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ABSTRACT: A simultaneous description of hadronic yields; pion, kaon, and proton
spectra; elliptic flows; and femtoscopy scales in the hydrokinetic model of A+A
collisions is presented at different centralities for the top BNL Relativistic
Heavy Ion Collider (RHIC) and CERN Large Hadron Collider (LHC) 2.76-TeV
energies. The initial conditions are based on the Glauber Monte-Carlo
simulations. When going from RHIC to LHC energy in the model, the only
parameters changed are the normalization of the initial entropy defined by the
number of all charged particles in most central collisions, contribution to
entropy from binary collisions and baryonic chemical potential. The
hydrokinetic model is used in its hybrid version (hHKM), which provides the
correct match (at the isochronic hypersurface) of the decaying hadron matter
evolution with hadronic ultrarelativistic quantum molecular dynamics cascade.
The results are compared with the standard hybrid models where hydrodynamics
and hadronic cascade are matching just at the non-space-like hypersurface of
chemical freeze-out or on the isochronic hypersurface. The modification of the
particle number ratios at LHC caused, in particular, by the particle
annihilations at the afterburn stage is also analyzed.
04/2012;
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ABSTRACT: A year ago, we presented a new approach to treat hadronic interactions or the initial stage of nuclear collisions [1,2]. It
is an effective theory based on the Gribov-Regge formalism, where the internal structure of the Pomerons at high energies
is governed by perturbative parton evolution, therefore the nameparton-based Gribov-Regge theory. The main improvement compared to models used so far is the appropriate treatment of the energy sharing between the different
elementary interactions in case of multiple scattering. It is clear that the above formalism is not yet complete. At high
energies (RHIC, LHC), the multiple elementary interactions (Pomerons) cannot be purely parallel, they interact. So we introduce
multiple Pomeron vertices into the theory.
Pramana 04/2012; 60(5):1121-1125. · 0.57 Impact Factor
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ABSTRACT: The study of very high transverse-momentum jets will be an important issue at the LHC, in particular since the corresponding
cross sections will be considerably larger than at RHIC energies. Jets are expected to provide information on QGP formation,
due to the energy loss of fast partons in the medium. Jet cross sections can in principle be compared to simple pQCD calculations,
based on the hypothesis of factorization. But often it is useful or even necessary to not only compute the production rate
of the very high-p
T jets, but in addition the “rest of the event”. The proposed talk is based on recent work, where we try to construct an event
generator—fully compatible with pQCD—which allows one to compute complete events, consisting of high-p
T jets plus all the other low p
T particles produced at the same time. Whereas in “generators of inclusive spectra” like Pythia one may easily trigger on high-p
T phenomena, this is not so obvious for “generators of physical events”, where in principle one has to generate a very large
number of events in order to finally obtain rare events (like those with a very high-p
T jet). We shall discuss how we overcome these difficulties in the framework of the EPOS model.
European Physical Journal C 04/2012; 62(1):145-150. · 3.63 Impact Factor
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ABSTRACT: We discuss a theoretical scheme that accounts for bulk matter, jets, and the
interaction between the two. The aim is a complete description of particle
production at all transverse momentum ($p_{t}$) scales. In this picture, the
hard initial scatterings result in mainly longitudinal flux tubes, with
transversely moving pieces carrying the $p_{t}$ of the partons from hard
scatterings. These flux tubes constitute eventually both bulk matter (which
thermalizes and flows) and jets. We introduce a criterion based on parton
energy loss to decide whether a given string segment contributes to the bulk or
leaves the matter to end up as a jet of hadrons. Essentially low $p_{t}$
segments from inside the volume will constitute the bulk, high $p_{t}$ segments
(or segments very close to the surface) contribute to the jets. The latter ones
appear after the usual flux tube breaking via q-qbar production (Schwinger
mechanism). Interesting is the transition region: Intermediate $p_{t}$ segments
produced inside the matter close to the surface but having enough energy to
escape, are supposed to pick up q-qbar pairs from the thermal matter rather
than creating them via the Schwinger mechanism. This represents a communication
between jets and the flowing bulk matter (fluid-jet interaction). Also very
important is the interaction between jet hadrons and the soft hadrons from the
fluid freeze-out. We employ the new picture to investigate Pb-Pb collisions at
2.76 TeV. We discuss the centrality and $p_{t}$ dependence of particle
production and long range dihadron correlations at small and large $p_{t}$.
