Can we produce hypernuclei without recoil at COSY?


Strangeness in nuclear systems has been of interest since long time. The question of medium modifications of strange hadrons in nuclear matter is a popular keyword. Another point of interest related to that are hypernuclei. Here a Lambda or a Sigma hyperon is bound in a nuclear potential. The modification of the Lambda lifetime and decay ratios in a heavy nucleus have already been a subject of studies also at COSY.

A very successful story was and still is the spectroscopy of single Lambda hypernuclei in counter experiments with the kinematical trick of close to recoilless (K-, pi-) strangeness exchange reactions with large forward cross sections of about 10 mb/sr.

All high statistics counter experiments with hypernuclei so far were done with secondary beams of K- mesons or even pi+ mesons. They all suffer however from the problem of comparatively miserable beam quality: At best some 10000 K mesons per second are available, contaminated by much more pions in general, emitted into order of 100 pi mm mrad emittance with duty factors around 0.1 with targets of big size and more than g/cm² thickness. These experiments all need sophisticated spectrometers already for the incoming K-mesons.

If it were possible to study hypernuclei at COSY using the extremely high quality proton beam we might open a new and very rewarding field of physics here. It should be particularly interesting to produce and tag well defined hypernuclear states. The very small target volumes would be a great advantage for observing their further decays.

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