V.L. Kashevarov. Crystal Collaboration Meeting, Edinburg,13-15 Sept Photoproduction of    on protons ► Identification of  p →  o  p reaction ► Total cross section ► Differential cross sections ► Data fitting ► Beam helicity asymmetry ► Spin observables In collaboration with A. Fix and M. Ostrick

- 4 or 5 clusters (4 of them are neutrals) - invariant mass for all possible  combinations (4 photons give 3 independent combinations) -  2 minimization and cut - background subtraction using missing mass distributions for each energy or angular bin V.L. Kashevarov. Crystal Collaboration Meeting, Edinburg, September 2009  p →  o  p Reaction identification

The best combination of  pairs after   minimization and rejection of  o  o events. Two entries for each event corresponding to the two photon pair. V.L. Kashevarov. Crystal Collaboration Meeting, Edinburg, September 2009  p →  o  p Reaction identification

(a) Data (blue) and the best fit by a gaussian + polynominal function (red line) (b) The fit components: gaussian (black) and polynomial (red dashed) (c) Data after background subtrction (blue) and GEANT simulation (red line) V.L. Kashevarov. Crystal Collaboration Meeting, Edinburg, September 2009  p →  o  p Reaction identification Missing mass distributions after subtraction of random coincidences and empty target contribution and aplying   cut E  < 1 GeV E  > 1.2 GeV

LNS and GRALL  stat +syst CB-ELSA  stat (syst ~15%)  stat (syst ~5%) Blue curve shows the energy dependence of the reaction phase space with arbitrary normalization V.L. Kashevarov. Crystal Collaboration Meeting, Edinburg, September 2009  p →  o  p Total cross section Data from July 2007 run

V.L. Kashevarov. Crystal Collaboration Meeting, Edinburg, September 2009  p →  o  p Differential cross sections a(W) = (A 3/2 / A 1/2 ) 2 r =  S 11 ) /  a = 0.7 (1.0 – 1.1 GeV) a = 1.2 (1.1 – 1.2 GeV) a = 1.7 (1.2 – 1.3 GeV) a = 2.0 (1.3 – 1.4 GeV) r = 2/3 Data from June and July 2007 runs

Solid black curve: r = 2/3, a =2.0 Dashed red curve: r = 1/6, a = 2.0 Dotted blue curve: r = 2/3, a =0.7 High sensitivity of the distributions W K (   ) and W H (   ) to a and W K (   ) and W H (   ) to r V.L. Kashevarov. Crystal Collaboration Meeting, Edinburg, September 2009  p →  o  p Differential cross sections

Black circles: 1.72<W<1.87 GeV Red circles: CB-ELSA 1.7<W<1.9 GeV V.L. Kashevarov. Crystal Collaboration Meeting, Edinburg, September 2009  p →  o  p Differential cross sections

V.L. Kashevarov. Crystal Collaboration Meeting, Edinburg, September 2009  p →  o  p Data fitting the best fits: green line: D33(1700) blue line: D33(1700) with d-wave red line: D 33 (1700) with d-wave + P 33 (1600) + P 31 (1750) + F 35 (1905)

V.L. Kashevarov. Crystal Collaboration Meeting, Edinburg, September 2009  p →  o  p Data fitting blue line: the best fit with D 33 (1700), P 33 (1600), P 31 (1750), F 35 (1905), and Born terms Partial contributions: Red line: D 33 (1700) Green line: P 33 (1600) Black line: P 31 (1750) Dashed red line: F 35 (1905) Dashed blue line: Born terms

V.L. Kashevarov. Crystal Collaboration Meeting, Edinburg, September 2009  p →  o  p Data fitting The quality of the phenomenological analysis can be greatly improved by accumulating additional data. For example, polarization observables on protons and neutrons. The simplest of them: Beam helicity asymmetry  only circularly polarized photon beam Such a data was taken already!

D. Krambrich, F. Zehr et al., Phys. Rev. Lett. 103, (2009)    c = in experimental data analysis: Usually is analized as   dependence in the helicity system and may be expanded over function sin n   (n is integer) n is determined by the orbital momenta of the contributing resonances Pure D 33 (1700) provides only sin   term P 31 (1750), P 33 (1600), F 35 (1905) appear in the sin 2   term due to interference with D 33 (1700) sin 3   term coming from the interference between s and d waves in the D 33   decay V.L. Kashevarov. Crystal Collaboration Meeting, Edinburg, September 2009  p →  o  p Beam helicity asymmetry + + - + + - + - - + - - Y+ + Y- Y+ + Y- Y+ - Y- Y+ - Y- P 1

V.L. Kashevarov. Crystal Collaboration Meeting, Edinburg, September 2009  p →  o  p Beam helicity asymmetry Fit function : F = P 1 sin  + P 2 sin 2  Data from July 2007 and April 2009 runs

V.L. Kashevarov. Crystal Collaboration Meeting, Edinburg, September 2009  p →  o  p Beam helicity asymmetry Fit function : F = P 1 sin  + P 2 sin 2  + P 3 sin 3  Data from July 2007 and April 2009 runs

V.L. Kashevarov. Crystal Collaboration Meeting, Edinburg, September 2009  p →  o  p Spin observables Our future plans are connected with the proposal A2-09/09: “Spin observables for ph photoproduction in D 33 (1700) region” We will measure the transverse spin observables T and F We need: - circulary polarized photon beam (only for F); - transversely polarized proton target  frozen-spin butanol (C 4 H 9 OH) target Disadvantage: additional background from reactions on 12 C and 16 O Estimation of this background: - analysis of data taken with a carbon target using the same procedure as for runs with LH 2 target; -normalization of the photon flux to LH 2 target run; - taking into account the number of 12 C nuclei in a carbon target with respect to butanol ( 16 O = 4/3 12 C)

V.L. Kashevarov. Crystal Collaboration Meeting, Edinburg, September 2009  p →  o  p Spin observables E  = 1.0 – 1.1 GeVE  = 1.1 – 1.2 GeV Expected missing mass spectra for butanol target red line: background contribution from 12 C and 16 O (data from June 2008 run, 12 C target) blue line: investigated reraction (data from July 2007 run, LH 2 target) Proposal A2-09/09 was supported by the PAC with the highest priority (A)

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