RESULTS FROM B-FACTORIES

Transcription

1 XL International Meeting on Fundamental Physics Benasque, May 12 RESULTS FROM B-FACTORIES (IFIC Valencia) τ - τ + τ - τ +

2 B factories KEKB s=10.58 GeV e + e- Υ(4s) Υ(4s) B B z ~ c βγ τ B ~ 200µm BaBar p(e - )=9 GeV p(e + )=3.1 GeV βγ=0.56 Belle p(e - )=8 GeV p(e + )=3.5 GeV βγ =0.42 2

3 B factories 492 BaBar Belle publications! 3

4 Outline B Physics: Charm Physics: τ Physics: Summary Radiative b sγ (NEW, Moriond 12) Rare B X (NEW, Moriond 12) Semileptonic B D (*) τν Time Reversal Violation (NEW, FPCP 12) CPV Mixing and CPV (RECENT, SUSY 11) (UPDATE, FPCP 12) (NEW, CHARM 12, FPCP 12) 4

5 B Physics

6 B X s γ Motivation: Flavor-Changing Neutral-Current processes, forbidden at tree level in the Standard Model LO radiative penguin diagram For photon energy Eγ>1.6 GeV SM-based prediction: HFAG average: New physics may increase the rate significantly [Misiak et al. PRL (2007)] B(B X s γ)= (3.15 ± 0.23)x10-4 B(B X s γ)= (3.55 ± 0.25 ± 0.09)x10-4 [HFAG arxiv: v3 (2011)] Photon energy spectrum important for understanding the b quark momentum distribution access to HQET parameters: m b and μ π 2 V ub 6

7 B X s γ Experimental method: 429 fb -1 m ES fits to a sum of 38 exclusive X s final states to extract signal yields ( X s = 1 or 3 kaons ( with 1 K s ( π + π - ); 1 η; 4 π s ( 2 π 0 s)) 1.4 GeV < m Xs < 1.5 GeV m Xs range from 0.6 to 2.8 GeV in18 bins E γ range from 1.9 < E γ < 2.61 GeV Signal and background separated using random forest classifiers: Signal: B energy and error, m Xs, event shape Background: event shape, B direction, veto to photons from π 0 Systematics includes quark hadronization models 7

8 B X s γ Fit to m Xs spectrum (HQET parameters): - Kinetic model [Bensen et al. Nucl. Phys. B (2005)] - Shape function model [Lange et al. PRD (2005)] m xs spectrum BaBar preliminary Compared to HFAG: E γ spectrum The total branching fraction (E γ >1.9GeV): BaBar preliminary In agreement with SM 8

9 B K (*) + - Motivation: b s + - forbidden at tree level in the Standard Model It is allowed in loop and box diagrams with BR~ 10-6 SM H eff factorizes short-distance C i from long-distance effects Three effective Wilson coefficients contribute: C 7 eff from γ penguin (also in b sγ processes) C 9 eff (C 10 eff ) from vector (axial-vector) part of Z penguin & W box Contribution from New Physics may alter the C eff values Observables: decay rates, rate asymmetries, angular distributions BSM 9

10 B K (*) + - Experimental method: Signal reconstructed in the decay channels: B 0,+ K 0 s,+ +, B 0,+ K* 0, * + ( Kπ) + - (µ and e) Fit to m ES (and m Kπ ) Veto J/ψ and ψ(2s) regions ( + - ) Background rejected using Bagged Decision Trees (BDT s) - E=E* B E CM /2, event shape, p T of the event, decay vertex, angular info of the event [BaBar, PRD, arxiv: ] s 4 Total fit Combinatorial Signal Fake µ 429 fb -1 Results in six bins (s 1 -s 6 ) + one (s 0 ) of s=m 2 10

11 B K (*) + - Total branching fractions: [BABAR, arxiv: ] [Belle, PRL 103, (2009)] [CDF, PRL 107, (2011)] Partial branching fractions: J/ψ ψ(2s) [Ball & Zwicky, PRD71, (2005), PRD71, (2005); [Ali et al, PRD 66, (2002)] Good agreement between experiments (also with LHCb, arxiv:1112:3515) and with SM predictions 11

