Analysis tools: the heavy quark sector. Gianluca Cavoto INFN Roma ATHOS 12 Jun 20 th -22 nd, 2012 Camogli, Italy

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1 Analysis tools: the heavy quark sector Gianluca Cavoto INFN Roma ATHOS 12 Jun 20 th -22 nd, 2012 Camogli, Italy Gianluca Cavoto 1

2 Outline B and D multibody decays at B factories Why Dalitz analyses were/are so attractive Dalitz (time dependent) analysis Measurement of γ Measurement of α D-mixing Some very recent highlights Many thanks to my BaBar colleagues for figures and plots Gianluca Cavoto 2

3 B factory (initial) mission Cabibbo Kobayashi Maskawa V ij Unitarity triangle Study CKM matrix parameter Search for deviations from Standard Model predictions (the Holy Graal of New Physics ) Gianluca Cavoto 3

4 The hadronic uncertainties B -> Kpi system Initially though to be a good place to measure CKM gamma angle In fact a place where hadronic interactions played a basic role. Theorists argued for years they can predict hadronic interactions effects, in fact selling their model An experiment driven approach (Ciuchini et al) was more solid (but not satisfactory) What about measuring hadronic interaction directly? Angular analysis in B or D multibody decays Gianluca Cavoto 4

5 B and D meson multibody decays Belle Coll., PRL. 98 (2007) M BB pairs. B0 --> pi+pi-pi0 BaBar, sub PRD, arxiv: M BB pairs. Full reconstruction of multibody final states with high efficiency Great particle ID (pi, K), good KS and pi0 reconstruction Well defined initial state kinematics and good momentum and angular (inv. mass) resolution Gianluca Cavoto 5

6 Dalitz plot in B and D decays Gianluca Cavoto 6

7 Three body decays Dalitz Resonance R dominated amplitude X: Heavy meson Angular distribution (Zemach/Helicity formalism) Isobar model (not overlapping resonances R) Form factor(s) ( Blatt-Weisskopf) Propagator (Breit Wigner) Gianluca Cavoto 7

8 D 0 decays and Charged B decays into D 0 K Measuring CKM γ BaBar Coll, Phys.Rev.Lett.105:121801,2010 Gianluca Cavoto 8

9 Weak and strong interaction Pictorial view of decay rate of B - D 0 K - with D 0 K S π + π - D0 decay amplitudes!!! D 0 decay amplitude used as input for B decay amplitude description Gianluca Cavoto 9

10 Dalitz models Gianluca Cavoto 10

11 ππ S-wave K-matrix No clear indication from scattering exp of BW structure ( Scattering matrix V. V. Anisovich and A. V. Sarantsev, Eur. Phys. J. A 16 (2003) 229 [arxiv:hep-ph/ ]. Production vector Parameters fitted! Gianluca Cavoto 11

12 Dalitz model details Gianluca Cavoto 12

13 or alternatively Very pure sample (95%) Gianluca Cavoto 13

14 CP violation and γ Opposite sign K* either Doubly Cabibbo suppressed decay OR Interference with b->u transition Gianluca Cavoto 14

15 γ extraction D0K D*0K D0K* Babar obtains: CP violation at 3.5sigmas! Model systematics Gianluca Cavoto 15

16 B 0 π + π - π 0 time-dependent Dalitz analysis The best place to measure alpha with no hadronic hassles BaBar Coll, PRD 76 (2007) Gianluca Cavoto 16

17 Time-dependence Time-dependent Dalitz analysis Mandelstam variables + (-) B 0 bar (B 0 )) decaying Isobar model: f(s i,s j ) Weak and strong phase charge of the ρ Gianluca Cavoto 17

18 Bilinear coefficients, U and I 27 real parameters Normalized to U + + determined from the fit Unique solution, gaussian!! Easy combination among exp. s κ,σ: charge of the ρ Sensitive to interference pattern! Branching fractions and direct CPV Mixing induced CPV Gianluca Cavoto 18

19 Dalitz Model ρ dominated Rel. BW Gounaris-Sakurai» ρ(770), ρ(1450),ρ(1700) mass and width from τ and e + e - data (Aleph & CMD-2 )» π + π - scalar allowed in systematics evaluation» Crosscheck relative phase on signal data Gianluca Cavoto 19

20 Square Dalitz Plot Signal only MC Helicity angle ρ + π - Most of sensitivity from interference region! Measure terms like cos (2α)sin(Δm d Δt) Extract strong phases directly ρ + π - ρ 0 π 0 Dashed lines: isocontour for Gianluca Cavoto 20

