Avakian, R.O.
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Photoproduction of Phi(1020) mesons on the proton at large momentum transfer.

The CLAS collaboration Anciant, E. ; Auger, T. ; Audit, G. ; et al.
Phys.Rev.Lett. 85 (2000) 4682-4686, 2000.
Inspire Record 528835 DOI 10.17182/hepdata.19491

The cross section for $\phi$ meson photoproduction on the proton has been measured for the first time up to a four-momentum transfer -t = 4 GeV^2, using the CLAS detector at the Thomas Jefferson National Accelerator Facility. At low four-momentum transfer, the differential cross section is well described by Pomeron exchange. At large four-momentum transfer, above -t = 1.8 GeV^2, the data support a model where the Pomeron is resolved into its simplest component, two gluons, which may couple to any quark in the proton and in the $\phi$.

1 data table
Table 1

The differential PHI photoproduction cross section. The errors shown are the quadratic sum of the statistics and the systematic uncertainties which include 3 PCT for normalization, 5 PCT for acceptance and 5-15 PCT for background subtraction.


Exclusive leptoproduction of rho0 mesons from hydrogen at intermediate virtual photon energies.

The HERMES collaboration Airapetian, A. ; Akopov, N. ; Akushevich, I. ; et al.
Eur.Phys.J.C 17 (2000) 389-398, 2000.
Inspire Record 526550 DOI 10.17182/hepdata.47010

Measurements of the cross section for exclusive virtual-photoproduction of rho^0 mesons from hydrogen are reported. The data were collected by the HERMES experiment using 27.5 GeV positrons incident on a hydrogen gas target in the HERA storage ring. The invariant mass W of the photon-nucleon system ranges from 4.0 to 6.0 GeV, while the negative squared four-momentum Q^2 of the virtual photon varies from 0.7 to 5.0 GeV^2. The present data together with most of the previous data at W > 4 GeV are well described by a model that infers the W-dependence of the cross section from the dependence on the Bjorken scaling variable x of the unpolarized structure function for deep-inelastic scattering. In addition, a model calculation based on Off-Forward Parton Distributions gives a fairly good account of the longitudinal component of the rho^0 production cross section for Q^2 > 2 GeV^2.

2 data tables
Table 1

Cross sections are corrected for radiative effects (which typically amount s to 18 PCT).

Table 2

Longitudinal cross sections. The listed uncertainties include both the total error on the measured RHO0 photoproduction cross sections and the error on theparametrization of R for W<7 GeV.


Measurement of the spin asymmetry in the photoproduction of pairs of high p(T) hadrons at HERMES.

The HERMES collaboration Airapetian, A. ; Akopov, N. ; Amarian, M. ; et al.
Phys.Rev.Lett. 84 (2000) 2584-2588, 2000.
Inspire Record 503784 DOI 10.17182/hepdata.43919

We present a measurement of the longitudinal spin asymmetry A_|| in photoproduction of pairs of hadrons with high transverse momentum p_T. Data were accumulated by the HERMES experiment using a 27.5 GeV polarized positron beam and a polarized hydrogen target internal to the HERA storage ring. For h+h- pairs with p_T^h_1 > 1.5 GeV/c and p_T^h_2 > 1.0 GeV/c, the measured asymmetry is A_|| = -0.28 +/- 0.12 (stat.) +/- 0.02 (syst.). This negative value is in contrast to the positive asymmetries typically measured in deep inelastic scattering from protons, and is interpreted to arise from a positive gluon polarization.

1 data table
Table 1

Asymmetry measurement with a PT cut of 1.5 GeV on the hadron with the higher PT, and 1.0 GeV on the hadron with the lower PT.


Measurement of the neutron electric form factor G(E,n) in the quasifree H-2(e(pol.),e' n(pol.))p reaction.

Ostrick, M. ; Herberg, C. ; Andresen, H.G. ; et al.
Phys.Rev.Lett. 83 (1999) 276-279, 1999.
Inspire Record 506748 DOI 10.17182/hepdata.19444

The electric form factor of the neutron GE,n has been measured in the quasifree 2H(e→,e′n→)p reaction using the 855 MeV polarized cw electron beam of the Mainz Microtron MAMI. The polarization of the scattered neutrons was analyzed in a polarimeter consisting of two walls of plastic scintillators. The precession of the neutron spin in a magnetic field was used for the first time to circumvent the measurement of the effective analyzing power of the polarimeter and the beam polarization. In this way GE,n could be determined with little model dependence and experimental uncertainties. The result GE,n(0.34GeV2/c2)=0.0611±0.0069stat({+0.0069}{−0.0055})syst is larger than previously assumed.

1 data table
Table 1

No description provided.


Near threshold photoproduction of eta mesons from He-4.

Hejny, V. ; Achenbach, P. ; Ahrens, J. ; et al.
Eur.Phys.J.A 6 (1999) 83-89, 1999.
Inspire Record 509583 DOI 10.17182/hepdata.43494

None

1 data table
Table 1

SIG(Q=N) and SIG(Q=P) ratio is extracted from the data of scattering on HE4.


Determination of the deep inelastic contribution to the generalised Gerasimov-Drell-Hearn integral for the proton and neutron.

