Investigating the Conjectured Nucleon Deformation at Low Q2
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Investigating the Conjectured Nucleon Deformation at Low Q2 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,

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Investigating the Conjectured Nucleon Deformation at Low Q2

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-ΔCollaboration

(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 Q2 region

Mainz Measurements:

Η(e,e’p)πomeasurements at low Q2 region (0.06 – 0.20 (GeV/c)2)

855 MeV 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 responsesand the quadrupole amplitudes will be presented


p(qqq)

I = J =

938 MeV

γ* Μ1, Ε2, C2

Μ1+ ,Ε1+,S1+πo

d

u

u

d

u

u

Ν  Δ(1232)

Δ(qqq)

I = J =

1232 MeV

Spherical  M1

Deformed  M1 , E2 , C2

Deformation signal


p

p0

Extracting the response functions

cross section measurements at various azimouthal angles

Η(e,e’p)πo


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 Q2 region

in an attempt to understand

the effect of the mesonic cloud

on the responses

CW beam

Maximum Ebeam = 855 MeV

Maximum Ibeam = 25 μA

Spectrometer A detecting electrons (in plane)

sequential

measurements:

Spectrometer B detecting protons (can go up to 10o out of plane)

Spectrometer C detecting electrons (luminosity monitor)


Mainz Ν  Δ measurements


Phase space

sequential measurements


Results: Q2 = 0.06 (GeV/c)2

(Mainz)

(Bates)


PRELIMINARY

Results: Q2 = 0.06 (GeV/c)2

S.Stave PhD


Results: Q2 = 0.20 (GeV/c)2


Results: Q2 = 0.127 (GeV/c)2

PRELIMINARY





M 1+


Conclusions & outlook

  • Results at all Mainz Q2 points will be finalized this year.

    Precise values for the quadrupole strengths will be extracted at Q2=0.06 (GeV/c)2 and 0.20 (GeV/c)2

  • The LT’ results at Q2=0.127 (GeV/c)2 are expected to enrich the world data base at this Q2.

    Provide more constrains to background amplitudes at this Q2.

  • Preliminary results indicate CMR around (-5 ± 0.5) % for both the Q2=0.06 GeV2 & 0.20 GeV2

  • The CMR and EMR results at Q2=0.06 (GeV/c)2 and 0.20 (GeV/c)2 will be evaluated along

    with the corresponding values at Q2=0.127 (GeV/c)2(Bates/Mainz) in order to understand the

    Q2 dependence of the quadrupole strengths at the low Q2 region.


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