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

2. 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

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

4. 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

5. 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

6. 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
?????

7. 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

8. NEW MEASUREMENTS IN PROGRESS (in-situ calibration tools)
absorption length
official photon tables based on AC9 in-situ measurements
simulation was repeated with:
labs %
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%

9. 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 %

10. 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

11. 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  % / 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 %

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

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

15. Comparison among primary model and recent measurements