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On visibility of NC π 0 events in T2K-LAr

On visibility of NC π 0 events in T2K-LAr. Paweł Przewłocki, Warsaw Neutrino Group, 2005 For T2K 2km meeting. The aim of this analysis. The problem lies in distinguishing electron events from pizero events in liquid argon detector

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On visibility of NC π 0 events in T2K-LAr

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  1. On visibility of NC π0 events in T2K-LAr Paweł Przewłocki, Warsaw Neutrino Group, 2005 For T2K 2km meeting

  2. The aim of this analysis • The problem lies in distinguishing electron events from pizero events in liquid argon detector • In this analysis we would like to find out how many pizero events can be identified by means of looking at the gap between the vertex and the point of gamma conversion (to properly identify a pizero this way, one has to have another visible particle to mark the primary vertex of interaction)

  3. Energy loss analysis (described in the proposal for NuSAG) • …is based on dE/dx measurement (single mip signal of a electron vs. double signal of e+e- pair)

  4. The energy loss analysis shows that: • With this method 96.3% pions are rejected for 90% electron efficiency (for 1GeV pions) • For 250MeV pions (these will be most frequent in T2K) 93.5% are rejected • The quality of rejection increases with energy – different from Cherenkov detectors in which the quality gets worse for higher energies (due to overlapping of two gamma induced rings)

  5. A supplemental method • Additionally, pizero can be visually recognized if the distance between the vertex and the point of gamma conversion is more than 1cm • Conversion length of a photon in LAr is 18cm; hence, we get 5.4% of pions confused with electrons • With these two methods combined we can get 0.2% (0.35% for 250MeV) pion efficiency, but… • We have to know where the vertex is, and this information is only available when some other particle (apart from two showering gammas) is visible at the vertex • This is the starting point for my analysis here

  6. γ2 γ1 Sample pizero events in the T2K LAr detector • Detector simulation by a dedicated version of Geant4 γγ(55 & 120MeV)+p+π+ Gammas ~ 80MeV + 1GeV proton γγ(1700 & 440MeV)+p+π-

  7. General info • Data simulated by Nuance 3.006 • T2K beam @ 2km • Two samples: w/o and with FSI (final state interactions in Ar nucleus) • Muon neutrinos, 100.000 interactions generated (ca 25.000 NC events) • No detector simulation • Simple C++ code used instead, to see which tracks are visible

  8. Some statistics Just to have a notion of how many events we’ve got in different channels:

  9. How to see a particle (in LAr) • We assume that for a particle to be seen we have to observe a signal on three consecutive wires • We take into account every charged particle track (protons, charged pions, muons, electrons, charged kaons), and calculate length of its track using known energy-range dependence for each type of particle • We project it onto the wire plane • We project it again, this time onto 2 directions perpendicular to the wires’ directions (45deg, -45deg) • If greater of these exceeds 9mm (3 wires times 3mm [wire pitch]) we conclude that the track is visible x z y • Exclusion of y coordinate • Rotation by 45deg. • x and z give us needed lengths

  10. From now on… • We take into account only NC sample • We take into account only potentially visible particles (protons, charged pions, charged kaons)

  11. Protons and pions – with and without FSI (momentum) Dashed line – w/o FSI Solid line – with FSI MeV/c MeV/c application of FSI gives us many low momentum protons

  12. Protons and pions - visibility Black – all, red – invisible MeV/c

  13. Visible protons and pions – with and without FSI (momentum) Dashed line – w/o FSI Solid line – with FSI MeV/c MeV/c

  14. Visibility - summary

  15. Visibility and pizeros – w/o FSI FSI: Less pizeros, but more of them identifiable!

  16. Conclusions • We have 35-50% of pizeros unidentifiable (35% would be nice, but this is caused by many low energetic protons in the ‘with FSI’ sample which we are not sure of) • To do: • Further study of nucleon rescattering is necessary • We should probably do the same analysis using reconstruction information from Qbatch (Fullreco)

  17. Backup

  18. Range - energy (kinetic!) Points – data, lines – fitted curves

  19. Number of wires with signal for each track with FSI w/o FSI More tracks with values close to zero - application of FSI gives us many low momentum protons – these light up only a small number of wires

  20. Visibility – protons, w/o FSI

  21. Visibility – protons, with FSI

  22. Visibility – charged pions, w/o FSI

  23. Visibility – charged pions, with FSI It is puzzling that despite the absorption process we still have so much pions – we are going to investigate it in the future

  24. Visibility – kaons, w/o FSI

  25. Visibility – kaons, with FSI

  26. Visibility – electrons, w/o FSI Scattering on electrons!

  27. Visibility – electrons, with FSI

  28. Visibility and pizeros With FSI No FSI

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