shms optics and background studies tanja horn hall c summer meeting 5 august 2008
TRANSCRIPT
SHMS Optics and Background Studies
Tanja Horn
Hall C Summer Meeting
5 August 2008
SHMS Experiment Requirements
• Charged particle detection with momenta up to the beam energy (11 GeV) at forward angles down to 5.5° even with HMS at small angles
• Well understood acceptance function to perform L/T separations
• High luminosity to measure small cross sections also requires well-shielded detectors
Experiment Target SHMS Angles (deg)
Momentum
(GeV)
Fpi12 8-cm 5.5-13 .0 2.261-8.070
Measurement of R in SIDIS
15-cm 5.5-20.0 5.40-5.80
Pion Factorization 8-cm 5.5-23.0 2.42-8.52
x>1 15-cm 8.0-16.0 4.80-10.60
g2, (A1N) 40-cm 11-15.5, (5.5-30.0) 2.25-7.50
GEp 30-cm 15.7-25.0 4.03-8.35
SHMS/HMS in Hall C
SHMS: dQQQD
HMS: QQQD
• SHMS scattering angle range: 5.5 to about 40 degrees
• SHMS can reach 5.5° with HMS at 12.5°
SHMS Layout
Electron beam
SHMS Acceptance
• Solid angle >4.5 msr for all angles
• Using a SHMS MC similar to the one used for the HMS
• Optics model will be updated to SHMS2008 this Fall, but expect no significant changes
50-cm target viewed at 90 degrees
Vertical: ± 35 mrad Horizontal: ± 65 mrad
SHMS detector size summary
• Nominal target length and angle set by approved experiments– 40cm target, 40deg
• Scattering chamber can accommodate 50cm targets
Detector Z
(cm)
Xsize
(cm)
Ysize
(cm)
NG Cerenkov -310 to -60 70 80
DC1 -40 75 80
DC2 +40 85 90
HG Cer +70 to +250 115 100
Calorimeter +280 to +360 130 120
Values are given for the back of the detectors
Beam envelope at selected detector locations
SHMS resolution
Δp/p (%) Δφ (radians) Δθ (radians)
-10% +22%
Spec’d Resolution
2x Spec’d Resolution & MCS
Experiment p (GeV)
Δp/p (%) Δθ (rad) Δφ (rad)
Pion Form Factor 2.2-8.1 2x10-3 1.5x10-3 1.5x10-3
Transition Form Factors*
1.0-8.5 1x10-3 1.0x10-3 1.0x10-3
SHMS Detectors and Shielding
Calorimeter PMTs
• Due to space requirement of the SHMS detector stack cannot have a uniform back concrete wall • Need window to access calorimeter PMTs for
maintenance etc.
Hall C Radiation Sources
Target Beam dump
Beam line
Electron beam
• Radiation is produced by interactions of the beam with material in the hall• There are three main sources of radiation in Hall C:
• Target, beam line, and beam dump
Radiation Types
• Scattered electrons• Produce radiation
• bremsstrahlung is the dominant process except at very low energy
• Neutral particles: photons and neutrons• Have a higher penetration power than charged particles• Are attenuated in intensity as traverse matter, but have no continuous
energy loss• Thickness of attenuating material vs. penetrating power
• Photons interact primarily with electrons surrounding atoms• Neutrons interact with nuclei
• Hadrons: protons, pions• Hadronic cross sections are small• 1m of concrete almost fully stops 1 GeV protons
HMS Shielding as Example
HMS shield house
Target
• The HMS shielding design provides good shielding for the detectors • The shielding of the electronics is sufficient down to angles of 20° (F1TDCs!)
SHMS Shielding Issues
• Experience shows that a shield house design like the HMS is a good solution, but the SHMS has additional requirements
Detectors
Space requirements at beam side at forward angles
Design of the back of the hut accounting for length of the detector stack
Electronics
Increased sensitivity of new SHMS electronics
Separate Electronics
Room
Proposed SHMS Shielding Design
1
2
3
4
5
6
100 cm concrete
Detector Hut
Electronics Hut
200 cm concrete
63.5 cm concrete
63.5 cm concrete
90 cm concrete
5 cm boron
5 cm lead
400x400x800cm
20 cm
50 cm
Electron beam
shield wall
Front Wall (1)
• The outgoing particle spectrum is soft (<10 MeV)
• Take electronics in the HMS at 20° as a relative starting point• Recent F1 TDC problems seem to dominate at lower angles
• Full Hall C GEANT simulation (includes walls, roof, floor, beam line components) suggests optimal front shielding thickness of 2 m
Addition of Lead and Boron to Front Wall
• 2 m of concrete reduce the total background flux for SHMS at 5.5° to half of HMS at 20°
• Boron eliminates the thermal neutron background, BUT produces 0.48 MeV capture γ’s
• Adding lead reduces the low energy photon flux and absorbs capture γ’s
leadconcreteboron
200 cm 5 cm 5 cm
• Radiation damage assumption: photons <100 keV will not significantly contribute to dislocations in the lattice of electronics components, while neutrons will cause damage down to thermal energies
Beam Side Wall (2)
• Beam side wall constraint is 107 cm total• Given by clearance between detector stack and side wall
• Optimal configuration: 90 cm concrete + 5 cm boron + 5 cm lead layer• Boron works like concrete, but in addition captures low energy neutrons
SHMS Back Shielding Configuration (5)
• Introduce a concrete wall to shield from the dump
• Example: shielding during the G0 experiment
Hall C top view
beam
HMS, 20°
Shield wall
• Adding the shield wall has the largest effect at forward angles• Reduces the rate at 5.5° by about a
factor of two
SHMS Back Shielding Configuration (6)
• Drawback: limits the maximum spectrometer angle to 35°
• 5°/0.5 m
GEANT3: Hall C top view
target
beam
HMS, 20°
SHMS electronic hut
SHMS detector hut
Plug
50cm
20cm
To beam dump
Cerenkov Calorimeter
Shield wall
Length (m) Max. Scattering Angle (deg)
24 27
23 35
22.5 39.5
• Add a concrete plug of 20-50cm thickness
• Suppresses low-energy background flux further to an acceptable level
SHMS Shielding Summary
• The separate electronics hut provides for even better radiation shielding
• The SHMS shield hut wall thicknesses have been optimized to provide proper shielding for the detectors
SHMS Design Parameters
• Using a SHMS MC similar to the one used for the HMS• Optics model will be updated to SHMS2008 this Fall, but expect no
significant changes
SHMS Back Configuration
SHMS at 5.5°
• Rates without additional shielding from radiation from the beam dump• At 20°, SHMS rates are comparable
to those for HMS• At forward angles, the SHMS rates
are about factor of two higher
Hall C top view
SHMS Back Shielding: (5) and (6)
Configuration Background Flux at forward angles
(norm)
No shield wall, no plug
1.9
Shield wall, 20-50cm plug
0.7
• Background rates comparable for both shielding options
• Adding thin plug provides more efficient shielding from low-energy background
• Depends on spectrometer angle