Search for LFV decays involving ’ at Belle

Y. Enari, Belle collaboration

Nagoya University

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 2

Motivation

• In MSSM at large tanmay have alarge branching ratio by Higgs mediated process.

• Comparison other mode.Mslepton > weak scale, Br( is not large.

M. Sher, Phys.Rev.D66 05731(2002)K.S.Babu PRL,89,241802 (2002)A. Dedes, et.al. PLB 549,2442 (2002)

is important process!!

Br() : Br(3) : Br() =

a. (ms/m)2

b. color factor c. phase space

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 3

110-7

Status of LFV decay search

Belle 3l

CLEO result (PDG2004)

Today’s report.

1/L @ ~ 9%

1/L @ ~3%

In MSSM, Br of LFV decay may have O(10-7~10-9).

Babar 3l1/ L @ ~3%

Efficiency BG level

l 3l.

l

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 4

KEKB & Belle detector

Lpeak = 13.91033/cm2/sec

Ldt = 287.85 fb-1

Cross section @ s =10.58GeV

: 0.9 nb

BB : 1.0 nb

KEKB is Factory!!!.

-ID eff. = 87.5% fake = 1.4 %

e-ID eff. = 92.4% fake = 0.25 %

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 5

Analysis.

• Modes

– e

– e•

– e ’, ’• ’

• Blind analysis

Blind region

±10

±5

±10

Invariant mass : M= E2

- p2

Energy difference : E = E – Ebeam

*

Blind region: -0.5< E < 0.5(GeV),

-5 < M < 5

Evaluation # of signal event

- Low BG level Counting signal candidates

using elliptical region

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 6

’

Selection criteria (l l l ’)

• Signal event reconstruction signal side ( e’) + tag side (1 trk + n+ missing.)

• BG suppression For QED BG.

– NOT (e) (for 1-1prong)– 5 < ECM

< 10.GeV

For qq and BG– 0 veto for ’s – 0.5 < cos < 0.95

– Mtag < 1.777 GeV/c2

– missing momentum towards tag side.– pmiss vs. mmiss

2 2-D cut.

total

Br(1 prong) = 84 %

(1prong or 3 prong)

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 7

Background suppression (1)Bhabha, , 2photon process

Total energy

not-(e or in tag side.

(Only 1-1 prong modes)

Hadronic process (u,d,s,c)

generic process

Opening angle

signal :　 5% loss : 80% reject.

sig : 2% loss : 67% rej.uds: 65% rej.

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 8

Background suppression(2)

• missing particle : pmiss towards detectable regions.

　　 signal event : is in only tag side costhrust-miss< -0.55 　 BG event : are in both sides

Effective missing mass

black: signal MC Blue: generic

After all kinematical cut applied: (except e/ ID for signal side)

eff.( = 3.8 10-6.

eff.(uds) = 3.0 10-7.

eff.( = 3.4 10-8.

eff.(ee) = 3.0 10-7.

signal : 17% loss : 95% reject

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 9

Mass distribution

• ’ mass peak.

(ID; 1.3<M<2.1; with Blind)

~5.2 MeV/c2 ~ 14 MeV/c2

m’ region

m– m

~12 MeV/c2

m– m

data:57ev. MC:48.1±4.0 data: 77ev. MC:81.6 ± 8.4data:109ev. MC:100±5.9

BG: Fake /K (80%) l 0 : true 0

others : mis-combination

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 10

E vs Minv. : l 0, l , l ’

BG estimation Nexp is calculated from the side band events

with assuming a flat distribution.Open blind.

Nexp=3.1±1.0

Nexp=0.15±0.15

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 11

E vs Minv. : l 0, l , l ’

BG estimation Nexp is calculated from the side band events

with assuming a flat distribution.Open blind.

Nexp=3.1±1.0

Nexp=0.15±0.15

Systematic uncertainties - eID:1%, ID: 2%, track: 2%, 0 veto 5.5%

Beam BG:2.3% Trigger:1.4% 4.5~8.7% - BG estimation: If Nexp<1, assume Nexp=0.

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 12

Result

Br is obtained from

• Upper limit evaluation (POisson Limit Estimator program)– Feldman-Cousins method

s02( BX N)

B =s0: signal events : efficiencyN: # of pairs

BX : B of sub-decay

Systematic uncertainty: using the Gaussian error.

First search!!

J. Conrad et al., PRD 012002 (2003)

Preliminary

10-70 timestighter limitfrom PDG2004

140M

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 13

Discussion - - (1)

• Statistics 4.7fb-1 154fb-1

• Signal efficiency

7.2%B 8.0%B

not use 7.2%B

• Observed events 0 1

CLEO Belle 33

1.7

Keeping BG level low.

Comparison with CLEO result

B () < 1.310-7@ 90% C.L.

