Recent Results from BABAR

Transcription

1 Recent Results from BABAR Vera Lüth SLAC - Stanford University Universität Mainz, April 24 th, 2013

2 Outline Study of B Dτν and B D*τν Motivation and Method Experimental Results Implications for Charged Higgs (Type II 2HDM Exclusive B D (*) τν ν B W V cb D τ *, D Observation of Time Reversal Violation in Y(4S) BB Motivation Experimental Method Γ(Δt) (Β 0 Β + ) Γ(Δt) (Β + Β 0 )?? Results Conclusions and Outlook V. Lüth U. Zürich, Nov. 28,

3 S.L. B Decays Involving the Heavy Lepton τ D (*) τν Η,W τ Phys.Rev. Lett. 109, (2012) V. Lüth U. Mainz, April 24,

4 Semileptonic B Decays : B X l + ν Very clean signature for a weak decay mediated by the W boson: the emission of a charged lepton and neutrino + + ( e, µ, τ ) τ b V qb W + c,u υ l b V qb Η + c,u υ l Large BF and clean signature: high momentum lepton These decays are 1 st order WI processes and allow us To measure fundamental SM parameters: CKM elements V cb and V ub. To probe decay dynamics and study strong interactions To search in decays involving τ lepton for contributions beyond SM, i.e. a charged Higgs boson or other mediators V. Lüth U. Mainz, April 24,

5 Semileptonic Decays at GeV v Cleanest source of B mesons: σ Υ 4S ) 1.05 nb ( 24% of σ ( had v Reconstruction of S.L. decays charged lepton: e ±, µ ± hadron: D, D*, π, ρ, ω, X c, X u ν: E miss, p miss ) e + e Υ(4S) BB bb Spectroscopy ΒB threshold v Exclusive B decays: kinematic variables: * * ΔE = EB Ebeam *2 *2 m = E p ES beam B signal at signal at ΔE 0 m ES m B v BB tag: full reconstruction of one B decay: B + tag D- π + π + Significant reduction in comb. backgrounds, improvement in Ε miss, p miss Low tag efficiency, % V. Lüth U. Mainz, April 24,

6 Detection of Semileptonic B Decays BABAR: e + e - B + tag B signal Y(4S) B + B - Β ρ 0 µ - ν ν (1.2 GeV) π + µ π 20 cm 80 cm V. Lüth U. Mainz, April 24,

7 Search for Charged Higgs Coupling in B Decays Decay Theory BF Comments B D (*) τν B τν Tree level ± 7% Tree level ± 20% 1-2 % Excellent Normalization 0.01% helicity suppressed B D (*) l ν Single charged particle plus 2-3 neutrinos B X s γ Loop ± 7% 0.03% Inclusive measurement, backgrounds! V. Lüth U. Mainz, April 24,

8 Ratio of B D (*) τ ν vs B D (*) l ν Decays Z. Phys, C46, 93 (1990) S.L. decays involving a τ ± have an additional helicity amplitude (for D*τν): For Dτν, only H 00 and H t contribute! To test the SM Prediction, we measure * Γ( B Dτν) * Γ( B D τν) Leptonic τ R( D) = R( D ) = Γ( B D ν ) * Γ( B D ν ) decays only Several experimental and theoretical uncertainties cancel in the ratio! BB events are fully reconstructed: Ø hadronic B tag (tag efficiency improved 2x) Ø e ± or µ ± : (extend to lower momenta, p l *>0.2 or 0.3 GeV) Ø no additional charged particles, E extra <0.5GeV (no cut) Ø kinematic selections: q 2 >4 GeV 2 Background suppression by BDT (combinatorial BG and D**lν) Full BABAR data sample, MC correction based on data control samples V. Lüth U. Mainz, April 24,

9 B D (*) τν: Extraction of Yields from M.L. Fit 2 2 m Unbinned M.L. fit miss = (Pee PBtag PD(*) P ) * Lepton momentum 2-D distributions: Missing mass sq in B rest frame 4 signal samples: D 0 l, D *0 l, D + l, D *+ l, (e ± or µ ± ) 4 D (*) π 0 lν control samples p 1ν PDFs from MC (approximated using Keys fct.) Fitted Yields 4 D (*) τν Signal 4 D (*) lν Normalization 4 D**lν Background 3ν MC Simulation Fixed Backgrounds B 0 -B + cross feed BB combinatorial BG Continuum e + e - ff (γ) V. Lüth U. Mainz, April 24,

