1. 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

2. 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.

3. TeV sources
By 2010 Oct.

4. 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.

5. 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.

7. Array configure ED array + MD array
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.
 m 
ED array MD array
 m 
MDs ( 36m2 ) are located with a side length of 30 m.

8. Outline Simulation data distribution Angular resolution
Efficiency of the KM2A
Ability for g/p discrimination
Sensitivity calculation

9. MC Simulation Air shower simulation: Km2a detector response simulation
Corsika 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

10. Reconstructed Events Distribution
Zenith angle distribution
Azimuth angle distribution

11. Core of events position distributionγ p
Unit: meter

12. Number of fired detectors p

13. Energy flux response  p
Log10(E0) distribution

14. Contribution for g/p discriminition
Inner events: Denote event core reconstructed within the radius 500 m from array center.
gamma
E0>20TeV
proton
E0>20TeV
muons of events as a function of Distance from array center

15. Moderate energy Energy(TeV)
For estimation events’ energy, the events are divided into 11 parts as the number of triger
Ntrig bin
Moderate energy Energy(TeV)
20-30
6.4
30-45
12.6
45-65
15.8
65-90
31.6
90-120
44.7
63.
125.9
251.2
416.9
1000.
700~
1584.9
10% of events Em
Eth

16. Linear Correlation of Moderate Energy with the number of trigered detector
log10(ntrig)
log10(Em (GeV))

17. Angular resolution
Space angle (degree) distribution dropping directions and reconstructed directions
That is the km2a’s angular resolution as the function of number of hits.
Opening angle as the function of Number of trigger. The plateau of the curve around 0.2 degree

18. Detecting efficiency
Number of trigger

19. g/p discrimination Gamma survival log（Em GeV） Proton survival
Ntrig>90 Em ~ 44.6TeV
log（Em GeV）

20. Calculation of significance to crab source
Crab flux：
CR flux：

21. 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
59.26
0.084
30-45
41285
111.05
0.045
45-65
24016
214.49
0.023
65-90
10732
973588
562.59
0.009
90-120
4976
390627
0.005
2260
144195
600.11
0.008
1015
51748
924.68
0.011
351
14146
335.56
0.030
126
4123
123.23
0.081 45
1023
44.50
0.225
700~ 11
256
11.43
0.875
Background free points

22. The KM2A’s sensitivity curve

23. How many by LHAASO??

24. 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.

25. THE END