A theoretical description of long-range correlations between observables measured in separated rapidity intervals for nucleus-nucleus collisions at high energies is given. With allowance for an ...actual distribution of nucleons in nuclei, the p{sub t}n and nn correlation functions and respective correlation coefficients are calculated at various values of the impact parameter. It is shown that fluctuations of the impact parameter at a level of 1 fm, which are irremovable in experiments, affect the correlation coefficients substantially. It is shown that p{sub t}n correlations become much more pronounced upon going over from the SPS to the RHIC and LHC energies. The p{sub t}n and nn correlation functions calculated for the minimumbias case (that is, without selection in centrality) are compared with experimental data on PbPb collisions at the SPS energies.
The strongly intensive observable between multiplicities in two acceptance windows separated in rapidity is calculated in the model with quark-gluon strings acting as particle emitting sources. The ...dependence of this observable on the two-particle correlation function of a string, the width of observation windows and the rapidity gap between them is presented. String fusion effects violate the property of strong intensity. Changes in the behaviour of this observable with energy and collision centrality, arising due to the string fusion phenomena, are discussed. Predictions for the NICA collision energy range are presented.
Charmonium production in heavy ion collisions is considered as an important diagnostic probe for studying the phase diagram of strongly interacting matter for potential phase transitions. The ...interpretation of existing data from the CERN SPS is hampered by a lack of knowledge on the properties of open charm particle production in the fireball. Moreover, open charm production in heavy ion collisions by itself is poorly understood. To overcome this obstacle, the NA61/SHINE was equipped with a Small Acceptance Vertex Detector (SAVD), which is predicted to make the experiment sensitive to open charm mesons produced in A-A collisions at the SPS top energy. This paper will introduce the concept and the hardware of the SAVD. Moreover, first running experience as obtained in a commissioning run with a 150
A
GeV/
c
Pb+Pb collision system will be reported.
Charmonium production in heavy ion collisions is considered as an important diagnostic probe for studying the phase diagram of strongly interacting matter for potential phase transitions. The ...interpretation of existing data from the CERN SPS is hampered by a lack of knowledge on the properties of open charm particle production in the fireball. Moreover, open charm production in heavy ion collisions by itself is poorly understood. To overcome this obstacle, the NA61/SHINE was equipped with a Small Acceptance Vertex Detector (SAVD), which is predicted to make the experiment sensitive to open charm mesons produced in A-A collisions at the SPS top energy. This paper will introduce the concept and the hardware of the SAVD. Moreover, first running experience as obtained in a commissioning run with a 150 AGeV/c Pb+Pb collision system will be reported.
Within the model with quark–gluon strings (color flux tubes) as sources, the properties of the strongly intensive variable
, which characterizes correlations between the number of particles, which ...are detected in
pp
interactions at LHC energies in two observation windows separated in rapidity, are investigated. It is found that the behavior of this variable observed in the ALICE experiment can be explained only in the presence of different type sources, the role of which in the model is played by single strings and the clusters formed by the fusion of several strings. It is shown that a comparison of the model results with the preliminary experimental ALICE data obtained in
pp
collisions at energies of 0.9 and 7 TeV makes it possible to extract data on the parameters characterizing the clusters with different numbers of fused strings. The dependence of the observable
on a degree of the
pp
-collision centrality is also studied. In general, it is shown that in
pp
collisions at LHC energies, the increase in this variable with the initial energy and centrality of collisions in
pp
interactions is explained by the increasing contribution from the formation of string clusters consisting of a growing number of fused strings.
We obtain an explicit analytic expression for the asymptotic behavior of the coefficient of correlation between the average transverse momenta of particles formed in a given event in ...rapidity-separated intervals. The asymptotic behavior is found for a large density of strings with their fusion taken into account by introducing a lattice in the transverse plane and using the translation invariance in rapidity of the string decay process at high energies. It is established that unlike the correlation between the momenta of individual particles, the correlation between the average transverse momenta of all particles created in a given event in two separated rapidity intervals does not decrease as the total number of formed strings increases, which makes this type of correlation promising for observation in nuclear collision processes at high energies. We also show that in this limit, the asymptotic behavior of the coefficient of correlation between the average transverse momenta is independent of the variance of the number of particles formed during the string fragmentation unlike previously studied correlations between multiplicities or between the average transverse momenta and the multiplicity.
A silicon vertex detector of the MPD tracking system was proposed for high-efficient registration of short-lived particles produced in nucleus–nucleus collisions. In this work the pointing resolution ...of the various vertex detector configurations based on monolithic active pixel sensors has been evaluated. It is shown that the five-layer model of the vertex detector surrounding a 40 mm diameter beam pipe has the best spatial resolution. This allows to reconstruct the decay vertices of short-lived charmed particles. The yield of D mesons, as well as the production of pions and protons, with momenta outside the region kinematically allowed for p+p interactions at central rapidities in Au+Au collisions at NICA collider energies, was estimated in the context of the application of this vertex detector.
By direct Monte Carlo simulations it is shown that the anisotropic flows can be successfully described in the colour string picture with fusion and percolation provided anisotropy of particle ...emission from the fused string is taken into account. Quenching of produced particles in the strong colour field of the string is the basic mechanism for this anisotropy. The concrete realization of this mechanism is borrowed from the QED. Due to dependence of this mechanism on the external field strength the found flows grow with energy, with values for v2 at LHC energies greater by 15% than at RHIC energies.
By the model with the fusion of quark-gluon strings on a transverse lattice the correlations between observables from separated rapidity intervals in high-energy hadronic interactions are considered. ...The asymptotes of the long-range rapidity correlation coefficients between the multiplicities (
n
–
n
) and between the event-mean transverse momentum and the multiplicity of charged particles (
pt
–
n
) in these observation windows at large string density were explicitly calculated with the additional condition fixing the total number of initial strings. It is shown that this condition, which imitates in our model the fixation of the collision centrality class, has a significant impact on the behavior of the
n
–
n
and
pt
–
n
correlation coefficients for both homogeneous and inhomogeneous distribution of strings in the transverse plane.
Ridge from strings Braun, M. A.; Pajares, C.; Vechernin, V. V.
The European physical journal. A, Hadrons and nuclei,
04/2015, Letnik:
51, Številka:
4
Journal Article
Recenzirano
Odprti dostop
.
In the colour string picture with fusion and percolation it is shown that long-range azimuthal-rapidity correlations (ridge) can arise from the superposition of many events with exchange of ...clusters of different number of strings and not from a single event. Relation of the ridge with the flow harmonics coefficients is derived. By direct Monte Carlo simulations, in the technique previously used to calculate these coefficients, ridge correlations are calculated for AA, pA and pp collisions. The azimuthal anisotropy follows from the assumed quenching of the emitted particles in the strong colour fields inside string clusters. It is confirmed that in pp collisions the ridge structure only appears in rare events with abnormally high multiplicity. Comparison with the experimental data shows a good agreement. Good agreement is also found for pPb collisions. For AA collisions a reasonable agreement is found for both near-side and away-side angular correlations although it worsens at intermediate angles.
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