The PrimEx-I Beam line

The PrimEx-I Beam line

A. Gasparian PrimEx-II Beam Line, August 5, 2010

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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


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MC Results for PrimEx-I confogureation:Beam Background on HyCal:

XY Distribution (for illustration)

Charged Particle Distribution on HyCal Photon Distribution on HyCal


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Step #1: What if we take the Permanent Magnet off from the beam line?

(Charged Particles only, for now)

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!!!

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%)


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Step #1: What if we take the Permanent Magnet off from the beam line?

(All Particles now)

Conclusion #2 Permanent magnet does not cut the Photon component of the background. But, the total net effectis ~30% reduction for 7KG

We need Permanent Magnet!!!

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%)


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Step#2: Different Diameter Pb-Shieldings(Bperm=7KG (current one), for now)

Charged ParticlesEffect of the Pb-shield diameteron 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!!!


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Step#2: Different Diameter Pb-Shieldings(Bperm=7KG (current one) for now)

Photons OnlyEffect of the Pb-shield diameteron 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!!!


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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 (33,120 58%Charged particles (24,210) 42%

Conclusion # 5 For this case Photon to Charged Ratio is about 50:50

Try to increase the Permanent Magnet !!!


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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 fieldin permanent magnet is needed.

We need smaller diam. Pb-shieldingAnd higher Bdl permanent magnet !!!


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XY-Distribution on HyCal for 0.8 “ Pb-Shielding (Bperm = 0 KG)

Charged Particle Distribution on HyCalPhoton Distribution on HyCal


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Conclusion # 7

Next question is: do we gain if we try to extend the distance from Collimator to Pb-shielding ?

MC simulations show that the optimum configuration for the PrimEx-II Beam line is:1)Pb-shielding with the 0.8” diameter hole;2)Permanent magnet with either one element (7KG) or two (14 KG)


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Effect of Moving Down the Target and PS (+50 cm) on Beam Background

for 0.8” diameter Pb-Shielding, All ParticlesRelative 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 fieldin permanent magnet is needed.



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Effect of Moving Down the Target and PS (+50 cm) on Beam Background for 0.8” diameter Pb-Shielding, Charged Particles

Conclusion # 8



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Effect of Main Collimator “Tapering” on Background

Charged Particles, 14 KG

Conclusion # 9

Tapered Collimator is better

Everything is the same as was in the Previous slide only the down half of the Permanent magnet is “tapered” by 1 mm

Relative efficiency of the main Collimator

PrimEx-I Conf., + 50 cm down, Bperm=7 KG existed collimator 100 % 1 mm tapered collimator 74 %


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Effect of Main Collimator “Tapering” on Background Photons, 14 KG

Conclusion # 10






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All Particles, 14 KG

Conclusion # 10






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All Particles, 21 KG

Conclusion # 10






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All Particles, 21 KG, 2 mm “tapering”

Conclusion # 11

1mm wall tapered Coll. is enough!





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Final Comparison of Background Net GainAll Particles

Conclusion # 12

We expect ~5 times less background!

The old PrimEx-I configuration vs. the Suggested new PrimEx-II configuration: (+50 cm, 21 KG perm. mag, 1mm tapered Collimator)

Relative gain:

PrimEx-I conf. 100 % sugg. PrimEx-II conf. 19 %


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Summary++

Based on the current Monte Carlo simulations:

1)We do not need to increase the Pb-shielding diameter;

2)The background on HyCal is significantly less for the smaller diameterPb-shielding;

3) 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); 4)“Tapered” main Collimator is another factor of 2 more effective

5) D. Kashy’s suggested version #3 is the best for the PrimEx-II beam line

6) It will potentially reduce the background on HyCal by factor of 5

Ø Interactive Geant shows that +32 cm down for PS is not critical for the 0 run. Detail simulations for this part will be provided in next few days.

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The PrimEx-I Beam line