186 research outputs found
Multiplicities for LHC Nuclear Collisions Using HERA Structure Functions
We compute in QCD perturbation theory the transverse energy carried by
gluons, quarks and antiquarks with GeV in Pb+Pb
collisions at GeV by using structure functions compatible
with the small- increase observed at HERA. This gives a perturbative
estimate for the energy and entropy density of the bulk system at times
fm. The predicted initial gluon entropy density gives a lower
limit of about 2200...3400 for the final charged multiplicity. Sources of
further entropy increase are discussed.Comment: HU-TFT-94-6, 7 pages, 3 PostScript figures included in the end of the
tex-fil
Transverse spectra of hadrons at RHIC
We present results on spectra of pions, kaons and (anti)protons from a study
of heavy ion collisions using the perturbative QCD + saturation model to
calculate the production of initial (transverse) energy and baryon number
followed by a hydrodynamic description of the expansion of produced matter. In
particular, we study how the hadron spectra and multiplicities depend on the
decoupling temperature \Tdec when the low temperature phase contains all
hadrons and and hadron resonances with mass below 2 GeV. We show that the
spectra and multiplicities of pions, kaons and (anti)protons measured at RHIC
in central Au+Au collisions with GeV can be obtained with a
single decoupling temperature 150160 MeV, common for both the chemical and
the kinetic freeze-out.Comment: 4 pages, 2 eps-figures, talk at Quark Matter '02, Nantes, France,
July 200
Multiplicities and Transverse Energies in Central AA Collisions at RHIC and LHC from pQCD, Saturation and Hydrodynamics
We compute the particle multiplicities and transverse energies at central and
nearly central AA collisions at RHIC and LHC. The initial state is computed
from perturbative QCD supplemented by the conjecture of saturation of produced
partons. The expansion stage is described in terms of hydrodynamics assuming
longitudinal boost invariance and azimuthal symmetry. Transverse flow effects,
a realistic list of hadrons and resonance decays are included. Comparison with
the data of the multiplicities at AGeV and 130 AGeV from RHIC is
done and predictions for the full RHIC energy and LHC energy are made for the
multiplicities and transverse energies. The reduction from the initially
released minijet transverse energy to the in the final state is less than
in the one-dimensional case but still dramatic: a factor of 2.7 at RHIC, and
3.6 at the LHC.Comment: The results for LHC have been correcte
The Effect of Shadowing on Initial Conditions, Transverse Energy and Hard Probes in Ultrarelativistic Heavy Ion Collisions
The effect of shadowing on the early state of ultrarelativistic heavy ion
collisions is investigated along with transverse energy and hard process
production, specifically Drell-Yan, , and production. We
choose several parton distributions and parameterizations of nuclear shadowing,
as well as the spatial dependence of shadowing, to study the influence of
shadowing on relevant observables. Results are presented for Au+Au collisions
at GeV and Pb+Pb collisions at TeV.Comment: Submitted to Phys. Rev.
Scaling of transverse energies and multiplicities with atomic number and energy in ultrarelativistic nuclear collisions
We compute how the initial energy density and produced gluon, quark and
antiquark numbers scale with atomic number and beam energy in ultrarelativistic
heavy ion collisions. The computation is based on the argument that the effect
of all momentum scales can be estimated by performing the computation at one
transverse momentum scale, the saturation momentum. The initial numbers are
converted to final ones by assuming kinetic thermalisation and adiabatic
expansion. The main emphasis of the study is at LHC and RHIC energies but it is
observed that even at SPS energies this approach leads to results which are not
unreasonable: what is usually described as a completely soft nonperturbative
process can also be described in terms of gluons and quarks. The key element is
the use of the saturation scale.Comment: 13 pages, includes 7 eps-figure
Non-equilibrium initial conditions from pQCD for RHIC and LHC
We calculate the initial non-equilibrium conditions from perturbative QCD
(pQCD) within Glauber multiple scattering theory for AGeV and
ATeV. At the soon available collider energies one will
particularly test the small region of the parton distributions entering the
cross sections. Therefore shadowing effects, previously more or less
unimportant, will lead to new effects on variables such as particle
multiplicities , transverse energy production , and the
initial temperature . In this paper we will have a closer look on the
effects of shadowing by employing different parametrizations for the shadowing
effect for valence quarks, sea quarks and gluons. Since the cross sections at
midrapidity are dominated by processes involving gluons the amount of their
depletion is particularly important. We will therefore have a closer look on
the results for , , and by using two different
gluon shadowing ratios, differing strongly in size. As a matter of fact, the
calculated quantities differ significantly.Comment: typo in ref's removed, ack's added, no change in result
Black Hole Production at LHC: String Balls and Black Holes from pp and Lead-lead Collisions
If the fundamental planck scale is near a TeV, then parton collisions with
high enough center-of-mass energy should produce black holes. The production
rate for such black holes at LHC has been extensively studied for the case of a
proton-proton collision. In this paper, we extend this analysis to a lead-lead
collision at LHC. We find that the cross section for small black holes which
may in principle be produced in such a collision is either enhanced or
suppressed, depending upon the black hole mass. For example, for black holes
with a mass around 3 TeV we find that the differential black hole production
cross section, d\sigma/dM, in a typical lead-lead collision is up to 90 times
larger than that for black holes produced in a typical proton-proton collision.
