τ Physics at B-factories.

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1 τ Physics at B-factories. University of Oregon March, 006 B-factories are τ-factories Standard Model tests Analysis of hadronic τ decays Searches for lepton flavour violating τ decays

2 τ physics at Υ(4S) Number of B and τ produced are very comparable σ B B Υ(4S) = 1.05 nb σ τ + τ Υ(4S) = 0.89 nb The cross-section at Υ(4S) is just a bit smaller than at production threshold σ τ + τ s=3.6gev 1. nb Number of τ decays recorded : ARGUS , CLEO , BABAR , BELLE τ decays : 1-prong τ lνν, πν, ρν, etc (85.35 ± 0.07)% 3-prong τ h h + (nπ 0 )ν τ (15.19 ± 0.07)% 5-prong τ 3h h + (nπ 0 )ν τ (1.00 ± 0.06) prong τ 4h 3h + (nπ 0 )ν τ < l = e, µ, h = π or K, n 0 DIF06

3 τ physics at Υ(4S) Typical 1-3 ττ event Decay products of taus are well separated in space and easily reconstructed (except ν). Backgrounds are 1. radiative Bhabha, di-muon events (mostly leptons). low multiplicity hadronic events (more isotropic, more neutrals) 3. two-photon events (large E miss and small p T ) Huge sample of ττ events with high purity DIF06 3

4 B τ factories detectors Multipurposes spectrometers: tracking with momentum measurement particle identification : e, µ, π, K, p reconstruction of neutrals large (although not complete) acceptance L = 330 fb 1 L = 550 fb 1 DIF06 4

5 Standard Model Tests τ mass, lifetime lepton universality CPV studies More tests (not discussed here): τ electric dipole moment, τ anomalous magnetic dipole moment, ν τ helicity, Michel parameters DIF06 5

6 τ Mass Measurement Pseudomass technique : M = M3π + (E beam E 3π )(E 3π p 3π ) M ν = 0, M < M τ, applied to τ 3πν, check with τ 3ππ 0 ν Systematics uncertainty(mev) Track momenta 0.39 Fit, MC stat 0.41 E beam 0.5 PID, backgrounds negligible Total 0.6 M τ = ( ± 0.5 stat ± 0.6 sys )MeV PDG: M τ = MeV hep-ex/ , Belle Preliminary, L = 53 fb 1 Entries/0.8MeV M τ + known bias 1.7 ISR 1.76 can be improved with L 1.8 M 1.84 (GeV) DIF06 6

7 7deg tau flight projection 00 um beam spot X: 100 um Y: 15 um 3 prong tau decay in plane transverse to the beams 00 um 106 micron 4 mrad (magnified by 10 in the drawing) τ Lifetime Measurement 530 um calculate λ τ = λ T sin Θ 3pr and then fit λ τ (φ) to minimize systematics τ τ = (89.40 ± 0.91 stat ± 0.90 sys )fs PDG: τ τ = (90.6 ± 1.1)fs Can be improved with L NPPS144(005)105, BABAR Preliminary, L = 80 fb 1 λτ Entries Underflow Overflow 0 Events per 160 µm data τ + τ - uds cc bb (µm) Systematics τ τ (%) Measurement bias ± 0.0 Background ± 0.14 Alignment ± Beam spot position ± Beam spot size ± Beam momenta ± τ mass ± τ momentum ± Total ± λ τ DIF06 7

8 Lepton Universality g e = g µ = g τ Extract lepton charged current coupling constants from τ leptonic decays ( g e g µ ) = B(τ eνν) B(τ µνν) (1 + C rad (1 + C rad τe ) τµ ) ( g µ g τ ) = (1 + Crad (1 + C rad τe ) µe ) τ τ τ µ ( m τ m µ ) 5 B(τ eνν) courtesy of A.Lusiani From PDG04 τ leptonic decays and new τ τ, m τ averaged with PDG04 g e g µ = ± g µ g τ = ± 0.00 Perfect agreement with SM DIF06 8

9 Tests of CPT violation M τ + M τ = 0.1 ± 0.45 stat ± 0.15 sys M τ + M τ M τ < at 90% CL hep-ex/ , Belle Preliminary, L = 53 fb 1 Entries/0.8MeV Belle τ τ τ τ + τ τ +τ τ + = (0.1 ± 0.3 stat ± X sys )% 400 NPPS144(005)105, BABAR Preliminary, L = 80 fb 1 00 the measurements are statistically limited, as many systematic uncertainties are canceled M 1.84 (GeV) DIF06 9

10 CP violation in τ decays SM ν non-sm ν τ h 1 τ h 1 W H h h F v = m ρ m ρ s im ρ Γ ρ (s) F s = Λ e iθ CP f s e iδ s, f s = 1 or BW(scalar h 1 h ) Interference between F v and F s due to CP violation would show up as a difference in decay angle distribution of τ and τ + DIF06 10

