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Analysis of the Decay = B0 → ω K0 Physical Motivation Summary and outlook S Study of the decay of B 0 → ω K 0 S at Belle Veronika Chobanova, Jeremy Dalseno, Christian Kiesling February 29th, 2012 Physical Motivation Analysis of the Decay = B 0 → ω K 0 S Summary and outlook Study of the decay of B 0 → ω K 0 Veronika Chobanova, Jeremy Dalseno, Christian Kiesling S at Belle

Analysis of the Decay = B0 → ω K0 Physical Motivation Summary and outlook S Introduction to CP Violation ◮ Universe today is matter dominated ◮ Violation of CP = C (charge) × P (parity) symmetry necessary to explain the matter-antimatter asymmetry ◮ CP violation in the Standard Model: Cabbibo-Kobayashi-Maskawa (CKM) mechanism ◮ CKM mechanism desribes the relation between the weak and the mass eigenstates of quarks ◮ CKM mechanism expressed through a complex, unitary 3 × 3 matrix CKM Matrix         d d V ud V us V ub d s = V CKM s ≡ V cd V cs V cb s         b b V td V ts V tb b weak mass mass Vij : quark flavor transition couplings CKM mechanism not enough to explain all the missing antimatter 2 Study of the decay of B 0 → ω K 0 Veronika Chobanova, Jeremy Dalseno, Christian Kiesling S at Belle

Analysis of the Decay = B0 → ω K0 Physical Motivation Summary and outlook S CP Violation in the Standard Model Wolfenstein parametrisation 1 − λ 2 A λ 3 ( ρ − i η )   λ 1 − λ 2 / 2 A λ 2  + O ( λ 4 ) V CKM = − λ  A λ 3 (1 − ρ − i η ) − λ 2 1 λ = sin θ C ≈ 0 . 22, θ C : Cabibbo angle 4 free parameters: 3 mixing angles and 1 complex phase CKM matrix is unitary ρ η ( , ) ⇒ V ud · V ∗ ub + V cd · V ∗ cb + V td · V ∗ tb = 0 O ( λ 3 ) O ( λ 3 ) O ( λ 3 ) φ 2 * |V V | relevant for the B meson system tb td * |V V | Sides with similar size ⇒ large angles, cb cd precise determination of the observables φ φ φ (3 angles and 2 sides) possible 3 1 1 problem over-constrained ⇒ leaves (0,0) (1,0) room for New Physics q (like B 0 → ω K 0 Decays via charmless b → sq ¯ S ) transitions sensitive to φ 1 3 Study of the decay of B 0 → ω K 0 Veronika Chobanova, Jeremy Dalseno, Christian Kiesling S at Belle

Analysis of the Decay = B0 → ω K0 Physical Motivation Summary and outlook S CP Violation in the B Meson System Time-dependent CP asymmetry N B0 (∆ t , f CP ) − N B 0 (∆ t , f CP ) a CP (∆ t , f CP ) = N B0 (∆ t , f CP ) + N B 0 (∆ t , f CP ) = A CP cos(∆ m ∆ t ) + S CP sin(∆ m ∆ t ) A CP measure for the direct CP S CP measure for the indirect CP violation violation B 0 → f CP � = B 0 → f CP B 0 → B 0 → f CP � = B 0 → B 0 → f CP A CP = 1 A CP = 0 S CP = 0 S CP = 1 4 Study of the decay of B 0 → ω K 0 Veronika Chobanova, Jeremy Dalseno, Christian Kiesling S at Belle

Analysis of the Decay = B0 → ω K0 Physical Motivation Summary and outlook S CP Violation Measurement B Meson production ◮ Υ(4 S ) resonance decays almost exclusively into a B 0 B 0 pair ◮ Υ(4 S ): J PC = 1 −− B : J PC = 0 −− ⇒ B meson pair in a p-wave ⇒ asymmetric wave function ⇒ B mesons have opposite flavour B 0 B 0 pair coherent 10 . 58 GeV / c 2 ≈ 2 × m B m Υ(4 S ) = 5 . 28 GeV / c 2 m B = 5 Study of the decay of B 0 → ω K 0 Veronika Chobanova, Jeremy Dalseno, Christian Kiesling S at Belle