The HERMES collaboration Ackerstaff, K. ; Airapetian, A. ; Akopov, N. ; et al.
Phys.Lett.B 444 (1998) 531-538, 1998.
Inspire Record 476388 DOI 10.17182/hepdata.44128

The virtual photon absorption cross section differences [sigma_1/2-sigma_3/2] for the proton and neutron have been determined from measurements of polarised cross section asymmetries in deep inelastic scattering of 27.5 GeV longitudinally polarised positrons from polarised 1H and 3He internal gas targets. The data were collected in the region above the nucleon resonances in the kinematic range nu < 23.5 GeV and 0.8 GeV**2 < Q**2 < 12 GeV**2. For the proton the contribution to the generalised Gerasimov-Drell-Hearn integral was found to be substantial and must be included for an accurate determination of the full integral. Furthermore the data are consistent with a QCD next-to-leading order fit based on previous deep inelastic scattering data. Therefore higher twist effects do not appear significant.

13 data tables
Table 1

Gerasimov-Drell-Hearn sum rule for proton as a function of Q2.

Table 2

Gerasimov-Drell-Hearn sum rule for neutron as a function of Q2 (integral spans from Q2/2M to infinity instead of zero to infinity, see paper).

Table 3

Cross section difference for the proton data. Statistical errors only.

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Measurement of the proton spin structure function g1(p) with a pure hydrogen target.

The HERMES collaboration Airapetian, A. ; Akopov, N. ; Akushevich, I. ; et al.
Phys.Lett.B 442 (1998) 484-492, 1998.
Inspire Record 473421 DOI 10.17182/hepdata.44220

A measurement of the proton spin structure function g1p(x,Q^2) in deep-inelastic scattering is presented. The data were taken with the 27.6 GeV longitudinally polarised positron beam at HERA incident on a longitudinally polarised pure hydrogen gas target internal to the storage ring. The kinematic range is 0.021<x<0.85 and 0.8 GeV^2<Q^2<20 GeV^2. The integral Int_{0.021}^{0.85} g1p(x)dx evaluated at Q0^2 of 2.5 GeV^2 is 0.122+/-0.003(stat.)+/-0.010(syst.).

2 data tables
Table 1

The second systematic errors listed for G1/F1 (G1) are the uncertainties concerning R (R and F2).

Table 2

G1 evolved at Q2 = 2.5 GeV**2, assuming G1/F1 to be independent of Q2. The second systematic errors listed for are the uncertainties concerning R and F2.


The flavor asymmetry of the light quark sea from semi-inclusive deep inelastic scattering.

The HERMES collaboration Ackerstaff, K. ; Airapetian, A. ; Akopov, N. ; et al.
Phys.Rev.Lett. 81 (1998) 5519-5523, 1998.
Inspire Record 473345 DOI 10.17182/hepdata.44248

The flavor asymmetry of the light quark sea of the nucleon is determined in the kinematic range 0.02<x<0.3 and 1 GeV^2<Q^2<10 GeV^2, for the first time from semi-inclusive deep-inelastic scattering. The quantity (dbar(x)-ubar(x))/(u(x)-d(x)) is derived from a relationship between the yields of positive and negative pions from unpolarized hydrogen and deuterium targets. The flavor asymmetry dbar-ubar is found to be non-zero and x dependent, showing an excess of dbar over ubar quarks in the proton.

1 data table
Table 1

The ratio of parton distribution functions (PDF) is determined from the ratio of the differencies between charged pion yields for proton and neutron targets: (N_p(pi-)-N_n(pi-))/(N_p(pi+)-N_n(pi+)).


Production of D*(2010)+ mesons by high energy neutrinos from the Tevatron.

The E632 collaboration Asratian, A.E. ; Aderholz, M. ; Ammosov, V.V. ; et al.
Z.Phys.C 76 (1997) 647-652, 1997.
Inspire Record 447761 DOI 10.17182/hepdata.47482

Charged vector D*+(2010) meson production is studied in a high energy neutrino bubble chamber experiment with mean neutrino energy of 141 GeV. The D*+ are produced in (5.6±1.8)% of the neutrino charged current interactions, indicating a steep increase of cross section with energy. The mean fractional hadronic energy of the D*+ meson is 0.55 ± 0.06.

1 data table
Table 1

No description provided.


Measurement of the neutron spin structure function g1(n) with a polarized He-3 internal target.

The HERMES collaboration Ackerstaff, K. ; Airapetian, A. ; Akushevich, I. ; et al.
Phys.Lett.B 404 (1997) 383-389, 1997.
Inspire Record 440904 DOI 10.17182/hepdata.44586

Results are reported from the HERMES experiment at HERA on a measurement of the neutron spin structure function $g_1~n(x,Q~2)$ in deep inelastic scattering using 27.5 GeV longitudinally polarized positrons incident on a polarized $~3$He internal gas target. The data cover the kinematic range $0.023<x<0.6$ and $1 (GeV/c)~2 < Q~2 <15 (GeV/c)~2$. The integral $\int_{0.023}~{0.6} g_1~n(x) dx$ evaluated at a fixed $Q~2$ of $2.5 (GeV/c)~2$ is $-0.034\pm 0.013(stat.)\pm 0.005(syst.)$. Assuming Regge behavior at low $x$, the first moment $\Gamma_1~n=\int_0~1 g_1~n(x) dx$ is $-0.037\pm 0.013(stat.)\pm 0.005(syst.)\pm 0.006(extrapol.)$.

2 data tables
Table 1

No description provided.

Table 2

Data extrapolated to full x region. Second systematic error is the error on this extrapolation.