Lepton Flavour Violation

Transcription

1 Michael Roney University of Victoria (Babar Collaboration) Electroweak Session, La Thuile, March 10-17, 2007

2 A bit of history the importance of earnestly seeing nothing μ γ μ γ μ γ μ μ μ

3 History of e-muon LFV Searches MEG MECO (?) hadronic FC (see Hogan Nguyen KTeV & Philip Bechtle Babar B π πeμ)

4 By beginning of 21 st Century: established! θ 12, θ 23 θ 13 eglee Shrock PRD α Δm τ μγ = θmixbr τ μνν PRL mw BR π τ eγμ eγ

5 Many SM extensions predict observable Charged LFV ν e.g.so(10) inspired model with SUSY imbedded in GUT Calibbi et al PRD 74(2006) univ. gaugino mass

6 μ γ, τ μγ μγ τ γ

7 PHYSICS RUN EXPECTED TO START IN AUTUMN 2007

8 Focus on in decays lepton-mass dependent couplings parameter space in some models touch current limits different sensitivity to 2-body & 3-body decays which mode will be discovered first is unknown Well motivated searches: complementary to potential LHC discoveries: Limits (or discovery!) will better constrain theories

9 B-Factory Detectors

10 Integrated luminosity

11 μπρτ γ ε signal event e τ τ μ γ e generic τ decay

12 cut based selection Neutal Net based selection

13 mass: γ γ σ σ signal region typically defined as 2σ box or ellipse Δ μγ σ Δ

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15 Preliminary Belle result on τ μγ signal data 94 events in 535 fb -1 σ σ σ # of events (b) s(90% CL) = 2.0 events Br<4.5x10-8 at 90%C.L hep-ex/

16 Preliminary Belle result on τ eγ 20 events within 5σ in 535 fb -1 σ σ # of events σ (b) s(90% CL) = 3.34 events Br<1.2x10-7 at 90%C.L hep-ex/

17 For each of the 6 channels, fit background shapes from MC with an unbinned maximum likelihood fit to (M ec vs E) Overall normalization taken from data 3σ GSB data σ tot σ = tot GSB σ data GSB σ

18 hep-ex/ PRL (2007) expected background/channel ~ Total expected background=3.1, Observed=2

19 τ μ μ π μ η μ η π 0 η η

20 τ π + π + π π π + π + + π +

21 Phys.Lett.B640: ,2006 τ τ ρ 0 μ - ρ 0 K (892) 0 K (892) 0 φ μ - K (892) 0 μ - K (892) 0 μ - φ

22 Summary of 90%CL Upper Limits on LFV τ decays Channel Belle BaBar μ γ μ π μ η γ π 0 η hh

23 σ ε±σ ε ±σ

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26 m = GeV > A = GUT μ

27 ν m ν R L GeVβ μ > A = M = = M E

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29 LFV in tau decays: how far can we go? BR UL N N N N bkg N N bkg UL UL bkg bkg N bkg

30 LFV in tau decays τ μγ τ μνν + ISRγ Δ

31 LFV in tau decays τ μγ NB: Not clear how to do this without some efficiency losses dropping mu-tag - significant efficiency loss using lifetime information? more refined tagging analysis

32 LFV in tau decays τ τ Situation different for neutrinoless 3-prong decays: no significant irreducible background (analogous QED radiative decays are suppressed by another α factor and lepton masses) negligible effect Backgrounds are at O(1) event per mode level. With no change to the analyses 1ab -1 expected 90%CL UL ~3-9x expt Best case analysis: no irreducible backgrounds, so expected limits could scale as get limits ~10-8

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36 τ - μ γ γ Br Lum. fb -1 < < Br, 10-7 Lum. fb -1 < < μ μ < < μ < < μ μ μ + < < μ μ < < μ < < < <