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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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Presentation on theme: "Polarization Observables in Hyperon Photoproduction with CLAS Craig Paterson University of Glasgow Eurotag Workshop Glasgow, 1 st September 2008."— Presentation transcript:

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

2 Introduction Search for Missing Resonances Undetected baryon states predicted to couple strongly to KL and KS channels Strongly correlated diquarks? Understand strangeness production off the proton Sensitive test of resonance structure –PDG star rating for missing resonances

3 Polarization Observables 4 Complex amplitudes completely describe pseudoscalar meson photoproduction This gives 16 real polarization observables Possible Measurements Require 8 observables for a complete measurement

4 Fully Polarized Lambda Evidence from previous CLAS analysis for a fully polarized Lambda Hyperon Creation of virtual strange quark – antiquark pair in a 3 S 1 state Spin Couplings treated at the quark level Analogous results for linearly polarized photons?!?

5 KL Reaction In CLAS Use 4p CLAS detector to search for the reactions gp -> K + L -> K + pp - gp -> K + S -> K + Lg -> K + pp - g

6 Photon Polarization Photon polarization calculated to be > 90% Underestimate of polarization for certain energies Improved measurements required Compare to previous data? Polarimeter would be nice!!!

7 Analysis: Event Selection Sophisticated analysis algorithm to select L and S events Initial selection based on mass calculated from time-of-flight Identify the correct photon Fiducial cuts

8 Analysis: Event Selection Correctly Identify Hyperon Events Remove mis-identifed kaons/pions Reconstruct hyperons from Missing mas Pions Lambda Sigma

9 Analysis: Extraction of Photon Asymmetry Photon Asymmetry, S, extracted from cos(2f) fit to azimuthal kaon distribution Fits shown for 1 energy bin 340 (20E, 17q) kinematic bins Almost full angular coverage

10 Photon Asymmetry Results – KL Results compared with previous results from GRAAL 7, 50MeV Energy bins > 1475MeV Good agreement with previous results PRELIMINARY

11 Photon Asymmetry Results – KL Results compared with previous results from LEPS 6, 100MeV Energy bins > 2050MeV More bins for our data!!! Increase the angular coverage to backward angles PRELIMINARY

12 Photon Asymmetry Results – KS Results compared with previous results from GRAAL 7, 50MeV Energy bins > 1475MeV Good agreement with previous results PRELIMINARY

13 Photon Asymmetry Results – KS Results compared with previous results from LEPS 6, 100MeV Energy bins > 2050MeV More bins for our data!!! Increase the angular coverage to backward angles PRELIMINARY

14 Analysis: Extraction of O x /O z /P and T O x /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 KL channel will be shown!!!

15 Results: Recoil Polarization results for KL Results compared to previous CLAS and GRAAL results Results: g8b Prev CLAS GRAAL ~Factor of 4 increase in statistics from best previous measurements

16 Results: O x Results compared with Regge-Plus-Resonance model from Gent group - Large Polarizations! - Some evidence for an important role for missing D 13 (1900) state PRELIMINARY

17 Results: O x 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) state PRELIMINARY

18 Results: O z Results compared with Regge-Plus-Resonance model from Gent group - Less polarization transfer along z-axis PRELIMINARY

19 Results: Target Asymmetry Results compared with Regge-Plus-Resonance model from Gent group - Large polarizations - Less discrimination between model calculations PRELIMINARY

20 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 PRELIMINARY

21 Summary High Statistics, High Quality Data Set for KL and KS photoproduction Large Improvement Over Previous Recoil and Photon Asymmetry Measurements Large Improvement Over Previous O x 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!!!


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