1. The PrimEx-I Beam line

2. MC Results for the PrimEx-I configuration. Beam Background on HyCal:
MC Results for the PrimEx-I configuration Beam Background on HyCal: Energy Distribution (arbitrary numbers)
(Photons)/(All)=(50,250/72,980)
= 69%
(Charged Part.)/(All)=(22,730/72,980)
= 31%
Charged particles dominate at E> 1 GeV
Photons dominate at E < 1 GeV
Pay attention the Y-scale is LOG
A. Gasparian
Hall B, June 1, 2009

3. MC Results for PrimEx-I confogureation:. Beam Background on HyCal:
MC Results for PrimEx-I confogureation: Beam Background on HyCal: XY Distribution (for illustration)
Charged Particle Distribution on HyCal
Photon Distribution on HyCal
A. Gasparian
Hall B, June 1, 2009

4. Step #1: What if we take the Permanent Magnet off from the beam line
Step #1: What if we take the Permanent Magnet off from the beam line? (Charged Particles only, for now)
Effect of the Permanent Magnet Field
On the CHARGED background:
Bperm=0 KG, total Number=42,680 (188%)
Bperm=7 KG (the Current)= 22,730 (100%)
Bperm=14 KG (doubled) = 7,769 (34%)
Conclusion #1
Permanent magnet effectively cuts
the Charged background at less than
~1 GeV range.
Total efficiency is a factor of 2.
We need Permanent Magnet!!!
A. Gasparian
Hall B, June 1, 2009

5. Step #1: What if we take the Permanent Magnet off from the beam line
Step #1: What if we take the Permanent Magnet off from the beam line? (All Particles now)
Effect of the Permanent Magnet Field
on all particle background:
Bperm=0 KG, total Number=95,170 (130%)
Bperm=7 KG (the Current)=72,980 (100%)
Bperm=14 KG (doubled) = 47,600 (74%)
Conclusion #2
Permanent magnet does not cut
the Photon component of the
background.
But, the total net effect
is ~30% reduction for 7KG
We need Permanent Magnet!!!
A. Gasparian
Hall B, June 1, 2009

6. Step#2: Different Diameter Pb-Shieldings (Bperm=7KG (current one), for now) Charged Particles
Effect of the Pb-shield diameter
on charged particle background:
Diam.= 2.5”, total Number=32,050 (141%)
diam.=1.53”(the Current) =22,730 (100%)
diam.=0.8” = 8,801 (39%)
Conclusion # 3
Pb-shield effectively cuts
the Charged background at less than
~2 GeV range. Total efficiency is
about factor of 2.5
We need smaller diam. Pb-shielding!!!
A. Gasparian
Hall B, June 1, 2009

7. Step#2: Different Diameter Pb-Shieldings (Bperm=7KG (current one) for now) Photons Only
Effect of the Pb-shield diameter
on Photon background:
Diam.= 2.5”, total Number=56,160 (112%)
diam.=1.53”(the Current) =50,250 (100%)
diam.=0.8” = 28,970 (58%)
Conclusion # 4
Smaller diam. Pb-shielding effectively
cuts the Photon background also.
Total efficiency: factor of ~2
We need smaller diam. Pb-shielding!!!
A. Gasparian
Hall B, June 1, 2009

8. Background Relative Composition for 0.8” Pb-Shild and Bperm = 0 KG
Relative composition of particles for
0.8 inch diam. Collimator and Bperm = 0 KG
All particles > 0.1 GeV (57,330) 100%
Photons (33, %
Charged particles (24,210) 42%
Conclusion # 5
For this case Photon to Charged
Ratio is about 50:50
Try to increase the Permanent
Magnet !!!
A. Gasparian
Hall B, June 1, 2009

9. Effect of Bperm on Charged Background for 0.8” diameter PB-Shielding
Relative cut efficiency of the Permanent
Magnet for the fixed collimator
(0.8 inch diam.)
B(perm. m.) = 0 KG 100%
B(perm. m. ) = 7 KG 36%
B(perm. m.) = 14 KG 10%
B(perm. m.) = 21 KG 5%
Conclusion # 6
For 0.8” Pb-shielding 7 KG or more field
in permanent magnet is needed.
We need smaller diam. Pb-shielding
And higher Bdl permanent magnet !!!
A. Gasparian
Hall B, June 1, 2009

10. XY-Distribution on HyCal for 0.8 “ Pb-Shielding (Bperm = 0 KG)
Photon Distribution on HyCal
Charged Particle Distribution on HyCal
A. Gasparian
Hall B, June 1, 2009

11. XY-Distribution on HyCal for 0.8 “ Pb-Shielding (Bperm = 7 KG)
Photon Distribution on HyCal
Charged Particle Distribution on HyCal
A. Gasparian
Hall B, June 1, 2009

12. XY-Distribution on HyCal for 0.8 “ Pb-Shielding (Bperm = 14 KG)
Photon Distribution on HyCal
Charged Particle Distribution on HyCal
A. Gasparian
Hall B, June 1, 2009

13. Conclusion # 7
MC simulations show that the optimum configuration for the PrimEx-II
Beam line is:
Pb-shielding with the 0.8” diameter hole;
Permanent magnet with either one element (7KG) or two (14 KG)
Next question is:
do we gain if we try to extend the distance
from Collimator to Pb-shielding ?
A. Gasparian
Hall B, June 1, 2009

14. Effect of Moving Down the Target and PS (+50 cm) on Beam Background for 0.8” diameter Pb-Shielding, All Particles
Relative cut efficiency of the Permanent
Magnet for the fixed collimator
(0.8 inch diam.)
PrimEx-I Conf., Bperm=7 KG 100%
+50 cm, Bperm = 7 KG 41%
+50 cm, Bperm =14 KG 35%
Conclusion # 7
For 0.8” Pb-shielding 7 KG or more field
in permanent magnet is needed.
We need smaller diam. Pb-shielding
And higher Bdl permanent magnet !!!
A. Gasparian
Hall B, June 1, 2009

15. Effect of Moving Down the Target and PS (+50 cm) on Beam Background for 0.8” diameter Pb-Shielding, Charged Particles
Conclusion # 8
We need smaller diam. Pb-shielding
And higher Bdl permanent magnet !!!
A. Gasparian
Hall B, June 1, 2009

16. Move down the Target, Pb-Shielding and PS for 50 cm, use that distance
Summary
Based on the current Monte Carlo simulations:
We do not need to increase the Pb-shielding diameter;
The background on HyCal is significantly less for the smaller diameter
Pb-shielding;
0.8” diameter is the smallest we can have. It can be done by inserting a
~10 r.l. ring inside of the existing beam pipe (Dave Kashy);
With that there are 2 options:
Leave the Collimator to Target distance as it is with the existing
7 KG Permanent Magnet;
Move down the Target, Pb-Shielding and PS for 50 cm, use that distance
to insert one more unit of Permanent Magnet (14 KG total).
This is the most desirable option if it is all possible for this short time.
A. Gasparian
Hall B, June 1, 2009