Constraints for nuclear gluon shadowing from DIS data

The $Q^2$ dependence of the ratios of the cross sections of deep inelastic lepton--nucleus scattering is studied in the framework of leading twist, lowest order perturbative QCD. The $\log Q^2$ slope of the ratio $F_2^{\rm Sn}/F_2^{\rm C}$ is computed by using the DGLAP evolution equations, and shown to be sensitive to the nuclear gluon distribution functions. Four different parametrizations for the nuclear effects of parton distributions are studied. We show that the NMC data on the $Q^2$ dependence of $F_2^{\rm Sn}/F_2^{\rm C}$ rule out the case where nuclear shadowing (suppression) of gluons at $x\sim 0.01$ is much larger than the shadowing observed in the ratio $F_2^A/F_2^{\rm D}$. We also show that the possible nonlinear correction terms due to gluon fusion in the evolution equations do not change this conclusion. Some consequences for computation of RHIC multiplicities, which probe the region x\gsim0.01, are also discussed.Comment: 11 pages, 3 eps figure

Constraints for nuclear gluon densities from DIS data

The $Q^2$ dependence of the ratios of nuclear structure functions $F_2^A$ is studied by performing QCD evolution of nuclear parton distribution functions. The log $Q^2$ slope of these ratios is very sensitive to the nuclear gluon distribution function. Taking different parametrizations, we show that the NMC data on the $Q^2$ dependence of $F_2^{\rm Sn}/F_2^{\rm C}$ rule out the case where nuclear shadowing (suppression) of gluons at $x\sim 0.01$ is much larger than the shadowing observed in the ratio $F_2^A/F_2^{\rm D}$. We also take into account modifications to the DGLAP evolution by including gluon fusion terms and see that the effect is small at present energies, and, in any case, a strong gluon shadowing is not favored. The region studied ($x \sim 0.01$) is the most relevant for RHIC multiplicities.Comment: 4 pages, 3 postscript figures. Contributed to 37th Rencontres de Moriond on QCD and Hadronic Interactions, Les Arcs, France, 16-23 Mar 200

Global DGLAP fit analyses of the nPDF: EKS98 and HKM

The DGLAP analyses of the nuclear parton distribution functions (nPDF) based on the global fits to the data are reviewed, and the results from EKS98 and HKM are compared. The usefulness of measuring hard probes in $pA$ collisions, at the LHC in particular, is demonstrated.Comment: 10 pages, 3 figures. Contribution to CERN Yellow Report on Hard Probes in Heavy Ion Collisions at the LH

Differential Rotation in Neutron Stars: Magnetic Braking and Viscous Damping

Diffferentially rotating stars can support significantly more mass in equilibrium than nonrotating or uniformly rotating stars, according to general relativity. The remnant of a binary neutron star merger may give rise to such a ``hypermassive'' object. While such a star may be dynamically stable against gravitational collapse and bar formation, the radial stabilization due to differential rotation is likely to be temporary. Magnetic braking and viscosity combine to drive the star to uniform rotation, even if the seed magnetic field and the viscosity are small. This process inevitably leads to delayed collapse, which will be accompanied by a delayed gravitational wave burst and, possibly, a gamma-ray burst. We provide a simple, Newtonian, MHD calculation of the braking of differential rotation by magnetic fields and viscosity. The star is idealized as a differentially rotating, infinite cylinder consisting of a homogeneous, incompressible conducting gas. We solve analytically the simplest case in which the gas has no viscosity and the star resides in an exterior vacuum. We treat numerically cases in which the gas has internal viscosity and the star is embedded in an exterior, low-density, conducting medium. Our evolution calculations are presented to stimulate more realistic MHD simulations in full 3+1 general relativity. They serve to identify some of the key physical and numerical parameters, scaling behavior and competing timescales that characterize this important process.Comment: 11 pages. To appear in ApJ (November 20, 2000

Nuclear parton distributions in the DGLAP approach

Determination of the nuclear parton distributions within the framework of perturbative QCD, the DGLAP equations in particular, is discussed. Scale and flavour dependent nuclear effects in the parton distributions are compared with the scale and flavour independent parametrizations of HIJING and of the Hard Probe Collaboration. A comparison with the data from deep inelastic lepton-nucleus scattering and the Drell-Yan process in proton-nucleus collisions is shown.Comment: 19 pages, 6 eps-figures, to appear in the Proceedings of the Hard Probe Collaboratio

Coalescing binary systems of compact objects: Dynamics of angular momenta

The end state of a coalescing binary of compact objects depends strongly on the final total mass M and angular momentum J. Since gravitational radiation emission causes a slow evolution of the binary system through quasi-circular orbits down to the innermost stable one, in this paper we examine the corresponding behavior of the ratio J/M^2 which must be less than 1(G/c) or about 0.7(G/c) for the formation of a black hole or a neutron star respectively. The results show cases for which, at the end of the inspiral phase, the conditions for black hole or neutron star formation are not satisfied. The inclusion of spin effects leads us to a study of precession equations valid also for the calculation of gravitational waveforms.Comment: 22 pages, AASTeX and 13 figures in PostScrip

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

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-$p_T$ hadron production data measured at RHIC in d+Au collisions. With the help of an extended definition of the $\chi^2$ 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 $\chi^2$ 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-$p_T$ 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