Bochum 1998 – wissenschaftliches Programm

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HK: Hadronen und Kerne

HK 40: Electromagnetic Probes VI, NN-Correlations

HK 40.2: Gruppenbericht

Dienstag, 17. März 1998, 17:30–18:00, F

Nucleon-nucleon correlation effects in ^3,4He(e,e′X) reactions — •H.P. Blok¹, G.E. Dodge¹, W.H.A. Hesselink¹, C. Kormanyos¹, S.I. Nagorny¹, A. Pellegrino¹, C.J.G. Onderwater¹, M. van Sambeek¹, C.M. Spaltro¹, R. Starink¹, J.A. Templon¹, D.J. Boersma², T. Botto², E. Jans², W.J. Kasdorp², L. Lapikás², J.J. van Leeuwe², M.A. van Uden², G. van der Steenhoven², J.J.M. Steijger², H. de Vries², Th.S. Bauer³, A. Misiejuk³, J.A. Tjon³, M. Yeomans³, M.N. Harakeh⁴, E. Cisbani⁵, S. Frullani⁵, F. Garibaldi⁵, M. Iodice⁵, G-M. Urciuoli⁵, R. Perrino⁶, R. DeLeo⁷, J. Golak⁸, J.M. Laget⁹, J.F.J. van den Brand¹⁰, H.J. Bulten¹⁰, O. Unal¹⁰, and R. Ent¹¹ — ¹Vrije Universiteit Amsterdam, de Boelelaan 1081, 1081 HV Amsterdam, The Netherlands — ²NIKHEF, P.O.Box 41882, 1009 DB Amsterdam, The Netherlands — ³Universiteit Utrecht, The Netherlands — ⁴KVI, Groningen, The Netherlands — ⁵INFN-Sezione Sanità, Rome, Italy — ⁶INFN-Lecce, Italy — ⁷Universitá di Bari, Italy — ⁸Institute of Physics, Jagellonian University, PL-30059 Cracow, Poland — ⁹CEN Saclay, Gif-sur-Yvette, France — ¹⁰University of Wisconsin, Madison, USA — ¹¹CEBAF, Newport News, VA 23606, USA

Nucleon-nucleon correlations play an important role in nuclear structure, but compared to the single-particle aspects they have much less been investigated. Here we report on coincidence electrodisintegration studies of such correlations in ³He and ⁴He, performed with the extracted electron beam from the pulse stretcher AmPS at NIKHEF. ^3,4He(e,e′d) data were taken in various kinematics at incident energies of 370 and 576 MeV, so that the structure functions W_L(+W_TT), W_T and W_LT could be separated. The ⁴He(e,e′d) reaction is especially interesting, since the transition to the ²H (break-up) state is of Δ T=0 (1) character. The results for ³He are compared to Faddeev calculations and a covariant and gauge invariant approach. Globally the cross sections, including the dependence on q and p_m, are well described. Larger differences show up in the separated structure functions.

In the ⁴He(e,e′p)³H reaction correlations are predicted to become manifest around 500 MeV/c missing momentum due to the zero in the underlying pT momentum distribution. Moreover, microscopic calculations predict a ridge in the semi-exclusive (e,e′p) cross section, which kinematically connects high (correlated) nucleon momenta with high removal energies. Data covering both kinematic regimes will be presented. Calculations accounting for effects due to final state interactions, meson exchange currents and isobar configurations are compared to the data.