106 research outputs found
Constraints for the nuclear parton distributions from Z and W production at the LHC
The LHC is foreseen to finally bring also the nuclear collisions to the TeV
scale thereby providing new possibilities for physics studies, in particular
related to the electro-weak sector of the Standard Model. We study here the Z
and W production in proton-lead and lead-lead collisions at the LHC,
concentrating on the prospects of testing the factorization and constraining
the nuclear modifications of the parton distribution functions (PDFs).
Especially, we find that the rapidity asymmetries in proton-nucleus collisions,
arising from the differences in the PDFs between the colliding objects, provide
a decisive advantage in comparison to the rapidity-symmetric nucleus-nucleus
case. We comment on how such studies will help to improve our knowledge of the
nuclear PDFs.Comment: The version accepted for publication in JHEP. New figures has been
added, and we also discuss the single charged lepton productio
Compatibility of neutrino DIS data and global analyses of parton distribution functions
Neutrino\antineutrino deep inelastic scattering (DIS) data provide useful
constrains for the flavor decomposition in global fits of parton distribution
functions (PDF). The smallness of the cross-sections requires the use of
nuclear targets in the experimental setup. Understanding the nuclear
corrections is, for this reason, of utmost importance for a precise
determination of the PDFs. Here, we explore the nuclear effects in the
neutrino\antineutrino-nucleon DIS by comparing the NuTeV, CDHSW, and CHORUS
cross-sections to the predictions derived from the latest parton distribution
functions and their nuclear modifications. We obtain a good description of
these data and find no apparent disagreement between the nuclear effects in
neutrino DIS and those in charged lepton DIS. These results also indicate that
further improvements in the knowledge of the nuclear PDFs could be obtained by
a more extensive use of these sets of neutrino data.Comment: 16 pages, 8 figure
On p_T-broadening of high energy partons associated with the LPM effect in a finite-volume QCD medium
We study the contributions from radiation to -broadening of a high
energy parton traversing a QCD medium with a finite length . The interaction
between the parton and the medium is described by decorrelated static multiple
scattering. Amplitudes of medium-induced gluon emission and parton self-energy
diagrams are evaluated in the soft gluon limit in the BDMPS formalism. We find
both the double-logarithmic correction from incoherent scattering, which is
parametrically the same as that in single scattering, and the logarithmic
correction from the LPM effect. Therefore, we expect a parametrically large
correction from radiation to the medium-induced -broadening in
perturbative QCD.Comment: 19 pages, focusing only on calculations about the medium-induced
diagrams, origin for double-log reinterpreted, final version to appear in
JHE
Probing Shadowed Nuclear Sea with Massive Gauge Bosons in the Future Heavy-Ion Collisions
The production of the massive bosons and could provide an
excellent tool to study cold nuclear matter effects and the modifications of
nuclear parton distribution functions (nPDFs) relative to parton distribution
functions (PDFs) of a free proton in high energy nuclear reactions at the LHC
as well as in heavy-ion collisions (HIC) with much higher center-of mass
energies available in the future colliders. In this paper we calculate the
rapidity and transverse momentum distributions of the vector boson and their
nuclear modification factors in p+Pb collisions at TeV and in
Pb+Pb collisions at TeV in the framework of perturbative QCD
by utilizing three parametrization sets of nPDFs: EPS09, DSSZ and nCTEQ. It is
found that in heavy-ion collisions at such high colliding energies, both the
rapidity distribution and the transverse momentum spectrum of vector bosons are
considerably suppressed in wide kinematic regions with respect to p+p reactions
due to large nuclear shadowing effect. We demonstrate that in the massive
vector boson productions processes with sea quarks in the initial-state may
give more contributions than those with valence quarks in the initial-state,
therefore in future heavy-ion collisions the isospin effect is less pronounced
and the charge asymmetry of W boson will be reduced significantly as compared
to that at the LHC. Large difference between results with nCTEQ and results
with EPS09 and DSSZ is observed in nuclear modifications of both rapidity and
distributions of and in the future HIC.Comment: 13 pages, 21 figures, version accepted for publication in Eur. Phys.
J.
Prompt atmospheric neutrino fluxes: perturbative QCD models and nuclear effects
We evaluate the prompt atmospheric neutrino flux at high energies using three
different frameworks for calculating the heavy quark production cross section
in QCD: NLO perturbative QCD, factorization including low-
resummation, and the dipole model including parton saturation. We use QCD
parameters, the value for the charm quark mass and the range for the
factorization and renormalization scales that provide the best description of
the total charm cross section measured at fixed target experiments, at RHIC and
at LHC. Using these parameters we calculate differential cross sections for
charm and bottom production and compare with the latest data on forward charm
meson production from LHCb at TeV and at TeV, finding good agreement
with the data. In addition, we investigate the role of nuclear shadowing by
including nuclear parton distribution functions (PDF) for the target air
nucleus using two different nuclear PDF schemes. Depending on the scheme used,
we find the reduction of the flux due to nuclear effects varies from to
at the highest energies. Finally, we compare our results with the
IceCube limit on the prompt neutrino flux, which is already providing valuable
information about some of the QCD models.Comment: 61 pages, 25 figures, 11 table
Back reaction effects on the dynamics of heavy probes in heavy quark cloud
We holographically study the effect of back reaction on the hydrodynamical
properties of strongly coupled super Yang-Mills (SYM) thermal
plasma. The back reaction we consider arises from the presence of static heavy
quarks uniformly distributed over SYM plasma. In order to
study the hydrodynamical properties, we use heavy quark as well as heavy
quark-antiquark bound state as probes and compute the jet quenching parameter,
screening length and binding energy. We also consider the rotational dynamics
of heavy probe quark in the back-reacted plasma and analyse associated energy
loss. We observe that the presence of back reaction enhances the energy-loss in
the thermal plasma. Finally, we show that there is no effect of angular drag on
the rotational motion of quark-antiquark bound state probing the back reacted
thermal plasma.Comment: 29 pages, 21 figure
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