Strangeness Photoproduction in FROST

Liam CaseyHugs 2008

• There are a number of “missing” resonances predicted by constituent quark models, but not verified experimentally.

• Diquark models present an alternative framework in which missing resonances do not exist.

• The absence of resonances in πN data can be explained as they may couple strongly to strange decay channels: ΚΛ, ΚΣ.

• FROST is designed to test these predictions.

Motivation

• By using a frozen spin polarized target we will measure the complete set of 16 single and double polarization observables with large acceptance that would be lost using a dynamically polarized target.

• These measurements, which go beyond the crucial 8 independent observables, will allow for an almost model-independent partial wave analysis .

• Any intermediate baryon resonances coupling strongly to γp and KΛ will be found through clear signatures in most of the 16 observables.

Circularly Polarized BeamLongitudinally polarized electrons on amorphous radiatorAngular spread larger than targetCollimated to reduce

Linearly Polarized BeamCoherent bremsstrahlung on thin diamondPolarization constant for 200 MeV around coherent edge

Frost Target Apparatus

Polarization > 80%Holding field = 0.56 T

Base temp = 28 mK

1/2+ 3/2+ 5/2+ 7/2+ 1/2- 3/2- 5/2 - 7/2 -

•D13(1960) questionExpected to be solvedin this analysis.

•KΛ can only involveisospin ½ states and so isexpected to couple to few resonances.

•Finding the resonance in the KΛ channel should be relatively simple.

SAPHIR

Previous Data

Mart-Bennhold without D13(1960)

Mart-Bennhold with D13(1960)

•Bennhold and Mart argue that the structure in SAPHIR data cannot be explained without the D13(1960).

•Saghai argues that off-shell effects for spin-3/2 resonances can produce this result.

Summary

• KΛ is a promising decay channel in the search for missing resonances with a relatively simple analysis due to the few states expected to couple to it.

•FROST in conjunction with g8 and g1 will provide a complete set of polarization observables for this channel.

•In particular, the presence of the D13(1960) in this channel should be made clear or ruled out.