c x and c x for k + Λ and k + s o photo-production
DESCRIPTION
C x and C x for K + Λ and K + S 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. Overview. What are C x and C z ? - PowerPoint PPT PresentationTRANSCRIPT
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Cx and Cx for K+Λ and K+o Photo-production
R. Bradford Department of Physics and Astronomy, University of
Rochester
R. SchumacherDepartment of Physics and Astronomy, Carnegie
Mellon University
for the CLAS Collaboration
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Overview
What are Cx and Cz? 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 Cx and Cz?
Measure polarization transfer from to Y in the production plane, along “z” or “x”
p
K+
Y
KCM
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 calorimetersLead/scintillator, 1296 photomultipliers
Gas Cherenkov counterse/ separation, 256 PMTs
Time-of-flight countersplastic scintillators, 684 photomultipliers
Drift chambersargon/CO2 gas, 35,000 cells
CEBAF Large Acceptance SpectrometerTorus magnet
6 superconducting coils
Liquid H2 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 Cx and Cz using beam helicity asymmetry, Ax/z:
Nx/z± = helicity-dependent yield
eff = Effective weak decay asymmetry = 0.642 for , -0.165 for o. = photon beam polarization
No acceptance correction necessary!!
pzxeffzxzx
zxzxpzx C
NN
NNA coscos /
//
///
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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(θp)
Bea
m H
elic
ity A
sym
met
ry
-
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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/
Pe
Rat
io
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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-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 Cx and Cz 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.
768.03
1eff
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