68 research outputs found
Full jet tomography of high-energy nuclear collisions
Parton energy loss in the hot QCD medium will manifest itself not only in
leading hadron spectra but also in reconstructed jet productions in high-energy
nucleus-nucleus collisions. In this paper we report on recent theoretical
efforts in studying full jet observables in relativistic heavy-ion collisions
by discussing the modifications of jet shapes, inclusive jet cross section and
the vector boson accompanied jet production in the presence of the QGP-induced
jet quenching.Comment: Plenary talk at Hard Probe 2010, October 10-15, 2010, Eilat, Israel.
8 pages, 6 figure
Coherent rho and J/psi photoproduction in ultraperipheral processes with electromagnetic dissociation of heavy ions at RHIC and LHC
We present predictions for the J/psi and rho meson production in the heavy
ion ultraperipheral collisions (UPC) for the current energy 2.76 TeV at the
LHC. Both total cross sections and cross sections with the neutron emission
from one or both nuclei are presented. We also analyse the RHIC rho meson
photoproduction data and emphasize importance of these data to test the current
model for nucleus break up in UPC.Comment: 16 pages, 7 figure
Generalization of radiative jet energy loss to non-zero magnetic mass
Reliable predictions for jet quenching in ultra-relativistic heavy ion
collisions require accurate computation of radiative energy loss. With this
goal, an energy loss formalism in a realistic finite size dynamical QCD medium
was recently developed. While this formalism assumes zero magnetic mass - in
accordance with the one-loop perturbative calculations - different
non-perturbative approaches report a non-zero magnetic mass at RHIC and LHC. We
here generalize the energy loss to consistently include a possibility for
existence of non-zero magnetic screening. We also present how the inclusion of
finite magnetic mass changes the energy loss results. Our analysis indicates a
fundamental constraint on magnetic to electric mass ratio.Comment: 4 pages, 2 figure
Quantitative constraints on the gluon distribution function in the proton from collider isolated-photon data
The impact of isolated-photon data from proton-(anti)proton collisions at
RHIC, SppbarS, Tevatron and LHC energies, on the parton distribution functions
of the proton is studied using a recently developed Bayesian reweighting
method. The impact on the gluon density of the 35 existing isolated-gamma
measurements is quantified using next-to-leading order (NLO) perturbative QCD
calculations complemented with the NNPDF2.1 parton densities. The NLO
predictions are found to describe well most of the datasets from 200 GeV up to
7 TeV centre-of-mass energies. The isolated-photon spectra recently measured at
the LHC are precise enough to constrain the gluon distribution and lead to a
moderate reduction (up to 20%) of its uncertainties around fractional momenta
x~0.02. As a particular case, we show that the improved gluon density reduces
the PDF uncertainty for the Higgs boson production cross section in the
gluon-fusion channel by more than 20% at the LHC. We conclude that present and
future isolated-photon measurements constitute an interesting addition to
coming global PDF analyses.Comment: 30 pages, 20 figures. Few minor changes to match the published NPB
versio
Eccentricity and elliptic flow in proton-proton collisions from parton evolution
It has been argued that high-multiplicity proton-proton collisions at the LHC
may exhibit collective phenomena usually studied in the context of heavy-ion
collisions, such as elliptic flow. We study this issue using DIPSY - a Monte
Carlo event generator based on the QCD dipole model. We calculate the
eccentricity of the transverse area defined by the spatial distribution of
produced gluons. The resulting elliptic flow is estimated to be about 6%,
comparable to the value in nucleus-nucleus collisions at RHIC and the LHC.
Experimentally, elliptic flow is inferred from the azimuthal correlation
between hadrons, which receives contributions from collective flow, and from
various other effects referred to as "nonflow". We discuss how to identify in
experiments the signal of flow in the presence of large nonflow effects.Comment: v2: Four-particle correlation added, improved discussions on the
signatures of flow. v3: Improved treatment of fluctuations in the flow
analysis. v4: Minor changes for journal submissio
Components of the elliptic flow in Pb-Pb collisions at 2.76 TeV
We calculate the elliptic flow of charged particles in Pb-Pb collisions at
2.76 TeV in relativistic viscous hydrodynamics. The recent data of the ALICE
Collaboration on the elliptic flow as function of the centrality can be very
well described using the hydrodynamic expansion of a fluid with a small shear
viscosity eta/s=0.08. The elliptic flow as function of the transverse momentum
shows systematic deviations from a hydrodynamic behavior in the small momenta
region pt<800MeV. It indicates that a non-negligible contribution of
non-thermalized particles from jet fragmentation is present
Medium-induced emissions of hard gluons
We present a derivation of the medium-induced gluon radiation spectrum beyond
the current limitation of soft gluon emission. Making use of the path integral
approach to describe the propagation of high-energy particles inside a medium,
we study the limiting case of a hard gluon emission. Analytical and numerical
results are presented and discussed within the multiple soft scattering
approximation. An ansatz interpolating between soft and hard gluon emissions is
provided. The Landau-Pomeranchuk-Migdal effect is observed in the expected
kinematic region.Comment: 17 pages, 6 figures. Minor corrections, references updated. Accepted
by Phys. Lett.
Out of Medium Fragmentation from Long-Lived Jet Showers
We study the time structure of vacuum jet evolution via a simple uncertainty
principle estimate in the kinematic range explored by current heavy ion
collisions at the LHC. We observe that a large fraction of the partonic
splittings occur at large times, of the order of several fm. We compare the
time distribution of vacuum splittings with the distribution of path lengths
traversed by jets in a heavy ion collision. We find that if no medium induced
modification of the jet dynamics were present, a very large fraction (larger
than 80% for inclusive jets) of the jet splittings would occur outside of the
medium. We confront this observation with current available data on jet
properties in heavy ion collisions and discuss its implications for the
dynamics of jet-medium interactions.Comment: 10 pages, 6 figure
Charged particle elliptic flow in p+p collisions at LHC energies in a transport model PACIAE
The parton and hadron cascade model PACIAE based on PYTHIA was used to
investigate the charged particle elliptic flow in minimum bias pp collisions at
the LHC energies. The strings were distributed randomly in the transverse
ellipsoid of the pp collision system with major axis of (proton radius) and
minor axis of before parton rescattering. The charged particle
elliptic flow as a function of the random number and transverse momentum
were investigated. The calculated as a function of
reaction energy increases monotonously with increasing reaction energy up to
7 TeV and then turns to saturation. With the parton-parton cross
section enlarges three times in parton rescattering, the rapidity integrated
charged particle elliptic flow may reach 0.025 at 2 GeV/c in the
minimum bias pp collisions at =7 TeV.Comment: 7 pages, 4 figure
Jet Evolution in the Quark-Gluon Plasma from RHIC to the LHC
The observed suppression of high- hadrons allows different
explanations. We discuss two possible scenarios: In scenario 1, parton energy
loss from scattering in the hot medium is complemented by final state
interactions in the resonance matter. Scenario 2 has an enhanced transport
parameter which is fitted to RHIC data. For LHC, the two scenarios
lead to very different predictions for the nuclear modification factor of
hadrons. In addition, jet reconstruction allows more specific tests of the
mechanisms responsible for jet quenching. We calculate the distribution of
partons inside a jet and find different results for the two scenarios.Comment: 25 pages, 6 figure
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