J.P. Gómez-González

1. Calibración temporal del telescopio de neutrinos ANTARES mediantetrazas de muonesatmosféricos J.P. Gómez-González

2. Outline • Introduction: • The ANTARES neutrino telescope • Time calibration • Muon track residuals based method: • Description and implementation • Inter-line calibration • Intra-line calibration • Cross-check with the OB system • Detector performance • Summary/Conclusions 1 • Bienal de Física 2013 • Calibración temporal en ANTARES

3. Neutrino astrophysics • Astroparticle physics: • Point-like sources • Diffuse flux, galactic plane neutrino flux • Flaring blazars / microquasars • GRBs • Fermi Bubbles • Particle physics: • Neutrino oscillation • Atmospheric neutrino and muonflux • Cosmic ray anisotropy / composition • Shower reconstruction • Electromagnetic showers p γ n ν • Detector related: • Timing / Positioning • Moon shadow • Water optical properties, group velocity of light • Acoustics, bioluminescence • Searches: • Dark matter annihilation,magnetic monopoles, nuclearites • Multi-messenger astronomy: • Gravitational waves, Auger CRs, • optical telescopes 1 • Bienal de Física 2013 • Calibración temporal en ANTARES

4. Detection principle Cherenkov light from m 42° Earth’s crust m nm interaction Detector: 3D array ofphotomultipliers Detection principle “We propose getting up an apparatus in an underground lake or deep in the ocean in orderto determine the location of charged particles with the help of Cherenkov radiation” M. Markov, 1960 At high energies the neutrino and the muon are almost collinear  Astronomy 1 • Bienal de Física 2013 • Calibración temporal en ANTARES

5. Physical background p, a nm p m nm nm Downgoingmuon flux is about 6 orders of magnitude higher than neutrino flux • Huge (downgoing) atmospheric muon contamination • Irreducible contribution from atmospheric neutrinos 1 • Bienal de Física 2013 • Calibración temporal en ANTARES

6. The ANTARES detector ANTARES is a submarine neutrino telescope made up by: 885 10” PMTs distributed in triplets of storeys along 12 strings of 450 meters longitude placed 2475 depth following an octagonal layout. 1 • Bienal de Física 2013 • Calibración temporal en ANTARES

7. Muon track reconstruction Time and position information of the hits registered by the PMTs is used for track reconstruction Offline strategy based on the time residual; difference between the measured hit time and the time expected from the fitted muon (given a certain set of track parameters) 1 • Bienal de Física 2013 • Calibración temporal en ANTARES

8. Time residuals The reconstruction algorithm is a multi-step approach which final step consists on the minimization of the time residuals PDF Time residuals PDF Time residual distribution for data events Distribution of the quality of the reconstruction parameter for data and MC events 1 • Bienal de Física 2013 • Calibración temporal en ANTARES

9. Time calibration • A good timing of the OMs is crucial to guarantee the expected performance of the telescope. • ANTARES is designed achive an angular resolution better than 0.5º at high energies (~10 TeV) • Relative time calibration • Intra-line: synchronize all the OMs within a line with respect to a common reference (one OM in the first storey) • Inter-line: calibrate all the OMs with respect to a unique (global) reference 1 • Bienal de Física 2013 • Calibración temporal en ANTARES

10. Method description Using physics events, time offsets are computed iteratively: A probe line is (randomly) selected which hits are not used in the track reconstruction Fit muon trajectory using the remaining hits Compute time residuals using the fitted track* parameters Distribution of these residuals are histogramed and fitted to a Gaussian (around peak) which mean value is interpreted as the line offset Time offsets measured in the previous step are accounted for in a new iteration The full process is repeated until the size of the correction is sufficiently small *Only rather good reconstructed events (Λ>-5.6) are used 1 • Bienal de Física 2013 • Calibración temporal en ANTARES

11. Inter-line offsets Time residual distributions for different iterations of the procedure Iteration 1 Iteration 5 1 • Bienal de Física 2013 • Calibración temporal en ANTARES

12. Inter-line offsets Time offsetsobtained for the 12 detection lines Cumulative correctionsas a function of the number of iterations of the procedure 1 • Bienal de Física 2013 • Calibración temporal en ANTARES

13. Inter-line time offsets Time offsets measured using physics runs with about 5 days livetime L1 L2 L5 L3 L4 L6 L9 L7 L8 L10 L11 L12 Detection lines layout Largest offsets is found for Line 8 (where laser beacon is located) 1 • Bienal de Física 2013 • Calibración temporal en ANTARES

14. Impact on the reconstruction Correcting the inter-line timing translates in an increase of the number of events better reconstructed(better data/MC agreement) Time residual distribution fro data events Distributions of the quality of the reconstruction parameter for vertical (left) and inclined (right) events 1 • Bienal de Física 2013 • Calibración temporal en ANTARES

15. Effect on the performance Why if we don’t correct the inter-line timing? By mis-calibrating the lines, and using MC simulation, we check the effect on the angular resolution Angular error between the reconstructed muon trajectory and the true neutrino direction: a wrong inter-line timing results in a ~40% degraded resolution 1 • Bienal de Física 2013 • Calibración temporal en ANTARES

16. Cross-check with the LB Using the laser beacon placed at the bottom of line 8 we have cross-checked the results obtained using atmospheric muons Difference of the time offsets measured with these two methods Several calibration runs are used to compute the time offset (fit to the green point) 1 • Bienal de Física 2013 • Calibración temporal en ANTARES

17. Cross-check with the LB Using the calibration constants provided by the method using atmospheric muon data improves (slightly) the reconstruction Distributions of the quality of the reconstruction parameter for vertical (left) and inclined (right) events 1 • Bienal de Física 2013 • Calibración temporal en ANTARES

18. Time offsets stability No variations are expected unless PMT HV tuning or replacement of a line reference OM is performed 1 • Bienal de Física 2013 • Calibración temporal en ANTARES

19. Intra-line timing Reconstruction uses the most updated calibration constants stored in the data-base check correction to the T0’s timing first obtained using the LED Beacon system Similar iterative procedure, but optimized to reduce the number of runs needed to accumulate good statistics Time residual distribution for one OM 1 • Bienal de Física 2013 • Calibración temporal en ANTARES

20. Intra-line timing Reconstruction uses the most updated calibration constanst stored in the data-base check correction to the T0’s timing first obtained using the LED Beacon system 90% of correction are smaller than 1ns 1 • Bienal de Física 2013 • Calibración temporal en ANTARES

21. Summary/Conclusions • Time calibration is crucial to achieve the best performance of the telescope: • A new method using atmospheric muon data has been implemented which canwork out the parameters of the relative timing calibration without stopping the physics data acquisition • Results on the inter-line timing: • Correcting the time offsets translates in up to a factor 2 enhancement of the number of good reconstructed events traversing diagonally the detector (improved data/MC agreement) • Improvement (40%) on the angular resolution is expected • Cross-chek of the laser beacon results. • Provides the official calibration constants used for data processing • Ongoing progress for the T0s calibration: • Cross-check of the results with the LED beacon 1 • Bienal de Física 2013 • Calibración temporal en ANTARES

22. Graciasporsuatención!