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