Tau Physics near Threshold

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Tau Physics near Threshold. Achim Stahl RWTH Aachen University. Beijing, June 2006. Basic Tau Properties. mass: 1.777 GeV. lifetime: 290.6 10 -15 sec c τ = 87.11 m m. approx. 100 known decays. υ τ. τ. f. W. f’. s in nb. √s in GeV. 4 p a 2 3 s. 3 – b 2 2. - PowerPoint PPT Presentation

Transcript of Tau Physics near Threshold

  • Achim StahlRWTH Aachen UniversityBeijing, June 2006

  • mass: 1.777 GeVlifetime: 290.6 10-15 sec c = 87.11 mmapprox. 100 known decaysWff

  • tau production near thresholdfor L = 1033 / cm2 s1 year [email protected] s = 1 nb 107 t-pairs

  • t-pairsbackgroundset points1. below threshold s = 3.50 s = 0 nb1 nb 107 tt

  • t-pairsbackgroundset points1. below threshold s = 3.50 s = 0 nb2. at threshold s = 3.55 s = 0.1 nb1 nb 107 tt

  • t-pairsbackgroundset points1. below threshold s = 3.50 s = 0 nb2. at threshold s = 3.55 s = 0.1 nb3. below Y(2s) s = 3.68 s = 2.4 nb1 nb 107 tt

  • t-pairsbackgroundset points1. below threshold s = 3.50 s = 0 nb2. at threshold s = 3.55 s = 0.1 nb3. below Y(2s) s = 3.68 s = 2.4 nb4. max. cross section s = 4.25 s = 3.5 nb1 nb 107 tt

  • Taus are produced at rest (Tauonium atom) Highly efficient and clean tagging of taus Kinematic decay channel identification Excellent particle identificationNon-Tau background measured below thresholdLow cross section (0.1 nb)Experimentally most favored situationNot good for rare decays

  • Kinematics of 2-body decaystt had ntphad (mhad)pmeasured - phad (mhad) = 0 ?

    kinematic constraint for example:t p nt pp = 883 MeVt K nt pK = 820 MeVhadnt

  • kinematic decay identificationt p ntt K ntt m nm nt

  • kinematic decay identificationt r nt p p0 ntt a1 nt p p0 p0 ntt p nt p p0 ntEmeasured - Ehad (mhad)fast simulation: finite p-resolution finite E-resolution realistic g efficiency fake g from hadrons

  • kinematic decay identificationt r nt p p0 ntt K* nt K p0 ntEmeasured - Ehad (mhad)fast simulation: finite p-resolution finite E-resolution realistic g efficiency fake g from hadrons

  • tthadToFmost difficult decay:t p nt vs. t K nt bp = 0.987 t = 3.34 nsecbK = 0.856 t = 3.88 nsecfor 1m flight distancewith 100 psec resolution at least 5 s separationTime-of-Flight

  • low mass drift chambert p nt pp = 883 MeVt K nt pK = 820 MeVmomentum resolution < 1%(BES-III design 0.5% @ 1 GeV)particle-ID through dE/dx (ex. BaBar)

  • Electromagnetic Calorimeter hermeticity minimal dead material best resolution CsI(Tl) crystalsabout 45% of all t-decays contain at least 1 p0BELLE

  • Hadron Calorimeterabout 1.5% of all t-decays contain a K0K0S drift chamberK0L hadron calorimeter almost all physics can be done with K0S some veto capability against K0L would be good muon identification with hadron calorimeter

    high granularity, medium resolution, no muon chambers

  • tau-masssystematics limited! beam-calibration energy spread efficiency background

  • PDG: 140 decay modes (excluding LFV)All have their own interesting aspectsExamples:enn / mnn lepton universalitypn / Kn fp, fKpp0n CVC, r, r, rhpn 2nd class current

  • describe the mass spectrum of hadrons produced in t-decayssensitive to: aS, mS, qC, many QCD testsexample: running of aSt-decays

  • OPAL Euro. Phys. J. C35 (04) 437non-strange vstrange vnon-strange astrange alarge uncertainties; especially in the strange sectorapprox. 500 ev.+ 500 bgd

  • ALEPH Eur. Phys. J. C11 (99) 599normalizationof the spectralfunction:branching ratios

  • tnthadronsorleptonsM = 4 G/2 S giel | Gi | n nt | Gi | tS,V,TL or RL or R(example: leptonic decays)derived from spectraand angular distributions

  • model independent interpretation:search for arbitrary new currentsbut leptonicdecays

  • the LHC will probably tell us what to look for.wild guess:Precise measurement of couplings at tau-charm-factory~

  • QCD tests + as:non-strange spectral function (much better resolution!)strange spectral function (real measurement, v/a, )2nd class currents, Wess-Zumino anomalycPT: test predictionsExclusive decays:many branching ratios can be improvedlight meson spectroscopy (i.e. r, r, r0 vs. r)Tau-mass:can you reduce calibration systematics compared to BES II?Michel parameters:substantial improvements possibleyou will probably know, what you are looking forVUS from inclusive strange decays:theory under control?Exotics:CP-violation in tau-decays(g-2)t

  • What you cannot do at tau-charm: rare decays (i.e. lepton-flavor violation) tau lifetime ( universality with m-decays) CP-violation in t-production (needs high q2) neutral current couplings nt mass (once was a very hot topic)

  • 1 month @ threshold: 100.000 very clean tau pairs enough to improve many existing measurements understand background and efficiency for higher energy running

    1 month below threshold calibrate non-tau background tune u,d,s Monte Carlos During the initial running period:During a later stage:More running @ thresholdUse high energy runs for some topics

  • Tau physics near threshold:Excellent experimental conditions for high precision measurementsNeeds an excellent detector, but all requirementswithin today's possibilitiesNeeds an excellent accelerator, with luminosity 1033/cm2 s and a not too large energy spreadMuch to be done, despite CLEO, LEP, b-fact

    TitleCross section; running pointsProperties of taus at thresholddecay kinematics of taus at restpi versus Krho Monte Carlorho Monte CarloDetector wishesBread and ButterExamples for branching ratiosQCD with taus strange spectral functionMichel parametersConclusions: comparison with b-factories