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Rare decays at B factories

Rare decays at B factories. Peter Kri ž an University of Ljubljana and J. Stefan Institute. Fundamental Questions in Flavor Physics. Are there n ew sources of CP v iolation ? Experiments: b s CPV, compare CPV angles from tree and loops

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Rare decays at B factories

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  1. Rare decays at B factories Peter Križan University of Ljubljana and J. Stefan Institute ITEP Meeting

  2. Fundamental Questions in Flavor Physics Are there new sources of CP violation? Experiments: bs CPV, compare CPV angles from tree and loops Are there new operators with quarks enhanced by New Physics ? Experiments: AFB(BK*l l), BK rates and asymmetries Are there right-handed currents ? Experiments: bs CPV, BV V triple-product asymmetries Are there new flavor changing neutral currents ? Experiments: bsννbar, D-Dbar mixing+CPV+rare, τγ Data sample of ∼50ab−1@Y(4S) needed to address these questions ITEP Meeting

  3. Contents • FCNC bs decays • bsg : inclusive rate, CP violation • bd penguins:B rg, wgdecays • Measurement of Afb vs q2 in B  K* l+ l- decays • Decays with >1 neutrino • Purely leptonic decays: B- t- nt ,B0 t+ t- • B- K-n n • Semileptonic decay: B- D(*)t- nt • ... Only a limited selection of topics. ITEP Meeting

  4. Why FCNC decays? Flavour changing neutral current (FCNC) processes (like bs, bd) are fobidden at the tree level in the Standard Model. Proceed only at low rate via higher-order loop diagrams. Ideal place to search for new physics. ITEP Meeting

  5. Radiative Decays • Inclusive Br(bsg) |C7|, SF for |Vub| • BK*g isospin asymmetry (D+-) sign of C7 • Mixing induced CPV • Direct CPV in BXsg • BXdg red: discussed in this talk ITEP Meeting

  6. Inclusive Br(bsg) Motivation: measure |C7| and shape function parameters(from Eg spectrum for |Vub| extraction) Inclusive and semi-inclusive  ITEP Meeting 38 modes, 55% rate

  7. Inclusive Br(bsg) BF(B  Xsg, Eg>1.6 GeV)=(3.55±0.24+0.09 ±0.03) x 10-4 -0.10 • consistent with SM expectations (3.57±0.30) x 10-4 However: theory error is expected to get reduced by a factor of ~2 (NNLL calculations are under way) interesting for charged Higgs mass limit need a better measurement of inclusive rate Also: important to fix the value of Wilson coeff. C7 and to determine the spectrum shape. At 5 ab-1 : Egmin down to 1.5 GeV and stat. error ~5% ITEP Meeting

  8. mb C7 ms ms mb p+ p- KS trajectory B vertex IP profile g g BXsg CP Asymmetry • Sensitive to NP – right handed currents • Theoretically clean. • Standard Model “~Zero”. • g is polarized, and the final state is almost flavor specific. • Helicity flip ofgsuppressed by ~ms/mbS ~ 0.06 sin2f1 • Time dependent CPV requires vertex reconstruction with KSp+p- g Vertex recon. eff. at Belle 51% (SVD2), 40% (SVD1) Possible at e+e- B-factory ITEP Meeting

  9. B0KSp0g time dependent CPV • Atwood, Gershon, Hazumi, Soni, • PRD71, 076003 (2005) M(KSp0) < 1.8GeV/c2 • NP effect is independent of the resonance structure. Example: Belle 386MBB • Two M(KSp0) regions(MR1:0.8-1.0GeV/c2/MR2:<1.8GeV/c2) • 70+-11 (45+-11) events in MR1(2). S= +0.08 ±0.41 ±0.10 A= +0.12±0.27±0.10 Good tag (0.5<r<1.0) ITEP Meeting

  10. B0KSp0g time dependent CPV Results: Belle hep-ex/0507059 S(BK*g, K*KSp0)=-0.01 ±0.52 ±0.11 S(B KSp0g)=0.08 ±0.41 ±0.10 BaBar PRD 71 (2005) 0501103 S(BK*g, K*KSp0)=-0.21±0.40 ±0.05 Prospects: Add more modes:BKSfg(with angular analyisis), higher K resonances, BKShg(recent observation by BaBar),... Present Belle (stat./syst.) 5ab-1 50ab-1 Acpmix(BK*g, K*KSp0) 0.41 / 0.10 0.14 0.04 Acpdir(BXsg) 0.051 / 0.038 0.011 0.005 ITEP Meeting