10 2-D PDFs Based on Keys Functions D 0 τν D 0 lν Ø 2-D m 2 miss vs p* l, difficult to describe analytically correlations irregular functions D* 0 lν D** 0 l/τν Ø Solution non-parametric Kernal Estimators (KEYS) optimize bias vs variance (smoothing) BB Blue bands mark 2σ variations due to the stat. uncertainties of MC samples V. Lüth m 2 miss (GeV2 ) FPCP Paris, November p l * (GeV) 26-28, 2012 p l * (GeV) U. Mainz, April 24,

11 Cross Checks: Fit Normalization B D (*) l ν D 0 l D 0 l Events with <1.6 GeV2 m 2 miss D* 0 l D* 0 l Events/50 MeV D + l Events/50 MeV D + l D 0 l D *+ l D *+ l M 2 miss (GeV2 ) p l * (GeV) V. Lüth U. Mainz, April 24,

12 Results of Fit: B Dτν and B D*τν BABAR, PRL (2012) Events/25 MeV D + D 0 D 0 D *0 D *0 Events/100 MeV D + Fit results, combined using Isospin relations: B D τ ν N signal 489 ± 63 R(D) ± syst. error ± B D* τ ν N signal 888 ± 63 R(D*) ± syst. error ± D *+ D *+ Fitted yields m 2 miss (GeV2 ) p l * (GeV) Fixed yield V. Lüth U. Mainz, April 24,

13 Systematic Uncertainties p* t (GeV) V. Lüth U. Mainz, April 24,

14 Cross Check on MC for Signal and Backgrounds Detailed comparisons of data control samples with MC Prior to fit (off- and on-resonance data) rescale distributions: p * l, m ES, E extra Post fit (unfitted distributions in signal region) Background subtracted distributions B D (*) τν (post-fit) m ES = E 2 beam - p2 B E extra =Σ E γ (other) D D Dτν D*τν D* D* V. Lüth U. Mainz, April 24,

15 S.M. Predictions of R(D) and R(D*) Comparison with S.M. calculation: R(D) R(D*) BABAR ± ± SM ± ± Difference 2.0 σ 2.7 σ SM: Z. Phys, C46, 93 (1990) PRD 82, (2010) PhD 85, (2012) and recent updates BABAR, Phys. Rev. Lett (2012) BABAR The combination of the two measurements (-0.27 correlation) yields χ 2 /NDF=14.6/2, i.e. Prob. = 6.9 x10-4!! The data are inconsistent with the SM prediction at 3.4 σ V. Lüth U. Mainz, April 24,

16 Comparison to Previous Measurements NB: Average does not include this measurement SM Average SM Average The new measurements are fully compatible with earlier results! V. Lüth U. Zürich, Nov. 28,

17 Can we Explain the Excess Events? A charged Higgs (2HDM type II) of spin 0 coupling to the τ will only affect H S s s - for Dτν +for D*τν PRD 78, (2008) PhD 85, (2012) This could enhance or decrease the ratios R(D*) depending on tanβ/m H We estimate the effect of 2HDM, accounting for difference in signal yield and efficiency. The data match 2HDM Type II contribution at tanβ/m H = 0.44 ± 0.02 for R(D) tanβ/m H = 0.75 ± 0.04 for R(D*) The combination of R(D) and R(D*) excludes the Type II 2HDM in the full tanβ-m H parameter space with P >99.8%, provided M H >15 GeV! R(D) R(D*) BABAR 2HDM II Data tanβ/m H (1/GeV) V. Lüth U. Mainz, April 24,

18 Dependence of MC Signal Yield on 2HDM II Ø τ Polarization in B Dτν Decays SM LH: 70%. RH: 30% 2HDM LH: 0% RH: 100% Ø Impact on fitted distributions large for B Dτν missing mass sq: m 2 miss ~ q2 p* l, momentum of secondary lepton from decays in B rest frame V. Lüth U. Mainz, April 24,

19 Dependence of MC Signal Yield on 2HDM II Dτν Dτν ε/ε SM (%) D*τν Fitted Yield D*τν tanβ/m H (1/GeV) tanβ/m H (1/GeV) Ø Change in tanβ/m H impacts m 2 miss : detection efficiency 5-10% for Dτν and D*τν fitted signal yield 40% for Dτν V. Lüth U. Mainz, April 24,

