The ANTARES detector: background sources and effects on detector performance S. Escoffier CNRS Centre de Physique des Particules de Marseille on behalf of the ANTARES Collaboration

S. Escoffier, ANTARES background sources and effects ICRC ’07, Merida Detection Principle   43° Sea floor Reconstruction of  trajectory (~ ) from timing and position of PMT hits interaction Cherenkov light from  3D PMT array

Background sources

S. Escoffier, ANTARES background sources and effects ICRC ’07, Merida Atmospheric muons and neutrinos Muons induced by atm Atmospheric  10TeV 1TeV 10TeV  (cm -2 s -1 sr -1 ) p  p,    

S. Escoffier, ANTARES background sources and effects ICRC ’07, Merida Rejection of the atmospheric background Optical Modules oriented downward Detector at great depth (~2475 m) Atmospheric muons Atmospheric neutrinos Energy spectral index E  : Some  atm can be reconstructed as upgoingProblem:  atm can be used for flux measurementAdvantage:  =-2.2 / -2.0 for from cosmic accelerators  =-3.7 for atm Diffuse flux: (moon shadow) Point-like sources: Reduced background (see J. Aguilar’s talk)  atm can be used for pointing accuracy

S. Escoffier, ANTARES background sources and effects ICRC ’07, Merida Optical background baseline bursts Bioluminescence bursts: Animal species which emit light by flashes, spontaneous or stimulated around the detector. Baseline: 40 K decays Bacteria luminescence

S. Escoffier, ANTARES background sources and effects ICRC ’07, Merida Absolute PMT efficiencies, stable in time 40 K decays 14.5 ± 0.4 Hz 40 K 40 Ca  e - (  decay)  Cherenkov 13 Hz ± 4 Hz (syst.) 40 K coincidence rate Conclusions: from Gaussian fit on data: from simulation: Agreement within 5% 40 K constant contribution at 40 kHz

S. Escoffier, ANTARES background sources and effects ICRC ’07, Merida Baseline variations Connection Line 1 Connection Line 2  Sometimes high bioluminescence activity 50 m 14.5 m 100 m Buoy top storey: 1 optical module current profiler middle storey: 3 optical modules bottom storey: LED beacon base: acoustic transducer MILOM 40 K

Effects of the background

S. Escoffier, ANTARES background sources and effects ICRC ’07, Merida Status Such a study requires detailed simulations for various values of baseline/burst fraction for each physics channel Such a study requires detailed simulations for various values of baseline/burst fraction for each physics channel Impact of bioluminescence will be very different for: Diffuse sources: no pointing accuracy, high energy cut ~50 TeV Point sources: high pointing accuracy, no or moderate energy cut Transient sources: reduced background due to time constraint Dark matter = low energy

S. Escoffier, ANTARES background sources and effects ICRC ’07, Merida Neutrino effective area

S. Escoffier, ANTARES background sources and effects ICRC ’07, Merida Impact on the data acquisition Bioluminescence burst > 500 kHz High rate veto : OM data is not transmitted to shore during burst. Baseline > 300 kHz Sampling : N / M frames are transmitted to shore Off-shore trigger L1: only local coincidences transmitted to shore Baseline < 300 kHz All data to shore

Some ideas are being studied…

S. Escoffier, ANTARES background sources and effects ICRC ’07, Merida Standard trigger New trigger : N local coincidences with a 3D causality trigger Old trigger : N local coincidences anywhere inside the detector For N=5, accidental trigger rate increases as  f 10 Problem: Online Data filter Level 1 Trigger (L1): Look for local coincidences (2/3 OMs in the same storey) or Charge > 3 p.e. on a single OM

S. Escoffier, ANTARES background sources and effects ICRC ’07, Merida Generated event 1 hit in storey 2 hits in storey in 1 same OM 3 hits in storey 2 hits in storey in 2 different OM  3 hits in storey in  2 different OM Trajectory of light from track to OM track  One event produce hits in cluster of storeys ANTARES lines

S. Escoffier, ANTARES background sources and effects ICRC ’07, Merida Alternatives trigger Causality algorithms : N x T2/T3 with a causality requirement Cluster trigger : Cluster T2 = Cluster T2 = Two L1 in adjacent storeys Cluster T3 = Cluster T3 = Two L1 in next to adjacent storeys To remove noise hits…  Work in progress

Conclusion

S. Escoffier, ANTARES background sources and effects ICRC ’07, Merida Review of the bioluminescence activity 2007 Connections Line 3, 4 & 5 (6 months) 2006 Connection Line 1 Connection Line 2

S. Escoffier, ANTARES background sources and effects ICRC ’07, Merida Latest bioluminescence activity Proportion of time where mean counting rate higher than given value Spring Spring2007 Summer Autumn Winter2006/7  Bioluminescence activity is very low since one year

S. Escoffier, ANTARES background sources and effects ICRC ’07, Merida Conclusions Background sources are being understood trigger and reconstruction efficiency To optimize trigger and reconstruction efficiency at high bioluminescence levels Bioluminescence activity is low since 1 year Studies are still in progress: Some seasonal effects can appear, due to biological activity To evaluate precise effects of high bioluminescence activities on the detector performances (effective area, pointing accuracy, dead time, …)  A lot of data to analyse