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The Nucleon Structure Functions F2N at Low Q2

(Niculescu, Benmouna, Berman)

The nucleon structure functions F2N, like their spin-structure counterparts g2N [Ben01], are fundamental to our understanding of physics at the nucleon scale. The structure functions F2N are well measured over a broad range in momentum transfer Q2 and Bjorken x. At large values of Q2 the structure functions are well understood in terms of logarithmic scaling violations. In this regime, perturbative Quantum Chromodynamics (pQCD) calculations of leading order and next-to-leading order terms, together with target-mass corrections, reproduce the data very well. Figure 16 shows a set of F2p data representative of the world's data plotted as a function of Q2, and binned in x.

At low values of Q2 and moderately low x, however, the theoretical understanding of F2N is less clear, and the data are sparse. Recent JLab work [Nic00] indicates that in this kinematic regime, we may be seeing the onset of a drop in F2p with decreasing Q2. This fall-off structure function may indicate insensitivity to the quark component of the nucleon sea at low Q2.

Figure 16. F2p data representative of the world's data, plotted as a function of Q2, and binned in x. At low values of Q2 and moderately low x, however, the theoretical understanding of F2N is less clear and data are sparse. It is in this region we will add to the data.

We are collaborators on a recent experiment at Jefferson Lab [Nic02] to measure the inclusive electron-nucleon scattering cross section in both the deep-inelastic and the resonance regions on hydrogen and deuterium. The objective is to map out F2N in both the low-Q2, low-x (W2 > 3.5 GeV2) region as well as in the low-Q2, moderate-x (resonance) region. These data will fill out our knowledge of the structure functions in this largely unexplored regime, and should aid the current efforts to develop global descriptions of inclusive electron-nucleon scattering in the low-Q2 region. In addition, the resonance data will allow a comprehensive study of Bloom-Gilman (or quark-hadron) duality [Blo96] at low Q2.

This experiment collected data during the month of April, 2003, for beam energies from 2.2 to 4.4 GeV. The Q2 coverage was between 0.03 and 1.4 (GeV/c)2 for x between 0.008 and 1.0. The systematic uncertainty for the inclusive cross section is expected to be around 3% while the statistical uncertainty will be at the 1% level or better for all x-bins.

 

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