1. Atmospheric muons in ANTARES
Claire Picq (CEA Saclay-APC)
On behalf of the ANTARES collaboration
Moriond 2009

2. Atmospheric muons
Incident cosmic ray

3.  350 m Storey 14.5 m Cable to shore 100 m Junction Box ~60 m
Link cable
Junction
Box
Cable to
shore
2500m depth
Storey
45° 

4. Muon bundle

5. First Line detector results
arxiv submitted to Astroparticle Physics
Data: 187 hours in 2006

6. Depth Intensity Relation
Systematic errors on the data ~50% mainly due to the PMT acceptance
Statistical errors are negligible

7.  Verticalization  Sea level H
H / cos 
To take into account the zenith dependence
( sec) of muon flux at sea level (up to 60°):

8. Depth Intensity Relation
Systematic errors on the data ~50% mainly due to the PMT acceptance
Statistical errors are negligible

9. FIVE LINE DETECTOR RESULTS
Data: 7 months in 2007 _ Two analyses:
Low energy threshold muon flux from adjacent storeys
Reconstructed muon flux
Simulation: Corsika
with Hörandel flux (1) and QGSJet 0.1
(1) On the knee in the energy spectrum of cosmic rays, Jörg R. Hörandel Astroparticle Physics 19 (2003) 193–220

10. Low energy threshold muon flux from adjacent storeys
L1 = two hits in OMs of the same storey
A2 = a pair of L1 on two adjacent storeys compatible with the muon travel time
Taking into account correlated A2  the number of muons at depths between 2030 to 2380 m
L1 = two hits in different OMs of the same storey in a time window of ±20 ns
A2 = a pair of L1 coincidences in two adjacent storeys of the same line, compatible with the muon travel time between two storeys.
Taking into account correlated A2, we count the number of muons at depths between 2030 to 2380 m

11. Low energy threshold muon flux from adjacent stories
Systematic errors:
OM angular acceptance: +40/-30%
absolute normalization of PMT efficiency : +/-15%
water properties +5/-15%.

12. FIVE LINE DETECTOR RESULTS
Two analyses:
Low energy threshold muon flux from adjacent storeys
Reconstructed muon flux

13. Measurement of the muon flux
<m>MC~1.19 is the simulated multiplicity (for every zenith angle)
Effreco~95% is the reconstruction efficiency
Areaeff is the effective area at the trigger level
∆T is the time duration of the data taking =
17.8 days

14. Effective Area at trigger level
Effective area for muons with
E>20 GeV

15. Angle between the optical module axis and the photon
Systematic effect (1)
preliminary
45° 
cos θ
angular acceptance
Dowgoing muon -> new measurements of the angular acceptance
Angle between the optical module axis and the photon
Loss in the muon flux when the angular acceptance is changed from simulation to measurements

16. Systematic effect (2)
Loss/gain in the muon flux when the absorption length is increased/decreased by 10%

17. Preliminary systematics
Charge calibration effect: ±10% (being estimated)
Absorption length : ±25%
Angular acceptance:
-35% presented
+20%due to uncertainty of angular acceptance between two different OMs
Summary from all of the above : [-44%;+33%]

18. Muon atmospheric flux at 2000 m
(1)
(2)
preliminary
(1) On the atmospheric muon energy spectrum in the deep ocean and its parameterization , Atsushi Okada, ICRC report
(2) A parameterisation of single and multiple muons in the deep water or ice, Y. Becherini et al. Astroparticle Physics 25 (2006) 1–13

19. Verticalization: reminder
Sea level  H 
H / cos 
To take into account the zenith dependence
( sec) of muon flux at sea level (up to 60°):

20. Depth Intensity Relation
preliminary

21. Comparison with world data
ANTARES:
This
measurement

22. Conclusion
ANTARES was designed to detect up-going muons (OMs looking downwards, upper part of the OMs in black).
The large number of downgoing muons allows a good understanding of our detector: first estimations of the muon flux in ANTARES  in agreement with the world data.

23. Back up

24. Comparison Mupage/okada

25. Data We choose 17.8 days of data in June 2006.
We have more that 2.3 M events.
In muon studies, we are limited by the systematic errors
With 2.3 M events, we do not have any “significative” statistical errors.

26. Effect of the MC on the flux
If number of events in the simulation increase, then the flux decreases

27. Angular resolution

28. Scattering between the measurements of two Oms
Angular acceptance and efficiency
A new parameterization for the angular acceptance (GEANT4 –Genova acceptance) have been sent to Annarita
The uncertainty to attribute to the a.a. is being presently evaluated:± 20%
Scattering between the measurements of two Oms
cosC