Preliminary T2K beam simulation using the G4 2km detector Maximilien Fechner In collaboration with C. Walter Status of the 2km simulator Performance of the 2km 8inch simulation + reconstruction Preliminary background estimation @ SK

Status of the GEANT4 simulator 1KT MODE Charge scale tuning with through-going muon K2K-1KT data Energy scale : comparison with K2K-1KT data Using k2k02a ( not 03b) in order to be consistent with the data

Event reconstruction 1KT MODE Vertex resolution : s = 24cm Direction resolution = 2.7°

Energy scale Without any tuning of the pe->MeV tables (ptasmo…) G4 : 141.5 ± 1.5 MeV/c² Data (2000-2001) : 148.1 ± 0.5 MeV/c² Without any tuning of the pe->MeV tables (ptasmo…)

Known problems See previous talks… PID : shifted towards negative values for µ events Can probably be explained because of the excess of indirect light also present in the thrumu simulation data

PID for 2 ring events First ring Second ring The efficiencies are different for the first ring  Differences in the reconstructed pi0 mass

T2K beam event simulation 2km det with 8 inch tubes, ‘old’ setting : length = 16m, 6160 tubes) NEUT 4.5.1 vectors, 2.5° off-axis, 40 GeV protons ( ‘04b’) Processed with k2k02a-special8inch : Geometrical changes only (RPMT=10.0, etc.) No tuning of the pe->MeV tables No optimization of the ring counting & PID cuts e/p0 separation using polfit5 : expected light library not tuned to the 8’’ configuration

Statistics ~45000 nm ~45000 ne With |R| < 300m, -400<Z<600m (‘FV +1m’)

Vertex reconstruction NUE EVENTS NUMU EVENTS Long tail for multi-ring events

Direction reconstruction NUMU : error = 1.9° NUE : error = 3.6°

Energy scale NUMU : energy = 170 MeV/c² NUE : 166 MeV/c²

Ring counting NUMU nue Need tuning ?

PID NUMU NUE Conclusion : k2k02a-8inch needs to be tuned to the MC output

Nue appearance analysis Standard cuts : polfit5 pi0 cuts : fully contained in FV (100.5t), visible energy > 100 MeV Single-ring E- PID 0.35 < rec. En < 0.85 GeV Differences with SK : decay e- are not tagged  less efficient Cosqne < 0.9 Pi0mass < 100 MeV && likelihood difference < 150.0

PI0 plots Numu, nue

Efficiencies (1year) nm CC nm NC Beam ne FC,FV,evis>100 200224 29866 3159 1R 162993 17764 2168 e-like 18219 10605 1971 0.35 < Enrec<0.85 (GeV) 2787 3648 393 pi0 cuts (polfit5) 1536.8 (0.7%) 271.2 (0.9%) 266 (8.4%) At SK (polfit2) : 0.03% 1% 7%

Nue BG @ 2km (1year) Reconstructed nue energy (MeV) nue, numu, total

Prediction @ SK Using flat F/N ratio 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 expected for 5years

Expectation @ SK Total : ~30 events with 0.4 < E < 0.9 GeV Comparable with SK MC expectation

Conclusion simulation of T2K events @ 2km  ne BG rough estimation @ SK (using MC true) : ~30 BG events (sin²2q13=0.1,Dm²=2.5eV²) Todo list for the 2km nue study : Change the geometry (shorter tank) Tune the reconstruction software to G4 Decay e- cut in the G4 simulator Improve the expected light pattern tuning for polfit5 Apply polfit5 to monoenergetic & JPARC MC @ SK (in progress)

Extra slides

BLUE = nue, BLACK = numu