final state study

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final state study

• Jaewon Park
• University of Rochester

MINERvA/Jupiter Group Meeting, May 09, 2007
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Processes involving with final state

• Proton or muon tracks will determine primary
  vertex
• decays into two gammas

NC
CC
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Energy vector for gammas
Actual primary vertex position

• Gamma track is not good for reconstructing pi0
• Extrapolating long distance makes big uncertainty
• Instead, we used center of energy position with
  respect to primary vertex, that is determined by
  proton track

?
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Overview of calorimetry
lead
iron
ID
ECAL
HCAL
scintillator
particle

• After careful study of energy response in each
  sub-detector with given energy of incoming
  particle, then we can determine the energy of
  particle

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Simple but fatal mistake on calorimetry
calculation

• While working on converting fortran analysis code
  to c based code, couple of lines look weird.
  Its turned out to be a big bug.
• Separating ECAL region from ID was wrong. It
  selected only half side of it.
• The impact is making ECAL energy lower.
• This error propagates all the way to old
  calibration calculation.
• I believe that primary particle in old data was
  pointed to the side that ECAL is selected
  correctly.

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Resolution of proton, pi0, and each gammas before
correction

• Asymmetric energy distribution having lower side
  tail.

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Resolution of proton, pi0, and each gammas after
correction

• Now it looks much better
• Also resolution gets smaller

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Reco E vs. True E of gamma

• Because lower energy gamma is shown to makes
  resolution worse, I used event selection that
  requires energy loss fraction in ID greater than
  10
• But this doesnt make sense because earlier
  calibration study shows such event election was
  only useful for HCAL
• Smart analysis technique cant beat up removable
  systematic error

gamma1
gamma2
gamma1
gamma2
corrected
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Pi0 mass before correction

• Pi0 mass is determined from two gamma energies
  and angle between them

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Pi0 mass after correction

• Lower-side tail has been reduced

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Enhance pi0 mass resolution using chi-squire
minimization with pi0 mass constraint
Guaranteed single solution
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Comparing Minuit solution with Mathematica
numerical solution
Mathematicas numerical solution
Minuit result
First and second run
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Chi-square minimization result gamma energy
resolution
are acquired from these plots
before

• True angle is used
• Chi-square minimization makes each gammas
  resolution work
• They become correlated with constraint

after
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Chi-square minimization result pi0 energy
resolution

• Pi0 resolution is enhanced
• We can apply chi-square cut to remove poor data
  points

before
after
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W resolution this part didnt use chi-square fit

• W invariant mass of hadrons
• Didnt use E(id)/E gt 0.1, so efficiency
  increased.
• Reconstruced proton direction means using
  reconstructed primary vertex
• Pi0 mass cut m(pi0)90, 150

true proton dir
reco proton dir
true proton dir Pi0 mass cut
Reco proton dir Pi0 mass cut