1. V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008 Photoproduction of    on protons ► Introduction ► Data analysis - overview - overview - timing - timing - identification of  p →  o  p reaction - identification of  p →  o  p reaction - tagging efficiency - tagging efficiency ► Results - overview - overview - total cross section - total cross section - invariant mass spectra - invariant mass spectra - angular distributions - angular distributions ► Summary

2. V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008Introduction The study of    photoproduction on proton has been performed recently in the energy region from threshold to 2.6 GeV [1-5]. The following important features of this process were found: - the process is dominated by the  (1232)  at E  < 1.4 GeV. At higher photon energies, a significant fraction of the process via N (1535)  and photon energies, a significant fraction of the process via N (1535)  and some pa o (980) is observed; some pa o (980) is observed; - two waves with P 33 and D 33 quantum numbers dominate the reaction; - at E  < 1.4 GeV the most important is the excitation of the  (1700) D 33 resonance, at higher energies  (1940) D 33 and  (1920) P 33 come into play; resonance, at higher energies  (1940) D 33 and  (1920) P 33 come into play; - Born terms seem to be insignificant. 1. T. Nakabayshi et al, Phys. Rev. C 74, 035202 (2006). 1. T. Nakabayshi et al, Phys. Rev. C 74, 035202 (2006). 2. I. Horn et al., (The CB-ELSA Collaboration), arXiv:0806.4251 [nucl-ex]; 2. I. Horn et al., (The CB-ELSA Collaboration), arXiv:0806.4251 [nucl-ex]; I. Horn, PhD Thesis, Universitat Bonn, Bonn (2004). I. Horn, PhD Thesis, Universitat Bonn, Bonn (2004). 3. J. Ajaka et al., (GRAAL Collaboration), Phys. Rev. Lett. 100, 052003 (2008). 3. J. Ajaka et al., (GRAAL Collaboration), Phys. Rev. Lett. 100, 052003 (2008). 4. M. Doring, E. Oset, and D. Strotmann, Phys. Rev. C 73, 045209 (2006). 4. M. Doring, E. Oset, and D. Strotmann, Phys. Rev. C 73, 045209 (2006). 5. A. Fix, M. Ostrick, and L. Tiator, Eur. Phys. J. A 36, 61 (2008). 5. A. Fix, M. Ostrick, and L. Tiator, Eur. Phys. J. A 36, 61 (2008). In spite of visible progress, a detailed empirical study of reaction dynamics is still needed.

3. V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008Introduction - after integration over   the distributions W CS and W HS are independent; - some of observables depend weakly on the model parameters; - determination of quantum number of resonances even for unpolarized measurements is possible. measurements is possible.Examples: for J = 1/2 resonances W HS (   ) and W CS (cos   ) are isotropic; for J = 1/2 resonances W HS (   ) and W CS (cos   ) are isotropic; for J = 3/2 these distributions depend only on the ratio a = (A 3/2 /A 1/2 ) 2 for J = 3/2 these distributions depend only on the ratio a = (A 3/2 /A 1/2 ) 2 moreover the distributions change the convex sign at a = 1. moreover the distributions change the convex sign at a = 1. Canonical CMS for (  N) Helicity CMS for (  N) Obtaining experimental angular distributions for further theoretical interpretation is main goal of the presented work

4. V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008 Data analysis: overview - Beam time periods: 7-21 June 2007 and 10-25 July 2007 - - electron beam energy: 1508 MeV - - beam current: 12 nA (full target) or 25 nA (empty target) - - radiator: 10  m Cu - - diameter of collimator: 4 mm - - target: LH2 (4.76 cm) - - detectors: CB, PID, TAPS - - tagger channels: 1-224 (617-1402 MeV) for analysis are used channels from 1 upto 147 (932-1402 MeV) - - trigger: M2+ and CB energy sum > 350 MeV Total number of raw events selected to be analyzed June July full target 5.78∙10 8 (~197 h) 4.62∙10 8 (~160 h) empty target 1.37∙10 7 (~10 h) 8.37∙10 7 (~60 h) main criteria for event sorting out: lost synchronization, wrong scaler readout, detector problems main analysis cuts: time, invariant mass, missing mass

5. Tagger-CB(photons) time (ns) Tagger-PID time (ns) FWHM 1.8 ns FWHM 1.4 ns Data analysis: timing V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008

6.  i  j  MeV) vs  k  l  (MeV) 4 photons, 3 combinations   cut    cut V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008  p →  o  p Data analysis: reaction identification

7. V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008 Data analysis: reaction identification    mp (MeV) Fit components: After BG subtraction Fit components: After BG subtraction Best fit gauss (black) & p3 (green) (red – GEANT sim.) Best fit gauss (black) & p3 (green) (red – GEANT sim.) 1.3-1.4 GeV GeV 0.932-1 GeV

8.   MeV) vs  6  (MeV) 8 photons, 28 combinations   cut   minimization Data analysis: reaction identification V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008  p →  o  o  p

