• Energy Research

Within the framework of the model with quark-gluon strings (color flux tubes) as sources, the properties of the strongly intense variable Σ, which characterizes the correlations between the number of particles in two observation windows separated in rapidity, are studied. It is shown that, in pp collisions at LHC energies, string fusion effects leading to the formation of string clusters have a significant effect on the behavior of this observable. The experimentally observed changes in this variable with the initial energy and centrality of the pp collision can only be explained by taking into account the formation of string clusters consisting of an increasing number of merged strings. It is demonstrated that the study of the behavior of the Σ observable as a function of the rapidity distance between the centers of the observation windows and the width of these windows with variable experimental conditions using different energies and centralities of pp-collisions makes it possible to extract the parameters of string clusters from the experimental data.

The ALICE Collaboration reports measurements of the semi-inclusive distribution of charged-particle jets recoiling from a high transverse momentum (high $p_T$) charged hadron, in pp and central Pb-Pb collisions at center-of-mass energy per nucleon–nucleon collision $\sqrt{s_{NN}}$ =5.02 TeV. The large uncorrelated background in central Pb-Pb collisions is corrected using a data-driven statistical approach which enables precise measurement of recoil jet distributions over a broad range in $p_T,_{chjet}$ and jet resolution parameter $R$. Recoil jet yields are reported for $R$= 0.2, 0.4, and 0.5 in the range $7 $<$p_T,_{chjet}$ <$140$ GeV/$c$ and $π/2$<$Δφ$<$π$, where $Δφ$ is the azimuthal angular separation between hadron trigger and recoil jet. The low-$p_T,_{chjet}$ reach of the measurement explores unique phase space for studying jet quenching, the interaction of jets with the quark–gluon plasma generated in high-energy nuclear collisions. Comparison of $p_T,_{chjet}$ distributions from $pp$ and central Pb-Pb collisions probes medium-induced jet energy loss and intra-jet broadening, while comparison of their acoplanarity distributions explores in-medium jet scattering and medium response. The measurements are compared to theoretical calculations incorporating jet quenching. Physical review / C 110(1), 014906 (2024). doi:10.1103/PhysRevC.110.014906 Published by Inst., Woodbury, NY

In this paper, the production of particles outside the region of nucleon–nucleon kinematics due to interactions involving dense cold clusters of quark-gluon matter in nuclei is calculated. The possibility of observing this process in the region of central rapidities and large transverse momenta in heavy ion collisions at low energies with MPD detector at the NICA collider is demonstrated.

Abstract The p T-differential production cross sections of non-prompt D0, D+, and $$ {\textrm{D}}_{\textrm{s}}^{+} $$ D s + mesons originating from beauty-hadron decays are measured in proton–proton collisions at a centre-of-mass energy $$ \sqrt{s} $$ s = 13 TeV. The measurements are performed at midrapidity, |y| < 0.5, with the data sample collected by ALICE from 2016 to 2018. The results are in agreement with predictions from several perturbative QCD calculations. The fragmentation fraction of beauty quarks to strange mesons divided by the one to non-strange mesons, f s /(f u + f d), is found to be 0.114 ± 0.016 (stat.) ± 0.006 (syst.) ± 0.003 (BR) ± 0.003 (extrap.). This value is compatible with previous measurements at lower centre-of-mass energies and in different collision systems in agreement with the assumption of universality of fragmentation functions. In addition, the dependence of the non-prompt D meson production on the centre-of-mass energy is investigated by comparing the results obtained at $$ \sqrt{s} $$ s = 5.02 and 13 TeV, showing a hardening of the non-prompt D-meson p T-differential production cross section at higher $$ \sqrt{s} $$ s . Finally, the $$ \textrm{b}\overline{\textrm{b}} $$ b b ¯ production cross section per unit of rapidity at midrapidity is calculated from the non-prompt D0, D+, $$ {\textrm{D}}_{\textrm{s}}^{+} $$ D s + , and $$ {\Lambda}_{\textrm{c}}^{+} $$ Λ c + hadron measurements, obtaining $$ \textrm{d}\sigma /\textrm{d}y=75.2\pm 3.2\left(\textrm{stat}.\right)\pm 5.2{\left(\textrm{syst}.\right)}_{-3.2}^{+12.3}\left(\textrm{extrap}.\right) $$ d σ / d y = 75.2 ± 3.2 stat . ± 5.2 syst . − 3.2 + 12.3 extrap . μb.

We estimate the impact of the fixation of the total number of sources (quark–gluon strings) on the long-range rapidity correlations between different observables. In our approach this condition models the fixation of the collision centrality class, what is the usual practice in modern collider experiments, like Relativistic Heavy Ion Collider (RHIC), Large Hadron Collider (LHC) and so on. The estimates are obtained under the assumption of the translational invariance in rapidity, which is usually assumed in mid-rapidity region at high energies. Based on these assumptions, we are developing a technique for the analytical calculation of various average values of extensive and intense variables at high string densities on the transverse lattice, taking into account the effects of string fusion, leading to the formation of string clusters. Using this technique we calculate the asymptotes of the correlations coefficients both between the multiplicities and between the multiplicity and the event-mean transverse momentum of particles in two separated rapidity intervals. As a result, we found that fixing the total number of strings has a significant effect on the behavior of both types of correlations, especially in the case of a uniform distribution of strings in the transverse plane.