1. MC Simulation and optimization of KM2A
Xinhua MA, Yujuan LIU
2nd workshop of air shower detection at high altitude
Feb. 18, 2011

2. outline introduction to km2a array simulation of detectors
data analysis
performance and optimization
summary

3. physics topics in LHAASO, particularly with KM2A
gamma astronomy below 30TeV
(WCDA)
gamma astronomy above 30TeV
(KM2A)
cosmic ray physics: ‘the 1st knee’
(KM2A+ WCDA+WFCA+SCDA)
chain to 1017eV- ‘the 2nd knee’
(KM2A+ WCDA+WFCA)
dark matter indirect search and hadronic interaction
Interdisciplinary Science at high altitude (Atmospheric Physics, geomagnetic physics, Space Environmental Biology, etc. )

4. KM2A: one km2 air shower array
“standard configuration”
ED(electron detectors), 5000m2, 0.5cm lead plate as γ converter, size 1mx1mx2cm, distance 15m
MD(muon detectors), 40000m2, 2.8m dirt overburden，size 6mx6m, distance 30m

5. KM2A simulation program
air shower generation: CORSIKA
program: Linux C (C++)
output file: ROOT

6. parameterization of detectors
ED γ conversion (from GEANT4):
Ne= Ne (ID, E,θ )
MD overburden for muons selection (from GEANT4):
Nμ= Nμ(ID, E, θ, R)
no scintillation detector response yet
ID: particle identification
E: particle energy
θ: zenith angle
R: distance from particle to the center of detector

7. signal pulse: timing y=Ae-λt height Time(ns) Rise time 5ns
fall time 30ns
10%
y=Ae-λt
height
90%
Time(ns)

8. signal pulse: height single particle: prob
Landau distribution of photoelectrons (mean value 10，sigma 2.5),
Nparticle:
Npe=Landau (mean ,sigma)
threshold Npe=7
prob
Npe

9. about electronics, noise
trigger: clock 10MHz, hit time keeping 600ns, Ntrig≥20, readout time window 10μs
single cosmic muon noise
ED: 1kHz/m2
MD: 300Hz/m2

10. data analysis ED: timing, Ne front surface, lateral distribution NKG
direction
core position
size, Ntrig, Ne → energy
MD: Nmu,
Ne vs Nmu→ gamma/hadron discrimination

11. problems solved MD ED punch through in MD→remove hits <10m to core;
MD noise → time window Ttrig ±30ns, ~3 noises in one event ED
For Ntrig<150, noises are many compared with real hits,→ Ttrig ± 500ns time window；
For Ntrig>150 and at the boundary,→ position window only use symmetric part inside the array

12. r<r_mean，shower
r<r_in

13. gamma/proton separation
efficiency(Ntrig<20 && r<500m)
gamma/proton separation
red: gamma
black: proton
lgE0(TeV)
lg(Ntrig)

14. core position resolution (m)
gamma
angular resolution (degree)
red: gamma
black: proton
proton

15. optimization: time precision changed

16. optimization: MD configuration changed

17. summary
a simulation program of KM2A is developed and give us confidence for its performance
optimization of KM2A is continuing
detector simulation (several reports here) will be added into the program to reach full simulation
besides of γastronomy, simulations for other physics topics are continuing