174 research outputs found
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.Comment: LaTeX, 8 pages, 4 ps figures, uses epsfig.sty. Talk delivered by F.
Murgia at the "IX Convegno su Problemi di Fisica Nucleare Teorica", October
9-12, 2002, Cortona, Ital
Single spin asymmetries, unpolarized cross sections and the role of partonic transverse momentum
Partonic intrinsic transverse momentum can be essential for the explanation
of large single spin asymmetries in hadronic reactions in the framework of
perturbative QCD. The status of an ongoing program investigating in a
consistent way the role of intrinsic transverse momentum both in unpolarized
and polarized processes is discussed. We compute inclusive cross sections for
hadron and photon production in hadronic collisions and for Drell-Yan
processes; the results are compared with available experimental data in several
different kinematical situations.Comment: LaTeX, 6 pages, 4 ps figures, uses graphicx.sty. Talk delivered by U.
D'Alesio at the ``15th International Spin Physics Symposium'', SPIN2002,
September 9-14, 2002, Brookhaven National Laboratory, Upton (NY), US
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.Comment: 8 pages, 3 figures, uses epsfig.sty. Talk delivered by U. D'Alesio at
the ``VIII Convegno su Problemi di Fisica Nucleare Teorica'', October 18-20,
2000, Cortona, Ital
Transverse Momentum Dependent Distributions in Hadronic Collisions: p(transv. polarized) p --> D + X and p(transv. polarized) p --> gamma + X
Our understanding of the transverse spin structure of hadrons might
definitely get improved by the information we gather on transverse momentum
dependent (TMD) distributions. These new functions could also be crucial for a
description of the observed transverse single spin asymmetries (SSA). In a hard
scattering model for inclusive hadronic reactions, based on a generalized QCD
factorization scheme, many mechanisms - namely the Sivers, Collins,
Boer-Mulders effects - might contribute to a SSA. We show how the k_T dependent
phases arising from the partonic kinematics together with a suitable choice of
experimental configurations could help in disentangling the above mentioned
effects. We discuss their potential role in two inclusive hadronic processes:
heavy meson and photon production in pp and p pbar collisions.Comment: LaTeX 2e, 4 pages, 4 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
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.Comment: LaTeX2e, 4 pages, 4 ps figures, uses ws-procs9x6. Talk delivered by
F. Murgia at the ``16th International Spin Physics Symposium'', SPIN2004,
October 10-16, 2004, Trieste, Ital
Towards a first estimate of the gluon Sivers function from data in collisions at RHIC
Within a generalized parton model approach, with inclusion of spin and
intrinsic transverse momentum effects, we show how the latest, highly precise,
midrapidity data on the transverse single spin asymmetry measured in
by the PHENIX Collaboration at RHIC [1], can be used to get a
first estimate on the still poorly known gluon Sivers distribution. To this end
we also adopt the present information on the quark Sivers functions, as
extracted from semi-inclusive deeply inelastic scattering data. This analysis
updates a previous study by some of us where a first bound on this distribution
was obtained [2].Comment: RevTex4, 10 pages, 7 eps figures. V2: discussion on the process
dependence of the quark Sivers function, with two new plots (Fig. 4), added
in Section II. One reference added. Results unchanged. Matches the published
versio
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.Comment: LaTeX, 8 pages, uses ws-procs9x6.cls. Talk delivered by S. Melis at
the ``X Convegno su Problemi di Fisica Nucleare Teorica'', October 6-9, 2004,
Cortona, Ital
On the importance of Lorentz structure in the parton model: target mass corrections, transverse momentum dependence, positivity bounds
We show that respecting the underlying Lorentz structure in the parton model
has very strong consequences. Failure to insist on the correct Lorentz
covariance is responsible for the existence of contradictory results in the
literature for the polarized structure function g_2(x), whereas with the
correct imposition we are able to derive the Wandzura-Wilczek relation for
g_2(x) and the target-mass corrections for polarized deep inelastic scattering
without recourse to the operator product expansion. We comment briefly on the
problem of threshold behaviour in the presence of target-mass corrections.
Careful attention to the Lorentz structure has also profound implications for
the structure of the transverse momentum dependent parton densities often used
in parton model treatments of hadron production, allowing the k_T dependence to
be derived explicitly. It also leads to stronger positivity and Soffer-type
bounds than usually utilized for the collinear densities.Comment: RevTeX4, 17 pages, 7 eps figure
Weak interactions in polarized semi-inclusive DIS
We calculate, within pQCD parton model at leading orders, the expression of
the polarization P of spin 1/2 hadrons (typically Lambda baryons), produced in
polarized semi-inclusive DIS in all possible cases in which weak interactions
are involved. We discuss how to gather new information on fragmentation and
distribution functions and give numerical estimates in the cases for which data
are or will soon be available.Comment: LaTeX, 33+1 pages, 12 ps figures, uses epsfig.st
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