03/2012;
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ABSTRACT: Based on results obtained with event generators we have launched the
core-corona model. It describes in a simplified way but quite successfully the
centrality dependence of multiplicity and $ $ of identified particles
observed in heavy-ion reaction at beam energies between $\sqrt{s}$ = 17 GeV and
200 GeV. Also the centrality dependence of the elliptic flow, $v_2$, for all
charged and identified particles could be explained in this model. Here we
extend this analysis and study the centrality dependence of single particle
spectra of $K^-$ and ${\bar p}$ measured by the PHENIX, STAR and BRAHMS
collaborations. We find that also for these particles the analysis of the
spectra in the core-corona model suffers from differences in the data published
by the different experimental groups, notably for the pp collisions. As for
protons and $K^+$ for each experience the data agree well with the prediction
of the core-corona model but the value of the two necessary parameters depends
on the experiments. We show as well that the average momentum as a function of
the centrality depends in a very sensitive way on the particle species and may
be quite different for particles which have about the same mass. Therefore the
idea to interpret this centrality dependence as a consequence of a collective
expansion of the system, as done in blast way fits may be premature.
01/2012;
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ABSTRACT: We discuss recent developments in the theoretical desciption of ultrarelativistic collisions, concerning an event-by-event treatment of the hydrodynamical evolution in heavy ion collisions and also in high multiplicity pp scatterings at the LHC. The initial conditions are flux-tubes, which are formed following elementary (multiple) scatterings. We show that this picture leads in a natural way to the so-called ridge structures, observed in heavy ion and proton-proton collisions
Journal of Physics Conference Series 09/2011; 316(1):012012.
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ABSTRACT: In pp scattering at 900 GeV, large numbers of elementary scatterings will contribute significantly, and the corresponding high-multiplicity events will be of particular interest. Elementary scatterings are parton ladders, identified with color flux tubes. In high-multiplicity events, many of these flux tubes are produced in the same space region, creating high-energy densities. We argue that there are good reasons to employ the successful procedure used for heavy-ion collisions: Matter is assumed to thermalize quickly, such that the energy from the flux tubes can be taken as an initial condition for a hydrodynamic expansion. This scenario gets spectacular support from very recent results on Bose-Einstein correlations in pp scattering at 900 GeV at LHC.
Phys. Rev. C. 04/2011; 83(4).
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ABSTRACT: We study untriggered di-hadron correlations in Pb+Pb at 2.76 TeV, based on an
event-by-event simulation of a hydrodynamic expansion starting from flux tube
initial conditions. The correlation function shows interesting structures as a
function of the pseudorapidity difference $\Delta\eta$ and the azimuthal angle
difference $\Delta\phi$, in particular comparing different centralities. We can
clearly identify a peak-like nearside structure associated with very low
momentum components of jets for peripheral collisions, which disappears towards
central collisions. On the other hand, a very broad ridge structure from
asymmetric flow seen at central collisions, gets smaller and finally disappears
towards peripheral collisions.
04/2011;
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ABSTRACT: Using a fluid dynamical scenario for $pp$ scattering at 7 TeV, we compute
correlation functions for $\pi^+\pi^+$ pairs. Femtoscopic radii are extracted
based on three-dimensional parametrizations of the correlation functions. We
study the radii as a function of the transverse momenta of the pairs, for
different multiplicity classes, corresponding to recent experimental results
from ALICE. We find the same decrease of the radii with $k_T$, more and more
pronounced with increasing multiplicity, but absent for the lowest
multiplicities. In the model we understand this as transition from string
expansion (low multiplicity) towards a three-dimensional hydrodynamical
expansion (high multiplicity).
04/2011;
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ABSTRACT: One of the most important experimental results for proton-proton scattering at the LHC is the observation of a so-called "ridge" structure in the two-particle correlation function versus the pseudorapidity difference Δη and the azimuthal angle difference Δφ. One finds a strong correlation around Δφ=0, extended over many units in Δη. We show that a hydrodynamical expansion based on flux tube initial conditions leads in a natural way to the observed structure. To get this result, we have to perform an event-by-event calculation, because the effect is due to statistical fluctuations of the initial conditions, together with a subsequent collective expansion. This is a strong point in favor of a fluidlike behavior even in pp scattering, where we have to deal with length scales of the order of 0.1 fm.
