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“THE OLYMPUS LUMINOSITY MONITORS”
Ozgur Ates
Hampton University
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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
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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!
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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.
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• Electrons/positrons (100mA) in multi-GeV storage ringDORIS at DESY, Hamburg, Germany
• Unpolarized internal hydrogen target (buffer system)
• Large acceptance detector for e-p in coincidenceBLAST detector from MIT-Bates available 4
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Luminosity Monitors: Telescopes
Forward telescopes
12o
2 tGEM telescopes, 1.2msr, 12o,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
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Control of Systematics
• Forward-angle (high-epsilon, low-Q) elastic scattering (se+ = se-) 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
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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 TechnologyMIT prototype:
Telescope of 3 Triple GEM prototypes (10 x 10 cm2) using TechEtch foils
F. Simon et al., NIM A598 (2009) 432
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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
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Resolution: generated - reconstructed
100micron, 50cm, LuMo+BLAST (Te=0-80 dg, Phe=+-15 dg)
δZp δZe
δTp δTe
δPhp δPhe
δPp δPe
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Resolution: generated - reconstructed100micron, 50cm, LuMo only (Te=6-13 dg, Phe=+-5 dg)
δZp δZe
δTp δTe
δPhp δPhe
δPp δPe
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Residuals: Te-TeTp (one sample)
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• 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.
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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./50cmLuMo Only
1.70 mm 1.68 cm 0.59 Deg. 0.15 Deg. 0.55 Deg. 0.39 Deg. 21 MeV 78 MeV
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Conclusions
• 10x10 cm2 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.
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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
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THANK YOU !!!