CP Violation in the Decay. Katsumi Senyo Osaka University

Transcription

1 CP Violation in the Decay K L p p - e e - Katsumi Senyo Osaka University

2 Contents Physics Motivations Recent results KTeV Detector Event Selection Form Factor Measurement CP Asymmetry Measurement Branching Ratio Measurement Conclusion

3 CP Violating Process in K L p p - e e - CP Violating CP Conserving CP violating effect comes from interference between IB and DE amplitudes.

4 Critical Angles in K L p p - e e -

5 Angular Asymmetry in dγ dφ 2 2 = Γ1 cos φ Γ2 sin φ Γ3 sinφ cosφ sin φ cos φ = n ee n p p p p ( n ee n ) n ee ( n ): Normal to e e ( - ) plane A = / 2 0 / 2 / 2 d d d d Γ φ Γ d d φ φ 0 / 2 p ( p ): Momentum of d d d d Γ φ Γ d d φ φ 14% ( ) in Kaon CM frame φ φ Sehgal and Wanninger Phys. Rev. D46, 1035(1992);ibid D46,5209(E)(1992) Angular Dist.(MC)

6 M1 Form factor gm1 F = ( M gm1 F 2 ρ a M 1 2 K ) 2M K E * γ a 2 M ρ : mass of ρ meson M K : mass of K * E γ = E e E e meson : Virtual photon Energy in Kaon CM frame a)with form factor b)without form factor E.J.Ramberg et al., Phys. Rev. Lett. 70, 2525(1993)

7 Recent Experimental Status Recent Publication: Branching Ratio ( (stat.) 0.4(syst.)) 10-7 Based on 46 events(one day of data) by KTeV J.Adams et al., Phys. Rev. Lett. 80, 4123(1998) Our analysis shown here based on whole(90 days) dataset.

8 KTeV Detector (plane view) Spectrometer(Magnet Drift Chambers) Measure the momentum of a charged particle Electromagnetic Calorimeter Measure the energy of a photon Particle identification

9 Spectrometer(Magnet Drift Chamber) Purpose: charged track trajectory reconstruction vertex reconstruction Measure the momentum of a charged particle 4 Drift Chambers(DC1 - DC4) Spatial resolution : 100mm Analysis Magnet (between DC3 and 4) Transverse momentum kick: 205 MeV/c Momentum Resolution: σ p p = 0.016% p(gev/c) 0.38%

10 Electromagnetic Calorimeter Measure the energy of a photon Particle identification 3100 CsI crystals(27 rad. lengths) Energy Resolution: σ E E 0.6% = E (GeV) 0.6%

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12 K L p p - e e - Signal Selection Strategy 4 charged tracks sharing a common vertex. Identified 2 pions and 2 electrons including charge consistency Invariant mass forms K L mass Total momentum consistent with KL flight direction Constraint from other kinematics relations

13 CsI calorimeter Signal: K L p p - e e - p e e - p - BG: K L p p - p 0 D CsI calorimeter p g e e - p -

14 Background sources Background sources ) ( 0 0 γ e e K D L ) ( 0 0 γγ K L γ K L g conversion at material(g e e - ) ) ( 0 0 e e e e K DD L ) ( ) ( 0 γ Λ Ξ e e p D ) ( ) ( ν ν e K e K L L g conversion at material(g e e - )

15 Background distribution

16 Total Momentum(pp ppee) ) Cut

17 Total Momentum Cut: Data and Background MC Overlay

18 Vertex c 2 (quality) Cut: Data and Background MC Overlay

19 Mee Cut

20 Mee Cut: Data and Background MC Overlay

21 p 2 t Cut

22 p 2 t Cut: Data and Background MC Overlay

23 Pp0kine Cut Assuming K L p p - p 0 kinematics Reject physically allowed region of K L p p - p 0

24 Pp0kine Cut

25 Pp0kine Cut: Data and Background MC Overlay

26 Data after all the cuts events in the signal region

27 Background Estimation Background Estimation Background Efficiency #Background ) ( 0 0 γ e e K D L ) ( 0 0 γγ K L γ K L ) ( 0 0 e e e e K DD L ) ( ) ( 0 γ Λ Ξ e e p D ) ( ) ( ν ν e K e K L L 2.4 x x < 1.2 x <0.8(90%CL) < 3.0 x 10-8 <0.7(90%CL) <0.7(90%CL)

28 Normalization with KL 0 D Dataset #events K L flux Winter x Summer x Total ( (stat.) 0.085(syst.)) x 10 11

29 Form Factor Measurement gm1 gm1 F F = ( M 2 ρ a M 1 2 K ) 2M K E * γ a 2 a 1 / a, a 2 1 Extracted from 5 parameter Maximum likelihood method. M, M ee, φ, cosθ, cos θ e In Kaon CM frame

30 Form Factor Fit Result a 1 / a a 2 1 = = 1.05± 0.14

31 Mpp Comparison Form Factor Constant gm1

32 CP violating Angular Asymmetry CP violating Angular Asymmetry 14% 2 / 0 2 / 2 / 0 2 / Γ Γ Γ Γ = φ φ φ φ φ φ φ φ d d d d d d d d d d d d A Sehgal and Wanninger Phys. Rev. D46, 1035(1992);ibid D46,5209(E)(1992)

33 Angular Distributions

34 The Raw Asymmetry N N sinφcosφ> 0 sinφcosφ> 0 = = Asym = = N N sin φ cosφ > 0 sin φ cosφ> 0 N N sin φ cosφ < 0 sin φ cosφ< ± 0.029( stat.) MC study MC with input asymmetry of gave the raw asymmetry of Acceptance correction should be applied to the raw asymmetry.