12 B K (*) + - Rate asymmetry and dimuon/dielectron rate have less theo. uncertainties (more sensitive to New Physics effects) CP asymmetry: Lepton flavour ratio: J/ψ ψ(2s) J/ψ ψ(2s) Consistent with null expectation (SM) Consistent with unity (SM) 12

13 Isospin asymmetry: B K (*) + - K + - In the SM, A I at s=0 expected ~9% ( 4%) [Feldmann & Matias, JHEP 0301, 074 (2003)] SM J/ψ ψ(2s) =m 2 For the low s region (0.1< s <8.12 GeV 2 ): K* + - [BABAR, arxiv: ] [Belle, PRL 103, (2009)] In agreement with SM predictions 13

14 B K (*) + - Angular observables: ϑ : angle between the lepton and the B in the rest frame ϑ K : K angle in K* rest frame, K* polarization F L : Fraction of longitudinal polarization of K * A FB : Forward-Backward Asymmetry of

15 B K (*) + - Fit results: BaBar Preliminary F L BaBar Preliminary A FB Good agreement between experiments. BaBar F L below SM predictions at low s s(gev 2 ) s(gev 2 ) Ali et al. PRD 61, (2000) Buchalla et al. PRD 63, (2001) Ali et al. PRD 66, (2002) Kruger et al. PRD 61, (2002) Kruger & Matias PRD71, (2005) Ball & Zwicky, PRD71, (2005) 15

16 Lepton Number Violation Motivation: Lepton Number Violation understanding of quantum nature of neutrinos test predictions in BSM models At B-factories LNV may be searched in L=2 B meson decays: B + K - /π (BaBar, PRD 85, (R) (2012)) B + D (Belle, PRD 84, (R) (2011)) Sensitive to heavy Majorana neutrinos (mν M 2-4 GeV ) BR s being ~ 10-7 Lepton-hadron mass enhancement by resonance production [J.-M. Zhang and G.-L. Wang, Eur. Phys. J. C 71, 1715(2011); A. Atre, T. Han, S. Pascali, and B. Zhang, J. High Energy Phys. 05 (2009) 030; T. Han and B. Zhang, Phys. Rev. Lett. 97, (2006).] 16

17 Lepton Number Violation Experimental method: Belle: D - K - π + π leptons of same charge 2D fit to E and m ES distributions [Belle, PRD 84, (R) (2011)] 700 fb -1 B + D - µ + µ + B + D - µ + µ + 90% CL Upper Limits: Comparison with LHCb: [LHCb, arxiv: ] 17

18 Lepton Number Violation Experimental method: B K or π (selection similar to B K ( * ) + - ) signal 429 fb -1 [BaBar, PRD 85, (R) (2012)] Limits on resonance production (m h ), sensitive to m νm 90 % CL Upper Limits: Comparison with other experiments: CLEO [PRD 65, (2002)] BF(B + (π,k ( * ),ρ) + + ) < ( ) 10-6 LHCb [PRL 108, (2012); arxiv: ] BF(B + (K -,π - )μ + μ + ) < ( )

19 B D (*) τν Motivation: Sensitive to charged-higgs effects Involve form factors which can be measured in B D ( * ) e/µν decays Observables: R(D) and R(D*) ratios - can be enhanced by the charged-higgs (tanβ/m H ) - several syst. and theo. uncertainties cancel out SM predictions: R(D) SM = ± R(D*) SM = ± [S. Fajfer, J. F. Kamenik, and I. Nisandzic, arxiv: ; J. F. Kamenik and F. Mescia, Phys. Rev. D 78, , (2008)] 19 19

