1. Coincidence analysis in ANTARES: Potassium-40 and muons  Brief overview of ANTARES experiment  Potassium-40 calibration technique  Adjacent floor coincidences as very basic atmospheric muon signal ITEP winter school Feb 12, 2008 Dmitry Zaborov (ITEP, Moscow, Russia)

2. Feb 12, 2008D. Zaborov. Coincidence analysis in ANTARES2 Detection principle   43° Sea floor p  10 4 atm  p,  10 7  atm  Reconstruction of  trajectory (~ ) from timing and position of PMT hits interaction Cherenkov light from  3D PMT array  1-100 cosm effective area ~ 0.1 km 2 in TeV range angular resolution ~ 0.3º at 10 TeV Hadronic showers from CC/NC interactions can be detected as well

3. Feb 12, 2008D. Zaborov. Coincidence analysis in ANTARES3 Detector layout ~70 m 12 lines (900 PMTs) 25 storeys / line 3 PMTs/storey 350 m 100 m 14.5 m Junction box Readout cables 40 km to shore Horizontal layout Sea bed ~ -2500 m a storey

4. Feb 12, 2008D. Zaborov. Coincidence analysis in ANTARES4 Current status L11 L9 L12 L7 L8 L6 L4 L2 L3 L5 L1 IL07 seismometer 100 m N Junction box Submarine cable to shore 42°50’ N 6°10’E 10 detector lines + instrumentation line operational (since December 07) (Feb. 2008) 2 more lines coming soon ~ 2 muons/sec ~ 5 neutrino/day (atmospheric) L10 * Cable path is shown only indicatively

5. Feb 12, 2008D. Zaborov. Coincidence analysis in ANTARES5 Basic detection and calibration elements Hydrophone: acoustic positioning Optical Module: 10” PMT in 17” glass sphere photon detection Local Control Module (in Ti container): Front-end ASIC, Clock, DAQ/SC, compass/roll/pitch Optical Beacon with blue LEDs: timing calibration

6. Feb 12, 2008D. Zaborov. Coincidence analysis in ANTARES6 In situ calibration with Potassium-40 40 K 40 Ca  e - (  decay)  Cherenkov Gaussian peak on coincidence plot Peak offset Rate of correlated coincidences High precision (~5%) monitoring of OM efficiencies time calibration confirmed 15 Hz MC prediction 13+/-4 Hz (“NIM” angular acceptance) Mean ≈ 0 RMS 0.7 ns No dependence on bioluminescent activity has been observed - this confirms the single photon character of bioluminescent emission

7. Feb 12, 2008D. Zaborov. Coincidence analysis in ANTARES7 Example: calibration of Line 8 Three OM sensitivity factors s i can be extracted using 3 equations rate ij = k * s i * s j factor k gives absolute scale; k can be determined from Monte-Carlo (or, in opposite, used to constrain parameters of Monte-Carlo) OM-OM time offsets determined using K-40 (basically single photoelectrons) w.r.t Dark room calibration (high amplitude laser pulse) * No charge calibration used * No walk correction included Unofficial technical plot I,j=1,2,3

8. Feb 12, 2008D. Zaborov. Coincidence analysis in ANTARES8 Time evolution (example) Time delays seem stable (within our accuracy) Gradual decrease is probably due to PMT gain drift Steep changes are threshold tunings Unofficial technical plot K40 runs are taken once a week K40 trigger can run in parallel with other triggers (e.g. GRB trigger or directional triggers) and can be even used for physics analysis as is

9. Feb 12, 2008D. Zaborov. Coincidence analysis in ANTARES9 Time evolution of average K-40 coincidence rate start at 12 Hz “degradation” tuning 2 One year of “degradation” could be fully compensated by the tuning tuning 2 -> 15.5 Hz * Other Lines show similar behavior tuning 1 Unofficial technical plot

10. Feb 12, 2008D. Zaborov. Coincidence analysis in ANTARES10 Delay between adjacent floors (theory) Δt = L / c ≈ 50 ns Δt ~ L n / c ~ 70 ns L Δt ~ 0 But light hits back of the OM ≈ fixed number for exactly vertical muonsa wide distribution in general from to The most basic signal of physics events in ANTARES Delay between storeys No systematic errors from trigger or reconstruction algorithms No background

11. Feb 12, 2008D. Zaborov. Coincidence analysis in ANTARES11 Adjacent floor coincidences: measurement Integral under the peak ~ muon flux Shape is sensitive to angular acceptance of optical modules and angular distribution of muon flux The effect of muon flux reduction with depth is directly (!) measured Low energy threshold (compared to full reconstruction) The analysis can be repeated for every detector storey separately This plot is preliminary Actual comparison of peak amplitude with Monte Carlo will be made after OM angular acceptance issues are fixed, OM efficiency is well known and all dead time corrections applied

12. Feb 12, 2008D. Zaborov. Coincidence analysis in ANTARES12 Summary A calibration technique using Cherenkov light from Potassium-40 decays in sea water has been developed –Sensitivity of optical modules is now controlled using K-40 –K-40 is also a useful tool for time calibration A simple but powerful technique for atmospheric muon measurement is developed based on the idea of adjacent floor coincidences –First results allowed to reject one of the models of OM angular acceptance –Depth dependence and absolute normalization of atmospheric muon flux can be extracted using this new approach –Possibility to reject certain hadronic interaction models or (less likely) primary flux models is being investigated –Promising prospects to use adjacent floor coincidences in the trigger