Analysis of the Decay = B0 → ω K0 Physical Motivation Summary and outlook S CP Violation Measurement - + l l K - coherent 0 B tagside 0 0 B-B pair + X high energy beam - ν ν e + e Y(4S) π - 0 B π + π - Δz CP side π + t t 1 2 B 0 or B 0 ? → Look at the other B (tag-side): If l − ⇒ B 0 on the tag-side and B 0 on the CP -side If l + ⇒ B 0 on the tag-side and B 0 on the CP -side ∆ t measurement Asymmetric beam energies at the Belle experiment: E e − = 8 GeV , E e + = 3 . 5 GeV ⇒ Boost in the center of mass system Measurement of ∆ z ∼ 100 µ m instead of ∆ t ∼ ps Obtain ∆ t = ∆ z / c � βγ � 6 Study of the decay of B 0 → ω K 0 Veronika Chobanova, Jeremy Dalseno, Christian Kiesling S at Belle

Analysis of the Decay = B0 → ω K0 Physical Motivation Summary and outlook S The Decay B 0 → ω K 0 S W − V ∗ V ub V tb b ts s b u t d K 0 u ω V ∗ S us B 0 B 0 s d K 0 ω S d d d d Matrix elements for the two Feynman diagrams ⇒ Decay is dominated by the us ∝ λ 3 · λ ∝ λ 4 ◮ M tree ∝ V ub · V ∗ penguin contribution ts ∝ 1 · λ 2 ∝ λ 2 ◮ M peng ∝ V tb · V ∗ Measurement of The branching fraction BR ( B 0 → ω K 0 S ) The CP parameters A CP and S CP = sin φ eff (pollution from the tree 1 diagram) 7 Study of the decay of B 0 → ω K 0 Veronika Chobanova, Jeremy Dalseno, Christian Kiesling S at Belle

Analysis of the Decay = B0 → ω K0 Physical Motivation Summary and outlook S Physical Motivation Why exactly the decay B 0 → ω K 0 S ? ◮ Theory predicts in the Standard Model that sin 2 φ eff from b → sq ¯ q 1 should be larger than for b → c ¯ cs (sin 2 φ eff − sin 2 φ 1 ǫ (0 . 0; 0 . 2)) 1 ◮ But the measurement may be systematically lower, giving a hint of New Physics ◮ Could be caused by unknown new particle in the loop carrying different weak phase ◮ Leads to a measured shift from sin 2 φ 1 ? V ∗ V tb ts s b t d K 0 S B 0 d ω d d 8 Study of the decay of B 0 → ω K 0 Veronika Chobanova, Jeremy Dalseno, Christian Kiesling S at Belle

Analysis of the Decay = B0 → ω K0 Physical Motivation Summary and outlook S Approach Goal 1 : Determination of BR ( B 0 → ω K 0 S ), A CP and S CP Goal 2 : Minimize the statistical and and systematic uncertainties Approach to Goal 1 ◮ Build an algorithm to reconstruct the events of interest ◮ Study the different backgrounds ◮ Build a model to separate the signal from the background (multidimensional fit) ◮ Test the model So far: Blind. Study only from Monte Carlo (MC) samples ◮ Apply model to the real data ◮ Determine BR ( B 0 → ω K 0 S ), A CP and S CP and the uncertainties Approach to Goal 2 ◮ Build a better model than the previous analysis ◮ Use the full available data 9 Study of the decay of B 0 → ω K 0 Veronika Chobanova, Jeremy Dalseno, Christian Kiesling S at Belle

