Curved Solenoid Spectrometer

1
Curved Solenoid Spectrometer

• 06 11/17 Y.Takubo

2
Introduction

• PRIME experiment
• Conversion electrons should be identified from
  backgrounds.
• Many low momentum backgrounds are generated at
  the stopping target and the other materials.

Detector region

• Curved solenoid spectrometer
• Curved solenoid spectrometer will be located
• after the muon stopping target region.
• Purpose Momentum selection
• Low momentum backgrounds are rejected.
• Detector rate is suppressed.
• ? Clean and effective experiment can be realized.

Target region
Curved solenoid spectrometer
3
Momentum threshold v.s. background rate
DIO spectrum (Target Al)
10-2

• DIO (decay in orbit) spectrum has high energy
  tail.
• Energy threshold for DIO determines the
  background rate.

10-4
10-6
10-8
10-10
10-12
10-14
10-16
10-18

• High momentum threshold of transport in the
  spectrometer is better for B.G. rejection.
• 102 DIO/s for the threshold of 85 MeV/c and 1011
  stopping-m/s.

4
Required DIO reduction rate

• Required DIO reduction rate
• Calorimeter
• Acceptable event rate 1 event/ms
• Very large margin is taken.
• Decay constant of GSO 60 ns
• Required reduction rate lt10-5
• _at_ 10-11 stopping-m /s
• Tracker
• Limit of tracker rate can be higher than
  calorimeter.

Required DIO reduction rate is less than 10-5.
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Requirement to spectrometer

• Requirement to spectrometer
• Good B.G. rejection
• High momentum threshold to transport
• Good transport efficiency for conversion
  electrons

• Recipe to satisfy the requirement
• Curved solenoid
• Collimator in side spectrometer
• Field gradient in target region

Each component is explained.
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Curved solenoid

• Motion in a curved solenoid
• Charged particles drift to the vertical
  direction.
• Drift length in the curved solenoid
• Compensating field to keep the signal
• in the same vertical level

• p Particle momentum
• q Charge of particles
• B0 magnetic field
• qbend Solenoid bending angle
• q Particle angle to horizontal plane
• r Solenoid bending radius

• For effective momentum separation
• Large qbend
• Suppression of particle angle spread
• Small B0.

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Collimator inside spectrometer
collimator

• Backgrounds drift to upward.
• Only backgrounds hit a collimator located at
  upward side in the spectrometer.
• Backgrounds drift upward effectively.

B.G.
signal
collimator
Collimator inside the spectrometer helps
effective B.G. reduction.
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Field gradient in target region(1)

• Effect of field gradient
• Good B.G. rejection
• Small angle spread is better for momentum
  selection.
• Field gradient suppresses the angle spread to
  forward direction.
• Increasing signal yield
• Mirror effect tanqm Bmin/(Bmax - Bmin)1/2
• qm The critical angle to be reflected

Large field gradient is better for signal
acceptance and B.G. rejection.
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Field gradient in target region(2)

• Other effects of field gradient
• B.G. filter
• Beam B.G. can be reflected before target
  section.
• B.G. reduction performance should be checked.

10
Simulation setup

• Simulation setup
• Target region
• Target solenoid R90cm
• Target 17 layers with 200 mm
• Field gradient is applied.
• Spectrometer solenoid
• qbend 180 degree
• Collimator
• Size 10cm x 10cm
• Region 1090 degree
• Not optimized

Collimator
Stopping target
Field strength with the field gradient of 3T-1T
and spectrometer radius is 55cm
Bs (T)
Target region
Spectrometer
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Electrons after target section

• Electrons after target section is checked.
• Electrons are generated at all layer and each
  position in a layer uniformly.
• Signal 105 MeV/c
• B.G. 0105 MeV/c
• About 70 of signal is accepted by field
  gradient.

Signal momentum distribution after target
section for 3T-1T
Signal radial distance after target section for
3T-1T
PT (mm)
PZ (mm)
R (mm)
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Estimation of DIO rejection performance
Momentum v.s. transport efficiency
DIO rejection performance is estimated.

• Momentum v.s. transport efficiency
• DIO spectrum

3T-1T R for spectrometer 550mm
MeV/c
DIO spectrum for Al
DIO rejection performance
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DIO reduction rate for B01T
Spectrometer radius v.s. DIO rejection performance

• Estimation DIO reduction rate
• DIO reduction performance for B01T is studied.
• 3(4)T-1T
• DIO reduction of 10-8 can achieved for R4050cm
• 103 Hz (_at_1011stopping-m/s)
• Signal acceptance 0.3

10-2
10-4
2T-1T
10-6
3T-1T
10-8
4T-1T
600
700
900
500
800
R(mm)
Spectrometer radius v.s. signal acceptance
3T-1T
4T-1T
2T-1T
600
700
900
500
800
R(mm)
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DIO reduction rate for B00.5T
Spectrometer radius v.s. DIO rejection performance
The DIO reduction rate is improved by decreasing
B0. ? Reduction rate is checked by B00.5T.
10-2
10-4
10-6
2T-0.5T

• DIO reduction of 10-8 can achieved for R60cm
• 103 Hz (_at_1011stopping-m/s)
• Signal acceptance 0.4

4T-0.5T
10-8
3T-0.5T
600
700
800
900
R(mm)
500
Spectrometer radius v.s. signal acceptance
Almost the same performance as B01T ? Since R
becomes larger for B00.5T, 3(4)T-1T for
R4050cm is recommended for DIO rejection. Of
course, more reduction performance is better.
4T-0.5T
3T-0.5T
2T-0.5T
600
700
800
900
500
R(mm)
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Other possible B.G. sources
There are many B.G. sources to determine detector
rate other than DIO.

