Post on 16-Jan-2016
description
Search for LFV tau decays
K.Inami (Nagoya-u) for the Belle collaboration
and eelll
Weak Interactions and Neutrinos workshop 2003/10/6-11 @ Lake Geneva
2003/10/6-11 Weak Interactions and Neutrinos workshop 2003 @ Lake Geneva 2
KEKB collider Asymmetric energy
e+:3.5 GeV, e-: 8 GeV for CPV search with B0
Very high luminosityLpeak=1.061034cm-2s-1
Int. L > 158fb-1
World record
1.44108 tau-pair events
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Belle detector F/B asymmetric detector
KLM (KL and detector) Efficiency > 90% Fake rate < 1.5%
for P>1.0 GeV/c ECL (Elec. calorimeter)
Electron and gamma e ID efficiency > 95% Fake rate < 1% Energy resolution
1.8% at E=1.0 GeV
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Forbidden in SM, while new physics allows LFV.ex. SUSY GUT with R (PRD59, 116005)
LFV through slepton mixing in the SUSY loop Br() = <10-6
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Analysis of 86.3fb-1 data (7.9x107 tau-pairs)
Select low-multiplicity events Signal side
Muon-ID High-momentum photon
Tag side Not-muon (to reject ee ) Missing momentum () ea1…
Main background ee
ee
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Event selection
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Event selection (2)
Tau-pair: neutrinos in both side Larger effective missing mass
Removed events by this selection- 24% signal- 98% tau-pair BG
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Signal Signal yield is evaluated
by likelihood fit methodfrom E-vs-Minv plot. (E = EEbeam in CM)
Signal distribution : tail due to initial radiation and energy leakage in calorimeter
To avoid bias on analysis,Blinded signal region 1.70<Minv<1.85 GeV/c2
Signal MC
Resolution by asymmetric GaussianE:75.4/33.7MeV, M:23.1/15.0MeV
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Background Main background
ee (N) with initial-state radiation, beam BG ee (N) due to muon inefficiency in tag side
Background shape (p.d.f. for likelihood fit) estimated by MC for N and data (both tracks be muons) for N
expressed by Gaussian + Landau function.Data(x ineff.= N)
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Selected sample
5 region: 54 observed events
- Good agreement between BG function and selected data- No peak around signal region
1.71<Minv<1.82GeV/c2
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Unbinned Extended Maximum Likelihood fit
Si : Signal probability density from MC simulation
Bi : BG probability density from MC(N) and data(N)
s, b : Number of signal and BG events (free param.)
s = 0, b = 54
Likelihood fit
5 region
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Result of Br() Systematic uncertainty
Signal yield : s0Muon-ID ineff. +0.06/-0.11 ev. BG function ±0.3 ev.Fit region 0.07 ev.
Efficiency & Luminosity : 2NTrack rec. eff. 2.0%Photon rec. eff. 2.8%Selection criteria 2.2%Luminosity 1.4%Trigger eff. 1.6%MC statistics 0.8%Total
4.7%
Br()<3.110-7 at 90%C.L.
Result
Upper limit : Toy-MC ( I.Narsky, NIM A450,444(2000) )
s0 = 5.1 event for 90% C.L.
= 11.0%N = 78.5106 (86.3fb-
1)
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e Analysis : same as 87.1fb-1 data (7.9x107 tau-pairs)
Background source tau-pair (fake gamma)
5 signal region20 observed events6.5% efficiencyS0= 3.8 for 90%C.L.
Br(e)<3.610-7 at 90%C.L.
e, preliminary
Preliminary result by likelihood fit
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, e and lll Constrained MSSM Higgs-mediated model
The anomalous LFV Yukawa coupling for Higgs boson is generated radiatively and not suppressed by the SUSY scale.
LFV is generated by Higgs mediation and B.R.s are comparable.
M. Sher, PR D66 057301 (2002)K.S. Bubu and C. Kolda, PRL 89, 241802 (2002)A. Dedes, J. Ellis, and M. Raidal, PL B549, 159 (2002)
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84.3fb-1 (7.8x107 tau-pairs)
Event selection:Essentially same as
BG: Signal region: ellipse
Bayesian method
Result of Br(, e)preliminary
e
data
signal MC
Preliminary result
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Result of Br(lll) 87.1fb-1 (7.9x107 tau-pairs)
Select 1-3 topology
BG: ee qq Count with signal box
Feldman&Cousins method
Selected data, preliminary
1 observed event: two-photon(eeee)?
Preliminary result
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Summary Search for LFV
use 7.9x107 tau-pairs
Br()<3.110-7
Br(e)<3.610-7 Br()<3.410-7
Br(e)<6.910-7
Br(lll)<1.4~3.110-7
at 90%C.L.
3~30 times higher sensitivity than previous results
1.44108 tau-pairs are ready. Br ~ 10-8 level in near future.