148 research outputs found
Direct Photon and Heavy Quark Jet Production at the LHC
The associated production of direct photons and heavy quarks at the LHC is
presented. Predictions for the nuclear modification factor to the cross-section
at ALICE are shown. It is demonstrated that this process is a great probe of
the gluon and heavy quark nuclear PDFs, as over 80 % of its nPDF dependence at
NLO comes from those nPDFs. Therefore measurements of this process will provide
an excellent constraint on the gluon nPDF, and will distinguish between
different nPDF sets currently out on the market.Comment: Proceedings for ICHEP 201
Heavy quark & direct photon production and heavy quark parton densities
Direct photon production in association with a heavy quark can serve as an
excellent tool for the study of the heavy quark distributions. Currently it is
believed that heavy quarks are produced radiatively inside the nucleon, and so
there is no need to take into account heavy quark parameters inside global PDF
analyses. Certain models taking into account the possibility of an intrinsic
charm component exist. Here we present how these affect the \gamma + c cross
section. While at pA collisions the potential of this process to constrain the
gluon nuclear PDF which is currently largely unconstrained is presented.Comment: Quarkonium 2010 Proceeding
Constraining the Intrinsic Heavy Quark PDF via Direct Photon Production in Association with a Heavy Quark Jet
We investigate a possible use of direct photon production in association with
a heavy quark to test different models of intrinsic heavy quark parton
distribution function (PDF) at the Tevatron, at the large hadron collider (LHC)
and at RHIC.Comment: 4 pages, to appear in proceedings of DIS201
Prompt photon in association with a heavy-quark jet in Pb-Pb collisions at the LHC
We present a phenomenological study of the associated production of a prompt
photon and a heavy quark jet (charm or bottom) in Pb-Pb collisions at the LHC.
This channel allows for estimating the amount of energy loss experienced by the
charm and bottom quarks propagating in the dense QCD medium produced in those
collisions. Calculations are carried out at next-to-leading order (NLO)
accuracy using the BDMPS-Z heavy-quark quenching weights. The quenching of the
single heavy-quark jet spectrum reflects fairly the hierarchy in the heavy
quark energy loss assumed in the perturbative calculation. On the contrary, the
single photon spectrum in heavy-ion collisions is only modified at low momenta,
for which less heavy-quark jets pass the kinematic cuts. On top of single
particle spectra, the two-particle final state provides a range of observables
(photon-jet pair momentum, jet asymmetry, among others) which are studied in
detail. The comparison of the photon-jet pair momentum, from p-p to Pb-Pb
collisions, is sensitive to the amount of energy lost by the heavy-quarks and
could therefore be used in order to better understand parton energy loss
processes in the heavy quark sector.Comment: 22 pages, 18 figures, gzipped tar file. Minor changes, 2 references
added. Version published in JHE
A Hybrid Scheme for Heavy Flavors: Merging the FFNS and VFNS
We introduce a Hybrid Variable Flavor Number Scheme for heavy flavors,
denoted H-VFNS, which incorporates the advantages of both the traditional
Variable Flavor Number Scheme (VFNS) as well as the Fixed Flavor Number Scheme
(FFNS). By including an explicit -dependence in both the Parton
Distribution Functions (PDFs) and the strong coupling constant , we
generate coexisting sets of PDFs and for at any
scale , that are related analytically by the
matching conditions. The H-VFNS resums the heavy quark contributions and
provides the freedom to choose the optimal for each particular data set.
Thus, we can fit selected HERA data in a FFNS framework, while retaining the
benefits of the VFNS to analyze LHC data at high scales. We illustrate how such
a fit can be implemented for the case of both HERA and LHC data.Comment: 15 pages, 11 figures, updated to match journa
Searching for intrinsic charm in the proton at the LHC
Despite rather long-term theoretical and experimental studies, the hypothesis
of the non-zero intrinsic (or valence-like) heavy quark component of the proton
distribution functions has not yet been confirmed or rejected. The LHC with
-collisions at 7--14 TeV will obviously supply extra unique
information concerning the above-mentioned component of the proton. To use the
LHC potential, first of all, one should select the parton-level (sub)processes
(and final-state signatures) that are most sensitive to the intrinsic heavy
quark contributions. To this end inclusive production of -jets
accompanied by photons is considered. On the basis of the performed theoretical
study it is demonstrated that the investigation of the intrinsic heavy quark
contributions looks very promising at the LHC in processes such as
.Comment: 13 pages, 6 figure
Heavy Quark Production in the ACOT Scheme Beyond NLO
We analyze the properties of the ACOT scheme for heavy quark production and
make use of the MS-Bar massless results at NNLO and N3LO for the structure
functions F2 and FL in neutral current deep-inelastic scattering to estimate
the higher order corrections. The dominant heavy quark mass effects at higher
orders can be taken into account using the massless Wilson coefficients
together with an appropriate slow-rescaling prescription implementing the phase
space constraints. Combining the exact ACOT scheme at NLO with these
expressions should provide a good approximation to the full calculation in the
ACOT scheme at NNLO and N3LO.Comment: 4 pages, 2 figures. Presented at DIS12, March 2012, Bonn, German
High \pt{} particle correlations in pp collisions at LHC/ALICE
Two-particle correlation triggered by high-\pt{} particles allows us to study
hard scattering phenomena when full jet reconstruction is challenging. An
analysis of the first ALICE pp data where charged and neutral particles
isolated or not are used as trigger particles is presented. The two-particle
correlation between the trigger () and the associate () particles is
studied as a function of the imbalance parameter \xe=- and interpreted in terms of jet
fragmentation function.Comment: 4 pages, 4 figures, QM2011 conference proceedings, will be published
on Journal of Physics
CTEQ nuclear parton distribution functions
We show for the first time preliminary results of nuclear parton distribution
function analysis of charged lepton DIS and Drell-Yan data within the CTEQ
framework including error PDFs. We compare our error estimates to estimates of
different nPDF groups.Comment: 5 pages, to appear in the proceedings of XXI International Workshop
on Deep-Inelastic Scattering and Related Subjects, Marseilles, Franc
- …