21 research outputs found
Measurement of single-spin azimuthal asymmetries in semi-inclusive electroproduction of pions and kaons on a longitudinally polarised deuterium target
Single-spin asymmetries have been measured for semi-inclusive
electroproduction of , , and mesons in
deep-inelastic scattering off a longitudinally polarised deuterium target. The
asymmetries appear in the distribution of the hadrons in the azimuthal angle
around the virtual photon direction, relative to the lepton scattering
plane. The corresponding analysing powers in the moment of the
cross section are for ,
for ,
for and for . The moments are
compatible with zero for all particles.Comment: Revised version shortened 9 pages, 3 tables, 7 figure
The -dependence of the generalised Gerasimov-Drell-Hearn integral for the deuteron, proton and neutron
The Gerasimov-Drell-Hearn (GDH) sum rule connects the anomalous contribution
to the magnetic moment of the target nucleus with an energy-weighted integral
of the difference of the helicity-dependent photoabsorption cross sections. The
data collected by HERMES with a deuterium target are presented together with a
re-analysis of previous measurements on the proton. This provides a measurement
of the generalised GDH integral covering simultaneously the nucleon-resonance
and the deep inelastic scattering regions. The contribution of the
nucleon-resonance region is seen to decrease rapidly with increasing . The
DIS contribution is sizeable over the full measured range, even down to the
lowest measured . As expected, at higher the data are found to be in
agreement with previous measurements of the first moment of . From data on
the deuteron and proton, the GDH integral for the neutron has been derived and
the proton--neutron difference evaluated. This difference is found to satisfy
the fundamental Bjorken sum rule at GeV.Comment: 12 pages, 10 figure
Quark fragmentation to , , , and in the nuclear environment
The influence of the nuclear medium on lepto-production of hadrons was
studied in the HERMES experiment at DESY in semi-inclusive deep-inelastic
scattering of 27.6 GeV positrons off deuterium, nitrogen and krypton targets.
The differential multiplicity for krypton relative to that of deuterium has
been measured for the first time for various identified hadrons (,
, , , , and ) as a function of the virtual
photon energy , the fraction of this energy transferred to the hadron,
and the hadron transverse momentum squared . The multiplicity ratio is
strongly reduced in the nuclear medium at low and high , with
significant differences among the various hadrons. The distribution of the
hadron transverse momentum is broadened towards high in the nuclear
medium, in a manner resembling the Cronin effect previously observed in
collisions of heavy ions and protons with nuclei.Comment: 8 pages, 5 figure
Double-spin asymmetries in the cross section of rho /sup 0/ and phi production at intermediate energies
Double-spin asymmetries in the cross section of electroproduction of rho /sup 0/ and phi mesons on the proton and deuteron are measured at the HERMES experiment. The photoabsorption asymmetry in exclusive rho /sup 0/ electroproduction on the proton exhibits a positive tendency. This is consistent with theoretical predictions that the exchange of an object with unnatural parity contributes to exclusive rho /sup 0/ electroproduction by transverse photons. The photoabsorption asymmetry on the deuteron is found to be consistent with zero. Double-spin asymmetries in rho /sup 0/ and phi meson electroproduction by quasireal photons were also found to be consistent with zero; the asymmetry in the case of the phi meson is compatible with a theoretical prediction which involves ss knockout from the nucleon