B Mesons (Experiment) Part 2

Transcription

1 B Mesons (Experiment) Part 2 Christoph Schwanda JENNIFER Summer School on ParBcle Physics and Detectors July 25-29, 2016, Sporthotel Grünberg 1

2 LeQover slides from yesterday 2

3 ExtracBng a B signal Using special Y(4S) kinemabcs, two nearly independent variables M B and ΔE can be used to select B meson signal: M B = (E * beam ) 2 (Σ P i ) 2 ΔE = ΣE i - E * beam Methods to extract B signal yield: 1) Cut on M B and fit to ΔE 2) Cut on ΔE and fit to M B 3) Double dimensional fit to M B and ΔE distribution 4) If B->P 1 P 2 P 3 : cut ΔE and M B box and look at resonant structures in M(P 1 P 2 ) mass distribution. 3

4 Belle physics analysis Measurement of the branching rabo of the decay B 0 à D *- π + (and charge conjugate) This is the fracbon of B 0 parbcles that decay into this mode Sub-decays D *+ à D 0 π s + D 0 à K - π + Data sample: 140/` (152 million BB events) of Belle data 4

5 MDST data (MDST_CHARGED table) Analysis module in C++ Ntuple (root file) Final selecbon in root An ntuple (or tree in root) is a 2d data structure with rows and colums Columns (leafs) correspond to observables, one row is wriben per observabon (event) 5

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7 DescripBon of the analysis module B 0 à D *- π + D 0 π - K + π - From this decay chain, four parbcles can be seen in the detector (one kaon, three pions) Strategy: for each event, try all combinabons of four tracks out of the reconstructed tracks Signal Combinatorial background Try to reduce the number of possible combinabons as much as possible by applying requirements to select signal combinabons ( cuts ) 7

8 Execute four nested loops for each event Loop 1 (kaon) Loop 2 (pion from D 0 decay) Loop 3 (pion from D * decay) Loop 4 (pion from B decay) Write ntuple (m(kπ), Δm, m bc, ΔE) 8

9 Loop 1 (Kaon loop) Loop over all charged tracks Kaon hypothesis: calculate the parbcle energy assuming the kaon mass Loop 2 (D 0 pion loop) Loop over tracks with opposite charge to kaon Pion hypothesis Compute the invariant Kπ mass Requirement: 1.76 GeV < m(kπ) < 1.96 GeV 9

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11 Loop 3 (slow pion loop) Loop over tracks with opposite charge to kaon Skip D 0 pion track Compute Δm, Δm < 250 MeV 11

12 Loop 4 (π from B decay) Loop over charged tracks with same charge as K Skip kaon track Compute beam-constrained mass and ΔE to select the B signal E * B and p* B are the measured B energy and momentum in the center-of-mass frame E beam is the energy of one beam in the c.m. frame m bc > 5.2 GeV, abs(δe) < 300 MeV 12

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14 Data on ntuple At the end of loop 4, the variables m(kπ), Δm, m bc and ΔE are wriben to an ntuple Every line in the ntuple corresponds to a combinabon passing all requirements menboned so far These requirements are loose, i.e., a lot of combinatorial background is wriben to the ntuple The final, Bght cuts are made in the interacbve analysis (e.g., in root) Loose cuts allow to study the background under the signal peak 14

15 Final cuts Signal window (to select signal events) 1.84 < m(kπ) < 1.89 GeV 140 < Δm < 151 MeV -69 < ΔE < 65 MeV Side-band (to esbmate the background below signal peak) 1.84 < m(kπ) < 1.89 GeV 140 < Δm < 151 MeV 110 < ΔE < 300 MeV 15

16 Signal window and sideband are scaled in the region m bc < 5.25 GeV; scale factor is 1000/

17 Yield in m bc > GeV error Rel. error Signal window % Sideband % Scale factor % Scaled sideband % Signal yield (N signal ) % 17

18 Let us assume PropagaBon of errors We have two independent random variables x and y With known variances, Var[x] = σ 2 x, Var[y] = σ2 y Standard deviabon of z = x +/- y Standard deviabon of z = xy or z = x/y 18

19 PropagaBon of errors (2) The general case n quanbbes m funcbons Covariance matrix of θ Then gets Or in matrix notabon 19

20 Branching rabo We assume that B + and B 0 are produced with equal probability error Rel. error N BB M 1.241M 0.82% Br(D *+ à D 0 π + ) 67.7% 0.5% 0.74% Br(D 0 à K - π + ) 3.91% 0.05% 1.28% 20

