1,954 research outputs found
Constraints on Gluon Sivers Distribution from RHIC Results
We consider the recent RHIC data on the transverse single spin asymmetry
(SSA) A_N, measured in p(transv. polarized) p --> pion X processes at
mid-rapidity by the PHENIX Collaboration. We analyze this experimental
information within a hard scattering approach based on a generalized QCD
factorization scheme, with unintegrated, transverse momentum dependent (TMD),
parton distribution and fragmentation functions. In this kinematical region,
only the gluon Sivers effect could give a large contribution to A_N; its
vanishing value is thus used to give approximate upper limits on the gluon
Sivers function (GSF). Additional constraints from the Burkardt sum rule for
the Sivers distributions are also discussed.Comment: LaTeX 2e, 4 pages, 2 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
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.Comment: LaTeX, 5 pages, 1 eps figure, uses epsfig, wrapfig. Talk delivered by
S. Melis at the ``XI Workshop on High Energy Spin Physics'', SPIN 05,
September 27 - October 1, 2005, Dubna, Russi
Helicity Formalism and Spin Asymmetries in Hadronic Processes
We present a generalized QCD factorization scheme for the high energy
inclusive polarized process, (A, S_A) + (B, S_B) -> C + X, including all
intrinsic partonic motions. This introduces many non-trivial azimuthal phases
and several new spin and k_T dependent soft functions. The formal expressions
for single and double spin asymmetries are discussed. Numerical results for
A_N[p(transv. polarized) p -> pi + X] are presented.Comment: 8 pages, 4 ps figures, uses ws-procs9x6.cls and rotating_pr.sty
(included). Talk delivered by F. Murgia at the "International Workshop on
Transverse Polarisation Phenomena in Hard Processes" (TRANSVERSITY 2005),
September 7-10 2005, Como, Ital
Proteomics of Cytochrome c Oxidase-Negative versus -Positive Muscle Fiber Sections in Mitochondrial Myopathy
The mosaic distribution of cytochrome c oxidase(+) (COX+) and COX - muscle fibers in mitochondrial disorders allows the sampling of fibers with compensated and decompensated mitochondrial function from the same individual. We apply laser capture microdissection to excise individual COX+ and COX- fibers from the biopsies of mitochondrial myopathy patients. Using mass spectrometry-based proteomics, we quantify >4,000 proteins per patient. While COX+ fibers show a higher expression of respiratory chain components, COX- fibers display protean adaptive responses, including upregulation of mitochondrial ribosomes, translation proteins, and chaperones. Upregulated proteins include C1QBP, required for mitoribosome formation and protein synthesis, and STOML2, which organizes cardiolipin-enriched microdomains and the assembly of respiratory supercomplexes. Factoring in fast/slow fiber type, COX (-) slow fibers show a compensatory upregulation of beta-oxidation, the AAA(+) protease AFG3L1, and the OPA1-dependent cristae remodeling program. These findings reveal compensatory mechanisms in muscle fibers struggling with energy shortage and metabolic stress
Sivers effect in Drell-Yan processes
The Sivers distributions recently extracted from semi-inclusive deep
inelastic scattering data [1] are used to compute estimates for Sivers
asymmetries in Drell-Yan processes which are being planned at several
facilities (RHIC, COMPASS, J-PARC, PAX, PANDA, NICA (JINR) and SPASCHARM
(IHEP)). Most of these asymmetries turn out to be large and could allow a clear
test of the predicted sign change of the Sivers distributions when active in
SIDIS and Drell-Yan processes. This is regarded as a fundamental test of our
understanding, within QCD and the factorization scheme, of single spin
asymmetries.Comment: RevTeX4, 12 pages, 23 eps figure
Sivers distribution functions and the latest SIDIS data
We present an extraction of the Sivers distribution functions from the most
recent experimental data of the HERMES and COMPASS experiments, assuming a
negligible contribution of sea quark Sivers functions.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 USA. Typo corrected in Table
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.Comment: 8 pages, 10 eps figures, uses ws-procs9x6.cls; Talk presented by F.
Murgia at the II International Workshop on Transverse Polarisation Phenomena
in Hard Processes (Transversity 2008), May 28-31, 2008, Ferrara (Italy
Single spin asymmetries in l p --> h X processes: a test of factorization
Predictions for the transverse single spin asymmetry (SSA), A_N, are given
for the inclusive processes l p(transv. pol.) --> h X and l p(transv. pol.) -->
jet + X, which could be measured in operating or future experiments. These
estimates are based on the Sivers distributions and the Collins fragmentation
functions which fit the azimuthal asymmetries measured in semi-inclusive deep
inelastic scattering (SIDIS) processes (l p(transv. pol.) --> l' h X). The
factorization in terms of transverse momentum dependent distribution and
fragmentation functions (TMD factorization) - which supplies the theoretical
framework in which SIDIS azimuthal asymmetries are analyzed - is assumed to
hold also for the l p --> h X inclusive process at large P_T. A measurement of
A_N would then provide a direct test of the validity of the TMD factorization
in this case and would have important consequences for the study and
understanding of SSAs in p p(transv. pol.) --> h X processes.Comment: RevTeX4, 16 pages, 13 ps figures; v2: a short paragraph and 3
references added in the introduction; matches the version published in Phys.
Rev.
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