1. Luminosity Monitor based on Forward Elastic Scattering Hampton University, Hampton, VA 23668 Jefferson Laboratory, Newport News, VA 23606 OLYMPUS Collaboration Meeting, DESY, Feb. 23 – 24, 2010 Michael Kohl

2. Electrons/positrons (100mA) in multi-GeV storage ring DORIS at DESY, Hamburg, Germany Unpolarized internal hydrogen target (buffer system) 3x10 15 at/cm 2 @ 100 mA → L = 2x10 33 / (cm 2 s) Large acceptance detector for e-p in coincidence BLAST detector from MIT-Bates available Measure ratio of positron-proton to electron-proton unpolarized elastic scattering to 1% stat.+sys. Redundant monitoring of (relative) luminosity (ratios) to ~1% per hour Proposed Experiment

3. Moller/Bhabha scattering - 1.3 degrees for symmetric Moller setup - requires knowledge of Moller/Bhabha cross sections Monitoring the Luminosities Pressure, temperature, flow, current measurements - limited in precision Small-angle elastic scattering - high count rate, no TPE at high epsilon / low Q 2 - single-arm and in coincidence with recoil proton - event-by-event with full track reconstruction - different acceptances for e + and e -

4. Luminosity monitors for lepton in coincidence with recoil proton detected in the opposite sector ~12 o Luminosity Monitors: Telescopes 2 forward tGEM telescopes, 1.2msr, 12 o, R=187/237/287cm, dR=50cm, 3 tracking planes Proposed version included in OLYMPUS TDR Sept. 2009 TOF

5. Forward Elastic Luminosity Monitor Forward-angle electron/positron telescopes with good angular and vertex resolution Coincidence with proton in opposite sector of main detector Single-arm tracks Two telescopes with 3 triple-GEM detectors, left-right symmetric High rate capability GEM technology MIT protoype: Telescope of 3 Triple GEM prototypes (10 x 10 cm 2 ) using TechEtch foils F. Simon et al., NIM A598 (2009) 432

6. Luminosity Monitors: Count rate Two symmetric GEM telescopes at 12 o Two-photon effect negligible at high-ε / low-Q 2 Sub-percent (relative) luminosity measurement per hour at 2.0 GeV Readout pitch of MIT prototype: 635  m; COMPASS: 400  m Number of electronics channels per telescope: 3x(100+100)/0.635 ~= 1000 (1500) 1.2 msr = 10 x 10 cm 2 at ~290 cm distance (rearmost plane) Three GEM layers with ~0.1 mm resolution with ~50 cm gaps → Match vertex resolution (z) of ~ 0.1 – 1 cm at 12 o with proton in BLAST Proposed version included in OLYMPUS TDR Sept. 2009

7. Providing GEM detectors Collaboration HU-MIT-Rome –TechEtch/MIT to provide tested GEM foils –Rome: Readout system developed for Hall A / SBS –Assembly of detectors at HU or Bates –Testing at HU / HUPTI / Jlab / DESY Establishing a GEM Lab at Hampton University –New research building to become available spring 2010 –Luminosity monitors for OLYMPUS (2009-2011) –C0 cylindrical and C1 planar GEM trackers for Time Reversal Experiment with Kaons (TREK) at J-PARC (~2013) –Augment 12 GeV program at Jlab (~2015) Funding: –Secured NSF Nuclear Physics/ARRA basic research grant ($405k) postdoc + travel; 1 graduate student supported by HU NSF group –Secured $216k within NSF MRI-R2 for luminosity monitors (125k), 1 graduate stipend + travel for commissioning

8. Tasks & Timeline for LuMo Construction New research building at HU to be move-in ready begin of 2010 MRI-R2 grant has been secured with $216k, of which $125k are equipment Testing with beam possible at HUPTI or Jlab in fall 2010; DESY? Integration of GEM readout system / summer-fall 2010 (Rome group) Development of analysis software / integrate into OLYMPUS analysis

9. Control of Systematics i = e+ or e- j= pos/neg polarity Geometric proton efficiency: Ratio in single polarity j Geometric lepton efficiency: Simple scheme to cancel detector efficiencies

10. Control of Systematics Super ratio: Cycle of four states ij Repeat cycle N times -> reduction of systematics by √N Change between electrons and positrons once a day Change BLAST polarity regularly, randomly Left-right symmetry = redundancy Monte Carlo studies Further (small) corrections for individual acceptances Small effects by backgrounds and inefficiencies Effects from beam sizes and offsets (~1%/mm)

11. Luminosity Monitoring Forward-angle (high-epsilon, low-Q) elastic scattering (  e+ =  e- ) Measure L ij relatively (i.e. N ij fwd ) and continuously to ~1%/hour At forward angle: Analogous scheme applied to monitor luminosity

12. Differential cross section Event counts: Bin-averaged differential cross section: a(x k ) = Acceptance function Phase space integral Require acceptance simulation to determine phase space integral numerically!