21 Efficiency calculabon The reconstrucbon efficiency of B 0 decaying along this decay chain can be determine from MC simulabon Out signal decays, combinabons are recovered aqer applying all cuts This means that the efficiency ε is ( /-.33)% 21

22 Branching rabo (2) error Rel. error N signal % N BB M 1.241M 0.82% Br(D *+ à D 0 π + ) 67.7% 0.5% 0.74% Br(D 0 à K - π + ) 3.91% 0.05% 1.28% ε 33.88% 0.33% 0.98% Br(B 0 à D *- π + ) 2.63x x % We measure (2.63 +/- 0.07) x 10-3 for B 0 à D *- π + ; the PDG value is (2.76 +/- 0.13) x

23 ConBnuum suppression Dominant Background for rare Decays: e + e - qq continuum (~4x BB) To suppress: use event shape variables continuum Y (4S) ΒΒ - Continuum Jet-like Fox-Wolfram moments Angle between B meson and beam axis direcbon B events Spherical qq e + e - e + e - Signal B Other B 23

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25 Tagging techniques for Y(4S) events PURITY EFFICIENCY Tagging provides: Background suppression InformaBon on B sig (4-momentum) Untagged No requirement on B tag High efficiency, low purity Semileptonic tag B tag D*lν Efficiency ~O(0.2%) Hadronic tag B tag hadrons Efficiency ~O(0.1%) 25

26 New Belle hadronic tag New hadronic tag based on Neurobayes 2-3x stabsbcal gain over previous analyses 26

27 Physics at the B factories 27

28 : B factory at KEK (Japan) Linac KEKB double ring e+e- collider e+e- Y(4S) BB Belle detector World largest B meson sample ~771 million BB events Over 400 Belle physics publicabons 28

29 The CKM mechanism Charged current interacbon in the SM [Kobayashi, Maskawa, Prog. Theor. Phys. 49, 652 (1973)] V CKM is a unitary 3x3 matrix of coupling constants of weak transibons It also contains the KM phase, responsible for all CP violabng phenomena observed so far! 29

30 The CKM unitarity triangle η (ρ,η) α = φ 2 B Xlν B ππ, ρπ γ = φ 3 β = φ 1 (0,0) B D (*) K (*) Dalitz B 0 J/ψK S (1,0) ρ 30

31 Measurement of time dependent CP violation time dependent indirect CP violation from interference of decay without mixing and decay with mixing t b c J/ b d c d K0 s s B 0 W + B0 W W B 0 s c Ks d d 0 b W J/ d c t 31 A. Leopold (HEPHY) Belle HEPMAD 2015/09/21 10 / 35

32 Measurement of time dependent CP violation produced B B pair is in coherent state flavor tagging reconstruct vertices e - e + measure t 32 A. Leopold (HEPHY) Belle HEPMAD 2015/09/21 11 / 35

33 Measurement of time dependent CP violation indirect CPV direct CPV B time dependent asymmetry A( t) =S sin( m d t) C cos( m d t)= B 0 ( t) B 0 ( t) B 0 ( t)+ B 0 ( t) B measure ( t) distribution for tagged B and B A( t) measure t extract S & C from fit to A( t) 33 A. Leopold (HEPHY) Belle HEPMAD 2015/09/21 12 / 35

34 1 from B 0! J/ K 0 S 1 = arg Vcd V cb V td V tb 1 measured from experimentally and theoretically clean golden mode B 0! J/ K 0 S S = sin(2 1 ) and C = 0 [Belle (PRL 108 (2012) )] 34 A. Leopold (HEPHY) Belle HEPMAD 2015/09/21 13 / 35

35 1 at B factories BaBar PRD 79 (2009) BaBar χ c0 K S PRD 80 (2009) Belle PRL 108 (2012) LHCb arxiv: Average HFAG b ccs C CP ± ± HFAG Moriond 2015 PRELIMINARY 0 ± ± ± ± ± ± ± measurement is compatible with C =0 sin(2β) sin(2φ 1 ) Average HFAG BaBar PRD 79 (2009) Belle PRL 108 (2012) Average HFAG BaBar PRD 79 (2009) Belle PRL 108 (2012) Average HFAG BaBar PRD 79 (2009) Belle PRL 108 (2012) Average HFAG BaBar PRD 79 (2009) Belle PRL 108 (2012) Average HFAG BaBar PRD 79 (2009) BaBar PRD 79 (2009) HFAG HFAG Moriond 2012 HFAG Moriond 2012 HFAG Moriond Moriond 2012 HFAG Moriond 2012 HFAG Moriond 2012 PRELIMINARY ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± S =0.679 ± A. Leopold (HEPHY) Belle HEPMAD 2015/09/21 14 / 35

