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
Motivation 2 main categories of rare decays: b! u transition CKM suppressed: V ub /V cb ~6 10-3 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 Jan25 2002 Mirna van Hoek 2
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 Jan25 2002 Mirna van Hoek Run1 Run2 3
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 Jan25 2002 Mirna van Hoek 4
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 Jan25 2002 Fisher Discriminant Mirna van Hoek 5
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 1 2 2 2 ( 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 Jan25 2002 Mirna van Hoek 6
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 0-0.3 5.2 Grand Side Band Blinding Box Signal Region m B m ES 5.3 Win02 Jan25 2002 Mirna van Hoek 7
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 Jan25 2002 Mirna van Hoek 8
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 Jan25 2002 Mirna van Hoek 9
B ππ,kπ,, KK Mode N S S (σ) "#(10-6 ) π + π 41±10±7 4.7 4.1±1.0±0.7 K + π 169±17±13 15.8 16.7±1.6±1.3 K + K - 8.2 +7.8-6.4±3.5 1.3 <2.5 (90% C.L.) π + π 0 37±14±6 3.4 <9.6 (90% C.L.) K + π 0 75±14±7 8.0 10.8 +2.1-1.9±1.0 K 0 π + 59 +11-10±6 9.8 18.2 +3.3-3.0±2.0 K 0 π + -4.1 +4.5-3.8±7 -- <2.4 (90% C.L.) K 0 π 0 17.9 +6.8-5.8±1.9 4.5 8.2 +3.1-2.7±1.2 K 0 K 0 3.4 3.4 2.4±3.5 1.5 <7.3 (90% C.L.) Win02 Jan25 2002 Mirna van Hoek 10
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 Jan25 2002 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
B 0 π + π - asymmetry result A To appear in PRD Rapid Communications + + 0.53 0.56 S( ππ ) = 0.03 ± 0.11 + + 0.45 0.47 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 ) ~ 0.10-0.15 Win02 Jan25 2002 Mirna van Hoek 12
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 ±1.6 7.4 ±0.9 15.0 ±2.1 yields 89 ±16 ±6 6.1 ±5.8 ±2.8 17.4 ±9.7 ±6.9 IV ρ 0 (1450)π 0 8.7 ±1.8-4.7 ±3.6 ±2.2 V (charged scalar)π ± 15.0 ±2.3 8.6 ±7.3 ±2.3 VI f 0 (400-1200)π 0 6.7 ±1.4-0.3 ±3.2 ±3.2 VII π + π - π 0 (NR) 7.5 ±1.0-4.2 ±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 Jan25 2002 Mirna van Hoek 13
B 0 ρπ Br( B ρ (770) π ) = (28.9± 5.4± 4.3) 10 Br( B0 ρ0(770) π0) < 10.6 10 6 Br( B0 πππ + 0( NR)) < 7.3 10 6 0 ± # 6 No evidence for direct CP violation: + + Γ Γ ( ρ π ) ( ρ π ) Aρπ = Γ + + ( ρ π ) +Γ( ρ π ) = 0.04 ± 0.18 ± 0. 02 Win02 Jan25 2002 Mirna van Hoek 14
Similar to ρπ Cut based analysis K 0 K + π - B K 0 π + + 0 + 6 Br( B K π ) = (15.5± 3.4 ± 1.5) 10 (5.3 σ significance) Win02 Jan25 2002 Mirna van Hoek 15
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 ) + 3.0 6 (S(σ)=3.7) 2.5 6 Br B = (6.2 ± 1.1) 10 < 11.5 10 (90% CL) Win02 Jan25 2002 Mirna van Hoek 16
B ωh Tree dominates (b u) Mode N Signal ωk + 6.4 +5.6-4.4 1.3 1.4 +1.3-1.0 ±0.3 (<4) ωk 0 3.2 6.4 +3.6-2.8 ±0.8 (<13) 8.1 +4.6-3.6 ωπ + 27.6+8.8-7.7 4.9 6.6 +2.1-1.8 ±0.7 ωπ 0 - -0.3±1.1±0.3 (<3) -0.9 +.5.0-3.2 S (σ) "#(10-6 ) (90%CL) clear signal Win02 Jan25 2002 Mirna van Hoek 17
B φk () b s(d) ss (pure) penguins First observations Mode N Signal S (σ) "#(10-6 ) φk + 31.4 +6.7-5.9 10.5 7.7+1.6-1.4±0.8 φk 0 6.4 8.1 +3.1-2.5 ±0.8 10.8 +4.1-3.3 φk + -- 4.5 9.7 +4.2-3.4 ±1.7 φk + Κ + π 0 7.1 +4.3-3.4 2.7 12.8 +7.7-6.1 ±3.2 φk 0 : CP eigenstate can measure sin2β φk + Κ 0 π + φk 0 φπ + 4.4 +2.7-2.0 20.8 +5.9-5.1 0.9 +2.1-0.9 3.6 7.5 0.6 8.0 +5.0-3.7 ±1.3 8.7 +2.5-2.1 ±1.1 < 1.4 (90% CL) Win02 Jan25 2002 Mirna van Hoek 18
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 Jan25 2002 Mirna van Hoek 19
B η ( ) K () ML fit with E,m EC,!,m res,($, PID pulls) Win02 Jan25 2002 Mirna van Hoek 20
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 6.3 +3.3 ηππ K 0-2.5 4.7 4.2 61 +22 η K 0 η ηππ π + N Signal 20.5±6.0 14.3±6.6 49.5 +8.1-7.3 87.6 +13.4-12.5 11 80+12-11 η K + 17 70 ±8± 5 5.7 +3.8-2.8 3.2 + 19.8+6.5 S (σ) "#(10-6 ) (90%CL) 5.4 15 3.2 63 +10-95 28 +15-11 η 20.8 +7.4 ργ K 0-6.5-19 5.9 42 +13-11±4 22.1 +11.1-9.2 ±3.3 (<33.9) 7.1 +4.8-3.5-5.6±1.7 η -0.9 +7.8 ργ π + -6.2 0.1 5.4 +3.5-0.7 +6.7 -.5.3 η π + 2.8-2.6±0.8 (<12) Win02 Jan25 2002 Mirna van Hoek 21
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 3 0 ± 0 B η' K nπ ( π ) Br( B X η ') = (6.8 ± 1.0 ) 10 + 0.7 + 0.0 4 1.0 0.5 Win02 Jan25 2002 Mirna van Hoek 22 S S Account for possible η D 0()
Summary of direct CP asymmetries Excluded @ 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 -1.0-0.5 0.0 0.5 1.0 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 ± 0.02 0.00 ± 0.18 ± 0.04 0.21 ± 0.18 ± 0.03 0.11 ± 0.11 ± 0.02 0.01 + 0.29 0.31± 0.03 Win02 Jan25 2002 Mirna van Hoek 23 0.05 ± 0.20 ± 0.03 + 0.36 0.43 0.06 0.30± 0.00 ± 0.27 ± 0.03 Updated 30.4 fb -1 20.7 fb -1
Summary and Outlook Large data sample (Run1: ~23 million BB pairs) Sensitive to Br down to few x10-6 ~30 modes analyzed -- 18 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 Jan25 2002 Mirna van Hoek 24