1. A PID based approach for antineutrino selection
Pedro Ochoa
Caltech
Work in progress
March

2. Basic idea
• Combine different information to obtain a nubar-ness indicator on which to cut.
• Take advantage of differences between neutrino and antineutrino interactions besides charge of resulting lepton.
• It is always easier to cut on one single parameter. People can adjust the cut on the PID to obtain a different efficiency or purity.
The implementation is analogous to that of David Petyt’s PID for NC/CC (ref. MINOS-doc-1347):
Input is 4 pdf distributions which are different for nu and nubar events.
For each event, calculate the product of probabilities that event comes from the nu or nubar distributions
The nubar-PID parameter is given by:
March

3. • So far method only implemented & tested in the Near Detector.
Basic cuts
• So far method only implemented & tested in the Near Detector.
• Used Mike Kordosky’s pans for this work (from Mad), for the carrot MC in the L configuration.
• Make pdf distributions with events that satisfy the following basic “non-negotiable” requirements:
• Event vertex in fiducial volume: 1.0m <vtx.z < 5.0m & r<1.0m
• Only CC events (using truth now, but could use DP-PID)
• Track quality cuts: i) at least 1 track
ii) track passes fit
iii) / ndf < 20
iv) UVasym < 6
74.4% of CC events in this fid. volume pass these cuts
Next 4 slides show the pdf distributions. All of them are normalized to unity.
March

4. PDF1: (q/p)/(σq/p) nu nubar
• This is probably the most powerful discriminant
March

5. PDF2: Event length (planes)nu
nubar
PDF2: Event length (planes)
planes
• Need more statistics!
• This is the “trickiest” of the PDFs because it is energy dependent.
 Could not use in searches (or when oscillations).
 Valid in ND, especially when cutting out antineutrinos.
• Will investigate what it does with energy (is it just cutting low energy stuff?)
March

6. PDF3: y distribution nu
nubar
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7. PDF4: cos(θz) nu
nubar
• This one probably doesn’t help that much, but it still contains differences between neutrinos and antineutrinos.
March

8. Performance of the method for selectionnu
nubar
• Observe clear separation
• Evaluate by looking at Purity vs. Efficiency
• Compare by using same basic track quality cuts of slide 3, but cutting on un-normalized (q/p)/(σq/p) only (see green).
• NuBar PID method shows a considerable advantage, except in the low purity region.
NuBar-PID
Efficiency
Purity
Increase NuBar-PID cut nu
nubar
(q/p/(σq/p) (not normalized)
Increase (q/p)/(σq/p) cut
• (q/p)/(σq/p) cut only
• NuBar-PID cut
March
does not include cuts of slide 3

9. Performance of the method for selection
• Again, evaluate by looking at Purity vs. Efficiency
• Make same comparison as in previous slide, i.e. cutting on (q/p)/(σq/p) only (see green).
• (q/p)/(σ q/p) cut only
• NuBar-PID cut
Purity
Efficiency nu
nubar
Increasing NuBar-PID cut
Increasing (q/p)/(σq/p) cut
PID
0.0
0.1
0.2
0.3
Purity %
99.2
99.0
98.8
98.4
Efficiency %
96.6
97.7
98.6
• NuBar-PID method works very good for neutrino selection !!!
March

10. Improving the separation
• Can improve purity by adding other to our set of basic cuts.
• For instance, added one of Jeff’s cuts: |σq/p/(q/p)|<0.3
• Now 65.6% of CC events in fid. volume pass the basic cuts (before it was 74.4%)
• Basically, this cut removes the central part of the PDF1 distribution (left):
Efficiency
Purity
Increasing NuBar-PID cut
• NuBar-PID cut (with |σq/p/(q/p)|<0.3)
• NuBar-PID cut
• Considerable improvement in purity (relative efficiency improves too, but extra cut removed ~9% more events). Will experiment with other cuts.
March

11. Implementation • Need to implement this in a practical way.
• Currently working on a package called NuBarPID, which so far has two classes:
- LoadPDF(char *filename) loads the PDF files and has methods to evaluate them.
- PIDCalculator(..track parameters…) calculates the PID given a certain track.
- Also contains a macro to calculate PDF distributions.
• Code needs to be flexible and allow for different options (for instance, allow for a given selection of PDFs, … etc).
• Will commit the code to CVS when ready.
March

12. Summary & Ongoing Work
A first pass at using a PID based approach for selecting antineutrinos was made. Method seems to do a good job ! However,
Need more statistics to create pdf distributions.
Need to evaluate whether my pdf selection is optimal (maybe need to add or remove some pdfs… suggestions?)
Want to evaluate the effect on energy and in particular for the 2nd pdf.
Purity can be improved by extra cuts. Will have to experiment more with these.
Working on a package. Will commit it to CVS soon.
March