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

Measured values of G1N ang G2N.


Precision measurement of the neutron spin asymmetries and spin-dependent structure functions in the valence quark region.

The Jefferson Lab Hall A collaboration Zheng, X. ; Aniol, K. ; Armstrong, D.S. ; et al.
Phys.Rev.C 70 (2004) 065207, 2004.
Inspire Record 650244 DOI 10.17182/hepdata.31726

We report on measurements of the neutron spin asymmetries $A_{1,2}^n$ and polarized structure functions $g_{1,2}^n$ at three kinematics in the deep inelastic region, with $x=0.33$, 0.47 and 0.60 and $Q^2=2.7$, 3.5 and 4.8 (GeV/c)$^2$, respectively. These measurements were performed using a 5.7 GeV longitudinally-polarized electron beam and a polarized $^3$He target. The results for $A_1^n$ and $g_1^n$ at $x=0.33$ are consistent with previous world data and, at the two higher $x$ points, have improved the precision of the world data by about an order of magnitude. The new $A_1^n$ data show a zero crossing around $x=0.47$ and the value at $x=0.60$ is significantly positive. These results agree with a next-to-leading order QCD analysis of previous world data. The trend of data at high $x$ agrees with constituent quark model predictions but disagrees with that from leading-order perturbative QCD (pQCD) assuming hadron helicity conservation. Results for $A_2^n$ and $g_2^n$ have a precision comparable to the best world data in this kinematic region. Combined with previous world data, the moment $d_2^n$ was evaluated and the new result has improved the precision of this quantity by about a factor of two. When combined with the world proton data, polarized quark distribution functions were extracted from the new $g_1^n/F_1^n$ values based on the quark parton model. While results for $\Delta u/u$ agree well with predictions from various models, results for $\Delta d/d$ disagree with the leading-order pQCD prediction when hadron helicity conservation is imposed.

6 data tables

Measurements of the HE3 asymmetries.

Measurements of the HE3 spin structure functions.

Measurements of the HE3 spin structure functions.

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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

Measured values of A1 and G1/F1.


Measurement of the neutron spin structure function g2(n) and asymmetry A2(n).

The E154 collaboration Abe, K. ; Akagi, T. ; Anderson, B.D. ; et al.
Phys.Lett.B 404 (1997) 377-382, 1997.
Inspire Record 443408 DOI 10.17182/hepdata.27082

We have measured the neutron structure function g$_{2}^{n}$ and the virtual photon-nucleon asymmetry A$_{2}^{n}$ over the kinematic range $0.014\leq x \leq 0.7$ and $1.0 \leq Q^{2} \leq 17.0$ by scattering 48.3 GeV longitudinally polarized electrons from polarized $^{3}$He. Results for A$_{2}^{n}$ are significantly smaller than the $\sqrt{R}$ positivity limit over most of the measured range and data for g$_2^{n}$ are generally consistent with the twist-2 Wandzura-Wilczek prediction. Using our measured g$_{2}^{n}$ we obtain results for the twist-3 reduced matrix element $d_{2}^{n}$, and the integral $\int$g$_{2}^{n}(x)dx$ in the range $0.014\leq x \leq 1.0$. Data from this experiment are combined with existing data for g$_{2}^{n}$ to obtain an average for $d_{2}^{n}$ and the integral $\int$g$_{2}^{n}(x)dx$.

4 data tables

Data measured using the 2.75 degree spectrometer.

Data measured using the 5.5 degree spectrometer.

Measured value of the twist-3 reduced matrix element D2.

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Next-to-leading order QCD analysis of polarized deep inelastic scattering data.

The E154 collaboration Abe, K. ; Akagi, T. ; Anderson, B.D. ; et al.
Phys.Lett.B 405 (1997) 180-190, 1997.
Inspire Record 443186 DOI 10.17182/hepdata.27078

We present a Next-to-Leading order perturbative QCD analysis of world data on the spin dependent structure functions $g_1^p, g_1^n$, and $g_1^d$, including the new experimental information on the $Q^2$ dependence of $g_1^n$. Careful attention is paid to the experimental and theoretical uncertainties. The data constrain the first moments of the polarized valence quark distributions, but only qualitatively constrain the polarized sea quark and gluon distributions. The NLO results are used to determine the $Q^2$ dependence of the ratio $g_1/F_1$ and evolve the experimental data to a constant $Q^2 = 5 GeV^2$. We determine the first moments of the polarized structure functions of the proton and neutron and find agreement with the Bjorken sum rule.

7 data tables

Data from the 2.75 degree spectrometer.

Data from the 2.75 degree spectrometer evolved to a mean Q**2 of 5 GeV**2 using the MSBAR parameterization. The second systematic error is due to the evolution.

Data from the 5.5 degree spectrometer.

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Precision determination of the neutron spin structure function g1(n).

