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OLYMPUS Overview

OLYMPUS Overview. Motivation for the experiment Progress to date on the experiment The path forward. Elastic Electron Scattering from Proton. +. +…. Dirac, Pauli FF. Sachs FF. Nucleon elastic form factors.

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OLYMPUS Overview

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  1. OLYMPUS Overview • Motivation for the experiment • Progress to date on the experiment • The path forward DESY April 6, 2009

  2. Elastic Electron Scattering from Proton + +… Dirac, Pauli FF Sachs FF DESY April 6, 2009

  3. Nucleon elastic form factors • Fundamental observables describing the distribution of charge and magnetism in the proton and neutron • Defined in the context of single photon exchange • Experimentally, data well described (to first order) by an exponential spatial fall off of nucleon’s charge and magnetism ~ e-µr => dipole form factor GD(Q2) ~ (1 + Q2/0.71)-2 • At Q2 >> 1, σ ~ σMott G2D ~ Q-12 • FF determined by quark structure of proton • Will be calculable in lattice QCD DESY April 6, 2009

  4. Unpolarized Elastic e-N Scattering For ~ 50 years unpolarized cross section measurements have determined the elastic FF GpE and GpM using the Rosenbluth separation σred = dσ/dΩ [ε(1+)/σMott] = GM2+ εGE2  = Q2/4M2ε = [ 1 + 2(1+)tan2θ/2 ] -1 DESY April 6, 2009

  5. Rosenbluth Separation GE2 tGM2 θ=180o θ=0o DESY April 6, 2009

  6. Proton Form Factor Ratio Jefferson Lab Dramatic discrepancy! • All Rosenbluth data from SLAC and Jlab in agreement. • Dramatic discrepancy between Rosenbluth and recoil polarization technique DESY April 6, 2009

  7. Calculation of Two Photon Exchange Effects +.... + • P.A.M. Guichon and M. Vanderhaeghen, PRL91, 142303 (2003) • P.G. Blunden, W. Melnitchouk, and J.A. Tjon, PRC72, 034612 (2005), PRL91, 142304 (2003) • M.P. Rekalo and E. Tomasi-Gustafsson, EPJA22, 331 (2004) • Y.C. Chen et al.,PRL93, 122301 (2004) • A.V. Afanasev and N.P. Merenkov, PRD70, 073002 (2004) DESY April 6, 2009

  8. P.G. Blunden et al., Phys. Rev. C 72, 034612 (2005) Estimation of TPE Contribution DESY April 6, 2009

  9. How do we verify that the TPE contribution interpretation is correct? Precision comparison of positron-proton and electron-proton elastic scattering over a sizable ε range at Q2 ~ 2-3 (GeV/c)2 J. Arrington PRC 69, 032201(R) (2004) SLAC data At low ε : <Q2> ~ 0.01 to 0.8 (GeV/c)2 At high ε : <Q2> ~ 1-5 (GeV/c)2 Θ=180o Θ=0o DESY April 6, 2009

  10. TPE calculation comparison with e+p/e-p scattering data P.G. Blunden et al., Phys. Rev. C 72, 034612 (2005) DESY April 6, 2009

  11. e+p/e-p cross section ratio P.G. Blunden et al., Phys. Rev. C 72, 034612 (2005) DESY April 6, 2009

  12. Proton form factor ratio Blunden et al. DESY April 6, 2009

  13. The OLYMPUS Experiment • Electrons/positrons (100mA) in multi-GeV storage ring DORIS at DESY, Hamburg, Germany • Unpolarized internal hydrogen target (like HERMES) 3 x 1015 at/cm2 @ 100 mA→ L = 2x1033 / (cm2s) • Measure elastic e+/e- proton scattering to 1% precision at 2 GeV energy with ε range from 0.4 to 1 at high Q2 ~ 2-3 (GeV/c)2 using the existing Bates Large Acceptance Spectrometer Toroid • Experiment requires switching from e+ beam to e- beam on timescale of ≤ 1 day. • Redundant monitoring of luminosity, pressure, temperature, flow, current measurements - small-angle elastic scattering at high ε and low Q2 DESY April 6, 2009

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  16. OLYMPUS kinematics DESY April 6, 2009

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  21. Projected OLYMPUS uncertainties DESY April 6, 2009

  22. Control of systematics BLAST @ DORIS θ→0o,ε→1 TPE effects → 0 Luminosity monitors 10o • Change BLAST polarity once a day • Change between electrons and positrons regularly • Left-right symmetry DESY April 6, 2009

  23. Control of systematics i = e+ or e- j= pos/neg polarity of BLAST field Geometric proton efficiency: Ratio in single polarity j Geometric lepton efficiency: DESY April 6, 2009

  24. Control of systematics Super ratio: Cycle of four states ij Repeat cycle many times • Change between electrons and positrons regularly • Change BLAST polarity every day • Left-right symmetry provides additional redundancy – two identical experiments simultaneously taking data DESY April 6, 2009

  25. December 17th 2008 DESY April 6, 2009

  26. Timeline • OLYMPUS proposal conditionally approved by DESY in December 2008 • Requests submitted to funding agencies: December 2008 (Germany) and January 2009 (US) • Remove ARGUS experiment in Summer 2009 • Ship BLAST/OLYMPUS detector and OLYMPUS target in summer/fall 2010 • Modify DORIS beamline and install OLYMPUS target in DORIS in winter 2010/11 shutdown. • Install complete OLYMPUS experiment in summer 2011 • Commission in fall 2011 • Take data in 2012 DESY April 6, 2009

  27. Summary • The OLYMPUS experiment has been approved by DESY conditional on the funds being available. • A schedule for the installation, commissioning and data taking has been established. • Detailed discussion of the technical issues are getting underway. • The critical path issue now is to secure the necessary funding required to carry out OLYMPUS. DESY April 6, 2009

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