  11. Acp(BXsg) vs SUSY models 50ab-1 5ab-1 Mixing CPV Direct CPV U(2) tanb=30 mSUGRA tanb=30 U(2) tanb=30 mSUGRA tanb=30 Acpdir Acpmix SU(5)+nR tanb=30 non-degenerate SU(5)+nR tanb=30 degenerate SU(5)+nR tanb=30 non-degenerate SU(5)+nR tanb=30 degenerate ITEP Meeting T. Goto, Y.Okada, Y.Shimizu,T.Shindou, M.Tanaka hep-ph/0306093, also in SuperKEKB LoI

  12. bd penguins • Interesting: • Measurement of |Vtd/Vts| • Addresses the same physics issue as Bs- Bs mixing(from a different perspective: box vs loop) • CP violation could be sizeable in SM (order 10%) • New physics could be quite different from b  sg Supressed by |Vtd/Vts |2vs b  sg Difference in dynamics Form factor ratio ITEP Meeting

  13. Belle: First observation of B rg, wg signal qq K*g other B Ref: PRL 96, 221601 (2006) Reconstructing rare B meson decays at Y(4s): use two variables, energy diference DEand beam constrained mass Mbc _ ITEP Meeting

  14. Vtd/Vtsfrom B rg, wg 68%CL r 95%CL Full UT fit The measured branching fraction BF(B r/wg)= 1.32 +0.34 (exp.) +0.10 (theo.) Translates to |Vtd|/|Vts| = 0.199 +0.026 (exp.) +0.018 (theo.) which is compatible with SM constraints based on fits of other CKM parameters. Ref: PRL 96, 221601 (2006) -0.31 -0.09 -0.025 –0.015 Together with the evidence of BK0 K decays modes,this demonstrates the existence of a new quark level transition: bd ITEP Meeting

  15. Implications of Belle’s observation of bd  • Comparison with the recent observation of Bs mixing at Tevatron: • green: Bellemeasurement of|Vtd/Vts|inbd  • yellow: CDF measurement of |Vtd/Vts|from Bs mixing The width of the Bsmixing contour islimited by theory whileBd γ needs much more data. ITEP Meeting

  16. bd future prospects • With 1-2 orders of magnitude more statistics (5 ab-1, 50 ab-1): • Direct CP violation and time-dependent CPV withBρ0 γ and B ωγ • Measurements of inclusive b  d γ ITEP Meeting

  17. B  K* l+ l- b  s l+l- was first measured in B K l+l- by Belle (2001). Important for further searches for the physics beyond SM Ci: Wilson coefficients ITEP Meeting

  18. l- l+ B B q q K* K* l+ l- Particularly sensitive: forward-backward asymmetry in K* l+l Backward event Forward event [γ* and Z* contributions in BK* l l interfere and give rise to forward-backward asymmetries c.f. e+e- + -] ITEP Meeting

  19. Sample used for AFB(BK*ll)(q2) Ref: PRL 96, 251801 (2006) Treat q2, cos(θ) dependence of bkgs. Sample for BK* l l: 113±13 events Unbinned fit to the variables q2 (di-lepton invariant mass) and cos(θ) for the BK* l l data. Fit parameters A9/A7 and A10/A7(Ai = leading term in Ci) ITEP Meeting

  20. Control sample BKll BK l l control sample: 96±12 events Consistent with flat Integrated asymmetry: ITEP Meeting

  21. * Constraints on Wilson coefficients from AFB(BK* l l)(q2) Projections of the full fit to q2, cos(θ) Integrated FB asymmetry J/y y’ Observed integrated AFB rules out some radical New Physics Models with incorrect signs/magnitudes of C9 and C10(red and pink curves) ITEP Meeting

  22. Results of the unbinned fit to q2 and cos(θ) distributions for ratios of Wilson coefficients. A10/A7 ＳＭ A9/A7 SM A10/A7 Best fit A9/A7 |A7| constrained from bs to be close to SM Ref: PRL 96, 251801 (2006) at 95% C.L. ITEP Meeting

  23. AFB(BK* l l)(q2), BaBar BaBar: 229 M BB PRD 73(2006) 092001  Integrated FB asymmetry AFB >0.55 (@ 95% CL) First bin excludes SM (blue) at 2s level? ITEP Meeting

  24. AFB(BK* l+ l-)[q2] at Super B Factory q02 Precision with 5ab-1 dC9 ~ 11% dC10 ~14% d q02/q02 ~11% 4AFB zero-crossingq02 will be determined with 5% error with 50ab-1 ITEP Meeting

