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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*
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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
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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
++
+
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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 !!
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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
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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
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Identification of p p 0 ` channelIdentification of p p 0 ` channel
S. Schumann(Mainz)
eliminatingbackgroundfrom p p 00
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beam asymmetry:
discrepancy between data and calculation !!
inclusion of Born terms will reduce discrepancy(M. Vanderhaegen, priv. com.)
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follow up experimentwith higher polarization needed !!
real polarisationrandomized polarisation
S. Schumann (Mainz)
dd
ddcirc
circular polarisation circ Re =5Re =3Re =1Re =0
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energy distribution of `
S. Schumann (Mainz)
B. Boillat (Basel)
M. Kotulla et al., PRL89 (2002) 272 001
improvement in statistics !!
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angular distribution of `
S. Schuman (Mainz)
B. Boillat (Basel)
M. Kotulla et al., PRL89 (2002) 272 001
improvement in statistics !!
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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 (+) !!!!
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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
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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
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theoretical predictionstheoretical predictions
dynamical model for the cross section predictions
M. Doering et al., PRC 73, 045209 (2006)
Δ*(1700)→ ηΔ Δ*(1700)→KΣ*
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M. Doering et al., nucl-th/ 0510015
theoretical predictionstheoretical predictions
EGeV
EGeV
EGeV
cosθ cosθ cosθ
bd
d
cos
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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
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kinematic fit: p p 40kinematic fit: p p 40
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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)
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angular distributionsangular distributions
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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 (+)
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Circular beam pol.:
580h @ 883 MeV
100h @ 550 MeV
circular polarisationcircular polarisation
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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)
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Recent calculation:
EFT to calculatep‘p
systematic ansatz (NLO)
includes rescatteringMDM acquires real and imaginary part
no Born terms
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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
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MAMI 1999-2000 100cm
beam
TAPS @ MAMI 1999TAPS @ MAMI 1999
6 62, 1 138 detectors with individualveto detector, solid angle: ~0.40 4 sr
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TAPS @ MAMI 1999TAPS @ MAMI 1999
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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