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Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008
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Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008.

Mar 28, 2015

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Page 1: Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008.

Polarization Observables in Hyperon Photoproduction with CLAS

Craig Paterson University of Glasgow Eurotag WorkshopGlasgow, 1st September 2008

Page 2: Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008.

Introduction

Search for Missing ResonancesUndetected baryon states predicted to couple strongly to andchannels

Strongly correlated diquarks?

Understand strangeness production

off the proton

Sensitive test of resonance structure

– PDG star rating for “missing resonances”

Page 3: Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008.

Polarization Observables

4 Complex amplitudes completely describe pseudoscalar meson photoproduction

This gives 16 real polarization observables

PossibleMeasurements

Require 8 observables for a “complete measurement”

Page 4: Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008.

Fully Polarized Lambda

Evidence from previous CLAS analysis for a fully polarized Lambda Hyperon

Creation of virtual strange quark – antiquark pair in a 3S1 state

Spin Couplings treated at the quark level

Analogous results for linearly polarized photons?!?

Page 5: Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008.

Reaction In CLAS

Use 4 CLAS detector to search for the reactions

p -> K+-> K+p-

p -> K+-> K+-K+p-

Page 6: Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008.

Photon Polarization

Photon polarization calculated to be > 90%Underestimate of polarization for certain energiesImproved measurements requiredCompare to previous data?Polarimeter would be nice!!!

Page 7: Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008.

Analysis: Event Selection

Sophisticated analysis algorithm to select and events

Initial selection based on mass

calculated from time-of-flight

Identify the correct photon

Fiducial cuts

Page 8: Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008.

Analysis: Event Selection

Correctly Identify Hyperon Events

Remove mis-identifed kaons/pions

Reconstruct hyperons from

Missing mas

Pions

LambdaSigma

Page 9: Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008.

Analysis: Extraction of Photon Asymmetry

Photon Asymmetry, , extracted from cos(2) fit to azimuthal kaon distribution

Fits shown for 1 energy bin

340 (20E, 17) kinematic bins

Almost full angular coverage

Page 10: Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008.

Photon Asymmetry Results –

Results compared with previous results from GRAAL7, 50MeV Energy bins

1175 -> 1475MeV

Good agreement with previous results

PRELIMINARY

Page 11: Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008.

Photon Asymmetry Results –

Results compared with previous results from LEPS6, 100MeV Energy bins

1550 -> 2050MeV

More bins for our data!!!

Increase the angular coverage to backward angles

PRELIMINA

RY

Page 12: Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008.

Photon Asymmetry Results –

Results compared with previous results from GRAAL7, 50MeV Energy bins

1175 -> 1475MeV

Good agreement with previous results

PRELIMINA

RY

Page 13: Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008.

Photon Asymmetry Results –

Results compared with previous results from LEPS6, 100MeV Energy bins

1550 -> 2050MeV

More bins for our data!!!

Increase the angular coverage to backward angles

PRELIMINA

RY

Page 14: Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008.

Analysis: Extraction of Ox/O

z /P and T

Ox/O

z extracted from fit to 2d asymmetry

Recoil Polarization extracted from acceptance corrected proton distribution

Target Asymmetry extracted from 2d Asymmetry

Only results for channel will be shown!!!

Page 15: Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008.

Results: Recoil Polarization results for

Results compared to previous CLAS and GRAAL resultsResults:

g8b

Prev CLAS

GRAAL

~Factor of 4 increase in statistics from best previous measurements

Page 16: Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008.

Results: Ox

Results compared with Regge-Plus-Resonance model from Gent group

- Large Polarizations!

- Some evidence for an important role for missing D

13(1900)

state

PRELIMINA

RY

Page 17: Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008.

Results: Ox

Results compared with Kaon-MAID calculations

- Calculations involving both “core” and missing resonances

- Failure at low energies

- Some evidence for an important role for missing D

13(1900)

statePRELIMINA

RY

Page 18: Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008.

Results: Oz

Results compared with Regge-Plus-Resonance model from Gent group

- Less polarization transfer along z-axis

PRELIMINA

RY

Page 19: Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008.

Results: Target Asymmetry

Results compared with Regge-Plus-Resonance model from Gent group

- Large polarizations

- Less discrimination between model calculations

PRELIMINA

RY

Page 20: Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008.

Results: Fully Polarized Lambda

Evidence for full lambda polarization with linearly polarized photons?

- Full polarization at forward angles

- Not repeated over full kinematic range

- Compare with previous results???

- More relations can be tested

PRELIMINA

RY

Page 21: Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008.

Summary

High Statistics, High Quality Data Set for and photoproduction

Large Improvement Over Previous Recoil and Photon Asymmetry Measurements

Large Improvement Over Previous Ox and O

z , and Target Asymmetry

Results

Measurements Display Good Discriminating Power Between Different Model Calculations – Sensitive to Resonant Contributions

Full Polarization Only Evident at Mid to Forward Angles

Further Theoretical Input Required

Better Calculation of Degree of Photon Polarization Required - Eurotag!!!