153 research outputs found
Azimuthal asymmetries for hadron distributions inside jets in hadronic collisions
Using a generalized parton model approach including spin and intrinsic parton
motion effects, and assuming the validity of factorization for large p_T jet
production in hadronic collisions, we study the azimuthal distribution around
the jet axis of leading pions, produced in the jet fragmentation process. We
identify the observable leading-twist azimuthal asymmetries for the unpolarized
and single-polarized case related to both quark and gluon-originated jets. We
account for all physically allowed combinations of the transverse momentum
dependent (TMD) parton distribution and fragmentation functions, with special
attention to the Sivers, Boer-Mulders, and transversity quark distributions,
and to the Collins fragmentation function for quarks (and to the analogous
functions for gluon partons).Comment: 8 pages, 5 figures, to appear in the proceedings of 19th
International Spin Physics Symposium (SPIN2010), Sep 27-Oct 2, 2010, Juelich
(Germany
Hadron Spin Structure: Novel Effects from Transverse Single Spin Asymmetries
Transverse single spin asymmetries can be a challenging tool in our
understanding of the internal structure of hadrons. Some aspects and recent
results are discussed.Comment: LaTeX 2e, 3 pages, 2 ps figures, uses aipproc.cls. Talk delivered at
the 6th Conference on ``Quark Confinement and the Hadron Spectrum'',
September 21-25, 2004, Villasimius, Ital
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
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
Target Fragmentation of the Nucleon at High Energies
We calculate target fragmentation in and reactions in the meson cloud picture of the nucleon. The reaction is used to fix the form factor for two different models. We take into account the possible destruction of the residual neutron by the projectile. Using the form factor from the hadronic reaction we calculate photoproduction and small electroproduction of forward neutrons at HERA. In photoproduction we observe about the same amount of absorption as in the hadronic reaction. For deep inelastic events screening is found to be negligible. The signature of this color transparency on the nucleon is a shift of the distribution to higher neutron energies for photofragmentation
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