1. Photoproduction of poh pairs on the proton
Motivation
Data analysis
- overview
- timing
- identification of g p → po h p reaction
- tagging efficiency
Results
- total cross section
- invariant mass spectra
- angular distributions
Summary
V.L. Kashevarov. Crystal Collaboration Meeting, Dubrovnik, 7-9 April 2008

2. g p → D(1700)D33 → D(1232)P33 h Motivation GRAAL CB@ELSA
Horn et al. arXiv: v1 [nucl-ex] (2007)
The systematic error of ±20% is not included
J. Ajaka et al. PRL, 100, (2008)
Hatched band: uncertainty of g pD(1700) coupling
M. Doring, E. Oset, and D. Strotmann, PR, C73, (2006)
Data near threshold on the both pictures: T. Nakabayashi et al. PR, C74, (2006)
g p → D(1700)D33 → D(1232)P33 h
V.L. Kashevarov. Crystal Collaboration Meeting, Dubrovnik, 7-9 April 2008

3. Motivation
a-f are Born terms, N* is S11(1535), (about 10% of the total cross section)
g,f are resonance R in intermediate state
A. Fix, M. Ostrick, and L. Tiator. EPJ, (2008) submitted, now is available in ArXiv
V.L. Kashevarov. Crystal Collaboration Meeting, Dubrovnik, 7-9 April 2008

4. Motivation
D(1900)S31 ** D(1920)P33 *** D(1930)D35 ***
D(1910)P31 **** D(1700)D33 **** D(1905)F35 ****
Canonical CMS for (pN)
Helicity CMS for (pN)
Examples: for J=1/2 resonances distribution over f p (HS) is uniform;
for J >1/2 resonances cosQ p depends on the ratio a =A3/2 /A1/2
and it is converx at a=1
Obtaining experimental angular distributions for further theoretical
interpretation is main goal of the presented work
V.L. Kashevarov. Crystal Collaboration Meeting, Dubrovnik, 7-9 April 2008

5. Data analysis: overview
- Beam time periods: 7-21 June 2007 and 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: ( MeV)
for analysis are used channels from 1 upto 147 ( MeV)
trigger: M2+ and CB energy sum > 350 MeV
Total number of raw events selected to be analyzed
June July
full target ∙108 (~197 h) ∙108 (~160 h)
empty target ∙107 (~10 h) ∙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 Collaboration Meeting, Dubrovnik, 7-9 April 2008

6. Data analysis: timing Tagger-PID time (ns)
The best channel (no 202) has FWHM ~ 1ns
1, 27,
167
Ch. 28
21, 23, 97
212,
217 29 28
Tagger TDC hits
Tagger-PID time (ns)
V.L. Kashevarov. Crystal Collaboration Meeting, Dubrovnik, 7-9 April 2008

7. Data analysis: timing Tagger-CB(photons) time (ns)
FWHM ns
FWHM ns
Tagger-PID time (ns)
Tagger-CB(photons) time (ns)
V.L. Kashevarov. Crystal Collaboration Meeting, Dubrovnik, 7-9 April 2008

8. 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 Collaboration Meeting, Dubrovnik, 7-9 April 2008

9. Data analysis: reaction identificationmp
MM cut
mpo mh
GeV
s = 8.6 MeV
s = 23 MeV
s = 5 MeV
GeV
s = 10 MeV
s = 8.8 MeV
s = 24 MeV
GeV
s = 15 MeV
s = 8.9 MeV
s = 24 MeV
GeV
s = 19 MeV
s = 8.9 MeV
s = 24 MeV
GeV
s = 23 MeV
s = 9.1 MeV
s = 25 MeV
MM(g, poh)
MM(g, poh)
M(gg )
M(gg )
Blue - full target, black - empty target, green - difference, red - simulation
V.L. Kashevarov. Crystal Collaboration Meeting, Dubrovnik, 7-9 April 2008

10. 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 Collaboration Meeting, Dubrovnik, 7-9 April 2008

