Hall C Users Meeting 31 January 2009

1. SHMS Optics Update Tanja Horn Hall C Users Meeting 31 January 2009

2. SHMS Optics Configuration • Need 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 • Most reasonable configuration: HBQQQD Focal Plane HB Q1 Q2 Q3 DIPOLE Deflection= 18.4 ° Deflection=3 °

3. Q1 Q2 Q3 D Collimator reduces uncertainties due to optics +10% < δ< +15% • Event loss at Q1 due to geometric effects • Acceptance at dipole entrance depends on aperture and δ • Events at negative δ are focused more • Collimator can eliminate events that would be lost inside the dipole • Reduces model dependent systematic uncertainty

4. Sieve Slit for Spectrometer Optics • Sieve slit is used to understand the optics properties the spectrometer • Figures show HMS sieve slit reconstruction data HMS H. Blok, T. Horn, G. Huber et al., Phys. Rev. C78 (2008)

5. HMS collimator/slit system • Sieve slit • 0.508 cm holes in 7 (9) columns at 1.524 cm (2.540 cm) intervals in the horizontal (vertical) direction • Center of sieve slit at 168 cm from target center • No holes at +1.524/+2.540 cm and -1.524 cm/-5.080cm for orientation checks • Outermost holes are at ±10.160 cm (±60.5 mr) • Octagonal collimators • 6.35 cm thick heavymet (90% W, 10% CuNi) HMS Collimator box D Q2 Q1 Q3

6. y SHMS collimator/sieve system • Sieve collimator in front of HB: standard optics calibration may be complicated • Aperture defining slits: best location in front of HB • Sieve collimator in front of Q1: optics modeling straightforward, but have to assume that perturbations due to HB are small Possible sieve collimator locations HB Q1 Q2 Q3 D x • Design will be octagonal shape • Dimensions depend on location in z

7. Place SHMS collimator after HB HB Q1 SHMS collimator box • No room before HB for collimator box with collimator(s) and sieve slit • Assume front of collimator is at 82 cm after the HB center or at 2.58 m from the pivot • Collimator is then ±0.055*258=±14.2 cm high and • ±0.030*258=±7.7 cm wide • Assume heavymet material for ±5cm at least need 40cm by 25cm per collimator

8. Slit Box Design Limitations: Width Slit box Q2 SHMS Q1 HB Guiding rod options: HMS • 35-cm wide slit box is possible • Move horizontally from SHMS left to beam axis • Mechanical (surveyed) stop at SHMS right • Guiding rods (w/ tooling balls) on top and bottom • Two options: guiding rods in the back or to sides

9. Slit Box Design Limitations: Depth • Analogous to HMS design, assume octagonal collimator thickness 6.4 cm • Sieve slit is thinner (e.g., HMS: 3.175 cm thick) Two octagonal collimators • Also take into account additional material for support etc. Sieve slit

10. SHMS Slit Box in Hall C Slit box fits between HB and Q1 • Front of slit box is 80 cm after the HB center, or at 2.56 m from target center • Sufficiently far away from HB to have minimum stray field

11. SHMS sieve slit design • Standard calibrations of SHMS with the sieve before Q1 possible • Preliminary simulations show small distortions of mid-plane symmetry • FP pattern of sieve before HB shows strong delta dependence of the bending z=120cm z=258cm • Size of sieve holes: 3 mrad • For comparison: HMS sieve holes diameter is 0.504cm (3 mrad) • Further studies of the focal plane patterns will determine the optimal design for optics reconstruction

12. Additional Sieve Slit before HB Special calibration sieve slit HB Q1 120 cm from target center • Assume front of sieve slit is 56 cm in front of HB center or at 1.20 m from the pivot • Need to cover at least ±0.055*120cm=±6.6 cm high and • ±0.030*120cm=±3.6cm wide for a point target • Assume heavymet material for ± 5 cm at least at the edges • Assume 30 cm wide by 25 cm high sieve (note: HB gap is 35cm by 36 cm) • Weighs about 40 kg, so movable by hand

13. Design Limitation: height of the sieve slit Special Sieve Slit Q2 SHMS Q1 HB HMS • Additional sieve slit (simple hand motion) before HB • Move horizontally from SHMS left to beam axis • Only inserted for special calibration runs

14. Design Limitation: depth of the sieve slit • Analogous to HMS design, assume octagonal sieve slit thickness 3.2 cm • But cannot forget about additional materials for support

15. Next Steps • Additional studies for understanding the optical properties of the SHMS including HB • Look how HB distorts the “image” of a collimator or sieve slit in front of it. • How does an entrance octogonal look like in position and angle space at the planned location at the entrance of Q1 – can easily be done using HB TOSCA HMS Q2 Q1’ Beamline Bender • Short report on simulation results • Optimization of the distance between and the size of the Q1 sieve holes and the special calibration sieve slit before HB HMS Q1 • Additional techniques for calibration techniques • Possibilities of H(e,e’p) for calibrations especially the HB part Target

16. Backup material

17. Q1 sieve

18. Special calibration sieve

19. Target Region Slot in Q2 for Beamline Slot in Q1’ for Beamline Vertical Slot in HB for HMS Q1 at 12° Slot in HB for Beamline