Rare Hadronic B decays at BaBar

Transcription

1 Rare Hadronic B decays at BaBar Mirna van Hoek University of Colorado On behalf of the BaBar Collaboration 18 th International Workshop on Weak Interactions and Neutrinos January 21-26, 2002 Christchurch, New Zealand

2 Motivation 2 main categories of rare decays: b! u transition CKM suppressed: V ub /V cb ~ b u W u b! s,d Induced FCNC and Penguins : W b u, c, t g d, s d, s Comparable order of magnitude to Penguin diagrams Interferences " Phases, CP violation u, d, s, c Massive particles can contribute to the loop: top, Higgs, SUSY Penguins complicate CP measurements Win02 Jan Mirna van Hoek 2

3 Data Sample Rare Decays (Br ~ 10-5 ) Need high luminosity Run1: ( 99-00) 20.7 fb -1 on-peak 2.6 fb -1 off-peak 22.7 x 10 6 B pairs Run2: ( 01-02) up to now 40 fb -1 (and counting) 20.7 Win02 Jan Mirna van Hoek Run1 Run2 3

4 Common Analysis Strategies Continuum background rejection: Event shape B candidate selection: E, m ES /m EC Further pre-selection: PID, resonance masses Signal extraction: Cut and count, ML fit, Neural Net All Analyses Blind! Win02 Jan Mirna van Hoek 4

5 Background Rejection Background dominated by continuum qq Use event shape variables: Ratio of Fox-Wolfram moments: R 2 /R 0 qq e + e - Cosine of B thrust axis / rest of event : cosθ T Cosine of B decay axis / beam axis : cosθ B Energy flow around B thrust axis And many more Other B e + e - Signal B Combine these variables into a Fisher discriminant or a Neural Net Win02 Jan Fisher Discriminant Mirna van Hoek 5

6 B signal variables e + e ϒ (4 S) BB B mesons ~ at rest ( 325 MeV/c) p! q = q E E E 2 2 B1 B2 B beam (CMS) B KK Kπ ππ Typical: σ( E) 25 40MeV q = m 2 2 B1 B E ππ (MeV) m E p EC B B (kinematic fit) (CMS) 0 ( ) + + B D π /ρ /a + 1 ES ( p0 pb) / 0 B 2 m s+ E p (LAB) Beam energy better known than B energy Typical: σ( m) 2.8 MeV/c 2 m ES (MeV/c 2 ) Win02 Jan Mirna van Hoek 6

7 Cut & Count Cut optimisation (signal MC & on-peak data GSB) Efficiency determination (signal MC) Extrapolate bkg GSB SR: #bkg SR (on-peak data GSB) Estimate #BB SR ( BB MC) Signal: #SR-#bkg SR -#BB SR 0.3 E Grand Side Band Blinding Box Signal Region m B m ES 5.3 Win02 Jan Mirna van Hoek 7

8 L = e ( nj) N Likelihood fit Li N! i= 1 m " where L = n P ( x ) i j j i j= 1 n j : population for each species (signal and/or background) P j (x i ) : Probability distribution function evaluated with a set of observables x i (m ES, E, Fisher etc ) Statistical error on the # of events: (χ 2-2 lnl/l max )= 1 Statistical significance S = S 2 χ 2 (no signal) - χ 2( minimum) Win02 Jan Mirna van Hoek 8

9 B ππ,kπ,, KK Very important modes to constrain CKM angles α and γ Time dependent asymmetry in B 0 (B 0 ) π + π measures sin(2α eff ) In absence of penguins, α eff =α Unfortunately, penguins are not small: B + π + π 0 : ~Pure Tree B + π + Κ 0 : ~Pure Penguin Br(B + π + Κ 0 ) > BR(B + π + π 0 ) Branching ratios constrain γ ML fit with E, m ES,! and Cherenkov angle And t for sin(2α eff ) Win02 Jan Mirna van Hoek 9

10 B ππ,kπ,, KK Mode N S S (σ) "#(10-6 ) π + π 41±10± ±1.0±0.7 K + π 169±17± ±1.6±1.3 K + K ± <2.5 (90% C.L.) π + π 0 37±14±6 3.4 <9.6 (90% C.L.) K + π 0 75±14± ±1.0 K 0 π ± ±2.0 K 0 π ±7 -- <2.4 (90% C.L.) K 0 π ± ±1.2 K 0 K ± <7.3 (90% C.L.) Win02 Jan Mirna van Hoek 10

11 Time dependent CP in B 0 π + π - Decay distributions f + (f - ) when other B tagged as B 0 (B 0 ) / ( ) e t τ f± t = [1 S sin( m t) C cos( m t)] 4 ππ d ππ τ ± # d tree diagram b u u penguin diagram b d u λ q p A A f C ππ = η 2i( β+γ) f # Motivation # Results # Summary ππ f e d Weak phase (only tree diagram) = η ππ = 0, S ππ = sin2α f e 2iα Win02 Jan Mirna van Hoek 11 u Additional phase from penguin diagram λ 1 must fit for direct CP Im (λ) sin2α need to relate asymmetry to α C ππ 0, S ππ = sin2α eff

12 B 0 π + π - asymmetry result A To appear in PRD Rapid Communications S( ππ ) = 0.03 ± C( ππ ) = 0.25 ± 0.14 CP ± # ( K π ) = 0.07 ± 0.08 ± 0.02 Measurement compatible with no CP in B 0! π + π Statistically limited due to small branching fraction Need ~500fb -1 for σ(s ππ ) ~ Win02 Jan Mirna van Hoek 12

