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25 April 2006 1
Antineutrino selection for constraining the e beam
Goal: extract component of rate from + decays
Requirement: High purity at low neutrino energy
Pedro Ochoa(CalTech) & David Jaffe(BNL)
This is what we are trying to measure
Result: Development of preliminary ‘standard’ cuts
ee
25 April 2006 2
First tried to reproduce Jeff’s cuts described in his talk at Oxford (minos-doc 1409):
For this, used tracks in fiducial volume (1m<vtxz<5m & vtxr < 1.0m), and:
1) q/p > 02) Fit.pass + chi2<ndf <10 + UVasym < 63)|(q/p)/(σ q/p)|<0.34) Prob(chi2,ndf)>0.15) Petyt PID > 0.4
Starting point: Jeff Hartnell’s cuts
Jeff’s cuts of Oxford
Using powerpoint, a miracle of modern technology, the current results are compared to Jeff’s Oxford results on next slide…
25 April 2006 3
Jeff
Jeff
Background
Comparable results achieved
All neutrinosSelected as antineutrinosBackground
Pedro
Overall efficiency: 52.5%Overall purity: 98.2%
Pedro
Background composition
25 April 2006 4
Overall efficiency: 52.5%Overall purity: 98.2%
Reconstructed neutrino energy (GeV) Reconstructed neutrino energy (GeV)
This is what we are trying to measure
All antineutrinosSelected as antineutrinosBackground
25 April 2006 5
Jeff’s cuts work well but for our analysis we want lower background at low energy. Worked on improving the NuBarPID !The first improvement came out by noticing that separation is better for longer events (all distributions normalized to unit area) :
Our selection
(q/p) / (σ q/p)0 < Planes < 30 30 <= Planes < 60 60 <= Planes < 90
90 <= Planes < 120 120 <= Planes < 153
25 April 2006 6
So tried the following 2D PDFs for the NuBarPID (in addition to number of planes, y, and dcosz)
neutrinos antineutrinos
Note: Every “row”, or slice of planes (for instance from 0 to 30) is normalized to unity, as seen in previous slide. This reduces the energy dependence of these 2D PDFs and keeps them independent of the PDF of the number of planes.
(q/p) / (σ q/p) (q/p) / (σ q/p)
Eve
nt le
ngth
(pl
anes
)
25 April 2006 7
An improvement is observed !
After
BeforeAfter
Pu
rity
Efficiency
Some (probably very long) events are really well separated !
Here the efficiency does not include the basic cuts.
Before
25 April 2006 8
Now for something slightly different: Scan 30 events with looser Petyt PID cut to try to increase low E acceptance
Cuts:1m<vtxz<5mvtxr<1.0mq/p > 0UVasym < 6 Prob(chi2,ndf)>0.1Petyt PID > 0.0 0.5<Rnear<2m
Rne
ar (
m)
Rne
ar (
m)
Rnear = smallest radius on track.Small radius: near coil hole, higher Bfield.Large radius: lower Bfield
Accept
Accept
25 April 2006 9
Scan results for non-CCthat passed cuts on previous page
identity
25 April 2006 10
Conclusion from scan:
Comparison of momentum from range and curvature can reject some
1) protons because conversion of range to momentum assumes muon mass and
2) - because range of kinked tracks is unchanged.
Effect of cut on (p(curve)-p(range))/p(range) for investigated on following pages.
Would it be useful for CC analysis?
Alternative might be to compare expected and measured dE/dx for strips on track.
25 April 2006 11
Based on scan result, Pedro tried adding an extra cut on (p(curvature)-p(range))/p(range), only for tracks that stopped in the detector, to the NuBarPID:
• Used NuBarPID with 4PDFs: 1) 2D q/p/(σ q/p) vs. planes 2) planes 3) y4) cosz
• The pdfs were made with with following basic cuts applied:
1 < Zvtx < 5m Rvtx < 1mAt least 1 trackTrk.fit.pass==1U-Vasym < 6 /ndf < 20
2
• Plots of Purity vs. Efficiency were made. The efficiency now includes all cuts (including a cut on ).
In other words, efficiency is measured with respect to all CC nubar events.
xP
pp
range
rangecurvature
25 April 2006 12
NuBarPID and
- No extra cut- x=1.0- x=0.5- x=0.3- x=0.15
A small improvement, but it’s not enough !
25 April 2006 13
NuBarPID and:
- No extra cut- x=0.15 cut- Prob(chi2,ndf)>0.1 cut
Combination of NuBarPID with one of Jeff’s cuts, Prob( ,ndf) > 0.1 = “fit significance cut” gave the best performance :
2
BINGO !
25 April 2006 14
Interesting ! Separation looks different when calculating doing the PDFs with and without the fit significance cut:
In both cases the fit significance cut is applied. The difference is whether or not the PDFs were calculated with it or not.
At the end, not much difference in separation even if shape above is so different
PDFs done with fit sig. cutPDFs done without fit sig. cut
NuBarPIDNuBarPID
PDFs done without fit sig. cut PDFs done with fit sig. cut
Pu
rity
Efficiency
25 April 2006 15
Tried combining NuBarPID + fit significance cut + cut: 4.0
range
rangecurvature
P
pp
Pu
rity
EfficiencyNuBarPID
NuBarPID + fit sig. + prange cutNuBarPID + fit sig.
No improvement. Will stick to NuBarPID + fit significance.
Note: PDFs were calculated with all corresponding cuts included.
25 April 2006 16
From now on always included fit significance cut (among all others) when calculating the PDFs.
Now, need to see what happens as a function of energy.
Make a NuBarPID cut at 0.7 and see what happens:
NuBarPID > 0.7 puts you here
Pu
rity
Efficiency
25 April 2006 17
Compare NuBarPID> 0.7 to purity & eff’y with Jeff’s cuts:
Purity Efficiency
Jeff’s cutsJeff’s cuts NuBarPID>0.7 and Prob(chi2,ndf)>NuBarPID>0.7 and Prob(chi2,ndf)>0.1
This is what we trying to measure
Overall efficiency: 50.2%Overall purity: 99.5%
Low energy purity improved Low energy purity improved but with some loss of efficiencybut with some loss of efficiencySome increase in higher energy efficiencySome increase in higher energy efficiency
25 April 2006 18
NuBarPID>0.7Eff’y 50.2%Purity 99.5%
NuBarPID>0.75Eff’y 48.5%Purity 99.6%
NuBarPID>0.80Eff’y 46.7%Purity 99.7%
Further tightening of NuBarPID cutCharacteristics of remaining events?
Current study probably suffers from lack of stats
25 April 2006 19
Conclusions• Jeff Hartnell did a good job.
• NuBarPID >0.7 improves purity at low energy with some loss of efficiency. We now have preliminary selection criteria for a sample to constrain the e flux.
• May still investigate possible further improvements in low energy selection
• Any of this applicable to other analyses?
25 April 2006 20
25 April 2006 21
If make cut at NuBarPID>0.7 find:
Overall efficiency: 50.21%Overall purity: 99.48%
All neutrinosSelected as antineutrinosBackground
25 April 2006 22
If make cut at NuBarPID=0.75 find:
Overall efficiency: 48.52%Overall purity: 99.63%
All neutrinosSelected as antineutrinosBackground
25 April 2006 23
If make cut at NuBarPID=0.80 find:
Overall efficiency: 46.67%Overall purity: 99.73%
All neutrinosSelected as antineutrinosBackground
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