82 research outputs found
Double polarization asymmetry as a possible filter for 's parity
We present an analysis of the Beam-Target double polarization asymmetry for
the photoproduction of in . We show that
this quantity can serve as a filter for the determination of the 's
spin-parity assignment near threshold. It is highly selective between
and configurations due to dynamical reasons.Comment: Proofread versio
Polarization observables of the gamma d --> PiNN reaction in the Delta(1232)-resonance region
Polarization observables of the three charge states of the pion for the
reaction with polarized photon beam and/or oriented
deuteron target are evaluated over the whole (1232)-resonance region
adopting a nonrelativistic model based on time-ordered perturbation theory.
Results for the -meson spectra, linear photon asymmetry, vector and tensor
target asymmetries are presented. Particular attention is given, for the first
time, to double polarization asymmetries for which we present results for
and . We found that all other double
polarization asymmetries of photon and deuteron target are vanished.Comment: 17 Pages, 8 Figures, accepted for publication in Int. J. Mod. Phys.
Role of nucleon resonance excitation in meson photoproduction
The resonance effects are investigated in the meson photoproduction
near threshold through a quark model approach with an effective Lagrangian. The
diffractive contribution is consistently estimated by the {\it t}-channel
Pomeron exchange. Another non-diffractive process, {\it t}-channel
exchange is also included. The numerical result shows that the Pomeron exchange
plays dominant role in the meson photoproduction, while the cross
sections of the non-diffractive processes, i.e. {\it s}- and {\it u}-channel
excitations, and {\it t}-channel exchange, are quite small. In the
polarization observables, we find that large asymmetries are produced in the
backward direction by the interferences from the {\it s}- and {\it u}-channel
resonances, while in the forward direction, only very small asymmetries are
generated. Meanwhile, we find that the effects from the exchange are
generally negligible.Comment: Contribution to "2nd International Conference on Perspectives in
Hadronic Physics", Trieste, ICTP, 10-14 May 1999, to appear in Few-body
Syste
Asymmetry in omega meson photoproduction and the phase of omega-pi-gamma coupling
We analyze the double polarization asymmetry of the omega-meson
photoproduction in the vector-meson-dominance model of diffractive production
and the one-pion exchange model. We find that the longitudinal beam-target
asymmetry is very sensitive to the real part of the diffractive photoproduction
amplitude and to the sign of the omega-pi-gamma coupling because of the
different spin structures of the amplitudes associated with the different
mechanisms.Comment: 9 pages, LaTeX with elsart.sty, uses epsfig.sty, amsbsy.sty and
amssymb.sty, 3 figures (5 eps files
Sneutrino Identification in Lepton Pair Production at ILC with Polarized Beams
Numerous non-standard dynamics are described by contact-like effective
interactions that can manifest themselves in electron-positron collisions only
through deviations of the observables (cross sections, asymmetries) from the
Standard Model predictions. If such a deviation were observed, it would be
important to identify the actual source among the possible non-standard
interactions as many different new physics scenarios may lead to very similar
experimental signatures. We study the possibility of uniquely identifying the
indirect effects of s-channel sneutrino exchange, as predicted by
supersymmetric theories with R-parity violation, against other new physics
scenarios in high-energy e^+e^- annihilation into lepton pairs at the
International Linear Collider. These competitive models are interactions based
on gravity in large and in TeV-scale extra dimensions, anomalous gauge
couplings, Z' vector bosons and compositeness-inspired four-fermion contact
interactions. To evaluate the identification reach on sneutrino exchange, we
use as basic observable a double polarization asymmetry, that is particularly
suitable to directly test for such s-channel sneutrino exchange effects in the
data analysis. The availability of both beams being polarized plays a crucial
role in identifying the new physics scenario.Comment: 10 pages, 3 figure
Spin observables for pion photoproduction on the deuteron in the (1232)-resonance region
Spin observables for the three charge states of the pion for the pion
photoproduction reaction on the deuteron, , with polarized
photon beam and/or oriented deuteron target are predicted. For the beam-target
double-spin asymmetries, it is found that only the longitudinal asymmetries
and do not vanish, whereas all the circular
and the other longitudinal asymmetries do vanish. The sensitivity of spin
observables to the model deuteron wave function is investigated. It has been
found that only and are sensitive to the model deuteron wave
function, in particular in the case of -production above the
-region, and that other asymmetries are not.Comment: 16 pages, 8 figures, accepted for publication in J. Phys. G: Nucl.
Part. Phy
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