Study of CP Violation at BABAR

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1 Study of CP Violation at BABAR Roland Waldi, Univ. Rostock Introduction Direct CP Violation in B Decay The Easy Part: β Additional Information: β and α Summary and Outlook März 25

2 CP Violation = asymmetry between particles and anti-particles ( C ) when summed over left and right since P-violation of weak interaction has opposite sign for particles and anti-particles use CP instead of C for left/right individually 2/ 6

3 CP Violation: History 1964 CP Violation in K Observed (Cronin, Fitch ) 1973 Quark Mixing Matrix CPV (Kobayashi, Maskawa) 1987 B B Oscillation Observed (ARGUS) 1988 Era of B Factory Proposals, Using ϒ(4S) BB Europe: USA: Japan: PSI CERN DESY Cornell SLAC KEK 1999 B Factories (PEP-2, KEK-B) Start Operation 21 CPV in B Observed (BABAR, BELLE) 24 Direct CPV in B Observed (BABAR, BELLE) 3/ 6

4 CP Violation in the Standard Model: CP-violation = interference due to the unitary Cabibbo-Kobayashi-Maskawa matrix V u c t W d s b d s b u c t 4/ 6

5 CP Violation in the Standard Model: CP-violation = interference due to one non-trivial phase in the unitary Cabibbo-Kobayashi-Maskawa matrix V with standard choice of 5 trivial phases: u c t W d s b = 5/ 6

6 Another Choice of Phases α 6/ 6

7 Two (of 6) Unitarity Triangles CKM matrix unitarity column 1 3 shape independent of phase convention sides and angles are observables CKM matrix unitarity row 1 3 ~ β = β + φ4 γ = ~ γ φ 4 δγ = γ γ = β β φ 2 7/ 6

8 if CKM Matrix not Unitary α triangle not closed but still α+β+γ = 18 γ β if α+β+γ 18 we have additional amplitudes, i.e. we have not measured the angle in the triangle which can also be found by measuring one angle in two different channels! 8/ 6

9 Hunt for New Physics measure α,β(β ),γ(γ ) in different modes and look out for discrepancies favoured candidates: loop-dominated decays (penguins) 9/ 6

10 PEP-2 / BABAR Collaboration: ca. 55 physicists from 1 Nations Canada China Germany France Great Britain Italy Netherlands Norway Russia USA 1 / 6

11 Asymmetric B Factory PEP II e e + ϒ(4S) Energies: GeV velocity: βγ=.55 ϒ(4S) BB ϒ(4S) e + e hadrons off-peak on ϒ(4S) 11 / 6

12 BABAR Detector Iron Yoke + RPCs/LSTs, Superconducting Coil DIRC (Cherenkov), CsI-Calorimeter Drift Chamber, Si Vertex-Tracker 1m 12 / 6

13 Data Sample L/day design luminosity: /cm 2 /s peak luminosity: /cm 2 /s 245 million BB pairs (1 ARGUS) 13 / 6

14 Study of CP Violation at BABAR Roland Waldi, Univ. Rostock Introduction Direct CP Violation in B Decay The Easy Part: β Additional Information: β and α Summary and Outlook

15 Direct CP Violation: 2 Interfering Amplitudes 15 / 6

16 Direct CP Violation: B K + π Asymmetry a = n n B B + n n B B A 1 =Penguin B g a sin(φ 1 φ 2 ) sin(δ 1 δ 2 ) φ 1 φ 2 = γ A 2 =Tree B 16 / 6

17 Unitarity Triangles γ = ~ γ φ 2 δγ = γ γ φ 2 17 / 6

18 Direct CP Violation: B K + π Asymmetry a = n n B B + n n B B A 1 =Penguin B g a sin(φ 1 φ 2 ) sin(δ 1 δ 2 ) φ 1 φ 2 = γ δ 1 δ 2 =??? A 2 =Tree Α 1 / Α 2 =? B 18 / 6