The E154 collaboration Abe, K. ; Akagi, T. ; Anderson, B.D. ; et al.
Phys.Rev.Lett. 79 (1997) 26-30, 1997.
Inspire Record 443170 DOI 10.17182/hepdata.19559

We report on a precision measurement of the neutron spin structure function $g^n_1$ using deep inelastic scattering of polarized electrons by polarized ^3He. For the kinematic range 0.014&lt;x&lt;0.7 and 1 (GeV/c)^2&lt; Q^2&lt; 17 (GeV/c)^2, we obtain $\int^{0.7}_{0.014} g^n_1(x)dx = -0.036 \pm 0.004 (stat) \pm 0.005 (syst)$ at an average $Q^2=5 (GeV/c)^2$. We find relatively large negative values for $g^n_1$ at low $x$. The results call into question the usual Regge theory method for extrapolating to x=0 to find the full neutron integral $\int^1_0 g^n_1(x)dx$, needed for testing quark-parton model and QCD sum rules.

3 data tables

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Deep Inelastic Scattering of Polarized Electrons by Polarized $^3$He and the Study of the Neutron Spin Structure

The E142 collaboration Anthony, P.L. ; Arnold, R.G. ; Band, H.R. ; et al.
Phys.Rev.D 54 (1996) 6620-6650, 1996.
Inspire Record 424108 DOI 10.17182/hepdata.22340

The neutron longitudinal and transverse asymmetries $A^n_1$ and $A^n_2$ have been extracted from deep inelastic scattering of polarized electrons by a polarized $^3$He target at incident energies of 19.42, 22.66 and 25.51 GeV. The measurement allows for the determination of the neutron spin structure functions $g^n_1 (x,Q^2)$ and $g^n_2(x,Q^2)$ over the range $0.03 < x < 0.6$ at an average $Q^2$ of 2 (GeV$/c)^2$. The data are used for the evaluation of the Ellis-Jaffe and Bjorken sum rules. The neutron spin structure function $g^n_1 (x,Q^2)$ is small and negative within the range of our measurement, yielding an integral ${\int_{0.03}^{0.6} g_1^n(x) dx}= -0.028 \pm 0.006 (stat) \pm 0.006 (syst) $. Assuming Regge behavior at low $x$, we extract $\Gamma_1^n=\int^1_0 g^n_1(x)dx = -0.031 \pm 0.006 (stat)\pm 0.009 (syst) $. Combined with previous proton integral results from SLAC experiment E143, we find $\Gamma_1^p - \Gamma_1^n = 0.160 \pm 0.015$ in agreement with the Bjorken sum rule prediction $\Gamma^p_1 - \Gamma ^n_1 = 0.176 \pm 0.008$ at a $Q^2$ value of 3 (GeV$/c)^2$ evaluated using $\alpha_s = 0.32\pm 0.05$.

12 data tables

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Transverse longitudinal asymmetry in the quasielastic He-3 ---> e ---> e-prime) reaction

Hansen, J.O. ; Titko, M.A. ; DeSchepper, D. ; et al.
Phys.Rev.Lett. 74 (1995) 654-657, 1995.
Inspire Record 386633 DOI 10.17182/hepdata.19655

The transverse-longitudinal asymmetry ATL′ in He→3(e→, e′) quasielastic scattering at momentum transfer Q2=0.14 (GeV/c)2 has been measured to be 1.52 ± 0.55(stat) ± 0.15(syst)%. The plane wave impulse approximation (PWIA) prediction for this measurement ranges from 2.1% to 2.9%, where the variation is due to uncertainty in the initial state wave function, nucleon form factors, and off-shell prescription. The data may suggest a suppression with respect to the PWIA, which has also been observed for the unpolarized longitudinal response function.

1 data table

QUASIELASTIC REACTION.


Determination of the neutron spin structure function..

The E142 collaboration Anthony, P.L. ; Arnold, R.G. ; Band, H.R. ; et al.
Phys.Rev.Lett. 71 (1993) 959-962, 1993.
Inspire Record 359353 DOI 10.17182/hepdata.19693

The spin structure function of the neutron g1n has been determined over the range 0.03<x<0.6 at an average Q2 of 2 (GeV/c)2 by measuring the asymmetry in deep inelastic scattering of polarized electrons from a polarized He3 target at energies between 19 and 26 GeV. The integral of the neutron spin structure function is found to be F01g1n(x)dx=-0.022±0.011. Earlier reported proton results together with the Bjorken sum rule predict F01g1n(x)dx=-0.059±0.019.

2 data tables

No description provided.

Extrapolarity to full x range.


Quasielastic scattering of polarized electrons from polarized He-3 and measurement of the neutron's form-factors

Thompson, A.K. ; Bernstein, A.M. ; Chupp, T.E. ; et al.
Phys.Rev.Lett. 68 (1992) 2901-2904, 1992.
Inspire Record 338099 DOI 10.17182/hepdata.19863

We report measurements of asymmetries in quasielastic scattering of polarized electrons from polarized He3 at Q2=-0.2 GeV/c)2. We measure AT′=(-2.6±0.9±0.46)% and ATL′=(+1.75±1.2±0.31)%. The asymmetry AT′ depends predominantly on the previously measured neutron magnetic form factor and provides a test of theories of spin-dependent quasielastic scattering. Our result for AT′ is consistent with a previously reported measurement and suggests that the current theoretical picture is incomplete and final-state-interaction and meson-exchange corrections are necessary if the electric form factor of the neutron is to be reliably extracted from the asymmetry of ATL′.

1 data table

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