Atmospheric Neutrino

1
Atmospheric Neutrino Event Reconstruction
Andy Blake Cambridge University September 2003
2
Introduction

• Cambridge reconstruction software
  development is ongoing.
• New version of AtNuReco now in CVS.
• AtNuReco is a track shower reconstruction
  package developed for use in atmos neutrino
  analysis.
• tracks showers reconstructed concurrently.
• This talk presents a study of atmos neutrino
  reconstruction and separation.

3
Monte Carlo Studies
DetSim

• 200,000 atmos neutrino events (500 kT-yrs)
• 200,000 cosmic muon events (0.05 kT-yrs)
• Study reconstruction efficiency/purity
  signal/background separation.

Cambridge Demultiplexer
Cambridge Reconstruction
Standard Reconstruction
Analysis
4
Reconstruction Efficiency/Purity
5
Reconstruction Quality

• Problems arise from tracking errors NC/?e
  background
• Define track quality
• Poor tracks occupy phase spaces away from good
  tracks
• Make pre-cuts (also helps background rejection)

C u t
C u t
6
Efficiency/Purity after Pre-cuts
purity
efficiency
7
Signal/Background Separation
(e.g. muon zenith angle)

• Can use track information to separate signal from
  background.
• Signal and background occupy separate regions of
  phase space.
• e.g. cosmic muon events are downward-going,
  high angle, close to detector edge.
• Signal can be separated from background by
  cutting away these regions.
• Use likelihood to define a multi-dimensional
  threshold between signal and background.
• Try calculating likelihood from many 1D PDFs.

signal
background
8
1D PDFs
R
cos ?
track direction
Signal
Background
9
Likelihood calculation
Ncosmic/Natmos 15,000 ( BUT VETO SHIELD
IGNORED IN THIS NORMALIZATION )
Cambridge Reconstruction
Standard Reconstruction
zoomed in to see tails
10
Results
atmos nu
cosmic mu
AtNu SR
100,000 100,000
48,600 48,600
15,100 25,500
11,300 13,000
6,900 6,800
AtNu SR
100,000 100,000
60,700 60,700
49,000 53,400
35,300 37,000
2 5

Interactions
Triggers
Tracks
Pre-cuts
Signal (Lgt0.5)
but 4 reconstructed as upward-going
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Contained Background Events
Cambridge Reconstruction
Standard Reconstruction
contained
rejected
contained
rejected
contained
rejected
12
Signal Efficiency
Some signal events are retained in all 1D phase
spaces.
R
cos ?
track direction
very good with upward-going partially contained
events (should also use vertex shower info)
heavy loss of downward-going events (reduced by
improving likelihood, fixing reco errors, using
veto shield in normalization)
13
Problems

1. 1D projections ignore correlations between
   variables.
2. Reconstruction errors pollute the signal region.

Cambridge Reconstruction
Standard Reconstruction
14
Combining Reconstruction Algorithms

• Reconstruction algorithms with contrasting
  systematics can be combined to enhance
  separation.
• Try using AtNu AND SR to filter signal

atmos nu
cosmic mu
AtNu SR
100,000 100,000
48,600 48,600
15,100 25,500
11,300 13,000
6,900 6,800
AtNu SR
100,000 100,000
60,700 60,700
49,000 53,400
35,300 37,000
2 5

Interactions
Triggers
Tracks
Precuts
Signal
AND
100,000
60,700
48,900
34,200
0
AND
100,000
48,600
15,000
9,800
4,200
for this sample, the background goes away
(but need much larger sample )
15
Conclusion

• Cambridge reconstruction effort continuing.
• Signal separation could be carried out using
  likelihood techniques but
• (i) need better likelihood functions.
• (ii) need improved reconstruction.
• Particularly promising for upward-going partially
  contained events.
• Reconstruction algorithms could be combined to
  improve background rejection.
• So much for Monte Carlo studies
• time to tackle the data too!