11. Data analysis: tagging efficiency
June run
July run
11764.dat – black
11881.dat – red
11884.dat – green
11943.dat – blue
11982.dat - yellow
12087.dat – black
12183.dat – red
12251.dat – green
12305.dat – blue (empty)
Tagging efficiency
Tagger channel
Tagger channel
V.L. Kashevarov, Crystal Collaboration Meeting, Dubrovnik, 7-9 April 2008

12. Data analysis: tagging efficiency
June run
Tagger Efficiency runs
± 5 %
July run
P2/tagger_scalr(224)
± 5 %
Number of scaler readout
V.L. Kashevarov, Collaboration Meeting, Dubrovnik, 7-9 April 2008

13. h(3po) h(gg) Results: overview
Total number of good events after all cuts, subtraction
of random coincidences and empty target contribution:
h(3po)
h(gg)
June run
July run
July run without TAPS
GRAAL
( GeV)
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 Collaboration Meeting, Dubrovnik, 7-9 April 2008

14. Results: total cross sections
g p → po h(gg) p
open circles – Tohoku 06
green – 07
blue – GRAAL 08
black – this work
red – this work (without TAPS)
July run only
Statistical errors only
Total cross section (mb)
g p → po h(3po) p
Total cross section without
TAPS are by ~25% lower
then GRAAL data
Photon energy (GeV)
V.L. Kashevarov, Crystal Collaboration Meeting, Dubrovnik, 7-9 April 2008

15. Results: invariant mass spectra
blue: experiment
red: g p  h D+(1232)
simulation
green: g p  po S11(1535)
GeV
GeV
GeV
GeV
GeV
M(po p)
M(h p)
M(po h)
V.L. Kashevarov. Crystal Collaboration Meeting, Dubrovnik, 7-9 April 2008

16. Results: angular distributions
Blue points:
experiment
Red curves:
best fit
GeV
data are corrected
for the detector
efficiency
integral over each
distribution
equals to 1
GeV
fp /p (HS)
fp /p (CS)
cosQp (HS)
cosQp (CS)
Photon decay amplitudes for D (1700)  N g :
A3/2 / A1/2 = (PDG 0.82±0.2, Arndt ±0.25)
Branching fractions for D (1700) decay modes:
(1232) h % (no PDG value)
S11(1535) p % (no PDG value)
V.L. Kashevarov, Crystal Collaboration Meeting, Dubrovnik, 7-9 April 2008

17. Results: invariant mass spectra
GeV
Blue points:
experiment
Red curves:
theory
GeV
M(po p)
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 Collaboration Meeting, Dubrovnik, 7-9 April 2008

18. Summary
> New experimental data for the total cross section, the angular distributions and the invariant mass spectra have presented;
> fit the data to Mainz-Tomsk model have resulted the following parameters of the D(1700)D33 resonance:
Things to do:
> estimate systematic errors;
> evaluate uncertainties of the fit;
> verify absolute normalization of the total cross section by obtaining the total cross section of g p → po po p
relation for helicity photon decay amplitudes:
A3/2 / A1/2 = 1.45
branching fractions for the decay modes:
(1232) h %
S11(1535) p %
V.L. Kashevarov, Crystal Collaboration Meeting, Dubrovnik, 7-9 April 2008

19. g p → p+ h(gg) n M(gg ) (MeV) Missing mass cut MM(g, p+h) – mn (MeV)
V.L. Kashevarov. Crystal Collaboration Meeting, Dubrovnik, 7-9 April 2008

20. g p → p+ h(3po) n M(3po) (MeV) Missing mass cut MM(g, p+h) – mn (MeV)
V.L. Kashevarov. Crystal Collaboration Meeting, Dubrovnik, 7-9 April 2008

21. Results: invariant mass spectra
blue: experiment
red: g p  h D+(1232)
simulation
green: g p  po S11(1535)
GeV
GeV
GeV
GeV
GeV
M(po p)
M(h p)
M(po h)
V.L. Kashevarov. Crystal Collaboration Meeting, Dubrovnik, 7-9 April 2008