Decadimenti senza charm e misure di α alle B-Factory

Transcription

1 Decadimenti senza charm e misure di α alle B-Factory Marcella Bona INFN e Università di Torino Incontri sulla Fisica delle Alte Energie Quark pesanti Lecce, 24 Aprile 2003 IFAE Lecce, Quark Pesanti, 24 Aprile

2 CP violation in the Standard Model: CP simmetry can be violated in any field theory with at least one irremovable phase in the Lagrangian This condition is satisfied in the SM through the three-generation CKM quark-mixing matrix Unitarity Triangle: The angles are related to CP-violating asymmetries in specific B decays already good precision on β(φ 1 ): (Maurizio's talk) IFAE Lecce, Quark Pesanti, 24 Aprile

3 Observing CP violation at the Y(4S): At the Y(4S), BB are produced in a coherent P-wave Three observable interference effects: CP violation in mixing ( q/p 1) (direct) CP violation in decay ( A/A 1) (indirect) CP violation in mixing and decay (Imλ 0) Observable in time evolution of BB system (assume Γ=0) direct CP violation C 0 indirect CP violation S 0 IFAE Lecce, Quark Pesanti, 24 Aprile

4 CP violation in B 0 π + π - : at tree (T) level: λ ππ = e 2iα C ππ = 0 S ππ = sin (2α) mixing with penguins (P): α from α eff : isospin analysis with π + π -, π + π 0, π 0 π 0 IFAE Lecce, Quark Pesanti, 24 Aprile

5 Analysis Overview: Charmless B decays: rare decays with BR ~ 10-5,-6 high background from continuum from other B decays for π 0 modes K/π separation: excellent particle ID needed (DIRC) D *+ D 0 π + D 0 K - π + kinematic variables and topological information to separate signal from light quark background this is to extract signal yields and CP-violating asymmetries In the time-dependent analysis: vertex position of both B σ( z) is dominated by the tag side flavour identification of the other B (tagging) based on PID this is to extract C ππ and S ππ IFAE Lecce, Quark Pesanti, 24 Aprile

6 Analysis Overview (Belle & BaBar): BaBar technique: maximum likelihood (ML) fit, including the particle ID info, to extract signal yields and CP-violating asymmetries the tagging efficiency and the t distribution are taken from a sample of fully reconstructed B which is included in the ML fit together with the signal sample to extract C ππ and S ππ Belle technique: ππ sample selection: PID cut to select 2-pion events, tight cuts on the kinematic variables. a topological-variable likelihood cut is used to select a clean sample to extract the ππ yields with a E fit maximum likelihood (ML) fit on the ππ sample to extract C ππ and S ππ IFAE Lecce, Quark Pesanti, 24 Aprile

7 Branching Ratio results: 81 fb fb -1 ππ Kπ ππ Kπ Kπ ππ IFAE Lecce, Quark Pesanti, 24 Aprile

8 CP Asymmetry Result from BaBar: fit projection in sample of ππ selected events S ππ = 0.02 ± 0.34 ± 0.05 C ππ = ± 0.25 ± 0.04 qq + Kπ hep-ex/ IFAE Lecce, Quark Pesanti, 24 Aprile

9 CP Asymmetry Result from Belle: S ππ = ± 0.41 ± 0.08 C ππ = ± 0.27 ± 0.08 hep-ex/ with this result CP conservation is ruled out at 3.4σ level B 0 tag background subtracted plots B 0 tag IFAE Lecce, Quark Pesanti, 24 Aprile

10 BaBar & Belle: Sagawa's talk at the CKM workshop Roos's talk at the CKM workshop S 2 +A 2 1 difference between the two results at the 2.2 σ level IFAE Lecce, Quark Pesanti, 24 Aprile

11 Getting α from α eff : isospin analysis The decays B π + π -, π + π 0, π 0 π 0 are related by isospin ππ states can have I = 2 or I = 0 gluonic penguins only contribute to I = 0 ( I=1/2) π + π 0 is a pure I = 2 ( I = 1/2) so it has only tree amplitude triangle relations allow determination of penguin-induced shift in α: 2α eff = 2α + κ ππ A+0 = A-0 Both BR(B 0 ) and BR(B 0 ) have to be measured in the ππ modes IFAE Lecce, Quark Pesanti, 24 Aprile

12 fit region The other sides of the isospin triangles: BR results for π ± π 0 and π 0 π 0 81 fb -1 ρπ Kπ 0 ππ 0 light-quark bkg 78 fb σ π 0 π 0 1.9σ BR WA (π 0 π 0 )= (1.8 ± 0.7) 10-6 IFAE Lecce, Quark Pesanti, 24 Aprile

13 Roos's talk at the CKM workshop Marcella Bona, INFN Torino B-Factory Trying the Isospin Analysis: using the BaBar C ππ and S ππ, WA BR with BR(π 0 π 0 )= (2.0 ± 0.7) 10-6 and A 00 = A 00 but scaling the errors to higher statistics: 500 fb -1 hope: not to measure such a high BR(π 0 π 0 ) IFAE Lecce, Quark Pesanti, 24 Aprile

14 With an upper limit on the BR(π 0 π 0 ): it is still possible to get information on α with only an upper limit on π 0 π 0 for example: Grossman-Quinn bound (assume only isospin) α eff - α < 51 90% CL from BaBar UL α eff - α < 68 90% CL from Belle UL many other bounds on the market: Charles, Gronau/London/Sinha/Sinha, etc... IFAE Lecce, Quark Pesanti, 24 Aprile

