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

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

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

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

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

Mode separation – 1 prong Need to separate leptonic, pinu, rhonu and a1nu 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

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

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…

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

Rho optimal observable 2 2

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

Polarization by ω P(eL) = -0.6382 ± 0.0066 P(eR) = 0.5083 ± 0.0079 (a1 not included)

Issues & prospects Tau selection – slightly worse than SiD NN tuning for 3-prong events a1 (very complicated formula) Tau direction can be used for a1 But need to calculate ω by ourselves Finalizing analysis and write a paper Analysis note updated: http://www.ilcild.org/groups/optimization/loi-physics-analyses-1/tau-pairs-at-500-gev/tau090617.pdf/view