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HK: Hadronen und Kerne
HK 18: Electromagnetic Probes III, Short Range NN-Correlations
HK 18.1: Group Report
Monday, March 16, 1998, 17:00–17:30, F
Measurement of the reaction 208Pb(e,e′p) in a large momentum-transfer and missing-energy domain — •L. Lapikás1, D.L. Groep1, E. Jans1, G. van der Steenhoven1, M.F. van Batenburg1, H.P. Blok1,2, W.H.A. Hesselink1,2, R. Starink1,2, J. Volmer1,2, D.J. Boersma1,3, J.E. Ducret4, C. Marchand4, R. Medaglia4, R. Perrino5, E. Cisbani6, S. Frullani6, F. Garibaldi6, M. Iodice6, G-M. Urciuoli6, R. De Leo7, D.G. Ireland8, and A. Scott8 — 1NIKHEF, P.O.Box 41882, 1009 DB Amsterdam, The Netherlands — 2Vrije Universiteit Amsterdam, de Boelelaan 1081, 1081 HV Amsterdam, The Netherlands — 3Universiteit Utrecht, The Netherlands — 4CEN Saclay, Gif-sur-Yvette, France — 5INFN-Lecce, Italy — 6INFN-Sezione Sanità, Rome, Italy — 7Universitá di Bari, Italy — 8University of Glasgow, Scotland
Previous 208Pb(e,e′p) experiments were all carried out at moderately low momentum transfers (q < 450 MeV/c), predominantly longitudinal kinematics and a small missing energy domain (Em< 30 MeV). Here we report on two new experiments that have largely extended this data set. The target consisted of two 42 mg/cm2 water cooled enriched lead foils. Their temperature, which was monitored continuously by a pyrometer, never exceeded 140∘C for beam currents up to 10 µA.
In the first experiment the (e,e′p) response of 208Pb has been measured at momentum transfers (q = 460-750 MeV/c) and proton energies (Tp=160-270 MeV) for dominantly transverse kinematics (є−1 ≈ 4). Data were taken in perpendicular kinematics, while keeping the q constant and equal to the momentum of the ejected proton. Hence, the leptonic part of the interaction was kept fixed. The measurements span a range in missing momentum of 0<pm<300 MeV/c. The emphasis in the analysis is on extracting the cross sections for transitions to the first five excited states in 207Tl. Through the dependence of these cross sections on q and Tp we study the structure of the hadronic current and of the final state interaction.
The aim of the second experiment is to determine the occupancy of the deepest lying orbitals in 208Pb from the angular momentum decomposition of the longitudinal cross section. The latter is extracted from a Rosenbluth separation of cross-sections for the reaction 208Pb(e,e′p) measured in parallel kinematics at beam energies of 462 and 675 MeV. The data span a domain of Em=0-110 MeV and pm=0-250 MeV/c. For a reliable extraction of the one-proton knockout part of the cross section we have also calculated the contribution from rescattering processes of the type (e,e′N)(N,p) in which the second nucleon (N) goes undetected.