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

1. Photoproduction of neutral pion pairs off the proton with the Crystal-Barrel-Detector at ELSA Michael Fuchs October 14th, 2005

2. Introduction◦Experiment◦Selection◦Acceptance◦Results◦SummaryIntroduction◦Experiment◦Selection◦Acceptance◦Results◦Summary • Introduction • Experiment • Selection • Acceptance • Problems • “Alternative” method • Results • Total cross section • Differential cross sections • Dalitz-Plots • Summary and Outlook

3. Introduction◦Experiment◦Selection◦Acceptance◦Results◦SummaryIntroduction◦Experiment◦Selection◦Acceptance◦Results◦Summary Missing resonances Nucleon resonances Löring, et.al. EPJA10, 309-346 (2001)

4. Introduction◦ Experiment◦Selection◦Acceptance◦Results◦Summary Crystal-Barrel@ELSA Setup • Tagging System • Energy: incoming g • Range: 25 – 95 % of Ee- • Inner Detector • Charged particle ident. • Crystal Barrel • Energy, direction: decay g • 1380 CsI(Tl) crystals • Covers 98% of 4p

5. 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

6. Invariant p0-mass (@ 3.2 GeV) Introduction◦ Experiment◦ Selection◦Acceptance◦Results◦Summary • Cuts on kinematic fit • E, p conservation • Confidence Level (PS) >1% • Final Cuts • CL ( p → p00) > 10% • Matching Protons: (pInner & pkin.Fit) • CL (p → p00) > CL (p → p0) • Decay of baryon resonances in: •  (1232)  • D13 (1520)  • X (1660) 

7. Introduction◦ Experiment◦ Selection◦Acceptance◦Results◦Summary Dalitzplots: m2(p0)vs m2(p0) 1800 < √s < 2000 MeV 2000 < √s < 2200 MeV Clear bandlike structures in Dalitzplot↓Cascading decays of baryon resonances

8. 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

9. 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 Original distribution (yellow) Target distribution (orange) Normalized weights: wnorm

10. 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 !!

11. Introduction◦ Experiment◦ Selection◦ Acceptance◦Results◦Summary Comparison of Acceptance: Phasespace MC PWA weighted MC

12. Introduction◦ Experiment◦ Selection◦ Acceptance◦ Results◦Summary Total Cross Section Preliminary

13. Introduction◦ Experiment◦ Selection◦ Acceptance◦ Results◦Summary Differential Cross Section: m(pp0) D(1232) D(1232) Preliminary Preliminary 1570 < √s < 1800 MeV 1350 < √s < 1570 MeV D13(1520) X(1660) Preliminary Preliminary 2060 < √s < 2550 MeV 1800 < √s < 2060 MeV

14. Introduction◦ Experiment◦ Selection◦ Acceptance◦ Results◦Summary Differential Cross Section: m(p0p0) Preliminary Preliminary 1570 < √s < 1800 MeV 1350 < √s < 1570 MeV f0(980) Preliminary Preliminary 2060 < √s < 2550 MeV 1800 < √s < 2060 MeV

15. Introduction◦ Experiment◦ Selection◦ Acceptance◦ Results◦Summary Dalitzplot m2(p0)vs m2(p0)

16. Introduction◦ Experiment◦ Selection◦ Acceptance ◦Results◦ Summary • Selection • Good identification of: p→p00 • Acceptance • MC contains correct dynamics of reaction • Cross Sections • Total and differential cross sections up to Eg ~ 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)

17. Introduction◦ Experiment◦ Selection◦ Acceptance ◦Results◦ Summary • Acknowledgements The Crystal-Barrel Collaboration • U. Thoma • E. Klempt • A. Sarantsev Thank you for your attention!

18. Acceptance(Phase space) Rec MC 4Vec: p, 0, 0E, ID PWA ID, wnorm Yes No r Copy Rndm() Acceptance (PWA weighted) Gen MC Rek MC Introduction◦ Experiment◦ Selection◦ Acceptance ◦Results◦ Summary◦ Add-Ons Gen MC wnorm< r

19. Introduction◦ Experiment◦ Selection◦ Acceptance ◦Results◦ Summary◦ Add-Ons Total cross section @ 1.4 GeV Preliminary

20. Introduction◦ Experiment◦ Selection◦ Acceptance ◦Results◦ Summary◦ Add-Ons Total cross section @ 3.2 GeV Preliminary

21. Introduction◦ Experiment◦ Selection◦ Acceptance ◦Results◦ Summary◦ Add-Ons Differential Cross Section Preliminary Preliminary

22. Introduction◦ Experiment◦ Selection◦ Acceptance ◦Results◦ Summary◦ Add-Ons Differential cross section: m(p0) for selected energie bins in E Preliminary Preliminary

23. Introduction◦ Experiment◦ Selection◦ Acceptance ◦Results◦ Summary◦ Add-Ons Differential cross section: m(00) for selected energie bins in E Preliminary Preliminary

24. Introduction◦ Experiment◦ Selection◦ Acceptance ◦Results◦ Summary◦ Add-Ons Dalitzplot m2(p0)vs m2(p0 0)