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Takeo Higuchi Institute of Particle and Nuclear Studies, KEK The Belle Collaboration / The Belle II Collaboration Results on CP Violation and CKM Unitary.

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Presentation on theme: "Takeo Higuchi Institute of Particle and Nuclear Studies, KEK The Belle Collaboration / The Belle II Collaboration Results on CP Violation and CKM Unitary."— Presentation transcript:

1 Takeo Higuchi Institute of Particle and Nuclear Studies, KEK The Belle Collaboration / The Belle II Collaboration Results on CP Violation and CKM Unitary Triangle Workshop on Synergy between High Energy and High Luminosity FrontiersJan.10,2011

2 Belle (Japan) BaBar (US) B-Factories in the World 2 Data taking finished on Jun.30 th, 2010 ∫ L dt = fb⁻¹ Data taking finished in Apr, 2008 ∫ L dt = 558 fb⁻¹

3 KEKB Accelerator 3 e⁻e⁻ e⁻e⁻ e⁺e⁺ e⁺e⁺ IR World highest luminosity 2.1x10³⁴cm⁻²s⁻¹ World highest integrated luminosity fb⁻¹ History of the integrated luminosity

4 Particle species γ and e ± energy Charged particle momentum B decay position Silicon Vertex Detector Four detection layers. Vertex resolution ~ 100 μm. Time-of-Flight Counter Plastic scintillation counter. K/π-ID of high range p. Time resolution ~100 ps. Aerogel Čerenkov Counter Refractive index n= K/π-ID of middle range p. 8.0GeV e⁻ 3.5GeV e⁺ Belle Detector K L μ Detector Sandwich of 14 RPCs and 15 iron plates. μ-ID with iron-punch-through power. Return path of magnetic flux. 4 Electromagnetic Calorimeter CsI (Tl) crystal. Energy measurements of γ and e 1 GeV. Central Drift Chamber 8,400 sense wires along the beam direction. Momentum resolution PID with dE/dx measurement. 1.5 T magnetic field.

5 Dec.,1998Detector construction had completed. Jan.,1999Cosmic-ray event taking had started. Feb.,1999The first e + -e – collision of KEKB. May.,1999The detector had been rolled in to the IR. Jun.4 th,1999The first physics event. … 9:00am Jun.30 th,2010 Data taking finished. History of Belle 5

6 End Run Ceremony The e + /e – beams were aborted by A. Suzuki, the director general of KEK. Collaborators’ snapshot at the run end: 6 I was here.

7 CKM Matrix and Unitarity Triangle One of the unitarity conditions: Wolfenstein Parameterization KM ansatz:Irreducible complex phases (in V ub and V td in Wolfenstein parameterization) cause the CP violation. iηiη O ρ Unitarity condition forms a untarity triangle in the complex plane. (φ₁, φ₂, φ₃) = (β, α, γ) 7

8 B 0 -B 0 Mixing and Mixing-Induced CPV WW t t b d d b B⁰B⁰B⁰B⁰ Vtd V*tb B⁰ and B⁰ mix with each other through a box diagram shown above. _ B⁰B⁰ B⁰B⁰ f CP B⁰B⁰ B⁰B⁰ B⁰B⁰ B⁰B⁰ phase == 0 phase difference = 2φ₁ _ Even if B⁰ and B⁰ decay to the same final state, the phase of the decay amplitude may differ depending on the B flavor at the decay time. interference _ _ __ _ CPV due to the interference is called “mixing-induced CP violation”. 8 ~ V td ² ~ e⁻² iφ₁

9 CP Violation in Proper-Time Distribution The e⁺-e⁻ collision produces a pair of B mesons through bb resonance. S= 0.65 A= 0.00 B tag = B 0 _ Δt (ps) The mixing-induced CP violation manifests itself in the signed time duration “Δt = t BCP – t Btag ”, where t BCP … time when one B decays to the CP eigenstate. t Btag … time when the other B decays to the flavor-specific state. 9