19 Signal Event Selection b-jet: 1 constraint = B-mass ϒ(4S): 2 constraints = E B and p B example signal B Dπ in cms E ) ( ED + Eπ E beam B D*π, DK B candidate m ES = E 2 beam r + r ( pd pπ ) 2 19 / 6

20 Data Analysis of K + π Maximum Likelihood Fit determines yields n ππ, n Kπ, n KK, and asymmetries a Kπ and a(bgrd) simultaneously: Event shape (Fisher discr.) B mass m ES B energy ( E) Particle ID (θ Č ) separate signal from qq background separate K from π Kπ separation(σ) DIRC calibrated with D + D π + (K π + )π + ππ Κπ p LAB (GeV/c) E using m=mπ 2 / 6

21 First Observation of Direct CP Violation in B decay fit a = n n B B + n n B B =.133±.3 ±.9 ( + K π ) n B ( K + π ) n B = = B K + π B K π + splot = signal fraction fit 4.2σ, syst. included signal enhanced E using m=m π 21 / 6

22 Systematics for B K + π Asymmetries consistent in different K momentum ranges in different running periods when including decay time Source Signal Fisher PDF DIRC θ c PDF Potential MC bias Potential charge bias Total Sys. Error BABAR: a =.133 ±.3 ±.9 Belle: a =.11 ±.25 ±.5 22 / 6

23 Study of CP Violation at BABAR Roland Waldi, Univ. Rostock Introduction Direct CP Violation in B Decay The Easy Part: β Additional Information: β and α Summary and Outlook

24 Interference mixed/unmixed B f B A A q p time-dependent asymmetries 24 / 6

25 CP-Asymmetry Example: B s x = m/γ: BB oscillation frequency xt = m t y = Γ/2Γ: BB lifetime difference yt = ( Γ/2) t x = m/γ y = Γ/2Γ T=t/τ 25 / 6

26 CP-Asymmetry Example: B J/ψ K S λ = -e -2iβ = = sin 2β = -cos 2β time dependent asymmetry other conventions: Λ Θ = S sin coefficient = A = C cos coefficient x =.77±.1 blue: y =.1 black: y = BABAR 24: y <.8 Theory:.1 < y <. 26 / 6

27 B J/ψ K S at ϒ(4S) CP-Asymmetry: a( T) = Λ sin xt = sin 2β sin m t e e + ϒ(4S) Energies: GeV velocity: βγ=.55 T = t /τ at ϒ(4S) BB, t = t s - t t ϒ(4S) B signal z = βγc t B tag Signal-B, Lifetime t s Tag-B, Lifetime t t 27 / 6

28 Measurement of sin 2β at the ϒ(4S) e measure decay rates R 1 (T), R 2 (T) for B or anti-b at time T = R2 ( T) R1 ( T) calculate a( T) = = Λ R ( T) + R ( T) ϒ(4S) e + B s B t 2 z µ J /ψ + + µ K S 1 π π sin l xt B-Meson Reconstruction K t-measurement B-Flavour-Tagging 28 / 6

29 Unitarity Triangles: β ~ β = β + φ4 29 / 6

30 Tagged (cc)k Decays CP sample N tag J/ψ K S (K S π + π - ) 2751 J/ψ K S (K S π π ) 653 ψ(2s) K S ( π + π - ) 485 χ c1 K S (K S π + π - ) 194 η c K S (K S π + π - ) 287 purity 96% 88% 87% 85% 74% Total CP= % J/ψ K * (K * K S π ) % J/ψ K L % Total % CP m ES E 3 / 6

