134 research outputs found
Partonic structure of the Nucleon in QCD and Nuclear Physics: new developments from old ideas
The nucleon is an ideal laboratory to solve QCD in the nonperturbative
regime. There are several experimental observations that still lack a rigorous
interpretation; they involve the nucleon as a (polarized) target as well as a
beam (in collisions and Drell-Yan processes). These data look like big
azimuthal and spin asymmetries, related to the transverse polarization and
momentum of the nucleon and/or the final detected particles. They suggest
internal reaction mechanisms that are suppressed in collinear perturbative QCD
but that are "natural" in Nuclear Physics: quark helicity flips, residual final
state interactions, etc.. In my talk, I will give a brief survey of the main
results and I will flash the most recent developments and measurements.Comment: to appear in the proceedings of the X Convegno su problemi di Fisica
Nucleare e Teorica, Cortona (Italy), 6-9 Oct. 2004; ws-proc9x6.cls include
Transversity and inclusive two-pion production
A model for dihadron fragmentation functions is briefly outlined, that
describes the fragmentation of a quark in two unpolarized hadrons. The
parameters are tuned to the output of the PYTHIA event generator for two-hadron
semi-inclusive production in deep inelastic scattering at HERMES. Then,
predictions are made for the unknown polarized fragmentation function and the
related single-spin asymmetry in the azimuthal distribution of
pairs in semi-inclusive deep inelastic scattering on transversely polarized
targets at HERMES and COMPASS. This asymmetry can be used to extract the quark
transversity distribution.Comment: 4 pages, 4 composite figures, talk presented at the 17th
International Spin Physics Symposium (SPIN2006), Kyoto (Japan), October 2-7,
200
Two-hadron Inclusive DIS and Interference Fragmentation Functions
We investigate the properties of interference fragmentation functions arising
from the emission of two leading hadrons inside the same jet for semi-inclusive
lepton-nucleon deep-inelastic scattering. Using an extended spectator model we
give numerical estimates for the example of the fragmentation into a
proton-pion pair with its invariant mass on the Roper resonance.Comment: 10 pages, 12 figures in .eps format, epsfig and sprocl style files
included, to appear in the Proceedings of the EPIC99 Workshop, April 8-11
1999, Bloomington (Indiana-USA
Alternative approaches to transversity: how convenient and feasible are they?
The complete knowledge of the nucleon spin structure at leading twist
requires also addressing the transverse spin distribution of quarks, or
transversity, which is yet unexplored because of its chiral-odd nature.
Elaborating strategies to extract it from (spin) asymmetry data represents a
unique opportunity to explore more generally the transverse spin structure of
the nucleon and the transverse momentum dynamics of partons inside it. Here, we
critically review some of the most promising approaches.Comment: 8 pages; 4 figures in .eps format; new version with modified fig.4;
to appear in the Proceedings of the International Workshop on Transverse
Polarisation Phenomena in Hard Processes (Transversity 2005), Villa Olmo
(Como), 7-10th September 2005; World Scientific style file include
Modeling dihadron fragmentation functions
We present a model for dihadron fragmentation functions, describing the
fragmentation of a quark into two unpolarized hadrons. We tune the parameters
of our model to the output of the PYTHIA event generator for two-hadron
semi-inclusive production in deep inelastic scattering at HERMES. Once the
parameters of the model are fixed, we make predictions for other unknown
fragmentation functions and for a single-spin asymmetry in the azimuthal
distribution of pi+ pi- pairs in semi-inclusive deep inelastic scattering on a
transversely polarized target at HERMES and COMPASS. Such asymmetry could be
used to measure the quark transversity distribution function.Comment: 16 pages, 10 figure
First Extraction of Transversity from a Global Analysis of Electron-Proton and Proton-Proton Data
We present the first extraction of the transversity distribution in the
framework of collinear factorization based on the global analysis of pion-pair
production in deep-inelastic scattering off transversely polarized targets and
in proton-proton collisions with one transversely polarized proton. The
extraction relies on the knowledge of di-hadron fragmentation functions, which
are taken from the analysis of electron-positron annihilation data. For the
first time, the chiral-odd transversity is extracted from a global analysis
similar to what is usually done for the chiral-even spin-averaged and helicity
distributions. The knowledge of transversity is important for, among other
things, detecting possible signals of new physics in high-precision low-energy
experiments.Comment: version identical to published one; supplemental material available
at http://link.aps.org/supplemental/10.1103/PhysRevLett.120.19200
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