10 Analysis Method 10 e⁻e⁻ e⁻e⁻ 8.0GeV e⁺e⁺ e⁺e⁺ 3.5GeV B⁰B⁰ B⁰B⁰ B⁰B⁰ B⁰B⁰ _ Beam pipe KS⁰KS⁰ KS⁰KS⁰ J/ψ π⁺ ℓ⁺ ℓ⁻ π⁻ 1.Reconstruct f CP (J/ψK S ⁰ …) π⁻ D⁺D⁺ D⁺D⁺ π⁺ K⁻K⁻ K⁻K⁻ 2.Determine the B meson flavor q opposite to the one decayed to f CP 3.Determine proper- time difference Δt of the two B mesons ΔtΔt 4.Determine S (= sin2φ₁) using the event-by-event q and Δt e⁺-e⁻ collision

11 The B⁰  J/ψK⁰ is mediated by b  ccs tree transition. SM prediction: S = –η CP sin2φ₁, A ≈ 0 – Test of Kobayashi-Maskawa theory.  Nobel prize in 2008 – Check for a NP phase with very precise unitarity tests. B⁰  J/ψK⁰: Golden Modes for φ₁ The decay diagram includes neither V ub nor V td.  The φ₁ is accessible. _ d b _ c c s d _ W B⁰B⁰ K⁰K⁰ b  ccs tree J/ψJ/ψ _ _ 11

12 B⁰  J/ψK⁰ Reconstruction Events / 1 MeV/c² Events / 50 MeV/c N sig = 6512 Purity = 59 % η CP = +1 B CP mass (GeV/c²)B CP momentum in the cms (GeV/c) + data MC: J/y K L X  MC: signal MC: J/y X MC: comb. N sig = 7482 Purity = 97 % η CP = –1 B CP  J/ψK S ⁰B CP  J/ψK L ⁰ Gaussian 5.28 GeV/c² 0 GeV ARGUS func. Event-by-event S/N is obtained from the model above. Event-by-event S/N is obtained from an MC simulation M BB _ slope

13 S and A from B  J/ψK⁰ (535M BB) (stat)(syst) Phys. Rev. Lett. 98, (2007). _ Dominant systematic error sources 13 B rec = J/ψK S ⁰ + J/ψK L ⁰ Dec.9,2010

14 S and A Update (772M BB) _ J/ψKL⁰J/ψKL⁰ J/ψKS⁰J/ψKS⁰J/ψKL⁰J/ψKL⁰ψ(2S)K S ⁰χ c1 K S ⁰N BB Signal yield (’10)12727± ± ±46943± x 10⁶ Purity (’10) [%] Signal yield (’06)7484±876512±123–– 535 x 10⁶ Purity (’06) [%]9759–– from 772 x 10⁶ BB pairs = final Belle data sample We have more yields than the N BB increase, for we have improved the track finding algorithm. Belle preliminary ccK S ⁰ _ 14 _

15 Latest Status of S and A Measurements We are finalizing the S and A in b  ccs modes using the full data set. Preliminarily expected statistical sensitivity ­ Predicted by a signal-yield scale applied to the ICHEP2006 results. – The statistical uncertainties are getting close to the systematic ones. _ 15

16 b  sqq Time-Dependent CP Violation Deviation of b  sqq CP-violating parameter from b  ccs indicates NP in the penguin loop _ d b _ c c s d _ W B0B0 J/ψJ/ψ K⁰K⁰ d b _ _ s s s d _ gt B0B0 K⁰K⁰ φ, f₀… W b  ccs tree _ b  sqq penguin _ S = sin2φ₁, A ≈ 0S = sin2φ₁ eff, A ≈ 0 In case of an extra CP phase from NP in the penguin loop _ _ 16 _

17 Interference in B⁰  K S ⁰K⁺K⁻ Final State B⁰  K S ⁰K⁺K⁻ final state has several different paths. – Fit to the Dalitz plot is need for the correct CPV measurement. φKS⁰φKS⁰ f₀(980)K S ⁰ Dalitz-plot φK S ⁰ CP = –1 A₁A₁ B⁰B⁰ B⁰B⁰ KS⁰K⁺K⁻KS⁰K⁺K⁻ KS⁰K⁺K⁻KS⁰K⁺K⁻ f₀(980)K S ⁰ CP = +1 Others … A₂A₂ ANAN Non-resonant s₊ = M²(K⁺K S ⁰) s₋ = M²(K⁻K S ⁰) Dalitz plot 17

