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Bochum 1998 – wissenschaftliches Programm

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HK: Hadronen und Kerne

HK 62: Hadronic Probes VI, Resonances, Reactions

HK 62.1: Gruppenbericht

Donnerstag, 19. März 1998, 14:00–14:30, C

The Search for the πNN resonance d at WASA/PROMICE — a Status Report — •W. Brodowski1, A. Betsch1, R. Bilger1, H. Clement1, G.J. Wagner1, and M. Schepkin21Physikalisches Institut der Universität Tübingen, Auf der Morgenstelle 14, D-72076 Tübingen — 2ITEP Moscow — for the WASA/PROMICE Collaboration

The search for dibaryons has a long, though not very glorious history. Despite a vast number of dedicated experiments no single clear-cut evidence for the existence of narrow dibaryon states has been found up to now. However, most of these investigations have not been sensitive to NN-decoupled states, which most likely are expected to have small decay widths. Evidence for such a narrow resonance in the πNN system, called d′, with m = 2.06 GeV, Γπ NN ≈ 0.5 MeV and I(JP) even (0), has previously been found in the pionic double charge exchange reaction on nuclei [1,2]. Since nuclear medium effects as a possible alternative explanation for the observed resonance-like structure in this reaction cannot be excluded definitely, we have been looking into reactions involving only the minimum number of nucleons necessary for the production of d′. For the hadronic production of d′ the most fundamental reaction is the two-pion production in nucleon-nucleon collisions. From the experimental point of view the most suitable reaction there is ppppππ+ with only charged particles in entrance and exit channels. We have carried out exclusive measurements of this reaction with the WASA/PROMICE setup at the CELSIUS storage ring at Uppsala. The analysis of the 1995 data indeed exhibits a narrow structure in the Mppπ spectrum, which would be consistent with the d′ hypothesis [3]. Checks of the detector performance have been made by analyses of single-pion production channels. Another run of higher statistics has been carried out 1996. The status of analysis of these data and problems associated with this run will be discussed together with the 1995 results.
[1] R. Bilger et al., Phys. Rev. Lett. 71 (1993) 42; 72 (1994) 2972
[2] K. Föhl et al., Phys. Rev. Lett. 79 (1997) 3849
[3] W. Brodowski et al., Z. Phys. A355 (1996) 5
supported by BMBF (06 TU 886), DAAD and DFG (Mu 705/3,
Graduiertenkolleg)

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