1. MUON FLUX MEASUREMENTS AT THE LSC JRA1-N2 Meeting, Zaragoza, Nov 23 rd 2007 Héctor Gómez Maluenda, University of Zaragoza. hgomez@unizar.es

2. JRA1-N2 Meeting, Zaragoza, Nov 23 rd 2007 Outline Introduction Detection system features Preliminary tests at sea level Measurements in LSC Outlook Summary and Conclusions

3. JRA1-N2 Meeting, Zaragoza, Nov 23 rd 2007 Introduction LSC Depth: 2450 mwe Expected Muon Flux: ~3 10 -3 m -2 s -1 Need to check the theoretical value for the muon flux

4. JRA1-N2 Meeting, Zaragoza, Nov 23 rd 2007 Detection system features Detectors 2 Plastic scintillators BICRON BC 408 of 80 x 40 x 5 cm 3. 2 light guides with PMTs coupled to the scintillators.

5. JRA1-N2 Meeting, Zaragoza, Nov 23 rd 2007 Detection system features Electronic Chain NIM Fast – Slow standard coincidence system.

6. JRA1-N2 Meeting, Zaragoza, Nov 23 rd 2007 Detection system features Readout C-code based acquisition program using a 32 channel I/O digital card. Storage of the energy of both detectors and time (up to 100  s accuracy) for each coincidence event allowing energy and time analysis.

7. JRA1-N2 Meeting, Zaragoza, Nov 23 rd 2007 Detection system features   Muons produce a coincidence event releasing an energy average of 2 MeV per cm. T ~10 MeV Most of the gammas coming from natural background (up to ~3 MeV) release all the energy in one detector  Rejected event. Our set up allows to detect muons coming from a solid angle of ~2 

8. JRA1-N2 Meeting, Zaragoza, Nov 23 rd 2007 Preliminary tests at sea level We made some measurements in Zaragoza (200 m above sea level) in order to adjust the DAQ (gain, thresholds…) and to check the efficiency of the system. The total muon flux expected for a 2  solid angle is 125 m -2 s -1. PDG. S. Eidelman et al., Physics Letters B 592, 1 (2004)

9. JRA1-N2 Meeting, Zaragoza, Nov 23 rd 2007 Preliminary tests at sea level 3 different regions in the spectra - Background region. - Intermediate region.

10. JRA1-N2 Meeting, Zaragoza, Nov 23 rd 2007 Preliminary tests at sea level 3 different regions in the spectra - Background region. - Intermediate region. - Muon region.

11. JRA1-N2 Meeting, Zaragoza, Nov 23 rd 2007 Preliminary tests at sea level 3 different regions in the spectra Muon Flux   = 105.64 ± 0.02 (stat.) m -2 s -1 Systematic errors (~10%): - Not 2  solid angle. - Unconsidered shielding. - Efficiency less than 100%. - Lose of muons: No coincidence. Less energy deposit than expected. COMPATIBLE RESULTS

12. JRA1-N2 Meeting, Zaragoza, Nov 23 rd 2007 Measurements in LSC Location

13. JRA1-N2 Meeting, Zaragoza, Nov 23 rd 2007 Measurements in LSC Results: 50.8 days of measurement.   = 3.94 ± 0.02 (stat.) ± 0.4 (sys.) 10 -3 m -2 s -1 Slightly higher than expected value WHY?

14. JRA1-N2 Meeting, Zaragoza, Nov 23 rd 2007 Measurements in LSC A Possible Explanation: Mountain Profile.

15. JRA1-N2 Meeting, Zaragoza, Nov 23 rd 2007 Measurements in LSC A Possible Explanation: Mountain Profile. Hall B5.04 ± 0.06(stat) ± 0.5(sys) 10 -3  m -1 s -1 +28% Hall A3.94 ± 0.02(stat) ± 0.4(sys) 10 -3  m -1 s -1 Old Lab3.59 ± 0.04(stat) ± 0.4(sys) 10 -3  m -1 s -1 -9%

16. JRA1-N2 Meeting, Zaragoza, Nov 23 rd 2007 Outlook Complete measurements in the Old Lab and Hall B at LSC trying to corroborate and quantify the influence of the mountain profile in the muon flux. Make a Monte Carlo study to estimate the muon flux in the different locations (ongoing).

17. JRA1-N2 Meeting, Zaragoza, Nov 23 rd 2007 Summary and Conclusions We developed and tested successfully an experimental set up to measure the muon flux. The muon flux measured at the Hall A of the LSC seems to be slightly higher than the expected value regarding the depth of the Lab. A possible explanation for this difference could be the dependence between the muon flux and the mountain profile. Preliminary measurements in other locations of the LSC and the Old Lab seem to corroborate this theory. More accurate measurements and Monte Carlo simulations are ongoing to obtain final conclusions.

18. MUON FLUX MEASUREMENTS IN THE LSC JRA1-N2 Meeting, Zaragoza, Nov 23 rd 2007 Héctor Gómez Maluenda, University of Zaragoza. hgomez@unizar.es

19. JRA1-N2 Meeting, Zaragoza, Nov 23 rd 2007 Stability of the Rate Different orientation

20. JRA1-N2 Meeting, Zaragoza, Nov 23 rd 2007 Different Analysis Methods Method i) Ch u & Ch l > 600 Method ii) Ch u & Ch l > 170 Method iii) Ch u || Ch l >170

21. JRA1-N2 Meeting, Zaragoza, Nov 23 rd 2007 Different Analysis Methods