Magnetic moments of baryon resonances Teilprojekt A3 Volker Metag II. Physikalisches Institut Universität Giessen Germany SFB/TR16 Mitgliederversammlung Bommerholz, SFB/TR16  the  + (1232) resonance:  summary and outlook  the S 11 (1535) resonance  motivation  strangeness production in  p  + K 0*

structure calculations    S 11  (1535) SU(3) Lattice QCD ( Cloet et al., PLB 563 (2003) ) 4.99(56)2.49(27)  QSM ( Yang et al., PRD 70 (2004) ) experimental values Castro et al., PLB 517 (2001)  0.51 M.Kotulla. et al., PRL 89, (2002) 2.7  2.2  3 PDG  2.2  3 — Magnetic moments of hadrons provided testing ground for the constituent quark model and baryon structure calculations SU(3) prediction: almost nothing is known about the magnetic moments of excited baryons

extrapolation:  lattice data (quenched): Leinweber (1992) Cloet,Leinweber,Thomas (2003) Lee et.al. (2004)  chiral calculations to NLO in δ expansion V. Pascalutsa, M. Vanderhaeghen PRL (2005)  for m π < (M Δ – M N ) : Δ decays imaginary part is model independent prediction in chiral EFT framework Lattice calculation and chiral extrapolation  ++ ++

1232 E / MeV 938    ´ proton  M1,(E2), M3  ´ transition M1 sensitive to    p p    ´   ' ' dE d ER         Magnetic moment of the  + (1232) resonance V. Pascalutsa, M. Vanderhaeghen PRL (2005)  EFT systematic annsatz (NLO) no Born terms !!

Pioneering experiment: improvements: higher statistics exploit sensitivity to polarisation observables linear and circular photon beam polarisation: ,  circ improved theoretical description MAMI MAMI 1999 MAMI MAMI 1999   + = (2.7±2.2±3)  N M. Kotulla et al., PRL 89 (2002) MAMI 1999

TAPS forward wall 384 BaF 2 – modules distance: 150 cm angles: – Crystal Ball 672 NaI - modules  -beam LH 2 CB (inside 2MWPCs, PID) TAPS  beam

Identification of  p  p  0  ` channel S. Schumann (Mainz) eliminating background from  p  p  0  0

beam asymmetry: discrepancy between data and calculation !! inclusion of Born terms will reduce discrepancy (M. Vanderhaegen, priv. com.)

follow up experiment with higher polarization needed !! real polarisation randomized polarisation S. Schumann (Mainz) circular polarisation  circ Re   =5 Re   =3 Re   =1 Re   =0

energy distribution of  ` S. Schumann (Mainz) B. Boillat (Basel) M. Kotulla et al., PRL89 (2002) improvement in statistics !!

angular distribution of  ` S. Schuman (Mainz) B. Boillat (Basel) M. Kotulla et al., PRL89 (2002) improvement in statistics !!

present data (preliminary) M. Kotulla et al. Comparison of present data to pioneering experiment current theoretical calculation does not reproduce reproduce spectral distribution! improved theoretical calculations needed to extract  (  + ) !!!!

Chiang et al., NPA 721 (2003) 731 unpol. LH 2 target:  S 11 + (1535):  p  p   ´  reaction calculation: effective Lagrangian model  total cross section: 10nb  Observables cross sections helicity asymmetry  circ expected sensitivity:  assuming 3200 counts (stat error)  assuming 5% systematic error  for m=1.8m N from energy differential cross section: magnetic moment of S 11 (1535) resonance

1/2 γ p Σ + (1189) K *0 K 0 s π 0 π 0 π 0 p π 0 1/3 E γ > 1840 MeV p π o 1/2 1/3 γ p Σ + (1189) K 0 π 0 K 0 s π 0 π 0 E γ > 1300 MeV reactions with p 4 π 0 final state γ p p π 0 η 3π 0 1/3 E γ > 930 MeV reactions with strangeness production to study baryon resonances through the measurement of poorly known meson-nucleon and meson-hyperon decay channels to study the coupling of vector meson-nucleon channels to kaon- hyperon states M. Nanova

theoretical predictions dynamical model for the cross section predictions M. Doering et al., PRC 73, (2006) Δ * (1700)→ ηΔΔ * (1700)→KΣ *

M. Doering et al., nucl-th/ theoretical predictions E   GeVE   GeVE   GeV cosθ

Q. Zhao et al., PRC 64, (2001) K* 0 Σ+Σ+ K0K0 p γ theoretical predictions quark model predictions for the K* 0 and K* + photoproductions significant t-channel kaon exchange

kinematic fit:  p  p 4  0

 p   + (1189) K 0 *  p  0 K 0  0  p 4  0 E  = MeV  + (1189) K 0 * (892) K s 0 (498)

angular distributions

Summary and outlook strangeness production:  p   + (1189) K 0 *  p 4  0 final analysis ongoing; paper in preparation magnetic dipole moments: pioneering experiment ongoing data analysis of improved follow up experiment:  higher statistics  polarization observables ,  circ improved calculation needed to exctract  (  + ) next step: magnetic moment of S 11 (1535) via  p  p   ‘ sensitivity to  (  + )

Circular beam pol.:  883 MeV  550 MeV circular polarisation

Summary and Outlook magnetic dipole moments:  valuable constaints for Baryon structure calculations  past: experiments     successful pioneering experiment for    in progress:  analysis of dedicated experiment Crystal Ball / MAMI cross sections, beam/helicity asymmetry  coherent program (tests - reaction calculation)  very large sensitivity to MDM future:  generalization to other resonances S 11 (1535)

Recent calculation:   EFT to calculate  p      ‘p  systematic ansatz (NLO)  includes rescattering MDM acquires real and imaginary part  no Born terms

based on effective Lagrangian description: Born terms,  t-channel exchange, rescattering included, gauge invariant describes simultanously W.-T. Chiang, M. Vanderhaeghen, S. N. Yang, D. Drechsel, hep-ph/ Reaction model calculation

MAMI cm beam MAMI  62, 1  138 detectors with individual veto detector, solid angle: ~0.40  4  sr

MAMI 1999

Hadron Structure:  + Magnetic Moment magnetic moments:  well known SU(3) octet baryons (   s), measured with spin precession techniques  almost unknown for excited states (except  (1232) )  a test for baryon structure calculations (wavefunction): e.g. SU(3): structure calculations    S 11  (1535) SU(3) Lattice QCD ( Cloet et al., PLB 563 (2003) ) 4.99(56)2.49(27)  QSM ( Yang et al., PRD 70 (2004) ) experimental values Castro et al., PLB 517 (2001)  0.51 M.Kotulla. et al., PRL 89, (2002) 2.7  2.2  3 PDG  2.2  3 — what are the effective degrees of freedom? M1