Estimation of KM2A@lhaaso’s Sensitivity
to Gamma Ray point Sources above 30TeV
Cui shuwang
Hebei Normal University
The 2nd workshop of air shower detection at high altitude
IHEP , CAS , Beijing 2011.02.18
Introduction
More and more TeV sources are identified by
ground based cosmic ray experiments so far.
Fine measurement of gamma ray energy spectra
above 30TeV is crucial to identify sources as
galactic cosmic ray accelerators or not
 it is one of important scientific goals of
LHAASO project.
TeV sources
By 2010 Oct.
Some of TeV sources have hard spectrum , A
few of them，showed observational evidences
of being universe accelerators with cosmic rays
being accelerated. This yet to be conformed in
the future experiments（for instance , LHAASO）
with more concrete evidences.
KM2A
KM2A is full duty cycle array of LHAASO
including about 5000 Electron Detectors(EDs) and
1000 Muon Detectors (MDs).
The leading aim of KM2A is to detect gamma
rays above 30TeV from sources with higher
particle discrimination.
Array configure
 EDs ( 1m2)are located in an equilateral triangular grid with a side
length of 15m. Covered area about 1km2. each ED has a 0.5cm
lead cover, and MD has 2.8m molasses overburden.
ED array + MD array

15m 

30m
 MDs ( 36m2 ) are located with a side length of 30 m.

Outline
Simulation data distribution
Angular resolution
Efficiency of the KM2A
Ability for g/p discrimination
Sensitivity calculation
MC Simulation
 Air shower simulation:
 Corsika6600 --- from data bank of Dr zhamin
 Primary energy of particle : 3TeV----10PeV
 Zenith angle: 0—45 degree
 Km2a detector response simulation
 Detector simulation and reconstructed code (detailed refer to
Ma Xinhua’s talk yesterday ).
 Events selection:
 reconstructed zenith angle < 45degree.
 number of triggered detector > 20.
 Inner events: Distance from array center about 500 meter
Reconstructed Events Distribution
Zenith angle distribution
Azimuth angle distribution
Core of events position distribution
γ
p
Unit: meter
Number of fired detectors

p
Energy flux response

Log10(E0) distribution
p
Contribution for g/p discriminition
N
Inner events: Denote event
core reconstructed within
the radius 500 m from array
center.
•gamma
•E0>20TeV
•proton
N
•E0>20TeV
muons of events as a function of Distance from array center
For estimation events’ energy, the events are
divided into 11 parts as the number of triger
Moderate energy
Energy(TeV)
20-30
6.4
30-45
12.6
45-65
15.8
65-90
31.6
90-120
44.7
120-180
63.
180-260
125.9
260-360
251.2
360-500
416.9
500-700
1000.
700~
1584.9
Em
10% of events
Ntrig bin
Eth
log10(Em (GeV))
Linear Correlation of Moderate Energy
with the number of trigered detector
log10(ntrig)
Angular resolution
Space angle (degree)
distribution dropping
directions and reconstructed
directions
Opening angle as the function of Number of trigger.
The plateau of the curve around 0.2 degree
Detecting efficiency
Number of trigger
Gamma survival
g/p discrimination
Proton survival
log（Em GeV）
Ntrig>90
Em ~ 44.6TeV
log（Em GeV）
Calculation of significance to crab source
S (N p ) 


E

E
N  ( Nhits)
N B ( Nhits)
Q
A eff ( E ) J  ( E )dE    ()  T (d )  f ( )
Q
A p eff ( E ) J B ( E )dE  (N trig )  T (d )  f ( )
J  2.86x10 -11 E-2.67cm2s-1 Sr -1TeV -1
 Crab flux：
 CR flux：
J cr  1.43 10-5 E -2.7 cm-2s -1Sr -1TeV -1
 ()  70%
T (d )  365
f ( )  6.53hour
f 015  1.87hour
f1530  2.37hour
f 3045  2.29hour
With One year’s observation , we can detect
events from crab direction are listed
Ntrig bin
N ( >Eth )
NCR ( >Eth )
significance
Icrab (5/yr)
20-30
45359
7345016
59.26
0.084
30-45
41285
5928410
111.05
0.045
45-65
24016
2770965
214.49
0.023
65-90
10732
973588
562.59
0.009
90-120
4976
390627
1042.66
0.005
120-180
2260
144195
600.11
0.008
180-260
1015
51748
924.68
0.011
260-360
351
14146
335.56
0.030
360-500
126
4123
123.23
0.081
500-700
45
1023
44.50
0.225
700~
11
256
11.43
0.875
Background
free points
The KM2A’s sensitivity curve
KM2A@LHAASO
How many by
LHAASO??
Summary
KM2A has the high sensitivity (lower than
0.001Icrab ) to gamma ray sources at above
30TeV region, even if we have not
consider in joint detection with other
equipments yet.
The optimization of Array’s configuration
and detector design is being study now.
THE END