Date

Backward electroproduction of pi0 mesons on protons in the region of nucleon resonances at four momentum transfer squared Q**2 = 1.0-GeV**2.

The JLab Hall A collaboration Laveissiere, G. ; Degrande, N. ; Jaminion, S. ; et al.
Phys.Rev.C 69 (2004) 045203, 2004.
Inspire Record 625669 DOI 10.17182/hepdata.25226

Exclusive electroproduction of pi0 mesons on protons in the backward hemisphere has been studied at Q**2 = 1.0 GeV**2 by detecting protons in the forward direction in coincidence with scattered electrons from the 4 GeV electron beam in Jefferson Lab's Hall A. The data span the range of the total (gamma* p) center-of-mass energy W from the pion production threshold to W = 2.0 GeV. The differential cross sections sigma_T+epsilon*sigma_L, sigma_TL, and sigma_TT were separated from the azimuthal distribution and are presented together with the MAID and SAID parametrizations.

12 data tables match query

Cross section SIG(T) + EPSILON*SIG(L) for COS(THETA*) = -0.975.

Cross section SIG(T) + EPSILON*SIG(L) for COS(THETA*) = -0.925.

Cross section SIG(T) + EPSILON*SIG(L) for COS(THETA*) = -0.875.

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Polarization transfer in proton Compton scattering at high momentum transfer.

The Jefferson Lab Hall A collaboration Hamilton, D.J. ; Mamyan, V.H. ; Aniol, K.A. ; et al.
Phys.Rev.Lett. 94 (2005) 242001, 2005.
Inspire Record 660894 DOI 10.17182/hepdata.19389

Compton scattering from the proton was investigated at s=6.9 (GeV/c)**2 and \t=-4.0 (GeV/c)**2 via polarization transfer from circularly polarized incident photons. The longitudinal and transverse components of the recoil proton polarization were measured. The results are in excellent agreement with a prediction based on a reaction mechanism in which the photon interacts with a single quark carrying the spin of the proton and in disagreement with a prediction of pQCD based on a two-gluon exchange mechanism.

1 data table match query

Polarization transfer parameters.


Photon electroproduction from hydrogen at backward angles and momentum transfer squared of Q**2 = 1.0-GeV**2.

The JLab Hall A collaboration Laveissiere, G. ; Degrande, N. ; Jaminion, S. ; et al.
JLAB-PHY-04-34, 2004.
Inspire Record 652965 DOI 10.17182/hepdata.38623

We have made the first measurements of the virtual Compton scattering process via the e p -> e p gamma exclusive reaction at Q**2 = 1 GeV**2 in the nucleon resonance region. The cross section is obtained at center of mass (CM) backward angle, theta_gamma_gamma*, in a range of total (gamma* p) CM energy W from the proton mass up to W = 1.91 GeV. The data show resonant structures in the first and second resonance regions, and are well reproduced at higher W by the Bethe-Heitler+Born cross section, including t-channel pi0-exchange. At high W, our data, together with existing real photon data, show a striking Q**2 independence. Our measurement of the ratio of H(e,e'p)gamma to H(e,e'p)pi0 cross sections is presented and compared to model predictions.

18 data tables match query

Cross section for the reaction E P --> E P GAMMA at a polar angle given by COS(THETA) = -0.975 and azimuthal angle PHI = 15 degrees both in the centre-of-mass frame of the GAMMA* P --> GAMMA* P reaction.

Cross section for the reaction E P --> E P GAMMA at a polar angle given by COS(THETA) = -0.975 and azimuthal angle PHI = 45 degrees both in the centre-of-mass frame of the GAMMA* P --> GAMMA* P reaction.

Cross section for the reaction E P --> E P GAMMA at a polar angle given by COS(THETA) = -0.975 and azimuthal angle PHI = 75 degrees both in the centre-of-mass frame of the GAMMA* P --> GAMMA* P reaction.

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The charge form factor of the neutron from the reaction H-2(pol.)(e(pol.),e' n)p.

Passchier, I. ; Alarcon, R. ; Bauer, T.S. ; et al.
Phys.Rev.Lett. 82 (1999) 4988-4991, 1999.
Inspire Record 504073 DOI 10.17182/hepdata.31239

We report on the first measurement of spin-correlation parameters in quasifree electron scattering from vector-polarized deuterium. Polarized electrons were injected into an electron storage ring at a beam energy of 720~MeV. A Siberian snake was employed to preserve longitudinal polarization at the interaction point. Vector-polarized deuterium was produced by an atomic beam source and injected into an open-ended cylindrical cell, internal to the electron storage ring. The spin correlation parameter A^V_{ed} was measured for the reaction \pol{2H}(\pol{e},e'n)p at a four-momentum transfer squared of 0.21 (GeV/c)^2 from which a value for the charge form factor of the neutron was extracted.

1 data table match query

No description provided.


Measurement of the neutral weak form factors of the proton.

The HAPPEX collaboration Aniol, K.A. ; Armstrong, D.S. ; Baylac, M. ; et al.
Phys.Rev.Lett. 82 (1999) 1096-1100, 1999.
Inspire Record 478059 DOI 10.17182/hepdata.31319

We have measured the parity-violating electroweak asymmetry in the elastic scattering of polarized electrons from the proton. The kinematic point (theta_lab = 12.3 degrees and Q^2=0.48 (GeV/c)^2) is chosen to provide sensitivity, at a level that is of theoretical interest, to the strange electric form factor G_E^s. The result, A=-14.5 +- 2.2 ppm, is consistent with the electroweak Standard Model and no additional contributions from strange quarks. In particular, the measurement implies G_E^s + 0.39G_M^s = 0.023 +- 0.034 (stat) +- 0.022 (syst) +- 0.026 (delta G_E^n), where the last uncertainty arises from the estimated uncertainty in the neutron electric form factor.