13. Control of Systematics i = e+ or e- j= pos/neg polarity A = Acceptance function (phase space integral) Proton ”detection” efficiency: Ratio in single polarity j Lepton detection efficiency: MORE REALISTICALLY:

14. Triple super ratio Separately determine three super ratios Blinding of final result until put together Left-right symmetry = redundancy Triple Super Ratio: Cycle of four states ij Repeat cycle many times Ratio of acceptances (phase space integrals) Ratio of luminosities Ratio of counts

15. Luminosity Monitoring Forward-angle (high-epsilon, low-Q) elastic scattering (  e+ =  e- ) Measure L ij relatively (i.e. N ij fwd ) and continuously to ~1%/hour At forward angle: MORE REALISTICALLY:

16. Control of Systematics Change between electrons and positrons every other day Change BLAST polarity regularly, randomly Left-right symmetry = redundancy Determine ratios of phase space integrals from Monte-Carlo simulation Super ratio (“triple ratio”): MORE REALISTICALLY: Cycle of four states ij Repeat cycle N times -> reduction of systematics by √N

17. Monte Carlo Studies GEANT4 simulation: OLYMPUS.cc as of August 2009 Specify design parameters Size and locations of tracking planes; resolutions and residuals Phase space integral(s) / acceptance (solid angle) Effects of beam size and offsets on systematics HU graduate student Ozgur Ates

18. Monte Carlo Studies with Geant4 Resolutions Generated and reconstructed variables Theta, Phi, P, Z electron/proton Resolutions δZp, δTp, δPhp, δPp, δZe, δTe, δPhe, δPe Residuals: Redundancy of variables / elastic scattering 4 variables: Pp, Tp, Pe, Te 3 constraints: 3 conservation equations 4 – 3 = 1 (DEGREES OF FREEDOM) TeTp: Te – Te(Tp) TePe: Te – Te(Pe) TePp: Te – Te(Pp) -> 6 independent correlations Coplanarity: PhePhp:Phe – Php – 180 Common vertex: ZeZp:Ze – Zp

19. Event distributions Generated and reconstructed variables Z, Theta, P, Phi proton/electron All events (LuMo + BLAST)

20. Resolution study Generated and reconstructed variables Z, Theta, P, Phi proton/electron All events (LuMo + BLAST) versus LuMo only (gen. 8-13 deg. + tagged)

21. Resolution: generated-reconstructed 100mu, 50cm, LuMo+BLAST (Te=0-80 dg, Phe=+-15 dg) δZp δZe δTp δTe δPhp δPhe δPpδPe

22. Resolution: generated-reconstructed 100mu, 50cm, LuMo only (Te=6-13 dg, Phe=+-5 dg) δZp δZe δTp δTe δPhp δPhe δPpδPe

23. Left Sec. RESOLUTIONSProton DeltaZ Electron DeltaZ Proton DeltaTheta Electron DeltaTheta Proton DeltaPhi Electron DeltaPhi Proton DeltaP Electron DeltaP Config 0 100mu/50cm LuMo+BLAST0.80 mm0.72 mm0.094 Deg.0.089 Deg.0.14 Deg.0.10 Deg.32 MeV39 MeV Config 3 100mu/50cm1.70 mm1.68 cm0.59 Deg.0.15 Deg.0.55 Deg.0.39 Deg.21 MeV78 MeV Config 4 100mu/10cm 1.16 mm5.17 cm0.57 Deg.0.39 Deg.0.57 Deg.0.40 Deg.21 MeV260 MeV Config 5 50mu/50cm1.79 mm1.65 cm0.57 Deg.0.16 Deg.0.55 Deg.0.38 Deg.21 MeV77 MeV Config 6 50mu/10cm 1.75 mm3.74 cm0.62 Deg.0.29 Deg.0.57 Deg.0.38 Deg.21 MeV237 MeV Resolutions Large differences for LuMo+BLAST versus LuMo-only Minor improvement with 50mu resolution versus 100mu Significant improvement with 50cm gaps instead of 10cm