  25. Purely leptonic decay Bt n • Proceed via W annihilation in the SM. • Branching fraction • Provide information of fB|Vub| • |Vub| from BXu l n fB cf) Lattice • Br(Btn)/Dmd |Vub| / |Vtd| • Expected branching fraction |Vub| = (4.39 ± 0.33)×10-3(HFAG) fB = (216 ± 22) MeV (lattice) • BF(B  t nt) = (1.59 ± 0.40)×10-4 ITEP Meeting

  26. H+/W+ t+ Charged Higgs contribution to Bt n ~ e0 =SUSY corrections to b Yukawa coupling Br(SM) ~ 1.59 x 10-4 ITEP Meeting

  27. Full Reconstruction Method • Fully reconstruct one of the B’s to • Tag B flavor/charge • Determine B momentum • Exclude decay products of one B from further analysis Decays of interest BXu l n, BKn n BDtn, tn B e- (8GeV) e+(3.5GeV) Υ(4S) p B full reconstruction BDpetc. (0.1~0.3%) Offline B meson beam! Powerful tool for B decays with neutrinos ITEP Meeting

  28. Fully reconstructed sample Belle (447M BB) 4.12x105 B0B0 + 6.80x105 B+B- ITEP Meeting

  29. Event candidate B- t- nt ITEP Meeting

  30. Bt n (Belle) hep-ex/0604018 - preliminary Obtained Eresidual • NBB (produced) = 447M • NB+B- (full recon.) = 6.80 x 105 (purity 0.57) • t decay modes • Cover 81% of t decays • Event selection • Main discriminant: residual ECL energy Fit to Eresidual 21.2+6.7signal events. 4.2σ significance including systematics -5.7 ITEP Meeting

  31. Impact of B- t- nt • From BF(B  t nt) Product of B meson decay constant fB andCKM matrix element |Vub|use |Vub| from HFAGfB • Use BF(B  t nt) with Dmd  constraint in the (r,h) plane The commonuncertainty from fBcancels in this ratio. ITEP Meeting

  32. Charged Higgs limits from B- t- nt If the theoretical prediction is taken for fB limit on charged Higgs mass vs. tanb ITEP Meeting

  33. Bt nprospects • Expected precision at Super-B • 13% at 5 ab-1 • 7% at 50 ab-1 • Search with D(*) l n tag will help.  BaBar 232M BBPRD73 (2006) 057101 • Tag eff ~ 1.75 x 10-3 • Signal selection eff. ~31% • Similar S/N to Belle (full recon. sample) ITEP Meeting

  34. If D|Vub| = 0 & DfB = 0 Future Prospects: B 95.5%C.L. exclusion boundaries DfB(LQCD) = 5% (for BFobs = BFSM) Extrapolations (T.Iijima) 50ab -1 rH

  35. B  t+t- • BaBar (232M BB) PRL96 (2006) 241802 • Challenging measurement: 2-4 neutrinos per event! • Fully reconstruct one B (D(*)X, X=combination of up to 5 pions and kaons), 280k events • t decay modes: lnn, p-n, r-n(51% of tt decays) • Reject events with KL,KS,K± and employ neural network (kinematics of charged track momenta and ECL residual energy) • 263±19 events (expect 281±40 from sidebands, MC) • BF(B t+t-) < 4.1 x 10-3 (90%CL)SM prediction: 0.12 x 10-6 •  First ever limit on this channel • Constrains leptoquark couplings and tanb enhancements ITEP Meeting

  36. B- K-n n • BK(*)ννis a particularly interesting and challengingmode (with B τνas a small background), theoretically clean • Experimental signature:B  K + nothing • The “nothing” can also be light dark matter with mass oforder 1 GeV. Direct dark-matter searches cannot see the M<10 GeV region. • SM prediction: (3.8+1.2) x 10-6 • B τν analysis is a proof that such a one prong decay can be studied at a B factory • Present limits: • BaBar (89M BB): BF(B+K+νν) < 52 x 10-6PRL 94 (2005)101801 • Belle (275M BB): BF(B+K+νν) < 36 x 10-6hep-ex/0507034 -0.6 ITEP Meeting

  37. B- K-n n prospects MC extrapolation to 50 ab-1 5s Observation of B± K±n n SM prediction: G.Buchalla, G.Hiller,G.Isidori (PRD 63 014015) Extra EM calorimeter energy Fig. From SuperKEKB LoI ITEP Meeting

  38. Charged Higgs search in BD t n c b Charged Higgs contribution H+/W+ t+ nt Decay amplitude Br(SM)~ 8 x 10-3 Tauonic decay is the most sensitive • Analysis:reject events with p, K, reject D*tn contamination, no remaining charged or p0 tracks, cut on the ECL residual energy, angle between two n’s and missing mass. ITEP Meeting

