Shape of Hadrons Athens 27.-29. April 2006

Real Photon Experiments

M. Kotulla

E2/M1 @ MAMI and LEGSmagnetic dipole moment of the

Nucleon Structure

first excited State

1 2 3 2

E / M eV

9 3 8

´

pro to n

precise electro- and photoproduction data: magnetic dipole transition M1

electric quadrupole transition E2

Coulomb quadrupole transition C2

incoming photon: M1, E2, C2

outgoing pion: 2/31

2/31

2/31 CEM

N transition intrinsic

methods:

isospin decomposition:

most sensitive:shape of angular distributionbeam asymmetry at 90° E1+ M1+

multipol analysis, dispersion relation

np pp 0

2/31

2/31

M

EREM

||

||

12A

CREM

REM Extraction

)(cos)cos()( 2

||/||/||/||/

CBAk

q

d

d

DAPHNE @ MAMI

TAPS @ MAMI

6 62, 1 138 detectors with individualveto detector, solid angle: ~0.40 4 sr

MAMI 1999-2000 100cm

beam

LEGS setup

Photon Asymmetry

Differential Cross Sections

Comparison LEGS - MAMI

P33 Partial Waves (MAMI)

MAMI Results:

DAPHNE measurement:C||/(12A||) dispersion relation analysismultiplol ana (S,P waves + Born)

LEGS Results:

multipol analysis (up to F waves + Born)

)%2.01.05.2( sysstatEMR 2)003.0085.0( fmQN

NN )03.046.3(

)%24.026.007.3( syssysstatEMR

2)034.0009.0108.0( fmQN

NN )085.0019.0642.3(

228.0 fmQd

R. Beck et al., PRC 61 031204 (2000) G. Blanpied et al., PRC 64 025203 (2001)

REM

for comparison:deuteron

The Beamline

LH2CB (inside 2MWPCs, PID)TAPS beam

production runs 22.6.2004-4.4.2005

CB:672 NaI(Tl)

covers 20° - 160°

TAPS:510 BaF2

covers 1° - 20°

)GeV(E

%.E

E

%.)GeV(E

%.E

E

Photon Asymmery

15% of total statistics

Photon Asymmetry :

@400MeV:

CBT =0.619 0.015

Leukel =0.592 0.036

pp

cosp)(dd

),(dd

@420MeV:

CBT =0.632 0.015

Leukel =0.591 0.033

E. Downie preliminary

Magnetic Moment

p p

´

measurement: excitation of the + and

identification of the ´p state

reaction description necessary

1 2 3 2

E / M eV

9 3 8

´

pro to n

M1, (E2), M3 ´transition

p

p´

p p

´

basic principle

resonance: isolated excited state of the nucleon

lifetime ~ 20-23 s

Pn

p Q;2

3

pp '0

M.Kotulla et al., PRL 89, 272001 (2002)

PDG2004 = (2.7 2.2 3)N

Reaction DescriptionPascalutsa, Vanderhaeghen PRL 94 102003 (2005)M. Kotulla et al., PRL 89, 272001 (2002)

''

1

dE

dER

Recent progress:

chiral effective field theory ansatzV. Pascalutsa, M. Vanderhaeghen PRL 94 102003 (2005)

systematic ansatz (NLO)error estimation

rescattering: MDM acquires real and imaginary part

pp '0

(1232) MDM cross sections:

angular distribution of ´

comparison:pioneering experiment

(TAPS1999) = (2.7 2.2 3)

M.K. et al., PRL 89, 272001 (2002)

preliminary Crystal Ball / TAPS data

much higher precision

new Crystal Ball / TAPS Data

(1232) MDM experiment:

p ´p

exclusive measurement

kinematical overdetermination

identification checks

preliminary

B. Boillat

new Crystal Ball / TAPS Data

checks:

photon beam asymmetry

p

meson

p

´

p

ppp

ppp 0

pp /0

E. Downie

=0.619 0.015

S. Schumann

preliminary

preliminary

Summary

magnetic moment

pioneering experiment TAPS@MAMI1999 (proof of principle)

new (CB/TAPS) measurement is currently being analyzedmuch higher precision

reaction calculation (systematic ansatz):chiral effective field theory

Outlook: experiment feasible

S11+(1535): p ´p

S110(1535): n ´n(LD2 target)

Nsys )35.17.2( 0.13.1

N REM: precise data from MAMI and LEGS

very good agreement in photon asymmetryslight deviation in (differential) cross sections

)%2.01.05.2( sysstatEMR

)%24.026.007.3( syssysstatEMR