Taikan Suehara, ILC-Asia physics meeting, 2009/06/13 page 1

Tau-pair analysis for LoI+Tau-pair analysis for LoI+

Taikan SueharaICEPP, The Univ. of Tokyo

Taikan Suehara, ILC-Asia physics meeting, 2009/06/13 page 2

[Observables] P(e-)=80%, P(e+)=30%, 500 fb-1

• σ, AFB (bg suppression)

• Polarization P()↑ Decay angle determination

Tau-pair processTau-pair process

σ=2600 fb-1 (e-Le+

R) σ=2000 fb-1 (e-

Re+L)

radiative events: ~70%

Difficulty on decay analysis

Taikan Suehara, ILC-Asia physics meeting, 2009/06/13 page 3

• Looser tau-selection cuts – to improve statistical error (compatible with SiD).

• More background of Bhabha and • Better decay-mode selection by a

neural network• ‘Optimal observable’ for polarization

measurement

ProgressProgress

Taikan Suehara, ILC-Asia physics meeting, 2009/06/13 page 4

• 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

Background eventsBackground events

Taikan Suehara, ILC-Asia physics meeting, 2009/06/13 page 5

• 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

Tau selection cutsTau selection cuts

Taikan Suehara, ILC-Asia physics meeting, 2009/06/13 page 6

• 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

Mode separation – 1 prongMode separation – 1 prong

Taikan Suehara, ILC-Asia physics meeting, 2009/06/13 page 7

Result of mode separation – 1pResult of mode separation – 1p

Better than SiD!

SiD

ILD

Taikan Suehara, ILC-Asia physics meeting, 2009/06/13 page 8

• 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…

Mode separation – 3 prongMode separation – 3 prong

Taikan Suehara, ILC-Asia physics meeting, 2009/06/13 page 9

Result of mode separation – 3pResult of mode separation – 3p

ILD

SiD

Need to improve?

Taikan Suehara, ILC-Asia physics meeting, 2009/06/13 page 10

Rho optimal observableRho optimal observable

Taikan Suehara, ILC-Asia physics meeting, 2009/06/13 page 11

ω = (PeL(ω) - PeR(ω)) / (PeL(ω) + PeR(ω))

No P dependence at ω=0, L(R) only at ω=±1

Omega distributionsOmega distributions

Electron channel Muon channel

Pion channel Rhonu channel

Taikan Suehara, ILC-Asia physics meeting, 2009/06/13 page 12

P(eL) = -0.591 ± 0.0067

P(eR) = 0.502 ± 0.0076

(a1 not included)

Polarization by ωPolarization by ω

Taikan Suehara, ILC-Asia physics meeting, 2009/06/13 page 13

• 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

Issues & prospectsIssues & prospects