1. 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 SK

2. 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

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

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

5. 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

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

7. T2K beam event simulation
2km det with 8 inch tubes, ‘old’ setting : length = 16m, 6160 tubes)
NEUT 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

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

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

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

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

12. Ring counting
NUMU
nue
Need tuning ?

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

14. 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

15. PI0 plots
Numu, nue

16. 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)
(0.7%)
271.2 (0.9%)
266 (8.4%)
At SK (polfit2) :
0.03% 1% 7%

17. Nue 2km (1year)
Reconstructed nue energy (MeV)
nue, numu, total

18. 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

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

20. Conclusion simulation of T2K events @ 2km
 ne BG rough 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 SK (in progress)

21. Extra slides

22. BLUE = nue, BLACK = numu