SPS Energies Research Articles

A continuous wavelet transform analysis of multiparticle emission data at SPS energies

Continuous wavelet transform approach has been applied to the pseudo-rapidity distribution of shower tracks produced in [Formula: see text]O–AgBr interactions at 60[Formula: see text]AGeV and [Formula: see text]S–AgBr interactions at 200[Formula: see text]AGeV. Multiscale analysis of wavelet pseudo-rapidity spectra has been performed in order to find out the overabundance of produced tracks at some preferred pseudo-rapidity values, i.e., production of particle clusters. Presence of ring-like correlation is not confirmed from the analysis in pseudo-rapidity space only. The clusterization effect may be attributed to the presence of Bose–Einstein correlation among the produced tracks. Comparison of experimental results with that obtained from analyzing events generated by FRITIOF and UrQMD codes is not reproduced.

Open charm measurements in NA61/SHINE at CERN SPS

The measurements of open charm production was proposed as an important tool to investigate the properties of the hot and dense matter formed in nucleus-nucleus collisions as well as to provide the means for model independent interpretation of the existing data on J/ψ suppression. Recently, the experimental setup of the NA61/SHINE experiment was supplemented with a Vertex Detector which was motivated by the importance and the possibility of the first direct measurements of open charm meson production in heavy ion collisions at SPS energies. First test data taken in December 2016 on Pb+Pb collisions at 150A GeV/c allowed to validate the general concept of D0 meson detection via its D0 → π+ + K− decay channel and delivered a first indication of open charm production.The physics motivation of open charm measurements at SPS energies, pilot results on open charm production, and finally, the future plans of open charm measurements in the NA61/SHINE experiment after LS2 are presented.

The QCD Phase Diagram from Statistical Model Analysis

In high multiplicity nucleus-nucleus collisions baryon-antibaryon annihilation and regeneration occur during the final hadronic expansion phase, thus distorting the initial equilibrium multiplicity ratios. We quantify the modifications employing the hybrid UrQMD transport model and apply them to the grand canonical partition functions of the Statistical Hadronization Model(SHM). We analyze minimum bias and central Pb+Pb collision data at SPS and LHC energy. We explain the Pion to Proton ratio puzzle. We also reproduce the deuteron to proton ratio at LHC energy by the SHM, and by UrQMD after attaching a phase space coalescence process. We discuss the resulting (T,μB) diagram.

Open charm measurements at CERN SPS energies with the new Vertex Detector of the NA61/SHINE experiment

The study of open charm meson production provides an efficient tool for detailed investigations of the properties of hot and dense matter formed in nucleus-nucleus collisions. The interpretation of the existing data from the CERN SPS suffers from a lack of knowledge on the total charm production rate. To overcome this limitation the heavy-ion programme of the NA61/SHINE experiment at CERN SPS has been expanded to allow for precise measurements of particles with a short lifetime. A new Small Acceptance Vertex Detector (SAVD) was designed and constructed to meet the challenges of open charm measurements in nucleus-nucleus collisions. SAVD was installed in December 2016 for data taking with Pb+Pb collisions at 150A GeV/c. An exploratory set of collected data allowed to validate the general concept of the D0 mesons detection via its D0→π++K- decay channel and delivered the first direct observation of open charm at SPS energies. In October and November of 2017 a large statistic data set has been taken for Xe+La at 150A, 75A, and 40A GeV/c, these data are currently under intense analysis. The physics motivation behind the open charm measurements at the SPS energies will be discussed. Moreover, the concept of the SAVD hardware and status of the analysis will be shown. Also, the future plans of open charm measurements in the NA61/SHINE experiment related to the upgraded Vertex Detector will be presented.