13 B 0 π + π - π 0 Important for determination of α: -Enough info to disentangle penguins zone I II III [putative dominant resonance] ρ ± (770)π! ρ 0 (770)π 0 ρ ± (1450)π! ε (%) 13.5 ± ± ±2.1 yields 89 ±16 ±6 6.1 ±5.8 ± ±9.7 ±6.9 IV ρ 0 (1450)π ± ±3.6 ±2.2 V (charged scalar)π ± 15.0 ± ±7.3 ±2.3 VI f 0 ( )π ± ±3.2 ±3.2 VII π + π - π 0 (NR) 7.5 ± ±7.3 ±3.8 Significant signal observed! m 2 ( π π 0 ) vs m 2 ( π + π 0 ) Cuts optimized for each Dalitz region separately Win02 Jan Mirna van Hoek 13

14 B 0 ρπ Br( B ρ (770) π ) = (28.9± 5.4± 4.3) 10 Br( B0 ρ0(770) π0) < Br( B0 πππ + 0( NR)) < ± # 6 No evidence for direct CP violation: + + Γ Γ ( ρ π ) ( ρ π ) Aρπ = Γ + + ( ρ π ) +Γ( ρ π ) = 0.04 ± 0.18 ± Win02 Jan Mirna van Hoek 14

15 Similar to ρπ Cut based analysis K 0 K + π - B K 0 π Br( B K π ) = (15.5± 3.4 ± 1.5) 10 (5.3 σ significance) Win02 Jan Mirna van Hoek 15

16 B 0 a 0± (η(γγ)π ± )π! Goal: measure α Assumption: factorization Main tree vanish (second class currents forbidden) Possible enhancement direct CP violation x>0.98 ML fit with NN, m(γγ), m EC, E 0 ± ± # ( a0 ( ηπ ) π ) (S(σ)=3.7) Br B = (6.2 ± 1.1) 10 < (90% CL) Win02 Jan Mirna van Hoek 16

17 B ωh Tree dominates (b u) Mode N Signal ωk ±0.3 (<4) ωk ±0.8 (<13) ωπ ±0.7 ωπ ±1.1±0.3 (<3) S (σ) "#(10-6 ) (90%CL) clear signal Win02 Jan Mirna van Hoek 17

18 B φk () b s(d) ss (pure) penguins First observations Mode N Signal S (σ) "#(10-6 ) φk ±0.8 φk ± φk ±1.7 φk + Κ + π ±3.2 φk 0 : CP eigenstate can measure sin2β φk + Κ 0 π + φk 0 φπ ± ±1.1 < 1.4 (90% CL) Win02 Jan Mirna van Hoek 18

19 B η ( ) K () Tree CKM suppressed Interference between Penguins ( g uu( ss)) Enhance B η K ; B ηk Suppress B ηk ; B η K Win02 Jan Mirna van Hoek 19

20 B η ( ) K () ML fit with E,m EC,!,m res,($, PID pulls) Win02 Jan Mirna van Hoek 20

21 B η ( ) K () η K: Confirm Cleo Larger than expected! Possibly due to QCD anomaly: gluon coupling to η Charming Penguins charm enhanced in loop Mode ηk 0 ηk η ηππ K + η ργ K + η ηππ K η K 0 η ηππ π + N Signal 20.5± ± η K ±8± S (σ) "#(10-6 ) (90%CL) η ργ K ± ±3.3 (<33.9) ±1.7 η ργ π η π ±0.8 (<12) Win02 Jan Mirna van Hoek 21

22 Semi-exclusive exclusive B ηb η X S b sg measurements direct CP violation High rate first observed in Cleo Interpreted as due to QCD anomaly η coupling to 2 gluons Select η with p > 2 GeV/c to remove most of b c η bkgd + ± 0 Reconstruct X S in 16 modes: B η' K nπ ( π ) with n = ± 0 B η' K nπ ( π ) Br( B X η ') = (6.8 ± 1.0 ) Win02 Jan Mirna van Hoek 22 S S Account for possible η D 0()

23 Summary of direct CP asymmetries 90% CL B 0 π K ± ± B ± π 0 K ± B ± π ± K 0 B ± η K ± B ± ωπ ± B ± φk ± B ± φk ± B 0 φk 0 BABAR A CP Γ( B f ) Γ( B f) ACP = Γ ( B f ) +Γ ( B f) No Evidence for direct CP violation yet 0.07 ± 0.08 ± ± 0.18 ± ± 0.18 ± ± 0.11 ± ± 0.03 Win02 Jan Mirna van Hoek ± 0.20 ± ± 0.00 ± 0.27 ± 0.03 Updated 30.4 fb fb -1

24 Summary and Outlook Large data sample (Run1: ~23 million BB pairs) Sensitive to Br down to few x10-6 ~30 modes analyzed with clear signals No evidence (yet) for direct CP violation (σ down to ~8%) Important to understand: Penguin/Tree contributions Factorization hypothesis Constraining (and measuring!) α Measuring β in B φk 0 S Run2: until summer 2002: ~ 100 million BB pairs More rare decays results + higher sensitivity Stay tuned!!! Win02 Jan Mirna van Hoek 24