Tau physics with BaBarTau physics with BaBarRoger BarlowBaBarFestQMUL, 1st April 2009

OverviewOverviewBaBar was a tau factoryCross section 0.9 nb850 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

1st April 2009 2Roger Barlow: Tau Physics with BaBar

ττ

ττ

ττ

ττ

ττ

ττ

ττ

ττ

τ

ττ

ττ

ττ

ττ

ττ

ττ

τ

ττ

ττ

ττ

ττ

ττ

ττ

ττ

ττ

τ

CataloguCataloguee

1st April 2009 3Roger Barlow: Tau Physics with BaBar

Search for Second-Class Currents in τ − → ωπ−νSearch for Lepton Flavour Violating Decays τ- l- K0

S with the BABAR ExperimentSearch for Lepton Flavor Violating Decays τ+- l+- ωMeasurement of the τ- η π- π+ π- ντ branching fraction and a search for a second-class current in the τ- η'(958) π- nuτ decayImproved Limits on the Lepton-Flavor Violating Decays τ- l- l+ l-

Measurement of the τ- K- π0 ντ branching fractionSearch for Lepton Flavor Violating Decays τ+- l+- π0, l+- η, l+- η’Exclusive Branching-Fraction Measurements of Semileptonic tau Decays into Three Charged Hadrons, into φ π- ντ, and into φ K- ντ

Search for the decay τ- 3π- 2π+ 2π0 ντ

Search for Lepton Flavor Violation in the Decay τ+- e+- γSearch for Lepton-Flavor and Lepton-Number Violation in the Decay τ- l-+ h+- h'-

Search for the decay τ- 4π- 3π+ (π0) ντ

Study of the τ- 3h- 2h+ ντ decaySearch for Lepton Flavor Violation in the Decay τ+- μ+- gammaSearch for Lepton Flavor Violation in the Decay τlll

8 on LFV6 Branching Ratios 1 general

Lepton Flavour Violation Lepton Flavour Violation Exists in Standard Model (νoscillations)

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)

τμμμ,μμe,μee,eee (6 combinations)

No events. ~10% efficiency, small backgrounds, limits 1-2 10-8

τμω, eω limits ~10-7

τμγ, eγ

τμh+h- , eh+h-

τμπ/η/η’ , eπ/η/η’

ΤΛh

1st April 2009 4Roger Barlow: Tau Physics with BaBar

No neutrinosCan use visible energy and mass to isolate signal (like B physics)

PropertiesProperties

Mass measured with 3 prong topology ‘pseudomass’

Mτ2=Mh

2+2(Eτ-Eh)(Eh-Ph Cosθ)

Set Cos θ to 1 and get limitMτ= 1776.68 ±0.12 ±0.41 MeV

M+-M-=-0.61 ± 0.23 MeV

Lifetime 289.40 ± 0.91 ps 1st April 2009 5Roger Barlow: Tau Physics with BaBar

BranchingBranchingRatiosRatios

B(τ → π π πντ ) = (8.83 ± 0.01 ± 0.13)%,B(τ → K−π−π+ντ ) = (0.273 ± 0.002 ± 0.009)%,B(τ → K−π−K+ ντ ) = (0.1346 ± 0.0010 ±0.0036)% B(τ → K− K−K+ ντ ) = (1.58 ± 0.13 ± 0.12) × 10−5 , B(τ − → φπ−ντ ) = (3.42 ± 0.55 ± 0.25) × 10−5 ,B(τ − → φK−ντ ) = (3.39±0.20±0.28)×10−5 Br(5pi)=(8.52 ±0.09±0.40)×10-4 Br(5 prongs + π0 π0) < 3.4 10-6(@90%CL) 7 prongs not seen < 3 10-7,

2009 6Roger Barlow: Tau Physics with BaBar

QCDQCD

Mass distribution (spectral function)These branching ratiosmeasures

αs(Mτ)=0.344±0.005±0.007

Extrapolates to αs(MZ)=0.1212±0.0011

Comparison is nice check of QCD1st April 2009 Roger Barlow: Tau Physics with BaBar 7

τ

W

ν

q

q

Hadrons

Decays with KaonsDecays with Kaons

1st April 2009 8Roger Barlow: Tau Physics with BaBar

Example: τK0sπ ν

Measure Br=(0.840±0.004±0.023)%

|Vus|=0.2146 ±0.0030

Incompatible with unitarity?Though BR (τK ν)/BR(τπ ν) is OK

This is also a good channel to look for CP violation due to charged Higgs

22ndnd class currents class currents

1st April 2009 9Roger Barlow: Tau Physics with BaBar

τωπν

Does this occur though the b1(1235) IG(JPC)=1+(1+-)This would be a second class current – forbidden by isospinWould show up as flat component in angular distribution

2nd class fraction < 0.7% (90% CL)Limits also from τηπν, τη’πν

FutureFutureMany tau analyses not yet

complete(many not even started)

Many more results to come – Tau10 conference should be really exciting

1st April 2009 Roger Barlow: Tau Physics with BaBar 10