Physical Review Letters 03/2011; 106(12):122004. · 7.37 Impact Factor
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B Alessandro,
D. Bergman,
M. Bongi,
A. Bunyatyan,
L. Cazon,
D. d'Enterria,
I. De Mitri,
P. Doll,
R. Engel,
K Eggert, [......],
N. Sakurai,
S. Sapeta,
S. Schleich,
H Schulz,
T. Sjostrand,
L Sonnenschein,
M. Sutton,
R. Ulrich, K. Werner,
K. Zapp
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ABSTRACT: The workshop on "Hadron-Hadron and Cosmic-Ray Interactions at multi-TeV
Energies" held at the ECT* centre (Trento) in Nov.-Dec. 2010 gathered together
both theorists and experimentalists to discuss issues of the physics of
high-energy hadronic interactions of common interest for the particle, nuclear
and cosmic-ray communities. QCD results from collider experiments -- mostly
from the LHC but also from the Tevatron, RHIC and HERA -- were discussed and
compared to various hadronic Monte Carlo generators, aiming at an improvement
of our theoretical understanding of soft, semi-hard and hard parton dynamics.
The latest cosmic-ray results from various ground-based observatories were also
presented with an emphasis on the phenomenological modeling of the first
hadronic interactions of the extended air-showers generated in the Earth
atmosphere. These mini-proceedings consist of an introduction and short
summaries of the talks presented at the meeting.
01/2011;
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ABSTRACT: The core-corona model describes quite successfully the centrality dependence of multiplicity and $$ of identified particles observed in heavy ion reaction at beam energies between $\sqrt{s}$ = 17 GeV and 200 GeV. Also the centrality dependence of the elliptic flow, $v_2$, for all charged and identified particles could be explained in this model. Here we extend this analysis and study the centrality dependence of single particle spectra of identified particles. We concentrate here on protons, antiprotons, kaons and pions which have all been measured by the PHENIX, STAR and BRAHMS collaborations. We find that an analysis of the spectra in the core-corona model suffers from differences in the data published by the different experimental groups, notably for the pp collisions. For each experience the data agree well with the prediction of the core-corona model but the value of the two necessary parameters depends onthe experiments. Comment: Proceedings to the Workshop on Dense Matter - DM 2010, Stellenbosch (South Africa), April 2010
12/2010;
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ABSTRACT: Since 2006, EPOS hadronic interaction model is being used for very high energy cosmic ray analysis. Designed for minimum bias particle physics and used for having a precise description of SPS and RHIC heavy ion collisions, EPOS brought more detailed description of hadronic interactions in air shower development. Thanks to this model it was possible to understand why there were less muons in air shower simulations than observed in real data. With the start of the LHC era, a better description of hard processes and collective effects is needed to deeply understand the incoming data. We will describe the basic physics in EPOS and the new developments and constraints which are taken into account in EPOS 2. Comment: Contributed presentation to the XVI International Symposium on Very High Energy Cosmic Ray Interactions (ISVHECRI 2010), Batavia, IL, USA (28 June 2 July 2010). 4 pages, 6 figures
11/2010;
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ABSTRACT: Event by event EPOS calculations in which the expansion of the system is described by {\it ideal} hydrodynamics reproduce well the measured centrality dependence of $v_2/\epsilon_{part}$, although it has been claimed that only viscous hydrodynamics can reproduce these data. This is due to the core - corona effect which manifests itself in the initial condition of the hydrodynamical expansion. The centrality dependence of $v_2/\epsilon_{part}$ can be understood in the recently advanced core-corona model, a simple parameter free EPOS inspired model to describe the centrality dependence of different observables from SPS to RHIC energies. This model has already been successfully applied to understand the centrality dependence of multiplicities and of the average transverse momentum of identified particles.
08/2010;
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ABSTRACT: Event by event EPOS calculations in which the expansion of the system is described by ideal hydrodynamics reproduce well the measured centrality dependence of v2/part, although it has been claimed that only viscous hydrodynamics can reproduce these data. This is due to the core–corona effect which manifests itself in the initial condition of the hydrodynamical expansion. The centrality dependence of v2/part can be understood in the recently advanced core–corona model, a simple parameter-free EPOS-inspired model to describe the centrality dependence of different observables from SPS to RHIC energies. This model has already been successfully applied to understand the centrality dependence of multiplicities and of the average transverse momentum of identified particles.
