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Hard exclusive electroproduction of $\omega$ mesons is studied with the HERMES spectrometer at the DESY laboratory by scattering 27.6 GeV positron and electron beams off a transversely polarized hydrogen target. The amplitudes of five azimuthal modulations of the single-spin asymmetry of the cross section with respect to the transverse proton polarization are measured. They are determined in the entire kinematic region as well as for two bins in photon virtuality and momentum transfer to the nucleon. Also, a separation of asymmetry amplitudes into longitudinal and transverse components is done. These results are compared to a phenomenological model that includes the pion pole contribution. Within this model, the data favor a positive $\pi\omega$ transition form factor.
The amplitudes of the five sine and two cosine modulations as determined in the entire kinematic region. The results receive an additional 8.2% scale uncertainty corresponding to the target-polarization uncertainty.
The definition of intervals and the mean values of the kinematic variables.
Results on the kinematic dependences of the five asymmetry amplitudes $A_{UT}$ and two amplitudes $A_{UU}$. The first two columns correspond to the $-t'$ intervals $0.00 - 0.07 - 0.20$ GeV$^2$ and the last two columns to the $Q^{2}$ intervals $1.00 - 1.85 - 10.00$ GeV$^2$. The results receive an additional 8.2% scale uncertainty corresponding to the target-polarization uncertainty.
The spin-spin correlation parameter C NN at 50° and 90° c.m. for elastic pp-scattering has been obtained in the energy range 0.69–0.95 GeV. It was found that the parameter C NN (90°) shows resonance-like structure at energies near 700 MeV. Its energy dependence does not agree with Hoshizaki's phase-shift analysis predictions. C NN (50°) agrees well with these predictions and does not show any structure within the accuracy of the measurements.
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The differential cross sections for they+ p-- n + 7T+ process were measured for y-quantum energies 200, 205 and 210 MeV and meson emission angles 16, 24, 36, 44, 56, 64, 76, 84, 96, 104, 116, 124, 136, 144 and 156° relative to the photon beam in the laboratory system. A phenomenological analysis of the results is carried out and some multipole charged-meson photoproduction amplitudes are determined. The results are compared with the predictions of the dispersion-relation theory.
Axis error includes +- 4.8/4.8 contribution.
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Exclusive electroproduction of $\omega$ mesons on unpolarized hydrogen and deuterium targets is studied in the kinematic region of Q$^2$>1.0 GeV$^2$, 3.0 GeV < W < 6.3 GeV, and -t'< 0.2 GeV$^2$. Results on the angular distribution of the $\omega$ meson, including its decay products, are presented. The data were accumulated with the HERMES forward spectrometer during the 1996-2007 running period using the 27.6 GeV longitudinally polarized electron or positron beam of HERA. The determination of the virtual-photon longitudinal-to-transverse cross-section ratio reveals that a considerable part of the cross section arises from transversely polarized photons. Spin density matrix elements are presented in projections of Q$^2$ or -t'. Violation of s-channel helicity conservation is observed for some of these elements. A sizable contribution from unnatural-parity-exchange amplitudes is found and the phase shift between those amplitudes that describe transverse $\omega$ production by longitudinal and transverse virtual photons, $\gamma^{*}_{L} \to \omega_{T}$ and $\gamma^{*}_{T} \to \omega_{T}$, is determined for the first time. A hierarchy of helicity amplitudes is established, which mainly means that the unnatural-parity-exchange amplitude describing the $\gamma^*_T \to \omega_T$ transition dominates over the two natural-parity-exchange amplitudes describing the $\gamma^*_L \to \omega_L$ and $\gamma^*_T \to \omega_T$ transitions, with the latter two being of similar magnitude. Good agreement is found between the HERMES proton data and results of a pQCD-inspired phenomenological model that includes pion-pole contributions, which are of unnatural parity.
The 23 unpolarized and polarized $\omega$ SDMEs from the proton and deuteron data.
The 23 unpolarized and polarized $\omega$ SDMEs for the proton data in $Q^2$ intervals: $1.00 - 1.57 - 2.55 - 10.00$ GeV$^2$.
The 23 unpolarized and polarized $\omega$ SDMEs for the proton data in $-t'$ intervals: $0.000 - 0.044 - 0.105 - 0.200$ GeV$^2$.
Multiplicities in semi-inclusive deep-inelastic scattering are presented for each charge state of \pi^\pm and K^\pm mesons. The data were collected by the HERMES experiment at the HERA storage ring using 27.6 GeV electron and positron beams incident on a hydrogen or deuterium gas target. The results are presented as a function of the kinematic quantities x_B, Q^2, z, and P_h\perp. They represent a unique data set for identified hadrons that will significantly enhance our understanding of the fragmentation of quarks into final-state hadrons in deep-inelastic scattering.
pi+ multiplicities from HERMES, Target: H, Target: D, VM subtracted.
pi- multiplicities from HERMES, Target: H, Target: D, VM subtracted.
K+ multiplicities from HERMES, Target: H, Target: D, VM subtracted.
A measurement of the virtual-photon asymmetry A_2(x,Q^2) and of the spin-structure function g_2(x,Q^2) of the proton are presented for the kinematic range 0.004 < x < 0.9 and 0.18 GeV^2 < Q^2 < 20 GeV^2. The data were collected by the HERMES experiment at the HERA storage ring at DESY while studying inclusive deep-inelastic scattering of 27.6 GeV longitudinally polarized leptons off a transversely polarized hydrogen gas target. The results are consistent with previous experimental data from CERN and SLAC. For the x-range covered, the measured integral of g_2(x) converges to the null result of the Burkhardt-Cottingham sum rule. The x^2 moment of the twist-3 contribution to g_2(x) is found to be compatible with zero.
The spin-structure function $xg_2(x,Q^2)$ and virtual-photon asymmetry $A_2(x,Q^2)$ of the proton in bins of $(x,Q^2)$, see text for details. Statistical and systematic uncertainties are presented separately.
The spin-structure function $xg_2$ and the virtual-photon asymmetry $A_2$ of the proton after evolving to common $Q^2$ and averaging over in each $x$-bin (see text for details). Statistical and systematic uncertainties are presented separately.
Correlation matrix for $xg_2$ in 9 $x$-bins (as in Table 2).
Inelastic interactions of nuclei accelerated to a momentum of 4.5 GeV/$c$ per projectile nucleon with photoemulsion nuclei have been investigated. The main features of these interactions - mean ranges of $^6$Li nuclei, mean multiplicities of secondaries, the isotopic composition of fragments, fragmentation channels, and the mean transverse momenta of projectile fragments - have been measured. The probability of the charge-exchange reaction featuring lithium nuclei has been determined. The results obtained for the $^6$Li nucleus have been compared with data for other nuclei. The observed features of $^6$Li interactions with other nuclei indicate that the $^6$Li structure in the form of the loosely bound system consisting of an $\alpha$-particle and a deuteron cluster clearly manifests itself in these interactions. Events resulting in the coherent dissociation of $^6$Li nuclei into $^4$He+$d$, $^3$He+$t$, and $t+d+p$ and involving low-lying excitations of $^6$Li have been observed.
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