Cross sections for semi-inclusive electroproduction of charged pions (π±) from both proton and deuteron targets were measured for 0.2<x<0.5, 2<Q2<4 GeV2, 0.3<z<1, and Pt2<0.2 GeV2. For Pt<0.1 GeV, we ...find the azimuthal dependence to be small, as expected theoretically. For both π+ and π−, the Pt dependence from the deuteron is found to be slightly weaker than from the proton. In the context of a simple model, this implies that the initial transverse momenta width of d quarks is larger than for u quarks and, contrary to expectations, the transverse momentum width of the favored fragmentation function is larger than the unfavored one.
A large set of cross sections for semi-inclusive electroproduction of charged pions (π±) from both proton and deuteron targets was measured. The data are in the deep-inelastic scattering region with ...invariant mass squared W2 > 4 GeV2 and range in four-momentum transfer squared 2 < Q2 < 4 (GeV/c)2, and cover a range in the Bjorken scaling variable 0.2 < x < 0.6. The fractional energy of the pions spans a range 0.3 < z < 1, with small transverse momenta with respect to the virtual-photon direction, Pt2 < 0.2 (GeV/c)2. The invariant mass that goes undetected, Mx or W', is in the nucleon resonance region, W' < 2 GeV. The new data conclusively show the onset of quark-hadron duality in this process, and the relation of this phenomenon to the high-energy factorization ansatz of electron-quark scattering and subsequent quark → pion production mechanisms. The x, z and Pt2 dependences of several ratios (the ratios of favored-unfavored fragmentation functions, charged pion ratios, deuteron-hydrogen and aluminum-deuteron ratios for π+ and π-) have been studied. The ratios are found to be in good agreement with expectations based upon a high-energy quark-parton model description. We find the azimuthal dependences to be small, as compared to exclusive pion electroproduction, and consistent with theoretical expectations based on tree-level factorization in terms of transverse-momentum-dependent parton distribution and fragmentation functions. In the context of a simple model, the initial transverse momenta of d quarks are found to be slightly smaller than for u quarks, while the transverse momentum width of the favored fragmentation function is about the same as for the unfavored one, and both fragmentation widths are larger than the quark widths.
A large data set of charged-pion (pi+/-) electroproduction from both hydrogen and deuterium targets has been obtained spanning the low-energy residual-mass region. These data conclusively show the ...onset of the quark-hadron duality phenomenon, as predicted for high-energy hadron electroproduction. We construct several ratios from these data to exhibit the relation of this phenomenon to the high-energy factorization ansatz of electron-quark scattering and subsequent quark-->pion production mechanisms.
The differential cross-section for the process p(e,e'p)eta has been measured at Q2 ~ 5.7 and 7.0 (GeV/c)2 for centre-of-mass energies from threshold to 1.8 GeV, encompassing the S11(1535) resonance, ...which dominates the channel. This is the highest momentum transfer measurement of this exclusive process to date. The helicity-conserving transition amplitude A_1/2, for the production of the S11(1535) resonance, is extracted from the data. This quantity appears to begin scaling as 1/Q3, a predicted signal of the dominance of perturbative QCD, at Q2 ~ 5 (GeV/c)2.
Cross sections for semi-inclusive electroproduction of charged pions (\(\pi^{\pm}\)) from both proton and deuteron targets were measured for \(0.2<x<0.5\), \(2<Q^2<4\) GeV\(^2\), \(0.3<z<1\), and ...\(P_t^2<0.2\) GeV\(^2\). For \(P_t<0.1\) GeV, we find the azimuthal dependence to be small, as expected theoretically. For both \(\pi^+\) and \(\pi^-\), the \(P_t\) dependence from the deuteron is found to be slightly weaker than from the proton. In the context of a simple model, this implies that the initial transverse momenta width of \(d\) quarks is larger than for \(u\) quarks and, contrary to expectations, the transverse momentum width of the favored fragmentation function is larger than the unfavored one.
The differential cross section for the process p(e,e{prime}p) {eta} has been measured at Q{sup 2} {approx} 5.7 and 7.0(GeV/c){sup 2} for center-of-mass energies from threshold to 1.8 GeV, ...encompassing the S{sub 11}(1535) resonance, which dominates the channel. This is the highest momentum-transfer measurement of this exclusive process to date. The helicity-conserving transition amplitude A{sub 1/2}, for the production of the S{sub 11}(1535) resonance, is extracted from the data. Within the limited Q{sup 2} now measured, this quantity appears to begin scaling as Q{sup -3} - a predicted, but not definitive, signal of the dominance of perturbative QCD at Q{sup 2} {approx} 5 (GeV/c){sup 2}.
Structure functions, as measured in lepton-nucleon scattering, have proven to be very useful in studying the quark dynamics within the nucleon. However, it is experimentally difficult to separately ...determine the longitudinal and transverse structure functions, and consequently there are substantially less data available for the longitudinal structure function in particular. Here we present separated structure functions for hydrogen and deuterium at low four--momentum transfer squared, Q^2< 1 GeV^2, and compare these with parton distribution parameterizations and a k_T factorization approach. While differences are found, the parameterizations generally agree with the data even at the very low Q^2 scale of the data. The deuterium data show a smaller longitudinal structure function, and smaller ratio of longitudinal to transverse cross section R, than the proton. This suggests either an unexpected difference in R for the proton and neutron or a suppression of the gluonic distribution in nuclei.
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