Photoproduction of K 0 Σ + with CLAS

Transcription

1 Photoproduction of K 0 Σ + with CLAS Franz Klein The Catholic University of America for the CLAS Collaboration

2 Physics Motivation Photoproduction of associated strangeness : Channels: significant data exist: γp K + Λ γp K + Σ 0 more data required to test theoretical predictions: γp K 0 Σ + (this analysis) γn K + Σ -

3 Physics Motivation Photoproduction of associated strangeness : Channels: significant data exist: γp K + Λ γp K + Σ 0 more data required to test theoretical predictions: γp K 0 Σ + (this analysis) γn K + Σ - couplings in SU(3)

4 γp K 0 Σ + (π + π - )(pπ 0 ) γp K 0 Σ + (π + π - )(nπ + ) K 0 >=1/ 2 { K 0 L > + K0 S > } K 0 S π+ π - π 0 π 0 (68.6 % branching ratio) (31.4 % branching ratio) Threshold energy GeV Σ + pπ 0 nπ + (51.6 % branching ratio) (48.3 % branching ratio)

5 Experimental Data Run period g1c: October-November, GeV beam energy data set 10 9 triggers Identified events: 4900 events for γp K 0 Σ + (π + π - )(pπ 0 ) 2700 events for γp K 0 Σ + (π + π - )(nπ + ) GeV beam energy data set 2.6x10 9 triggers Identified events: 6000 events for γp K 0 Σ + (π + π - )(pπ 0 ) 3900 events for γp K 0 Σ + (π + π - )(nπ + ) Events from previous experiments: ABBHHM (1969) 18 events SAPHIR(1999) 405 events

6 Jefferson Lab Newport News, VA

7 CLAS (CEBAF Large Acceptance Spectrometer)

8 Photon tagger

9 Photon Flux (flux per tagger E-counter)

10 Monte Carlo Generator γp K 0 Σ + Data Processing... Monte Carlo Generator background processes GSIM Experimental Data GPP Calibration A1C Simulated pπ + π - π 0 events Experimental pπ + π - π 0 Filter Experimental nπ + π + π - Simulated nπ + π + π - events

11 Filtered pπ + π - π 0 events Filtered nπ + π + π - events Charged particle identification Identification of π 0 or n by missing mass Identification of K 0 by invariant mass Selected K 0 events Event selection on Σ + mass region Selected Σ + events Sideband K 0 events Event selection on Σ + mass region Sideband Σ + events Sideband subtraction Final event sample Cross sections

12 π + γp K 0 Σ + (π + π - )(pπ 0 ) π + π + p proton p Charged particle identification γp K 0 Σ + (π + π - )(nπ + ) π +

13 Filtered pπ + π - π 0 events Filtered nπ + π + π - events Charged particle identification Identification of π 0 or n by missing mass Identification of K 0 by invariant mass Selected K 0 events Event selection on Σ + mass region Selected Σ + events Sideband K 0 events Event selection on Σ + mass region Sideband Σ + events Sideband subtraction Final event sample Cross sections

14 Identification of π 0 by missing mass γp K 0 Σ + (π + π - )(pπ 0 )

15 Filtered pπ + π - π 0 events Filtered nπ + π + π - events Charged particle identification Identification of π 0 or n by missing mass Identification of K 0 by invariant mass Selected K 0 events Event selection on Σ + mass region Selected Σ + events Sideband K 0 events Event selection on Σ + mass region Sideband Σ + events Sideband subtraction Final event sample Cross sections

16 Identification of K 0 by invariant mass γp K 0 Σ + (π + π - )(pπ 0 )

17 Filtered pπ + π - π 0 events Filtered nπ + π + π - events Charged particle identification Identification of π 0 or n by missing mass Identification of K 0 by invariant mass Selected K 0 events Event selection on Σ + mass region Selected Σ + events Sideband K 0 events Event selection on Σ + mass region Sideband Σ + events Sideband subtraction Final event sample Cross sections

18 Identification of Σ + by missing mass (for Σ + pπ 0 ) γp K 0 Σ + (π + π - )(pπ 0 )

19 Identification of Σ + by missing mass (for Σ + nπ + ) γp K 0 Σ + (π + π - )(nπ + )

20 A Acceptance γp K 0 Σ + (π + π - )(pπ 0 )

21 Desired process: γp K 0 Σ + (π + π - )(pπ 0 ) Background processes which can pass our event selection criteria and contaminate the data: γp π + π - pπ 0 (phase space) γp pω π + π - pπ 0 γp + ρ 0 π + π - pπ 0 These backgrounds are almost completely eliminated from our final event sample by our event selection criteria.

22 Simulated processes Experimental data γp K 0 Σ + (π + π - )(pπ 0 ) Simulated processes Experimental data

23 Acceptance γp K 0 Σ + (π + π - )(nπ + )

24 Simulated processes Experimental data γp K 0 Σ + (π + π - )(nπ + ) Simulated processes Experimental data

25 Systematic Errors Non-contiguous regions of selected and sideband events Photon Statistical Systematic Energy (GeV) Error Error % 11% % 6% % 6% % 7% % 7% % 10%

26 Sideband subtraction versus Gaussian fit

27 Differential cross sections

28 Extrapolation for missing angular regions

29 Integrated and extrapolated cross sections

30 Integrated Cross Sections for γp K 0 Σ + (π + π - )(pπ 0 ) for the three data sets

31 Total cross section comparison with ABBHHM and SAPHIR results

32 Differential cross section comparison with SAPHIR results

33 σ tot dσ dω p,n * s-channel E γ σtot -1 cos ϑ dσ dω 1 K t-channel E γ σ tot -1 1 cos ϑ dσ dω Σ + u-channel E γ -1 cos ϑ 1

34 Comparison with Coupled Channel model by Penner & Mosel Phys. Rev. 66, (2002)

35 Comparison with Coupled Channel model by Penner & Mosel Phys. Rev. 66, (2002)

36 Comparison with Coupled Channel model by Penner & Mosel (diff. Xsection)

37 Comparison with KAON-MAID predictions

38 Differential cross sections compared with KAON-MAID predictions

39 Partial wave decomposition for total cross section (KAON-MAID) W=1900 MeV

40 Partial wave decompositions for differential cross sections (KAON-MAID)

41 Conclusions - our results for γp K 0 Σ + in the range 1.15<E γ <2.35 GeV greatly expand upon existing data. -at E γ <1.55 GeV where previous data existed, our data are similar in shape for total cross section, but lower in magnitude than previous data and the KAON-MAID isobar model. -for E γ >1.55 GeV our data differ from KAON-MAID predictions. Our data suggest decreasing the t- and u-channel Born terms. - future experimental data will refine these results: recoil asymmetry (CLAS-g1c and CLAS-g8b) photon beam asymmetry (CLAS-g8b) target asymmetry (E02-112) beam-recoil and target-recoil polarization (E02-112)