9,087 research outputs found

### Jet Quenching: the medium modification of the single and double fragmentation functions

The physics of the quenching of hard jets in dense matter is briefly
reviewed. This is presented within the framework of the partonic medium
modification of the fragmentation functions. Modifications in both deeply
inelastic scattering (DIS) off large nuclei and high-energy heavy-ion
collisions are presented.Comment: 4 pages, 4 figures, Proceedings of the First Meeting of the APS
Topical Group on Hadronic Physics, Fermilab, Batavia, Illinois, Oct 24-26,
200

### Suppression of the high $p_T$ charged hadron $R_{AA}$ at the LHC

We present a parameter free postdiction of the high-$p_T$ charged-hadron
nuclear modification factor ($R_{AA}$) in two centralities, measured by the CMS
collaboration in $Pb$-$Pb$ collisions at the Large Hadron Collider (LHC). The
evolution of the bulk medium is modeled using viscous fluid dynamics, with
parameters adjusted to describe the soft hadron yields and elliptic flow.
Assuming the dominance of radiative energy loss, we compute the medium
modification of the $R_{AA}$ using a perturbative QCD based formalism, the
higher twist scheme. The transverse momentum diffusion coefficient $\hat{q}$ is
assumed to scale with the entropy density and normalized by fitting the
$R_{AA}$ in the most central $Au$-$Au$ collisions at the Relativistic Heavy-Ion
Collider (RHIC). This set up is validated in non-central $Au$-$Au$ collisions
at RHIC and then extrapolated to $Pb$-$Pb$ collisions at the LHC, keeping the
relation between $\hat{q}$ and entropy density unchanged. We obtain a
satisfactory description of the CMS $R_{AA}$ over the $p_{T}$ range from 10-100
GeV.Comment: 4 pages, 3 figures, revtex4, new experimental data used, new
calculations with systematic error bands, changed abstract and contents,
conclusions unchange

### Extending Soft-Collinear-Effective-Theory to describe hard jets in dense QCD media

An extension to the Soft-Collinear-Effective Theory (SCET) description of
hard jets is motivated to include the leading contributions between the
propagating partons within the jet with partons radiated from a dense extended
medium. The resulting effective Lagrangian, containing both a leading and a
power suppressed (in the hard scale $Q^2$) contribution, arises primarily from
interactions between the hard collinear modes in the jet with Glauber modes
from the medium. In this first attempt, the interactions between the hard jet
and soft and collinear partonic modes have been ignored, in an effort to focus
solely on the interactions with the Glauber modes. While the effect of such
modes on vacuum cross sections are suppressed by powers of the hard scale
compared to the terms from the SCET Lagrangian, such sub-leading contributions
are enhanced by the extent of the medium and result in measurable corrections.
The veracity of the derived Lagrangian is checked by direct comparison with
known results from full QCD calculations of two physical observables: the
transverse momentum broadening of hard jets in dense media and a reanalysis of
the transverse momentum dependent parton distribution function (TMDPDF).Comment: 19 pages, 6 figures, revtex4, discussion on power counting updated,
references adde

### A General Relativistic study of the neutrino path and calculation of minimum photosphere for different stars

A detailed general relativistic (GR) calculation of the neutrino path for a
general metric describing a rotating star is studied. We have calculated the
neutrino path along a plane, with the consideration that the neutrino does not
at any time leave the plane. The expression for the minimum photosphere radius
(MPR) is obtained and matched with the Schwarzschild limit. The MPR is
calculated for the stars with two different equations of state (EOS) each
rotating with two different velocities. The results shows that the MPR for the
hadronic star is much greater than the quark star and the MPR increases as the
rotational velocity of the star decreases. The MPR along the polar plane is
larger than that along the equatorial plane.Comment: 13 pages, 5 figures and 1 tabl

### Dihadron fragmentation functions and high Pt hadron-hadron correlations

We propose the formulation of a dihadron fragmentation function in terms of
parton matrix elements. Under the collinear factorization approximation and
facilitated by the cut-vertex technique, the two hadron inclusive cross section
at leading order (LO) in e+ e- annihilation is shown to factorize into a short
distance parton cross section and the long distance dihadron fragmentation
function. We also derive the DGLAP evolution equation of this function at
leading log. The evolution equation for the non-singlet quark fragmentation
function is solved numerically with a simple ansatz for the initial condition
and results are presented for cases of physical interest.Comment: Latex, 4 pages, 4 figures, talk given at Quark Matter 2004, To appear
in J. Phys.

### Squeezing lepton pairs out of broken symmetries

We discuss two possible signatures of symmetry breaking that can appear in
dilepton spectra, as measured in relativistic heavy ion collisions. The first
involves scalar-vector meson mixing and is related to the breaking of Lorentz
symmetry by a hot medium. The second is related to the breaking of Furry's
theorem by a charged quark-gluon plasma. Those signals will be accessible to
upcoming measurements to be performed at the GSI, RHIC, and the LHC.Comment: 5 pages, 4 figures, talk given at the INPC 2001 (International
Conference on Nuclear Physics), 30 July - 3 August 2001, Berkeley, C

### Jet modification in three dimensional fluid dynamics at next-to-leading twist

The modification of the single inclusive spectrum of high transverse momentum
($p_T$) pions emanating from an ultra-relativistic heavy-ion collision is
investigated. The deconfined sector is modelled using a full three dimensional
(3-D) ideal fluid dynamics simulation. Energy loss of high $p_T$ partons and
the ensuing modification of their fragmentation is calculated within
perturbative QCD at next-to-leading twist, where the magnitude of the higher
twist contribution is modulated by the entropy density extracted from the 3-D
fluid dynamics simulation. The nuclear modification factor ($R_{AA}$) for pions
with a $p_T \geq 8$ GeV as a function of centrality as well as with respect to
the reaction plane is calculated. The magnitude of contributions to the
differential $R_{AA}$ within small angular ranges, from various depths in the
dense matter is extracted from the calculation and demonstrate the correlation
of the length integrated density and the $R_{AA}$ from a given depth. The
significance of the mixed and hadronic phase to the overall magnitude of energy
loss are explored.Comment: 5 pages, 4 figures, Revte

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