Tauonic and Leptonic Decays Toru Iijima Nagoya University

Tauonic and Leptonic Decays Toru Iijima Nagoya University December 19, 2006 BNM-II Workshop, Nara-WU 1

Contents n Introduction n B tn n B Dtn, Xtn n B ln n ’s in the final state (missing energy) Technical issues; - Tagging - Background n B ll (ee, mm, tt) n B K(*)nn, nn 2

Hunting Rare Decays n High luminosity Evidence of B tn n Good detector (PID, vertex…) n Analysis techniques Observation of b dg – qq background suppression FB asymmetry in B K* l+l– Fully reconstructed tag Direct CPV in B 0 K+p. Beginning of B->f. K 0 saga Observation of B K l+ l. CPV in B decay Success of B factories brought rare B decays in leptonic and neutrino modes on the stage ! 3

Full Reconstruction Method n Fully reconstruct one of the B’s to tag – B production – B flavor/charge – B momentum B e- (8 Ge. V) e+(3. 5 Ge. V) Υ(4 S) p B Decays of interests B Xu l n, B K n n B Dtn, tn full (0. 1~0. 3%) reconstruction B Dp etc. Single B meson beam in offline ! Powerful tools for B decays w/ neutrinos 4

B t n (within the SM) n Proceed via W annihilation in the SM. n Branching fraction is given by n Provide information of f. B|Vub| – |Vub| from B Xu l n – Br(B tn)/Dmd f. B |Vub| / |Vtd| cf) Lattice (d~10%) n Expected branching fraction HFAG [hep-ex/0603003] HPQCD [PRL 95, 212001(2005)] 5

B t X as a Probe to Charged Higgs n Charged Higgs contribution to B decays In two Higgs doublets model, charged Higgs exchange interferes with the helicity suppressed W-exchange. Br(SM) ~ 9 x 10 -5 H+/W+ 2006/05/15 t+ 6

The First B tn Evidence n The final results are deduced by unbinned likelihood fit to the obtained EECL distributions. Signal + background S : Statistical Significance Background B tn Observe 17. 2 +5. 3 events in the signal - 4. 7 region. Significance decreased to 3. 5 s after including systematics Signal shape : Gauss + exponential Background shape : second-order polynomial + Gauss (peaking component) To appear in Phys. Rev. Lett. hep-ex/0604018 v 3 7

Results (Br & f. B Extraction) n Measured branching fraction; n Product of B meson decay constant f. B and CKM matrix element |Vub| n Using |Vub| = (4. 39 0. 33)× 10 -3 from HFAG 15% 16% = 14%(exp. ) + 8%(Vub) f. B = 216 22 Me. V [HPQCD, Phys. Rev. Lett. 95, 212001 (2005) ] 8

Constraints on Charged Higgs These regions are excluded. stat. syst. f. B |Vub| f. B from HPQCD |Vub| from HFAG Much stronger constraint than those from energy frontier exp’s. 9

Future Prospect: B tn n Br(B t n) measurement: More luminosity help to reduce both stat. and syst. errors. – Some of the syst. errors limited by statistics of the control sample. n |Vub| measurement: < 5% in future is an realistic goal. n f. B from theory: ~10% now 5% ? My assumption Df. B(LQCD) = 5% Lum. DB(B tn) exp D|Vub| 414 fb-1 36% 7. 5% 5 ab-1 10% 5. 8% 50 ab-1 3% 4. 4% If D|Vub| = 0 & Df. B = 0 5 ab-150 ab-1 10

Cont’d Charged Higgs Mass Reach (Ge. V) (95. 5%CL exclusion @ tanb=30) Only exp. error (DVub=0%, Df. B=0%) DVub=2. 5%, Df. B=2. 5% DVub=5%, Df. B=5% Luminsoity(ab-1) 11

Constraints at Super-B (cont. ) Df. B(LQCD) = 5% 5 s potential Charged Higgs Mass Reach with 5 s 5 ab -1 50 ab r. H 5 s -1 r. H 5 s

Ratio may help ? n Deviation of Br. exp. f. B |Vub| n Ratio to cancel out f. B (G. Isidori&P. Paradisi, hep-ph/0605012) exp. BBd |Vub| 13

B D(*) t n n Semileptonic tauonic decays c b Br(SM) ~ 8 x 10 -3 H+/W+ t+ nt – Ratio (t/m) is modified by the charged Higgs effect. – Provide good cross check to B t n – Y. Okada • H-b-u vertex by B t n • H-b-c vertex by B Dtn • H-b-t vertex by LHC direct search. 14

Lo. I l Signal selection efficiency 10. 2% 2. 6% l 26. 1% 13. 3% Expectation at 5 / 50 ab-1 for B+ decay 5 ab-1 Mode Nsig Nbkg 280 550 620 3600 50 ab-1 S 12. 7 d. B/B 7. 9% Nsig Nbkg 2800 5500 6200 36000 S d. B/B 40. 3 2. 5% 5 s observation possible at 1 ab-1 l Major background source Missing charged and g tracks from B D(*) l n X (incl. slow p) 15

Sensistivity to H± 50 ab-1 DFF=5% 5 ab-1 DFF=15% Similar to B tn 16

B mn (en) n B mn is the next milestone decay. When do we see the signal ? Precision at Super-B ? Br(tn)=1. 6 x 10 -4 Br(mn)=7. 1 x 10 -7 Br(en)=1. 7 x 10 -11 n Precise B t n/m n data provide lepton universality test. – Higgs effect itself is universal. RHtn = RHmn – Good probe to distinguish NP models. 17

