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BdK0K0 and Other Hadronic bd Decays Jed Biesiada Princeton University (for the BaBar Collaboration) 4th International Workshop on the CKM Unitarity Triangle Nagoya, Japan December 12, 2006 Virtual Loops: Low-Energy Probe of High Energy Physics Virtual-loop, or “penguin”, diagrams are sensitive to new physics contributions Many models beyond the Standard Model contribute additional CP-violating phases Penguin modes are suppressed in the standard model relative to the treedominated decays Small branching fractions Many interesting bs penguin decays have been investigated at the B Factories fK, h’K0, K0K0K0, K00, … Standard Model Supersymmetry 2 BdK0K0 : b → d Penguin B0K0K0 is dominated by the bd transition Analogous to bs penguins in fKS Even more suppressed in the SM: 2 (b d ) Vtd ~ ~ 4% 2 (b s ) Vts New physics might affect bd differently than bs Same penguin as in B0+- and B+K0K+ Useful for extracting the UT angle in the former and the annihilation contribution in the latter d K BK0K0 : Expectations from the Standard Model Assuming top-quark dominance: BF ~ 10-6 Decay weak phase exactly cancels mixing phase d s s q A Vtb*Vtd VtbVtd* * 1 * p A VtbVtd VtbVtd Expect zero indirect CP violation K0 R. Fleischer and S. Recksiegel, S(K0K0) = 0 Eur.Phys.J.C38:251-259,2004 → any non-zero value would indicate 2 sin 2 α 2 r cos δ sin ( 2 β γ)-r sin 2 β New Physics S KK (SM) 2 Expect a small contribution from uand c-penguins CKK (SM ) K0 S(K0K0) < 0.10, sensitive to combination of all three UT angles Predictions (using QCD FA): 1 r 2r cos δ cos γ 1 Pct 2r sin sin r 2 h 2 Put 1 r 2 2r cos cos 0.02 S KK (SM) 0.13 0.17 C KK (SM) 0.15 Evidence for B→K0K0 (ICHEP 2004) N ( K S0 K S0 ) 23.0 76..77 1.9 2.0 (4.5 ) 40 ( B 0 K 0 K 0 ) (1.19 00..35 0.13) 10 6 PRL 95: 221801, 2005 (227 million BB pairs) N ( K S0 K S0 ) 15.6 5.810..16 (3.5 ) ( B 0 K 0 K 0 ) (0.8 0.3 0.1) 10 6 PRL 95: 231802, 2005 (275 million BB pairs) Next Step: Observe the mode and measure CP asymmetries with ~350-450 million BB pairs 5 Measuring SKK Challenge: Need to vertex a decay with no primary tracks from the e+einteraction point Solution: Exploit precise knowledge of the interaction point and fit the entire (4S) decay chain using beam-spot constraints. Method developed by BaBar, described in PRL 93: 131805, 2004 and PRD 71: 111102, 2005 + 1. Constrain Brec decay y to beam-spot in x-y z Ks B0 e 4s B e+ Beam 0 2. Use a neural-net algorithm to determine the Btag flavor Ks Btag- Standard Method 3. Determine the proper-time difference t between Brec and Btag decay vertices 6 Use KS’s that decay in the Silicon Vertex Tracker Classes of KS decays: 35% 25% 40% Have two KS‘s but need only one to vertex the signal B Class I – both pions have hits in inner layers Class II – not Class I, both pions have hits in SVT Class III and IV: not used for time-dependent measurement Class I B0’s: 58% Class II B0’s: 26% Class I Class II 7 Experimental Method: find the signal… Kinematics e B *2 mES Ebeam p*B2 BK0K0KSKS B Candidate KS mass spectrum KS+- e pB* ~ 300 MeV / c * E B* Ebeam KS mass selection * E EB* Ebeam Main Background is “Continuum” e+e- qq Background Suppression Background Use event-shape variables to separate from signal Need rejection of >106, but a fake signal event must have two highmomentum KS’s, pLAB 3 GeV low-background mode Signal Analysis Overview Common Features BK0K0 reconstructed in K0K0KSKS and KS+Loose selection cuts KS mass