18 Interference in B⁰  K S ⁰K⁺K⁻ Final State B⁰  K S ⁰K⁺K⁻ final state has several different paths. – Fit to the Dalitz plot is need for the correct CPV measurement. φK S ⁰ CP = –1 A₁A₁ B⁰B⁰ B⁰B⁰ KS⁰K⁺K⁻KS⁰K⁺K⁻ KS⁰K⁺K⁻KS⁰K⁺K⁻ f₀(980)K S ⁰ CP = +1 Others … A₂A₂ ANAN Non-resonant Dalitz plot B⁰B⁰ B⁰B⁰ mixing _ B⁰-B⁰ mixing _ φKS⁰φKS⁰ f₀(980)K S ⁰ Dalitz-plot s₊ = M²(K⁺K S ⁰) s₋ = M²(K⁻K S ⁰) 18

19 Interference in B⁰  K S ⁰K⁺K⁻ Final State B⁰  K S ⁰K⁺K⁻ final state has several different paths. – Fit to the Dalitz plot is need for the correct CPV measurement. φK S ⁰ CP = –1 A₁A₁ B⁰B⁰ B⁰B⁰ KS⁰K⁺K⁻KS⁰K⁺K⁻ KS⁰K⁺K⁻KS⁰K⁺K⁻ f₀(980)K S ⁰ CP = +1 Others … A₂A₂ ANAN Non-resonant B⁰-B⁰ mixingDalitz plot B⁰B⁰ B⁰B⁰ mixing _ + _  CPV measurement φKS⁰φKS⁰ f₀(980)K S ⁰ Dalitz-plot s₊ = M²(K⁺K S ⁰) s₋ = M²(K⁻K S ⁰) 19

20 B⁰  K S ⁰K⁺K⁻ Reconstruction # of reconstructed events – Estimation by unbinned-maximum- likelihood fit to the ΔE-M bc distribution B⁰  K S ⁰K⁺K⁻ N sig = 1176±51 – Reconstruction efficiency ~16% Background – Continuum ~ 47% – Other B decays ~ 3% – Signal purity ~ 50% signal continuum M bc ΔEΔE from 657 x 10⁶ BB pairs _ 20

21 CPV Measurement in B⁰  K S ⁰K⁺K⁻ The (φ₁, A) are determined by an unbinned-ML fit onto the time-dependent Dalitz distribution. – The signal probability density function: Four parameter convergences from the fit – They are statistically consistent with each other. – Which is the most preferable solution? 21

22 CPV Measurement in B⁰  K S ⁰K⁺K⁻ Solution #1 is most preferred from an external information. – The Br(f₀(980)  π⁺π⁻)/Br(f₀(980)  K⁺K⁻) favors solutions with low f₀(980)K S ⁰ fraction, when compared to the PDG. – The Br(f₀(1500)  π⁺π⁻)/Br(f₀(1500)  K⁺K⁻) favors solutions with low f₀(1500)K S ⁰ fraction, when compared to the PDG. ­ Here, we assume f X as f₀(1500). Intermediate state-by-state fraction 22

23 CPV Measurement in B⁰  K S ⁰K⁺K⁻ Y.Nakahama et al., Phys. Rev. D 82, (2010) BG The third error accounts for an uncertainty arises from Dalitz model. SM prediction [solution #1] 657 x 10⁶ BB pairs _ Only in the φ mass region 23

24 CP Violation in b  s Penguin Latest tension in between tree and penguin – S b  c = S b  s SM – W.A.: S b  s = 0.64±0.04 – W.A.: S b  c = 0.673± σ deviation B⁰  J/ψK⁰ (b  c) B⁰  φK⁰, η’K⁰ (b  s) 24

25 Measurement of φ₂ φ₂ can be measured using B⁰  π⁺π⁻, ρ⁺ρ⁻ decays. d b u d u d W π⁺, ρ⁺ B⁰B⁰ π⁻, ρ⁻ d b d u d gt W u B⁰B⁰ π⁺, ρ⁺ π⁻, ρ⁻ _ _ _ _ _ _ If no penguin contribution …  In presence of penguin, (θ can be given from the isospin analysis.) 25 treepenguin

26 Extraction of φ₂ from Isospin Analysis Complex amplitude: A S = … A = … B  ππ branching fraction B  ππ DCPV parameters B  ππ branching fraction B  ππ DCPV parameters Input φ₂ can be solved 26 _ _

