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Water Cherenkov simulation status report

Performance study and preliminary neutrino results of the water Cherenkov simulation at CEA Saclay. Issues with decay electron cuts, software tuning, and momentum resolution. Comparison with Super-Kamiokande results and neutrino events analysis.

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Water Cherenkov simulation status report

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  1. Water Cherenkov simulation status report Maximilien Fechner CEA Saclay DAPNIA/SPP Special thanks to K. Okumura &C. Walter • Performance study • VERY preliminary neutrino results &decay e- cut issues

  2. Software tuning • Cannot just reuse the code from last summer because the simulator has changed too much. • New ‘asmo’ tables (p.e->MeV,MeV->p.e) • Tune AFIT (critical for the rest) • Tune ringcounting (1R vs multiring): dlfct < -5 • Tune PID : use Okumura-san’s angle PID + new cut tuning • Use mono-energetic e-&mu- FV issue : this study shows that performance (AFIT->PID) is degraded when the Vertex is too close to the wall -> 2m is not enough !! (PMT shapes, coseff ?) I suggest we use a ~56t FV : 2.5m away from the walls, 4m away from the downstream wall

  3. Momentum resolution RTOT Not as good as SK (µ~3%, e-~0.5+2.5/sqrt(P(GeV)) ) True momentum MeV/c

  4. Ring counting efficiency > 94 % > 98 %

  5. PID < 1.5 % Over the whole range <3% if dist to wall >=200.cm Correlated to the Performance of AFIT (here wall>300.cm)

  6. Neutrino events • NEUT 4.5.1, JPARC 40 GeV, etc

  7. FC/PC cut • Mono-energetic study shows that the FC/PC cut should be ‘maximum charge<100 pe’ (not 200 pe) • Confirmed by neutrino results (esp. Numu) : Maxq (pe) nue numu

  8. Energy scale numu nue Peak = 140 MeV/c² Peak = 141 MeV/c² Was 170 MeV/c² a month ago…

  9. Ddirection & vertex reconstruction numu nue

  10. numu Nue

  11. Ring counting

  12. PID for neutrinos numu nue PID is defined by ‘probms’ : probms(e-like)<probms(mu-like) => mulike After the tuning probms(mu) can become positive (not very physical but effective) Do not use the standard PID estimator sqrt(|probms(e)|)-sqrt(|probms(mu)|), because those events change the usual shape (although they are correctly PIDed by the software) and will appear to be misPIDed.

  13. Nue appearance analysis • Standard cuts : • polfit5 pi0 cuts : • fully contained in FV (100.5t), visible energy > 100 MeV • Single-ring • E- PID (elike) : probms(e)>probms(mu) • 0.35 < rec. En < 0.85 GeV (‘Enu’) Differences with SK : decay e- are not tagged  less efficient Cosqne < 0.9 Pi0mass < 100 MeV && likelihood difference < 150.0 Remark : In the 2KM vectors, the average neutrino direction is (1.3535E-2 ; -2.24288E-2 ; 0.9996556) Not (0 ; 0 ; 1). The new value is used in this study. comes from JNUBEAM ? The 2km detector should be along the beam axis ?

  14. Decay e- issues • At SK : muedcy==0 -> condition based on the results of the ‘muechk’ program : finds decay e- either in the event (gate) or in subevents (time+#hits+ goodness of low energy fit) -> efficiency based on timing, #hits, goodness (muedcy.f) • In Geant4 : different event structure (no subevent), but all the light is saved (no integration window) -> the decay e- are always saved. • I added a call to ‘muechk’ in the reconstruction program • Decay e- are identified as ‘gate’ e- (need to quantify the efficiency) . Still unclear at this point what can mimick decay e- and confuse muechk in GEANT4 events. • Timing+#hit distributions from G4 under study, not the same as at SK (muechk is not used to processing G4 events) -> unable to copy directly muedcy.f • A simple cut is ‘ngate==0’ ( but it is too efficient, see next slide) • No BG plots with this yet. Need to do better.

  15. Efficiencies (1year) FCFV 1R elike pi0 Enu New : dcy e- (under study) Nue BG Numu CC numuNC 2km (no dcy e- ) : 0.3% 1% 4.5% Enu Cut too strong ? 2km (with ngate==0) : 0.01% 0.9% 3.1% 0.03% 1% 7% At SK (polfit2) :

  16. Prediction @ SK • Using flat F/N ratio (2km/295km)^2 • Using MC true info : oscillate the CC nm, not the NC nm nor the beam ne • Taking into account the efficiency differences between SK & 2km • Sin²2q13 = 1.0, Dm² = 2.5 eV² • From the SK study : 23 BG events expected for 5years

  17. BG at 2km nue, numu, total Reconstructed En energy (MeV) The excess Numu CC BG caused by the untuned reconstruction software Has been successfully removed.

  18. Prediction @ SK Getting closer…

  19. Conclusion • Reconstruction software operational • Performance OK for mono-e. MC and neutrinos • Reconstruction in progress • FV issues : may need to regenerate events in order to compensate the drop in statistics • Decay e- cut : under study • Need to refine the BG plots and understand the nue BG efficiencies (too low) .

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