21 Signal description 22% ρ + π - and 13% ρ 0 π 0 are misrecontructed (track or cluster from other B)» Self-Cross Feed events» Concentrate in corners: where interference sits Detailed parametrization on Dalitz efficiency ε(m,θ) SCF rate f SCF (m,θ) and SCF resolution function on Dalitz Δt resolution ε(m,θ) f SCF (m,θ) Gianluca Cavoto 21

22 B-background Dalitz distributions MC simulation Gianluca Cavoto 22

23 Dalitz distributions Smallest of the three di-pion inv. mass (signal enhanced) + SCF + B-background Continuum Gianluca Cavoto 23

24 Fit results U + + average BF(ρ+π-) interference Q-2body Excess of ρ 0 π 0 U - k Direct CPV ρ + π - Mixing induced CPV Statistical and systematic errors Full covariance Matrix available (both statistical and systematics) Gianluca Cavoto 24

25 Finally, α and δ Relative phase Strong isospin: No constraint on α at 2σ Gianluca Cavoto 25

26 D 0 Κ + π - π 0 time-dependent Dalitz analysis A constraint on D0 mixing parameters Gianluca Cavoto 26

27 Neutral mesons oscillations Time evolution for meson of known flavor at t=0 Short-range Long-range M 0 oscillates into M 0! (also dubbed mixing ) An opposite flavor component appears after a while! Gianluca Cavoto 27

28 Flavor tagging Flavor at production Flavor at decay Same flavour: Wrong-Sign (WS) mixing may have occured Opposite flavour: Right-Sign (RS) unmixed events Gianluca Cavoto 28

29 Double-Cabibbo Suppressed Decays V us V* ud V* cd V cs Gianluca Cavoto 29

30 Separating x and y First evidence Phys.Rev.Lett. 98 (2007) in D 0 Κπ BUT Κπ only cannot separate x and y D 0 K - π + π 0 Need info on strong phases CF DCS DCS decays proceed primarily through K *+ π - while CF through K - ρ + Gianluca Cavoto 30

31 Mixing in D 0 K + π - π 0 Two ways to reach same final state interference! Time dependent WS rate DCS mix Interference Mixing δ Kππ 0 : strong phase difference between CF and DCS decay amplitudes Gianluca Cavoto 31

32 RS and WS (m Kππ, Δm) fits Determine signal and background yields in subsequent Dalitz analyses. m Δm signal mis-tagged D 0 mis-reconstructed D 0 combinatoric signal and sideband regions m Δm signal box yields: Gianluca Cavoto 32

33 D 0 K - π + π 0 RS Dalitz fit Time-integrated analysis to determine CF amplitudes, K π + K π 0 π + π 0 Gianluca Cavoto 33

34 RS Dalitz fit results Effective range parametrization for Kπ S-Wave D. Aston et al., LASS Collaboration, Nucl. Phys. B 296, 493 (1988). Scattering amplitude Non-res Resonant Gianluca Cavoto 34

35 D 0 (t) K + π - π 0 WS Dalitz Through t-dependence, distinguish DCS amplitudes from the CF amplitudes arising from mixing. t K π + K π 0 π + π 0 - signal - mis-tagged D 0 - mis-rec. D 0 +combinatoric Gianluca Cavoto 35

36 D0 mixing World Average x and y must be measured independently to understand nature of D0 mixing Mutlibody decays play a fundamental role in this D 0 K - π + π 0, D 0 Ksπ + π - D 0 KsΚ + Κ - Gianluca Cavoto 36

37 Summary Multibody heavy mesons decays amplitude analysis have played an important role in weak interactions (CKM paradigm) investigation Measurements of α and γ Multibody essential to understand short range interaction. D 0 mixing This experimental program need a detector able to reconstruct with good resolution and high efficiency several different multibody final states (π 0 rec and particle ID are must) Gianluca Cavoto 37

38 And today, what is at the cutting edge? LHCb (and CDF) is adding new information on B and charm physics. Charm physics seems to provide excitement CP violation (CHARM12) Is this New Physics or only some (tricky) Standard Model long-range effect? Gianluca Cavoto 38

39 Back to multibody! D 0 π + π - π 0 Y.Grossmann, et al., Measure amplitudes in D -> PV, VV decays Use isospin relations between amplitude Identify ΔI =1/2 and ΔI =3/2 amplitude SM ΔI =3/2 A 3 carries no weak phase. If this diffirence is not zero, NP! PHYSICAL REVIEW D 78, (2008) Dominated by I=0 amplitude (WHY??) A Dalitz analysis to discover New Physics at high scale? Gianluca Cavoto 39