27 S and A from B⁰  π⁺π⁻, ρ⁺ρ⁻ (535M BB) _ B⁰  π⁺π⁻B 0  ρ⁺ρ⁻ 27 H.Ishino et al., Phys. Rev. Lett. 98, (2007) A.Somov et al., Phys. Rev. D 76, (R) (2007)

28 Constraint on φ₂ 28 J.Charles et al. [CKMfitter Group], Eur. Phys. J. C41, 1 (2005).

29 Kπ Puzzle in B⁰/B⁺ CP Violation σ deviation  Hint of NP TP C P EW P EW contribution to CPV is large due to NP…? S.-W. Lin et al. (The Belle collaboration), Nature 452, 332 (2008). Diagrams contributing to both B⁰ and B⁺ B⁰  K⁻π⁺B⁰  K⁺π⁻ B⁻  K⁻π⁰B⁻  K⁻π⁰B⁺  K⁺π⁰ B⁰B⁰ B⁺B⁺ _ Diagrams contributing only to B⁰ and B⁺

30 Kπ Puzzle in B⁰/B⁺ CP Violation 30 Four precise measurements of CP-violating parameters related to the Kπ and the “sum rule” will give the answer ± 0.13 ± 600 fb⁻¹ (Belle) CPV in K⁰π⁰ is statistically difficult to measure  Need for SuperKEKB. Significant deviation may be seen with 10 ab⁻¹ data. 50 ab⁻¹Present Sum Rule

31 Direct CP Violation in B⁺  J/ψK⁺ Physics motivation – The B⁺  J/ψK⁺ decay mediated by the b  s u-penguin has a different weak phase from the tree. – The interference between the tree and penguin can cause the direct CP violation in B⁺  J/ψK⁺. Tree Penguin Belle–2.6±2.2±1.7 Phys. Rev. D67, (2003) BABAR+3.0±1.4±1.0 Phys. Rev. Lett. 94, (2005) D0+0.75±0.61±0.30 Phys. Rev. Lett. 100, (2008) W/A+0.9±0.8 (PDG2009) Previous measurements of A CP (B⁺  J/ψK⁺) [%] 31 NEW!!

32 B ±  J/ψK ± event reconstruction – B ± candidates are reconstructed from J/ψ and K ±. Raw asymmetry: A CP raw – Measured raw asymmetry, which still includes K⁺/K⁻ charge asymmetry in detection, is: A CP raw = (–0.33±0.50)% ­ The “raw asymmetry” is obtained from yields of the B⁺  J/ψK⁺ and the B⁻  J/ψK⁻ in a signal region. Raw Asymmetry in B⁺  J/ψK⁺ Signal = single Gaussian Background = ARGUS BG Peaking BG is negligibly small  systematic uncertainty. Yield: 41188±205 Mean: ±0.01 MeV/c² Width: 2.69±0.01 MeV/c² ΔE region: |ΔE|< 40 MeV 772 x 10⁶ BB pair data _ K-π likelihood ratio For K ± (average), 80.5% K efficiency and 9.6% π fake rate. 32

33 K⁺/K⁻ charge asymmetry in detection: A ε K⁺ – The K + /K – charge asymmetry in detection arises due to ­ Non-symmetric detector geometry, ­ Different interaction rates in material of K⁺/K⁻, and ­ Different KID efficiencies of K⁺/K⁻. The raw asymmetry A CP raw should be corrected for by the K⁺/K⁻ charge asymmetry A ε K⁺. K⁺/K⁻ Charge Asymmetry 33

34 K⁺/K⁻ Charge Asymmetry Estimation K⁺/K⁻ charge asymmetry estimation – The K⁺/K⁻ detection asymmetry is estimated using the D s ⁺  φ[K⁺K⁻]π⁺ and D⁰  K⁻π⁺, and their charge conjugate. – Estimated K⁺/K⁻ charge asymmetry in detection (averaged over bins) is: A ε K⁺ = (–0.43±0.07±0.17)% assuming The K⁺/K⁻ charge asymmetry depends on the cosθ K lab and p K lab. We bin the signal regions in the (cosθ K lab, p K lab ) plane into 10 boxes, and measure the charge asymmetry for each bin. Each box corresponds to one of the 10 signal bins. #1 #10 Real data 34

