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Preliminary Comparison of T2K and K2K Water Cherenkov Detector Simulations

Comparison and preliminary studies of e/p0 separation using JHF2km with 8-inch & 20-inch PMTs. Evaluating T2K and K2K water Cherenkov detector simulations, including initial results and improvements to G4 simulation. Detailed analysis and comparison of charge, time, total charge, and hit distributions, as well as profiles and distributions of stable muon and electron events. Assessing the validity of ARAS fwdetsim internal parameter for Rayleigh scattering and converting tube numbers between 1kt and 2km schemes. Concluding with insights on G4 simulation tuning progress and future polfit enhancements.

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Preliminary Comparison of T2K and K2K Water Cherenkov Detector Simulations

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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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