1 data table match query

Longitudinally polarized beam. C=L and C=R means left- and right polarization. The second systematic uncertainty arises from the estimated uncertainty inthe neutron electromagnetic from factor.


Measurement of T(20) in elastic electron deuteron scattering.

Bouwhuis, M. ; Alarcon, R. ; Botto, T. ; et al.
Phys.Rev.Lett. 82 (1999) 3755-3758, 1999.
Inspire Record 477409 DOI 10.17182/hepdata.31372

We report on a measurement of the tensor-analyzing power T20 in elastic electron-deuteron scattering in the range of four-momentum transfer from 1.8 to 3.2 fm-1. Electrons of 704 MeV were scattered from a polarized deuterium internal target. The tensor polarization of the deuterium nuclei was determined with an ion-extraction system, allowing an absolute measurement of T20. The data are described well by a non-relativistic calculation that includes the effects of meson-exchange currents.

1 data table match query

No description provided.


The transverse asymmetry A(T') from quasielastic polarized He-3(pol.)(e(pol.),e') process and the neutron magnetic form factor.

Xu, W. ; Dutta, D. ; Xiong, F. ; et al.
Phys.Rev.Lett. 85 (2000) 2900-2904, 2000.
Inspire Record 531416 DOI 10.17182/hepdata.31474

We have measured the transverse asymmetry from inclusive scattering of longitudinally polarized electrons from polarized 3He nuclei at quasi-elastic kinematics in Hall A at Jefferson Lab with high statistical and systematic precision. The neutron magnetic form factor was extracted based on Faddeev calculations with an experimental uncertainty of less than 2 %.

1 data table match query

Ratio of neutron magnetic form-factor to dipole value.


Compton scattering cross section on the proton at high momentum transfer.

The Hall A collaboration Danagoulian, A. ; Mamyan, V.H. ; Roedelbronn, M. ; et al.
Phys.Rev.Lett. 98 (2007) 152001, 2007.
Inspire Record 743383 DOI 10.17182/hepdata.31472

Cross-section values for Compton scattering on the proton were measured at 25 kinematic settings over the range s = 5-11 and -t = 2-7 GeV2 with statistical accuracy of a few percent. The scaling power for the s-dependence of the cross section at fixed center of mass angle was found to be 8.0 +/ 0.2, strongly inconsistent with the prediction of perturbative QCD. The observed cross-section values are in fair agreement with the calculations using the handbag mechanism, in which the external photons couple to a single quark.

4 data tables match query

Cross section of proton Compton Scattering at centre of mass energy squared of 4.82 GeV.

Cross section of proton Compton Scattering at centre of mass energy squared of 6.79 GeV.

Cross section of proton Compton Scattering at centre of mass energy squared of 8.90 GeV.

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The Q**2-dependence of the neutron spin structure function g2(n) at low Q**2.

Kramer, K. ; Armstrong, D.S. ; Averett, T.D. ; et al.
Phys.Rev.Lett. 95 (2005) 142002, 2005.
Inspire Record 684137 DOI 10.17182/hepdata.31614

We present the first measurement of the Q^2-dependence of the neutron spin structure function g_2^n at five kinematic points covering 0.57 (GeV/c)^2 <= Q^2 <= 1.34 (GeV/c)^2 at x~0.2. Though the naive quark-parton model predicts g_2=0, non-zero values for g_2 occur in more realistic models of the nucleon which include quark-gluon correlations, finite quark masses or orbital angular momentum. When scattering from a non-interacting quark, $g_2^n$ can be predicted using next-to-leading order fits to world data for g_1^n. Deviations from this prediction provide an opportunity to examine QCD dynamics in nucleon structure. Our results show a positive deviation from this prediction at lower Q^2, indicating that contributions such as quark-gluon interactions may be important. Precision data obtained for g_1^n are consistent with next-to-leading order fits to world data.

1 data table match query

Measured values of G1N ang G2N.


Precision measurement of the neutron spin asymmetry A(1)(n) and spin-flavor decomposition in the valence quark region.

The Jefferson Lab Hall A collaboration Zheng, X. ; Aniol, K. ; Armstrong, D.S. ; et al.
Phys.Rev.Lett. 92 (2004) 012004, 2004.
Inspire Record 625890 DOI 10.17182/hepdata.31679

We have measured the neutron spin asymmetry $A_1^n$ with high precision at three kinematics in the deep inelastic region at $x=0.33$, 0.47 and 0.60, and $Q^2=2.7$, 3.5 and 4.8 (GeV/c)$^2$, respectively. Our results unambiguously show, for the first time, that $A_1^n$ crosses zero around $x=0.47$ and becomes significantly positive at $x=0.60$. Combined with the world proton data, polarized quark distributions were extracted. Our results, in general, agree with relativistic constituent quark models and with perturbative quantum chromodynamics (pQCD) analyses based on the earlier data. However they deviate from pQCD predictions based on hadron helicity conservation.

1 data table match query

Measured values of A1 and G1/F1.