs in pp collisions obtained by the ALICE experiment at the LHC are presented and compared with phenomenological predictions. Correlations between particles carrying the same and opposite quantum numbers are studied to understand the hadron production mechanism, and the difference between same-sign and opposite-sign correlations is used to probe charge-dependent effects in particle production. Correlation measurements dominated by minijet fragmentation agree well with the models, but other results, in particular correlations between baryons and strange hadrons, are not yet understood.
Particle production in small systems (pp and p-Pb collisions) has unveiled unexpected collective-like behavior. In this work an overview of the current investigation on the similarities between small systems and heavy-ion collisions is presented. Recent results from the experiments at the LHC are discussed. They include measurements of multi-particle correlations, as well as, identified particle production as a function of charged-particle multiplicity density, and more recently, as a function of transverse spherocity.
The interpretation of the new effect of the superfluidity in reactions with small number of particles is discussed in a simple model where the exact solution is accessible. It is find that the fluctuations of observable with the gauge angle reproduce well the exact fluctuations. Then a method of projection is proposed and tested to determine the transfer probabilities between two superfluid systems.
At LHC energies, the charged-particle multiplicity dependence of particle production is a topic of considerable interest in $pp$ collisions. It has been argued that multiple partonic interactions play an important role in particle production mechanisms, not only affecting the soft processes but also the hard processes. Recently, ALICE has measured $J/psi$ production as a function of charged-particle multiplicity to study the correlation between soft and hard processes. In this contribution, we present the $J/psi$ production versus multiplicity for $pp$ and $p-Pb$ collisions measured by ALICE. We compare the results with different theoretical models.
A study investigating a possible jet shape dependence on the charged event multiplicity was performed on collision samples generated by Monte-Carlo (MC) event generators PYTHIA and HIJING++. We calculated the integral jet shape and found a significant modification caused by multiple-parton interactions. By interchanging and enabling different model ingredients in the simulations and analyzing the results in several $p_T$ bins and event multiplicity classes, we found a characteristic jet size measure that was independent of the chosen tunes, settings, and jet reconstruction algorithms.