Bochum 1998 – wissenschaftliches Programm

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HK: Hadronen und Kerne

HK 22: Plenar

HK 22.3: Gruppenbericht

Dienstag, 17. März 1998, 10:30–11:00, P

Short-range-correlations in ¹⁶O studied with the reaction ¹⁶O(e,e′pp)¹⁴C — •C.J.G. Onderwater^1,2, R. Starink^1,2, K. Allaart^1,2, W.J.W. Geurts^1,2, W.H.A. Hesselink^1,2, P. Heimberg^1,2, A.R. Pellegrino^1,2, M. Steenbakkers^1,2, J.A. Templon^1,2, D.L. Groep², E.C. Aschenauer², E. Jans², L. Lapikás², W-J. Kasdorp², G. van der Steenhoven², M. van Batenburg², J.J. van Leeuwe², J.J.M. Steijger², M.A. van Uden², E. Cisbani³, S. Frullani³, F. Garibaldi³, M. Iodice³, G-M. Urciuoli³, Th.S. Bauer^4,2, D.J. Boersma^4,2, A. Misiejuk^4,2, N. Kalantar-Nayestanaki⁵, R. De Leo⁶, R. Perrino⁷, and L.B. Weinstein⁸ — ¹Free University, Amsterdam,The Netherlands — ²NIKHEF, Amsterdam, The Netherlands — ³INFN-Sezione Sanità, Rome, Italy — ⁴Universiteit Utrecht, Utrecht, The Netherlands — ⁵KVI, Groningen, The Netherlands — ⁶Universitá di Bari, Italy — ⁷INFN-Lecce, Italy — ⁸Old Dominion University, Norfolk, USA

The reaction ¹⁶O(e,e′pp)¹⁴C has been studied at an energy transfer in the range ω=160−260 MeV and an average three-momentum transfer q=300 MeV/c. The electrons were scattered off ¹⁶O nuclei contained in a waterfall target. Triple coincidence data were taken over a wide range of proton emission angles using two highly segmented plastic scintillator arrays with solid angles of 235 and 550 msr, respectively. >From the momenta of the scattered electrons and the emitted protons the excitation-energy and the momentum of the residual ¹⁴C nucleus were determined. If final state interactions are neglected the latter is equal to the centre-of-mass momentum of the proton-pair in ¹⁶O. A first indication for the importance of short-range-correlations (SRC) has been obtained by comparing the data, taken for ω=190−230 MeV with a simple factorized-approach of the cross sections for the transitions to the ground-state and the lowest excited states in ¹⁴C. It is found that the excitation-energy spectrum of the ¹⁴C nucleus and the corresponding pair centre-of-mass momentum distributions can be reconciled with direct knock-out of two protons from the 1p shell and that the proton-pairs were most likely in a ¹S₀ state. This result is confirmed by calculations, that fully account for the dynamics of the protons in the initial and final state and the various processes contributing to the reaction. These calculations indicate that knockout of ¹S proton-pairs mainly originates from SRC, whereas emission of ³P pairs is largely due to two-body (Δ) currents. Additional information on the reaction mechanism, in particular on the contribution of two-body hadronic currents, has been obtained from the measurements at various values of the energy transferred by the virtual photon.