1.Aim and Definitions

1Mitchell Naisbit Manchester University Elba 2003

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1.Aim and Definitions

• Aim is to formulate an efficient selection procedure for π πo

decays of the τ

• Analysis will optimise:

s

s

Nnefficiency

bnn

s

s

purity rej. factor

b

bb

N

nNr

• To combine MC will scale to a data sample of (so far) 0.134 fb-1 of data

Ns=number signal decays in MC sample (2NxBR), ns=number truth-matched candidates selectedb=total number of background decays selected

Nb= number background decays in sample, nb=number background decays selected

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Mitchell Naisbit Manchester University Elba 2003

2.TauUser PreselectionNano Cuts

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Input 1M generic τ+τ- events

Mitchell Naisbit Elba 2003Mitchell Naisbit Manchester University Elba 2003

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2. TauUser PreselectionNano Cuts

Level-3 trigger cut


Mitchell Naisbit Elba 2003

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2. TauUser Preselection

Nano Cuts

Level-3 trigger cut

42% pass nanofilter

Stream19



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2.TauUser Preselection

Micro Cuts

Events input from nanofilter


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Micro Cuts

Events Input from nanofilter

# tracks even and <8


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Micro Cuts



Zero net charge


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Micro Cuts



Zero net charge

Topology classification

36% pass preselection


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3.Selection Procedure

e

e

oFor 1-1 events backgrounds reduced by tag

Selection requirements π PID (piLHLoose)

π not in eMicroLoose

Single AWG πo

e or μ PID as tag

or

As above for ρ tag


Signal side

Tag side

Selection for data and MC samples:

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4.Monte Carlo truth matching

Reconstruction Requirements

for signal τ decays

recon. π, πo, γA, γB must match back to particle in truth list of same identity

π and πo must have same mother which is a

true ρ

γA and γB must have same mother which is a

true πo


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5.Results – τ+τ- MC

Running on 1M generic τ+τ- events

Truth codes for selected decays

(1)

(2)

(3)

Ns= 508,200 signal decays

(1)

Truth codes for truth-matched candidates

(2)

ns = 48,613

Backgrounds(3)

btau = 21,401

Main τ backgrounds are a1 decays and improperly reconstructed signal decays.


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5.Results – background MC

Analysed MC samples of -

Ns=61,385 ns=5,872 bτ=2,585 bother=2,208

bbccssdduu ,,,, (hadronic)

),1(),(

),15030(),14220(

GeVEeeinEMCeee

oee

oee

(leptonic)

(photon) 4,4, e

ee

Giving scaled results-

b = bτ + bother = 4,793Mitchell Naisbit Elba 2003

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5.Results

π = 55.10 %ε = 9.57 %

Main backgrounds •Non-signal τ (a1)

•Improperly reconstructed signal decays

•Leptonic (bhabha+FSR) and some hadronic


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6.Event Parameter Distributions - τ+τ- MC

nNeutrals

nChargedTracks

Ranges 0 to ~6

nNeutrals

Ranges from 2 to ~15

thrustMag Ranges from ~0.79 to ~0.99


(but no quantities are of use to eliminate τ)

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nNeutrals

nChargedTracks

Ranges 0 to ~6

nNeutrals





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nNeutrals

nChargedTracks

Ranges 0 to ~6

nNeutrals





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6.Event Parameter Distributions - background

MC

nNeutrals nChargedTracks

cut >~ 12 (hadronics) cut all >~ 6 (hadronics) Mitchell Naisbit Elba 2003

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6.Event Parameter Distributions - background

MC

thrustMag

cut <~ 0.8 (hadronics) cut >~ 0.99 (leptonics)


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7.Efficiency and Purity Optimisation nNeutrals

cut > 12


nCharged Tracks

thrustMag thrustMag

cut > 6

cut < 0.79 cut > 0.988

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8.Invariant Mass Spectrum


π = 65.52%

ε = 9.51%

r ~100%

ε = 9.57 %

π = 55.10 %

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9.Future Work


• Finalise Selection Procedure

• Complete study into τ + non-τ backgrounds and how to minimise them

• Perform fits to the invariant mass spectrum

• Implement detector unfolding techniques

1.Aim and Definitions

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