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