13 research outputs found
Parton intrinsic motion: unpolarized cross sections and the Sivers effect in inclusive particle production
We present a detailed study, performed in the framework of LO perturbative
QCD with the inclusion of spin and k_T effects, of unpolarized cross sections
for the Drell-Yan process and for inclusive pion and photon production in
hadronic collisions, in different kinematical situations. We find a
satisfactory agreement between theoretical predictions and experimental data.
This supports the study of spin effects and transverse single spin asymmetries
(SSA) within the same scheme. We then present results for SSA, generated by the
so-called Sivers effect, in inclusive pion production in proton-proton
collisions
Phenomenology of single transverse spin asymmetries
A unified and consistent phenomenological approach to single transverse spin
asymmetries in the framework of perturbative QCD, with the inclusion of a new
class of spin and k_T dependent distribution and fragmentation functions, is
presented. As an example, results on A_N(p(pol) p --> pion X) and P_Lambda(p p
-->Lambda(pol) X) are shown
An improved analysis of k_T effects for SSA in hadronic collisions
The role of intrinsic transverse momentum both in unpolarized and polarized
processes is discussed. We consider inclusive cross sections for pion
production in hadronic collisions and for Drell-Yan processes. We reanalyze
transverse single spin asymmetries (SSA) in inclusive pion production,
p(transv. polarized) p --> pion + X, in terms of Sivers effect and show its
contribution to A_{UL} in semi-inclusive DIS (SIDIS)
Cross sections and single spin asymmetries in hadronic collisions with intrinsic transverse momentum effects
The role of intrinsic transverse momentum both in unpolarized and polarized
processes is discussed. We consider inclusive cross sections for pion
production in hadronic collisions and for Drell-Yan processes; the results are
compared with available experimental data in several different kinematical
situations. We reanalyze transverse single spin asymmetries (SSA) observed in
inclusive pion production, p(transv. polarized) p --> pion + X, in terms of
Sivers effect and show how it can be disentangled in polarized Drell-Yan
processes by suitably integrating over some final configurations. Estimates for
RHIC experiments are given
Sivers effect and transverse single spin asymmetries in Drell-Yan processes
Sivers asymmetry, adopted to explain transverse single spin asymmetries (SSA)
observed in inclusive pion production, p(transv. polarized) p --> pion + X and
p-bar(transv. polarized) p --> pion + X is used here to compute SSA in
Drell-Yan processes; in this case, by considering the differential cross
section in the lepton-pair invariant mass, rapidity and transverse momentum,
other mechanisms which may originate SSA cannot contribute. Estimates for RHIC
experiments are given
A general formalism for single and double spin asymmetries in inclusive hadron production
We present a calculation of single and double spin asymmetries for inclusive
hadron production in hadronic collisions. Our approach is based on Leading
Order (LO) perturbative QCD and generalized factorization theorems, with full
account of intrinsic parton momentum, k_T, effects. This leads to a new class
of spin and k_T-dependent distribution and fragmentation functions. Limiting
ourselves to consider leading twist functions, we show how they could play a
relevant role in producing non-vanishing spin asymmetries
Transverse single spin asymmetries in Drell-Yan processes
Recently, it has been shown, contrary to previous beliefs, that the k_T
distribution of quarks in a transversely polarized proton can be asymmetric.
This ``Sivers effect'' had already been used to explain transverse single spin
asymmetries (SSA) observed in inclusive pion production, p(transv. polarized) p
--> pion + X and p-bar(transv. polarized) p --> pion + X. In such channels,
however, other mechanisms, like the ``Collins effect'' (a k_T asymmetric
fragmentation of a transversely polarized quark into pions), may generate SSA.
The Sivers asymmetry is used here to compute SSA in Drell-Yan processes; in
this case, by considering the differential cross-section in the lepton-pair
invariant mass, rapidity and transverse momentum, other mechanisms which may
originate SSA cannot contribute. Estimates for RHIC experiments are given
General helicity formalism for Single and Double Spin Asymmetries in p p --> pion + X
We consider within a generalized QCD factorization approach, the high energy
inclusive polarized process p p --> pion + X, including all intrinsic partonic
motions. Several new spin and k_T-dependent soft functions appear and
contribute to cross sections and spin asymmetries. We present here formal
expressions for transverse single spin asymmetries and double longitudinal
ones. The transverse single spin asymmetry, A_N, is considered in detail, and
all contributions are evaluated numerically. It is shown that the azimuthal
phase integrations strongly suppress most contributions, leaving at work mainly
the Sivers effect
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
Transversity and Collins Functions: from e+ e- --> h1 h2 X to SIDIS Processes
We present [1] the first simultaneous extraction of the transversity
distribution and the Collins fragmentation function, obtained through a
combined analysis of experimental data on azimuthal asymmetries in
semi-inclusive deep inelastic scattering (SIDIS), from the HERMES and COMPASS
Collaborations, and in e+ e- --> h1 h2 X processes, from the Belle
Collaboration