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Measurement of the Coulomb quadrupole amplitude in the γ *p  Δ (1232)

Measurement of the Coulomb quadrupole amplitude in the γ *p  Δ (1232) i n the low momentum transfer region. Hall A Proposal PR-08-010. N. Sparveris MIT S. Gilad MIT A. Sarty Saint Mary’s University D. Higinbotham JLab. Nikos Sparveris

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Measurement of the Coulomb quadrupole amplitude in the γ *p  Δ (1232)

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  1. Measurement of the Coulomb quadrupole amplitude in the γ*pΔ(1232) in the low momentum transfer region Hall A ProposalPR-08-010 N. Sparveris MIT S. Gilad MIT A. Sarty Saint Mary’s University D. Higinbotham JLab Nikos Sparveris Massachusetts Institute of Technology

  2. p I = J = 938 MeV d u u d u u The issue Experimental confirmation of the deviation of the proton structure from spherical symmetry is fundamental and has been the subject of intense experimental and theoretical interest Studied through the measurement of the electric and Coulomb quadrupole amplitudes (E2,C2) in the predominantly M1 (magnetic dipole-quark spin flip) NΔ(1232) transition γ* Μ1, Ε2, C2 Δ I = J = 1232 MeV Ν  Δ(1232) Μ1+ ,Ε1+,S1+πo CMR = C2/M1 EMR = E2/M1 Spherical  M1 Deformation signal Deformed  M1 , E2 , C2

  3. The status Experimental activity: MAMI, Bates (low-Q2), JLab (Hall A, B & C) mapping from Q2=0.06 (GeV/c)2 up to 6 (GeV/c)2 Theoretical activity: dynamical calculations, phenomenology, ChEFT, Lattice (Sato-Lee, DMT, MAID, SAID, Pascalutsa-Vanderhaeghen, Alexandrou et al) Quark model predictions are  30% too low for M1 and an order of magnitude lower for the quadrupole amplitudes This issue of the quark core and pion cloud contributions has been addressed in meson exchange models (Sato & Lee) – quantitatively makes up for the deficiencies of the quark model The dynamical calculations are in good agreement down to Q2=0.20 (GeV/c)2 But:  Calculations not in agreement with the low Q2 data taken at Bates and MAMI near (and lower) the predicted peak of the pion cloud contribution at  0.1 (GeV/c)2.  No data available lower than Q2 = 0.06 (GeV/c)2 There are some discrepancies between the MAMI and the Bates data at Q2 = 0.126 (GeV/c)2 that make the picture unclear at a crucial point.

  4. Sato-Lee calculation effect of quark core + pion cloud effect of quark core

  5. Resonant amplitudes in the low Q2 region

  6. Multipole Truncation Η(e,e’p)πo RLT RL+RT RTT RLT’ CMR , EMR Model interpretation p Multipole decomposition po Extracting the signal Separation of the partial cross sections with measurements at various azimouthal angles Background Signal Data

  7. Why Hall A ? Capability to place the spectrometers in small angles and high resolution spectrometers The lowest Q2 measurements taken at MAMI (Q2=0.06 (GeV/c)2) were constrained by space limitations (lower limits for the 2 MAMI spectrometers are 23o and 15.1o) The 2 HRS spectrometers in Hall A can go down to 12.5o thus providing access to lower Q2 values.

  8. MAMI - 23o to +15o HRS ± 12.5o p Q2 = 0.025 (GeV/c)2 HALL A e p MAMI e

  9. Experiment requirements  Hall A standard equipment only The 2 HRS spectrometers for e and p detection respectively (with their standard detector packages: VDCs, scintillators, Cherenkov, lead-glass)  A 6 cm LH2 target Beam: Eο=1115 MeV (Q2=0.125…0.040 (GeV/c)2) and Eο=910 MeV (Q2=0.025 (GeV/c)2) at I=75 μΑ Beam energy can be easily adjusted around the above values to accommodate beam energies of other experiments

  10. Φpq= 0o Φpq= 180o p po The Experiment H(e,e’p)πo σLT = ( σ(Φpq=180o) - σ(Φpq=0o)) / 2vLT

  11. 8.5 hrs 9 hrs 29.5 hrs 47 hrs production + 8 hrs calibrations + 17 hrs config. changes = 72 hrs 6 cm LH2 target , Eo = 1115 MeV , I=75 μA 20% dead-time & 99% detection efficiency have been assumed Kinematical Settings

  12. Trues / Accidentals 2 ns timing window & 60 MeV Missing-mass cut around pion mass

  13. Data analysis • Phase space (W,θpq,Q2) will be matched for Φpq = 0o , 180o measurements • analysis bin size: ΔW = ± 4 MeV , Δθpq = ± 2.5o , ΔQ2 = ± 3*10-3– 4.5*10-3 (GeV/c)2 • theoretical calculations folded over the acceptance for the extraction of point cross sections • cross section uncertainties : statistical < ± 1% , systematic < ± 3% , avg.-to-point < ± 0.4% • σLT uncertainty < ± 8%(depending on kinematics) • resonant amplitudes will be fitted to the cross sections • CMR (statistical+systematic) uncertainty < ± 0.20% to < ± 0.28% (from Q2=0.125 to 0.04 (GeV/c)2) • contributions from background amplitudes from all available models will be introduced to the fits • Model uncertainty introduced to the CMR < ± 0.30% in all cases • σLT will be extracted down to Q2= 0.038 (GeV/c)2 and unmatched cross sections in (W,θpq,Q2) will be extracted down to Q2= 0.036 (GeV/c)2

