# Presentation: 478763

## Hall C Summer Meeting
5 August 2008

- 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

- 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

**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

**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)

**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

**lead**

- 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) 

**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

- Plug

**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

## Slide 20

## 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 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