Search for Lepton Flavor Violating Tau decays at B-factory

2006/2/27-3/2 K.Inami Nagoya university, Belle

- Introduction- Experimental results- Future prospects- Summary

International workshop e+e- collisions from phi to psi

2006/2/27-3/2 International workshop e+e- collisions from phi to psi at BINP 2

Lepton flavor violating decays have a very small probability in the Standard Model (even with neutrino oscillation).

New physics effects (SUSY, Extra-D, etc.) may allow us to observe LFV with the present experimental sensitivity.

Previous results from CLEO were sensitive to Br~O(10-6).

The B factories (Belle and BaBar) have sensitivities of O(10-7~10-8).

Introduction

2006/2/27-3/2 International workshop e+e- collisions from phi to psi at BINP 3

B-factories Asymmetric-energy e+e- coll

ider at Upsilon(4S) For CPV search with B0

Very high luminosity Integrated luminosity

>500fb-1 for Belle >300fb-1 for BaBar

Tau factory! ()~0.9nb, (BB)~1.1nb

300fb-1

500fb-1

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Detectors at B-factories F/B asymmetric detectors

Good vertex resolution and particle ID ability

Accumulated data: >4.5x108 -pairs at Belle, >3.0x108 -pairs at BaBar

Br~O(10-8) sensitivity!

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Analysis method Event Selection

Low multiplicity events Separate into hemispheres

Signal and tag sides Missing momentum

Low missing mass Small N Lepton tag etc.

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Analysis method (2) Signal extraction

Calc. Minv and E E=Erec-Ebeam

Blinded signal region Event selection study

Estimate backgroundusing sideband data

Open blind and estimate signal yield

Estimate upper limits

BG reduction is important to improve the sensitivity.

Signal MC of Signal

region

Background

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Belle

86.3fb-1 data

Br<3.1x10-7 at 90%C.L.PRL 92, 171892 (2005).

BaBar 232fb-1 data

Br<0.68x10-7

PRL 95, 041802 (2005). Background: + ISR

Small contamination of BG in E>0

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: Belle vs BaBar Belle : Br<3.1x10-7 / 86.3 fb-1

= 11.1% 2D EML fit with 5 signal box Nsignal= 0, NBG= 54

Nsignal is constrained to be 0.

BaBar : Br<0.68x10-7 / 232 fb-1

= 9.4% 1D EML fit with 2 E band Nsignal= 2.2, NBG= 143

N is allowed to be negative. Negative yield gives lower U.L. tha

n expected.

Belle : 5 box

BaBar : 2 band

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BaBar 232fb-1 data

Br<1.1x10-7

PRL 96, 041801 (2006).

e Belle

86.7fb-1 data

Br<3.9x10-7 at 90%C.L.PLB 613, 20 (2005).

Background: e + ISR

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l Belle: 87.1fb-1, BaBar: 91.5fb-1

PLB 598, 103 (2004), PRL 92, 121801 (2004).

Br<(1.1~3.5)x10-7 at 90%C.L.

Background: low level qq around E<0, QED( or Bhabha) around E>0

Belle’s results

Signal region

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lhh Belle: 158fb-1, BaBar: 221fb-1

Br<(1.6~8.0)x10-7 by Belle (preliminary) Br<(0.7~4.8)x10-7 by BaBar, PRL 95, 191801 (2005).

Background: qq(flat) and (corner) ehh: negligible BG level

BaBar’s results

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l0//’ Lepton + Pseudoscalar

meson

Belle: 154fb-1

Br()<1.5x10-7

Br < (1.5~10)x10-7

PLB 622, 218 (2005).

Background : + qq e: negligible

Data qq

’

e

e

e’

Signal region

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lKs Belle: 281fb-1

Br(Ks)<0.52x10-7

Br(eKs)<0.60x10-7

(Preliminary, hep-ex/0509014) Most stringent U.L. among tau L

FV searches High efficiency (14%,12%) and

Low BG

Background: negligible D± l±Ks, ±Ks

Ks

eKs

Belle preliminary

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lV0

Lepton+Vector meson Belle: 158fb-1

Br<(2.0~7.7)x10-7

(Preliminary)

Background: V0: + qq eV0: +2photon (eeeeuu, eess etc.)

Belle preliminary

e e

ee

Signal region

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Baryons p, p0

Belle (preliminary) B(p)<3.0x10-7 (87fb-1) B(p0)<6.5x10-7 (154fb-1) Background: many , qq

p/ misidentification

Belle: 154fb-1

B()<1.4x10-7

B()<0.72x10-7

PLB 632, 51 (2006). Background: (a1), qq

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B.R. summary

Br < O(10-6) in PDG (by CLEO) Br < O(10-7) by Belle and BaBar

New Physics

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For Future B-factories are accumulating data stably.

Currently, >7.5x108 -pairs in two B-factories. However, improvement of LFV sensitivity will be sl

ow. Non-negligible backgrounds

Need better / separation Low energy -factory may have an advantage.

Effects of ISR and qq may be reduced.

/

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Future prospect Super B-factory : >10 times more data

B.R. sensitivity: ~1/n for negligible BG case ~1/n for BG dominated modes

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Future prospect (2) Possible sensitivity with Super B-factory

Red band for 5~10ab-1

SuperB-factory

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Summary A data sample of >7.5x108 -pairs has been succe

ssfully obtained by the B-factories. LFV sensitivities are Br~1x10-7.

Exploring possible parameter space of New Physics

For some modes, it will be hard to improve the sensitivity due to backgrounds. Better muon identification Tau-factory at around energy threshold may be better to

reduce ISR effects.?

Super B-factory will produce 1010 -pairs at 10ab-1. LFV sensitivity will reach Br~O(10-9).

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Effect to physics parameter MSSM with Seesaw

PRD 60, 055008 (1999).

Higgs mediated in MSSMPRD 66, 057301 (2002).

Heavy Dirac neutrino modelPRD 62, 0306010 (2000).

B(lV0) constrain y2e and y2

.