University of Groningen Strangeness photoproduction on the ...
Strangeness Photoproduction in FROST
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Strangeness Photoproduction in FROST
Liam CaseyHugs 2008
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• 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
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• 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.
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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
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Frost Target Apparatus
Polarization > 80%Holding field = 0.56 T
Base temp = 28 mK
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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.
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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.
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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.