Helicity Parton Distributions from Spin Asymmetries in W-Boson Production at RHIC

We present a next-to-leading order QCD calculation of the cross section and longitudinal spin asymmetry in single-inclusive charged-lepton production, pp -> l X, at RHIC, where the lepton is produced in the decay of an electroweak gauge boson. Our calculation is presented in terms of a multi-purpose Monte-Carlo integration program that may be readily used to include experimental spin asymmetry data in a global analysis of helicity parton densities. We perform a toy global analysis, studying the impact of anticipated RHIC data on our knowledge about the polarized anti-quark distributions.Comment: 22 pages, 13 figures included. Typos in Figs 2, 6, 8 and scales correcte

Measurement of the nuclear modification factor of electrons from heavy-flavour decays at mid-rapidity in Pb-Pb collisions at sNN\sqrt{s_{\rm NN}} = 2.76 TeV with ALICE

We present results on inclusive electrons for 1.5 $< p_{\rm T} <$ 6 GeV/$c$ in {Pb-Pb} collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV measured with ALICE at the LHC and compare these to a cocktail of background electron sources. The excess of electrons beyond the cocktail at high momenta ({$p_{\rm T} >$ 3.5 GeV/$c$}) is attributed to electrons from heavy-flavour decays. The corresponding nuclear modification factor indicates heavy-flavour suppression by a factor of 1.5-4.Comment: 4 pages; 4 figures; QM 2011 proceeding

Single transverse-spin asymmetry in high transverse momentum pion production in pp collisions

We study the single-spin (left-right) asymmetry in single-inclusive pion production in hadronic scattering. This asymmetry is power-suppressed in the transverse momentum of the produced pion and can be analyzed in terms of twist-three parton correlation functions in the proton. We present new calculations of the corresponding partonic hard-scattering functions that include the so-called "non-derivative" contributions not previously considered in the literature. We find a remarkably simple structure of the results. We also present a brief phenomenological study of the spin asymmetry, taking into account data from fixed-target scattering and also the latest information available from RHIC. We make additional predictions that may be tested experimentally at RHIC.Comment: 32 pages, 14 figure

Polarized semi-inclusive electroweak structure functions at next-to-leading-order

We present a next-to-leading order (NLO) computation of the full set of polarized and unpolarized electroweak semi-inclusive DIS (SIDIS) structure functions, whose knowledge is crucial for a precise extraction of polarized parton distributions. We focus on the phenomenology of the polarized structure functions for the kinematical conditions that could be reached in an Electron-Ion-Collider. We show that the NLO corrections are sizeable, particularly in the small-$x$ range. We test the sensitivity of these structure functions on certain quark distributions and compare it to the situation of inclusive DIS and electromagnetic SIDIS.Comment: 17 pages, 5 figure

Direct Photons at RHIC

The PHENIX experiment has measured direct photons in $\sqrt{s_{NN}} = 200$ GeV Au+Au collisions and p+p collisions. The fraction of photons due to direct production in Au+Au collisions is shown as a function of $p_T$ and centrality. This measurement is compared with expectation from pQCD calculations. Other possible sources of direct photons are discussed.Comment: 7 pages, 5 figures, presented at Hot Quarks 2004, Taos, N

Direct Photons in Nuclear Collisions at FAIR Energies

Using the extrapolation of existing data estimations of prompt photon production at FAIR energies have been made. At $y=y_{c.m.}$ the rapidity density of prompt photons with $p_{t}>$ 1.5 GeV/c per central Au+Au event at 25 AGeV is estimated as $\sim 10^{-4}$ . With the planed beam intensity $10^{9}$ per second and 1% interaction probability, for 10% of most central events one can expect the prompt photon rate $\sim 10^{2}$ photons per second. Direct photons from the hadron scenario of ion collisions generated by the Hadron-String-Dynamics (HSD) transport approach with implemented meson scatterings $\pi\rho\to\pi\gamma, \pi\pi\to\rho\gamma$ have been analyzed. Photons from short-living resonances (e.g. $\omega \to \pi^{0} \gamma$) decaying during the dense phase of the collision should be considered as direct photons. They contribute significantly in the direct photon spectrum at $p_{t}=0.5 - 1$ GeV/c. At the FAIR energy 25 AGeV in Au+Au central collisions the HSD generator predicts, as a lower estimate, $\gamma_{direct}/\gamma_{\pi^{0}} \simeq$ 0.5% in the region $p_{t}=0.5 - 1$ GeV/c. At $p_{t}=1.5 - 2$ GeV/c $\gamma_{prompt}/\gamma_{\pi^{0}} \simeq$ 2%. Thermal direct photons have been evaluated with the Bjorken Hydro-Dynamics (BHD) model. The BHD spectra differ strongly from the HSD predictions. The direct photon spectrum is very sensitive to the initial temperature parameter $T_{0}$ of the model. The 10 MeV increase in the $T_{0}$ value leads to $\sim$ 2 times higher photon yield.Comment: 9 pages, 5 figures, Talk at the session of Russian Academy of Sciences, ITEP, Moscow, 26 - 30 November 200

Soffer's inequality and the transversely polarized Drell-Yan process at next-to-leading order

We check numerically if Soffer's inequality for quark distributions is preserved by next-to-leading order QCD evolution. Assuming that the inequality is saturated at a low hadronic scale we estimate the maximal transverse double spin asymmetry for Drell-Yan muon pair production to next-to-leading order accuracy.Comment: 20 Pages, LaTeX, 7 figures as eps file