• DIO
• Protons and neutrons from muon capture
• B.G. by ms penetrating the target
• Protons and neutrons from solenoid
• Decay in flight
• Radiative muon capture
• Anti-proton
• Radiative p capture
• Cosmic ray muon
• Pion decay in flight

lt103 Hz by spectrometer
Especially important to estimate detector rate
Enough small (see LOI)

• No influence on detector rate
• Significant backgrounds to contaminate in signal
  region.

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Summary

• Curved solenoid spectrometer is studied with
  target section to reduce the detector rate.
• DIO B.G. can be rejected to 10-8 level with
  B01T and qbend 180 degree.
• Signal acceptance is about 0.3.
• B.G. rate other than DIO should be studied to
  know real detector rate.

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????????DIO????
????????????????????????????DIO?????????
??????????? ????????????(?)? DIO???????(?)

• DIO????
• 4T,3T lt 2.3 x 10-4(MC?????)
• 2T 10-3
• ????????????????DIO???????
• ???????????????????????
• ?????3T-1T?R600mm?????
• Ee???????????
• ???B.G.??????????

4T-1T
3T-1T
2T-1T
4T-1T
3T-1T
2T-1T
MC?????
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?????????DIO????(1)

• ?????
• D ? qbend/B0
• qbend?B01T??10-6
• 90C.L.??lt2.3 x 10-4 (MC?????)
• 1011stopping-m/s??105Hz
• ?????????

?????????????B.G.???????
3T-1T R600mm
MeV/c

• qbend??????B0?????????????
• B01T??lt60MeV????
• B00.5T??lt80MeV????
• ? B0?????????

3T-0.5T R600mm
MeV/c
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?????????DIO????

• ????
• ?????????? R900mm
• ????? 200mm 17layer
• ???? B.G.??
• 9layer?????????
• ??
• ???? B.G.??
• ?layer???????????

• ?????????????0.4 (??0.4)
• ?????3T-0.5T????DIO?10-8?????? (??10-9)

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?????????DIO????

• ????
• ?????????? R900mm
• ????? 200mm 17layer
• ???? B.G.??
• 9layer?????????
• ??
• ???? B.G.??
• ?layer???????????

• ?????????????0.4 (??0.4)
• ?????3T-0.5T????DIO?10-8?????? (??10-9)

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Signal acceptance
Field gradient v.s. signal acceptance at the
entrance of the spectrometer
??????????????????(????)
R900mm????????
4T-1T
2T-1T
3T-1T
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B.G. transport efficiency
Transport efficiency is compared with different
magnetic field.
Momentum v.s. transport efficiency
3T-1T R600mm
For 1T, momentum threshold to transport is about
60 MeV/c.
MeV/c
For 0.5T, Momentum threshold becomes about 80
MeV/c.
3T-0.5T R600mm
Low B is effective to realize high momentum
threshold.
MeV/c
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DIO reduction rate
Spectrometer radius v.s. DIO rejection performance

• Estimation DIO reduction rate
• Electrons are generated at all layer and each
  position in a layer uniformly.
• 4T-1T 10-7 for R60cm
• 104 Hz (_at_1011stopping-m/s)
• 3(4)T-0.5T 10-8 for R60cm
• 103 Hz (_at_1011stopping-m/s)

10-2
10-4
2T-1T
10-6
3T-1T
10-8
4T-1T
600
700
900
500
800
R(mm)
10-2
10-4
DIO rejection performance for 0.5T is better by
one order than 1T.
10-6
2T-0.5T
4T-0.5T
10-8
3T-0.5T
600
700
800
900
R(mm)
500
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Signal acceptance

• Estimation acceptance
• Acceptance for conversion signal is estimated.
• Accep. at target section x Trans. Eff.
• Not transport efficiency
• Electrons are generated at all layer and each
  position in a layer uniformly.
• 4T-1T 0.4 for R60cm
• 3(4)T-0.5T 0.4 for R60cm

Spectrometer radius v.s. signal acceptance
4T-0.5T
3T-0.5T
2T-0.5T
Signal acceptance for 1T and 0.5T is the same
level.
600
700
800
900
500
R(mm)
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Current option for spectrometer design

• Option for reduction of DIO B.G. to more than
  10-8 level
• Easy option
• Field gradient 3(4)T-1T
• R for spectrometer 4050cm
• qbend 180 degree
• Advanced option
• Field gradient 3(4)T-1T
• R for spectrometer 60cm
• qbend 360 degree

• Since the DIO reduction performance seems to be
  enough, Easy option is taken as a base design.
• Of course, backgrounds can be more rejected with
  larger qbend and smaller magnetic field of
  spectrometer solenoid.