  39. BD t n (MC studies) • Signal selection efficiency 10.2% 2.6% 26.1% 13.3% • Expectation at 5 / 50 ab-1 for B+ decay 5s observation possible at 1ab-1 ITEP Meeting

  40. Form factor error BD t n constraint on charged Higgs Reach in R Once branching fraction is measured, we can determine R. M.Tanaka, Z.Phys. C67 (1995) 321 BF error  Reach in R: 11 at 5ab-1 ITEP Meeting

  41. BD t n  charged Higgs Constraint From bsg D(Form-factor) ~5% D(Form-factor) ~15% ITEP Meeting

  42. Super-B and LHCb: complementary • Clean environment  measurements that no other experiment can perform. Examples: CPV in BgfK0, Bgh’K0 for new phases, BgKSp0gfor right-handed currents. • “B-meson beam” technique  access to new decay modes; proof BgtnExample: discover BgKnn. • Measure new types of asymmetries. Example: forward-backward asymmetry in bgsmm, see • Rich, broad physics program including B, t and charm physics. Examples: searches for tgmg and D-D mixing with unprecedented sensitivity. LHCb LHCb LHCb ITEP Meeting

  43. Summary • Radiative,electroweak and tauonicB decays are of great importance to probe new physics. • We are starting to measure Btn, Dtn, AFB(K*ll), ACP(Kp0g) etc. at the current B factories. Hot topics in the coming years ! Watch out for updates (including this week)... • For precise measurements, we need a Super-B factory! Observe K(*)nn, zero crossing in AFB, D(*)tn Expected precision (5ab-150ab-1); • Br(tn): 13%7% • Br(D(*)tn): 7.9%2.5% • q02 of AFB(K*ll): 11%5% • ACP(Kp0g) tCPV: 0.140.04 ITEP Meeting

  44. Additional slides ITEP Meeting

  45. Charged Higgs from Br(bsg) ITEP Meeting

  46. Radiative decays: prospects Summary by M.Nakao1st Super-B workshopat Hawaii (2004) ITEP Meeting

  47. B- e- ne, m- nm • Helicity supressed with respect to B τν • B- m-nmSM prediction: 0.4 x 10-6 • (Possibly better for charged Higgs limits than tn at high stat) • Present limits: • Belle (152M BB): BF(B- m-nm) < 2 x 10-6hep-ex/0408132 • BaBar (89M BB): BF(B- m-nm) < 6.6 x 10-6PRL 92 (2005)221803 • B- e- neSM prediction: ~0.00001 x 10-6 • Present limit: • Belle (65M BB): BF(B- e- ne) < 5.4 x 10-6BELLE-CONF-0247 ITEP Meeting

  48. B- e+e-, m+m- • No new results from B factories... • BaBar (120M BB): BF(B  e+e-) < 0.083 x 10-6 BF(B m+m-) < 0.061 x 10-6 PRL94(2005)221803 • Belle (85M BB): BF(B  e+e-) < 0.19 x 10-6 BF(B m+m-) < 0.16 x 10-6 PRD68 (2003)111101 • .... With present statistics we could be competitive with Tevatron • Limits from Tevatron: hep-ex/0508058 • BF(Bdm+m-) < 0.032 x 10-6 SM prediction: 0.0001 x 10-6 • BF(Bsm+m-) < 0.12 x 10-6 SM prediction: 0.0035 x 10-6 ITEP Meeting

  49. BD t n (MC studies) • Use fully reconstructed samples. • t decay modes • Analysis cuts; • Reject events withp, KL • Reject D*t n contamination • No remaining charged or p0 tracks • ECL residual energy • Angle between two n’s • Missing mass Signal BG ITEP Meeting

  50. B  t nt hep-ex/0604018 - preliminary BF(B  t nt)=(1.06+0.34 (stat.) +0.18 (syst.)) x 10-4 -0.28 -0.16  Product of B meson decay constant fB andCKM matrix element |Vub| fB |Vub| = (7.73 +1.24 (stat.) +0.66 (syst.)) 10-4 GeV Using |Vub| = (4.39 ± 0.33)×10-3 from HFAG fB = (176+28 (stat.) +20 (syst.)) MeV First measurement of fB! fB = (216 ± 22) MeV (an unquenched lattice calc.) [HPQCD, Phys. Rev. Lett. 95, 212001 (2005) ] -1.02 -0.58 -23 -18 ITEP Meeting

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