Photoproduction of neutral pion pairs off the proton with the Crystal-Barrel-Detector at ELSA

Michael Fuchs October 14th, 2005

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary

➢ Introduction➢ Experiment➢ Selection➢ Acceptance

➢ Problems➢ “Alternative” method

➢ Results➢ Total cross section➢ Differential cross sections➢ Dalitz-Plots

➢ Summary and Outlook

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary

Missing resonances

Nucleon resonances Löring, et.al. EPJA10, 309-346 (2001)

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary

Crystal-Barrel@ELSA Setup

➢ Tagging System➢ Energy: incoming ➢ Range: 25 – 95 % of Ee-

➢ Inner Detector➢ Charged particle ident.

➢ Crystal Barrel➢ Energy, direction: decay ➢ 1380 CsI(Tl) crystals➢ Covers 98% of 4

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary

➢ Cuts on reconstructed information➢ Tagging System

➢ Coincident hit in MWPC and Scintillator

➢ Inner detector➢ At least: 2 of 3 layers

→ Charged Particle

➢ Crystal-Barrel➢ 4 or 5 PEDs

➢ Invariant masses➢ Two invariant masses of two photons:

m() in interval: 134.97 ± 16.00 MeV

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary

➢ Decay of baryon resonances in:

➢ (1232) ➢ D

13 (1520)

➢ X (1660)

➢ Cuts on kinematic fit➢ E, p conservation

➢ Confidence Level (PS>1%

➢ Final Cuts➢ CL (p → p 00) > 10%➢ Matching Protons: (p

Inner & p

kin.Fit)

➢ CL (p → p00) > CL (p → p0)

Invariant p0-mass (@ 3.2 GeV)

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary

Dalitzplots: m2 (p0) vs m2 (p0)

Clear bandlike structures in Dalitzplot↓

Cascading decays of baryon resonances

1800 < √s < 2000 MeV 2000 < √s < 2200 MeV

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary

➢ Problems:➢ Areas with missing Acceptance

➢ Extrapolation necessary

➢ MC events➢ Distribution by phase space➢ Dynamics of reaction not included

➢ 3 particle final states➢ 5 independent variables➢ Automatic Integration

➢ Solution:➢ Use MC-events with correct reaction dynamics

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary

➢ Weighting procedure➢ Preparation

➢ Use➢ Original distr. (PS-MC)➢ Target distr. (Correct dynamics)

➢ Create➢ Normalized weights: wnorm

➢ Copy➢ By event➢ Generate random number: r➢ If: wnorm < r

➢ Copy whole eventin new dataset

➢ Next Step:➢ Weight factors using PWA

Normalized weights: wnorm

Original distribution (yellow) Target distribution (orange)

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary

➢ Partial wave analysis➢ Determination of resonance properties

➢ Masses➢ Partial widths➢ Coupling constants

➢ Version by A. Sarantsev, U. Thoma et. al.➢ Isobar - model➢ Breit-Wigner (or K-Matrix) parametrization ➢ Unbinned Maximum-Likelihood fit

➢ Event based➢ All correlations correctly taken into account➢ (5 independent variables)

➢ No fitting of projections !!

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary

Comparison ofAcceptance:

Phasespace MC

PWA weighted MC

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary

Total Cross Section

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary

135

0 <

√s

< 1

57

0 M

eV

157

0 <

√s

< 1

80

0 M

eV

180

0 <

√s

< 2

06

0 M

eV

206

0 <

√s

< 2

55

0 M

eV

Differential Cross Section: m(p0)

(1232)

D13(1520) X(1660)

(1232)

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary

135

0 <

√s

< 1

57

0 M

eV

157

0 <

√s

< 1

80

0 M

eV

180

0 <

√s

< 2

06

0 M

eV

206

0 <

√s

< 2

55

0 M

eV

Differential Cross Section: m(00)

f0(980)

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary

Dalitzplot m2 (p0) vs m2 (p0)

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary

➢ Selection➢ Good identification of: p→p00

➢ Acceptance➢ MC contains correct dynamics of reaction

➢ Cross Sections➢ Total and differential cross sections up to E ~ 3 GeV

➢ Data used for Partial Wave Analysis➢ Search for new baryon resonances

➢ Determination of resonance properties: ➢ Masses, Partial widths, Coupling constants

➢ Cascading decays of baryon resonances observed via

➢ (1232)D13

(1520)X(1660)

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary

➢ Acknowledgements

The Crystal-Barrel Collaboration➢ U. Thoma➢ E. Klempt➢ A. Sarantsev

Thank you for your attention!

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary ◦ Add-Ons

Gen MC Rek MC

Yes

Copy

Gen MC Rec MC Acceptance(Phase space)

PWA

4Vec: p, 0, 0

E, ID

Acceptance (PWA weighted)

wnorm

< r

Rndm()

r No

ID, wnorm

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary ◦ Add-Ons

Total cross section @ 1.4 GeV

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary ◦ Add-Ons

Total cross section @ 3.2 GeV

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary ◦ Add-Ons

Differential Cross Section

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary ◦ Add-Ons

Differential cross section: m(p0) for selected energie bins in E

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary ◦ Add-Ons

Differential cross section: m(00) for selected energie bins in E

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary ◦ Add-Ons

Dalitzplot m2 (p0) vs m2 (0)