1.aim and definitions
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1Mitchell Naisbit Manchester University Elba 2003
o
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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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
Input 1M generic τ+τ- events
Mitchell Naisbit Elba 2003
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2. TauUser Preselection
Nano Cuts
Level-3 trigger cut
42% pass nanofilter
Stream19
Input 1M generic τ+τ- events
Mitchell Naisbit Elba 2003
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2.TauUser Preselection
Micro Cuts
Events input from nanofilter
Mitchell Naisbit Elba 2003
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2.TauUser Preselection
Micro Cuts
Events Input from nanofilter
# tracks even and <8
Mitchell Naisbit Elba 2003
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Mitchell Naisbit Manchester University Elba 2003
2.TauUser Preselection
Micro Cuts
Events Input from nanofilter
# tracks even and <8
Zero net charge
Mitchell Naisbit Elba 2003
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Mitchell Naisbit Manchester University Elba 2003
2.TauUser Preselection
Micro Cuts
Events Input from nanofilter
# tracks even and <8
Zero net charge
Topology classification
36% pass preselection
Mitchell Naisbit Elba 2003
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Mitchell Naisbit Manchester University Elba 2003
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
Mitchell Naisbit Elba 2003
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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Mitchell Naisbit Manchester University Elba 2003
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
Mitchell Naisbit Elba 2003
(but no quantities are of use to eliminate τ)
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Mitchell Naisbit Manchester University Elba 2003
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
Mitchell Naisbit Elba 2003
(but no quantities are of use to eliminate τ)
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Mitchell Naisbit Manchester University Elba 2003
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
Mitchell Naisbit Elba 2003
(but no quantities are of use to eliminate τ)
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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
Mitchell Naisbit Elba 2003
nCharged Tracks
thrustMag thrustMag
cut > 6
cut < 0.79 cut > 0.988
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8.Invariant Mass Spectrum
Mitchell Naisbit Elba 2003
π = 65.52%
ε = 9.51%
r ~100%
ε = 9.57 %
π = 55.10 %
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9.Future Work
Mitchell Naisbit Elba 2003
• 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
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