Analysis of the Decay = B0 → ω K0 Physical Motivation Summary and outlook S Prevoius Measurements of B 0 → ω K 0 S BR ( B 0 → ω K 0 B 0 B 0 -pairs S ) A CP S CP (4 . 4 +0 . 8 388 × 10 6 − 0 . 7 ± 0 . 4) × 10 − 6 Belle - - 657 × 10 6 Belle - − 0 . 09 ± 0 . 29 ± 0 . 06 0 . 11 ± 0 . 46 ± 0 . 07 535 × 10 6 (5 . 4 ± 0 . 8 ± 0 . 3) × 10 − 6 − 0 . 52 +0 . 22 0 . 55 +0 . 26 BaBar − 0 . 20 ± 0 . 03 − 0 . 29 ± 0 . 02 Challenging analysis BR ( B 0 → ω K 0 S ) ∼ 10 − 6 small Large background contribution Our method Use loose cuts on the observables to collect maximum signal Multidimensional fit to the observables including the event shape to separate signal and background 10 Study of the decay of B 0 → ω K 0 Veronika Chobanova, Jeremy Dalseno, Christian Kiesling S at Belle

Analysis of the Decay = B0 → ω K0 Physical Motivation Summary and outlook S Measurement of BR ( B 0 → ω K 0 S ) Extract BR ( B 0 → ω K 0 S ) by a 6D extended unbinned maximum likelihood fit Fit variables: ∆ E , F B¯ q , m 3 π , H 3 π , q , ∆ t B / q¯ ∆ E = E B rec − E beam F B¯ q Fisher discriminant, event-shape dependent B / q¯ q = 1 for B 0 and q = − 1 for B 0 New in this analysis : H 3 π , powerful observable for background discrimination Multidimensional analysis ⇒ model for signal and background necessary ◮ signal MC ◮ misreconstructed signal MC ◮ continuum ( e − e + → q ¯ sideband data (high E rec , low q ) beam ) 2 − ( p cms � M bc = ( E cms ) 2 ) B ◮ charmed and charmless B 0 B 0 (B + B − ) decays MC ◮ peaking background MC (5 π final states): B 0 → D ∗− π + , B 0 → D − π + , B 0 → D − ρ + 11 Study of the decay of B 0 → ω K 0 Veronika Chobanova, Jeremy Dalseno, Christian Kiesling S at Belle

Analysis of the Decay = B0 → ω K0 Physical Motivation Summary and outlook S Toy MC studies for B 0 → ω K 0 S Expectations for B ( B 0 → ω K S ) Test the model with Toy MC Events / (1e-07) Expected number of events 30 µ =2.49 ± 0.03 =0.25 0.02 σ ± 25 signal ∼ 230 20 15 q ¯ q ∼ 5300 10 B ¯ B ∼ 130 5 -6 10 × 0 1 2 3 4 5 BF 180 Events / (0.005 GeV) Fit 160 Uncertainty 9.2% 140 Error scaled to final data sets 120 Belle (previous): 13% , BaBar: 13% ⇒ Our method is better 100 80 Pull distribution of B ( B 0 → ω K S ) 60 16 40 Events / (0.2) 14 µ =-0.09 ± 0.11 20 σ =1.07 ± 0.08 12 10 Normalised 8 Residuals 2 6 0 4 -2 2 -0.15 -0.1 -0.05 0 0.05 0.1 -5 -3 -1 1 3 5 Pull BF ∆ E (GeV) Fit No bias, correct error estimation 12 Study of the decay of B 0 → ω K 0 Veronika Chobanova, Jeremy Dalseno, Christian Kiesling S at Belle

Analysis of the Decay = B0 → ω K0 Physical Motivation Summary and outlook S Results from the Fit to the Data Events / (0.005 GeV) 35 Black: Full PDF 30 Total background B ¯ 25 B background 20 Preliminary Result from 15 135 × 10 6 B ¯ B Pairs 10 5 B ( B 0 → ω K 0 ) = [4 . 94 +1 . 28 − 1 . 14 ] × 10 − 6 Normalised World average Residuals 2 B ( B 0 → ω K 0 ) = [5 . 0 ± 0 . 6] × 10 − 6 0 -2 -0.15 -0.1 -0.05 0 0.05 0.1 ∆ E (GeV) 13 Study of the decay of B 0 → ω K 0 Veronika Chobanova, Jeremy Dalseno, Christian Kiesling S at Belle