9 research outputs found
Spin dependent structure function at small and small
Theoretical expectations concerning the low and low behaviour of
are summarized and compared with the recent SMC data.Comment: 4 pages, plain LATEX, 1 eps figure; contribution to 3rd UK
Phenomenology Workshop on HERA Physics, St. John's College, Durham, UK,
September 199
Regge description of spin-spin asymmetry in photon diffractive dissociation
We explore the possibility whether the gluon helicity distribution can be extracted from a comparison of experimental data on the
longitudinal spin-spin asymmetry in diffractive deep
inelastic scattering with calculations performed within the framework of
perturbative QCD (pQCD). The data could be obtained at the future HERA collider
in scattering of polarized electrons/positrons off polarized protons. In this
paper we look for such kinematical regions where contributions to from
soft processes (reggeon exchanges) are suppressed to guarantee an applicability
of pQCD. It is shown that for the square of the center-of-mass energy
, the hadronic diffractive mass , the momentum transferred to the proton , and
the longitudinal spin-spin asymmetry due to reggeon
exchanges is less than 10^{-4}. This value is presumably lower than the
asymmetry which can be measured with modern experimental technique. This means
that the pQCD prediction can be reliably compared with data in this kinematical
region.Comment: 44 pages, LaTeX, 12 figure
Spin density matrix elements in exclusive electroproduction on and targets at 27.5 GeV beam energy
Spin Density Matrix Elements (SDMEs) describing the angular distribution of
exclusive rho^0 electroproduction and decay are determined in the HERMES
experiment with 27.6 GeV beam energy and unpolarized hydrogen and deuterium
targets. Eight (fifteen) SDMEs that are related (unrelated) to the longitudinal
polarization of the beam are extracted in the kinematic region 1 GeV^2 < Q^2 <
7 GeV^2, 3.0 GeV < W < 6.3 GeV, and -t < 0.4 GeV^2. Within the given
experimental uncertainties, a hierarchy of relative sizes of helicity
amplitudes is observed. Kinematic dependences of all SDMEs on Q^2 and t are
presented, as well as the longitudinal-to-transverse rho^0 electroproduction
cross section ratio as a function of Q^2. A small but statistically significant
deviation from the hypothesis of s-channel helicity conservation is observed.
An indication is seen of a contribution of unnatural-parity-exchange
amplitudes; these amplitudes are naturally generated with a quark-exchange
mechanism.Comment: 41 pages, 20 figures, 16 table; revised version corrects small typos,
text clarified on 6 pages, two references added and new data added to figure
2