ICHEP06 - Moscow

Lepton Flavor ViolationSearches at B-FactoriesK.Hayasaka (Nagoya U.)

On behalf of Belle and BaBar

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Introduction

• New Physics (NP) search with Lepton Flavor Violating (LFV) decays– LFV decays are forbidden in the SM

Observation of LFV is a clear signal of NP.– lepton is expected to be strongly coupled to NP. proportional to (m)n >> (m)n,(me)n

• Results to be reported in this talkllh0(h0=0,,’,Ks)hh,K

l+V0(V0=,K*,K*,)e+el

n=1 n=2

(m/m)n ~16 ~300

(l=e)

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• A B-factory is also a -factory! ()~0.9nb, (bb)~1.1nb

• DetectorsF/B asymmetric high momentum particle ID capability

• Accumulated data:

>4.5x108 -pairs at Belle, >3.0x108 -pairs at BaBar

Br~O(10-8) sensitivity!

B-factories

500fb-1

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Results of LFV searches

• results up to 2005mode x10-7 mode x10-7

BaBar 0.68 lll 1.13.5

e Belle 3.1 ee BaBar 1.1

Belle 1.5 ee Belle 1.9

e Belle 2.4 lhh BaBar 0.74.8

' Belle 10 BaBar 0.7

e' Belle 4.7 lV0 CLEO 2075

Belle 4.1 e0 CLEO 20

e Belle 1.9

Ks CLEO 9.5 Belle 1.4

eKs CLEO 9.1 Belle 0.72

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History of searches

Before B factories B factories

# of pairs

10-1/10-year improvement achieved

10-1/4or5-year improvement?

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New physics and

• Most promising LFV decay modee.g. MSSM+ seesaw model• Br(ee) / Br() ~1/94• Br()/ Br() ~ 1/440 • assuming

426

TeV160

tan100.3)(

SUSYM

Br

1 LR

hep-ex/0406071

slepton

gaugino

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Analysis of search I

• e+e+

ee

generic decay

signal event

(signal side)

1 prong + missing ( tag side)

)( 22 pEM

CMbeam

CM EEE

0~,~ EmM

for signal event

signal MC

3 ellipse: blinded region

Signal extraction: ME plane

•Blind analysis

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Analysis of search II

• Main BGs:– +ISR ()– +ISR

• Requirement on missing mass useful to reduce BG

(signal: 1or2; :>2)• Signal extraction:

– Unbinned Extended Maximum Likelihood fit

likelihood function:

e

e

ISR

BG: +ISR

e

e

ISR

BG: +ISR

generic decay

signaldata

N

iBGsig

bs

bPDFsPDFN

e

1

)(

)(!

L

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Previous search

• BaBar( 232 fb-1)– Signal detection eff.: 9.4%– Not only 1-prong but 3-prong events in tag side; 8.8%9.4%– Neural Network selection – Beam energy constraint mass

• Signal distribution: – 1D UEML fit with 2 E band– s= 2.2, b= 143 (prob. 30%)

Br<6.8x10-8 at 90%CL

Phys. Rev. Lett. 95, 041802 (2005)

)(22 CMCM

beamEC pEM

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New search

• Belle(535fb-1)

preliminaryno signal events are found.

distribution in 2 band

•Analysis similar to the previousone of 86fb-1 data sample

•Tighter requirements to reduce BG

•Remaining events: 54ev./86fb-1 94ev./535fb-1

•Signal detection eff.: 11% 6.7%

•Signal region: 5box 2ellipse

•Signal extraction: UEML fit

Result:s=-3.9, b=13.9 (allow negative s and its prob. 25%)

Br<4.5x10-8 at 90%C.L.

proj

ectio

n

signaldata

2D fit on ME plane

blinded region

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Development of results on

• MSSM + seesaw42

6

TeV160

tan100.3)(

SUSYM

Br

old newLuminosity: 86fb-1 535fb-1 (x 6.2)U.L. of Br: 3.1x10-7 4.5x10-8 (x 6.8)negative signal yield: forbidden allowed

New result

tan

0

100

80

60

40

20

0 1 2 3 4mSUSY (TeV/c2)

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New results on e

• Belle(535fb-1) • BaBar(232fb-1)

preliminaryBr<12.0x10-8 at 90%CLPhys. Rev. Lett. 96, 041801(2006)

Br<11.0x10-8 at 90%CL

Select 2 or 4 tracks eventsSignal extractionCounting method in 2 boxeff: 4.7%

Select 2 tracks eventsSignal extraction:2D UEML fit in 2 ellipseeff: 3.0%

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New physics and

• Higgs mediated model predicts a process …

In the case of Higgs mediated model,

decay may be observed earlier than .

PRD 66, 057301 (2002).

427

GeV10060

tan104.8)(

AMBr

1:5.1:4.8

)3(:)(:)(

BrBrBr

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Previous result for

• Belle(154fb-1)– Not only but are

used for analysis.– eff. 8.0%(),7.2%()– By reconstructing mass,

BG can be suppressed.

