Magnetic moments of baryon resonances Teilprojekt A3

Magnetic moments of baryon resonances Teilprojekt A3

Volker MetagII. Physikalisches Institut

Universität GiessenGermany

SFB/TR16 MitgliederversammlungBommerholz, 28.11.2006

SFB/TR16

the + (1232) resonance:

summary and outlook

the S11(1535) resonance

motivation

strangeness production in p+K0*

structure calculations S11(1535)

SU(3) 5.58 2.79

Lattice QCD (Cloet et al., PLB 563 (2003)) 4.99(56) 2.49(27)

QSM (Yang et al., PRD 70 (2004)) 5.39 2.66

experimental values

Castro et al., PLB 517 (2001) 339 6.14 0.51

M.Kotulla. et al., PRL 89, 272001 (2002) 2.7 2.2 3

PDG2004 3.7 - 7.5 2.7 2.2 3 —

• Magnetic moments of hadrons provided testing ground for the constituent quark model and baryon structure calculations

; BBB

PQ SU(3) prediction:

;2

3

n

p

• almost nothing is known about the magnetic moments of excited baryons

Nm

e

2

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 94 102003 (2005)

for mπ < (MΔ – MN) : Δ decays imaginary part is model independent prediction in chiral EFT framework

Lattice calculation and chiral extrapolationLattice calculation and chiral extrapolation

++

+

1232

E / MeV

938

proton

M1, (E2), M3 transitionM1 sensitive to

p p

'' dE

dER

Magnetic moment of the +(1232) resonanceMagnetic moment of the +(1232) resonance

V. Pascalutsa, M. Vanderhaeghen PRL 94 102003 (2005)

EFT systematic annsatz (NLO)

no Born terms !!

Pioneering experiment:Pioneering experiment:

• improvements:

• higher statistics

• exploit sensitivity to polarisation observables linear and circular photon beam polarisation: , circ

• improved theoretical description

TAPS@MAMI: += (2.7±2.2±3)N

M. Kotulla et al., PRL 89 (2002) 272 001

TAPS @ MAMI 1999

TAPS forward wall384 BaF2 – modulesdistance: 150 cmangles: 1.10 – 20.00

Crystal Ball672 NaI - modules

CB/TAPS@MAMI-beam

LH2

CB (inside 2MWPCs, PID)TAPS

beam

Identification of p p 0 ` channelIdentification of p p 0 ` channel

S. Schumann(Mainz)

eliminatingbackgroundfrom p p 00

beam asymmetry:

discrepancy between data and calculation !!

inclusion of Born terms will reduce discrepancy(M. Vanderhaegen, priv. com.)

follow up experimentwith higher polarization needed !!

real polarisationrandomized polarisation

S. Schumann (Mainz)

dd

ddcirc

circular polarisation circ Re =5Re =3Re =1Re =0

energy distribution of `

S. Schumann (Mainz)

B. Boillat (Basel)

M. Kotulla et al., PRL89 (2002) 272 001

improvement in statistics !!

angular distribution of `

S. Schuman (Mainz)

B. Boillat (Basel)

M. Kotulla et al., PRL89 (2002) 272 001

improvement in statistics !!

present data (preliminary)

dE

dER

1

M. Kotulla et al.

Comparison of present data to pioneering experimentComparison of present data to pioneering experiment

current theoretical calculation does not reproduce reproduce spectral distribution! improved theoretical calculations needed to extract (+) !!!!

N11S

N

mm

)1(

Chiang et al., NPA 721 (2003) 731

28.4,06.3,84.1,61.0,61.0

6,4,2,0,2

unpol. LH2 target:

S11+(1535): p p ´

reaction calculation: effective Lagrangian model

total cross section: 10nb

Observablescross sectionshelicity asymmetry circ

expected sensitivity:

assuming 3200 counts (stat error)

assuming 5% systematic error

for m=1.8mN from energy differential

cross section:

N exp57.08.1

magnetic moment of S11(1535) resonancemagnetic moment of S11(1535) resonance

1/21/2

γ p Σ + (1189) K*0

K0

s π0

π0 π0

p π01/3

Eγ > 1840 MeV

p πo

1/21/2

1/3

γ p Σ + (1189) K 0 π0

K0

s π0 π0

Eγ > 1300 MeV

reactions with p 4 π0 final state reactions with p 4 π0 final state

γ p p π0 η 3π0

1/3

Eγ > 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 predictionstheoretical predictions

dynamical model for the cross section predictions

M. Doering et al., PRC 73, 045209 (2006)

Δ*(1700)→ ηΔ Δ*(1700)→KΣ*

M. Doering et al., nucl-th/ 0510015

theoretical predictionstheoretical predictions

EGeV

EGeV

EGeV

cosθ cosθ cosθ

bd

d

cos

Q. Zhao et al., PRC 64 ,052201 (2001)

K*0

Σ+

K0

p

γ

theoretical predictionstheoretical predictions

quark model predictions for the K*0 and K*+ photoproductions

significant t-channel kaon exchange

kinematic fit: p p 40kinematic fit: p p 40

p + (1189) K0* p0 K0 0 p 40 p + (1189) K0

* p0 K0 0 p 40 E= 2000-2150 MeV

+ (1189)

K0*(892) Ks

0(498)

angular distributionsangular distributions

Summary and outlookSummary and outlook

• strangeness production: p + (1189) K0* p 40

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 S11(1535) via p p ‘

sensitivity to (+)

Circular beam pol.:

580h @ 883 MeV

100h @ 550 MeV

circular polarisationcircular 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 / TAPS @ MAMIcross sections, beam/helicity asymmetry

coherent program (tests - reaction calculation)

very large sensitivity to MDM

future:

generalization to other resonances S11(1535)

Recent calculation:

EFT to calculatep‘p

systematic ansatz (NLO)

includes rescatteringMDM acquires real and imaginary part

no Born terms

based on effective Lagrangian description: Born terms, t-channel exchange,

rescattering included, gauge invariant

describes simultanously

n'p

p'p

W.-T. Chiang, M. Vanderhaeghen, S. N. Yang, D. Drechsel, hep-ph/0409078

Reaction model calculationReaction model calculation

MAMI 1999-2000 100cm

beam

TAPS @ MAMI 1999TAPS @ MAMI 1999

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

TAPS @ MAMI 1999TAPS @ MAMI 1999

Hadron Structure: + Magnetic MomentHadron Structure: + Magnetic Momentmagnetic moments: well known SU(3) octet baryons ( 10-10 s),

measured with spin precession techniques almost unknown for excited states

(except (1232) ) a test for baryon structure calculations

(wavefunction):

e.g. SU(3):

Pn

p Q;2

3

structure calculations S11(1535)

SU(3) 5.58 2.79

Lattice QCD (Cloet et al., PLB 563 (2003)) 4.99(56) 2.49(27)

QSM (Yang et al., PRD 70 (2004)) 5.39 2.66

experimental values

Castro et al., PLB 517 (2001) 339 6.14 0.51

M.Kotulla. et al., PRL 89, 272001 (2002) 2.7 2.2 3

PDG2004 3.7 - 7.5 2.7 2.2 3 —

Nm

e

2

what are the effective degrees of freedom?

BBB

M1