SHMS Optics Studies Tanja Horn JLab Hall C

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

SHMS experiment requirements • Hall C 12 Ge. V 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 Experiment Target SHMS angles (deg) Fpi 12, P 12 8 -cm 5. 5 -13 (~23) R=σL/σT 15 -cm 5. 5 x>1 15 -cm 8. 0 -16. 0 g 2, (A 1 N) 40 -cm 11 -15. 5, (5. 5 -30. 0) GEp 30 -cm 15. 7 -25. 0 PV LD 2 40 -cm 13. 5 L/T separations

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

SHMS horizontal acceptance • Acceptance limited by well known magnet sizes and magnet gradients • Losses before the dipole are dominated by the aperture of Q 1 • The figure shows the δ dependence 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 -10% < δ < +22%

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 Q 1: optics modeling straightforward, but have to assume that perturbations due to HB are small Possible sieve collimator locations HB Q 1 Q 2 Q 3 • • D Design will be octagonal shape Dimensions depend on location in z y x

Collimated SHMS acceptance Slit at 110 cm (HB) Slit at 267 cm (Q 1) • 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

Collimator reduces uncertainties due to optics +10% < δ < +15% Q 1 Q 2 Q 3 D • Event loss at Q 1 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

Collimated SHMS acceptance corrected for loss at the dipole entrance Slit at 110 cm (HB) Slit at 267 cm (Q 1) • 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

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 <3 cm – 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. 3 cm), but still under study – dimensions in x and y depend on location in z – both locations in front of HB and Q 1 would be possible • Mechanical design: currently fixed, but moving design may also be feasible

SHMS sieve slit design Z=110 cm Z=267 cm • 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. 504 cm (3 mrad) • Further studies of the focal plane patterns will determine the optimal design for optics reconstruction

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. Le. Rose using SNAKE – Final studies will be done using COSY after real magnets are implemented

Study of SHMS detector sizes • Nominal target length and angle set by approved experiments – 40 cm target, 40 deg • Scattering chamber can accommodate 50 cm targets Detector Z (cm) Xsize (cm) Ysize (cm) Atm. Cer -310 to -60 70 80 DC 1 -40 75 80 DC 2 +40 85 90 C 4 F 10 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 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 m. K • Detector hut shielding – Initial estimate from PDG: 1 -2 m concrete – More detailed simulation for SHMS structure review in March 2008 D Q 3 SHMS 18° vertical bend Q 2 Q 1 HB

SHMS information updates • Documentation about SHMS R&D and upgrade in Hall C 12 Ge. V database – http: //www. hallcweb. jlab. org/doc-public/Document. Database • User: 12 gev • Password: xxxx (hornt@jlab. org for password) • Updates to the 12 Ge. V web site currently are currently located here: • http: //www. jlab. org/~hornt/hallc_12 gev. html Links to: – Experiment requirements – Document database – SHMS Optics studies Other 12 Ge. V links: – Monte Carlo – Spectrometer Layout Nominal SHMS parameters