SHMS Optics Studies

1. SHMS Optics Studies Tanja Horn JLab 18 January 2008 JLab Hall C meeting

2. SHMS experiment requirements • Hall C 12 GeV experiments can be categorized according to their requirements for understanding the SHMS acceptance • L/T separations (e.g. Fπ, factorization) require pt-to-pt systematic of 0.4% in a momentum region of -15% to +10% • Asymmetry measurements ok with 1.0-2.0% systematic L/T separations

3. Context • The purpose of the collimator is to define a geometrical acceptance in which the spectrometer optical properties are sufficiently well understood • Acceptance depends on dp/p (δ) and target length • Characterized through event loss: Acceptance=1-loss • Geometric effects (apertures) – well understood • Efficiency of the optical transport – more difficult to model • Sieve slit allows for studies of the variation of optical properties over the full solid angle acceptance of the spectrometer • Populate a region simultaneously with many particle trajectories

4. SHMS horizontal acceptance -10% < δ< +22% • Acceptance limited by well known magnet sizes and magnet gradients • Losses before the dipole are dominated by the aperture of Q1 • The figure shows the δdependence of the acceptance after the quadrupoles • Events in the red region fall outside of at least one of the nominal detector apertures • The green lines denote the acceptance determined by the nominal detector configuration

5. y SHMS collimator placement • 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

6. Collimated SHMS acceptance Slit at 110 cm (HB) Slit at 267 cm (Q1) • Acceptance excludes losses before the dipole and detector geometry • The yellow and blue bands indicate the maximum δ range for L/T separations at positive δ

7. 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

8. Collimated SHMS acceptance corrected for loss at the dipole entrance Slit at 110 cm (HB) Slit at 267 cm (Q1) • Acceptance shows losses inside the dipole and exit • Understanding of losses inside the dipole could be improved through optics studies using actual data or precise mapping of the fields

9. SHMS Collimator Summary • Small collimator could be used for L/T separations • good understanding of acceptance function • In general, size of the collimator depends on the target length • Effective target length for all L/T separations is <3cm • May need a special small collimator for extended targets typically used in asymmetry measurements • Large collimator also possible if rates more important than systematics • Shape: octagonal, material: heavymet • thickness: same as for HMS (6.3cm), but still under study • dimensions in x and y depend on location in z – both locations in front of HB and Q1 would be possible • Mechanical design: currently fixed, but moving design may also be feasible

10. SHMS sieve slit design Z=110cm Z=267cm • Sieve slit is used to understand the optics properties the spectrometer • Figures show simulations of possible sieve hole configurations • 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

11. SHMS Optics: plans • Implement real magnets in the Monte Carlo • Current SHMS Monte Carlo uses ideal magnets • HB field map differences – effect on optics • Initial check by J. LeRose using SNAKE • Final studies will be done using COSY after real magnets are implemented

12. Study of SHMS detector sizes • Nominal target length and angle set by approved experiments • 40cm target, 40deg • Scattering chamber can accommodate 50cm targets Beam envelope at selected detector locations Values are given for the back of the detectors

13. SHMS further studies • SHMS horizontal bender prototype tests for radiative heating studies • Performed prototype tests in summer 2006 • Analysis is complete • Improvement of MC requires more data • Additional measurement near end of GEp with improved sensitivity less than 100 mK • Detector hut shielding • Initial estimate from PDG: 1-2m concrete • More detailed simulation for SHMS structure review in March 2008 D Q3 Q2 Q1 HB SHMS 18° vertical bend

14. SHMS information updates • Documentation about SHMS R&D and upgrade in Hall C 12 GeV database • http://www.hallcweb.jlab.org/doc-public/DocumentDatabase • User: 12gev • Password: xxxxxxxx (hornt@jlab.org for password) • Updates to the 12 GeV web site currently are currently located here: • http://www.jlab.org/~hornt/hallc_12gev/hallc_12gev.html • Links to: • Experiment requirements • Document database • SHMS Optics studies Nominal SHMS parameters • Other 12 GeV links: • Monte Carlo • Spectrometer Layout