Münster 2002 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 36: Plenary Session

HK 36.2: Plenarvortrag

Donnerstag, 14. März 2002, 11:45–12:15, Plenarsaal

Search for Missing Baryon Resonances — •Ulrike Thoma — Thomas Jefferson National Laboratory, 12000 Jefferson Avenue, Newport News, VA 23606, USA

It is widely accepted that QCD is most probably the correct theory of strong interactions. But a major goal of QCD is still unfulfilled: to provide the theory of quark confinement. Instead, constituent quark models have been developed which describe the baryon spectrum with good success. However there is an interesting controversy in baryon spectroscopy. Constituent quark model calculations predict much more resonances than have been observed so far. Two very different explanations have been proposed:
1) The No-dqmissingNo-dq states are not missing. They have not been observed so far because of lack of high quality data in channels different from π N. If these states decouple from π N they would not have been observed so far.

2) The No-dqmissingNo-dq states are not missing, they do not exist. The nucleon-resonances could have a quark-diquark structure. This reduces the number of internal degrees of freedom and therefore the number of existing states.

Photoproduction experiments investigating channels different from π N are expected to have a big discovery potential if these states really exist. This is one of the goals of the CB-ELSA experiment in Bonn and of the CLAS experiment at Jefferson Laboratory. Recent progress in the search for these No-dqmissingNo-dq states will be discussed.