9. V.L. Kashevarov, Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008 Data analysis: tagging efficiency Tagger channel July run 12087.dat – black 12183.dat – red 12251.dat – green 12305.dat – blue (empty)

10. V.L. Kashevarov, Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008 Results: overview Total number of good events after all cuts, subtraction of random coincidences, residual background, and empty target contribution:       For total cross sections are used only July run data (both  decay modes) For angular distributions – June and July data (  to  decay mode) June run 230.500 75.500 July run 187.700 60.500 July run without TAPS 136.000 21.700 GRAAL 57.400 CB@ELSA (0.93-2.5 GeV) 16.500

11. V.L. Kashevarov, Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008 Results: total cross sections Photon energy (GeV) Total cross section (  b) circles: blue – Tohoku 06 red – CB@ELSA 04 (syst. err. 20% is not included) green – GRAAL 08 black – this work lines: violet – best fit light-blue –  (1700)D 33 red –  (1600)P 33 green – Born terms   p →  o  p   p →  o    p Total cross section without normalization are by ~30% lower then GRAAL data Systematic errors: - acceptance ~3% - event selection ~3% - photon flux ???

12. V.L. Kashevarov, Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008 Results: total cross sections   (1700) D 33 at E  < 1.4 GeV is dominate;  at the near threshold region becomes determinative the contribution of the  (1600) P 33 resonance. contribution of the  (1600) P 33 resonance. Other possible resonances: -  (1620) S 31,  (1920) P 33,  (1930) D 35,  (1905) F 35 - negligible partial contributions; -  (1620) S 31,  (1920) P 33,  (1930) D 35,  (1905) F 35 - negligible partial contributions; -  (1750) P 31,  (1940) D 33 – one star status. -  (1750) P 31,  (1940) D 33 – one star status. Energy region of 1.2-1.4 GeV is the best to study the angular distributions because of the low remaining background and insignificant contribution of other resonances.

13. V.L. Kashevarov, Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008 Results: angular distributions GeV 1.2-1.3 GeV GeV 1.3-1.4 GeV Black points: data curves: red – best fit green – A 3/2 /A 1/2 =0.8 Blue – Γ( S 11 (1535)  ) / Γ total = 2% cos   (HS) cos   (CS)      (HS)      (CS) - data are corrected for the detector for the detector efficiency efficiency - integral over each distribution distribution equals to 1 equals to 1 Best fit parameters: photon decay helicity amplitudes for  (1700) D 33 : photon decay helicity amplitudes for  (1700) D 33 : A 3/2 / A 1/2 = 1.45 ± 0.04 (PDG 0.82 ± 0.2); A 3/2 / A 1/2 = 1.45 ± 0.04 (PDG 0.82 ± 0.2);  (1700) D 33 branching ratios :  (1700) D 33 branching ratios : Γ(  (1232)  ) / Γ total = (2.1 ± 0.2)% (no PDG value), Γ(  (1232)  ) / Γ total = (2.1 ± 0.2)% (no PDG value), Γ( S 11 (1535)  ) / Γ total = (0.10 ± 0.02)% (no PDG value). Γ( S 11 (1535)  ) / Γ total = (0.10 ± 0.02)% (no PDG value).

14. V.L. Kashevarov, Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008 GeV 1.2-1.3 GeV GeV 1.3-1.4 GeV Results: invariant mass spectra    p  p    (GeV) Blue points: experiment Red curves: theory - experimental data are corrected for the detector acceptance - integral over each spectrum equals to 1

15. V.L. Kashevarov, Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008Summary  New high statistics experimental data for the total cross section, the angular distributions, and the invariant mass section, the angular distributions, and the invariant mass spectra have been presented; spectra have been presented;  the cross section agrees well with previous results from GRAAL, but is lower than CB@ELSA results especially at the GRAAL, but is lower than CB@ELSA results especially at the near threshold region; near threshold region;  the dominance of the  (1700) D 33 at E  < 1.4 GeV is confirmed, but at the near threshold region becomes confirmed, but at the near threshold region becomes determinative the contribution of the  (1600) P 33 resonance; determinative the contribution of the  (1600) P 33 resonance;  fit of the Mainz-Tomsk model to the data gives the following parameters of the  (1700) D 33 resonance: parameters of the  (1700) D 33 resonance: A 3/2 / A 1/2 = 1.45 ± 0.04, A 3/2 / A 1/2 = 1.45 ± 0.04, Γ (  (1232)  ) / Γ total = (2.1 ± 0.2)%, Γ (  (1232)  ) / Γ total = (2.1 ± 0.2)%, Γ ( S 11 (1535)  ) / Γ total = (0.10 ± 0.02)% ; Γ ( S 11 (1535)  ) / Γ total = (0.10 ± 0.02)% ;  normalization of the total cross section is still open question;  plans:  p →  +  n reaction.