3,416 research outputs found
Black hole solutions of dimensionally reduced Einstein-Gauss-Bonnet gravity with a cosmological constant
We study the phase space of the spherically symmetric solutions of the system
obtained from the dimensional reduction of the six-dimensional
Einstein-Gauss-Bonnet action with a cosmological constant. We show that all the
physical solutions have anti-de Sitter asymptotic behavior.Comment: 13 pages, plain Te
Phenomenology of Sivers Effect with TMD Evolution
Following the TMD evolution scheme recently proposed for the unpolarized and
the Sivers distribution function, we propose a simple strategy to take into
account this TMD Q^2 dependence in our phenomenological extraction of the
Sivers function from SIDIS data. New results are presented and possible future
applications are discussed.Comment: Contribution to the Proceedings of the XX International Workshop on
Deep-Inelastic Scattering and related subjects (DIS2012), 26-30 March 2012,
Bonn, Germany. One figure correcte
Partonic Transverse Motion in Unpolarized Semi-Inclusive Deep Inelastic Scattering
We analyse the role of partonic transverse motion in unpolarized
Semi-Inclusive Deep Inelastic Scattering (SIDIS) processes. Imposing
appropriate kinematical conditions, we find some constraints which fix an upper
limit to the range of allowed kt values and lead to interesting results,
particularly for some observables like the azimuthal modulation of
the unpolarized SIDIS cross section and the average transverse momentum of the
final, detected hadron.Comment: To appear in the Proceedings of the XIX International Workshop on
Deep-Inelastic Scattering and Related Subjects (DIS 2011), April 11-15, 2011,
Newport News, VA US
Transverse single-spin asymmetries in proton-proton collisions at the AFTER@LHC experiment in a TMD factorisation scheme
The inclusive large- production of a single pion, jet or direct photon,
and Drell-Yan processes, are considered for proton-proton collisions in the
kinematical range expected for the fixed-target experiment AFTER, proposed at
LHC. For all these processes, predictions are given for the transverse
single-spin asymmetry, , computed according to a Generalised Parton Model
previously discussed in the literature and based on TMD factorisation.
Comparisons with the results of a collinear twist-3 approach, recently
presented, are made and discussed.Comment: RevTex4, 12 pages, 36 eps figures. V2: Few paragraphs and comments
added. Several references added. Results unchanged. Matches the published
versio
Constraints on Gluon Sivers Distribution from RHIC Results
We consider the recent RHIC data on the transverse single spin asymmetry
(SSA) A_N, measured in p(transv. polarized) p --> pion X processes at
mid-rapidity by the PHENIX Collaboration. We analyze this experimental
information within a hard scattering approach based on a generalized QCD
factorization scheme, with unintegrated, transverse momentum dependent (TMD),
parton distribution and fragmentation functions. In this kinematical region,
only the gluon Sivers effect could give a large contribution to A_N; its
vanishing value is thus used to give approximate upper limits on the gluon
Sivers function (GSF). Additional constraints from the Burkardt sum rule for
the Sivers distributions are also discussed.Comment: LaTeX 2e, 4 pages, 2 ps figures, uses aipproc.cls. Talk delivered by
U. D'Alesio at the "17th International Spin Physics Symposium", SPIN2006,
October 2-7, 2006, Kyoto, Japa
A strategy towards the extraction of the Sivers function with TMD evolution
The QCD evolution of the unpolarized Transverse Momentum Dependent (TMD)
distribution functions and of the Sivers functions have been discussed in
recent papers. Following such results we reconsider previous extractions of the
Sivers functions from semi-inclusive deep inelastic scattering data and propose
a simple strategy which allows to take into account the Q^2 dependence of the
TMDs in comparison with experimental findings. A clear evidence of the
phenomenological success of the TMD evolution equations is given, mostly, by
the newest COMPASS data off a transversely polarized proton target.Comment: 15 pages, 7 figures, 2 table
Sivers and Collins effects in polarized pp scattering processes
We summarize the present phenomenology of Sivers and Collins effects for
transverse single spin asymmetries in polarized proton-proton collisions within
the framework of the generalized parton model (GPM). We will discuss a
reassessment of the Collins effect and some preliminary predictions for SSA's
in p(pol) p -> pi,K + X processes at RHIC obtained using updated information
from SIDIS data and a new set of meson fragmentation functions.Comment: 8 pages, 10 eps figures, uses ws-procs9x6.cls; Talk presented by F.
Murgia at the II International Workshop on Transverse Polarisation Phenomena
in Hard Processes (Transversity 2008), May 28-31, 2008, Ferrara (Italy
Unpolarised Transverse Momentum Dependent Distribution and Fragmentation Functions from SIDIS Multiplicities
The unpolarised transverse momentum dependent distribution and fragmentation
functions are extracted from HERMES and COMPASS experimental measurements of
SIDIS multiplicities for charged hadron production. The data are grouped into
independent bins of the kinematical variables, in which the TMD factorisation
is expected to hold. A simple factorised functional form of the TMDs is
adopted, with a Gaussian dependence on the intrinsic transverse momentum, which
turns out to be quite adequate in shape. HERMES data do not need any
normalisation correction, while fits of the COMPASS data much improve with a
-dependent overall normalisation factor. A comparison of the extracted TMDs
with previous EMC and JLab data confirms the adequacy of the simple Gaussian
distributions. The possible role of the TMD evolution is briefly considered.Comment: 21 pages, 16 figure
A phenomenological analysis of azimuthal asymmetries in unpolarized semi-inclusive deep inelastic scattering
We present a phenomenological analysis of the cos-phi and cos-2phi
asymmetries in unpolarized semi-inclusive deep inelastic scattering, based on
the recent multidimensional data released by the COMPASS and HERMES
Collaborations. In the TMD framework, valid at relatively low transverse
momenta, these asymmetries arise from intrinsic transverse momentum and
transverse spin effects, and from their correlations. The role of the Cahn and
Boer-Mulders effects in both azimuthal moments is explored up to order 1/Q. As
the kinematics of the present experiments is dominated by the low-Q^2 region,
higher-twist contributions turn out to be important, affecting the results of
our fits.Comment: 18 pages, 5 figures, one paragraph added at the end of Section IV,
one reference added. PRD versio
A study on the interplay between perturbative QCD and CSS/TMD formalism in SIDIS processes
We study the Semi-Inclusive Deep Inelastic Scattering (SIDIS) cross section
as a function of the transverse momentum, . In order to describe it over a
wide region of , soft gluon resummation has to be performed. Here we will
use the original Collins-Soper-Sterman (CSS) formalism; however, the same
procedure would hold within the improved Transverse Momentum Dependent (TMD)
framework. We study the matching between the region where fixed order
perturbative QCD can successfully be applied and the region where soft gluon
resummation is necessary. We find that the commonly used prescription of
matching through the so-called Y-factor cannot be applied in the SIDIS
kinematical configurations we examine. In particular, the non-perturbative
component of the resummed cross section turns out to play a crucial role and
should not be overlooked even at relatively high energies. Moreover, the
perturbative expansion of the resummed cross section in the matching region is
not as reliable as it is usually believed and its treatment requires special
attention.Comment: Two references and an appendix added, 22 pages, 11 figure
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