Search for LFV tau decays

K.Inami (Nagoya-u) for the Belle collaboration

and eelll

Weak Interactions and Neutrinos workshop 2003/10/6-11 @ Lake Geneva

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KEKB collider Asymmetric energy

e+:3.5 GeV, e-: 8 GeV for CPV search with B0

Very high luminosityLpeak=1.061034cm-2s-1

Int. L > 158fb-1

World record

1.44108 tau-pair events

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Belle detector F/B asymmetric detector

KLM (KL and detector) Efficiency > 90% Fake rate < 1.5%

for P>1.0 GeV/c ECL (Elec. calorimeter)

Electron and gamma e ID efficiency > 95% Fake rate < 1% Energy resolution

1.8% at E=1.0 GeV

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Forbidden in SM, while new physics allows LFV.ex. SUSY GUT with R (PRD59, 116005)

LFV through slepton mixing in the SUSY loop Br() = <10-6

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Analysis of 86.3fb-1 data (7.9x107 tau-pairs)

Select low-multiplicity events Signal side

Muon-ID High-momentum photon

Tag side Not-muon (to reject ee ) Missing momentum () ea1…

Main background ee

ee

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Event selection

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Event selection (2)

Tau-pair: neutrinos in both side Larger effective missing mass

Removed events by this selection- 24% signal- 98% tau-pair BG

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Signal Signal yield is evaluated

by likelihood fit methodfrom E-vs-Minv plot. (E = EEbeam in CM)

Signal distribution : tail due to initial radiation and energy leakage in calorimeter

To avoid bias on analysis,Blinded signal region 1.70<Minv<1.85 GeV/c2

Signal MC

Resolution by asymmetric GaussianE:75.4/33.7MeV, M:23.1/15.0MeV

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Background Main background

ee (N) with initial-state radiation, beam BG ee (N) due to muon inefficiency in tag side

Background shape (p.d.f. for likelihood fit) estimated by MC for N and data (both tracks be muons) for N

expressed by Gaussian + Landau function.Data(x ineff.= N)

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Selected sample

5 region: 54 observed events

- Good agreement between BG function and selected data- No peak around signal region

1.71<Minv<1.82GeV/c2

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Unbinned Extended Maximum Likelihood fit

Si : Signal probability density from MC simulation

Bi : BG probability density from MC(N) and data(N)

s, b : Number of signal and BG events (free param.)

s = 0, b = 54

Likelihood fit

5 region

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Result of Br() Systematic uncertainty

Signal yield : s0Muon-ID ineff. +0.06/-0.11 ev. BG function ±0.3 ev.Fit region 0.07 ev.

Efficiency & Luminosity : 2NTrack rec. eff. 2.0%Photon rec. eff. 2.8%Selection criteria 2.2%Luminosity 1.4%Trigger eff. 1.6%MC statistics 0.8%Total

4.7%

Br()<3.110-7 at 90%C.L.

Result

Upper limit : Toy-MC ( I.Narsky, NIM A450,444(2000) )

s0 = 5.1 event for 90% C.L.

= 11.0%N = 78.5106 (86.3fb-

1)

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e Analysis : same as 87.1fb-1 data (7.9x107 tau-pairs)

Background source tau-pair (fake gamma)

5 signal region20 observed events6.5% efficiencyS0= 3.8 for 90%C.L.

Br(e)<3.610-7 at 90%C.L.

e, preliminary

Preliminary result by likelihood fit

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, e and lll Constrained MSSM Higgs-mediated model

The anomalous LFV Yukawa coupling for Higgs boson is generated radiatively and not suppressed by the SUSY scale.

LFV is generated by Higgs mediation and B.R.s are comparable.

M. Sher, PR D66 057301 (2002)K.S. Bubu and C. Kolda, PRL 89, 241802 (2002)A. Dedes, J. Ellis, and M. Raidal, PL B549, 159 (2002)

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84.3fb-1 (7.8x107 tau-pairs)

Event selection:Essentially same as

BG: Signal region: ellipse

Bayesian method

Result of Br(, e)preliminary

e

data

signal MC

Preliminary result

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Result of Br(lll) 87.1fb-1 (7.9x107 tau-pairs)

Select 1-3 topology

BG: ee qq Count with signal box

Feldman&Cousins method

Selected data, preliminary

1 observed event: two-photon(eeee)?

Preliminary result

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Summary Search for LFV

use 7.9x107 tau-pairs

Br()<3.110-7

Br(e)<3.610-7 Br()<3.410-7

Br(e)<6.910-7

Br(lll)<1.4~3.110-7

at 90%C.L.

3~30 times higher sensitivity than previous results

1.44108 tau-pairs are ready. Br ~ 10-8 level in near future.