35 CP Violation Measurement in B⁺  J/ψK⁺ Fit result – From the sum of A CP raw and A ε K⁺, we preliminarily determine – We observe no significant CP violation in B⁺  J/ψK⁺. K.Sakai et al., Phys. Rev. D82, (R) (2010). 772 x 10⁶ BB pairs _ 35

36 Unitarity Triangle Opened? Unitarity triangle opened? 36

37 Summary Following items have been presented: – Mixing-induced CPV (φ₁) measurement in b  ccs – Mixing-induced CPV measurement in b  sqq – Mixing-induced CPV (φ₂) measurement in B⁰  π⁺π⁻, ρ⁺ρ⁻ – Kπ Puzzle in B⁰/B⁺ CP violation – Direct CPV in B⁺  J/ψK⁺ – Prospect of unitarity check by Belle II _ _ 37

38 Backup Slides 38

39 Δt: proper-time difference of the two B mesons – The Δt is calculated from a Δz: displacement of decay vertices of the two B mesons. Decay vertex reconstruction – Assume all decay tracks goes through a common point (vertex). – Minimizes ­ The V i is the i-th inverse error matrix. – RMS of the vertex resolution is ~ 120 μm Reconstruction of Δt B vertex decay products vertex j-th track i-th track δhjδhj δhiδhi 39

40 Δt Resolution Function One of dominant systematic error sources to the S/A Convolution of the following 4 components – Detector resolution … modeled by σ and χ² of the vertex fit. – Secondary track effect of B tag decay … modeled by exponential. ­ Higher priority is given to the ℓ of the B tag  D*ℓν decay. – Effect from... exactly calculated. – “Outlier” component... Gaussian with σ ~ 10τ B⁰. 40 ℓ D*D* K π B tag true vertex primary tracks secondary tracks reconstructed vertex

41 Determination of B tag Flavor Memory lookup method – Assign flavor to B tag decay products track-by-track referring the MC-generated lookup table – Combine the track-by-track flavors and get flavor of the event. – Determine B tag flavor (q:±1) and its ambiguity (w: 0…1). Calibration of MC-originated w – The w is calibrated using B⁰-B⁰ mixing. 41 B tag = B 0 unambiguous no info. B tag = B 0 –10+1 _ r = q(1–2w) _ A chg |Δt| (ps)

42 Unbinned-Maximum Likelihood Fit Δt resolution wrong tagging probability background contamination  background CPV-parameter determination from the UML fit wrong tagging probability B tag = B⁰ _ _ 42 Δt resolution

43 B⁰  K S ⁰K⁺K⁻ CPV Systematic Uncertainty List of the systematic-uncertainty sources for the solution #1 43

44 B⁺  J/ψK⁺ Reconstruction B ±  J/ψK ± event reconstruction: J/ψ – J/ψ candidates are reconstructed from e⁺e⁻ or μ⁺μ⁻ pairs. ­ (Tightly identified lepton) + (tightly or loosely identified lepton). Tightly identified e dE/dx && E ECL /p && ECL shower shape Loosely identified e dE/dx || E ECL /p Tightly identified μ # of penetrating iron plates && shower Loosely identified μ E ECL ≈ E deposit by MIP e⁺e⁻μ⁺μ⁻μ⁺μ⁻ tight + loosetight + tighttight + loosetight + tight < M ee < GeV/c²3.037 < M μμ < GeV/c² 44

45 B⁺  J/ψK⁺ CPV Systematic Uncertainty List of the systematic-uncertainty sources 45

46 CP Violation Measurement in B⁺  J/ψK⁺ List of bin-by-bin CP violation and charge asymmetry 46

47 SuperKEKB SuperKEKB Accerelator Installation of damping ring SR Beam [Beam Channel] [SR Channel] [NEG Pump] Improvements in beam pipe Improvements in the RF components 7.0GeV e⁻ 4.0GeV e⁺ IR x40 luminosity of KEKB L = 2x10³⁵cm⁻²s⁻¹ Better “squeezing” magnet

48 Belle II Detector Central drift chamber Smaller cell, longer lever arm 2-layer DEPFET pixel 4-layer DSSD Electromagnetic calorimeter Barrel part: CsI(Tℓ) Endcal part: pure CsI Ring image Čerenkov counter K L μ detector Barrel part: RPC Endcap part: scintillator + SiPM Fast data acquisition system Intelligent hardware trigger Larger mass storage system Time-of-propagation counter


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