20 Impact of 2HDM II on q 2 Distribution Ø q 2 is closely related to m 2 miss : D*τν: small impact on q 2 as expected Dτν: for tanβ/m H 0.45 GeV -1 the 2HDM type II is excluded at 2.9 σ, other 2HDM with small scalar terms cannot be excluded, Also, NP with spin 1 can explain the excess in R(D(*) and do not impact q 2 q tanβ/m H =0 GeV -1 tanβ/m H =0.3 GeV -1 tanβ/m H =0.45 GeV -1 D D D D* D* D* V. Lüth U. Mainz, April 24,

21 Observation of Time Reversal Violation in Y(4S) BB decays Γ(Δt)(B 0 B + ) - Γ(Δt)(B + B 0 ) 0?? BABAR, PRL 109,21801 (2012) Bernabeau, Martinez-Vidal, Villanueva-Perez, arxiv: JHEP08,064 (2012) V. Lüth U. Mainz, April 24,

22 Time Reversal: t t, in> out> Ø Ø The dynamical laws of physics are generally symmetric under Time Reversal t t at the microscopic scale: Invariance under reversal of motion v -v, exchange of initial and final state states Experimentally verified with high precision in certain nuclear reactions At the macroscopic level, processes are not time-reversible: In complex processes associated with large number of d.o.f. the initial and final states are irreversible!: Entropy in thermodynamics grows! V. Lüth U. Mainz, April 24,

23 Scenarios for Violation of Time Reversal Ø T-odd observables for certain stationary, non-degenerate states: Example: A finite electric di-pole moment (EDM) of particles with spin: violates T (and also P) EDM of neutron very small! d n < 2.9 x e-cm Ø Reverse Time flow for transitions P(A B) P(B A)??? For stable particles: transitions or mixing P(ν e ν µ ) = P(ν µ ν e ) For unstable particles: decay vs annihilation?! t -t and exchange in> out> very difficult, if not impossible experimentally V. Lüth U. Zürich, Nov. 28,

24 Violation of Time QM Scale Ø The CPT theorem: A locally Lorentz-invariant Quantum Field Theory conserves CPT. CPT: Where there s CP-violation, there s TR-violation, and vice versa! Ø Can Violation of Time Reversal be directly observed? In the strong decay ϒ(4S) B 0 B 0, the final state B 0 B 0 conserves the ϒ(4S) quantum numbers: J pc =1, The two B mesons remain in an entangled P-wave state up to the 1 st B decay Einstein: Spukhafte Fernwirkungen: Einstein, Podolsky, Rosen (PL 47, 777 (1935) B B + State described by an asymmetric function terms of of in terms of two orthogonal states: Ø, B B B -- V. Lüth U. Mainz, April 24,

25 B Mixing and Flavor Tagging A unique feature of (K 0,D 0,B 0 ) are transitions to (K 0,D 0,B 0 ) via 2 nd order weak Interactions! This leads to a lifetime dependent oscillation with a frequency depending on Δm: N B/B ~ e -Γt (1+ sin(δmt)) The flavor of the B or the CP eigenstate at the time of decay can be determined The charge of K or lepton tags flavor of both B at time t 1 l K K - l - B K Δt=t 2 -t 1 V. Lüth U. Mainz, April 24,

26 CP-V in Interference of Mixing and Decay of B Mesons Large CP Violating asymmetry in decay of B and B to common CP eigenstates f CP : B 0 tag B 0 tag BABAR HFAG: S f = sin2β= ± Cannot be interpreted as T Violation! Assumes CPT invariance and ΔΓ=0! No exchange of t t and initial final state! V. Lüth U. Mainz, April 24,

27 Time Reversal in B Decays Bernabeau, Martinez-Vidal, Villanueva-Perez, arxiv: JHEP08,064 (2012) Solution: Exploit B 0 B 0 entanglement in Y(4s) B 0 B 0 decays to define time dependent processes related by T-reversal., and define the ratio: B 0 l + X e- e + e- e + B 0 t 1 B B + Κ L J/ψ B B 0 t 2 J/ψ Κ S l X a: Flavor eigenstate B 0 or B 0, identified by semileptonic decay: l + or l - b: CP eigenstate B - or B + identified by decay to J/ K S or J/ K L Measure sequential decays of both B decays, time difference defined as Δt= t CP t Flavor > 0 for B0 B - < 0 for B - B 0 This is one of 4 pairs of transitions related by Time Reversal, Also, 4 pairs each for CP and CPT. V. Lüth U. Mainz, April 24,

