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