Magentic Moment of the Δ + -Resonance via γp → pπ o γ Crystal Ball, TAPS collaborations Introduction Experiment Results Conclusions PhD theses of: B. Boillat, Basel E. Downie, Glasgow S. Schumann, Mainz B. Krusche, Gordon Conference on Photonuclear Reactions, Tilton, New Hampshire, August 2008
16
Embed
Introduction Experiment Results Conclusions · Introduction Experiment Results Conclusions PhD theses of: B. Boillat, Basel E. Downie, Glasgow S. Schumann, Mainz B. Krusche, Gordon
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Magentic Moment of the ∆+-Resonance via γp→ pπoγCrystal Ball, TAPS collaborations
Introduction
Experiment
Results
Conclusions
PhD theses of: B. Boillat, BaselE. Downie, GlasgowS. Schumann, Mainz
B. Krusche, Gordon Conference on Photonuclear Reactions, Tilton, New Hampshire, August 2008
magnetic moments of baryons
anomalous magnetic moments of the nucleon: first hint for nucleon sub-structure
magnetic moments are fundamental properties of baryons→ sensitive tests of quark model wave functions
precisely known for octet baryons from spin-precesion experiments
for decuplet baryons only possible for Ω−
prediction for ∆ baryons in SU(3) isospin symmetry: µ∆ = Q∆ × µp
some predictions from more realistic models: experimental status:
but background from many otherdiagrams (bremsstrahlung):
→ sophisticated models←for extraction of µ(∆+) needed
B. Krusche, Gordon Conference on Photonuclear Reactions, Tilton, New Hampshire, August 2008
models for the γp→ pπoγ reaction
principle: start with model for γp→ pπo, then add radiative photonsdifferent approaches:• Machavariani and Faessler: Born approximation with different models for ∆-propagator
• Chiang, Drechsel, Vanderhaeghen, Yang: unitary model with on-shell πN re-scattering
example: result for γp→ pπo tree level approximation on-shell re-scattering
150 200 250 300 350 400 4500
50
100
150
200
250
300
350
Ahrens
MacCormick
σ tot [
µb]
Eγ
lab [MeV]
• Pascalutsa and Vanderhaeghen: chiral effective field theory
v ; +t ; v v +(b) ( )(a) k0 k0
B. Krusche, Gordon Conference on Photonuclear Reactions, Tilton, New Hampshire, August 2008
B. Krusche, Gordon Conference on Photonuclear Reactions, Tilton, New Hampshire, August 2008
experimental setup - Crystal Ball and TAPS and...Crystal Ball detector:672 NaI crystals covering full azimuthal angle for polar angles between 20 - 160o
TAPS derector:510 BaF2 crystals covering forward polar angles down to 4o
TAPS-Veto detector, MWPC, and ∆E-detectorfor charged particle identification
10 cm
B. Krusche, Gordon Conference on Photonuclear Reactions, Tilton, New Hampshire, August 2008
TAPS Crystal Ball - at MAMI
B. Krusche, Gordon Conference on Photonuclear Reactions, Tilton, New Hampshire, August 2008
analysis first step: single πo production
identification with invariant mass and missing mass
comparison to previous results
0
5
10
15
20
25
30
0 30 60 90 120 150 180
dσ/d
Ω[µ
b/sr
]
Boillat 08, preliminary
Leukel 01
Θπ[deg]*
325-375 MeV
0
5
10
15
0 30 60 90 120 150 180
dσ/d
Ω[µ
b/sr
]
Boillat 08, preliminary
Leukel 01
Θπ[deg]*
375-425 MeV
0
2
4
6
8
10
0 30 60 90 120 150 180
dσ/d
Ω[µ
b/sr
]
Boillat 08, preliminary
Leukel 01
Θπ[deg]*
425-475 MeV
B. Krusche, Gordon Conference on Photonuclear Reactions, Tilton, New Hampshire, August 2008
analysis pπoγ first step
accept events with exactly three photons and one proton
identification with πo invariant mass and πoγ missing mass ?