1. The PrimEx-I Experiment
Setup:
Photon tagger (upper 10%)
Pair Spectrometer
HyCal calorimeter
PrimEx-I achieved 2.8% precision (total):
(0) = 7.82 eV1.8% (stat)2.1% (syst)
PrimEx-I
7.82eV2.8%
Publication:
ready for submission to PRL
“… With the 2.8% total uncertainty, this result is a factor of 2.5 more precise
than the current PDG average of this fundamental quantity and it is consistent
with current theoretical predictions. …”
A. Gasparian
Hall B meeting, August 16, 2010

2. Upcoming PrimEx-II Experiment
PrimEx-II proposed 1.4% precision:
0.5% (stat.) 1.3% (syst.)
Precision test of chiral anomaly and
corrections to chiral anomaly in QCD
PrimEx-II
projected 1.4%
PrimEx-I
7.82eV2.8%
To achieve 1.4% precision:
Is a difficult task !!!
A. Gasparian
Hall B meeting, August 16, 2010

3. 1.4% Total Error in PrimEx-II: How to get it?
0.5 % Stat.
1.3 % Syst.
New DAQ with 5 kHz rate,
(factor of 5 gain) (work in progress)
Implement more stringent trigger (factor of 2 gain)
(better HyCal gain equalizing)
However, the allocated time is barely enough for one target only with 0.5% stat error.
Better control of Background:
Add timing information in HyCal
Improve photon beam line
Improve PID in HyCal (add more veto
counters, X and Y direction)
Measure HyCal detection efficiency
(with TAC module)
A. Gasparian
Hall B meeting, August 16, 2010

4. Improvements in Photon Beam Line
Make the primary collimator “tapered”:
(with 1 mm thick and 10 cm long insertion,
diameter 12.7 mm).
Upgrade the Permanent Magnet from
1 unit to 3 units.
Make the Pb-shielding wall’s hole
diameter smaller (from 1.53” to 0.8”).
Extend distance from primary coll. to
Pb-shielding wall by 32 cm
(moving PS with production targets).
Total relative gain:
PrimEx-I config %
suggested PrimEx-II config %
Expect ~5 times less background events !!!
A. Gasparian
Hall B meeting, August 16, 2010

5. Add Timing in HyCal
A. Gasparian
Hall B meeting, August 16, 2010

6. Participation in PrimEx-II
PrimEx-I got critical help from Hall B Staff and Engineering group – THANK you!
More help needed for PrimEx-II – THANK you!!!
A. Gasparian
Hall B meeting, August 16, 2010

7. Add Timing in HyCal Simple version Limitation:
Each dynode output goes to one of 36
Inputs of UVA120A sum module.
Two analog outputs from
UVA120A go to “electronics area”
One of them used for further summation,
The second one was not used in the
PrimEx-1 configuration.
Simple version
Use the second signal (cable) for the timing;
Needs
52 Discriminator channels
52 TDC channels
Limitation:
timing information only from groups.
A. Gasparian
Hall B meeting, August 16, 2010

8. The PrimEx-I Beam line