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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
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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
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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
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Our data came from Jlab... Tagged beam on LH2 target. 2.4 and 3.1 GeV endpoint energies. Polarization ~ 65%.
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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
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An advertisement... This analysis has also produced differential cross section measurements. See nucl/ex0509033
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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!!
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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 -
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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
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Results Models: F.X.Lee et al, Nucl Phys A 695, 237, 2001; S. Janssen, PhD Thesis, Univ. of Gent, 2001
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Mid-Angles
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Mid-Forward
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Foward Angles
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o : Backward angles
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o : Mid angles
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o : Forward angles
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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....
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Supplemental Slides
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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
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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
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