28 Define 4 Processes Related by T Transformation Bernabeau, Martinez-Vidal, Villanueva-Perez, arxiv: JHEP08,064 (2012) T transformations implies: opposite sign Δt opposite flavor states opposite B+ and B- states We build independent sets of 4 pairings related by T transformation CP transformation CPT transformation B - B 0 J/ψ K L B - B 0 B 0 B + CP B 0 B + CPT T B + B 0 B 0 B - J/ψ K S B + B 0 B 0 B - l + l - Δt=0 Δt=0 V. Lüth Zürich, November 28,

29 Signal Selection and Background Suppression Signal Selection Use m ES and ΔE variables, making use of well known beam energy: Select best candidate based on reconstructed masses Background Rejection Veto dominant BB backgrounds suppress qqγ backgrounds based on jet-like event shapes V. Lüth U. Mainz, April 24,

30 Event Selection Standard reconstruction methods for CP tags 7796 Events Purity 86-96% 5,813 Events Purity: ~ 56% m ES = E *2 beam p * 2 B ΔE = E * B E * beam V. Lüth U. Mainz, April 24,

31 Fit to Time-Dependent Asymmetries!t = t CP " t Flavor g ( Δt ) e {1 + S sin( Δm Δ t ) + C cos( Δm Δt )} Ø 8 decays as function of ± Γ Δ t ± ± αβ, αβ, d αβ, with 8 different pairs of S and C parameters with indices ± {Δt>0, Δt <0} α flavor tag { l +, l } β CP tag { K L,K S } determined by Max. Likelihood fit. Ø Differences in fitted S and C parameters for transitions related by T, (CP, or CPT) transformations measure asymmetries: d for perfect reconstruction Ø For TR violation, one expects: ΔS 0 or ΔS 0 or ΔS ΔS or ΔS ΔS T T CP CPT CP CPT U. Mainz, April 24, 2013 V. Lüth 31

32 Visualization of T Asymmetries Neglecting experimental effects B 0 B - BABAR B + B 0 B 0 B + B - B 0 T Violation: Significance: 14σ BABAR, PRL 109,21801 (2012) V. Lüth U. Mainz, April 24,

33 Visualization of CP Asymmetries BABAR B 0 B - B 0 B - B + B 0 B + B 0 B 0 B + B 0 B + B - B 0 B - B 0 CP Violation: Significance: 17σ V. Lüth U. Mainz, April 24,

34 Visualization of CPT Asymmetries B 0 B - B - B 0 B + B 0 B 0 B + BABAR B 0 B + B + B 0 B - B 0 B 0 B - CPT Violation: Significance: 0.3σ V. Lüth U. Mainz, April 24,

35 Systematic Uncertainties for T Asymmetries V. Lüth U. Mainz, April 24,

36 Interpretation of Results: T Violation BABAR BABAR, Accepted by PRL arxiv: [hep-ex} V. Lüth U. Mainz, April 24,

37 Interpretation of Results: CP and CPT Violation BABAR, PRL 109,21801 (2012) BABAR CP violation parameters BABAR CPT violation parameters V. Lüth U. Mainz, April 24,

38 Conclusions Based on suggestions made more than 10 years ago, BABAR has studied the evolution of B mesons produced coherently in Y(4S) decays. The comparison of conjugate processes that can only be related by T reversal and not CP transformation reveal T violation with a significance of 14σ. This novel approach does not assume CPT invariance or any relation to CP violation. The results are consistent with equal CP and T Violation, and with CPT Invariance. V. Lüth U. Mainz, April 24,

39 Summary More than 4 years after the termination of data taking, the BABAR Collaboration is still producing interesting results, based on the full data and MC samples. This year two measurements stand out: A puzzling excess (3.4 σ) of events in B Dτν and B D*τν decays, which cannot be explained by a 2DHM Higgs of Type II, though extensions of 2HDM appear to work, as do NP contributions with spin 1 coupling. Confirmation by Belle and new theoretical ideas are expected soon. Based on the methods derived for CP Asymmetry studies, BABAR has first and very convincing evidence for T violation in neutral B mesons. In some ways, this closes the cycle of the CPT theorem. V. Lüth U. Mainz, April 24,

40 B D (*) τν: Report from Belle Merci de votre attention