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Maximilien Fechner(Saclay)

Comparison between T2K and and K2K Water Cherenkov detector simulations (JHF2km & fwdetsim) Preliminary e/ p 0 separation studies using JHF2km (8inch & 20 inch PMTS). Maximilien Fechner(Saclay). Comparison between the k2k water Ch. simulation and the G4 ‘1KT’ setting

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Maximilien Fechner(Saclay)

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  1. Comparison between T2K and and K2K Water Cherenkov detector simulations(JHF2km & fwdetsim)Preliminary e/p0 separation studies using JHF2km (8inch & 20 inch PMTS) Maximilien Fechner(Saclay) • Comparison between the k2k water Ch. simulation • and the G4 ‘1KT’ setting • 2. Polfit preliminary results

  2. Improvements of the G4 simulation • In order to compare both programs, the ‘1kt’ geant4 geometry setting must be used • In order to make sure JHF2km is properly tuned : • I compare qmaps (amount of collected charge vs. PMT number) • time distributions (tisk) • total charge distributions (qismsk) • Nhit distributions (nqisk) • I generated 1000 e- events @500 MeV/c , at the center of the detector in both geant4 and fwdetsim_5.21 • 1000 « stable » µ- @500 MeV/c in the same conditions (ie muon decay is turned off in both simulations) • The ARAS fwdetsim internal parameter (for Rayleigh scattering) was varied within the currently accepted range (0.6 to 1.5) • Here I only show the comparisons with the ARAS=0.6 fwdetsim samples • The 1kt tube numbers are converted to 2km tube numbers (remember both • numbering schemes are different)

  3. Charge vs angle profiles Opening angle wrt track (deg) « stable muons » electrons More charge in the Cherenkov ring area (absorption ?, Rayleigh scattering ?)

  4. K2k geant4 Qmaps « stable µ- » Accumulated charge e- Tube number

  5. K2k geant4 Total charge distributions electrons « Stable muons »

  6. K2k geant4 Number of hits and qisk distributions qisk(i) = amount of charge recorded by the ith PMT e- « Stable  µ- » qisk

  7. K2k geant4 Nhit distributions e- « Stable  µ- » Number of hit PMTs Good agreement between k2k and JHF2km simulations

  8. K2k geant4 Timing distributions e- Changes since the last meeting Offset value = 940 ns Reflection  second peak ns New digitizer µ- ns

  9. Polfit results • G4 tuning using a 1kt-like geometry seems reasonable • Generation of e/p0 data using the 2km geometry setting, in order to compare the performance of 8&20 inch tubes • 1000 e-, 1000 p0 @500 MeV/c were generated (random vertices + random direction) using both PMT settings • Reconstructed using ‘ktpolfit2’ (adapted to the geometry) • At the moment MC truth is used as input for polfit (since the performance of the full reconstruction is still being studied for G4) • Polfit is meant to be applied on 1ring e-like events (after full reconstruction) : here there is no such selection

  10. POLfit (pattern of light fit) reduce p0 BG in FC 1R-e for ne search (ex. JHF-LOI) • Input:(vertex,1stg direction, total visible energy) from MC truth banks • First : Fit the 2nd g ring by changingits direction & energy fraction(note: vertex & 1st dir. are fixed) • compare observed with expected(direct+scatter) charge until the best match found using a “simplex” algorithm • Second : compute the likelihood that the event has one single e- track • Output: (2 likelihoods, energy & direction for each ring Initial guess g-g plane(q=0) E2 E1 -f vertex highest charge dir f = E2/ Evis 1st dir g2 g1

  11. Delta likelihood distributions

  12. Invariant mass distributions MeV/c²

  13. Energy fraction distributions

  14. Conclusion • Progress on G4 simulation tuning • Preliminary polfit results : 8 inch tubes seem to significantly improve the signal/noise ratio needs to be confirmed with more statistics and with fully reconstructed input • Next : polfit improvement underway

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