31 Results on sin2β from (cc)k CP= 1 CP=+1 ± Λ = sin 2β =.722 ±.4 λ =.95 ±.31±.13 ± / 6

32 B Vector-Vector B: Spin VV: L=S, Σ S z = Clebsch-Gordan-Table: L= L z = 1 2 A +1 S z = +1, 1 1/3 1/2 1/6 A, 1/3 2/3 A 1 1,+1 1/3 1/2 1/6 CP = Amplitudes: longitudinal : A transversal : A +1, A 1 or better: A = A +1 + A 1 (CP +) ( circular linear polarisation) A = A +1 A 1 (CP ) (CP +) 32 / 6

33 Tagged (cc)k Decays CP sample N tag J/ψ K S (K S π + π - ) 2751 J/ψ K S (K S π π ) 653 ψ(2s) K S ( π + π - ) 485 χ c1 K S (K S π + π - ) 194 η c K S (K S π + π - ) 287 purity 96% 88% 87% 85% 74% Total CP= % J/ψ K * (K * K S π ) % J/ψ K L % Total % CP CP odd fraction ( A 2 ): (23±2)% [BABAR*] (21±1)% [world av.] * of accepted events 33 / 6

34 cos(2β) with B J/ψ K * (K S π ) -Γ t... ± e [ f4 A A cos( δ -δ ) + f6 A A cos( δ -δ )]cos(2β )sin( xt ) CP +/ interference amplitudes and phases use also non-cp charged final states LASS data, K p K π + n resolve sign ambiguity of strong phase δ differences using Kπ scalar/vector interference cos2β = 2.7 ±.8(stat) ±.3 (syst) 86% CL possible from sin 2β: +.69, / 6

35 Status of Unitarity Triangle cos 2β < cos 2β > world average now: β = 23.2 ±1.5 J/ψ K-modes also theoretically clean, i.e. β precise at the.1% level 35 / 6

36 Study of CP Violation at BABAR Roland Waldi, Univ. Rostock Introduction Direct CP Violation in B Decay The Easy Part: β Additional Information: β and α Summary and Outlook

37 Unitarity Triangles: β & β ~ β = β + φ 4 β β = φ 2 φ / 6

38 sin(2β ) in sss Final States B φ K S, L CP+ and CP eigenstates B φ K S B φ K L 114 ± 12 signal events 98 ± 18 signal events + B K K K S 452 ± 28 signal events mixture CP+/ in Dalitz plot, excluding φ region 38 / 6

39 sin(2β ) in sss Final States φ K S ± Λ Θ = = sin 2β =.5 ±.25. ±.23± φ K L K + K K S sin 2β = f CP+.55 ±.22 ±.4 ±.11 =.89 ±.8 ±.6 39 / 6

sin(2β ) in sss Final States B K S K S K CP+ eigenstate S BF Λ Θ = ( +.9 6.9 ±.6) =.71 =.

40 sin(2β ) in sss Final States B K S K S K CP+ eigenstate S BF Λ Θ = ( ±.6) =.71 = ±.4 ± ± 1 signal events Θ : = sin 2β = ±.4 4 / 6

41 More Penguins: B! ω K S 96 ± 14 signal events Λ Θ = = +.5 ± +.56 ± ±.2 ±.3 41 / 6

42 sin(2β) Comparison BABAR & Belle: Belle 3 (cc)k sin 2β =.725±.37 new new penguins sin 2β =.43±.7 3.7σ discrepancy but sin 2β 42 / 6

43 Λ sin 2β : SM corrections b d b d b d VV W tb t g VV tb W t g ts VV W tb t g ts ts 2 ~ λ 2 ~ λ 2 ~ λ s s s d s s s d s d d d φ K η ', f K B b d b d V V ~ λ R e 4 ub us W u V V g u 4 ~ λ R e ub us u V V W iγ s s s d iγ 4 ~ λ R e ub us u u u s d iγ φ K η ', f K b u K π, ρ, ω d W u π, ρ, ω s K d up to 2% corrections for relation Λ sin 2β possible 43 / 6

44 Study of CP Violation at BABAR Roland Waldi, Univ. Rostock Introduction Direct CP Violation in B Decay The Easy Part: β Additional Information: β and α Summary and Outlook

