Sanjay K Swain, SLAC BABAR Collaboration 27th July 2007

Outline• Introduction• l (l = e, )• lKs

• lP0 (P0 =’)• lll / lhh (h = K, )• h• Conclusion

-decays in B-factories

Lepton Flavor Violation (LFV) in -decays • In the minimal Standard Model, the lepton flavor is conserved for each generation

e.g is not allowed LLL = 1 L =0 L 1 L = -1 but L = 0

• But neutrino oscillation implies:

e => Lepton Flavor is violated

• The LFV in neutral sector induces LFV in charged lepton sector

ee-

Le =1 L L L = Le + L + L

But B) M

Mw2

2

Mw ~ 1011 eV

M2 ~ 10-3 eV2

~ 10-54

Lee-Shrock, Phys. Rev. D 16, 1444 (1977)

New physics phenomena in -decays

Things would be completely if we replace

Now B) MMx

2

M and Mx have different (higher) mass scale~~

2

The slepton have same lepton numbers and do have mixing

~ ~

The branching fraction can be enhanced significantly

1.

2.

2

KEKB at KEK

BelleBaBar

9GeV (e) 3.1GeV (e+)peak luminosity:

1.121034cm2s1

8GeV (e)3.5GeV (e+) peak luminosity:

1.711034cm2s1

PEP-II at SLAC

B-factories

Two asymmetric energy B-factories

PEP-IIfor BaBar

July 2006

KEKBfor Belle

KEKB + PEP-II

710/fb (Jan 07)710/fb (Jan 07)

391/fb (Jan 07)391/fb (Jan 07)

Integrated Luminosity

more than 1 billion (109) -pairs

Cross Section 1.05 nb 0.92 nb

-decay topology

e+e-

electron/muon

Signal side

Tag side

tag

missing

• Two hemispheres thrust (separated in space)

• Signal side: neutrino-less 1-prong decay electron / muon (all the particles are fully reconstructed)

• Tag side: 1-prong or 3-prong e

MEC : beam energy constrained mass

E: energy difference E - Ebeam

Sometimes, variables used are Eand M = Mrec – M

Signal MC

-1.0 0.51.5

2.0M

ec (

Gev

/c2 )

E (Gev) 0.0

±3 blinded region

±2 signal region

For lthe expected background in the signal box is obtained by fitting the sidebands of MEC distribution from the ±2 band in E where as

for lP0, the background is obtained by 2D un-binned maximum likelihood fit to un-blinded region in MEC and E.

We look for the expected and observed backgroundin the neighboring regions to validate the fit

Analysis methodology

GSB: E[-1.0, 0.5] and MEC[1.5,2.0]

For lP0: -0.8

Results from l

Efficiency=2.99%

BF (e ) < 12 x10-8

Efficiency=5.07%

BF ( < 4.5 x 10-8

Efficiency=(4.7±0.3)%

BF (e ) < 11 x10-8

Efficiency=(7.42±0.65)%

BF ( < 6.8 x 10-

8

PRL 96, 041801 (2006)

PRL 95, 041802 (2006)

ar-Xiv:0705.0650 [hep-ex]

Signal MC

Data

MSSM with seesaw:

Results from land impact on new physics

tan<vu>

<vd>

Vu,d are VEVs of neutral higgs coupledto up-type or down-type fermion fields

S. Banerjee (Tau06)Nucl. Phys. Proc.Suppl. 169, 199 (2007)

lKs (l= e or ) BELLE used 281 fb-1 data

B (eKs ) < 5.6 x 10-8

@90% CL

B (Ks ) < 4.9 x 10-8

In R-parity violating SUSY scenario , ’, ’’ ( with 45 couplings)

2. This result can be used to constrain new physics scale in dimension-six fermionic effective operator involving flavor violation motivated by neutrino oscillations

1.

lower bounds on axial-vector and pseudo-scalar operators: 36.2TeV and 37.2 TeV

PLB 639, 159 (2006)

decays lKs via tree level scalar neutrino exchange by ’ coupling

Signal MC

Data

Signal box(±2 in E and MEC)

Shaded regioncovers 68% ofsignal MC

Total expected events = 3.1

Total observed events = 2

lP0 (P0 = ’)

Using 339 fb-1 data, the upper limit is (1 - 6 ) x 10-7

Data

PRL 98, 061803 (2007)

401

fb-1

data

These improved upper limit can be used to constrain the parameters of Heavy Dirac neutrino model.

Branching fractions of different modes are evaluated in terms of Model Parameters: ye and y

Using lye 0.17 and y@ 90% C.L

lP0 (P0 = ’)

PLB 648, 341 (2007)

The left plot shows the Exclusion regions in the mA and tan plane bydifferent experiments

New result from BABAR

Competitive with the direct Higgs searches at CDF and D0

(@ 95% C.L.)

Constraining new physics using result

M.Sher, PRD 66, 057301 (2002)

CDF: pp H fb_

D0: pp H bbfb _

_

fb-1S.Banerjee (Tau 06) Nucl. Phys. Proc. Suppl. 169, 199 (2007)]

376 fb-1 BABAR data used

Total expected events = 4.2Total observed events = 6

90% of the selected MC events

Signal box

lll ( l = e or )

Upper limits ~ ( 4 – 8) x 10-8

lhh’ and lV0

Belle used 158 fb-1 datah (h’) K or V0 K

These improved upper limit can be used to constrain the parameters of Heavy Diracneutrino model.

Using lye2 < 0.24 and y

@ 90% C.L

Constraint the energy scale of dimension-six fermionic effective operator

uu,dd 29.4TeV, ss 24.8 TeV and ds 26.8 TeV

1.

2

Signal Box

Decay modes used:

[ e, ] x [ +-, --, +K-,K+-,K--,K-K+,K-K-,

0, k*0, K*0, ] _

22 decay modes

The upper limit varies (1.6 - 8.0) X 10-7

VectorPLB 640, 138 (2006)

(including modes violating total lepton number)

• The baryon asymmetry of the universe Baryon number violation (Sakharov condition)

• For lepton -> baryon + meson decays, the angular momentum conservation requires, (B-L) = 0 or 2

The following decays modes used in this analysis: (237 fb-1)

Lepton and baryon number violating -decay

(hep-ex: 0607040)

• If LFV is discovered in near future, it is possible that LFV-inducing particles will be produced directly at high energy. The LFV effects from real particles production may then also be seen at colliders

• Further probe into the LFV using more data can put constraint on different theoretical models.

• None of the lepton flavor violating processes has been observed yet.

• For l, the best upper limit is ~ 4.5 X 10-8

• For lP0, the best upper limits are ~ (1-9) X 10-8

• For lKS, the upper limits are ~ 5 X 10-8

• For lll (hh’), the upper limits are ~ (1 - 8) X 10-8

Summary