1. C x and C x for K + Λ and K +  o Photo-production R. Bradford Department of Physics and Astronomy, University of Rochester R. Schumacher Department of Physics and Astronomy, Carnegie Mellon University for the CLAS Collaboration

2. Overview What are C x and C z ? Experimental Setup/Jefferson Lab Overview of measurement/analysis techniques Results for K + Λ and K +  o  comparison with available models

3. What are C x and C z ? Measure polarization transfer from  to Y in the production plane, along “z” or “x”  p K+K+ Y  K CM In CM frame: Z X y

4. Our data came from Jlab... Tagged  beam on LH2 target. 2.4 and 3.1 GeV endpoint energies.  Polarization ~ 65%.

5. The CLAS Detector in Hall B Electromagnetic calorimeters Lead/scintillator, 1296 photomultipliers Gas Cherenkov counters e/  separation, 256 PMTs Time-of-flight counters plastic scintillators, 684 photomultipliers Drift chambers argon/CO 2 gas, 35,000 cells CEBAF Large Acceptance Spectrometer Torus magnet 6 superconducting coils Liquid H 2 target +  start counter; e minitorus

6. An advertisement... This analysis has also produced differential cross section measurements. See nucl/ex0509033

7. Analysis Strategy Extract C x and C z using beam helicity asymmetry, A x/z : N x/z ± = helicity-dependent yield  eff = Effective weak decay asymmetry = 0.642 for , -0.165 for  o.  = photon beam polarization No acceptance correction necessary!!

8. Analysis Details For both channels, detect K + p.  or  o hyperon recreated from p( ,K + )X missing mass. Yield extracted with fit. Construct helicity asymmetries Extract slope from linear fit.   cos(θ p ) Beam Helicity Asymmetry -

9. Photon Polarization Determination Polarization of e - beam measured with Moller Polarimeter. Polarization of  beam calculated using the Maximon and Olson relation (See: L.C. Maximon and H. Olson, Phys Rev 114, 887 (1959). P  /P e Ratio

10.  Results Models: F.X.Lee et al, Nucl Phys A 695, 237, 2001; S. Janssen, PhD Thesis, Univ. of Gent, 2001

11.  Mid-Angles

13.  Mid-Forward

14.  Foward Angles

15.  o : Backward angles

16.  o : Mid angles

17.  o : Forward angles

18. Summary... We have made first measurements of C x and C z for  p→K +  and  p→K +  o. The recoil  is shown to be almost maximally polarized along the direction of the incident  polarization. The recoiling  o has nonzero polarization, but with no preferred direction. A paper is in the works....

19. Supplemental Slides

20. A note about  o : We study  o through its decay to . This results to changes in the effective value of the weak decay asymmetry parameter. Dillution to decay of  o. Correction related to reference frame  weak decay asymmetry parameter = 0.642

21. A note about  o, cont’d: Source: R.A. Schumacher, et al. Proton angular distribution in the  o rest frame. CLAS-Note 2005-013. Posted at: http://www1.jlab.org/ul/Physics/Hall%2DB/clas/analysisIndex.cfm?note_year=2005