24. PeTp: Data Points(Pe:Tp) and Calculation(PeTp) 24

25. TpTe: Data Points(Tp:Te) and Calculation(TpTe) 25

26. Residuals (100mu/50cm) Te-TeTp Te-TePp Te-TePe Phe-Php Ze-Zp

27. Left Sec. RESIDUALS PpTp/ MeV PeTe/M eV PePp/ MeV TpTe/D eg. PpTe/ MeV PeTp/ MeV TeTp/D eg. TePp/D eg. PpPe/ MeV TpPp/ Deg. TePe/ Deg. TpPe/D eg. ZeZp PhePhp /Deg. Config 0 100mu/50cm LuMo+BLAST3239480.1034390.171.41570.942.181.34 1.13 mm0.18 Config 3 100mu/50cm2780780.5421810.430.512030.995.807.29 1.67 cm0.58 Config 4 100mu/10cm272712670.73252670.540.59970.991.302.1 5.08 cm0.60 Config 5 50mu/50cm2681820.5522810.440.521800.995.906.50 1.64 cm0.65 Config 6 50mu/10cm262352370.63242350.450.581770.971.351.90 3.78 cm0.58 Residuals Lepton momentum Pe is a poor constraint TeTp and TePp residuals are balanced for LuMo-only events (TeTp preferred over TePp for LuMo+BLAST events) Substantial improvement for vertex residual w/ 50cm gaps instead of 10cm Minor improvement with 50mu resolution

28. Conclusion from November Distance between tracking planes mostly affects δZe Intrinsic resolution, too, mostly affects δZe δZe always >> than corresponding δZp -> maximize gaps (distance) Solid angle ~1/dist^2 -> minimize distance Elastic count rate still sufficient w/ 50cm gaps Least distance of first element 187cm for clearance Bending angle is small enough so does not limit acceptance -> acceptance (solid angle) determined by rearmost tracking element Intrinsic resolution significantly affecting Ze, but only for small (10cm) gaps (not yet dominated by multiple scattering) Current conclusion: use large gaps (50cm) and <100mu resolution Technical Report is in Preparation

29. HOWEVER …

30. Deflection Angle Bending of lepton track due to presence of magnetic field: ~2 degrees That’s 6-7 cm horizontal offset at detector planes Studying hit distributions at tracking planes to check for acceptance losses Difference of straight line from 3 tracking points and reconstructed track

31. Reconstructed Angle Straight line between vertex and GEM3 Reconstructed angle 50 cm gaps

32. Reconstructed Angle Straight line between vertex and GEM3 Reconstructed angle 10 cm gaps

33. Hit correlations 50 cm gaps

34. Hit correlations 10 cm gaps

35. Next Steps Finalize design parameters (geometry) –Optimize distances between planes, investigate reduced magnetic field –Specifications (No. of channels) (to be updated with new target window design) –Produce drawings Continue to work on GEANT4 simulation (Ozgur Ates, HU graduate student of HU nuclear physics group) –use new, faster codes with better bookkeeping features –higher MC statistics Simulations of phase space integral(s), acceptance; expected counts Study of systematic effects (beam offset, slope, width; etc.) on counts per bin Simulation of backgrounds (Moller/Bhabha; Inelastics)

36. Realization of Detectors Construction project now fully funded (NSF, MRI-R2) Postdoc opening to be filled as soon as possible Purchase GEM foils, anticipate delivery by April/May(?) Ordering of parts / Bates support for drawing/manufacturing? –Parts to be available by June/July Visit MIT and Bates in May (O.A. and M.K.) –Test foils (Optical checks; HV conditioning) –Work on MC studies with new codes Assembly at HU? At Bates? Eventually visit Bates again in July? –Postdoc TBA, O.A., up to 2 HU undergraduate students Have detectors constructed by August, transfer to HU Implement test readout in August (Rome group) Cosmic ray testing in August / September Testing with beam in October 2010 – January 2011 –HUPTI / 100 MeV protons with low intensity (initial proton track may be known) –Jlab / Qweak – parasitically (scatt. electron tracks only known if comb. w. Qweak) –DESY testbeam (tracks well known)

37. Backup slides

38. Luminosity Monitors: Telescopes Forward telescopes 2 tGEM telescopes, 3.9 msr, 10 o, R=160cm, dR=10cm, 3 tracking planes 10 o Proposed version included in OLYMPUS proposal Sept. 2008 TOF

39. Luminosity Monitors: Count rate Two symmetric GEM telescopes at 10 o Two-photon effect negligible at high-ε / low-Q 2 Sub-percent (relative) luminosity measurement per hour for all energies 3.9 msr = 10 x 10 cm 2 at ~160 cm distance Three GEM layers with ~0.1 mm resolution with ~10 cm gaps → Vertex resolution (z) of ~1cm at 10 o to match that of proton in BLAST Same readout pitch as in MIT prototype (635  m) Number of electronics channels per telescope: 3x(100+100)/0.635 ~= 1000 Proposed version included in OLYMPUS proposal Sept. 2008

40. Luminosity Monitors: Cost estimate Proposed version included in OLYMPUS TDR Sept. 2009