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V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008

Photoproduction of p o h on protons. Introduction Data analysis - overview - timing - identification of g p → p o h p reaction - tagging efficiency Results - overview - total cross section - invariant mass spectra - angular distributions Summary.

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V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008

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  1. Photoproduction of poh on protons • Introduction • Data analysis - overview - timing - identification of g p →po h preaction - tagging efficiency • Results - overview - total cross section - invariant mass spectra - angular distributions • Summary V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008

  2. Introduction • The study of p oh 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 D(1232)hat Eg < 1.4 GeV. At higher • photon energies, a significant fraction of the process via N(1535)p and • some pao(980) is observed; • two waves with P33 and D33 quantum numbers dominate the reaction; • at Eg < 1.4 GeV the most important is the excitation of the D(1700)D33 • resonance, at higher energies D(1940)D33 and D(1920)P33 come into play; • Born terms seem to be insignificant. 1. T. Nakabayshiet al, Phys. Rev. C 74, 035202 (2006). 2. I. Horn et al., (The CB-ELSA Collaboration), arXiv:0806.4251 [nucl-ex]; I. Horn, PhD Thesis, Universitat Bonn, Bonn (2004). 3. J. Ajakaet al., (GRAAL Collaboration), Phys. Rev. Lett. 100, 052003 (2008). 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). In spite of visible progress , a detailed empirical study of reaction dynamics is still needed. V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008

  3. Introduction Canonical CMSfor (pN) Helicity CMSfor (pN) • - after integration over Qhthe distributions WCS and WHSare independent; • some of observables depend weakly on the model parameters; • determination of quantum number of resonances even for unpolarized • measurements is possible. • Examples: • for J = 1/2 resonances WHS (fp) and WCS (cosQp ) are isotropic; • for J = 3/2 these distributions depend only on the ratio a = (A3/2/A1/2)2 • moreover the distributions change the convex sign at a = 1. Obtaining experimental angular distributions for further theoretical interpretation is main goal of the presented work V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008

  4. 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 mm 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 • JuneJuly • full target 5.78∙108 (~197 h) 4.62∙108 (~160 h) • empty target 1.37∙107 (~10 h) 8.37∙107 (~60 h) • main criteria for event sorting out: • lost synchronization, wrong scaler readout, detector problems • main analysis cuts: time, invariant mass, missing mass V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008

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

  6. Data analysis: reaction identification g p → po(gg) h(gg) p 4 photons, 3 combinations c2 cut po h cut M(gigj ) (MeV) vs M(gkgl) (MeV) V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008

  7. Data analysis: reaction identification Fit components: After BG subtraction Best fit gauss (black) & p3 (green) (red – GEANT sim.) 0.932-1GeV 1.3-1.4 GeV MM(g, poh) - mp (MeV) V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008

  8. Data analysis: reaction identification g p → po(gg) h(3po) p 8 photons, 28 combinations c2 minimization c2 cut M(gg) (MeV) vs M(6g) (MeV) V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008

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

  10. Results: overview Total number of good events after all cuts, subtraction of random coincidences , residual background, and empty target contribution: h(3po) h(gg) 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 For total cross sections are used only July run data (both h decay modes) For angular distributions – June and July data ( h to gg decay mode) V.L. Kashevarov, Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008

  11. Results: total cross sections 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 – D(1700)D33 red – D(1600)P33 green – Born terms g p → po h(gg) p Total cross section (mb) g p → po h(3po) p • Total cross section without • normalization are by ~30% • lower then GRAAL data • Systematic errors: • acceptance ~3% • event selection ~3% • photon flux ??? Photon energy (GeV) V.L. Kashevarov, Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008

  12. Results: total cross sections • D(1700) D33 at Eg < 1.4 GeV is dominate; • at the near threshold region becomes determinative the • contribution of the D(1600)P33 resonance. • Other possible resonances: • - D(1620)S31, D(1920)P33, D(1930)D35, D(1905)F35 - negligible partial contributions; • - D(1750)P31, D(1940)D33 – 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. V.L. Kashevarov, Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008

  13. Results: angular distributions Black points: data curves: red – best fit green – A3/2/A1/2=0.8 Blue – Γ(S11(1535)p) / Γtotal = 2% 1.2-1.3 GeV • data are corrected • for the detector • efficiency • integral over each • distribution • equals to 1 1.3-1.4 GeV fp /p(HS) fp /p(CS) cosQp (HS) cosQp (CS) Best fit parameters: photon decay helicity amplitudes for D(1700)D33 : A3/2 / A1/2 = 1.45 ± 0.04 (PDG 0.82 ± 0.2); D(1700)D33 branching ratios : Γ(D(1232)h) / Γtotal = (2.1 ± 0.2)% (no PDG value), Γ(S11(1535)p) / Γtotal = (0.10 ± 0.02)% (no PDG value). V.L. Kashevarov, Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008

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

  15. Summary • New high statistics experimental data for the total cross • section, the angular distributions, and the invariant mass • spectra have been presented; • the cross section agrees well with previous results from • GRAAL, but is lower than CB@ELSA results especially at the • near threshold region; • the dominance of the D(1700) D33 at Eg < 1.4 GeV is • confirmed, but at the near threshold region becomes • determinative the contribution of the D(1600)P33 resonance; • fit of the Mainz-Tomsk model to the data gives the following • parameters of the D(1700)D33 resonance: • A3/2 / A1/2 = 1.45 ±0.04 , • Γ(D(1232)h) / Γtotal = (2.1 ± 0.2)% , • Γ (S11(1535)p) / Γtotal = (0.10 ± 0.02)% ; • normalization of the total cross section is still open question; • plans:g p →p+ h nreaction. V.L. Kashevarov, Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008

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