Onset of Deconfinement and the Critical Point at SPS Energies

Onset of Deconfinement and the Critical Point at SPS Energies

Transverse momentum spectra of mesons in p+p collisions at CERN SPS energies from the UrQMD transport model

The UrQMD transport model, version 3.4, is used to study the new experimental data on total yields, rapidity distributions and transverse momentum spectra of π±, K±, p and $\bar p$ produced in inelastic p + p interactions at SPS energies, recently published by the NA61/SHINE Collaboration. The comparison of model predictions to these new measurements is presented as a function of collision energy. In addition, we compare with the experimental data the results on kaon-over-pion multiplicity ratio and the inverse slope parameter of negative kaons produced at midrapidity. A complicated pattern of discrepancies between the experimental data and the UrQMD transport model is apparent. We conclude that new experimental data analyzed in this contribution still constitute a challenge for the present version of the model.

Electromagnetic Effects on Charged Pion Spectra at SPS Energies

Electromagnetic Effects on Charged Pion Spectra at SPS Energies

New results on energy and momentum conservation in meson production for A+A collisions at SPS energies

We review our recent findings on electromagnetic (EM) effects in Ar+Sc and Pb+Pb collisions at CERN SPS energies, and discuss them in the context of our earlier results on the EM splitting of π+/π- meson directed flow. A specific space-time picture emerges, on the basis of which we construct a simple model of the collision. Starting from local energy and momentum conservation, we nicely describe the centrality dependence of π meson rapidity distributions in Pb+Pb collisions at $\rad{}{s_{NN} } = 17.3\,{\rm{GeV}}$. We discuss the resulting implications on the role of energy and momentum conservation for the dynamics of meson production in A+A collisions. We present our conclusions on the link between the initial stages of the nuclear collision and the final state observables connected to strong and electromagnetic phenomena in charged meson emission. We also discuss the possibility to use the latter EM phenomena to obtain new insight into the spectator space-time evolution and excitation energy.

Pseudorapidity dependence of multiplicity and transverse momentum fluctuations at the SPS energies

A search for the critical behavior of strongly interacting matter was done by studying the event-by-event fluctuations of multiplicity and transverse momentum of charged hadrons produced in inelastic p+p collisions and central Be+Be and Ar+Sc collisions at the NA61/SHINE experiment. Results for energy dependence of the scaled variance of the multiplicity distribution and for two families of strongly intensive measures of multiplicity and transverse momentum fluctuations Δ[PT, N] and Σ[PT, N] were presented. The study was performed in rapidity-integrated way and for different pseudorapidity regions, which corresponds to changing the rapidity averaged baryo-chemical potential and the value of temperature at the freeze-out stage. The strongly intensive measure Σ[NF, NB], evaluated in rapidity separated windows, was used in the analysis of short- and long-range multiplicity correlations and is considered to be sensitive for the initial conditions of particle production such as string fragmentation and fusion.

Some proposed fixed target experiments with the LHC beams

The physics opportunities offered by using the multi-TeV LHC beams for a fixed target experiment have been widely discussed in recent years. This mode is convenient to investigate rare processes of particle production and polarization phenomena because the expected luminosity exceeds the luminosity of the collider. The main physical goals of these experiments are: i) investigations of the large-xgluon, antiquark and heavy quark content in the nucleon and nucleus; ii) investigations of the dynamics and spin of quarks and gluons inside nucleus; iii) studies of the ion-ion collisions between SPS and RHIC energies towards large rapidities. With the LHC lead beam energy scan on a fixed target it would be possible to investigate the energy range up to 72 GeV to search for the critical point for the phase transition to the Quark Gluon Plasma (QGP).

Recent results of strong interaction program from NA61/SHINE experiment at CERN SPS

