Photoproduction of neutral pion pairs off the proton

Photoproduction of neutral pion pairs off the proton with the Crystal-Barrel-Detector at ELSA Michael Fuchs October 14 th, 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. EPJA 10, 309 -346 (2001)

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

Introduction ◦ Experiment ◦ ➢ Selection ◦ Acceptance ◦ Results ◦ Summary Cuts on reconstructed information ➢ Tagging System ➢ ➢ Inner detector ➢ ➢ At least: 2 of 3 layers → Charged Particle Crystal-Barrel ➢ ➢ Coincident hit in MWPC and Scintillator 4 or 5 PEDs Invariant masses ➢ Two invariant masses of two photons: m( ) in interval: 134. 97 ± 16. 00 Me. V

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: (p. Inner & pkin. Fit) ➢ CL ( p → p 0 0) > CL ( p → p 0 ) Invariant p 0 -mass (@ 3. 2 Ge. V) ➢ Decay of baryon resonances in: ➢ (1232) ➢ D 13 (1520) ➢ X (1660)

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary Dalitzplots: m 2 (p 0) vs m 2 (p 0) 1800 < √s < 2000 Me. V 2000 < √s < 2200 Me. V Clear bandlike structures in Dalitzplot ↓ Cascading decays of baryon resonances

Introduction ◦ Experiment ◦ Selection ◦ ➢ Problems: ➢ Areas with missing Acceptance ➢ ➢ Acceptance ◦ Results ◦ Summary 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 ◦ ➢ Weighting procedure ➢ Preparation ➢ Use ➢ ➢ Original distr. (PS-MC) Target distr. (Correct dynamics) Create ➢ Normalized weights: wnorm Copy ➢ ➢ ➢ Original distribution (yellow) Target distribution (orange) By event Generate random number: r If: wnorm < r ➢ ➢ Acceptance ◦ Results ◦ Summary Copy whole event in new dataset Next Step: ➢ Weight factors using PWA Normalized weights: wnorm

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 of Acceptance: Phasespace MC PWA weighted MC

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Total Cross Section Results ◦ Summary

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary 1350 < √s < 1570 Me. V (1232) 1570 < √s < 1800 Me. V (1232) 1800 < √s < 2060 Me. V D 13(1520) 2060 < √s < 2550 Me. V Differential Cross Section: m(p 0) X(1660)

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary 1350 < √s < 1570 Me. V 1570 < √s < 1800 Me. V 1800 < √s < 2060 Me. V 2060 < √s < 2550 Me. V Differential Cross Section: m( 0 0) f 0(980)

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary Dalitzplot m 2 (p 0) vs m 2 (p 0)

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ ➢ Selection ➢ ➢ MC contains correct dynamics of reaction Cross Sections ➢ ➢ Good identification of: p→p 0 0 Acceptance ➢ ➢ Total and differential cross sections up to E ~ 3 Ge. V Data used for Partial Wave Analysis ➢ Search for new baryon resonances ➢ Determination of resonance properties: ➢ ➢ Summary Masses, Partial widths, Coupling constants Cascading decays of baryon resonances observed via ➢ (1232) D 13(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 ◦ Gen MC Rec MC Add-Ons Acceptance (Phase space) 4 Vec: p, 0 E , ID PWA ID, wnorm< r r Rndm() Gen MC No Yes Copy Rek MC Acceptance (PWA weighted)

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary ◦ Total cross section @ 1. 4 Ge. V Add-Ons

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary ◦ Total cross section @ 3. 2 Ge. V Add-Ons

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

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

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

Introduction ◦ Experiment ◦ Selection ◦ Acceptance ◦ Results ◦ Summary ◦ Dalitzplot m 2 (p 0) vs m 2 ( 0 0) Add-Ons