1,257 research outputs found
Global analysis of helicity PDFs: past - present - future
We discuss the current status of the DSSV global analysis of
helicity-dependent parton densities. A comparison with recent semi-inclusive
DIS data from COMPASS is presented, and constraints on the polarized
strangeness density are examined in some detail.Comment: Talk presented at the XIX Int. Workshop on Deep-Inelastic Scattering
and Related Subjects (DIS 2011); 4 pages; 2 figure
Drell-Yan Lepton Angular Distribution at Small Transverse Momentum
We investigate the dependence of the Drell-Yan cross section on lepton polar
and azimuthal angles, as generated by the lowest-order QCD annihilation and
Compton processes. We focus in particular on the azimuthal-angular
distributions, which are of the form cos(phi) and cos(2phi). At small
transverse momentum q_T of the lepton pair, q_T << Q, with Q the pair mass,
these terms are known to be suppressed relative to the phi-independent part of
the Drell-Yan cross section by one or two powers of the transverse momentum.
Nonetheless, as we show, like the phi-independent part they are subject to
large logarithmic corrections, whose precise form however depends on the
reference frame chosen. These logarithmic contributions ultimately require
resummation to all orders in the strong coupling. We discuss the potential
effects of resummation on the various angular terms in the cross section and on
the Lam-Tung relation.Comment: 13 pages, 2 figures; reference added, minor other changes, matches
version to be published in PR
Transverse Double-Spin Asymmetries for Muon Pair Production in pp-Collisions
We calculate the rapidity dependence of the transverse double-spin asymmetry
for the Drell-Yan process to next-to-leading order in the strong coupling.
Input transversity distributions are obtained by saturating the Soffer
inequality at a low hadronic mass scale. Results for the polarized BNL-RHIC
proton-proton collider and the proposed HERA-N fixed-target experiment are
presented, and the influence of the limited muon acceptance of the detectors on
measurements of the asymmetry is studied in detail.Comment: 7 pages including 5 figures; significantly shortened, to be published
in Phys. Rev.
Twist Three Distribution f_\perp(x,k^\perp) in Light-front Hamiltonian Approach
We calculate the twist three distribution f_\perp(x,k^\perp) contributing to
Cahn effect in unpolarized semi-inclusive deep inelastic scattering. We use
light-front Hamiltonian technique and take the state to be a dressed quark at
one loop in perturbation theory. The 'genuine twist three' contribution comes
from the quark-gluon interaction part in the operator and is explicitly
calculated. f_\perp(x,k^\perp) is compared with f_1(x,k^\perp).Comment: Two figures added, one author added, some parts rewritten for
clarificatio
Magnetic trapping of buffer-gas cooled chromium atoms and prospects for the extension to paramagnetic molecules
We report the successful buffer-gas cooling and magnetic trapping of chromium
atoms with densities exceeding atoms per cm at a temperature of
350 mK for the trapped sample. The possibilities to extend the method to
buffer-gas cool and magnetically trap molecules are discussed. To minimize the
most important loss mechanism in magnetic trapping, molecules with a small
spin-spin interaction and a large rotational constant are preferred. Both the
CrH ( ground state) and MnH () radicals appear to be
suitable systems for future experiments.Comment: 9 pages, 4 Figure
Next-to-leading Order Evolution of Transversity Distributions and Soffer's Inequality
We present a calculation of the two-loop splitting functions for the
evolution of the twist-2 `transversity' parton densities of transversely
polarized nucleons. We study the implications of our results for Soffer's
inequality for the case of valence quark densities.Comment: 23 Pages, LaTeX, 2 figures as eps files, final, slightly modified
version, to appear in Phys. Rev.
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
Measurement of the nuclear modification factor of electrons from heavy-flavour decays at mid-rapidity in Pb-Pb collisions at = 2.76 TeV with ALICE
We present results on inclusive electrons for 1.5 6 GeV/
in {Pb-Pb} collisions at = 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 ({ 3.5
GeV/}) 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
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-
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
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