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
Vertex resolution : s = 24cm
Direction resolution = 2.7°
1KT MODE
Energy scale
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 :
• 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
• polfit5 pi0 cuts :
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