40 Back up Gianluca Cavoto 40

41 B - D 0 (K S π + π - )K - Pictorially: 2 2 A( m K +, m! " Ks" s ) 2 (assuming СР-conservation in D 0 decays) Amplitude ratio: r B * V 0 ubvcs!!! 0! = A( B " D K ) / A( B " D K ) "![color supp] ~ 0. 1 * V V cb us Higher r B higher sensitivity Extract from data Need input for D decay amplitude High D 0 flavour tagged sample: Dalitz model 41

42 Events selection Kinematics and topology» To suppress continuum background c + = GeV c - = GeV c = GeV Remove ΔE dependence on π 0 momentum N π + π π 0 =1847 ± 69 ε ρ + π = 24% Gianluca Cavoto 42

43 Backgrounds Mainly continuum» Neural Network with several inputs Neutral and charged B» Hundred exclusive final states analyzed» 18 categories 6 B 0 charmless decays 8 B + charmless decays 2 b c decays» (ρπ) +,ρρ,ρκ,κππ,a 1 π,dπ,... Continuum Flavor- Dalitz correlation + B-background accounted for Maximum likelihood fit + SCF Gianluca Cavoto 43

44 Resolution effects Gianluca Cavoto 44

45 Δt distribution Gianluca Cavoto 45

46 Systematics studies Dalitz plot model: toymc: Generate with alternative models: Nonresonant (uniform) component Scalar π + π - component» [low mass scalar, f 0 (980),f 2 (1270)] ρ lineshape Check relative amplitude assumption Vary mass and width B-background Assumption on CP contents And more Fit bias (negligible) Parameters other PDF (background Dalitz, f SCF ) Relevant for interference parameters Relevant for Q-2b parameters Gianluca Cavoto 46

47 Quasi-2body parameters asymmetry ρ + π - ρ - π + ρ + π - ρ - π +» They include interference effects» Averaging S and C Systematics dominated by B-background CP content Gianluca Cavoto 47

48 Q-2b interpretation Compare B 0 /ρ + and B 0 /ρ - more intuitively: 3σ effect (syst. included) Gianluca Cavoto 48

49 Summary of B background Gianluca Cavoto 49

50 Off-resonance Dalitz distr. Gianluca Cavoto 50

51 Q-2b parameters cov. matrix Multiplied by 1000 Gianluca Cavoto 51

52 A. Poluetkov Belle data set Belle result (357 fb -1 ) [hep-ex/ , PRD 73, (2006)] B ± DK ± B ± D*K ± B ± DK* ± 331±17 events 81±8 events 54±8 events B - B + B - B + B - B + 52

53 Belle fit results Fit parameters are x ± = r B cos(±φ 3 +δ) and y ± = r B sin(±φ 3 +δ) (better behaved statistically than, δ, ϕ ) Unbinned maximum likelihood fit with event-by-event background treatment (ΔE-M bc included into likelihood) r B 3 B ± D*K ± B ± DK* ± B ± DK ± x = y = x + = y + = x - = y - = x + = y + = x = y = x + = y + =

54 S. Descotes-Genon Dalitz plot, resonaces, K-matrix Isobar Approximation K-matrix parametrization for overlapping resonances Better for ππ S-wave description 54

55 Theory helps J.Zupan Model independent Unknowns: CLEO-c CP tagged Sample! 55

56 A. Poluetkov Binned analysis of CLEO-c data -i i Number of events in D 0 -plot: Number of events in B-plot 2 M h [ K + r K + K K ( xc + N i i = B i B i i i Number of events in D CP -plot = h CP Ki [ Ki + K i ± 2 KiK ici ] i ys i )] Ci =< cos Δδ ( D ) > D S i =< sin Δδ ( D ) > D C 2 i 2 + S i 1 ( =1 if bin size is small enough) C i, S i can be obtained from B data (M i ) only Very poor sensitivity C i from D CP, S i from B data Poor sensitivity for y S i constrained as S i = ± 2 1 Ci Bias if bin size is large 56

57 Measurements of γ in B D 0 K Basic idea Tree level only B " A B D 0 K " A D f A B r B e i(δ Β -γ) D 0 K " AD Multiple incarnations: D decay to CP eigen., flavour eigen., multibody decays Use of D* 0 (both D 0 π 0 and D 0 γ!) and K* Neutral and charged B decays 57

58 Charm physics with B-factory Run1-5 Gianluca Cavoto 58