George%20Lafferty

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Tau Physics from the B Factories

• George Lafferty
• University of Manchester
• Charm 2006 International Workshop on Tau-Charm
  Physics
• June 5-7 2006, Beijing

Combining the strengths of UMIST and The Victoria
University of Manchester
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Topics covered

• Tests of the Standard Model
• Tau mass and lifetime lepton
• universality and CPT
• Non-strange hadronic tau decays
• t - ? p-p0n and gm-2
• 5-prong BFs and limits on 7-particle modes
• Strange hadronic tau decays
• Strange spectral functions
• t - ? K-p0n and t - ? K0p-n
• Lepton-flavour violation in tau production
• and decay
• Constraints on physics BSM
• Outlook for tau physics at the B factories

With thanks to Olya Igonkina and everyone else
whose slides I have borrowed from
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Tau-pair production in ee- collisions at ?s MU

• The B factories are also t factories
• At , ?s MU sB B 1.05 nb and s tt-
  0.89 nb ?
• approximately 1M tau pairs per fb-1
• samples of 400M (BaBar) and 600M (Belle) tau
  pairs
• c.f. 100k pairs for each LEP experiment and 14M
  at CLEO
• Much cleaner event environment at LEP means
  much lower
• systematic errors there
• LEP is better for measuring the large branching
  fractions
• B factories are better for rare and forbidden
  decays
• Ongoing work at B factories to reduce systematic
  errors
• Huge statistics at B factories allow detailed
  study of the structure
• of the hadronic mass spectra

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The tau mass and lifetime test CPT and lepton
universality
Belle study using 253 fb-1
Belle hep-ex/0511038
BaBar prelim study using 80 fb-1
BaBar prel.
BaBar NPPS144(2005)105
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Hadronic tau decays t- ? p-p0n and gm-2
Muon magnetic moment anomaly given by am (gm-2)
/ 2
e
p
n
p 0
e-
p -
t -
p -
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Hadronic tau decays t- ? p-p0n and gm-2
Belle study using 72 fb-1 fits to model of
Gounaris and Sakurai
BF (t- ? p-p0n) (25.15 ? 0.04 ? 0.31)
Belle
hep-ex/0512071
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Hadronic tau decays t- ? 3h-2h n
BaBar study using 232 fb-1
kk2fTauola for signal Monte Carlo
BF (t- ? 3h-2h n)
BF (t- ? 3h-2h n) (8.56 ? 0.05 ? 0.42) x 10-4
Phys Rev D72 (2005) 072001
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Hadronic tau decays t- ? 3h-2h n
Resonances in final state include r(770)0 and
f1(1285) mesons
BF (t- ? f1h- n) (3.9 ? 0.7 ? 0.5) x 10-4
Phys Rev D72 (2005) 072001
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Hadronic tau decays Search for t- ? 3p-2p 2p0
n
BaBar study using 232 fb-1

• Decay mode allowed, but highly suppressed by
  phase space
• Observation could limit mass of nt
• Interest in multipion decay dynamics
• Isobar models predict dominance of 2wp-n

BF (t- ? 3p-2p 2p 0n) lt 3.4 x 10-6 BF (t- ?
2wp- n) lt 5.4 x 10-7 at 90
CL
Phys Rev D in press
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Hadronic tau decays Search for t- ? 4p-3p
(p0) n
BaBar study using 232 fb-1
BF (t- ? 4p-3p (p 0)n) lt 3.0 x 10-7 BF (t- ?
4p-3p n) lt 4.3 x 10-7
at 90 CL BF (t- ? 4p-3p p 0n) lt 2.5 x
10-7
Phys Rev D72 (2005) 012003
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Hadronic tau decays strange spectral functions
The route to world-best measurements of Vus and
ms
Branching fractions for strange decay modes
(from PDG 2005)
? 10-3

• All measurements so far are limited by
  statistics
• The total error is important large errors on
  small BFs can dominate
• Systematic errors are highly correlated (e.g.
  charged, neutral kaon ID) and scale with BF

BaBar and Belle preliminary measurements of t ?
Kpn are already better than previous world
averages lots more to come (e.g. Tau 2006)
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Hadronic tau decays t- ? K-p0n
BaBar preliminary study using 124 fb-1
evidence for higher mass resonances
BF (t- ? K-p0n) (0.438 ? 0.004 ? 0.022)
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Hadronic tau decays t- ? K0sp-n
Belle study using 351 fb-1 Fits to mass
spectrum need more than K(892)
BF (t- ? K0sp-n) (0.391 ? 0.004 ? 0.014)
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Lepton flavour violation in t decays
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Lepton flavour violation in t decays
Current BF upper limits for LFV using up to a
few x 100 fb-1
all ? 10-7
BaBar Belle
t- ? m- g t- ? e- g 0.7 1.1 3.4 3.8 Creates most interest Enhanced if mn3 ltlt mn1 mn2
t- ? e- e e- t- ? m- m m- t- ? l- l? l 2.0 1.9 1 3 3.5 2.0 2 4 Can expose SUSY Higgs
t- ? l- h h- t- ? l h- h- t- ? l- V0 t- ? l- K0s 1 3 0.7 5 1.6 8 2.0 7.7 0.5 Violates lepton number Limits MSSM (small tanb) Limits R-violating SUSY Limits scale for dim-6 fermionic operators
t- ? l- p0 / h/ h 2 10 Limits MSSM (large tanb)
t- ? L p- t- ? L p- 0.7 1.4 Violates B-L Conserves B-L
-

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Lepton flavour violation Search for t ? lepton
hh/V
Recent Belle results from 158 fb-1

• MSSM with small tanb could
• give BF(t - ? m-r0) 10-8
• Also t - ? e-r0 and m-r0 constrain
• models with heavy Dirac
• neutrinos
• Limits also on models with
• dimension-six effective fermionic
• operators that induce t m mixing

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Lepton flavour violation Search for t- ? m- h
Belle BF (t- ? m-h ) lt 3.4 x 10-7
MSSM SUSY
Belle
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Lepton flavour violation Search for t- ? m- g
BaBar BF (t- ? m- g ) lt 8.6 x 10-8
MSSM SUSY with seesaw
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The outlook

• Current results based on a few x 100 fb-1
• Expected final BaBar and Belle datasets 2 x gt
  1 ab-1
• ? gt 2 billion ?-pairs by
  end 2008
• Statistical accuracy will improve by up to ?5
• Improvements in muon detection (BaBar), and
  further work
• ongoing to reduce systematic errors (e.g. on
  p0 efficiency)
• Potential for lots more ? physics
• Improved limits on LFV (down to 10-8 for some
  channels)
• possible evidence for New Physics
• can probe regions that are inaccessible at LHC
• Strange spectral functions should give best
  measurements of Vus, ms (and maybe as)
• Important contributions to resolving the muon g ?
  2 problems
• Structure of non-strange and strange hadronic
  states
• CP-violation in t decays

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And to finish on behalf of the UK Tourist Board
another great wall
Hadrians Wall, built 122-132 AD