V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Edinburg ,13-15 Sept. 2009

Photoproduction of poh on protons

► Identification of g p → po h 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 gg combinations (4 photons give 3 independent combinations) - c2 minimization and cut - background subtraction using missing mass distributions for each energy or angular bin

V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Edinburg, 13-15 September 2009

g p → po h p

Reaction identification

The best combination of gg pairs after c2 minimization and rejection of po

po events. Two entries for each event corresponding to the two photon pair.

V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Edinburg, 13-15 September 2009

g p → po h 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 Ball@MAMI Collaboration Meeting, Edinburg, 13-15 September 2009

g p → po h p

Reaction identification

Missing mass distributions after subtraction of random coincidences and empty target contribution and aplying c2 cut

E g < 1 GeV

E g > 1.2 GeV

LNS and GRALL stat +systCB-ELSA stat (syst ~15%)CB@MAMI stat (syst ~5%)

Blue curve shows the energy dependence of the reaction phase space with arbitrary normalization

V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Edinburg, 13-15 September 2009

g p → po h p

Total cross section

Data from July 2007 run

V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Edinburg, 13-15 September 2009

g p → po h p

Differential cross sections

a(W) = (A 3/2 / A 1/2 ) 2

r = (G p S 11 ) / ( )G h D

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 fromJune and July 2007 runs

Solid black curve: r = 2/3, a =2.0Dashed red curve: r = 1/6, a = 2.0Dotted blue curve: r = 2/3, a =0.7

High sensitivity of the distributions WK(Qp) and WH(fp) to aand WK(fp) and WH(Qp) to r

V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Edinburg, 13-15 September 2009

g p → po h p

Differential cross sections

Black circles: CB@MAMI 1.72<W<1.87 GeVRed circles: CB-ELSA 1.7<W<1.9 GeV

V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Edinburg, 13-15 September 2009

g p → po h p

Differential cross sections

V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Edinburg, 13-15 September 2009

g p → po h p

Data fitting

the best fits:

green line: D33(1700)

blue line: D33(1700) with d-wave

red line: D33(1700) with d-wave + P33(1600) + P31(1750) + F35(1905)

V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Edinburg, 13-15 September 2009

g p → po h p

Data fitting

blue line: the best fit with D33(1700), P33(1600), P31(1750), F35(1905), and Born terms

Partial contributions:

Red line: D33(1700)Green line: P33(1600)Black line: P31(1750)Dashed red line: F35(1905)Dashed blue line: Born terms

V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Edinburg, 13-15 September 2009

g p → po h p

Data fitting

The quality of the phenomenological analysis can be greatly improvedby 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, 052002 (2009) pp Sc = in experimental data analysis:

Usually is analized as fp dependence in the helicity system and may be expanded over function sin nfp (n is integer)

n is determined by the orbital momenta of the contributing resonances

Pure D33(1700) provides only sin fp term

P31(1750), P33(1600), F35(1905) appear in the sin 2fp term due tointerference with D33(1700)

sin 3fp term coming from the interference between s and d waves inthe D33 h D decay

V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Edinburg, 13-15 September 2009

g p → po h p

Beam helicity asymmetry

s+ + s-

s+ - s-

Y+ + Y-

Y+ - Y-

P 1

V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Edinburg, 13-15 September 2009

g p → po h p

Beam helicity asymmetry

Fit function : F = P1 sin f + P2 sin 2f

Data from July 2007 andApril 2009 runs

V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Edinburg, 13-15 September 2009

g p → po h p

Beam helicity asymmetry

Fit function : F = P1 sin f + P2 sin 2f + P3 sin 3f

Data from July 2007 andApril 2009 runs

V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Edinburg, 13-15 September 2009

g p → po h p

Spin observables

Our future plans are connected with the proposal A2-09/09:“Spin observables for ph photoproduction in D33(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 (C4H9OH) target

Disadvantage: additional background from reactions on 12C and 16O

Estimation of this background: - analysis of data taken with a carbon target using the same procedure as for runs with LH2 target; -normalization of the photon flux to LH2 target run; - taking into account the number of 12C nuclei in a carbon target with respect to butanol (16O = 4/3 12C)

V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Edinburg, 13-15 September 2009

g p → po h p

Spin observables

Eg= 1.0 – 1.1 GeV Eg= 1.1 – 1.2 GeV

Expected missing mass spectra for butanol target

red line: background contribution from 12C and 16O (data from June 2008 run, 12C target)blue line: investigated reraction (data from July 2007 run, LH2 target)

Proposal A2-09/09 was supported by the PAC with the highest priority (A)

This article was accepted on 28.08.09 for publication in EPJA