68 research outputs found
in inclusive lepton-proton collisions: TMD and twist-3 approaches
We consider the inclusive production of hadrons in lepton-nucleon scattering.
For a transversely polarized nucleon this reaction shows a left-right azimuthal
asymmetry, which we compute this asymmetry in both TMD and in twist-3 collinear
factorization formalisms. All non-perturbative parton correlators of the
calculation are fixed through information from other hard processes. Our
results for the left-right asymmetry agree in sign with recent data for charged
pion production from the HERMES Collaboration and from Jefferson Lab. We
discuss similarities and differences of two formalisms.Comment: 6 pages, 4 figures, to appear in the proceedings of the TRANSVERSITY
2014, Chia, Italy, 9-13 June, 201
The Boer-Mulders effect in unpolarized SIDIS: an analysis of the COMPASS and HERMES data on the asymmetry
We present a phenomenological analysis of the asymmetry
recently measured by the COMPASS and HERMES collaborations in unpolarized
semi-inclusive deep inelastic scattering. In the kinematical regimes explored
by these experiments the asymmetry arises from transverse-spin and intrinsic
transverse-momentum effects. We consider the leading-twist contribution,
related to the so-called Boer-Mulders transverse-polarization distribution
, and the twist-4 Cahn contribution, involving
unpolarized transverse-momentum distribution functions. We show that a
reasonably good fit of the data is achieved with a Boer-Mulders function
consistent with the main theoretical expectations. Our conclusion is that the
COMPASS and HERMES measurements represent the first experimental evidence of
the Boer-Mulders effect in SIDIS.Comment: 11 pages, 7 figures, published version in PR
Scheme dependence and Transverse Momentum Distribution interpretation of Collins-Soper-Sterman resummation
Following an earlier derivation by Catani-de Florian-Grazzini (2000) on the
scheme dependence in the Collins-Soper-Sterman (CSS) resummation formalism in
hard scattering processes, we investigate the scheme dependence of the
Transverse Momentum Distributions (TMDs) and their applications. By adopting a
universal -coefficient function associated with the integrated parton
distributions, the difference between various TMD schemes can be attributed to
a perturbative calculable function depending on the hard momentum scale. We
further apply several TMD schemes to the Drell-Yan process of lepton pair
production in hadronic collisions, and find that the constrained
non-perturbative form factors in different schemes are remarkably consistent
with each other and with that of the standard CSS formalism.Comment: 10 pages, 2 figure
Azimuthal asymmetries in unpolarized Drell-Yan processes and the Boer-Mulders distributions of antiquarks
Using a previous extraction of the quark Boer-Mulders distributions from
semiinclusive deep inelastic scattering data, we fit the unpolarized Drell-Yan
data on the asymmetry, determining the antiquark Boer-Mulders
distributions. A good agreement with the data is found in the region of low
, where the transverse-momentum factorization approach applies.Comment: 7 pages, 3 figure
Connections between collinear and transverse-momentum-dependent polarized observables within the Collins-Soper-Sterman formalism
We extend the improved Collins-Soper-Sterman (iCSS) construction
recently presented in~\cite{Collins:2016hqq} to the case of polarized
observables, where we focus in particular on the Sivers effect in
semi-inclusive deep-inelastic scattering. We further show how one recovers the
expected leading-order collinear twist-3 result from a (weighted)
-integral of the differential cross section. We are also able to
demonstrate the validity of the well-known relation between the (TMD) Sivers
function and the (collinear twist-3) Qiu-Sterman function within the iCSS
framework. This relation allows for their interpretation as functions yielding
the average transverse momentum of unpolarized quarks in a transversely
polarized spin- target. We further outline how this study can be
generalized to other polarized quantities.Comment: 14 pages, Version to be published in PL
Evolution of the helicity and transversity transverse-momentum-dependent parton distributions
We examine the QCD evolution of the helicity and transversity parton distribution functions when including also their dependence on transverse momentum. Using an appropriate definition of these polarized transverse momentum distributions (TMDs), we describe their dependence on the factorization scale and rapidity cutoff, which is essential for phenomenological applications
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