Spin density matrix elements in exclusive $\omega$ electroproduction on $^1$H and $^2$H targets at 27.5 GeV beam energy

The HERMES collaboration Airapetian, A. ; Akopov, N. ; Akopov, Z. ; et al.
Eur.Phys.J.C 74 (2014) 3110, 2014.
Inspire Record 1305286 DOI 10.17182/hepdata.70751

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.

9 data tables match query

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$^2$.

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Transverse-target-spin asymmetry in exclusive $\omega$-meson electroproduction

The HERMES collaboration Airapetian, A. ; Akopov, N. ; Akopov, Z. ; et al.
Eur.Phys.J.C 75 (2015) 600, 2015.
Inspire Record 1391139 DOI 10.17182/hepdata.75465

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.

4 data tables match query

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.

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Measurement of the virtual-photon asymmetry A2 and the spin-structure function g2 of the proton

The HERMES collaboration Airapetian, A. ; Akopov, N. ; Akopov, Z. ; et al.
Eur.Phys.J.C 72 (2012) 1921, 2012.
Inspire Record 1082840 DOI 10.17182/hepdata.66230

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.

4 data tables match query

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).

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Multiplicities of charged pions and kaons from semi-inclusive deep-inelastic scattering by the proton and the deuteron

The HERMES collaboration Airapetian, A. ; Akopov, N. ; Akopov, Z. ; et al.
Phys.Rev.D 87 (2013) 074029, 2013.
Inspire Record 1208547 DOI 10.17182/hepdata.62097

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.

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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.

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Measurement of Asymmetry in Photoproduction of pi0 Meson in the Resonance Region

Avakian, R.O. ; Avakian, E.O. ; Avetisian, A.E. ; et al.
Yad.Fiz. 26 (1977) 1014-1017, 1977.
Inspire Record 126317 DOI 10.17182/hepdata.19036

None

1 data table match query

Axis error includes +- 10/10 contribution.


MEASUREMENT OF POLARIZATION OF RECOIL PROTONS IN PI0 PHOTOPRODUCTION FOR THETA* (PI0) = 60-degrees IN RESONANCE REGION. (IN RUSSIAN)

Avakian, R.O. ; Avakian, E.O. ; Avetisian, A.E. ; et al.
Sov.J.Nucl.Phys. 37 (1983) 199-201, 1983.
Inspire Record 183972 DOI 10.17182/hepdata.17739

None

1 data table match query

Axis error includes +- 0.0/0.0 contribution (?////NO DISCUSSION OF ERRORS AT ALL).


MEASUREMENT OF POLARIZATION OF PROTONS IN THE REACTION GAMMA P ---> P PI0 IN A PHOTON LINEARLY POLARIZED BEAM. (IN RUSSIAN)

Avakian, R.O. ; Avakian, E.O. ; Avetisian, A.E. ; et al.
Yad.Fiz. 36 (1982) 393-399, 1982.
Inspire Record 183654 DOI 10.17182/hepdata.17730

None

1 data table match query

Axis error includes +- 0.0/0.0 contribution (?////ERROR IN POLARIZATION OF INITIAL GAMMAS IS NOT GIVEN).


No description provided.

No description provided.

No description provided.


Asymmetry of the cross section of the reaction $\gamma$P $\rightarrow$ P$\pi^{0}$ in the energy interval 0.9-1.65 GeV at $\theta _{\pi}^{0 cms}$ = 110°

Abramyan, L.O. ; Avakyan, R.O. ; Akopov, N.Z. ; et al.
JETP Lett. 23 (1976) 375-378, 1976.
Inspire Record 1393126 DOI 10.17182/hepdata.39803

None

2 data tables match query

THE ERRORS INCLUDE THE 10 PCT ERROR IN THE EFFECTIVE PHOTON POLARIZATION.

No description provided.


Spin observables in neutron proton elastic scattering.

Ahmidouch, A. ; Arnold, J. ; van den Brandt, B. ; et al.
Eur.Phys.J.C 2 (1998) 627-641, 1998.
Inspire Record 471273 DOI 10.17182/hepdata.11376

The analyzing power,$A_{oono}$, and the polarization transfer observables$K_{onno}$,$K_{os''so}$

20 data tables match query

Position 'A' (see text for explanation).

Position 'A' (see text for explanation).

Position 'A' (see text for explanation).

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