1. Performances of the KM2A prototype array J.Liu for the LHAASO Collaboration Institute of High Energy Physics, CAS 32nd International Cosmic Ray Conference, Beijing, China, 11-18 August 2011

2. Outline: 1. Introduction 2. Experiment setup 3. Performances of the KM2A prototype array 4. Conclusion

3. 1. Introduction The LHAASO project focuses on the study of subTeV-1Pev gamma ray astronomy and 5Tev-1Eev cosmic ray physics by using a compound detector array distributed in one square kilometer

4. 2. Experiment setup Electromagnetic particle Detector 1.2m 1m

5. KM2A prototype array in Beijing

7. Red stars show the location of 42 cassettes of the plastic scintillation in ARGO array

8. KM2A prototype array overlaps with the ARGO array, so we can match event one by one. (above 95% event of km2a prototype array can match to ARGO’s) Fig. An example shower front observed by ARGO-YBJ (blue) and the prototype array (red).

9. Current status Data taken since October 2010 Trigger rate about 49Hz 1.5 GB/day transferred to IHEP

10. 3. Performances of the KM2A prototype array 1) ADC count of single muon; 2) Single channel rate; 3) Trigger rate; 4) Shower direction reconstruction; 5) Angular resolution; 6) Long term stability;

11. MPV amplitude of each ED in case of single particle ADC count 1) ADC count of single particle

12. Single channel rate vs. threshold value 2.5 3.75 5 6.25 7.5 8.75 8 threshold value (mv) Hz The trigger threshold 2) Single channel rate

13. The measured trigger rates (blue) vs. event trigger threshold is consistent with that estimated by the ARGO-YBJ data (red).  dt distribution under the trigger condition ( 5 cassettes “fired” out of 42 cassettes )  event rate is about 49Hz 3) Trigger rate

14. 4) Shower direction reconstruction Zenith (degree) Azimuth (degree)

15. Fig. Space angles distribution between the direction reconstructed with ARGO data (conic fit) and the one with prototype array data (plane fit) Events chosen: the shower reconstructed core location of 10 m to the center of the array 5) Pointing and Angular resolution

16. Result Km2a nhit ARGO nhitShower Energy Angular resolution (in degree) >5190413Tev2.0 >10346635Tev1.4 >15503950Tev1.2 >206610100Tev1.1 >258176140Tev1.0 >309684180Tev0.9

17. The charge of single muon vs. time (MJD) 6) Long term stability The event rate vs. time (MJD)

18. 4. Conclusion KM2A prototype array has been in stable operation since October 2010 The performances of KM2A prototype array meet design requirements.

19. Thank you! We would like to express their gratitude to the ARGO-YBJ collaboration for the powerful support.