SLAC Proposal End Station A Measurement of the Nuclear Dependence and Momentum Transfer Dependence of Quasielastic (e,e’p) Scattering at Large Momentum Transfer & Measurement of Nuclear Structure Functions at x > 1 and Large Momentum Transfer American University Argonne National Laboratory California Institute of Technology California State University, Los Angeles Rensselaer Polytechnic Institute Lawrence Livermore National Laboratory Massachusetts Institute of Technology Stanford Linear Accelerator Center University of Base1 University of Colorado University of Illinois University of Virginia University of Wisconsin-Madison May 1992ABSTRACT We present two experiments, color transparency a& nuclear structure fur&ons at z > 1, that use a new 16 GeV/c spectrometer and the present 8 GeV/c spectrometer. These experiments require the full Linac beam to End Station A, and use virtually the same detector packages, electronics, and data acquisition. We propose to make coincidence measurements of the quasielastic (e,e’p) cross section on several nuclei in the Q2 range of 6 to 15 (GeV/c)2 using the 23 GeV linac beam and spectrometers in End Station A at SLAC. A fixed-angle magnetic spectrometer will be constructed from existing SLAC magnets and used for detection of quasielastically scat- tered electrons. The presently cor&gured 8 GeV/c spectrometer will be used for detection of recoil protons with momenta up to 8.9 GeV/c. B ecause of the kinematic focussing of the recoil protons which occurs at high Q2, a large fraction of the Fermi cone is accepted in the kinematic range of the experiment. The measurement will have sufficient missing energy resolution to determine that the struck proton did not emit a pion. The proposed measurements will significantly extend those recently carried out by members of this col- laboration in experiment NE18. Beam energies from 12.1 to 23 GeV at maximum current will be required from the SLAC linac. The goal of the experiment is to study quasielastic scattering from nuclei at high Q2 as an exclusive process in &CD, and in particular to look for evidence of color transparency. All theoretical calculations that include color transparency predict large effects in the kinematic region of the proposed experiment. We also propose an inclusive electron-nucleus scattering experiment in the domain of large x and Q2, to measure the nuclear structure function F!. Previous data for x > 1 have been limited to Q2 < 4 (GeV/c)2. W e p ro ose to extend this Q2 range for x = 2 up to p Q2 = 7 (GeV/c)2 and x = 1.2 up to Q2 = 40 (GeV/c)2. These data can provide important information on the scaling of the nuclear structure function, constrain the components of the nuclear wave function at large momentum and binding energy, and put limits on non- nucleonic degrees of freedom in nuclei. In addition, these inclusive data may also provide complementary information on color transparency. These two experiments address complementary physics issues and make use of the same apparatus. They require the assembly of a new fixed-angle 16 GeV/c spectrometer and a fully instrumented 8 GeV/c spectrometer. The detector packages can be assembled from existing hardware in End Station A. The beam requirements are one beam month or two calendar months at 50% efficiency of long-pulse running at energies from 8 - 23.5 GeV.I. color Transparency I. Color Transparency 1.1 Introduction Measurement of exclusive processes from nuclei at high Q2 is important as a con- straint on the theory of the strong interaction [I.l]. Where perturbative QCD (PQCD) is applicable, the scattering process can be understood in terms of a simple counting rule argument II.21 and indeed the Q2 dependence of the prediction is in agreement with the measured cross section for many exclusive processes at high momentum transfer [1.3]. How- ever, significant problems arise when one undertakes a more detailed calculation [I.41 and the question of the applicability of PQCD in exclusive processes remains an open question. The argument centers on how much of the interaction is described by processes which are hard (strong interactions acting for a short time and over a distance small compared to N 1 fermi) and how much by processes which are soft (strong interactions acting over distance scales of order 1 fermi). The high Q2 measurement of quasielastic (e,e’p) scattering from nuclei by the recently completed SLAC experiment NE18 has increased the maximum momentum transfer by about one order of magnitude to 6.8 (GeV/c)2. In this proposal we propose to extend the measurements up to Q2 = 15(GeV/c)2. Th e motivation is a striking prediction of PQCD for the (e,e’p) quasielastic process in nuclei. At large momentum transfer, diminishing elastic and inelastic final-state interactions of the recoil proton in the nuclear medium are predicted [1.5,6]. This effect is called “color transparency”. These measurements can provide important information on the applicability of PQCD to exclusive processes. Measurements have been carried out in quasielastic (p,2p) scattering at Brookhaven and an energy dependence to the transparency has been observed [I.7]. This has been interpreted as evidence for soft contributions due to high mass dibaryon resonances [I.81 or Landshoff contributions [1.9]. H owever, the (p,2p) data contain little information on the missing energy distribution of the struck nucleon. In addition, the p-p elastic scattering cross section contains an oscillation superimposed on the hard scattering scaling behaviour. Further (p,2p) measurements are underway [I.lO] in a Q2 regime comparable to that in the measurements proposed here. Quasielastic proton knockout with