The NA61/SHINE experiment at the CERN SPS pursues a rich program of strong interactions. The main physics goals of this program are the study of properties of the onset of deconfinement and search for the signatures of the critical point of strongly interacting matter by performing the two-dimensional scan in a broad region of energy (beam momentum 13A-158A GeV/c) and system size (p+p, Be+Be, Ar+Sc and Xe+La). Recent NA61/SHINE results on particle spectra and event-by-event fluctuations in p+p, Be+Be and Ar+Sc collisions are shown with emphasis on the measurements of particle ratios, namely of pion a strangeness production, multiplicity fluctuations versus energy and the system size of colliding nuclei. It will be shown that the hadron production properties in heavy ion collisions which change rapidly in the low SPS energy domain and are interpreted as the beginning of quark-gluon plasma production – onset of deconfinement could be also the case in inelastic p+p interactions and probably in Be+Be collisions. The paper presents a selection of NA61/SHINE results on particle production properties discussed together with existing data from the NA49 collaboration. The evolution of non-monotonic structures in the pion and strangeness production as a function of the system size and energy is addressed. The rapid change of hadron production properties from p+p and Be+Be up to Ar+Sc and Pb+Pb collisions can be interpreted as the beginning of the large clusters formation of strongly interacting matter - the onset of fireball. The NA61/SHINE strong interaction programme is presented including the recent status on proton intermittency analysis and strongly intensive fluctuation observables of particle multiplicity and transverse momentum.

Role of the Spectator System in Electromagnetic Effects

The electromagnetic effects on charged pion ($\pi^+,\pi^-$) spectra provide new, independent information on the space-time evolution of the ultrarelativistic heavy ion collision. The spectator life time and its excitation energy may also be of importance for the understanding of the space-time evolution of the participant zone. This paper gives an overview of our coordinated effort to understand the interplay between electromagnetic phenomena and processes related to the fragmentation of the spectator system at forward rapidity in peripheral $Pb$+$Pb$ collisions at top CERN SPS energies. Our study includes on one hand the experimental analysis of electromagnetic effects and corresponding phenomenological Monte Carlo simulations, and on the other hand dedicated theoretical calculations based on the Abrasion-Ablation model ABRABLA and the 4D Langevin approach.

Event-by-event fluctuations in p+p and central A+A collisions within relativistic transport models

Event-by-event multiplicity fluctuations in nucleus–nucleus collisions are studied within the relativistic transport models: EPOS, PHSD, and UrQMD. As measures of particle number fluctuations we consider the scaled variances ω[X] for positive, negative, and all charged hadrons, and the strongly intensive quantities for K+ and π+ yields. At the SPS energy range the fluctuation measures are calculated for proton–proton, Ar+Sc, and Pb+Pb collisions. Comparison with recent NA61/SHINE and older NA49 measurements of the multiplicity fluctuations is done. A validity of the model of independent sources, a role of the experimental acceptance, and the centrality selection procedure are studied.

Ψ(2S) production in p + A collisions

We have analyzed the data of ψ(2S) production in proton-nucleus (p + A) collisions, available from the NA50 Collaboration in the SPS energy domain. The investigated data sets include the absolute production cross-sections as well as ψ(2S)-to-Drell-Yan (DY) cross-section ratios. An adapted version of the two-component QVZ model has been employed to calculate ψ(2S) production cross-sections. For both ψ(2S) and DY production, nuclear modifications to the free nucleon structure functions are taken into account. For ψ(2S), the final state interaction of the produced pairs with the nuclear medium is also taken into account, in accordance with the previously analyzed data. A satisfactory description of the data in p + A collisions is obtained. Model calculations are extrapolated to predict the ψ(2S) suppression in proton-induced collisions at near-threshold energies.

HBT Radii: Comparative Studies on Collision Systems and Beam Energies

Two-particle Hanbury-Brown-Twiss (HBT) interferometry is an important probe for understanding the space-time structure of particle emission sources in high energy heavy ion collisions. We present the comparative studies of HBT radii in Pb+Pb collisions at sNN = 17.3 GeV with Au+Au collisions at sNN = 19.6 GeV. To further understand this specific energy regime, we also compare the HBT radii for Au+Au collisions at sNN = 19.6 GeV with Cu+Cu collisions at sNN = 22.4 GeV. We have found interesting similarity in the Rout/Rside ratio with mT across the collision systems while comparing the data for this specific energy zone which is interesting as it acts as a bridge from SPS energy regime to the RHIC energy domain.