35 Before proceeding to the acceptance correction... Raw Asymmetry = Consistent with zero asymmetry

36 Input-Raw asymmetry relation with Monte Carlo Simulation Raw Asym. = 1.75 Input Asym.

37 Raw asymmetry in different Mass region No obvious asymmetry found in outside region.

38 MC study on the relation between input and raw asymmetries Distribution in acceptable region has larger asymmetry.

39 Raw Asymmetry... Measured raw asymmetry of data is (stat.) while the MC with input parameter of gave the raw asymmetry of The detector or analysis did not induce the raw asymmetry. This is also supported by the signal MC with zero input asymmetry. The input and raw asymmetry have the simple linear relation which suggests the asymmetry enhancement. The KTeV detector only accepted events with high momentum electrons. Those events showed the large asymmetry.

40 Singal Acceptance in f

41 Acceptance Corrected Data and MC Acceptance Corrected Asymmetry

42 Detector Smearing

43 Detector Smearing; continue X track swapping causes the dilution. Track in sinφ cosφ region sinφ cosφ region

44 Detector Smearing; continue

45 Systematic Uncertainty Detector resolution 8.7%(0.011) M1 form factor 2.4%(0.003) Physics Input parameter 6.9%(0.007) Vertex quality 0.8%(0.001) DC ineff. <0.1%(0.000) Background subtraction 0.9%(0.001) Analysis dependency 4.7%(0.005) Total 12.4%(0.016)

46 Asymmetry: Result Asym. = (stat.) 0.016(syst.) Theoretical Prediction Asym. ~ 14% Sehgal and Wanninger Phys. Rev. D46, 1035(1992);ibid D46,5209(E)(1992)

47 Branching Ratio Measurement Recent Publication: ( (stat.) 0.4(syst.)) 10-7 Based on 46 events(one day of data) by KTeV J.Adams et al., Phys. Rev. Lett. 80, 4123(1998)

48 Data Selection Relax pt2 cut and Pp0kine cut to increase acceptance. Pt2 cut : < GeV 2 /c 2 < GeV 2 /c 2 Pp0kine cut : < GeV 2 /c 2 N/A #events in the signal region 1173 events 1731 events

49 Mass distribution after final cuts

50 Pt2 Sideband GeV 2 /c 2 <pt 2 < GeV 2 /c 2

51 Background Estimation Background Estimation Background #Background ) ( 0 0 γ e e K D L ) ( 0 0 γγ K L γ K L ) ( 0 0 e e e e K DD L ) ( ) ( 0 γ Λ Ξ e e p D ) ( ) ( ν ν e K e K L L

52 Signal peak after background subtraction #signal after background subtraction: events

53 Statistical/Systematic Uncertainty(BR) Statistical Error 3.13% BR( K L 0 ) 3.14% D Physics Input parameter 2.60% Normalization 0.33% Chamber inefficiency 0.17% Vertex quality 0.87% MC statistics 0.25% Background subtraction 1.6% Analysis dependency 0.7% Total ( 3.13( stat.) 2.00( syst. internal) 4.08( syst. external))%

54 Branching Ratio: Result ( (stat.) 0.07(syst.internal) 0.14 (syst.external)) 10-7 Based on events Good agreement with recent experimental result; ( (stat.) 0.4(syst.)) 10-7 J.Adams et al., Phys. Rev. Lett. 80, 4123(1998) And theoretical prediction; ~ Sehgal and Wanninger Phys. Rev. D46, 1035(1992);ibid D46,5209(E)(1992)

55 Discussion: Asymmetry Measurement Origin of the asymmetry Final State Interaction: negligible. (M.J.Savage,1999) T Violation: (strictly speaking,)rejected. CPT Violation: unnatural, but not yet rejected. (J. Ellis and N.E. Mavromatos, 1999) (I.I.Bigi and A.I.Sanda, 1999) CP Violation/CPT Conservation: Most probable interpretation. (L.M.Sehgal and M.Wanninger, 1992)

56 Conclusion CP Violating Angular Asymmetry Asym. = (stat.) 0.016(syst.) Form Factor Measurement: a 1 / a a 2 1 = = 1.05± 0.14 Branching Ratio ( (stat.) 0.07(syst.internal) 0.14 (syst.external)) 10-7 Based on events

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