27/September./2008 Satellite Meeting on Super Tau-Charm Factory

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Search for -> /e at the Super--charm Factory

[Comments from Belle experience]

This talk is based on a study done for Super-B factory by T. Iijima, K. Hayasaka

(Nagoya U.)

H. Hayashii (Nara)

27/September./2008 Satellite Meeting on Super Tau-Charm Factory

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Introduction Lepton flavor violation (LFV) in charged lepton⇒negligibly small probability in the Standard Model (SM) even including neutrino oscillation

- Br(→ℓ) <O(10-54)

Why SM + mprediction is so small ?

(or e)

W-

γ

(or e)22* 54

21,2

3( ) 10

32li

i ii w

mBr U U

m

U2 2 2ij i jm m m

: PMNS neutrino mixing matrix

:Neutrino mass square difference

-Lepton Flavor is conserved accidentally.

-If O(1TeV) particles exit, Br is enhanced significantly, Theory needs some suppression mechanism.

-Almost all Beyond Standard Model predict LFV

27/September./2008 Satellite Meeting on Super Tau-Charm Factory

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Status of LFV Decay Searches (Tau08)(based on 　　　　　　 data)

B-f

acto

ryC

LEO

ℓf0(980)

ℓℓℓℓhh’ ℓV0

ℓℓ//0

ℓKs10-7

10-8

10-6

10-5

Upp

er li

mits

for

LF

V

dec

ay

Improve by factor ~100 from CLEO

update from TAU06

500/ fb

27/September./2008 Satellite Meeting on Super Tau-Charm Factory

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→e(PLB666,16(2008)) Data: 535fb-1 Br(→)<4.5x10-8 at 90%C.L. Br(→e)<1.2x10-7 at 90%C.L.

Results from Belle (1) signaldata

→

→(→)→e/+(’) (PLB648, 341 (2007))

Data: 401fb-1

Expected BG : (0.0-0.6) events

Nobs : 1 event Br(→,’,0)<(6.5-13)x10-8 Br(→e,e’,e0)<(8.0-16)x10-8

signal region

Final state: 1-prong decays and others

Remaining many BG from e+e-→+-sensitivity is limits by the background

27/September./2008 Satellite Meeting on Super Tau-Charm Factory

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Super-B and Super -c Factory

B-factory ( nb, root(s)=10.6 GeV)

• L =1036 cm-1s-1 　　 /year Super-B at Roma =3x1035 cm-1s-1 Super KEKB

-c factory ( nb, root(s)=4.25 GeV)

L= 1035 cm-1s-1 3.5x109/year -Final reach depends on , efficiency, background -Typical efficiency in B-factory exp.: 5-10%. -Background

Ldt

27/September./2008 Satellite Meeting on Super Tau-Charm Factory

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Super B-factory

Expected sensitivity→ℓ Br~O(10-8~9) →ℓℓℓ, l+meson Br~O(10-9~10) ▲

Super (KEK)B-factory:(10~50) ab-1

Br(→)<3x10-10@50ab-1

Current UL@BelleBr(→) <3.2x10-8@543fb-1

Super (KEK) B GOAL:

Improve the sensitivity by additional factor of 100 and achieve 10-10

and >e

Background dominated

27/September./2008 Satellite Meeting on Super Tau-Charm Factory

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Some detail of search • 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 regionsignal extraction: ME plane

•blind analysis

-Tag side is not muon.

27/September./2008 Satellite Meeting on Super Tau-Charm Factory

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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

27/September./2008 Satellite Meeting on Super Tau-Charm Factory

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Result of search• Lum:535fb-1(Belle)

•more tight requirements to reduce BG

than the previous 86 fb-1.

•remaining events: 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.

signaldata

2D fit on ME plane

blinded region

27/September./2008 Satellite Meeting on Super Tau-Charm Factory

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BG events in analysis

If we can remove BG events caused by ISR completely…

When we run an accelerator with lower energy than (4s),Can we reduce these ISR BG events?

1.5 ab-1 generic MC sample

removed by MC generator info.

90% events removed!

27/September./2008 Satellite Meeting on Super Tau-Charm Factory

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ISR Spectrum• At near threshold

– E for ee background cannot be as high as E for .– Background from ee will become more important.

good MUID is essential.

s =10.58GeV s =5.0GeV

s =4.25GeV s =4.0GeV

E (CMS) from and ISR()

(4s)

maximum

27/September./2008 Satellite Meeting on Super Tau-Charm Factory

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Summary

• Background source: 1) ISR ee-> 2) ee-> where tag-side muon is miss identified as

pion.• Achievable sensitivity in Super (KEK) B-factory sensitivity

will be limited by ISR BG although there is a room to optimize selection criteria.

• High intensityc factory running at root (s)= 4.25 GeV is ideal place for as well as->e searches.• Very good separation is essential to suppress ee-

> background.

27/September./2008 Satellite Meeting on Super Tau-Charm Factory

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Backup Slide

27/September./2008 Satellite Meeting on Super Tau-Charm Factory

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pair production cross section

• Threshold at 3.55GeV• Maximum at 4.25GeV ( ((4s))x 4)

2 30 4 (3 )

3 2s

: velocity of B-factory