20 B D (*) τν Experimental method: BaBar: Btag fully reconstructed into hadrons (Improved efficiencies (lepton and Btag)) Bsig: D ( * ) and lepton (µ, e) - 4 signal samples: (D 0, D +, D* 0, D* + ) ν (to extract B D ( * ) τν) - 4 control samples: (D 0, D +, D* 0, D* + )π 0 ν (to derive D** ν bkg) 426 fb -1 τ µν µ ν τ τ eν e ν τ m miss 2 = (p e+e- -p Btag -p D(*) -p ) 2 2D unbinned ML fit m miss2 -p* Yields for: B (D 0, D +, D* 0, D* + )τν B (D 0, D +, D* 0, D* + ) ν B (D 0, D +, D* 0, D* + )π 0 ν R(D) and R(D*) Large signal significance : 16σ (D*) and 8σ (D) 20 20

21 B D (*) τν New Results (FPCP 12): to be submitted to PRL Comparison with the SM: R(D) = ± SM = 0.297(17) R(D*) = ± SM = 0.252(3) 2.0σ 2.7σ The combination of the two measurements (-0.27 correlation) yields χ 2 /NDF=14.6/2 (i.e. Prob. = 6.9 x10-4 ) The SM prediction is excluded at 3.4 σ 21 21

22 B D (*) τν Comparison with previous measurements: SM Average (w/o BaBar 2012) SM Average (w/o BaBar 2012) Good agreement between experimental results 22

23 B D (*) τν Interpretation Beyond the Standard Model: A charged Higgs (2HDM type II) could enhance or decrease the R(D) and R(D*) ratios depending on tanβ/mh BaBar 2HDM Effect of 2DHM (accounting for difference in efficiency): 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 a probability of >99.8% (M H >10GeV) 23

24 Charm Physics

25 CPV in charm Motivation: Direct CP violation in D decays arises through interference between: In the SM is CKM suppressed O(10-3 ) or less: Vcs New Physics can increase or reduce the effect: - e.g. additional CP phase from charged Higgs boson SCS decays are more likely to show the effect if present Current experimental sensitivity O(10-3 ) [PRD 75, (2007)] [hep-ph/ (2001)] [PRD 51, (1995)] LHCb results at 3.5σ, CDF at 2.7σ: PRL 108, (2012) 25

26 CPV in charm CP violation in various SCS modes has been searched by B-factories Ex. of recent result: ( Corrected by A FB and A π ε ) No CP violation 26

27 CPV in charm Due to CPV in mixing in the kaon sector, the direct CP asymmetry for D + K s π + A CP Γ Γ = is expected to be [hep-ph/ (2001)] Γ +Γ ( D π Ks) ( D π Ks) ( D π Ks ) ( D π Ks ) A CP = -(0.332 ± 0.006)% Belle results consistent with SM expectation (CPV in the K sector) 27

28 Time dependent analyses CPV in charm Measurement of lifetime difference between D 0 Kπ and D 0 KK,ππ allow to determine the D 0 -D 0 mixing parameter y CP y CP 0 Mixing If CP is conserved y CP =y Differences in D 0 and D 0 lifetimes are sensitive to contributions from CPV in mixing and decay 28

29 CPV in charm Similar techniques at BaBar (468 fb -1 ) and Belle (976 fb -1 ) Tagged analysis: Use D* + π + D 0 to tag the D 0 flavour and suppress the background, and reconstruct the D 0 into Kπ, KK and ππ modes (BaBar uses for Y CP measurement an additional untagged D 0 Kπ, KK sample (stat. X 4, less pure)) Reject D* from B decays (p D* > 2.5GeV) Signal yield from mass distributions, bkg from sidebands Measure D 0 proper decay time: t and σ t, by reconstructing the D momentum and flight length L: Fit the proper decay time distribution 29

30 CPV in charm 976 fb -1 CHARM 12 Preliminary y CP = (+1.11 ± 0.22± 0.11)% A Γ = (-0.03 ± 0.20 ± 0.08)% No mixing excluded at 4.5σ A Γ consistent with no indirect CPV 468 fb -1 Preliminary y CP = (+0.72 ± 0.18± 0.12)% Υ= (0.09 ± 0.26 ± 0.06)% Tagged Untagged Υ=(1+y CP )A Γ No mixing excluded at 3.3σ No indirect CPV 30