– main BGs: + qq– Signal extraction

• Counting method

– Br()<1.5x10-7

Phys. Lett. B622, 218 (2005)

generic decay

e

e

e e

generic decay

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New result from BaBar

• BaBar(315fb-1)• Counting method in 2 box

on MECE plane mode– eff: 7.0%– Nexpexted=0.64– Nobserved=1 mode– eff: 3.7%– Nexpexted=0.07– Nobserved=0

• combined 2 modes

preliminary

Br<1.6x10-7

2 box

data

a region which contains 70% of signal MC events

hep-ex/0607045

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New result from Belle

• Belle(401fb-1) • Based on previous analysis of Belle• Counting method in 90% ellipse

on ME plane mode– eff: 6.4%– Nexpected=0.40– Nobserved=0 mode– eff: 6.8%– Nexpected=0.24– Nobserved=0

• combined 2 modes

preliminary

Br<6.5x10-8

90% ellipse:a region whichcontains 90% ofsignal MC events

signaldata

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Impact on SUSY of

427

GeV10060

tan104.8)(

AMBr

Our result has good sensitivity in comparison with Tevatron results.

Higgs mediated model predictsD0

CDF

Belle(90%CL)

BaBar(90%CL)

CDF• search/310pb-1

D0• search/325pb-1

• bb search/260pb-1

Belle(95%CL)

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New results onh0 / eh0(h0=,,’)

• Belle(401fb-1)• Based on previous analysis, optimize

d requirements mode by mode.(Lum.:154fb-1401fb-1)

• e’ / ’ : ’ mode is now included.– eff.: 4.3%(e’ ,’),

4.8%(e’ ,’)– 4.9%(’ ,’),

5.4%(’ ,’)

• Main BGs:– : – othersnegligible small BGs

preliminaryBr(e)<9.2x10

Br(e’)<1.6x10

Br(e)<8.0x10 Br()<1.2x10

Br(’)<1.3x10

signaldata

3-6 times more sensitive results obtained

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New result onKs / eKs

• Belle(281fb-1)Ks eKs

Phys. Lett. B639, 159(2006)

Br(Ks)<4.9x10-8 Br(eKs)<5.6x10-8

Main BGs:D lKs, Ks But negligible

signaldata

signal region

eff.:13.5%Nexpected=0.2Nobserved=0

eff.:11.8%Nexpected=0.2Nobserved=0

previousresultCLEO:14fb-1

Ks:<9.5x10-7

eKs:<9.1x10-7

20 times improvement!

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Results onV0 / e+V0 (V0=,K*,K*,)

e e

ee

• Belle(158fb-1) Br<(2.0~7.7)x10-7

accepted by PLB

hep-ex/0603036

e e

lepton

h

hV0

BGs for some modes are negligible because requirements for V0 mass efficiently reduce BGs.Main BGs: +qq (V0) +2photon (eV0)

generic decay

signal boxdata

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Previous resultonh (h=,K)

• Belle(154fb-1)– First search– Baryon number violati

ng process– Not only (B-L) conserving process

but (B-L) violating process– pBr

eff.:11.8%(),

11.7%()

Main BGs: (a1), qq

– Br()<1.4x10-7

– Br()<7.2x10-8

Phys. Lett. B632, 51 (2006)

generic decay

e e

p

signaldata

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New results onh (h=,K)

• BaBar(237fb-1)– First search for

eff.: Nobs Br<5.9x10-8

eff.: Nobs Br<7.2x10-8

preliminary

(B-L

) vi

olat

ing

(B-L

) co

nser

ving

hep-ex/0607040

signaldata

eff.: Nobs Br<5.8x10-8

eff.: Nobs Br<15x10-8

Consistent with proton decay prediction

Br~O(10~-30) (Phys. Rev. D72 095001)

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Result on e+e+l(l=e,)

• signal extraction– 2D UEML fit

(m-pl plane)

(ee)<4.6fb (eee)<10.1fb

at 95%CL

massleptonmomentum

eeee-

e+e/

3LBr

s

:eff. Br:Br of tag side mode L:lum.

22 |||)|( CMCMCM ppEm

• BaBar(211fb-1)

preliminary

hep-ex/0607044submitted to PRD

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Summary

•Data samples of B-factory ( -factory ):>500fb-1

•Studies of LFV decays have made great progress and now reach the O(10-8) level.

•No signals are found in any of the LFV decay modes.• is the most sensitive to possible NP.• is predicted to have largest BR by Higgs

mediated model.

•Many ULs of Br for LFV are updated by the results of B-factories…

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Results of LFV searches

mode x10-7 mode x10-7

Belle 0.45 lll 1.13.5

e BaBar 1.1 +ee BaBar 1.1

Belle 0.65 ee+ Belle 1.9

e Belle 0.92 lhh BaBar 0.74.8

' Belle 1.3 + BaBar 0.7

e' Belle 1.6 lV0 Belle 2.07.7

Belle 1.2 0 Belle 2.0

e Belle 0.80 BaBar 0.59

Ks Belle 0.52 BaBar 0.58

eKs Belle 0.60 BaBar 0.72

BaBar 1.5

red: shown results in this talk