15 CP-violating asymmetries in B ρ + π -, ρ + K - in principle: direct measurement of α with the full three-body analysis [R. Aleksan et al., Nucl. Phys. B361, 141 (1991)] but: much more difficult than in the ππ case three-body topology with a neutral pion: huge combinatorics, lower efficiency high background from other B decays a quasi two-body analysis is performed: selection of the ρ-dominated Dalitz plane region use of multivariate techniques to suppress light quark bkg fit for ρ + π -, ρ + K - at the same time IFAE Lecce, Quark Pesanti, 24 Aprile

16 B ρ + π - final state π - π + π 0 : not a CP eigenstate at least four amplitudes contribute: B 0 ρ + π - + B 0 ρ - π + and B 0 ρ - π + + B 0 ρ + π - time evolution includes: (S ρh ±Q S ρh ) sin( m t) - (C ρh ±Q C ρh ) cos( m t) Q being the charge of the ρ ρk is self-tagging: C ρk =0, C ρk =-1, S ρk =0, S ρk =0 C and S are insensitive to CP violation fit for A CP ρπ, A CP ρk, C ρπ, C ρπ, S ρπ, S ρπ direct CP violation: A CP and C 0, indirect: S 0 IFAE Lecce, Quark Pesanti, 24 Aprile

17 B ρ + π -, ρ + K - results: yields and asymmetries 81 fb -1 IFAE Lecce, Quark Pesanti, 24 Aprile

18 B ρ + π -, ρ + K - results: time-dependent asymmetries 81 fb -1 hep-ex/ BB and qq BB systematic error dominated by uncertainty on B backgrounds IFAE Lecce, Quark Pesanti, 24 Aprile

19 Trying the Isospin Analysis for ρπ: on 500 fb -1 with the current WA BR, C and S values and BR(B 0 ρ 0 π 0 ) = (0.9 ± 0.3) 10-6 not much sensibility to α Stark's talk at the CKM workshop assume BR(B 0 ρ 0 π 0 ) to be below experimental sensitivity: improved constraints, SU(2) analysis gives meaningful constraints on α above 2 ab -1 IFAE Lecce, Quark Pesanti, 24 Aprile

20 Summary and conclusions: Time-dependent asymmetry measurement for B 0 π π + S ππ = 0.02 ± 0.34 ± 0.05 S ππ = ± 0.41 ± 0.08 C ππ = ± 0.25 ± 0.04 C ππ = ± 0.27 ± 0.08 still not enough statistics for drawing conclusions the inputs for the Isospin Analysis are starting to be usable: π + π 0 has been measured still an uppel limit in π 0 π 0 if high BR, IA not feasible? too early for a significant constraint Charmless three-body decays: quasi-two-body analysis performed by BaBar first measurement on CP asymmetry in ρπ and ρk next years will be really interesting in the α land: σ(sin2α eff ) ~ 0.03 in 10 ab -1 IFAE Lecce, Quark Pesanti, 24 Aprile

21 Back Up Slides IFAE Lecce, Quark Pesanti, 24 Aprile

22 BR analysis of B -> ππ, Kπ and KK: Two steps of the analysis: BR and time-independent asymmetry measurement time-dependent fit for C ππ and S ππ Kinematically select B candidates with m ES and E suppress light-quark continuum background with a Fisher discriminant Fit yields and charge asymmetry π + θ* p* π - IFAE Lecce, Quark Pesanti, 24 Aprile

23 Vertexing reconstruction: z resolution is dominated by the tag side average resolution ~ 180 µm e + e - -> qq Resolution function taken from data for both signal and background signal: fully reco B bkg: data sideband B -> ππ IFAE Lecce, Quark Pesanti, 24 Aprile

24 B-Flavour tagging: Tagging algorithm with physics-based neural network inputs include leptons, kaons, slow-pions (from D*), and high-momentum tracks outputs combined and categorized by mistag probability (w) 5 mutually exclusive categories (Maurizio's talk) hh sample splitted by tag category efficiency by category and for signal vs bkg bkg suppression for categories with the lowest mistag prob IFAE Lecce, Quark Pesanti, 24 Aprile

25 K/π separation with the BaBar: Cherenkov angle θ C measured by the DIRC used in the ML fit to separate final states with kaons or pions resolution and K-π separation measured in data D *+ -> D 0 π + D 0 -> K - π + π hypothesis K hypothesis IFAE Lecce, Quark Pesanti, 24 Aprile

26 A Specific Model: QCD Factorization Data 2001 Data 2003 Inconsistent? IFAE Lecce, Quark Pesanti, 24 Aprile

27 Per Gino IFAE Lecce, Quark Pesanti, 24 Aprile

28 B π + π - : time-dependent analysis BaBar & Belle: 81 fb -1 S ππ = 0.02 ± 0.34 ± 0.05 C ππ = ± 0.25 ± fb -1 S ππ = ± 0.41 ± 0.08 C ππ = ± 0.27 ± 0.08 difference between the two results at the 2.2 σ level S 2 +A 2 1 IFAE Lecce, Quark Pesanti, 24 Aprile

29 Roos's talk at the CKM workshop Marcella Bona, INFN Torino B-Factory Trying the Isospin Analysis: using the BaBar C ππ and S ππ, WA BR and A 00 = A 00 but scaling the errors to higher statistics: 500 fb -1 hope: not to measure such a high BR(π 0 π 0 ) IFAE Lecce, Quark Pesanti, 24 Aprile

30 B ρ + π -, ρ + K - : 81 fb -1 time-dependent analysis hep-ex/ BB and qq BB with the Isospin Analysis: on 500 fb -1 with the current WA BR, C and S values not much sensibility to α IFAE Lecce, Quark Pesanti, 24 Aprile