36 1 world average sin(2β) sin(2φ 1 ) BaBar PRD 79 (2009) BaBar χ c0 K S PRD 80 (2009) BaBar J/ψ (hadronic) K S PRD 69 (2004) Belle PRL 108 (2012) ALEPH PLB 492, 259 (2000) OPAL EPJ C5, 379 (1998) CDF PRD 61, (2000) LHCb arxiv: Belle5S PRL 108 (2012) Average HFAG HFAG Moriond 2015 PRELIMINARY 0.69 ± 0.03 ± ± 0.52 ± 0.04 ± ± 0.42 ± ± 0.02 ± ± ± ± 0.04 ± ± 0.58 ± ± = 1 = (21.9 ± 0.7) 36 A. Leopold (HEPHY) Belle HEPMAD 2015/09/21 15 / 35

37 Measurement of 2 2 = arg Vtd V tb V ud V ub access B 0! B 0! B 0! 2 via time-dependent CP asymmetry in: penguin contribution has to be controlled: e.g. isospin analysis S =sin 2 eff 2 with eff 2 = C 6= 0 ) direct CP violation from interference of tree and penguin 37 A. Leopold (HEPHY) Belle HEPMAD 2015/09/21 16 / 35

38 Results on 2 from B 0! : [PRD 88, (2013)] 1.0 CKM f i t t e r EPS 15 ππ/ρρ/ρπ (BABAR) ππ/ρρ/ρπ (Belle) ππ/ρρ/ρπ (WA) CKM fit 0.8 p-value WA 2 = ( ) (deg) φ 2 all 2 = ( ) [CKM fitter] 38 A. Leopold (HEPHY) Belle HEPMAD 2015/09/21 17 /

39 Measurement of φ 3 If D 0 and D 0 decay to the same final state, both diagrams contribute to the observed rate The subsequent interference allows to determine the relabve phase between these diagrams δ ± φ 3, φ 3 = Arg(V ud V * ub /V cd V* cb ) 3 approaches Gronau-London-Wyler (GLW): uses D 0 decays to a CP eigenstate Atwood-Dunietz-Soni (ADS): uses Cabibbo-favored and doubly-cabibbo-suppressed D 0 modes Dalitz plot analysis: uses three-body decays, e.g., D 0 K S π + π - 39

40 φ 3 with a Dalitz plot analysis Giri, Grossman, Soffer, Zupan [PRD 68, (2003)] m 2 - = M2 (K S π - ) D 0 K S π + π - Dalitz plot Amplitude M + of B + D(K S π + π - ) K + M + = A(m 2 +,m2 - ) + rei(δ+φ3) A(m 2 -,m2 + ) Amplitude M - of B - D(K S π + π - ) K - M - = A(m 2 -,m2 + ) + rei(δ-φ3) A(m 2 +,m2 - ) m 2 + = M2 (K S π + ) r = A(B DK) / A(B DK) B +/- Dalitz plot density: D related strong phase difference (model-dependent!) 40

41 Binned Dalitz plot analysis Measure the D related strong phase difference at CLEO-c in ψ(3770) DD events [PRD 82, (2010)] Convert model into experimental error OpBmal binning (8 bins) CLEO measurement compared to Belle model 41

42 Measurement of CKM f i t t e r CKM 14 Belle GLW+ADS Belle GGSZ Belle Combined 1.0 CKM f i t t e r CKM 14 Belle LHCb Full Frequentist treatment on MC basis Combined BaBar p-value p-value γ γ GGSZ 3 = ( ± 3.6(sys) ± 8.9(model)) GGSZ 3,MI = ( ± 4.1 ± 4.3) Belle 3 = ( ) World 3 = ( ) [CKM fitter] A. Leopold (HEPHY) Belle HEPMAD 2015/09/21 20 / 35