11 I I I I CLEO CP violation in τ decays CLEO, L = 13.3fb 1, PRL88(00)111803, PRD64 (001)09005 MC, no CP MC, max CP fs = 1 ( a ) fs = 1 ( b ) fs = BW[a0(980)] fs = BW[a0(980)] fs = BW[a0(1450)] fs = BW[a0(1450)] Analysis of variable ξ = P odd /P even optimized for interference of W and H, ξ is function of helicity and mass of (h 1 h ). Arbitrary Scale τ Kπν 0.17 < Λ sin Θ CP < (90%CL) f s = BW (K (1430)) τ ππ 0 ν < Λ sin Θ CP < 0.0 (90%CL) f s = 1 Very little from B-factories yet: only Belle preliminary result in 001 on L = 6.7fb 1 without yet full analysis of systematics. However, CLEO limits are statistically limited - Belle/BABAR should be able to improve, although hard work on systematics is anticipated. DIF06 11

12 Hadronic τ decays spectral functions non-strange: τ π π 0 ν = a had µ strange: τ X (S= 1) ν = m s and V us 5-prong τ decays search for 7-prong τ decays DIF06 1

13 τ ππ 0 ν The largest and the most studied τ decay keeps its secrets: Should it be used for calculation of anomalous magnetic moment of muon of not a SM µ = a QED µ + ( a had,lo µ + a had,ho µ + a had,lbl µ ) + a weak µ a had,lo µ = α (0) 3π 4m π ds K(s) s σ e + e hadrons(s) σ e + e µ + µ (s) 73% of a had,lo µ is covered by two pion final state dominated by ρ(770) resonance due to QED kernel K(s). Assuming isospin invariance : σ I=1 e + e π + π = 4πα m τ 6 V ud (1 + C rad ) s B(τ π π 0 ν) B(τ eνν) dn π π 0 N π π 0ds ( (1 s m τ )(1 + s m τ ) ) 1 comparison of g- results with SM: a exp µ a SM µ = (5. ± 9.) (e + e : CMD, KLOE ) a exp µ a SM µ = (9.4 ± 10.5) (τ: ALEPH, CLEO) DIF06 13

14 τ ππ 0 ν hep-ex/051071, Belle Preliminary, L = 7. fb 1 Gounaris-Sakurai fit of the unfolded M (π π 0 ) from τ decays (corrected for efficiency and resolution). a ππ µ = (46.4 ± 0.6 stat ± 3. sys ±.3 isospin ) a exp µ a SM µ = (11 ± 10.5) (τ: Belle) Good agreement with previous τ data DIF06 14

15 Strange spectral functions Analysis of τ X (S= 1) ν allows to improve m s, V us using OPE via moments of the spectral function R kl τ = M τ 0 ds(1 s m τ ) k ( s m τ ) l B(τ X (S= 1) ν) B(τ eνν) dn X (S= 1) N X (S= 1)ds R kl τ are calculable in OPE +phenomenological hadronic parametrization OPAL DIF06 15

16 Extraction of V us and m s J.Prades et al, hep-ph/ δr kl τ Rkl τ,v +A V ud Rkl τ,s V us δr 00 τ has small dependence on m s, take m s (GeV) = (95 ± 0)MeV and OPAL data = V us = 0.08 ± exp ± th - Competative with V us = 0.00 ± from K e3 [PDG] use above V us and high order moments (,0),(3,0), (4,0) from OPAL = m s (GeV) = (81 ± )MeV simultaneous fit of m s and V us is forseen, but is awaiting new data DIF06 16

17 Strange spectral functions, experimental perspectives From online PDG005, [10 3] B(τ Kν) 6.86 ± 0.3 B(τ Kπ 0 ν) 4.50 ± 0.30 B(τ Kην) 0.7 ± 0.06 B(τ Kπ 0 ν) 0.58 ± 0.3 B(τ K3π 0 ν) 0.38 ± 0. B(τ π K 0 ν) 8.9 ± 0.4 B(τ π K 0 π 0 ν) 3.7 ± 0.4 B(τ π K 0 π 0 ν) 0.4 ± 0.4 B(τ Kππ 0π 0 ν) 3.9 ± 0.4 B(τ X (S= 1) ν) 9.3 ± 0.8 All available measurements are statistically limited The total error is important - channel with small B gives equally bad uncertainty The systematics uncertainties are largerly correlated and scale with B The potential of B-factories is fantastic - e.g. preliminary BABAR result with 14fb 1 B(τ Kπ 0 ν) = (4.38 ± 0.04 stat ± 0. sys ) 10 3 The improvement can be expected in statistics but also in systematics DIF06 17

18 Study of τ 3h h + ν B(τ 3h h + ν) = (8.56 ± 0.05 ± 0.4) 10 4 BABAR, L = 3fb 1, PRD7(005) BABAR OPAL ALEPH CLEO PDG Events/0.04 GeV/c BABAR Data Signal MC Tau MC qqbar M(5π) Mass (GeV/c (GeV/c ) ) B(τ 3h h + ν) Clear disagreement with MC based on phase-space distribution DIF06 18

