Systematic uncertainties in MonteCarlo simulations of the atmospheric muon flux in the 5-lines ANTARES detector VLVnT08 - Toulon 22-24 April 2008 Annarita Margiotta Università di Bologna and INFN on behalf of the ANTARES Collaboration

interaction neutrino downgoing muon flux (vertical) upgoing muon flux  muon interaction neutrino  muon interaction downgoing muon flux (vertical) upgoing muon flux ANTARES = neutrino telescope BUT atmospheric ms are the most abundant signal study of detector response to the passage of atmospheric muon flux tool to check our understanding of the detector

outline MC simulation of the atmospheric muon flux in ANTARES discussion on systematic effects due to: physics uncertainties environmental parameters geometrical parameters conclusions

simulation of atmospheric muons ANTARES PRESENT TOOLS full simulation MUPAGE parameterization FULL SIMULATION huge CPU time requirement weighted production fully adaptable to user request PARAMETERIZATION : MUPAGE see Maurizio Spurio talk at this workshop

DATA full MC simulation of atmospheric muons MUSIC CORSIKA + QGSJET generation of atmospheric showers sampling on the surface of the “can” Primary ions -> p, He, N, Mg, Fe Primary energy -> 1  105 TeV/nucleon Primary zenith angles –> 0° 85° Energy threshold for muons at sea level -> 0.5 TeV for 0° < q < 60° 1 TeV for 60° < q < 85° primary spectrum  E-2 ~1010 showers propagation of muons through water photon tables hit probabilities Cherenkov light generation muon transport through det volume detector response DATA format conversion & trigger processor reconstruction & analysis J. Horandel, Astrop. Phys., 19(2003)193

NO quality cuts applied checks on systematic effects zenith and azimuth distributions of reconstructed events with 5-lines detector agreement within 10 % between data and MonteCarlo  maybe too optimistic checks on systematic effects Systematic effects due to physics hadronic interaction model  ~ 20 % ÷ 40 % primary cosmic ray model  ~ 30 % Systematic effects due to environmental and geometrical parameters water absorption length photomultiplier efficiency and geometry ?????

physics uncertainties 1: primary cosmic ray flux hadronic interaction model full MC simulation of atmospheric muons MUSIC CORSIKA + QGSJET generation of atmospheric showers sampling on the surface of the “can” propagation of muons through water photon tables hit probabilities Cherenkov light generation muon transport through det volume detector response absorption length DATA format conversion & trigger processor reconstruction & analysis photomultiplier description physics uncertainties 2: primary cosmic ray flux J. Horandel, Astrop. Phys., 19(2003)193

NEW MEASUREMENTS IN PROGRESS (in-situ calibration tools) absorption length official photon tables based on AC9 in-situ measurements simulation was repeated with: labs - 10 % labs +10 % no effect on the shape of the distribution - 20 % in reconstructed track rate  + 25 % in reconstructed track rate NEW MEASUREMENTS IN PROGRESS (in-situ calibration tools) expected uncertainty < 10%

photomultiplier parameterization - 1 Hamamatsu sheet and nominal values as reference photon tables produced using PMT efficiency decreased by 10 % NEW MEASUREMENTS IN PROGRESS expected uncertainty reduction PMT total efficiency: photocatode area quantum efficiency collection efficiency mu-metal cage shadow 15 % reconstructed track rate (for atmospheric m flux) effect on n flux  - 7 %

photomultiplier parameterization - 2 cut-off on the angle between PMT axis and Cherenkov photon direction neutrino region muon region -0.8 -0.65 uncertainty ~20-25 % on reconstructed track rate mainly downward tracks

summary new measurements in progress to reduce errors systematic uncertainties on reconstructed track rate in MC simulations due to environmental and geometrical parameters atmospheric muon flux in the 5-lines detector absorption length : labs ± 10 %  + 25 % / - 20 % PMT effective area : – 10 %  - 15 % effect strongly reduced (about 7%) for neutrinos cutoff in angular efficiency  20 % / 25 % mainly affects downward going track reduced effect on neutrinos total systematic uncertainties ~ ± 35 % no effect on angular distribution shape GOOD UNDERSTANDING OF ANTARES DETECTOR new measurements in progress to reduce errors uncertainties due to hadronic model and primary flux 30 – 50 %

the “can” can detector instrumented volume sea floor extension of ~2.5 - 3 att w.r.t. the instrumented volume particle tracking only detector instrumented volume particle tracking AND Cherenkov light generation sea floor

Simplified version of the polygonato model (only 5 mass groups)

Comparison among primary model and recent measurements