V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008 Photoproduction of on protons ► Introduction ► Data analysis

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

Photoproduction of Photoproduction of on protons on protons

► IntroductionIntroduction► Data analysisData analysis - overview- overview - timing- timing - identification of - identification of p p →→ oo p p reactionreaction - tagging efficiency- tagging efficiency► ResultsResults - overview- overview - total cross section- total cross section - invariant mass spectra- invariant mass spectra - angular distributions- angular distributions► SummarySummary


IntroductionIntroductionThe study of The study of photoproduction on proton has been performed photoproduction on proton has been performed recently in the energy region from threshold to 2.6 GeV [1-5]. recently in the energy region from threshold to 2.6 GeV [1-5].

The following important features of this process were found:The following important features of this process were found:

- the process is dominated by the the process is dominated by the (1232)(1232)at Eat E < 1.4 GeV. At higher < 1.4 GeV. At higher photon energies, a significant fraction of the process via photon energies, a significant fraction of the process via NN(1535)(1535) and and some some papaoo(980) is observed;(980) is observed;- two waves with two waves with PP3333 and and DD3333 quantum numbers dominate the reaction; quantum numbers dominate the reaction;- at Eat E < 1.4 GeV the most important is the excitation of the < 1.4 GeV the most important is the excitation of the (1700)(1700)DD3333 resonance, at higher energies resonance, at higher energies (1940)(1940)DD3333 and and (1920)(1920)PP3333 come into come into play;play;- Born terms seem to be insignificant.Born terms seem to be insignificant.

1. T. Nakabayshi 1. T. Nakabayshi et al,et al, Phys. Rev. C Phys. Rev. C 7474, 035202 (2006)., 035202 (2006). 2. I. Horn 2. I. Horn et al.,et al., (The CB-ELSA Collaboration), arXiv:0806.4251 [nucl-ex]; (The CB-ELSA Collaboration), arXiv:0806.4251 [nucl-ex]; I. Horn, PhD Thesis, Universitat Bonn, Bonn (2004). I. Horn, PhD Thesis, Universitat Bonn, Bonn (2004). 3. J. Ajaka 3. J. Ajaka et al.,et al., (GRAAL Collaboration), Phys. Rev. Lett. (GRAAL Collaboration), Phys. Rev. Lett. 100100, 052003 (2008)., 052003 (2008). 4. M. Doring, E. Oset, and D. Strotmann, Phys. Rev. C 4. M. Doring, E. Oset, and D. Strotmann, Phys. Rev. C 7373, 045209 (2006)., 045209 (2006). 5. A. Fix, M. Ostrick, and L. Tiator, Eur. Phys. J. A 5. A. Fix, M. Ostrick, and L. Tiator, Eur. Phys. J. A 3636, 61 (2008). , 61 (2008).

In spite of visible progress , a detailed empirical study of reaction dynamics is In spite of visible progress , a detailed empirical study of reaction dynamics is still needed. still needed.


IntroductionIntroduction

- after integration over - after integration over the distributions Wthe distributions WCSCS and W and WHSHS are independent; are independent; - some of observables depend weakly on the model parameters; some of observables depend weakly on the model parameters; - determination of quantum number of resonances even for unpolarized determination of quantum number of resonances even for unpolarized measurements is possible. measurements is possible. Examples: Examples: for J = 1/2 resonances Wfor J = 1/2 resonances WHSHS ( () and W) and WCSCS (cos (cos ) are isotropic; ) are isotropic; for J = 3/2 these distributions depend only on the ratio a = (Afor J = 3/2 these distributions depend only on the ratio a = (A3/23/2/A/A1/21/2))2 2

moreover the distributions change the convex sign at a = 1.moreover the distributions change the convex sign at a = 1.

Canonical CMS for (N) Helicity CMS for (N)

Obtaining experimental angular distributions for further theoretical interpretation is main goal of the presented work


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: 10m 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 5.78∙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

Tagger-CB(photons) time (ns)

Tagger-PID time (ns)

FWHM 1.8 ns

FWHM 1.4 ns

Data analysis: timingData analysis: timing


ij MeV) vs kl (MeV)

4 photons,3 combinations cut c

ut


p p → → oo p p

Data analysis: reaction identificationData analysis: reaction identification



mp (MeV)

Fit components: After BG Fit components: After BG subtractionsubtraction Best fit gauss (black) & p3 (green) (red – GEANT Best fit gauss (black) & p3 (green) (red – GEANT sim.) sim.)

