Bochum 1998 – scientific programme
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HK: Hadronen und Kerne
HK 62: Hadronic Probes VI, Resonances, Reactions
HK 62.1: Group Report
Thursday, March 19, 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. Schepkin2 — 1Physikalisches 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 pp
→ ppπ−π+ 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)