Investigating the Conjectured Nucleon Deformation at Low Q

Investigating the Conjectured Nucleon Deformation at Low Q 2 at the Mainz Microtron N. F. Sparveris Department of Physics, University of Athens and Institute of Accelerating Systems and Applications, Athens, Greece for the Mainz N-Δ Collaboration (Athens, MIT, Mainz, RIKEN, U. Kentucky, U. Zagreb, U. Ljubljiana) Electromagnetic Interactions with Nucleons and Nuclei Milos, September 2005

Overview Objective: Measure with high precision EMR and CMR Ratios Investigate the role of the pion cloud at the low Q 2 region Mainz Measurements: Η(e, e’p)πo measurements at low Q 2 region (0. 06 – 0. 20 (Ge. V/c)2) 855 Me. V polarized electron beam High precision measurements involving in- and out of - plane detection Experiment performed in 2 stages (spring 2003 & fall 2003) Observables: cross sections extract: responses (LT, TT, LT’, L+T) quadrupole strengths (CMR and EMR) Preliminary results for the responses and the quadrupole amplitudes will be presented

Ν Δ(1232) γ* Μ 1 , Ε 2 , C 2 p(qqq) I= J= u d u u 938 Me. V Δ(qqq) d u Μ 1+ , Ε 1+ , S 1+ πo Spherical M 1 Deformed M 1 , E 2 , C 2 Deformation signal I= J= 1232 Me. V

Extracting the response functions p cross section measurements at various azimouthal angles Η(e, e’p)πo p 0

Response functions … precise Response measurements … and extensive mapping versus θ

Ν Δ program @ Mainz “Mainz Ν Δ collaboration” (IASA (Athens), MIT, , Mainz. . ) Focus on the low Q 2 region in an attempt to understand the effect of the mesonic cloud on the responses CW beam Maximum Ebeam = 855 Me. V Maximum Ibeam = 25 μA sequential measurements: Spectrometer A detecting electrons (in plane) Spectrometer B detecting protons (can go up to 10 o out of plane) Spectrometer C detecting electrons (luminosity monitor)

Mainz Ν Δ measurements Q 2 (Ge. V/c)2 W (Me. V) Θ pq (deg. ) April 2003 0. 060 1232 0 - 40 “ 0. 127 1232 0 - 60 “ 0. 200 1232 0 - 60 0. 060 W - scan 0 “ 0. 200 W - scan 0 “ 0. 060 1155 0 - 26 October 2003

Phase space sequential measurements

Results: Q 2 = 0. 06 (Ge. V/c)2 (Mainz) (Bates)

Results: Q 2 = 0. 06 (Ge. V/c)2 EL PR A IN IM RY S. Stave Ph. D

Results: Q 2 = 0. 20 (Ge. V/c)2

Results: Q 2 = 0. 127 (Ge. V/c)2 RY A IN IM EL PR

Latest Compilation of Bates Data @ Q 2 = 0. 127 (Ge. V/c)2

CMR

EMR

M 1+

Conclusions & outlook ü Results at all Mainz Q 2 points will be finalized this year. Precise values for the quadrupole strengths will be extracted at Q 2=0. 06 (Ge. V/c)2 and 0. 20 (Ge. V/c)2 ü The LT’ results at Q 2=0. 127 (Ge. V/c)2 are expected to enrich the world data base at this Q 2. Provide more constrains to background amplitudes at this Q 2. ü Preliminary results indicate CMR around (-5 ± 0. 5) % for both the Q 2=0. 06 Ge. V 2 & 0. 20 Ge. V 2 ü The CMR and EMR results at Q 2=0. 06 (Ge. V/c)2 and 0. 20 (Ge. V/c)2 will be evaluated along with the corresponding values at Q 2=0. 127 (Ge. V/c)2 (Bates/Mainz) in order to understand the Q 2 dependence of the quadrupole strengths at the low Q 2 region.