1. D. J. Margaziotis HAPPEX Collaboration Meeting 12-1-06
Lead Target
D. J. Margaziotis
HAPPEX Collaboration Meeting

2. Lead Target Status Pb target intended for E06-007: 208Pb(e,e’p)207Tl
Scheduled to run in 2007:
Officially, starting April 27
Unofficially (more likely but not confirmed), starting ~February 24
E06-007:
Study correlations and relativistic effects in nuclear medium
Measure cross sections for low-lying 207Tl states for pm < 500 MeV/c
Extract ATL for pm < 300 MeV/c
Quasi-elastic xB=1 conditions, perpendicular kinematics
Fixed q=1.0 GeV/c, =0.433 GeV; Q2=0.81 (GeV/c)2
I = 100 µA

3. Past Hall A Experience with Pb
Test #1
0.5 mm Pb foil in “beer can” cell with flowing LH2 cooling
3 foils, at 45°, 1” apart.
First upstream foil survived I = 60 µA, with only horizontal raster
Expect single foil could take I > 60 µA with 4 x 4 mm2 raster
Test #2
Single-slot target-ladder block designed for PREX experiment
0.5 mm Pb foil “sandwiched” between two 0.15 mm diamond foils
Actively cooled – cryogen through block
Successfully tested with up to I = 80 µA
Calculations indicate OK with I = 100 µA
Difficulty with knowing beam spot position relative to target center
Conclusion: Pb target is feasible for I ≤ 100 µA

4. Simulations for Target Choice
Best available Hall A resolution will not cleanly separate low-lying Tl states
Peak extraction through peak fitting necessary
A successful peak fitting procedure was developed
GEANT simulations to assess attainable Em resolution
GEANT assumed Em profile and location of states are known
Both target configurations simulated
Result: Lead-Diamond sandwich preferred solution
Peak fitting works well even with modest number of counts to be fitted provided the line shape is known well.
Em profile will be determined experimentally by measuring a clean peak from 209Bi

5. Effect of Target Thickness-GEANT
Weighted sum
Weighted sum
0.5 mm Pb-No diamond sandwich mm Pb-No diamond sandwich
GEANT shows good peak extraction possible given good statistics

6. Choice of Pb Foil Thickness-GEANT
pm = 100 MeV/c missing mass spectra
0.1 mm Pb sandwich mm Pb sandwich
0.1 mm foil count rates too low
0.2 mm Pb is a good compromise between resolution and statistics
0.17 mm is effective thickness of 0.15 mm Pb foils at 30°

7. Present Plan for E06-007 Pb Target
Single-slot target ladder block
Similar design to previously tested target block (Test #2)
Design details TBD (by target group)
Have requested active cryo-cooling
Pb sandwich:
0.15 mm 208Pb foil
2 x 0.15 mm diamond foils
Positioned at 30° toward HRS-p
Bi sandwich:
0.20 mm 209Bi foil – measure line shape of a clean lead-like peak
Other targets on ladder:
Carbon (thickness TBD) – for background studies
BeO
Beam Current: 100 µA