  14. Phase space : Q2 = 0.125 (GeV/c)2 ΔW cut = ± 5 MeV ΔW cut = ± 5 MeV ΔQ2 = ± 0.0045 (GeV/c)2 ΔW = ± 4 MeV Δθpq = ± 2.5o analysis bin widths

  15. Phase space Q2 = 0.04 (GeV/c)2 Q2 = 0.09 (GeV/c)2 ΔW cut = ± 5 MeV ΔW cut = ± 5 MeV ΔQ2 = ± 0.003 (GeV/c)2 ΔW = ± 4 MeV Δθpq = ± 2.5o ΔQ2 = ± 0.004 (GeV/c)2 ΔW = ± 4 MeV Δθpq = ± 2.5o

  16. Projected Results: Q2 = 0.125 (GeV/c)2 Bates results seem to overestimate the MAMI ones at Q2=0.125 (GeV/c)2 Disagreement in the description of the parallel cross section as a function of W

  17. W-dependence at low Q2 Q2 = 0.125 (GeV/c)2 proposed measurements Q2 = 0.06 (GeV/c)2 Q2 = 0.20 (GeV/c)2 Mainz data Mainz data

  18. Projected Results Q2 = 0.04 (GeV/c)2 Q2 = 0.09 (GeV/c)2

  19. Q2 = 0.025 (GeV/c)2 Eo = 910 MeV at I=75 μA

  20. Projected Results: CMR

  21. Summary • CMR will be precisely mapped from Q2=0.125 (GeV/c)2 down to 0.025 (GeV/c)2 • this experiment will provide the lowest Q2 CMR measurements and the most precise ones • in the low momentum transfer region • cross sections will be also be extracted down to 0.020 (GeV/c)2 • discrepancies of other labs (Bates/MAMI) will be resolved • strong constrains to the most recent theoretical calculations will be provided • valuable insight to the mechanisms that contribute to the nucleon deformation Request: The 2 HRS spectrometers (with their standard detector packages)  A 6 cm LH2 target Beam: Eο=1115 MeV and Eο=910 MeVat I=75 μΑ (central Eo value adjustable if needed) 3 days + 0.5 days of running (including production, calibrations and configuration changes)

  22. Measurement of the Coulomb quadrupole amplitude in the γ*pΔ(1232) in the low momentum transfer region

  23. BACK – UP SLIDES

  24. Results: Q2 = 0.20 (GeV/c)2

  25. Results: Q2 = 0.127 (GeV/c)2 Latest compilation of Bates data and comparison with Mainz data

  26. Phase space at Q2 = 0.025 (GeV/c)2 ΔQ2 = ± 0.003 (GeV/c)2 ΔW = ± 4 MeV Δθpq = ± 2.5o

  27. Deformed Spherical Deformed Spherical The Nucleon is Deformed

  28. Ποιοτική διερεύνηση MAID στα αποτελέσματα RCM (MAID)~ - 6.5% CMR = RCM (MAID)• 1 CMR = RCM (MAID)• 0.5 CMR = RCM (MAID)• 0 ( … spherical )

  29. Projected Results: CMR

  30. Why Hall A ? Capability to place the spectrometers in small angles and high resolution spectrometers The lowest Q2 measurements taken at MAMI (Q2=0.06 (GeV/c)2) were constrained by space limitations (lower limits for the 2 MAMI spectrometers are 23o and 15.1o) The 2 HRS spectrometers in Hall A can go down to 12.5o thus providing access to lower Q2 values. Experiment requirements:  Hall A standard equipment only The 2 HRS spectrometers for e and p detection respectively (with their standard detector packages: VDCs, scintillators, Cherenkov, lead-glass)  A 6 cm LH2 target Beam: Eο=1115 MeV and Eο=910 MeV at I=75 μΑ Beam energy can be easily adjusted around the above value to accommodate beam energies of other experiments

  31. p I = J = 938 MeV d u u d u u The issue Experimental confirmation of the deviation of the proton structure from spherical symmetry is fundamental and has been the subject of intense experimental and theoretical interest Studied through the measurement of the electric and Coulomb quadrupole amplitudes (E2,C2) in the predominantly M1 (magnetic dipole-quark spin flip) NΔ(1232) transition γ* Μ1, Ε2, C2 Δ I = J = 1232 MeV Ν  Δ(1232) Μ1+ ,Ε1+,S1+πo Spherical  M1 Deformation signal Deformed  M1 , E2 , C2

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