We also discuss the cross-sections for `string ball' production in these
collisions. For string balls of mass about 1 (2) TeV, we find that the
differential production cross section in a typical lead-lead collision may be
enhanced by a factor up to 3300 (850) times that of a proton-proton collision
at LHC.Comment: Added some discussion, final version to appear in Phys. Rev. D (rapid
communications
Centrality dependence of multiplicity, transverse energy, and elliptic flow from hydrodynamics
The centrality dependence of the charged multiplicity, transverse energy, and
elliptic flow coefficient is studied in a hydrodynamic model, using a variety
of different initializations which model the initial energy or entropy
production process as a hard or soft process, respectively. While the charged
multiplicity depends strongly on the chosen initialization, the p_t-integrated
elliptic flow for charged particles as a function of charged particle
multiplicity and the p_t-differential elliptic flow for charged particles in
minimum bias events turn out to be almost independent of the initial energy
density profile.Comment: 11 pages RevTex, including 10 postscript figures. Slightly modified
discussion of Figs. 5 and 6, updated references. This version to appear in
Nuclear Physics
Impact of CMS dijets in 5.02 TeV pPb and pp collisions on EPPS16 nuclear PDFs
The CMS measurement of dijet pseudorapidity distributions in pPb versus pp collisions at 5.02 TeV provides a direct probe on nuclear gluon PDFs. We show that while the predicted pPb pseudorapidity distributions suffer from sizable free-proton PDF uncertainties, the ratios of the pPb and pp distributions are practically insensitive to scale and free-proton PDF choices. We find the CMS data on pPb to pp ratios to be in good agreement with the EPPS16 nuclear modifications. Using a non-quadratic extension of the Hessian PDF reweighting method, we study the impact of these data on the EPPS16 nuclear PDFs. Relative to EPPS16, we find stronger evidence for mid-x gluon antishadowing as well as indication for larger gluon shadowing at small x. The data are also able to further constrain the gluon PDF in the EMC region.Peer reviewe
Impact of CMS 5.02 TeV dijet measurements on gluon PDFs : A preliminary view
We discuss the implications of the preliminary CMS dijet data from 5.02 TeV pp and pPb collisions for gluon PDFs of the proton and nuclei. The preliminary pp data show a discrepancy with NLO predictions using for example the CT14 PDFs. We find that this difference cannot be accommodated within the associated scale uncertainties and debate the possible changes needed in the gluon PDF. A similar discrepancy is found between the CMS pPb data and NLO predictions e.g. with the EPPS16 nuclear modifications imposed on the CT14 proton PDFs. When a nuclear modification ratio of the pp and pPb data is constructed, the uncertainties in the scale choices and in proton PDFs effectively cancel and a good agreement between the data and EPPS16 is found, except in some bins at backward rapidities corresponding to large x of the nucleus. To assess the impact of these data on the EPPS16 nuclear PDFs, we use a non-quadratic extension of the Hessian PDF reweighting method. A significant reduction in EPPS16 uncertainties is obtained with the fit supporting strong nuclear shadowing and valence-like antishadowing for gluons. We also indicate the possible extensions needed in the EPPS16 parametrization at large x.Peer reviewe
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