230 likes | 345 Views
Goal: extract component of n m rate from m + decays Requirement: High purity at low neutrino energy. Antineutrino selection for constraining the n e beam. This is what we are trying to measure. Result: Development of preliminary ‘standard’ cuts.
E N D
Goal: extract component of nm rate from m+ decays Requirement: High purity at low neutrino energy Antineutrino selection for constraining the ne beam This is what we are trying to measure Result: Development of preliminary ‘standard’ cuts Pedro Ochoa(CalTech) & David Jaffe(BNL)
Starting point: Jeff Hartnell’s cuts 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 > 0 2) Fit.pass + chi2<ndf <10 + UVasym < 6 3)|(q/p)/(σ q/p)|<0.3 4) Prob(chi2,ndf)>0.1 5) Petyt PID > 0.4 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…
All neutrinos Selected as antineutrinos Background Pedro Jeff Background Comparable results achieved Background composition Pedro Jeff Overall efficiency: 52.5% Overall purity: 98.2%
All antineutrinos Selected as antineutrinos Background Overall efficiency: 52.5% Overall purity: 98.2% Reconstructed neutrino energy (GeV) Reconstructed neutrino energy (GeV) This is what we are trying to measure
nm nm Our selection 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) : (q/p) / (σ q/p) 0 < Planes < 30 30 <= Planes < 60 60 <= Planes < 90 90 <= Planes < 120 120 <= Planes < 153
So tried the following 2D PDFs for the NuBarPID (in addition to number of planes, y, and dcosz) neutrinos antineutrinos Event length (planes) (q/p) / (σ q/p) (q/p) / (σ q/p) 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.
nm nm • An improvement is observed ! Before After Some (probably very long) events are really well separated ! Here the efficiency does not include the basic cuts. Purity Before After Efficiency
Now for something slightly different: Scan 30 events with looser Petyt PID cut to try to increase low E acceptance Cuts: 1m<vtxz<5m vtxr<1.0m q/p > 0 UVasym < 6 Prob(chi2,ndf)>0.1 Petyt PID > 0.0 0.5<Rnear<2m Rnear (m) Accept Rnear = smallest radius on track. Small radius: near coil hole, higher Bfield. Large radius: lower Bfield Rnear (m) Accept
Conclusion from scan: Comparison of momentum from range and curvature can reject some • protons because conversion of range to momentum assumes muon mass and • m- because range of kinked tracks is unchanged. Effect of cut on (p(curve)-p(range))/p(range) for nm investigated on following pages. Would it be useful for CC nm analysis? Alternative might be to compare expected and measured dE/dx for strips on track.
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) y 4) cosz • The pdfs were made with with following basic cuts applied: 1 < Zvtx < 5m Rvtx < 1m At least 1 track Trk.fit.pass==1 U-Vasym < 6 /ndf < 20 • 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.
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 !
Combination of NuBarPID with one of Jeff’s cuts, Prob( ,ndf) > 0.1 = “fit significance cut” gave the best performance : NuBarPID and: - No extra cut - x=0.15 cut - Prob(chi2,ndf)>0.1 cut BINGO !
nm nm Interesting ! Separation looks different when calculating doing the PDFs with and without the fit significance cut: PDFs done without fit sig. cut PDFs done with fit sig. cut NuBarPID NuBarPID 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 Purity PDFs done with fit sig. cut PDFs done without fit sig. cut Efficiency
Tried combining NuBarPID + fit significance cut + cut: nm nm Purity NuBarPID + fit sig. + prange cut NuBarPID + fit sig. NuBarPID Efficiency No improvement. Will stick to NuBarPID + fit significance. Note: PDFs were calculated with all corresponding cuts included.
nm nm 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 Purity Efficiency
Compare NuBarPID> 0.7 to purity & eff’y with Jeff’s cuts: Overall efficiency: 50.2% Overall purity: 99.5% Purity Efficiency Low energy purity improved but with some loss of efficiency Some increase in higher energy efficiency Jeff’s cuts NuBarPID>0.7 and Prob(chi2,ndf)>0.1 This is what we trying to measure
Further tightening of NuBarPID cut Characteristics of remaining events? NuBarPID>0.7 Eff’y 50.2% Purity 99.5% NuBarPID>0.75 Eff’y 48.5% Purity 99.6% NuBarPID>0.80 Eff’y 46.7% Purity 99.7% Current study probably suffers from lack of stats
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 nm sample to constrain the ne flux. • May still investigate possible further improvements in low energy nm selection • Any of this applicable to other analyses?
All neutrinos Selected as antineutrinos Background If make cut at NuBarPID>0.7 find: Overall efficiency: 50.21% Overall purity: 99.48%
All neutrinos Selected as antineutrinos Background If make cut at NuBarPID=0.75 find: Overall efficiency: 48.52% Overall purity: 99.63%
All neutrinos Selected as antineutrinos Background If make cut at NuBarPID=0.80 find: Overall efficiency: 46.67% Overall purity: 99.73%