54 research outputs found
An improved global analysis of nuclear parton distribution functions including RHIC data
We present an improved leading-order global DGLAP analysis of nuclear parton
distribution functions (nPDFs), supplementing the traditionally used data from
deep inelastic lepton-nucleus scattering and Drell-Yan dilepton production in
proton-nucleus collisions, with inclusive high- hadron production data
measured at RHIC in d+Au collisions. With the help of an extended definition of
the function, we now can more efficiently exploit the constraints the
different data sets offer, for gluon shadowing in particular, and account for
the overall data normalization uncertainties during the automated
minimization. The very good simultaneous fit to the nuclear hard process data
used demonstrates the feasibility of a universal set of nPDFs, but also
limitations become visible. The high- forward-rapidity hadron data of
BRAHMS add a new crucial constraint into the analysis by offering a direct
probe for the nuclear gluon distributions -- a sector in the nPDFs which has
traditionally been very badly constrained. We obtain a strikingly stronger
gluon shadowing than what has been estimated in previous global analyses. The
obtained nPDFs are released as a parametrization called EPS08.Comment: 26 pages, 14 figures; for v2, we have revised the Table 1 and Fig.
13, and added the Fig. 14 and the Table 3 along with some more discussio
Weak boson production measured in PbPb and pp collisions by CMS
The unprecedented center-of-mass energy available at the LHC offers unique
opportunities for studying the properties of the strongly-interacting QCD
matter created in PbPb collisions at extreme temperatures and very low parton
momentum fractions. Electroweak boson production is an important benchmark
process at hadron colliders. Precise measurements of Z production in heavy-ion
collisions can help to constrain nuclear PDFs as well as serve as a standard
candle of the initial state in PbPb collisions at the LHC energies. The
inclusive and differential measurements of the Z boson yield in the muon decay
channel will be presented, establishing that no modification is observed with
respect to next-to-leading order pQCD calculations, scaled by the number of
incoherent nucleon-nucleon collisions. The status of the Z measurement in the
electron decay channel, as well as the first observation of W \rightarrow \mu
{\nu} in heavy ion collisions will be given. The heavy-ion results will be
presented in the context of those obtained in pp collisions with the CMS
detector.Comment: Quark Matter 2011 conference proceeding
The Emerging QCD Frontier: The Electron Ion Collider
The self-interactions of gluons determine all the unique features of QCD and
lead to a dominant abundance of gluons inside matter already at moderate .
Despite their dominant role, the properties of gluons remain largely
unexplored. Tantalizing hints of saturated gluon densities have been found in
+p collisions at HERA, and in d+Au and Au+Au collisions at RHIC. Saturation
physics will have a profound influence on heavy-ion collisions at the LHC. But
unveiling the collective behavior of dense assemblies of gluons under
conditions where their self-interactions dominate will require an Electron-Ion
Collider (EIC): a new facility with capabilities well beyond those In this
paper I outline the compelling physics case for +A collisions at an EIC and
discuss briefly the status of machine design concepts. of any existing
accelerator.Comment: 11 pages, 9 figures, prepared for 20th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions: Quark Matter 2008 (QM2008),
Jaipur, India, 4-10 Feb. 200
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
A global DGLAP analysis of nuclear PDFs
In this talk, we shortly report results from our recent global DGLAP analysis
of nuclear parton distributions. This is an extension of our former
EKS98-analysis improved with an automated minimization procedure and
uncertainty estimates. Although our new analysis show no significant deviation
from EKS98, a sign of a significantly stronger gluon shadowing could be seen in
the RHIC BRAHMS data.Comment: Talk given at EPS HEP 200
The physics potential of proton-nucleus collisions at the TeV scale
The LHC brings nuclear collisions to the TeV scale for the first time and the
first data show the qualitative differences of this new regime. The
corresponding phase-space available encompasses completely uncharted regions of
QCD in which high-density or high-temperature domains can be identified.
Proton-nucleus runs are essential for a complete interpretation of the data and
for the study of new regimes dominated by large occupation numbers in the
hadronic wave function. I comment here the physics opportunities for p+Pb runs
at the LHC and d+Au runs at RHIC and the corresponding needs in view of the new
Pb+Pb data from the LHC.Comment: Proceedings of the conference Quark Matter 2011, Annecy (France) May
201
Gluon Shadowing in DIS off Nuclei
Within a light-cone quantum-chromodynamics dipole formalism based on the
Green function technique, we study nuclear shadowing in deep-inelastic
scattering at small Bjorken xB < 0.01. Such a formalism incorporates naturally
color transparency and coherence length effects. Calculations of the nuclear
shadowing for the \bar{q}q Fock component of the photon are based on an exact
numerical solution of the evolution equation for the Green function, using a
realistic form of the dipole cross section and nuclear density function. Such
an exact numerical solution is unavoidable for xB > 0.0001, when a variation of
the transverse size of the \bar{q}q Fock component must be taken into account.
The eikonal approximation, used so far in most other models, can be applied
only at high energies, when xB < 0.0001 and the transverse size of the \bar{q}q
Fock component is "frozen" during propagation through the nuclear matter. At xB
< 0.01 we find quite a large contribution of gluon suppression to nuclear
shadowing, as a shadowing correction for the higher Fock states containing
gluons. Numerical results for nuclear shadowing are compared with the available
data from the E665 and NMC collaborations. Nuclear shadowing is also predicted
at very small xB corresponding to LHC kinematical range. Finally the model
predictions are compared and discussed with the results obtained from other
models.Comment: 29 pages including 7 figures; Fig.7 modified, some references and
corresponding discussion adde
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