31 CPV in charm HFAG updated values: Good agreement between experiments, BaBar and Belle increase precision 31

32 τ Physics

33 CPV in τ decays Motivation: CP violation not yet observed in the lepton sector Search for direct CP violation in tau decays: τ - π - K s ν τ within the SM, due to the K s presence, the decay rate asymmetry: Γ Γ ACP = Γ +Γ ( τ π Ksντ ) ( τ π Ksντ ) ( τ π Ksντ ) ( τ π Ksντ ) τ Tree W s d K 0 ν τ u d π is expected to be A SM CP = (0.332 ± 0.006)% (same argument than for D K s π decays) [Bigi and Sanda, PLB 625, 47 (2005)] A deviation of the measured A CP from A SM CP would be a hint of New Physics o e.g. an additional CP violating phase from an exotic charged Higgs boson [PLB 398, 407 (1997)] Can consider τ - π - K s (>=0π 0 )ν τ since π 0 s are not expected to change the asymmetry 33

34 CPV in τ decays Experimental method: Reconstruct from continuum τ - π - K s (>=0π 0 )ν τ (up to 3π 0 s) 476 fb -1 [PRD85, (2012)] Electron and muon tags with p * > 4 GeV (reduce bkg from non-τ-pairs) Reconstructed hadronic mass < 1.8 GeV (rejects qq bkg) Remaining background further reduced using information of: qq events: visible energy, number of neutral clusters, thrust, total transverse momentum Fake K 0 s: displaced vertex, invariant mass, momentum and polar angle of the K 0 s candidate Invariant mass of the hadronic final state (0π 0 s) 340k events 34

35 CPV in τ decays Measured raw A CP value (after subtraction of qq background and non-k 0 sτ decays) has to be corrected by: o Different nuclear reaction cross-section of K 0 and K 0 with material detector o (0.14±0.03)% for e-tag, (0.14±0.02)% for µ-tag o Uncertainties from kaon-nucleon cross-sections and isospin o Dilution from background modes including K 0 s Source Fraction e-tag (%) Fraction µ-tag (%) SM expected A CP τ - π - K 0 S( 0π 0 )ν τ 78.7 ± ± 4.0 (0.33±0.01)% τ - K - K 0 S( 0π 0 )ν τ 4.2 ± ± 0.3 ( 0.33±0.01)% τ - π - K 0 K 0 ( 0π 0 )ν τ 15.7 ± ± Result: A CP = (-0.36 ± 0.23 ± 0.11)% 2.8σ from the SM prediction 35

36 CPV in τ decays CP violation in τ decay is possible generally if there is an interference between the SM diagram and the CP violating scalar boson exchange diagrams. (Kuhn, Mirkes 1993) Search for a CPV decay angle asymmetry at Belle ( ) ϑ = K - direction ψ = τ - direction in Kπ rest frame 36

37 Experimental method: CPV in τ decays 699 fb -1 of Belle data at the Υ(3S), Υ(4S), Υ(5S) Reconstruct τ νk s π Signal events: (162.2±0.4) x 10 3 events for τ + νk s π + (162.2±0.4) x 10 3 events for τ - νk s π - Background: 23% After applying small corrections for A FB and A π ε (measured in τ νπππ), the A CP gives: m(k s π) m(k s π) No significant A CP asymmetry Limits for the CP violating parameter (depending on the hadronic form factors param.) at 90%CL 37

38 Summary Flavour Physics is a very active field, as you have already seen in this meeting (look for additional info at CHARM 12, FPCP 12 ) B factories are still providing high precision results in B, c and τ sectors In general, good agreement with the SM predictions ~3σ effects involving τ leptons: B D ( * ) τν, CPV in τ νk s π (BaBar) No CPV in charm (contrary to LHCb, CDF) Now that we have huge data samples and sophisticated analysis techniques it would be nice to have feedback from theorists And be prepared for the near future 38

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