Belle Results n Inclusive reconstruction – Reconstruct the accompanying B via a 4 -vector sum of everything else in the event. – Efficiency: 2. 18± 0. 06% (mn), 2. 39± 0. 06% (en) – NSM: 2. 8± 0. 2 (mn), (7. 3± 1. 4)x 10 -5 (ev) mn @90%CL Br(mn) < 1. 7 x 10 -6 253 fb -1 en Br(en) < 9. 8 x 10 -7 hep-ex/0611045, submitted to Phys. Lett. B 18

n Extrapolation from the present Belle analysis. K. Ikado at BNM 1 (Sep. 2006) ~50 events @ 5 ab-1 ~500 events @ 50 ab-1 Standard Deviation Future Prospect: B mn n Method? S. Robertson at CERN WS (May 2006) – Inclusive-recon method has high efficiency but poor S/N. Extrapolation from the present Belle analysis (inclusive-recon. ) 3 s at 1. 3 ab-1 5 s at 3. 7 ab-1 Luminosity (ab-1) – Hadronic tag will provide very clean and ambiguous signals, but very low efficiency. 19

B 0 l+ln Proceeds via box or penguin annihilation SM Branching fractions l d l l Flavor violating channel (B 0 e +m –, etc. ) are forbidden in SM. l d n New Physics can enhance the branching fractions by orders of magnitude. ex. ) loop-induced FCNC Higgs coupling A 0, H 0, h 0 20

B 0 l+l- (e+e-, m+m-, e+m-) Signal regions e+ e– Events observed m+ m– 111 fb-1 e- m + 78 fb-1 B(B 0 e+e–) < 6. 1 × 10 -8 (90%CL) B(B 0 m+m–) < 8. 3 × 10 -8 (90%CL) B(B 0 e+ m–) < 18 × 10 -8 (90%CL) Phys. Rev. Lett. 94, 221803 (2005) B(B 0 e+e–) < 1. 9 × 10 -7 (90%CL) B(B 0 m+m–) < 1. 6 × 10 -7 (90%CL) B(B 0 e+ m–) < 1. 7 × 10 -7 (90%CL) Phys. Rev. D 68, 111101 (2003) 780 pb-1 B(B 0 d m+m-) < 2. 3× 10 -8 (90% CL) 21

B 0 l+l- at B factories ? Pre-LHC era n Present CDF limit; Br(Bs mm) < 2. 3 x 10 -8 (90%CL) is equivalent to Br(Bd mm) < 1 x 10 -9. n Interesting to see results with full Belle/Ba. Bar data. LHC era n Who knows the background at LHC ? n Bs mm from U(5 S) runs at Super-B ? See talk by E. Baracchini – We can study background using the present U(5 S) data! n Bd tt is an unique opportunity at B factories. But, how clean are they ? 22

B 0 t+ t- (Ba. Bar @ 210 fb-1) n Experimentally very challenging (2 -4 neutrinos in the final state ! ) n High sensitive to NP Bs mm at hadron machines n Analysis • Reconstruct one B in a fully hadronic final state B D(*) X =>280 k events • In the event remainder, look for two t decays (t lnn, pn, rn) • Kinematics of charged partilce momenta and residual energy are fed into a neutral network to separate signal and BG Data Nobs=263± 19 Control sample Nexpect=281± 48 @90%C. L. Phys. Rev. Lett. 96, 241802 (2006) 23

Plots to be made… n Region in tanb-m. H for 5 s evidence. – B t n + B D t n – LHC direct search for the same 5 s effect – Other measurements from B decays • B Xsg • B ll n Combine B tn and D(*) tn to show – m. H reach at tanb=30 as a function of L. – Significance at tanb=30 and m. H=500 Ge. V as a function of L. n Precision for Br(tn), Br(mn) and their ratio as a function of L 24

Need to study… n Tagging strategy for neutrino modes – Inclusive recon. – Semileptonic tag. – Hadronic tag. Bar’s B tn search (324 x 106 BB) Tag by B Dln. X Tag B recon. eff. =0. 7% n Data quality in large L environment – Tagging efficiency – Beam background – Neutrino reconstruction Extra energy distribution in Belle’s B tn search 25

Backup 26

New Physics in large tanb n Leptonic decays (B ln, ll) are theoretically clean, free from hadronic uncertainty. n In particular, they are good probes in large tanb region, together with other measurements; Dm. BS, Bs mm, B Xsg and also t decays (t mh, t mg). Ex. ) G. Isidori & P. Paradisi, hep-ph/0605012 H+ t+ Neutral Higgs tanb Charged Higgs A 0, H 0, h 0 See talk by A. Weiler MH(Ge. V) 27

Constraint to Charged Higgs n Once branching fraction is measured, we can constrain R. M. Tanaka, Z. Phys. C 67 (1995) 321 Form factor error r can be determined experimentally by B semiletonic decays at 5 ab-1 28

Future Prospect: B Knn n Belle @ 250 fb-1 (preliminary) cf. ) K. Ikado @ BNM 2006 Fully reconstructed tag (by modifying the PID criteria used in B tn analysis). Belle preliminary Consistent with BG expected Signif. Lum (ab-1) 3 s 12 5 s 33 Need Super-B ! 29