and lifetime significance ( or vertex displacement) mES( or mbc) – E fit region Extended unbinned maximum-likelihood fit Differences Dataset Vertexing BaBar Belle 347 million BB pairs (316 fb-1) 449 million BB pairs (409 fb-1) beam-constrained none Cut on likelihood ratio Event-shape continuum suppression Efficiency (including secondary BFs) Fit variables Physics quantities in the fit Loose cut on sphericity angle Optimized Fisher discriminant used in the fit (Legendre moments) Modified Fox-Wolfram moment (Fisher) B polar angle Optimization dependent on tagging quality of the other B 8.5 0.3% 5.9% mES , E, Fisher, t mbc , E signal and background yields, time-dependent CP-violating parameters S and C signal and background yields, partialrate flavor asymmetry, ACP Unbinned Maximum Likelihood Fit and Discriminating Variables for BaBar ni = candidate category, signal or background Pi = probability density for category i N = number of events Kinematic Event-shape mES Fisher discriminant E F a0 pi* a2 pi* cos 2 i* i * i i pB* , pi* Solid histogram = Dashed histogram = Signal Background t PDFs B0tag B0tag MC Fit result closely tracks the generated CPviolating structure Data Resolution function characterizes the data well 11 Results: Observation of bdg Penguins PRL 97: 171805, 2006 BABAR: BABAR N ( K S0 K S0 ) 32 8 3 (7.3 ) 347 M BB ( B 0 K 0 K 0 ) (1.08 0.28 0.11) 10 6 Dominant systematic uncertainties: Fitter bias Uncertainty in PDF shapes in the fit BABAR M.Pivk and F.R.Le Diberder, “sPlot: A Statistical Tool to Unfold Data Distributions,” Nucl. Instrum. Meth. A 555, 356 (2005) Belle: Belle Belle hep-ex/0608049 N ( K S0 K S0 ) 23 6 3 (6.0 ) 449 M BB ( B 0 K 0 K 0 ) (0.86 0.23 0.09) 106 Dominant systematics: Cuts on variables not shown to enhance signal KS reconstruction Event-shape likelihood selection Results: CP Asymmetry Likelihood Projection Plots PRL 97: 171805, 2006 n Contours physical region BABAR 1 = 68% 2-D C.L. 2 = 95% 2-D C.L. 3 = 99.7% 2-D C.L. fit result S ( K S0 K S0 ) 1.2800..80 73 0.11 0.16 C ( K S K S ) 0.40 0.41 0.06 0 0 Belle: ACP ( K 0 K 0 ) 0.57 00..72 6513 0.13 B+→K0K+ Penguin + Annihilation Amplitudes Same penguin amplitude as in B0K0K0 Annihilation contribution may affect branching fraction Need comparison with B0K0K0 to estimate the size of this effect K+ K0 15 Analysis Overview B+K0h+ reconstructed in KS+-, h=K, No vertexing BaBar PID Belle KID: Cut on a K- likelihood ratio to form separate candidate samples for each species Constrain crossfeed and signal yields in the two samples in a simultaneous fit Pion mass is assumed for the track Use the Detector of Internally Reflected Cherenkov light to separate pion and kaon bachelor tracks in the fit DIRC model is the same as in the BK+-/+analysis Additional PID from E, where the KSK+ peak is displaced -45 MeV relative to the KS+ peak Efficiency: BaBar: 12.9 0.4 % KS+, 12.6 0.4 % KSK+ Belle: 12.2 % KS+ 6.7 % KSK+ BaBar Particle ID: DIRC cos C 1 n D* D0 , D0 K Results BABAR: Belle: 347 M BB 449 M BB N K 0 1072 46 32 37 N K 0 1252 41 39 N K 0 K 71 19 4 (5.3 ) N K 0 K 36.6 89..37 (5.3 ) ( B K 0 ) (23.9 1.1 1.0) 10 6 ( B K 0 ) (22.9 00..78 1.3) 10 6 ( B K 0 K ) (1.61 0.44 0.09) 10 6 33 ( B K 0 K ) (1.22 00..28 AK 0 0.029 0.039 0.010 AK 0 0.03 0.03 0.01 AK 0 K 0.10 0.26 0.03 23 AK 0 K 0.1300..24 0.02 S S S S S S 0.13 0.16 S S Dominant systematic uncertainties: Dominant systematics: Uncertainty in PDF shapes in the fit Cross-feed KS reconstruction Cross-feed constraint 17 ) 10 6 Projection Results BABAR KS+ KSK+ KS+ KSK+ KSKS Belle KSKS Belle PRL 97: 171805, 2006 hep-ex/0608049 18 B0→K+K- W Exchange Amplitude B(B0→K+K-) ~ (0.78) x 10-8 in the standard model Beneke and Neubert, Nucl. Phys. B 675, 333 (2003) Rescattering or new physics could enhance the branching fraction Yield extracted from the B0K+/+- fit Use DIRC and E to separate from the other two components K+K- peak in E lies on the low tail of the large K+- peak Difficult to measure KK+ +K+K+K- 40 20 Results Belle: BABAR: 227 million BB pairs 3±13±7 events B(B0→K+K-) < 0.40 10-6 (90% confidence level) Submitted to PRD 449 million BB pairs 2.5 53..07 events B(B0→K+K-) < 0.25 10-6 (90% confidence level) hep-ex/0608049 21 Summary Observations of B0K0K0 and B+ K0K+, dominated by the b → dg penguin amplitude Non-observation of B0 K+K- is so far consistent with the standard model First observations of BdKK Branching fractions at SM predicted values The only Bhh’ (h=K,) charmless mode left to be observed First time-dependent CP measurement in a b → d penguin Large positive values of S are disfavored Method is feasible at BaBar Opens a new area of enquiry for the B factories More data will provide stronger constraints in this new sector K*K modes not yet seen but will be available at 1 ab-1 22 State of the Art Backup Slides Im(23)RR Flavor-Changing New Physics in Theory and Experiment M. Ciuchini and L. Silvestrini, Phys. Rev. Lett. 97 (2006) 021803 bs Im(13)LL Re(23)RR M. Ciuchini et al., hep-ph/0512141 bd The experimental program is just beginning: B B KK … Re(13)LL Need to explore the bd sector and add another constraint BK0K0 : Example of a Potential New Physics Scenario d d d A. Giri and R. Mohanta, JHEP 11, 084 (2004) Predictions for various assumptions on the weak phase NP and strong phase NP between NP amplitudes: NP 4 , 3 , 2 , 0 NP 2 Note: this scenario does not include all experimental constraints New-Physics Predictions for TDCP A. Giri and R. Mohanta, JHEP 11, 084 (2004) Predictions for various assumptions on the weak phase NP and strong phase NP between NP amplitudes Depending on the NP phase, SKK (NP) could be large Current BF measurement consistent with NP scenario NP 4 , 3 , 2 , 0 NP 2 New physics in b → d penguins is highly constrained assuming threegeneration unitarity But there’s still room for NP Measure TDCP in b →d penguins for the first time and add another constraint Vertexing Results Signal MC 28 KSKS PDFs double Gaussian Argus double Gaussian bifurcated Gaussian 1-degree polynomial double Gaussian Background Parameters Floated 29 KSh+ PDFs Cruijff double Gaussian bifurcated Gaussian Argus 1-degree polynomial double Gaussian 30 KK Vector Decays Useful for constraining sin2 in vector bs decays (e.g. BfK0) Not yet seen Require Dalitz-plot window selection Grossman, et al., Phys. Rev. D 68, 015004 (2003). Loss of efficiency Full Dalitz plot analysis with more data Single vector modes expected at ~ 0.5 10-6 level (bigger if NP/rescattering effects are sizable) Current upper limits (HFAG): K*0 K0 < 1.9 10-6 K*0 K+ < 5.3 10-6 K*0 K*0 < 22 10-6 K*+ K*0 < 71 10-6 K*+ K*- < 141 10-6 within reach of the B factories 31 Future Outlook with 1 ab-1 15% statistical error on B0K0K0 and B+ K0K+ BF’s from each experiment Meaningful comparison with theoretical predictions Constraint on annihilation contribution in B+K0K+ Time-dependent measurement from Belle? S ~ 0.40, C ~ 0.25 from each experiment Waiting for the first K*K signals with 1ab-1 32