986 research outputs found

### Off-diagonal helicity density matrix elements for heavy vector mesons inclusively produced in N-N, gamma-N, l-N interactions

Final state interactions in quark fragmentation may give origin to non zero
values of the off-diagonal element rho_(1,-1) of the helicity density matrix of
vector mesons V produced in current jets, with a large energy fraction x_E; the
value of rho_(1,-1)(V) is related to the hard constituent dynamics and tests
unusual properties of it. Some recent data on phi, K^* and D^* produced in e^+
e^- annihilations at LEP show such effects. Predictions are given here for
rho_(1,-1) of heavy mesons produced in nucleon-nucleon, gamma-nucleon and
lepton-nucleon interactions.Comment: LaTeX, 10 pages, 1 postscript figure, uses epsfig.sty. Revised
version, to be published on Phys. Lett. B. Some statements added to clarify
tex

### An Interesting Charmonium State Formation and Decay : $p \bar p \to ^1D_2 \to ^1P_1 \gamma$

Massless perturbative QCD forbids, at leading order, the exclusive
annihilation of proton-antiproton into some charmonium states, which, however,
have been observed in the $p\bar p$ channel, indicating the significance of
higher order and non perturbative effects in the few GeV energy region. The
most well known cases are those of the $^1S_0$ ($\eta_c$) and the $^1P_1$. The
case of the $^1D_2$ is considered here and a way of detecting such a state
through its typical angular distribution in the radiative decay $^1D_2 \to$
$^1P_1 \gamma$ is suggested. Estimates of the branching ratio $BR(^1D_2 \to
p\bar p)$, as given by a quark-diquark model of the nucleon, mass corrections
and an instanton induced process are presented.Comment: 9 pages (no figures), Plain TeX, CBPF-NF-014/94, INFNCA-TH-94-

### A strategy towards the extraction of the Sivers function with TMD evolution

The QCD evolution of the unpolarized Transverse Momentum Dependent (TMD)
distribution functions and of the Sivers functions have been discussed in
recent papers. Following such results we reconsider previous extractions of the
Sivers functions from semi-inclusive deep inelastic scattering data and propose
a simple strategy which allows to take into account the Q^2 dependence of the
TMDs in comparison with experimental findings. A clear evidence of the
phenomenological success of the TMD evolution equations is given, mostly, by
the newest COMPASS data off a transversely polarized proton target.Comment: 15 pages, 7 figures, 2 table

### $^1P_1$ charmonium state decay into $p \bar p$ in QCD models including constituent quark mass corrections

Stimulated by the experimental observation, made by the E760 Collaboration at
Fermilab, of the $^1\!P_1$ state of charmonium resonantly formed in $p\,\bar p$
annihilation, we perform a calculation of the decay width for the $^1\!P_1\to
p\,\bar p$ process. To this end, we employ a phenomenological model which adds
constituent quark mass corrections to the usual massless QCD models for
exclusive processes. For massless models, in fact, the process under
consideration is forbidden by the so-called helicity selection rules, while it
is allowed in our extended model. We find $\Gamma(^1\!P_1\to p\,\bar p)$ to be
in the range $1-10$ eV. We also compare our results with previous, indirect
estimates, based on QCD multipole expansion models.Comment: 17 pages, REVTeX 3.0, 1 postscript figure included. Revised version,
to be published in Physical Review D. Brief discussion of the role of other
nonperturbative effects and three references added in the introduction;
Comparison with QCD multipole expansion model slightly reformulated; Some
sentences added in the conclusions; Results unchange

### New proton polarized structure functions in charged current processes at HERA

Estimates for longitudinal spin asymmetries which single out new polarized
nucleon structure functions in deeply inelastic charged current interactions at
HERA energies are given, exploiting their interpretation in terms of polarized
quark distributions. These asymmetries turn out to be large and allow a
measurement of the new polarized structure functions $g_1^{W}$ and $g_5^{W}$,
which would add valuable tests and information on the spin content of quarks
inside a polarized proton. We also show that single spin asymmetries in neutral
current interactions are very small.Comment: LaTeX, 8 pages, 6 figure

### Single transverse spin asymmetries in inclusive hadron production

A consistent phenomenological approach to the computation of transverse
single spin asymmetries in inclusive hadron production is presented, based on
the assumed generalization of the QCD factorization theorem to the case in
which quark intrinsic motion is taken into account. New k_T and spin dependent
quark distribution and fragmentation functions are considered: some of them are
fixed by fitting data on p(transv. polarized) + p -> pion + X and predictions
are given for single spin asymmetries in l + p(transv. polarized) -> pion + X
and gamma^* + p(transv. polarized) -> pion + X processes.Comment: LaTeX, 3 pages, 2 eps figures, uses epsfig.sty, fleqn.sty, npb.sty.
Talk delivered by M. Anselmino at the 7th International Workshop on Deep
Inelastic Scattering and QCD (DIS99), Zeuthen, April 1999, to appear in Nucl.
Phys. B (Proc. Suppl.

### Phenomenology of Sivers Effect with TMD Evolution

Following the TMD evolution scheme recently proposed for the unpolarized and
the Sivers distribution function, we propose a simple strategy to take into
account this TMD Q^2 dependence in our phenomenological extraction of the
Sivers function from SIDIS data. New results are presented and possible future
applications are discussed.Comment: Contribution to the Proceedings of the XX International Workshop on
Deep-Inelastic Scattering and related subjects (DIS2012), 26-30 March 2012,
Bonn, Germany. One figure correcte

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