Journal of Physics G Nuclear and Particle Physics 08/2010; 37(9):094006. · 4.18 Impact Factor
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ABSTRACT: Jet cross sections can be in principle compared to simple pQCD calculations, based on the hypothesis of factorization. But often it is useful or even necessary to not only compute the production rate of the very high pt jets, but in addition the "rest of the event". The proposed talk is based on recent work, where we try to construct an event generator fully compatible with pQCD which allows to compute complete events, consisting of high pt jets plus all the other low pt particles produced at the same time. Whereas in "generators of inclusive spectra" like Pythia one may easily trigger on high pt phenomena, this is not so obvious for "generators of physical events", where in principle one has to generate a very large number of events in order to finally obtain rare events (like those with a very high pt jet). We recently developped an independnat block method which allow us ta have a direct access to dedicated variables 1. We will present latest results concerning this approach. Comment: Moriond 2010 Porceeding
06/2010;
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ABSTRACT: We present a realistic treatment of the hydrodynamic evolution of ultrarelativistic heavy ion collisions, based on the following features: initial conditions obtained from a flux tube approach, compatible with the string model and the color glass condensate picture; event-by-event procedure, taking into the account the highly irregular space structure of single events, being experimentally visible via so-called ridge structures in two-particle correlations; use of an efficient code for solving the hydrodynamic equations in 3+1 dimensions, including the conservation of baryon number, strangeness, and electric charge; employment of a realistic equation-of-state, compatible with lattice gauge results; use of a complete hadron resonance table, making our calculations compatible with the results from statistical models; hadronic cascade procedure after an hadronization from the thermal matter at an early time. Comment: 29 pages, 49 figures
04/2010;
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R Bernhard,
R Field,
R Chierici,
M Cacciari,
A. Moraes,
M. Strikman,
D. Treleani,
T. C. Rogers,
A. M. Stasto,
A. Achilli, [......], K. Werner,
T. Pierog,
S. Porteboeuf,
H Hoeth,
P. Skands,
D. d'Enterria,
C. Marquet,
A. Mischke,
M. Estienne,
K Reygers
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ABSTRACT: The objective of this first workshop on Multiple Partonic Interactions (MPI) at the LHC is to raise the profile of MPI studies, summarizing the legacy from the older phenomenology at hadronic colliders and favouring further specific contacts between the theory and experimental communities. The MPI are experiencing a growing popularity and are currently widely invoked to account for observations that would not be explained otherwise: the activity of the Underlying Event, the cross sections for multiple heavy flavour production, the survival probability of large rapidity gaps in hard diffraction, etc. At the same time, the implementation of the MPI effects in the Monte Carlo models is quickly proceeding through an increasing level of sophistication and complexity that in perspective achieves deep general implications for the LHC physics. The ultimate ambition of this workshop is to promote the MPI as unification concept between seemingly heterogeneous research lines and to profit of the complete experimental picture in order to constrain their implementation in the models, evaluating the spin offs on the LHC physics program. Comment: MPI'08 international workshop has been held in October 27-31, 2008, Perugia, Italy - 349 pages
03/2010;
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Mario Deile,
David D'Enterria,
Albert De Roeck,
M. G. Albrow,
A. Alkin,
E. Avsar,
V. A. Bednyakov,
R. Brower,
A. Bunyatyan,
H Burkhardt, [......],
C-I Tan,
M Tasevsky,
O. V. Teryaev,
A Tricomi,
S. M. Troshin,
N. E. Tyurin,
G Watt,
G. Weiglein, K. Werner,
S. Yaschenko
[show abstract]
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ABSTRACT: Proceedings of the 13th International Conference on Elastic and Diffractive
Scattering (Blois Workshop) - Moving Forward into the LHC Era
02/2010;
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ABSTRACT: Recently we have shown that the centrality dependence of the multiplicity of different hadron species observed in RHIC and SPS experiments can be well understood in a simple model, dubbed core-corona model. There it is assumed that those incoming nucleons which scatter only once produce hadrons as in pp collisions whereas those which scatter more often form an equilibrated source which decays according to phase space. In this article we show that also kinematical variables like $v_2/\epsilon_{part} (N_{part})$ as well as $v_2^i/\epsilon_{part} (N_{part})$ and $$ of identified particles are well described in this model. The correlation of $$ between peripheral heavy ion collisions and pp collisions for different hadrons, reproduced in this model, questions whether hydrodynamical calculations are the proper tool to describe non-central heavy ion collision. The model explains as well the centrality dependence of $v_2/\epsilon_{part}$ of charged particles, considered up to now as an observable which allows to determine the viscosity of the quark gluon plasma. The observed dependence of $v_2^i/\epsilon_{part}(N_{part})$ on the particle species is a simple consequence of the different ratios of core to corona particles. Comment: Figure added, text partially rewritten, interpretation of v2 of identified particles
01/2010;
