1. “THE OLYMPUS LUMINOSITY MONITORS” Ozgur Ates Hampton University 1  OLYMPUS  Two Photon Exchange in Elastic Scattering  Principle of The Experiment  LUMINOSITY MONITORS  Control of Systematics  Technique * Supported by NSF grant No. 0855473 * APS APRIL MEETING, 2010

2.  All Rosenbluth data from SLAC and Jlab in agreement  Dramatic discrepancy between Rosenbluth and recoil polarization technique  Multi-photon exchange considered the best candidate to explain the dramatic discrepancy. Jefferson Lab Proton Form Factor Ratio Dramatic Discrepancy! 2

3. Elastic e + -p / e - -p Ratio ‏ Two-photon exchange theoretically suggested : Interference of one- and two- photon amplitudes  Measure ratio of positron-proton to electron-proton unpolarized elastic scattering to 1% Precision!! in stat.+sys. 3

4. Electrons/positrons (100mA) in multi-GeV storage ring DORIS at DESY, Hamburg, Germany Unpolarized internal hydrogen target (buffer system) Large acceptance detector for e-p in coincidence BLAST detector from MIT-Bates available 4

5. 5

6. Luminosity Monitors: Telescopes Forward telescopes 12 o 2 tGEM telescopes, 1.2msr, 12 o, R=187/237/287cm, dR=50cm, 3 tracking planes TOF Luminosity monitors for LEPTON in coincidence with Recoil PROTON detected in the opposite sector, and vice versa. LEPTON PROTON LEPTON PROTON

7. Control of Systematics Forward-angle (high-epsilon, low-Q) elastic scattering (s e+ = s e- ) means there is no two-photon exchange Separately determine three super ratios Left-right symmetry = Redundancy Triple Super Ratio: Run the Exp. For the “4 different states” i= e - vs e + j=toroidal magnet polarity(+-) Repeat cycle many times Ratio of acceptances (phase space integrals) Ratio of luminosities Ratio of counts 7

8. Forward Elastic Luminosity Monitor Forward angle electron/positron telescopes or trackers with good angular and vertex resolution Coincidence with proton in BLAST High rate capability It will be built at Hampton University this year! GEM Technology MIT prototype: Telescope of 3 Triple GEM prototypes (10 x 10 cm 2 ) using TechEtch foils F. Simon et al., NIM A598 (2009) 432

9. Monte Carlo Studies by using Geant4 Generated and reconstructed variables Theta, Phi, Momentum, Z(vertex) Proton & Electron Resolutions δZp, δTp, δPhp, δPp, δZe, δTe, δPhe, δPe Residuals: Redundancy of variables / elastic scattering 4 variables: Pe, Pp, Te, Tp 3 constraints: 3 conservation equations 4 – 3 = 1 (DEGREES OF FREEDOM) TeTp: Te – Te(Tp) TePe: Te – Te(Pe) TePp: Te – Te(Pp) Coplanarity: PhePhp:Phe – Php – 180 Common vertex: ZeZp:Ze – Zp 9

10. Resolution: generated - reconstructed 100micron, 50cm, LuMo+BLAST (Te=0-80 dg, Phe=+-15 dg) δZp δZe δTp δTe δPhp δPhe δPpδPe 10

11. Resolution: generated - reconstructed 100micron, 50cm, LuMo only (Te=6-13 dg, Phe=+-5 dg) δZp δZe δTp δTe δPhp δPhe δPp δPe 11

12. 12 Residuals: Te-TeTp (one sample)

13. Many configurations were simulated. Varied intrinsic res. and distance between tracking planes. 100 µm intrinsic res. and 50 cm gap between Gem1/2 and Gem2/3 show the optimum performance. 13 Design Parameters: Resolutions Left Sec. RESOLUTIONS Proton DeltaZ Electron DeltaZ Proton Del.Theta Electron Del.Theta Proton DeltaPhi Electron DeltaPhi Proton DeltaP Electron DeltaP 100mic./50cm LuMo Only 1.70 mm1.68 cm0.59 Deg.0.15 Deg.0.55 Deg.0.39 Deg.21 MeV78 MeV

14. Conclusions 10x10 cm 2 GEM detector size for active area at 12 degree. Least distance of first element 187cm for clearance The second should sit 237cm and third gem 287cm away from the target. Elastic count rate still sufficient with 50cm gaps 100 µm intrinsic resolutions of GEM’s meet the experimental requirement. 14

15. Next Steps 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 Build and test the detectors by end of this year! Implement in OLYMPUS in 2011, run in 2012 15

16. THANK YOU !!!