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The study of open charm meson production provides an efficient tool for the investigation of the properties of hot and dense matter formed in nucleus–nucleus collisions. The interpretation of the existing di-muon data from the CERN SPS suffers from a lack of knowledge on the mechanism and properties of the open charm particle production. Due to this, the heavy-ion programme of the NA61/SHINE experiment at the CERN SPS has been extended by precise measurements of charm hadrons with short lifetimes. A new Vertex Detector for measurements of the rare processes of open charm production in nucleus–nucleus collisions was designed to meet the challenges of track registration and high resolution in primary and secondary vertex reconstruction. A small-acceptance version of the vertex detector was installed in 2016 and tested with Pb + Pb collisions at 150 A GeV / c . It was also operating during the physics data taking on Xe + La and Pb + Pb collisions at 150 A GeV / c conducted in 2017 and 2018. This paper presents the detector design and construction, data calibration, event reconstruction, and analysis procedure.

The flow of light charged particles from the Au+Au reaction at 400 AMeV measured with the KRATTA detector is presented. The results are compared with the FOPI data. The KRATTA detector (Krakow Triple Telescope Array) [1] has been used to measure the energy, emission angles and isotopic composition of light charged reaction products in the ASY-EOS experiment at GSI laboratory [2]. This versatile, low threshold, broad energy range system consists of 38 independent modules which can be arranged in an arbitrary configuration - Fig. 1 presents the used 7x5 array. A single module, covering actively about 4.5 msr of the solid angle at the optimal distance of 40 cm from the target, consists of three identical, 500 mu m thick, large area photodiodes, used also for direct detection, and of two CsI(1500 ppm Tl) crystals of 2.5 and 12.5 cm length, respectively. The presented results come from the analysis of the experimental data for Au+Au at 400 MeV/nucleon incident energy. Signals from the KRATTA modules have been stored for the off-line analysis using the 100 MHz V1724 CAEN digitizers. The pulse shape analysis allowed to decompose the complex signals from the middle photodiode (Single Chip Telescope [3] segment, SCT) into the ionization and scintillation components and to obtain a satisfactory isotopic resolution with a single readout channel.

Measurements of inclusive spectra and mean multiplicities of π ± , K ± , p and p ¯ produced in inelastic p + p interactions at incident projectile momenta of 20, 31, 40, 80 and 158  GeV / c ( s = 6.3, 7.7, 8.8, 12.3 and 17.3  GeV , respectively) were performed at the CERN Super Proton Synchrotron using the large acceptance NA61/SHINE hadron spectrometer. Spectra are presented as function of rapidity and transverse momentum and are compared to predictions of current models. The measurements serve as the baseline in the NA61/SHINE study of the properties of the onset of deconfinement and search for the critical point of strongly interacting matter.

A simple method to reduce the background from secondary reactions in telescopes composed of long CsI(Tl) crystals is presented. The method has been developed for the KRATTA [1] modules.

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 ASY-EOS experiment at GSI laboratory measured the direct and elliptic flow of neutrons and light charged particles in the reaction 197Au+197 Au at 400 A MeV incident energy. The ratio of elliptic flow of neutrons with respect to that of the light charged particles was used as main experimental observable to probe the density dependence of the symmetry energy term of the nuclear equation of state. Results, obtained by comparison of the experimental data with the UrQMD model predictions, strongly support a moderately soft to linear density dependence of the symmetry energy at suprasaturation densities below 2ρ0.

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.

We present experimental results on inclusive spectra and mean multiplicities of negatively charged pions produced in inelastic p+p interactions at incident projectile momenta of 20, 31, 40, 80 and 158 GeV/ c ( s = 6.3, 7.7, 8.8, 12.3 and 17.3 GeV, respectively). The measurements were performed using the large acceptance NA61/SHINE hadron spectrometer at the CERN super proton synchrotron. Two-dimensional spectra are determined in terms of rapidity and transverse momentum. Their properties such as the width of rapidity distributions and the inverse slope parameter of transverse mass spectra are extracted and their collision energy dependences are presented. The results on inelastic p+p interactions are compared with the corresponding data on central Pb+Pb collisions measured by the NA49 experiment at the CERN SPS. The results presented in this paper are part of the NA61/SHINE ion program devoted to the study of the properties of the onset of deconfinement and search for the critical point of strongly interacting matter. They are required for interpretation of results on nucleus–nucleus and proton–nucleus collisions.