Bochum 1998 – wissenschaftliches Programm
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HK: Hadronen und Kerne
HK 48: Electromagnetic Probes VII, Electro-, Photoproduction
HK 48.2: Gruppenbericht
Mittwoch, 18. März 1998, 14:30–15:00, B
Coherent π0 electroproduction on 4He in the Δ region — •T. Botto1, M.J.M. van Sambeek1,2, Th.S. Bauer1,3, H.P. Blok1,2, D.J. Boersma1,3, G.E. Dodge2,4, D.L. Groep1, P. Heimberg1,2, W.H.A. Hesselink1,2, D. Higinbotham1,5, C.W. de Jager1, E. Jans1, T.J. Ketel1,2, D.J.J. de Lange1, L. Lapikás1, B.E. Norum5, I. Passchier1, V.M. Pugatch6, M.F.M. Steenbakkers1,2, J.J.M. Steijger1, L. Todor4, P.E. Ulmer4, H. de Vries1, and K. Wang5 — 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 — 4Department of Physics, Old Dominion University, Norfolk, VA 23529, USA — 5University of Virginia, Charlottesville, Virginia, VA 22901, USA — 6Institute for Nuclear Research, Ukrainian Academy of Sciences, Kiev, Ukraine
Pure coherent π0 production on a composite nucleus is of particular interest for testing of the Δ degrees of freedom in the nuclear medium. Unfortunately, almost no data exist. Coherent π0 electroproduction on 4He was studied at the Internal Target Facility of NIKHEF by scattering electrons of 677 MeV from 4He atoms, contained in a 15 mm diameter open-ended storage cell inside the ring vacuum.
The detection of neutral pions was avoided by making use of a dedicated detector for the recoiling 4He nuclei (1-95 MeV). This recoil detector is placed at 17 cm from the target cell and has a solid angle of 250 msr.
The scattered electrons were detected in the BigBite large-acceptance magnetic spectrometer. The spectrometer consists of a non-focusing dipole magnet, two sets of multi-wire drift chambers for track reconstruction, a Čerenkov detector for charged pion discrimination and a scintillator for timing and trigger purposes.
The experiment featured an on-line calibration by the simultaneous observation of 4He(e,e′ 4He) elastic scattering events. First results will be shown and compared to Δ-hole type and DWIA models.