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We investigate the possibility to constrain the intrinsic charm probability \\[w_{\\mathrm{c} {\\bar{{\\mathrm{c}}}= P_{{\\mathrm{c}{\\bar{\\mathrm{c}}} /\\mathrm{p}}\\] using first ATLAS data on the associated production of prompt photons and charm-quark jets in pp collisions at \\[\\sqrt{s} = 8\\] TeV. The upper limit \\[w_{\\mathrm{c} {\\bar{{\\mathrm{c}}}< 1.93\\] % is obtained at the 68 % confidence level. This constraint is primarily determined from the theoretical scale and systematical experimental uncertainties. Suggestions for reducing these uncertainties are discussed. The implications of intrinsic heavy quarks in the proton for future studies at the LHC are also discussed.

A common library, TMDlib2, for Transverse-Momentum-Dependent distributions (TMDs) and unintegrated parton distributions (uPDFs) is described, which allows for easy access of commonly used TMDs and uPDFs, providing a three-dimensional (3D) picture of the partonic structure of hadrons. The tool TMDplotter allows for web-based plotting of distributions implemented in TMDlib2, together with collinear pdfs as available in LHAPDF.

Inclusive spectra of the kaons produced in ArSc collisions as functions of their transverse momentum p T at mid-rapidity have been calculated within the approach based on the assumption of the similarity of inclusive spectra of the hadrons produced in nucleus–nucleus collisions at their small transverse momenta in the mid-rapidity region taking into account the quark-gluon dynamics in nucleon–nucleon interactions. This article gives a satisfactory description of NA61/SHINE data on p T -spectra of the K ± mesons produced in ArSc collisions at the mid-rapidity ( y ≃ 0).

We report on newest results in -factorization approach for -processes. We describe HERA data on longitudinal structure function measurements as well as on associated prompt photon and jet photoproduction. The calculations include first application of the new LLM-2022 transverse momentum dependent gluon distribution developed by the authors. The study includes also the first implementation of parton showers for photoproduction processes in -factorization. The data are described well with the simulations. The -processes are included to the new version of Monte-Carlo generator pegasus.

Further development of the approach to the study of relativistic nuclear interactions in the space of four-dimensional velocities using the similarity principle is reported. In essence, the approach is modified by including quark–gluon dynamics in hadron generation during nucleus–nucleus interactions in the central rapidity region. Inclusive spectra of pions and kaons produced in pp and nucleus–nucleus, collisions are studied as a function of their transverse momentum p T in the central rapidity region calculated within the modified approach based on the assumption of similarity of inclusive hadron spectra. A satisfactory description is given of the NA61/SHINE data for the yield ratios K + /π + and K − /π − as a function of in pp and BeBe collisions. Calculations of antiparticle-to-particle yield ratios ( , , ) in proton–proton and nucleus–nucleus reactions are presented.

A review on the gluon transverse momentum dependent distribution (TMD) and its application to the analysis of the DIS at the HERA energies, hard and soft processes at LHC energies and mid-rapidity is presented.

This paper reports measurements of two-pion femtoscopic correlations in Be+Be collisions at a beam momentum of 150 A GeV / c  (energy available in the center-of-mass system for nucleon pair s NN = 16.84 GeV) by the NA61/SHINE experiment at the CERN SPS accelerator. The obtained momentum space correlation functions can be well described by a Lévy distributed source model. The transverse mass dependence of the Lévy source parameters is presented, and their possible theoretical interpretations are discussed. The results show that the Lévy exponent α is approximately constant as a function of m T  , and far from both the Gaussian case of α = 2 or the conjectured value at the critical endpoint, α = 0.5 . The radius scale parameter R shows a slight decrease in m T  , which can be explained as a signature of transverse flow. Finally, an approximately constant trend of the intercept parameter λ as a function of m T  was observed, similar to previous NA44 S + Pb results (obtained with a Gaussian approximation, but unlike RHIC results).

The NA61/SHINE experiment at the CERN Super Proton Synchrotron studies the onset of deconfinement in strongly interacting matter through a beam energy scan of particle production in collisions of nuclei of varied sizes. This paper presents results on inclusive double-differential spectra, transverse momentum and rapidity distributions and mean multiplicities of π ± , K ± , p and p ¯ produced in 40 Ar+ 45 Sc collisions at beam momenta of 13 A , 19 A , 30 A , 40 A , 75 A and 150 A   Ge V / c . The analysis uses the 10% most central collisions, where the observed forward energy defines centrality. The energy dependence of the K ± / π ± ratios as well as of inverse slope parameters of the K ± transverse mass distributions are placed in between those found in inelastic p + p and central Pb + Pb collisions. The results obtained here establish a system-size dependence of hadron production properties that so far cannot be explained either within statistical or dynamical models.

Strong interactions preserve an approximate isospin symmetry between up ( u ) and down ( d ) quarks, part of the more general flavor symmetry. In the case of K meson production, if this isospin symmetry were exact, it would result in equal numbers of charged ( K + and K − ) and neutral ( K 0 and K ¯ 0 ) mesons produced in collisions of isospin-symmetric atomic nuclei. Here, we report results on the relative abundance of charged over neutral K meson production in argon and scandium nuclei collisions at a center-of-mass energy of 11.9 GeV per nucleon pair. We find that the production of K + and K − mesons at mid-rapidity is (18.4 ± 6.1)% higher than that of the neutral K mesons. Although with large uncertainties, earlier data on nucleus-nucleus collisions in the collision center-of-mass energy range 2.6 < s N N < 200 GeV are consistent with the present result. Using well-established models for hadron production, we demonstrate that known isospin-symmetry breaking effects and the initial nuclei containing more neutrons than protons lead only to a small (few percent) deviation of the charged-to-neutral kaon ratio from unity at high energies. Thus, they cannot explain the measurements. The significance of the flavor-symmetry violation beyond the known effects is 4.7 σ when the compilation of world data with uncertainties quoted by the experiments is used. New systematic, high-precision measurements and theoretical efforts are needed to establish the origin of the observed large isospin-symmetry breaking. Strong interaction is blind to quark flavor, so collisions of nuclei with the same number of protons and neutrons should generate the same number of charged and neutral kaons. Here, instead, the authors show a significant excess of charged over neutral kaon production in Ar+Sc nuclei collisions, compatibly with earlier measurements which however suffered from larger uncertainties, and show that known effects cannot explain the result.

The critical point of strongly interacting matter is searched for at the CERN SPS by the NA61/SHINE experiment in central 40 Ar +  45 Sc collisions at 13  A , 19  A , 30  A , 40  A , and 75  A  GeV/ c . The dependence of the second-order scaled factorial moments of proton multiplicity distributions on the number of subdivisions in transverse momentum space is measured. The intermittency analysis uses statistically independent data sets for every subdivision in transverse and cumulative-transverse momentum variables. The results obtained do not indicate the searched intermittent pattern. An upper limit on the fraction of correlated protons and the intermittency index is obtained based on a comparison with the Power-law Model.