3 research outputs found
Medium information from anisotropic flow and jet quenching in relativistic heavy ion collisions
Within a multiphase transport (AMPT) model, where the initial conditions are
obtained from the recently updated HIJING 2.0 model, the recent anisotropic
flow and suppression data for charged hadrons in Pb+Pb collisions at the LHC
center of mass energy of 2.76 TeV are explored to constrain the properties of
the partonic medium formed. In contrast to RHIC, the measured centrality
dependence of charged hadron multiplicity dN_ch/deta at LHC provides severe
constraint to the largely uncertain gluon shadowing parameter s_g. We find
final-state parton scatterings reduce considerably hadron yield at midrapidity
and enforces a smaller s_g to be consistent with dN_ch/deta data at LHC. With
the parton shadowing so constrained, hadron production and flow over a wide
transverse momenta range are investigated in AMPT. The model calculations for
the elliptic and triangular flow are found to be in excellent agreement with
the RHIC data, and predictions for the flow coefficients v_n(p_T, cent) at LHC
are given. The magnitude and pattern of suppression of the hadrons in AMPT are
found consistent with the measurements at RHIC. However, the suppression is
distinctly overpredicted in Pb+Pb collisions at the LHC energy. Reduction of
the QCD coupling constant alpha_s by ~30% in the higher temperature plasma
formed at LHC reproduces the measured hadron suppression.Comment: Talk given by Subrata Pal at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS
Jet Quenching via Jet Collimation
The ATLAS Collaboration recently reported strong modifications of dijet
properties in heavy ion collisions. In this work, we discuss to what extent
these first data constrain already the microscopic mechanism underlying jet
quenching. Simple kinematic arguments lead us to identify a frequency
collimation mechanism via which the medium efficiently trims away the soft
components of the jet parton shower. Through this mechanism, the observed dijet
asymmetry can be accomodated with values of that lie in the
expected order of magnitude.Comment: 6 pages, 4 figure
Proton-Nucleus Collisions at the LHC: Scientific Opportunities and Requirements
Proton-nucleus (p+A) collisions have long been recognized as a crucial
component of the physics programme with nuclear beams at high energies, in
particular for their reference role to interpret and understand nucleus-nucleus
data as well as for their potential to elucidate the partonic structure of
matter at low parton fractional momenta (small-x). Here, we summarize the main
motivations that make a proton-nucleus run a decisive ingredient for a
successful heavy-ion programme at the Large Hadron Collider (LHC) and we
present unique scientific opportunities arising from these collisions. We also
review the status of ongoing discussions about operation plans for the p+A mode
at the LHC.Comment: 33 pages, 15 Figure