987 research outputs found
Long-range rapidity correlations in high energy AA collisions in Monte Carlo model with string fusion
The magnitude of long-range correlations between observables in two separated
rapidity windows, proposed as a signature of the string fusion and percolation
phenomenon, is studied in the framework of non-Glauber Monte Carlo
string-parton model, based on the picture of elementary collisions of color
dipoles. The predictions, obtained with and without string fusion, demonstrate
effects of color string fusion on the observables in Pb-Pb collisions at the
LHC: decrease of n-n correlation coefficient with centrality and negative pt-n
correlations, if the sufficiently effective centrality estimator is applied. In
general case it is shown that the values of n-n and pt-n correlation
coefficients strongly depend on the method of collision centrality fixation. In
contrast, the predictions obtained for pt-pt correlation have almost no effect
of centrality determination method and the corresponding experimental data
would produce the strong limitation on the transverse radius of a string.Comment: 5 pages, 4 figures, to be published in EPJ Web of Conferences
(INPC2013 proceedings
Forward-backward multiplicity correlations in pp collisions at high energy in Monte Carlo model with string fusion
The correlations between multiplicities in two separated rapidity windows, is
studied in the framework of the Monte Carlo model based on the picture of
string formation in elementary collisions of colour dipoles. The hardness of
the elementary collisions is defined by a transverse size of the interacting
dipoles. The dependencies of the forward-backward correlation strength on the
width and position of the pseudorapidity windows, as well as on transverse
momentum range of observed particles were studied. It is demonstrated that
taking into account of the string fusion effects improves the agreement with
the available experimental data.Comment: 4 pages, 3 figures, proc. PANIC 201
Model of pp and AA collisions for the description of long-range correlations
Soft processes in pp and AA interactions are considered in the framework of
phenomenological model with color strings formation and fusion. Elementary
parton collisions are realized in the model as the interaction of two colour
dipoles from projectile and target nucleons. Modeling of the exclusive
distributions of parton momentum fractions and transverse coordinates is
performed. The interaction of colour strings in transverse plane is carried out
in the framework of local string fusion model with the introduction of the
lattice in the impact parameter plane and taking into account the finite
rapidity length of strings. The parameters were fixed with experimental data on
pp total inelastic cross section and charged multiplicity. The model was used
for the calculation of long-range correlations between the multiplicities (n)
and the mean transverse momenta (pt) of charged particles. The dependence of
n-n, pt-n, pt-pt correlations on the width and position of the backward and
forward rapidity windows was studied. Note that the model enables to describe
the AA interactions without referring to the Glauber picture based on the
concept of elementary nucleon-nucleon collisions. In this connection the
charged multiplicity, the mean numbers of participant nucleons and binary
collisions and their variances in the case of PbPb collisions were calculated
and compared with the predictions of alternative models and the experimental
data. The influence of different ways of centrality determination on the
multiplicity fluctuations and long-range correlations was also discussed.Comment: 20 pages, 14 figures, proc. Baldin ISHEPP XX
Strongly intensive observable between multiplicities in two acceptance windows in a string model
The strongly intensive observable between multiplicities in two acceptance
windows separated in rapidity and azimuth is calculated in the model with
quark-gluon strings acting as 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 analyzed. In the case with independent
identical strings the model calculation confirms the strongly intensive
character of this observable: it is independent of both the mean number of
string and its fluctuation. For this case the peculiarities of its behaviour
for particles with different electric charges are also analyzed. In the case
when the string fusion processes are taken into account and a formation of
strings of a few different types takes place in a collision, this observable is
proved to be equal to a weighted average of its values for different string
types. Unfortunately, in this case through the weight factors this observable
becomes dependent on collision conditions and, strictly speaking, can not be
considered any more as strongly intensive variable. For a comparison the
results of the calculation of considered observable with the PYTHIA event
generator are also presented.Comment: 20 pages, 9 figure
Correlation between heavy flavour production and multiplicity in string fusion approach
The multiplicity dependence of heavy flavour production in pp-collisions at LHC energies is studied in the framework of string fusion approach. We applied a Monte Carlo model [1, 2], with the string configurations simulating event-by-event. We assumed that the heavy flavour yield is proportional to the number of initial strings, whereas a total charged particle multiplicity is influenced by the string fusion process and can be obtained according to the standard string fusion prescriptions. We show that under this assumption the faster-than-linear growth of the open charm production, observed in experiment [3], can be related to the reduction of the total multiplicity due to string overlapping and fusion. The influence of this effect on forward-backward correlations involving heavy flavours is also discussed
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