Hadron resonance gas model with induced surface tension

Here we present a physically transparent generalization of the multicomponent Van der Waals equation of state in the grand canonical ensemble. For the one-component case the third and fourth virial coefficients are calculated analytically. It is shown that an adjustment of a single model parameter allows us to reproduce the third and fourth virial coefficients of the gas of hard spheres with small deviations from their exact values. A thorough comparison of the compressibility factor and speed of sound of the developed model with the one and two component Carnahan-Starling equation of state is made. It is shown that the model with the induced surface tension is able to reproduce the results of the Carnahan-Starling equation of state up to the packing fractions 0.2-0.22 at which the usual Van der Waals equation of state is inapplicable. At higher packing fractions the developed equation of state is softer than the gas of hard spheres and, hence, it breaks causality in the domain where the hadronic description is expected to be inapplicable. Using this equation of state we develop an entirely new hadron resonance gas model and apply it to a description of the hadron yield ratios measured at AGS, SPS, RHIC and ALICE energies of nuclear collisions. The achieved quality of the fit per degree of freedom is about 1.08. We confirm that the strangeness enhancement factor has a peak at low AGS energies, while at and above the highest SPS energy of collisions the chemical equilibrium of strangeness is observed. We argue that the chemical equilibrium of strangeness, i.e. $\gamma_s \simeq 1$, observed above the center of mass collision energy 4.3 GeV may be related to the hadronization of quark gluon bags which have the Hagedorn mass spectrum, and, hence, it may be a new signal for the onset of deconfinement.

Pseudorapidity Dependence of Multiplicity and Transverse Momentum Fluctuations in pp Collisions at SPS Energies

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Rapid Change of Multiplicity Fluctuations in System Size Dependence at SPS Energies

Recent preliminary results on multiplicity fluctuations in p+p, Be+Be and Ar+Sc collisions from the NA61/SHINE collaboration are presented. The scaled variance of charged hadron multiplicity changes little when going from p+p to Be+Be collisions and drops dramatically from Be+Be to Ar+Sc interactions. The centrality selection procedure and the influence of volume fluctuations are discussed. Comparisons with the EPOS event generator are shown.

Open Charm Measurements at CERN SPS Energies with the New Vertex Detector of the NA61/SHINE Experiment

The heavy-ion programme of the NA61/SHINE experiment at the CERN SPS has been expanded to allow precise measurements of exotic particles with short lifetime. The study of open charm meson production is a sensitive tool for new detailed investigations of the properties of hot and dense matter formed in nucleus-nucleus collisions. In particular, it offers new possibilities for studies of such phenomena as in- medium parton energy loss and quarkonium dissociation and possible regeneration, thus providing new information to probe deconfinement. A new high resolution Vertex Detector was designed for the NA61/SHINE experiment for measurements of the very rare processes of open charm production in nucleus- nucleus collisions at the SPS. It will meet the challenges of track registration and of very precise spatial resolution in primary and secondary vertex reconstruction required for the identification of

Evidence of forward–backward multiplicity correlation at SPS energy

In this paper, a detailed study of two-particle rapidity correlation has been presented by measuring the dynamical fluctuation variable [Formula: see text] in forward and backward pseudo-rapidity window of shower particles produced in the relativistic heavy ion collision, [Formula: see text]O–AgBr interactions at 60[Formula: see text]AGeV and [Formula: see text]S–AgBr interactions at 200[Formula: see text]AGeV. Variations of [Formula: see text] with rapidity gap between forward and backward zones and with the width of each zone have been studied. For both cases, [Formula: see text] increase with increasing either width of the zone or gap between the zones. Our findings show the presence of strong long-range correlation. Comparison of experimental results with MC-RAND events confirms the present correlation to be dynamical in nature. We have also compared our results with FRITIOF and UrQMD events. Such events also show the presence of correlation, but found to fail to reproduce the experimental results both quantitatively and qualitatively. Strength of correlation is dependent on the centrality of collision for experimental events, it decreases with centrality.