45 Unitarity Triangles: α b uʉd like B π + π ~ α = π β ~ γ 45 / 6

46 α: the Penguin Pollution d W d B b d u u π + B b d u, c, t g d u u Θ Λ sin( δ ) = ( ± ) 1 Θ 2 sin(2α + κ) 46 / 6

47 Isospin Analysis B B π + π π π Gronau, London, 199 Ι= π π Ι=2 twofold ambiguity 47 / 6

48 α from B ππ + B π π BF = Λ Θ π π + + π π B π BF = Θ π π ( 4.7 ±.6 ±.2) =.3±.17±.3 =.9±.15±.4 π ( 1.17±.32±.1) B ± π ± π BF = ( 5.8 ±.6 ±.4) 1 =.12±.56±.6 a =.1±.1± B π κ π Isospin analysis: α α eff < 35 o at 9% CL 48 / 6

49 α from B ππ 1 - C.L α (degrees) small range 9% CL 49 / 6

50 B Vector-Vector B: Spin VV: L=S, Σ S z = Clebsch-Gordan-Table: A +1 A A 1 S z = L z = +1, 1, L= 1,+1 CP = Amplitudes: longitudinal : A 1/3 1/3 1/3 +1 (CP +) 1 1/2 1/ /6 2/3 1/6 +1 transversal : A +1, A 1 parallel : A = A +1 + A 1 (CP +) perpendicular : A = A +1 A 1 (CP ) 5 / 6

51 B ρ + ρ the ρ + ρ system is longitudinally polarized! f(a ) =.978±.14±.28 CP = ± 52 signal events BF = (3.±.4±.5) / 6

52 B ρ ρ BF ( B ρ ρ ) = (.54 < ±.19) 1 9% CL 6 Isospin analysis gives correction to α: κ < 68% CL 33 ± 24 signal events 52 / 6

α with B ρρ B ρ Λ Θ ρ ρ + + + ρ ρ ρ B ρ ρ BF < 1.1 1 B ± ρ ± ρ =.33±.24 +.8.14 =.3±.18±.

53 α with B ρρ B ρ Λ Θ ρ ρ ρ ρ ρ B ρ ρ BF < B ± ρ ± ρ =.33± =.3±.18±.9 6 ( ) 6 BF = α = 1 ± f ( A ) =.96.7 including ±11 from κ (penguin) 53 / 6

54 α with B (ρπ) MC ρ + π ρ π Dalitz plot has ρ + π, ρ π +, ρ π and radial excitations ρ π ± 58 signal events 54 / 6

55 α with B (ρπ) ρ π very small; still many asymmetry parameters B + ρ π strong Phase δ + a CP B ρ + π Λ +,Θ + + A Λ +,Θ + ρπ B + ρ π B ρ + π Λ +,Θ +,,Λ +,Θ + average Λ,Θ and difference 55 / 6

56 α with B (ρπ) Λ Θ a CP ρπ ρπ =.88 ±.49 ±.13 =.1 ±.14 ±.4 =.34 ±.11±.5 Λ =.22 ±.15 ±.3 Θ =.15 ±.11±.3 A A + ρπ + ρπ =.21±.11±.4 =.47 BF asymmetries ±.6 3σ + 28 ( 67 ± ) δ + = α = ± 6 56 / 6

57 Combined Constraints on α α = / 6

58 Combined Constraints on α α = / 6

59 Summary observation of direct CPV in B decay various measurements of β(β ) differ (2 4σ) more data will distinguish new physics from statistical fluctuation sensible α measurements available from 3 channels (γ also started, errors still large) Standard Model (still?) in good shape 59 / 6

60 Outlook BABAR just restarted expect datasample 2 by summer 26 expect datasample 4 by end 28 then we need a next generation collider with L = 1 36 /cm 2 /s 6 / 6

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