258 research outputs found
Status of Spin Physics
Fundamental spin physics has made striking progresses in the last years; new
ideas, experiments and data interpretations have been proposed and keep
emerging. A review of some of the most important issues in the spin structure
of nucleons is made and prospects for the future are discussed.Comment: Few corrections and additions in reference
What do we know about the proton spin structure?
A brief summary of the theoretical and experimental knowledge of the spin
structure of the proton is presented. The helicity distributions of quark and
gluons are discussed, together with their related sum rules. The transversity
distribution is also introduced with possible strategies for its measurement.
Novel spin dependent and \bfk_\perp unintegrated distribution and
fragmentation functions are discussed, in connection with a new and rich
phenomenology of transverse single spin asymmetries.Comment: 8 pages, 5 figures, talk delivered at GDH02, July 3-6 2002, Genova,
Ital
An Instanton-Induced Contribution to the Decay of the Eta_c into P-Pbar
We compute the decay rate for the process using an
effective helicity-flipping proton-antiproton-gluon vertex which incorporates
nonperturbative chiral symmetry breaking effects induced by instantons. We fix
the strength of the vertex by requiring it to account for the screening of the
proton's axial charge observed in deep-inelastic scattering, and we estimate
the size of the instanton effects by assuming them to depend linearly on the
instanton density. We find that, despite a large suppression, the
instanton-induced process occurs with a sizable rate comparable to the observed
one, whereas the process is forbidden in perturbative QCD and not understood
using standard methods.Comment: plain TeX with harvmac (b mode); 15 pages, 1 figure (included as a
plain uncompressed postscript file); DFTT 73/9
Double hadron lepto-production in the current and target fragmentation regions
We study the inclusive production of two hadrons in deep inelastic processes,
l N ---> l h_1 h_2 X, with h_1 in the current fragmentation region (CFR) and
h_2 in the target fragmentation region (TFR). Assuming a factorized scheme, the
recently introduced polarized and transverse momentum dependent fracture
functions couple to the transverse momentum dependent fragmentation functions.
This allows the full exploration of the fracture functions for transversely
polarized quarks. Some particular cases are considered.Comment: 14 pages, 2 figure
Transversity and Lambda polarization
Two related issues are discussed, which might be easily explored by present
and future COMPASS experiments. The first one deals with the new world of
transversity, the fundamental polarized parton distribution so far totally
unknown. The second issue concerns Lambda production in polarized
semi-inclusive processes, with a measurement of the Lambda polarization, which
might give novel information on distribution and fragmentation properties of
polarized partons. In case of transverse polarization the detection of Lambda's
gives access to a new way of measuring transversities. Also the interesting
case of Lambda polarization in unpolarized processes is discussed.Comment: 9 pages, 4 figures, talk delivered at the Workshop on Future Physics
@ COMPASS, Sept. 26-27, 2002, CER
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