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Tau-pair analysis for LoI+

Tau-pair analysis for LoI+. Taikan Suehara ICEPP, The Univ. of Tokyo. Tau-pair process. Difficulty on decay analysis. [Observables] P(e - )=80%, P(e + )=30%, 500 fb -1 σ, A FB (bg suppression) Polarization P( t ) ↑ Decay angle determination.

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Tau-pair analysis for LoI+

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  1. Tau-pair analysis for LoI+ Taikan Suehara ICEPP, The Univ. of Tokyo

  2. Tau-pair process Difficulty on decay analysis [Observables] P(e-)=80%, P(e+)=30%, 500 fb-1 • σ, AFB(bg suppression) • Polarization P(t)↑Decay angle determination σ=2600 fb-1 (e-Le+R)σ=2000 fb-1 (e-Re+L) radiative events: ~70%

  3. Progress • Looser tau-selection cuts – to improve statistical error (compatible with SiD). • More background of Bhabha and gg-tt • Better decay-mode selection by a neural network • ‘Optimal observable’ for polarization measurement

  4. Background events • SM background of the mass production • 2-photon and Bhabha have low statistics. • Bhabha – re-preselection • Compatible with looser cut |cos(q)| < 0.95 • |cos(q)|<0.96, opening angle < 15 deg • ~200k events for 1 fb-1 • 2 photons – tautau • Preselection cuts:Opening angle < 10 deg, Evis > 30 GeV • ~150k events for about 10 fb-1

  5. Tau selection cuts • Signal increase: ~20% • Evis cut changed: 40 to 70 GeV • Background level: almost the same • Results are still worse than SiD about 20%... • Might be difference on tau-clustering: they accept neutral clusters

  6. Mode separation – 1 prong • Need to separate leptonic, pinu, rhonu.(Also a1nu if possible) • Neural net tried • Variables (9 params) • Ecalo/Etrack (muon ID) • EECAL/(EECAL + EHCAL) (electron ID) • Echarged , Eneutral ,En3 (Third-largest photon energy),Nn • Mall, Mn w/neutral hadrons, Mn wo/neutral hadrons • 18-10 hidden neurons, 5 output neurons • Selected among 16-10, 16, 10-5, 10 (before adding Mn w/n) • Double layers give much better results • 1000 epochs, a half of tau-pair (250000 events): ~5-10 hours

  7. Result of mode separation – 1p Better than SiD! ILD SiD

  8. Mode separation – 3 prong • Need to separate a1nu.Neural net tried • Variables (8 params) • Ecalo/Etrack (muon ID) • EECAL/(EECAL + EHCAL) (electron ID) • Echarged , Eneutral • Number of neutral particles • Invariant mass of all visible decay daughters • Invariant mass of charged particles • Invariant mass of neutral particles • 10 hidden neurons, 1 output neurons, single layer • Not optimized…

  9. Result of mode separation – 3p ILD SiD Need to improve?

  10. Rho optimal observable

  11. Omega distributions ω = (PeL(ω) - PeR(ω)) / (PeL(ω) + PeR(ω)) No P dependence at ω=0, L(R) only at ω=±1 Electron channel Muon channel Pion channel Rhonu channel

  12. Polarization by ω P(eL) = -0.591 ± 0.0067 P(eR) = 0.502 ± 0.0076 (a1 not included)

  13. Issues & prospects • Tau selection – slightly worse than SiD • NN tuning for 3-prong events • Polarization value is not consistent with MC distribution (Measured: ~10% lower) • Check generator distribution • Identify experimental effects • a1 (very complicated formula (wo/tau dir)) • Tau direction can be used for a1 • But need to calculate ω by ourselves • Paper

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