1.3-1.4 GeV1.3-1.4 GeV

0.932-1 GeV GeV

MeV) vs 6(MeV)

8 photons,28 combinations cut minimization



p p → → oooo p p

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

Data analysis: tagging efficiencyData analysis: tagging efficiency

Tagger channelTagger channel

July runJuly run

12087.dat – black12183.dat – red12251.dat – green12305.dat – blue (empty)


Results: overviewResults: overview

Total number of good events after all cuts, subtraction of random Total number of good events after all cuts, subtraction of random coincidences , residual background, and empty target contribution:coincidences , residual background, and empty target contribution:

For total cross sections are used only July run data (both For total cross sections are used only July run data (both decay modes) decay modes)For angular distributions – June and July data ( For angular distributions – June and July data ( to to decay mode) decay mode)

June run 230.500 June run 230.500 75.500 75.500

July run 187.700 July run 187.700 60.50060.500

July run without TAPS 136.000 July run without TAPS 136.000 21.70021.700

GRAAL 57.400GRAAL 57.400

CB@ELSA (0.93-2.5 GeV) 16.500CB@ELSA (0.93-2.5 GeV) 16.500


Results: total cross sectionsResults: total cross sections

Photon energy (GeV)Photon energy (GeV)

Tota

l cr

oss

sect

ion (

Tota

l cr

oss

sect

ion ( b

)b)

circles:blue – Tohoku 06red – CB@ELSA 04(syst. err. 20% is not included)green – GRAAL 08black – this work

lines:violet – best fitlight-blue – (1700)D33

red – (1600)P33

green – Born terms

p p → → oo pp

p p → → oo p p

Total cross section withoutTotal cross section withoutnormalization are by ~30% normalization are by ~30% lower then GRAAL datalower then GRAAL data

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


Results: total cross sectionsResults: total cross sections

(1700)(1700) D D3333 at E at E < 1.4 GeV is dominate; < 1.4 GeV is dominate;

at the near threshold region becomes determinative the at the near threshold region becomes determinative the contribution of the contribution of the (1600)(1600)PP3333 resonance. resonance.

Other possible resonances:Other possible resonances: - - (1620)(1620)SS3131, , (1920)(1920)PP3333, , (1930)(1930)DD3535, , (1905)(1905)FF3535 - negligible partial contributions; - negligible partial contributions; - - (1750)(1750)PP3131, , (1940)(1940)DD3333 – one star status. – one star status.

Energy region of 1.2-1.4 GeV is the best to study the angular Energy region of 1.2-1.4 GeV is the best to study the angular distributions because of the low remaining background and distributions because of the low remaining background and insignificant contribution of other resonances. insignificant contribution of other resonances.


Results: angular distributionsResults: angular distributions

1.2-1.3 GeV GeV

1.3-1.4 GeV GeV

Black points: data curves: red – best fitgreen – A3/2/A1/2=0.8Blue – Γ(Γ(SS1111(1535)(1535)) / ) / ΓΓtotaltotal = 2% = 2%

coscos (HS) (HS) coscos (CS) (CS) (HS)(HS) (CS)(CS)

- data are correcteddata are corrected for the detector for the detector efficiencyefficiency- integral over each integral over each distributiondistribution equals to 1equals to 1

Best fit parameters: Best fit parameters: photon decay helicity amplitudes for photon decay helicity amplitudes for (1700)(1700)DD33 33 :: AA3/2 3/2 / A/ A1/2 1/2 = 1.45 ± 0.04 = 1.45 ± 0.04 (PDG 0.82 ± 0.2); (PDG 0.82 ± 0.2); (1700)(1700)DD3333 branching ratios : branching ratios : ΓΓ(((1232)(1232)) / ) / ΓΓtotaltotal = (2.1 ± 0.2)% = (2.1 ± 0.2)% (no PDG value),(no PDG value), ΓΓ((SS1111(1535)(1535)) / ) / ΓΓtotaltotal = (0.10 ± 0.02)% = (0.10 ± 0.02)% (no PDG value).(no PDG value).


1.2-1.3 GeV GeV

1.3-1.4 GeV GeV

Results: invariant mass spectraResults: invariant mass spectra

p p (GeV)

Blue points: experiment

Red curves: theory

- experimental data are corrected for the detector acceptance- experimental data are corrected for the detector acceptance- integral over each spectrum equals to 1- integral over each spectrum equals to 1


SummarySummary New high statistics experimental data for the total cross New high statistics experimental data for the total cross section, the angular distributions, and the invariant masssection, the angular distributions, and the invariant mass spectra have been presented;spectra have been presented; the cross section agrees well with previous results fromthe cross section agrees well with previous results from GRAAL, but is lower than CB@ELSA results especially at theGRAAL, but is lower than CB@ELSA results especially at the near threshold region;near threshold region; the dominance of the the dominance of the (1700)(1700) D D3333 at E at E < 1.4 GeV is < 1.4 GeV is confirmed, but at the near threshold region becomes confirmed, but at the near threshold region becomes determinative the contribution of the determinative the contribution of the (1600)(1600)PP3333 resonance; resonance; fit of the Mainz-Tomsk model to the data gives the followingfit of the Mainz-Tomsk model to the data gives the following parameters of the parameters of the (1700)(1700)DD3333 resonance: resonance: AA3/23/2 / A / A1/2 1/2 = 1.45 = 1.45 ±± 0.04 ,0.04 , ΓΓ(((1232)(1232)) / ) / ΓΓtotal total = (2.1 ± 0.2)% ,= (2.1 ± 0.2)% , ΓΓ ( (SS1111(1535)(1535)) / ) / ΓΓtotaltotal = (0.10 ± 0.02)% ; = (0.10 ± 0.02)% ;

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

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V.L. Kashevarov. Crystal Ball@MAMI Collaboration Meeting, Mainz, 21-23 September 2008 Photoproduction of on protons ► Introduction ► Data analysis