Upper limit : B () < 9.6 10-6

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 14

Discussion - - (2)

Constraint on tan vs mA

Preliminary

• CDF result : measurement (ppA/bbbbbb)• LEP result : LEP Higgs Working Group,

PRL 86,4472 (2002)

http://lephiggs.web.cern/LEPHIGGS/paper/Note2001-04

B () < 1.310-7@ 90% C.L.

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 15

• Search for l l l ’ meson mode using 154fb-1.

• No indication of signal events.

B(l l l ’) < 1.3 ~ 1010–7 @ 90%C.L.. 10-70 times tighter bounds. First searches in e’, ’.

Summary

1/L @ ~ 9%

1/L @ ~3%

1/ L @ ~3%l 3l.

l

Preliminary

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 16

Backup slides

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 17

Signal efficiency and BG - muon mode -

side bandMC : data : b0

12.5±2.7 132.7 ± 0.7

0.8 ± 0.32

0.6 ± 0.4

9.2 ± 2.39

3.1 ± 1.0

5.5 ± 1.95

1.4 ± 0.6

(153.8, 428, 232, 160 fb-1)

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 18

Signal efficiency and BG - electron modes -

side bandMC : data : b0

0.7±0.7 0 0 – 0.0

0.0 ± 0.71

0.23 ± 0.23

0.0 ± 0.71

0.15 ± 0.15

0.8 ± 0.31

0.16 ± 0.16+0.4

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 19

Result: l 0, l , l ’

5ev./2.7±0.7

1ev./0.2±0.2

1ev./3.1±1.0

0ev./0.0+0.4 0ev./0.2±0.2 0ev./0.2±0.2

0ev./0.6±0.4 0ev./1.4±0.6

Preliminary

= 4.7% = 6.8% = 5.7% = 8.5%

= 6.4% = 7.2% = 8.0% = 8.4%

-0.0

Nobs/Nexp

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 20

History of integrated luminosity

Continuous injection

2003 Summer: SVD/CDC inner partreplacement

Ldt = 154fb-1

Ldt = 288fb-1

Ldt = 244fb-1

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 21

KEKB

HER: 8.0 GeV e–

LER: 3.5 GeV e+

Lpeak = 13.9×1033/cm2/sec

Ldt = 287.85 fb-1

Cross section @ s =10.58GeV

: 0.9 nb

BB : 1.0 nb

performance snap shot (2004.3.1)Continuous injection mode

LER 1.6A

HER 1.1A

L ~ 1.1×1034/cm2/sec

KEKB is Factory!!!.

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 22

Belle detector

/ KL detection 14/15 lyr. RPC+Fe

Central Drift Chamber small cell +He/C2H5

CsI(Tl) 16X0

Aerogel Cherenkov cnt. n=1.015~1.030

Si vtx. det. 3 lyr. DSSD

TOF conter Scinti + FM-PMT

SC solenoid 1.5T

8 GeV e

3.5 GeV e

-ID eff. = 87.5% fake = 1.4 %

e-ID eff. = 92.4% fake = 0.25 %

proton ID eff. ~ 70 % fake ~ 1 %

E resol.E /E = 1.8% @E=1GeV

Trk. resol. pt/pt ~ 0.19pt 0.30/ %

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 23

Status of LFV search in Belle

New result of this summer.CLEOBabar

Belle Published Preliminary

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 24

Summary table of LFV search in Belle

Preliminary result

Published resultsNew result in this summer.

First search result.

B < O(10-7) are obtained

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 25

Systematic uncertainty

• Related sensitivity

• Related BG– Using statistical error as systematic error. (30~45%)

– If b0 < 1, we set b0=0 in order to obtain conservative limit.

In Total : 4.5 ~ 8.7 %

POLE program

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 26

2.1 Selection criteria ( 1-3 prong + ’)

– 1-3 prong + n2

E > 0.1 GeV , barrel and endcap

ptrk>0.06GeV/c barrel.

ptrk >0.1GeV/c endcap. net charge=0.

dzrms < 1cm, drrms < 1cm to reject junk track.

signal side: eID > 0.9 + 2trk(+,–).

– Missing momentum towards tag side.– pmiss vs. mmiss

2 2-D cut.– 0.5 < cos’ < 0.92– -3 < M < 3

using thrust axis, divide 2 hemisphere

for tag side, mtag < 1.777 GeV/c2

’

e/

9/15/2004 Search for LFV tau decay involving neutral meson at Belle 27

2.2 Selection criteria (1-1 prong + )

– 1-1 prong + n 2

signal side:

eID > 0.9 + 2 .

Pe>0.7GeV/c, E > 0.22GeV

– 0 veto for ’s

tag side:– NOT (e)

– Mtag < 1.777 GeV/c2

Kinematical cut.

– Missing momentum towards tag side.

– pmiss vs. mmiss2 2-D cut.

– 0.5 < cos’ < 0.92

– -5 < M < 3

e/