We report results for the virtual photon asymmetry $A_1$ on the nucleon from new Jefferson Lab measurements. The experiment, which used the CEBAF Large Acceptance Spectrometer and longitudinally polarized proton ($^{15}$NH$_3$) and deuteron ($^{15}$ND$_3$) targets, collected data with a longitudinally polarized electron beam at energies between 1.6 GeV and 5.7 GeV. In the present paper, we concentrate on our results for $A_1(x,Q^2)$ and the related ratio $g_1/F_1(x,Q^2)$ in the resonance and the deep inelastic regions for our lowest and highest beam energies, covering a range in momentum transfer $Q^2$ from 0.05 to 5.0 GeV$^2$ and in final-state invariant mass $W$ up to about 3 GeV. Our data show detailed structure in the resonance region, which leads to a strong $Q^2$--dependence of $A_1(x,Q^2)$ for $W$ below 2 GeV. At higher $W$, a smooth approach to the scaling limit, established by earlier experiments, can be seen, but $A_1(x,Q^2)$ is not strictly $Q^2$--independent. We add significantly to the world data set at high $x$, up to $x = 0.6$. Our data exceed the SU(6)-symmetric quark model expectation for both the proton and the deuteron while being consistent with a negative $d$-quark polarization up to our highest $x$. This data setshould improve next-to-leading order (NLO) pQCD fits of the parton polarization distributions.
A1 and g1/F1 for the P target at incident energy 1.6000 GeV and W = 1.1300 GeV.
A1 and g1/F1 for the P target at incident energy 1.6000 GeV and W = 1.1500 GeV.
A1 and g1/F1 for the P target at incident energy 1.6000 GeV and W = 1.1700 GeV.
We measured the inclusive electron-proton cross section in the nucleon resonance region (W < 2.5 GeV) at momentum transfers Q**2 below 4.5 (GeV/c)**2 with the CLAS detector. The large acceptance of CLAS allowed for the first time the measurement of the cross section in a large, contiguous two-dimensional range of Q**2 and x, making it possible to perform an integration of the data at fixed Q**2 over the whole significant x-interval. From these data we extracted the structure function F2 and, by including other world data, we studied the Q**2 evolution of its moments, Mn(Q**2), in order to estimate higher twist contributions. The small statistical and systematic uncertainties of the CLAS data allow a precise extraction of the higher twists and demand significant improvements in theoretical predictions for a meaningful comparison with new experimental results.
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We report the results of a new measurement of spin structure functions of the deuteron in the region of moderate momentum transfer ($Q^2$ = 0.27 -- 1.3 (GeV/c)$^2$) and final hadronic state mass in the nucleon resonance region ($W$ = 1.08 -- 2.0 GeV). We scattered a 2.5 GeV polarized continuous electron beam at Jefferson Lab off a dynamically polarized cryogenic solid state target ($^{15}$ND$_3$) and detected the scattered electrons with the CEBAF Large Acceptance Spectrometer (CLAS). From our data, we extract the longitudinal double spin asymmetry $A_{||}$ and the spin structure function $g_1^d$. Our data are generally in reasonable agreement with existing data from SLAC where they overlap, and they represent a substantial improvement in statistical precision. We compare our results with expectations for resonance asymmetries and extrapolated deep inelastic scaling results. Finally, we evaluate the first moment of the structure function $g_1^d$ and study its approach to both the deep inelastic limit at large $Q^2$ and to the Gerasimov-Drell-Hearn sum rule at the real photon limit ($Q^2 \to 0$). We find that the first moment varies rapidly in the $Q^2$ range of our experiment and crosses zero at $Q^2$ between 0.5 and 0.8 (GeV/c)$^2$, indicating the importance of the $\Delta$ resonance at these momentum transfers.
The measured virtual photon asymmetry (A1D+ETA*A2D) for the Q** region 0.27to 0.39 GeV**2.
The measured virtual photon asymmetry (A1D+ETA*A2D) for the Q** region 0.39to 0.65 GeV**2.
The measured virtual photon asymmetry (A1D+ETA*A2D) for the Q** region 0.65to 1.3 GeV**2.
We present a next-to-leading order QCD analysis of the presently available data on the spin structure function g1 including the final data from the Spin Muon Collaboration. We present results for the first moments of the proton, deuteron, and neutron structure functions, and determine singlet and nonsinglet parton distributions in two factorization schemes. We also test the Bjorken sum rule and find agreement with the theoretical prediction at the level of 10%.
The second systematic (DSYS) error is due to QCD evolution.
First moments of the fitted function G1 evaluated on unmeasured X regions. Total uncertainties due to experimental systematics and theoretical sourc es in the QCD evolution.
First moment of fitted G1 evaluated on the whole X region.
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Differential cross sections for electrons scattered inelastically from hydrogen have been measured at 18°, 26°, and 34°. The range of incident energy was 4.5 to 18 GeV, and the range of four-momentum transfer squared was 1.5 to 21 (GeVc)2. With the use of these data in conjunction with previously measured data at 6° and 10°, the contributions from the longitudinal and transverse components of the exchanged photon have been separately determined. The values of the ratio of the photoabsorption cross sections σSσT are found to lie in the range 0 to 0.5. The question of scaling of 2MpW1 and νW2 as a function of ω is discussed, and scaling is verified for a large kinematic range. Also, a new scaling variable which reduces to ω in the Bjorken limit is introduced which extends the scaling region. The behavior of σT and σS is also discussed as a function of ν and q2. Various weighted sum rules of νW2 are evaluated.
Axis error includes +- 0.0/0.0 contribution (0. TO 2.////DUE TO PION CONTAMINATION).
Axis error includes +- 0.0/0.0 contribution (0. TO 2.////DUE TO PION CONTAMINATION).
Axis error includes +- 0.0/0.0 contribution (0. TO 2.////DUE TO PION CONTAMINATION).
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Cross sections for inelastic scattering of electrons from hydrogen were measured for incident energies from 7 to 17 GeV at scattering angles of 6° to 10° covering a range of squared four-momentum transfers up to 7.4 (GeV/c)2. For low center-of-mass energies of the final hadronic system the cross section shows prominent resonances at low momentum transfer and diminishes markedly at higher momentum transfer. For high excitations the cross section shows only a weak momentum-transfer dependence.
Axis error includes +- 0.0/0.0 contribution (?////FROM UNCERTAINTY IN ELECTRON-DETECTION EFFICIENCY).
Axis error includes +- 0.0/0.0 contribution (?////FROM UNCERTAINTY IN ELECTRON-DETECTION EFFICIENCY).
Axis error includes +- 0.0/0.0 contribution (?////FROM UNCERTAINTY IN ELECTRON-DETECTION EFFICIENCY).
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