Inclusive Electron-Nucleus Scattering at Large Momentum Transfer

Abstract

Inclusive electron scattering is measured with 4.045 GeV incident beam energy from C, Fe, and Au targets. The measured energy transfers and angles correspond to a kinematic range for Bjorken x . 1 and momentum transfers from Q 2 1 7 ͑GeV͞c͒ 2 . When analyzed in terms of the y-scaling function the data show for the first time an approach to scaling for values of the initial nucleon momenta significantly greater than the nuclear matter Fermi momentum (i.e., .0.3 GeV͞c). High energy electron scattering from nuclei can provide important information on the wave function of nucleons in the nucleus. In particular, with simple assumptions about the reaction mechanism, scaling functions can be deduced that, if shown to scale (i.e., are independent of length scale or momentum transfer), can provide information about the momentum and energy distribution of nucleons in a nucleus. Several theoretical studies [1][2][3][4] have indicated that such measurements may provide direct access to short-range nucleon-nucleon correlations.The concept of y scaling in electron-nucleus scattering was first introduced by West [5] and Kawazoe et al. [6]. They showed that in the impulse approximation, if quasielastic scattering from a nucleon in the nucleus was the dominant reaction mechanism, a scaling function F͑ y͒ could be extracted from the measured cross section which was related to the momentum distribution of the nucleons in the nucleus. In the simplest approximation the corresponding scaling variable y is the minimum momentum of the struck nucleon along the direction of the virtual photon. In general the scaling function depends on both y and momentum transfer-F͑ y, Q 2 ͒-but at sufficiently high Q 2 (2Q 2 is the square of the four-momentum transfer) the dependence on Q 2 should vanish yielding scaling. However, the simple impulse approximation picture breaks down when the final-state interactions (FSI) of the struck nucleon with the rest of the nucleus are included. Previous calculations [7][8][9][10][11][12][13][14] suggest that the contributions from final-state interactions should vanish at sufficiently high Q 2 . A previous SLAC measurement [15] suggested an approach to the scaling limit for heavy nuclei but only for low values of j yj , 0.3 GeV͞c at momentum transfers up to 3 ͑GeV͞c͒ 2 . The data presented here represent a significant increase in the Q 2 range compared to previous measurements while also extending the coverage in y.The present data were obtained in Hall C at the Thomas Jefferson National Accelerator Facility (TJNAF), using 4.045 GeV electron beams with intensities from 10-80 mA. The absolute beam energy was calibrated to 0.08% using 0.8 GeV elastic scattering from carbon and BeO targets and 4.0 GeV elastic scattering from hydrogen. The beam current was monitored with three calibrated resonant cavities. The beam energy resolution was better than 0.05% as defined by the accelerator acceptance. Solid targets of C (2.1% and 5.9% of a radiation length), Fe (1.5% and 5.8% of a radiation length), and Au (5.8% of a r...

Final-state interactions in the nuclear response at large momentum transfer

“…[33] and to the 56 Fe data of Ref. [34] at beam energy E e = 4 GeV and electron scattering angle θ e = 30 deg. The proposed approach appears to provide a quantitative description of the measured cross sections over a range exceeding five orders of magnitude.…”

“…For comparison, the crosses also show the cross section of Ref. [34], measured in the same kinematical setup using an 56 Fe target.…”

First measurement of the Ti(e,e′)X cross section at Jefferson Lab

“…The cross section in each bin i is computed as the product of the Monte Carlo (MC) cross section [31] times the ratio of the data to simulation yields. The MC cross section is a fit to existing data, including preliminary Hall C [32] data, and includes radiative corrections computed by using the peaking approximation [33] and Coulomb corrections implemented with an effective momentum approximation [34].…”

Tensor spin observables and spin stucture at low Q2

“…[25] suggests that to resolve the microscopic structure of nuclei, we need to study scattering at sufficiently large momentum transfer and large relative momenta of the produced nucleons. This logic was confirmed [26] by a series of experiments at SLAC [27] and JLab [28,29] that directly observed short-range correlations (SRC) in a series of nuclei, and established a similar effect in the deuteron and in heavier nuclei with pn correlations giving the dominant contribution.…”