Using Muon Removed files to assess the purity of the nubar-PID selection

P. Ochoa, September 2006

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Using Muon Removed files to assess the purity of the nubar-PID selection

Pedro OchoaMINOS Collaboration Meeting

September 2006


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all

NC

vv

L010185 MC

For a cut at nubar-PID=1.0, MC shows:

Overall purity: 99.75%Overall efficiency: 45.98%

• Do we believe this high purity?

Introduction

• Nubar-PID selection allows to separate antineutrinos with very high purity and reasonable efficiency:

fiducial volume track quality fit probability

1m < Zvtx < 5mrvtx < 1m

track fit pass / ndf < 20

2UVasym < 6

+ +Prob( , ndf) > 0.1

2Basic cuts:

then apply nubar-PID:


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Background (124 events total) • Can separate the background into two categories:

Category 1: - is reconstructed as + due to hard scattering and/or pattern recognition problems = misidentified

Category 2: tracker fooled by positive particle (decay in flight, proton, pion, kaon… ) = fake

• Use IdHEP of tracked particle: trkIdHEP=13 Category 1

trkIdHEP!=13 Category 2

+

-

+ + p

About ~1/3 of the background pertains to category 2:124 background events of

nubarPID > 1.0 selectionSelection Category 2 %

nubarPID > 1.0 32.3 ± 4.2

nubarPID > 0.9 31.8 ± 3.3

nubarPID > 0.5 25.2 ± 1.4

*Note: Category 1 contains a small component of misidentified negative stuff from hadronic shower.


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Category 2 example – NC ( decay in flight)

tracked particle


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Category 2 example – NC (proton)


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c

Category 2 example – CC (Λc+)


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Category 2 example – CC (K+)


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True_y of CC , category 2

• CC subcategory of Category 2 events seem to be high y

• “Good” MRCC selection:

Means:Data: 0.952MC: 0.958

dataMC scaled to POT


Means:Data: 0.975MC: 0.973

best_purity > 0.8best_complete > 0.8best_purity_phw > 0.8best_complete_phw > 0.8

Can use MRCC files to answer whether category 2 events are reasonably well modeled.

Event has to be best match to original

Purity=

Completeness=

(see Anna H. talk, minos-doc 2164)


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dataMC scaled to # events


Run MRCC Data and MC though selection

data/MC

data/MC


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MC: 38.8 ± 10.4

•nubar-PID > 1.0 region:

Data: 30 ± 5.5

MC: 34.2 ± 9.1•nubar-PID > 1.0 region:

Data: 30 ± 5.5


MC: 88.8 ± 9.4

Data: 96 ± 9.8


MC: 78.1 ± 8.8

Data: 96 ± 9.8

Scaled to # events:

Scaled to POT:

Looking at the signal region:


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data/MC

data/MC

nubar-PID > 1.0 selection

nubar-PID > 0.5 selection

• What about energy dependence?


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Summary

Nothing crazy. Lack statistics…

Analysis shows so far that “category 2” background in our nubar-PID > 1.0 selection can be scaled overall by a factor of 0.77 ± 0.25

Ultimately also need to:Account for MRCC efficiency and purity Compare subcategories in MRCC and in MC

What to do if more statistics reveal a considerable energy dependence?

One possibility: use ratios in previous slides to scale background binned in reco energy (removing primary CC energy if applicable).


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BACKUP


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NC - Pion decay in flight


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CC - Pion


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nubar-PID > 0.0 signal:

MC: 1895 ± 72

Data: 2123 ± 46

nubar-PID > 0.0 signal:

MC: 1666 ± 64

Data: 2123 ± 46




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nubarPID>1.0

nubarPID>0.5 nubarPID>0.0

Using Muon Removed files to assess the purity of the nubar-PID selection

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