279 research outputs found
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
p p Elastic Scattering at LHC and Nucleon Structure
High energy elastic scattering at the Large Hadron Collider (LHC) at
c.m. energy 14 TeV is predicted using the asymptotic behavior of
and known from dispersion relation calculations and
the measured elastic differential cross section at . The effective field theory model underlying the phenomenological
analysis describes the nucleon as having an outer cloud of quark-antiquark
condensed ground state, an inner core of topological baryonic charge of radius
and a still smaller valence quark-bag of radius . The LHC experiment TOTEM (Total and Elastic Measurement), if carried
out with sufficient precision from to , will be
able to test this structure of the nucleon.Comment: 13 pages, 6 figures, to be published in the Modern Physics Letters
Role of transverse momentum dependence of unpolarised parton distribution and fragmentation functions in the analysis of azimuthal spin asymmetries
Information on the Sivers distribution and the Collins fragmentation
functions and their transverse momentum dependence is mainly based on fitting
single spin asymmetry data from semi-inclusive deep inelastic scattering
(SIDIS). Independent information, respectively on the Sivers distribution and
the Collins fragmentation, can be obtained from Drell-Yan and
annihilation processes. In the SIDIS case, the transverse momentum of the final
observed hadron, which is the quantity measured, is generated both by the
average transverse momentum in the distribution and in the fragmentation
functions. As a consequence, these are strongly correlated and a separate
extraction is made difficult. In this paper we investigate, in a simple
kinematical Gaussian configuration, this correlation, its role on the
transverse single spin asymmetries in SIDIS and the consequences for
predictions of the Sivers asymmetry in Drell-Yan processes and for the Collins
asymmetry in annihilation. We find that, in some cases, these effects
can be relevant and must be carefully taken into account.Comment: 21 pages, 9 figures (18 eps plots
Study of the sign change of the Sivers function from STAR Collaboration W/Z production data
Recent data on the transverse single spin asymmetry measured by the
STAR Collaboration for reactions at RHIC
allow the first investigation of the Sivers function in Drell-Yan processes and
of its expected sign change with respect to SIDIS processes. A new extraction
of the Sivers functions from the latest SIDIS data is performed and a critical
assessment of the significance of the STAR data is attempted.Comment: 17 pages, 16 pdf figures, uses jheppub.st
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 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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