Mitchell Naisbit Manchester University Elba 2003

1
1.Aim and Definitions

• Aim is to formulate an efficient selection
  procedure for p po decays of the t
• Analysis will optimise

efficiency
purity
rej. factor
Nsnumber signal decays in MC sample (2NxBR),
nsnumber truth-matched candidates selected
btotal number of background decays selected
Nb number background decays in sample, nbnumber
background decays selected

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

Mitchell Naisbit
Manchester University
Elba 2003
2
2.TauUser Preselection
Nano Cuts

Input 1M generic tt- events
Mitchell Naisbit

Elba 2003
Mitchell Naisbit
Manchester University
Elba 2003
3
2. TauUser Preselection
Nano Cuts

Input 1M generic tt- events
Level-3 trigger cut
Mitchell Naisbit

Elba 2003
4
2. TauUser Preselection
Nano Cuts
Input 1M generic tt- events
Level-3 trigger cut
Stream19
42 pass nanofilter
Mitchell Naisbit

Elba 2003
5
2.TauUser Preselection

Micro Cuts
Events input from nanofilter
Mitchell Naisbit

Elba 2003
6
2.TauUser Preselection

Micro Cuts
Events Input from nanofilter
tracks even and lt8
Mitchell Naisbit

Elba 2003
7
2.TauUser Preselection
Micro Cuts

Events Input from nanofilter
tracks even and lt8
Zero net charge
Mitchell Naisbit

Elba 2003
8
2.TauUser Preselection
Micro Cuts
Events Input from nanofilter
tracks even and lt8
Zero net charge
Topology classification
36 pass preselection
Mitchell Naisbit

Elba 2003
9
3.Selection Procedure
Selection for data and MC samples
For 1-1 events backgrounds reduced by tag
Selection requirements
p PID (piLHLoose)
p not in eMicroLoose
Signal side
Single AWG po
e or µ PID as tag
Tag side
or
As above for ? tag
Mitchell Naisbit

Elba 2003
10
4.Monte Carlo truth matching
recon. p, po, ?A, ?B must match back to particle
in truth list of same identity
Reconstruction Requirements for signal t decays
p and po must have same mother which is a true ?
?A and ?B must have same mother which is a true
po
Mitchell Naisbit

Elba 2003
11
5.Results tt- MC
(1)
Running on 1M generic tt- events
Ns 508,200 signal decays
(1)
Truth codes for selected decays
(2)
(2)
Truth codes for truth-matched candidates
ns 48,613
(3)
Backgrounds
(3)
btau 21,401
Main t backgrounds are a1 decays and improperly
reconstructed signal decays.
Mitchell Naisbit

Elba 2003
12
5.Results background MC
Analysed MC samples of -
(hadronic)
(leptonic)
(photon)
Giving scaled results-
Ns61,385 ns5,872 bt2,585
bother2,208
b bt bother 4,793
Mitchell Naisbit

Elba 2003
13
5.Results
p 55.10
e 9.57
Main backgrounds

• Non-signal t (a1)
• Improperly reconstructed
• signal decays
• Leptonic (bhabhaFSR)
• and some hadronic

Mitchell Naisbit

Elba 2003
14
6.Event Parameter Distributions - tt- MC
nNeutrals
Ranges from 2 to 15
nChargedTracks
Ranges 0 to 6
thrustMag
nNeutrals
Ranges from 0.79 to 0.99
(but no quantities are of use to eliminate t)
Mitchell Naisbit

Elba 2003
15
6.Event Parameter Distributions - tt- MC
nNeutrals
Ranges from 2 to 15
nChargedTracks
Ranges 0 to 6
thrustMag
nNeutrals
Ranges from 0.79 to 0.99
(but no quantities are of use to eliminate t)
Mitchell Naisbit

Elba 2003
16
6.Event Parameter Distributions - tt- MC
nNeutrals
Ranges from 2 to 15
nChargedTracks
Ranges 0 to 6
thrustMag
nNeutrals
Ranges from 0.79 to 0.99
(but no quantities are of use to eliminate t)
Mitchell Naisbit

Elba 2003
17
6.Event Parameter Distributions - background MC
nNeutrals
nChargedTracks
cut gt 12 (hadronics)
cut all gt 6 (hadronics)
Mitchell Naisbit

Elba 2003
18
6.Event Parameter Distributions - background MC
cut lt 0.8 (hadronics)
cut gt 0.99 (leptonics)
thrustMag
Mitchell Naisbit

Elba 2003
19
7.Efficiency and Purity Optimisation
nNeutrals
nCharged Tracks
cut gt 6
cut gt 12
thrustMag
thrustMag
cut gt 0.988
cut lt 0.79
Mitchell Naisbit

Elba 2003
20
8.Invariant Mass Spectrum
e 9.57
e 9.51
p 55.10
p 65.52
r 100
Mitchell Naisbit

Elba 2003
21
9.Future Work

• Finalise Selection Procedure
• Complete study into t non-t backgrounds and how
• to minimise them
• Perform fits to the invariant mass spectrum
• Implement detector unfolding techniques

Mitchell Naisbit

Elba 2003