“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

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APS APRIL MEETING, 2010

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

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

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

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)

• 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

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 !!!