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

Atmospheric muons Incident cosmic ray

 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° 

Muon bundle

First Line detector results arxiv 0812.2095 submitted to Astroparticle Physics Data: 187 hours in 2006

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

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

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

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

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

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%.

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

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

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

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

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

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%]

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 319-94-1 (2) A parameterisation of single and multiple muons in the deep water or ice, Y. Becherini et al. Astroparticle Physics 25 (2006) 1–13

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

Depth Intensity Relation preliminary

Comparison with world data ANTARES: This measurement

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.

Back up

Comparison Mupage/okada

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.

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

Angular resolution

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