19 Resonance structure in τ 3h h + ν BABAR, L = 3fb 1, PRD7(005)07001 Events/0.04 GeV/c 3 isospin (3h h + ) states are allowed and of them contain ρ meson BABAR K S Data Signal MC Bkgd MC ρ M(π + π ) (GeV/c Mass ) ρ contribution is evident (h h + ) mass exhibit f 1 meson Events/0.006 GeV/c BABAR M(π + π Mass (GeV/c ) (GeV/c ) ) B(τ f 1 h ν τ ) = (3.9 ± 0.7 ± 0.5) 10 4 agrees with SM ( ); confirms CLEO observation DIF06 19

20 Search for τ 4π 3π + (π 0 )ν decay SM prediction < 10 9 BABAR, L = 3fb 1, PRD7 (005) Entries per 5 MeV/c B(τ 4π 3π + (π 0 )ν) B(τ 4π 3π + ν τ ) B(τ 4π 3π + π 0 ν τ ) BABAR Pseudo Mass (GeV/c ) ε = (9.4 ± 0.6)% N bgr = 1.6 ± 1. N obs = 4 Entries per 5 MeV/c BABAR Pseudo Mass (GeV/c ) ε = (5.5 ± 0.3)% N bgr = 3.9 ± 0.8 N obs = 8 Entries per 5 MeV/c BABAR Pseudo Mass (GeV/c ) ε = (3.6 ± 0.3)% N bgr = 8. ± 0.5 N obs = 7 B(τ 4π 3π + (π 0 )ν) < B(τ 4π 3π + ν τ ) < B(τ 4π 3π + π 0 ν τ ) < at 90% CL (Bayesian UL calculation) 10 times improvement first measurement DIF06 0

21 Lepton Flavour violating τ decays DIF06 1

22 Theoretical expectations for τ LFV τ ν τ ν µ µ W W γ τ W µ µ + W + µ + τ µ H 0 µ + µ τ ν χ χ γ µ Model τ lγ τ lll Ref. SM + lepton mixing hep-ph/ SM + left-h. heavy Dirac neutrino < < SJNP5(1977)340 SM + right-h. heavy Majorana neutrino < 10 9 < PRD66(00) SM + left and right-h. neutral singlets < 10 8 < 10 9 PRD66(00) msugra + seesaw < 10 7 < 10 9 hep-ph/006110, hep-ph/ , etc SUSY SU(5) < 10 4 hep-ph/ SUSY flipped SU(5) < 10 7 hep-ph/ SUSY SO(10) < 10 8 < hep-ph/009303, hep-ph/ SUSY anomalous U(1) < 10 7 hep-ph/ neutral SUSY Higgs < < 10 7 hep-ph/ charged SUSY Higgs triplet < 10 7 hep-ph/ MSSM+nonuniversal soft SUSY breaking < < 10 6 hep-ph/ Non universal Z (technicolor) < 10 9 < 10 8 PLB547(00)5 two Higgs doublet III < < hep-ph/ extra dimensions < hep-ph/ DIF06

23 Lepton Flavor Violation in τ decays Upper limits ( 10 7 ) at 90% CL BABAR Belle τ µ γ most discussed τ e γ enchanced if m ν3 m ν1 m ν τ e e + e τ µ µ + µ can expose SUSY Higgs τ l l ± l (1-3) (-4) τ l h + h (1-3) τ l + h h (0.7-5) violates lepton number τ l KS τ l π 0, η, η -10 τ Λπ 0.7 violate B L τ Λπ 1.4 conserve B L Both collaborations are actively searching for τ LFV decays. The samples are to be doubled in a year DIF06 3

24 LFV constrains on SUSY Parameter space Obtained limits can be used to constrain e.g. different SUSY models, or to set model independent limits on off-diagonal elements of slepton mixing matrix. m1/, GeV τ µγ in msugra-nur, tanβ = 55 stau is LSP allowed by CDM super-b factory M L3 /M L model independent limits from τ µγ now Babar in Babar+Belle in Babar+Belle in now LEP excluded no RESB m0, GeV tanβ = 55, m 1/ = m m 0 (GeV) Experimental sensitivity of B-factories to LFV τ decays start to probe region sensitive to SUSY contributions. However, it is not yet sufficient to discriminate between different models DIF06 4

25 Conclusions B-factories have a right to be called τ-factories The samples of τ decays collected by BABAR and Belle allows to perform high precision SM tests, detailed study of rare τ decays and search for physics beyond SM. Number of important measurements such as strange spectral functions, CP violation in τ decays and analysis of sub-resonant structure of haronic τ decays are to be performed soon. BABAR and Belle might be lucky to observe lepton flavour violation in τ decays, however the sensitivity is limited to 10 8 branching fractions. A lot of hard and interesting work is ahead of BABAR and Belle. But, there will be tasks left for future experiments DIF06 5