1. CEA DSM Irfu Reconstruction and analysis of ANTARES 5 line data Niccolò Cottini on behalf of the ANTARES Collaboration XX th Rencontres de Blois 21 / 05 / 2008

2. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini2 Outline of the talk The ANTARES experiment –Detector layout –Data acquisition system Data analysis –Event reconstruction –Selection of neutrino events standard approach an example of the work being pursued

3. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini3 The ANTARES detector 12 lines, 900 PMTs -2500 m 450 m ~60 m

4. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini4 The detected signal Muon (Cherenkov) –2 µs crossing time 40 K decay –Continuous background  30 kHz * Bioluminescence –Continuous background  30 kHz * –Occasional bursts ~MHz Simulation 2 min * PMT 10’’, threshold 0,3 p.e.

5. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini5 The Trigger Front end chip digitizes charge and time of a light signal “ALL DATA TO SHORE” SCHEME: all data transmitted through multiplexed Gigabit links computer farm running a software trigger:  the whole data flow can not be written to disk look in all directions for light signals compatible with a muon track muon triggered event rate: ~1 Hz

6. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini6 The physics signal Keep all the muon tracks; then filter to extract the neutrino signal Muon flux at the detector Atmosphere Earth Sea 10 7 atmospheric  per year 3000 atmospheric per year Cosmic

7. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini7 5 line data analyzed 169 days 29 Jan 20074 Dec 2007 310 days

8. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini8  43° interaction Sea floor Cherenkov light from  3D PMT array  Event reconstruction Reconstruction of  trajectory from time, charge and position of PMT hits

9. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini9 Event reconstruction z-t event display z y x

10. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini10 Event reconstruction Complicated pattern; a bundle can be misreconstructed as an upward going track Atmospheric muon bundle

11. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini11 Reconstruction algorithm Muon track fit in 3 steps: 1) Prefit: (x,y,z,t) linear fit through the photon hits 2) Improved  2 minimization (charge weights) 3) Time residual pdf (charge weights) Direct Cherenkov emission Diffused light Electronics effect Local minima possible: reiteration with 8 different starting points (prefit rotations)

12. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini12 Reconstruction quality (MC simulation with 12 lines detector)

13. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini13 5 line data reconstruction Dominated by the tail of atmospheric muons badly reconstructed as upward going

14. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini14 Neutrino events in standard analysis:  cut 107 neutrino events 90% purity, 0.6 / day 169 days live time 0.17 (~7 reconstructed / day) Preliminary

15. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini15 An alternative approach under study Likelihood ratio method 4 discriminative variables: cos(  ) Data,  MC, MC

16. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini16 An alternative approach under study Likelihood ratio method 4 discriminative variables: cos(  )  of the prefit Data,  MC, MC

17. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini17 An alternative approach under study Likelihood ratio method 4 discriminative variables: cos(  )  of the prefit Fraction of direct hits (time res<3 ns) Data,  MC, MC

18. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini18 An alternative approach under study Likelihood ratio method 4 discriminative variables: cos(  )  of the prefit Fraction of direct hits (time res<3 ns) Distance covered by the last in time photon Data,  MC, MC

19. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini19 s(x) = pdf of MC atmospheric neutrinos b(x) = pdf of MC atmospheric muons y = s(x) / [ s(x) + b(x) ] An alternative approach under study Likelihood ratio method 4 discriminative variables: cos(  )  of the prefit Fraction of direct hits (time res<3 ns) Distance covered by the last in time photon Data,  MC, MC (x100) y

20. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini20 y y Data,  MC, MC (x100) y An alternative approach under study  – y correlation Purity = 90%; Efficiency = 27% y = s(x) / [ s(x) + b(x) ]

21. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini21 An alternative approach under study: neutrino events Only   + y Under study PRELIMINARY Data MC (Bartol flux)  MC (arXiv:0802.0562) 62 ± 8 (stat)95 ± 3 (stat) ± 18 (theor)* * assumed 20% uncertainty on the absolute neutrino flux Preliminary result: 1.1 / day in data; from MC:  90% purity,  1° angular resolution Real data: 56.4 days live time

22. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini22 Conclusion Analysis of ANTARES 5 line data in progress –Present results Good agreement in MC and data down going flux 107 in 169 days of 5 line data –Still room for improvement an alternative study leads to 1.1 / day, with 90% purity 10 lines data now available 12 lines soon available! Search for neutrino cosmic sources started…

23. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini23 BACKUP: track equation Time resolution: ~2 ns Position resolution: ~10 cm

24. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini24 BACKUP: reconstruction algorithm details (1) Step 1: linear prefit with coincidences and large amplitude hits Step 2: minimization of the M-estimator formula A i = charge, r i = time residual, f ang = angular factor, K=0.05 (from MC simulation)

25. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini25 Step 3: maximum likelihood fit with simple time residual PDF P( event | track ) = prod i P( t i | t i th ) BACKUP: reconstruction algorithm details (2)

26. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini26 Step 4: maximum likelihood fit with full PDF (charge bins) Distributions obtained from MC muons 100 GeV < E < 100 TeV BACKUP: reconstruction algorithm details (3)

27. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini27 BACKUP: direct hits Data,  MC, MC

28. CEA DSM Irfu 21 / 05 / 2008Niccolò Cottini28 BACKUP: last in time photon  MC