Tau physics with BaBar

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Tau physics with BaBar

• Roger Barlow
• BaBarFest
• QMUL, 1st April 2009

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Overview

• BaBar was a tau factory
• Cross section 0.9 nb
• 850 Million tau leptons
• Compared to LEP
• More statistics
• Better detector
• Less hemisphere separation
• Higher background from q-qbar
• Compared to CLEO and ARGUS
• Way better in every respect

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Catalogue
8 on LFV 6 Branching Ratios 1 general
Search for Second-Class Currents in t - ?
?p-? Search for Lepton Flavour Violating Decays
t- ? l- K0S with the BABAR Experiment Search for
Lepton Flavor Violating Decays t- ? l-
? Measurement of the t- ? ? p- p p- ?t branching
fraction and a search for a second-class current
in the t- ? ?'(958) p- nut decay Improved Limits
on the Lepton-Flavor Violating Decays t- ? l- l
l- Measurement of the t- ? K- p0 ?t branching
fraction Search for Lepton Flavor Violating
Decays t- ? l- p0, l- ?, l- ? Exclusive
Branching-Fraction Measurements of Semileptonic
tau Decays into Three Charged Hadrons, into f p-
?t, and into f K- ?t Search for the decay t- ?
3p- 2p 2p0 ?t Search for Lepton Flavor Violation
in the Decay t- ?e- ? Search for Lepton-Flavor
and Lepton-Number Violation in the Decay t- ?l-
h- h'- Search for the decay t- ? 4p- 3p (p0)
?t Study of the t- ? 3h- 2h ?t decay Search for
Lepton Flavor Violation in the Decay t- ? µ-
gamma Search for Lepton Flavor Violation in the
Decay t?lll
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Lepton Flavour Violation

• Exists in Standard Model (?oscillations)
• Enhanced Beyond the Standard Model (Charged
  Higgs, SUSY, etc) to 10-7, 10-9..
• Large Tau mass makes it good place to look (Higgs
  link)
• t?µµµ,µµe,µee,eee (6 combinations)
• No events. 10 efficiency, small backgrounds,
  limits 1-2 10-8
• t?µ?, e? limits 10-7
• t?µ?, e?
• t?µhh- , ehh-
• t?µp/?/? , ep/?/?
• ???h

No neutrinos Can use visible energy and mass to
isolate signal (like B physics)
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Properties

• Mass measured with 3 prong topology pseudomass
• Mt2Mh22(Et-Eh)(Eh-Ph Cos?)
• Set Cos ? to 1 and get limit
• Mt 1776.68 0.12 0.41 MeV
• M-M--0.61 0.23 MeV
• Lifetime 289.40 0.91 ps

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BranchingRatios

• B(t ? p p p?t ) (8.83 0.01 0.13),
• B(t ? K-p-p?t ) (0.273 0.002 0.009),
• B(t ? K-p-K ?t ) (0.1346 0.0010 0.0036)
• B(t ? K- K-K ?t ) (1.58 0.13 0.12) 10-5
  ,
• B(t - ? fp-?t ) (3.42 0.55 0.25) 10-5 ,
• B(t - ? fK-?t ) (3.390.200.28)10-5
• Br(5pi)(8.52 0.090.40)10-4
• Br(5 prongs p0 p0)
• lt 3.4 10-6(_at_90CL)
• 7 prongs not seen lt 3 10-7,

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QCD
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Hadrons
W
q

• Mass distribution (spectral function)
• These branching ratios
• measures as(Mt)0.3440.0050.007
• Extrapolates to as(MZ)0.12120.0011
• Comparison is nice check of QCD

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Decays with Kaons
Example t?K0sp ? Measure Br(0.8400.0040.023)
Vus0.2146 0.0030
Incompatible with unitarity? Though BR (t?K
?)/BR(t?p ?) is OK
This is also a good channel to look for CP
violation due to charged Higgs
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2nd class currents
t??p?
Does this occur though the b1(1235)
IG(JPC)1(1-) This would be a second class
current forbidden by isospin Would show up as
flat component in angular distribution
2nd class fraction lt 0.7 (90 CL) Limits also
from t??p?, t??p?
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Future

• Many tau analyses not yet complete
• (many not even started)
• Many more results to come Tau10 conference
  should be really exciting