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

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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. - PowerPoint PPT Presentation

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  • V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008Photoproduction of poh on protonsIntroductionData analysis - overview - timing - identification of g p po h p reaction - tagging efficiencyResults - overview - total cross section - invariant mass spectra - angular distributionsSummary

  • V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008IntroductionThe 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)h at 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. Nakabayshi et 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. 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). 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 2008Introduction- after integration over Qh the distributions WCS and WHS are 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 (cos Qp ) 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.Canonical CMS for (pN)Helicity CMS for (pN)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 2008Data 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 June July full target 5.78108 (~197 h) 4.62108 (~160 h) empty target 1.37107 (~10 h) 8.37107 (~60 h) main criteria for event sorting out: lost synchronization, wrong scaler readout, detector problems

    main analysis cuts: time, invariant mass, missing mass

  • Tagger-CB(photons) time (ns)Tagger-PID time (ns)FWHM 1.8 nsFWHM 1.4 nsData analysis: timingV.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008

  • M(gigj ) (MeV) vs M(gkgl) (MeV)4 photons,3 combinationsc2 cut po h cutV.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008 g p po(gg) h(gg) pData analysis: reaction identification

  • V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008Data analysis: reaction identificationMM(g, poh) - mp (MeV) Fit components: After BG subtraction Best fit gauss (black) & p3 (green) (red GEANT sim.) 1.3-1.4 GeV0.932-1 GeV

  • M(gg ) (MeV) vs M(6g) (MeV)8 photons,28 combinationsc2 cutc2 minimizationData analysis: reaction identificationV.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008 g p po(gg) h(3po) p

  • V.L. Kashevarov, Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008Data analysis: tagging efficiencyTagger channelJuly run12087.dat black12183.dat red12251.dat green12305.dat blue (empty)

  • V.L. Kashevarov, Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008Results: overviewTotal number of good events after all cuts, subtraction of random coincidences , residual background, and empty target contribution: h(gg) h(3po) 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)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

  • V.L. Kashevarov, Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008Results: total cross sectionsPhoton energy (GeV)Total cross section (mb) circles:blue Tohoku 06red CB@ELSA 04(syst. err. 20% is not included)green GRAAL 08black this work

    lines:violet best fitlight-blue D(1700)D33red D(1600)P33green Born terms g p po h(gg) p g p po h(3po) pTotal cross section withoutnormalization are by ~30% lower then GRAAL data

    Systematic errors: acceptance ~3% event selection ~3% photon flux ???

  • V.L. Kashevarov, Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008Results: 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 2008Results: angular distributions1.2-1.3 GeV1.3-1.4 GeVBlack points: data curves: red best fitgreen A3/2/A1/2=0.8Blue (S11(1535)p) / total = 2% cosQp (HS)cosQp (CS)fp /p (HS)fp /p (CS) data are corrected for the detector efficiency integral over each distribution equals to 1Best 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 : (D(1232)h) / total = (2.1 0.2)% (no PDG value), (S11(1535)p) / total = (0.10 0.02)% (no PDG value).

  • V.L. Kashevarov, Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 20081.2-1.3 GeV1.3-1.4 GeVResults: invariant mass spectraM(po p)M(h p)M(po h) (GeV)Blue points: experiment

    Red curves: theory - 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 2008Summary 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 , (D(1232)h) / total = (2.1 0.2)% , (S11(1535)p) / total = (0.10 0.02)% ;

    normalization of the total cross section is still open question; plans: g p p+ h n reaction.

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