PowerPoint Presentation Pair Polarimeter

1
A Silicon m-strip Polarimeter for High Energy
Photons
D.J. Tedeschi, N. Baltzell, T. Garrett University
of South Carolina B. Wojtsekhowski Thomas
Jefferson National Laboratory B. Vlahovic North
Carolina Central University M. Khandakar Norfolk
State University, JLab G. Feldman, G.V.
ORielly The George Washington University F.
Klein Florida International University, JLab
2
Need for New Polarimetry
Nuclear and particle physics experiments at
Jefferson Lab (CEBAF) using linearly polarized
photons with Eg gt 1 GeV

• Search for missing resonances
• hyperon production beam asymmetry
• r and w meson production asymmetry
• Search for proton strangeness component
• f meson production mechanisms
• Search for exotic mesons and hybrid states

3
Pair Production
Well known reaction with a polarization-dependent
angular distribution
C.N. Yang, Phys. Rev. 77, 722 (1950). Berlin and
Madansky, Phys Rev 78, 623 (1950). G.C. Wick,
Phys. Rev. 81, 467 (1951). L.C. Maximon, H.
Olsen, Phys. Rev. 120, 310 (1962). Kobayashi and
Kondo, NIM 104, 101 (1972). B. Wojtsekhowski et
al., TJNAF Technical Note 98-039.
4
New Calculation

• Find large asymmetry in angle of ee- plane (w)
  relative to polarization direction (rather than
  in f)
• ? Reproduce the total cross section of pair
  production
• ? Reproduce the results of Maximon and Olsen

5
Expected Asymmetry
Energy sharing Ee/Eg
Pair Angle w (deg)
Calculations performed by USC undergraduate
Nathan Baltzell
6
Pair Production
Silicon m-strips 50 mm spacing
qpp 1/Eg10-4
7
The Detector Schematic
Converter
m-strips
Magnet
Scintillators
Simulations performed by USC undergraduate Travis
Garrett
8
The Prototypes
I. Tested at Duke FEL (39 MeV) m-strip
detectors 100 mm Al converter
II. Tested at LEGS (300 MeV) Larger area
m-strips Active converter
9
Determining Hit Positions
Require 2 clusters in each plane. Measure axis of
polarimeter relative to the beam-line.
10
Coordinate Readout
y position (strips)
y position (strips)
x position (strips)
x position (strips)
All events
Single event
11
Monte Carlo Simulation
u
v
w
GEANT Collimation, Multiple scattering, Detector
alignment, Position resolution
12
Monte Carlo Simulation
Polarization Angle 135º
Pair angle w
13
P1(1P2cos(2(w-P3)))
14
Conclusions and Future for Pair Polarimetry

• New calculations show large asymmetry for pair
  production in the variable w
• Advances in m-strip detector technology make
  asymmetry measurement possible
• Polarimeter prototype result agrees with
  expectations
• Improved design will tested at high energy
  (SPring8) in 2001.