Strangeness Production

Contributors: S. Cotanch and R. Schumacher.

Progress toward understanding the electromagnetic production of strangeness requires:

• An understanding of hyperon-nucleon interactions.
• Comprehensive measurements of kaon EM production on a variety of targets, probing isospin and spin dependence.
• A rigorous theoretical framework (beyond QHD).
• Including $\phi$ electro-production.
• Extraction of the nucleon time-like form factor for 0 < q2 < 4 MN2 using $p(\pi^-,e^+e^-)n$.
• A consistent treatment of strange matrix elements in the nucleon.
• A reliable many-body treatment for hypernuclei.

Electromagnetic production of strangeness off the nucleon at resonance energies is a field ripe for additional theoretical and experimental exploration. Jefferson Lab, Bonn, and GRAAL are all producing or are about to produce a large amount of new data on all the isospin channels and several new spin observables for these reactions. Several theory groups have produced up-to-date models of elementary strangeness production which have extracted about all that can be learned from previous data; they are looking forward to new data with which to test their models.

On the theory side the main challenge in this field is to go beyond the isobar models with their numerous free parameters, and to make connections to more fundamental concepts in QCD. Most present phenomenological models of strangeness photo- and electro- production use (nearly) ad hoc couplings with ad hoc combinations of intermediate states to model the data. Once higher quality data are available, a reconsideration of the foundations of these models is in order. There has been recent work using chiral perturbation theory and Regge-type analyses in regions of their applicability, but these efforts are still exploratory and incomplete. No published work has addressed the issue of final state interactions, rescattering, or the issue of unitarity.

These efforts should be undertaken because the electromagnetic production of strange quarks at resonance energies is a fundamental strong interaction process. Understanding these processes directly from QCD will be very difficult as they occur (by definition) in the non-perturbative regime. The fact that strange quarks are being produced from non-strange targets may help the situation. In five years we hope to see an improved understanding of strangeness electromagnetic production, and progress toward a rigorous understanding of the reaction mechanism.

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