1. HLAB meeting paper 2011/1/18 T.Gogami CLAS ( CEBAF Large Acceptance Spectrometer ) Clam shell is open

2. Paper

3. Abstract

4. Introduction

5. In this article CLAS g11a data set (5/7/2004 – 7/29/2004) – γp → K + Λ differential cross section – Λ recoil polarization (P Λ )

6. Experimental setup

7. Tagger ΔE/E ≈ 10 -3 MAGNET photon electron 4.023 [GeV] gravity 6.06 [m] E-plane (384) T-plane (61) 4mm thickness 20mm thickness σ time ≈ 110 [ps] ( intrinsic resolution 2×10 -4 ) Radiator Gold foil (10 -4 rad. length ) The bremsstrahlung tagged photon beam in Hall B at JLab, D.I. Sober, Nuclear Instruments and Methods in Physics Research A 440 (2000) 263}284

9. CLAS CLAS ( CEBAF Large Acceptance Spectrometer )

10. Toroidal Magnet Superconducting toroidal magnet – Temperature : 4.4 [K] (Liquid He) – 1920 [A], 1.8 [T] ( Max : 3861[A], 3.5 [T] ) B B People

11. Toroidal Magnet Superconducting toroidal magnet – Temperature : 4.4 [K] (Liquid He) – 1920 [A], 1.8 [T] ( Max : 3861[A], 3.5 [T] ) B B Magnetic field in midplane between two coils

12. CLAS (CEBAF Large Acceptance Spectrometer) Target : Liquid H 2 (cylindrical Kapton chamber 40cm L × 4cm D ) Momentum resolution ~ 5×10 -3 Trigger – tagger × 2/6 ( Start × TOF ) DAQ rate ~ 5 [kHz] Tracking ~300 [μm] Timing (~80 – 160 [ps]) γp → K + Λ

13. Spec The CEBAF large acceptance spectrometer (CLAS), B.A. Mecking, Nuclear Instruments and Methods in Physics Research A 503 (2003) 513–553

14. DATA and EVENT selection Want to see “γp → K + Λ” – γp → K + pπ - ・・・ Tree track analysis – γp → K + p(π - ) ・・・ Two track analysis +28% of full set 1.Momentum, Energy correction 2.Loose cut – Missing mass, Invariant mass 3.Kinematic fit  confidence level cut

15. Confidence level cut Λ Λ σ ~ 8 [MeV/c 2 ] Confidence level The effect of the confidence level cut is dramatic ! Missing mass

16. Background reduction Cut misidentified particles

17. Background reduction (2) 1.Given event “i” 2.100 neighbors 3.Missing mass 4.Maximum likelihood fit – Gaussian signal (s) – linear background (b) 5.Quality factor weighted by (1-Q) All events Missing Mass √s = 2.105 GeV bin

18. Other consideration Detector acceptance Extracting P Λ Normalization

19. Systematic Uncertainties

20. Result

21. Mandelstam variables proton photon Kaon Lambda

22. Cross section Count Corrected Number of photons Target Binning width Acceptance

23. Cross section( イ ) Red : two track analysis Blue : three track analysis Error Statistic Acceptance

24. Cross section( ロ ) Red : two track analysis Blue : three track analysis Error Statistic Acceptance

25. Cross section( ハ ) Red : two track analysis Blue : three track analysis Error Statistic Acceptance

26. Agreement between the two analysis Agreement between the two analysis, Very little systematic offset Consistent within statistical and acceptance uncertainties

27. Weighted mean differential cross sections Weighted mean differential cross sections : i = 2,3 j = 2,3 ρ = 0.28 For kinematic points where only a two-track measurement exists, Cross section : its value Uncertainty : scaling by 1 + |μ| = 1.136

28. Cross section γp → K + Λ Red : CLAS Blue : previous CLAS Green : SAPHIR Measurement of p->K+ Λ and p->K+ Σ 0 at photon energies up to 2.6 GeV, K.H. Glander, arXiv:nucl-ex/0308025v1 26 Aug 2003 The γ p → K+ and γ p → K+0 reactions at forward angles with photon energies from 1.5 to 2.4 GeV, M. Sumihama, PHYSICAL REVIEW C 73, 035214 (2006) Measurement of the γ p → K+ reaction at backward angles, K. Hicks, PHYSICAL REVIEW C 76, 042201(R) (2007) LEPS SAPHIR

29. Model comparison ( イ ) K-MAID (fit with SAPHIR) – K+,K*(892),K 1 (1270) RPR (fit with p CLAS) – K+ Regge trajectory, K* Regge trajectory – N(1650)S 11,N(1710)P 11, N(1720)P 13,N(1900)P 13, missing D 13 – Forward angle Bonn-Gatchina (fit with p CLAS) – Partial wave analysis

30. Model comparison ( ロ ) K-MAID (fit with SAPHIR) – K+,K*(892),K 1 (1270) RPR (fit with p CLAS) – K+ Regge trajectory, K* Regge trajectory – N(1650)S 11,N(1710)P 11, N(1720)P 13,N(1900)P 13, missing D 13 – Forward angle Bonn-Gatchina (fit with p CLAS) – Partial wave analysis

31. Model comparison ( ハ ) K-MAID (fit with SAPHIR) – K+,K*(892),K 1 (1270) RPR (fit with p CLAS) – K+ Regge trajectory, K* Regge trajectory – N(1650)S 11,N(1710)P 11, N(1720)P 13,N(1900)P 13, missing D 13 – Forward angle Bonn-Gatchina (fit with p CLAS) – Partial wave analysis

32. Conclusion

33. END

34. Start counters

36. Introduction (γp → K + Λ) γp → K + Λ – Polarization Pseudoscalar nature of the K+ Self-analyzing decay of the Λ – Isospin structure of the final state Allows coupling only to I=1/2 N* (not the I=3/2 Δ*)

37. PΛPΛ CLAS : Blue SAPHIR2004 : Green GRALL2007 : Black

38. Tagger