43 Semileptonic B decays to charm B X q allow to determine the magnitude of the Cabibbo- Kobayashi-Maskawa (CKM) matrix element V cb Two types of measurements Exclusive: A specific charm final state is reconstructed (e.g., Dlν, D*lν) Inclusive: All X c lν final states within a region of phase are reconstructed 43

44 V cb from exclusive decays B D*lν B Dlν The form factors F(w) and G(w) can be parameterized with a precision beber than 2% [NPB 530, ] B D*lν parameters: F(1), ρ D*2, R 1 (1) and R 2 (1) B Dlν parameters: G(1), ρ D 2 44

45 Outline of the measurement 1 Experiments measure the B D(*)lν decay width in bins of w = v B. v D(*) 2 Fi ng with the theorebcal expressions yields F(1) V cb, ρ D* 2 (D*lν) or G(1) V cb, ρ D 2 (Dlν) 3 La ce QCD or heavy flavour sum rule predict the form factor normalizabon at w = 1 ( zero recoil ), F(1) and G(1) determinabon of V cb [PoS LATTICE2010, 311 (2010); PRD81, (2010); NPPS 140, (2005); PLB585, (2004)] 45

46 B Xlν V cb from inclusive decays Based on the Operator Product Expansion (OPE) <O i >: hadronic matrix elements (non-perturbabve) c i : coefficients (perturbabve) Parton-hadron duality the hadronic ME depend only on the inibal state KineBc scheme [JHEP 1109 (2011) 055] 1S scheme [PRD70, (2004)] O(1) m b, m c m b O(1/m 2 b ) µ2 π, µ2 G λ 1, λ 2 O(1/m 3 b ) ρ3 D, ρ3 LS ρ 1, τ

47 Moments of the E l and M 2 X spectrum Also other observables in B à Xlν can be expanded into an OPE with the same heavy quark parameters, e.g., The n th moment of the (truncated) lepton energy spectrum The n th moment of the (truncated) M 2 X spectrum Master plan: Measure the quark masses and heavy quark parameters using moments SubsBtute them in the formula of the semileptonic width Determine V 47 cb from the semileptonic branching fracbon

48 Analysis in the kinebc scheme with 50 moments from BaBar, Belle, CDF, CLEO and DELPHI [P. Gambino, CS, Phys.Rev.D89, (2014)] 48

49 [Phys.Rev.D89, (2014)] Global fit (kinebc scheme) 49

50 Results on V cb preliminary B! D` results (as presented by R. Glattauer at EPS-HEP 2015) exclusive inclusive V cb EW (BGL) = (42.09 ± 1.07) 10 3 V cb EW (CLN) = (40.93 ± 1.33) A. Leopold (HEPHY) Belle HEPMAD 2015/09/21 28 / 35

51 V ub ~3 sigma discrepancy between inclusive/exclusive inclusive (BLNP) CLEO (E e ) 4.28 ± BELLE sim. ann. (m, q 2 ) X 4.49 ± BELLE (E e ) 4.93 ± BABAR (E e ) 4.54 ± BABAR (E max ) e, s h 4.53 ± BELLE multivariate (p*) 4.49 ± BABAR (m <1.55) X 4.30 ± BABAR (m <1.7) X 4.04 ± 0.22 ± BABAR (m <1.7, q >8) X 4.30 ± BABAR (P + <0.66) 4.15 ± BABAR (p*>1gev) 4.32 ± BABAR (p*>1.3gev) 4.32 ± Average +/- exp + th. - th ± χ 2 /dof = 9.0/11 (CL = %) Bosch, Lange, Neubert and Paz (BLNP) Phys.Rev.D72:073006,2005 HFAG PDG V [ 10 ] ub exclusive 2 2 Khodjamirian et al. q < 12 GeV 3.41 ± Ball-Zwicky q < 16 GeV 3.58 ± HPQCD q > 16 GeV 3.52 ± FNAL/MILC q > 16 GeV 3.36 ± HFAG PDG V ub [10 ] 51 A. Leopold (HEPHY) Belle HEPMAD 2015/09/21 32 / 35

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53 As late as 2001, the two parbcle detectors BaBar at Stanford, USA and Belle at Tsukuba, Japan, both detected broken symmetries independently of each other. The results were exactly as Kobayashi and Maskawa had predicted almost three decades earlier. 53

54 Important results not covered here Rare decays ( B X s γ, B X s l + l + ) Charm physics ( mixing, CP violabon ) Tau physics ( lepton flavour violabon, )... 54

55 End of part 2 55