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Ciro Bigongiari, Salvatore Mangano

Ciro Bigongiari, Salvatore Mangano. Results of the optical properties of sea water with the OB system. Outline. The idea MC templates Data and MC comparison Conclusions. The idea. Take data with flashing optical beacon Plot the hit arrival time distributions for all OMs

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Ciro Bigongiari, Salvatore Mangano

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  1. Ciro Bigongiari, Salvatore Mangano Results of the optical properties of sea water with the OB system

  2. Outline The idea MC templates Data and MC comparison Conclusions

  3. The idea • Take data with flashing optical beacon • Plot the hit arrival time distributions for all OMs • Simulate many MC samples with different input values: λa and λs • Compare hit arrival time distributions from MC samples and data • Choose MC with λa and λswhich describes best data

  4. MC samples • New CALIBOB • Different MC input parameters For example: la = 35, 40, 45, 50, 55, 60, 65, 70, 75 m 9 values ls = 35, 40, 45, 50, 55, 60, 65, 70, 75 m 9 values • 9*9 = 81 MC samples for each data run • Each data run has his: • detector geometry • charge calibration • PMT efficiency • background noise

  5. Histogram Comparison Data MC We compare many histograms one for each OM considered To quantify the agreement between the histograms we calculate the χ2

  6. Changing Absorption (MC templates) 70 m 50 m Normalized at first histogram Absorption effects the direct photons (see peak) =>More light at larger distance for larger absorption

  7. Changing Scattering (MC templates) Normalized at first histogram Scattering effects the indirect photons Photons from peak region go to tail region 50 m 90 m

  8. MC and Data comparison Find MC which describes data

  9. Chi2 Procedure • Loop over selected floors/OMs of one line • Cut a fixed range of hit arrival time distribution • Merge all the cut histogram ranges in one super-histogram • Compare super-histogram from data with MC • Repeat for all lines (except OB) • χ2 calculated with Chi2Test function of ROOT • Robust, flexible and well tested

  10. Super-Histogram example Entries MCDATA Time

  11. Super-Histogram MC shifted time MCDATA Time

  12. OM selection Some OMs are rejected • OMs too close to the OB Floor > 13 ARS token ring effect • OMs too far away Floor < 21 Not enough statistics • OMs whose efficiency ε< 0.5 or ε > 1.5 • Backwards looking OMs PMT acceptance uncertainty • OMs very inclined Led emission uncertainty • OMs after visual inspection of their distributions

  13. Binning and statistics The Chi2 values depend: • on histogram binning • Very small bins  large statistical errors (Small Chi2 values for all MC models) • Chi2 ~ 1  • Independent of the MC model  • Very large bin  small statistical errors (Large Chi2 values for many MC models) • Sensitive to Attenuation length only • on MC statistics

  14. MC and Data for Line 2 with small χ2 MC Data OM1 OM2 OM3 OM1 Time

  15. Absorption vs. scattering for Line 2 Calculate Chi2 for each MC Eta=0.3

  16. All linesRun 58120 • Different Lines show • similar results • Last Figure shows sum ..over all lines

  17. Data runs We use data runs taken with the 6 LEDs of the TOP group of one OB flashing at the same time

  18. All linesRun 58607

  19. All linesRun 58609

  20. All linesRun 61514

  21. All linesRun 61518

  22. All linesRun 64766

  23. All linesRun 64769

  24. Final Bologna result Take from lines the MC with smallest chi2 (four runs, eliminate too distant lines)

  25. PreFinal Oudja result Take from lines the MC with smallest chi2 (four runs, eliminate too distant lines)

  26. Abs per line

  27. Scat per line

  28. abs per run

  29. scat per run

  30. Conclusions • Improved Data-MC comparison technique • Consistent results between different lines and runs • Soon new Calibob version with only λa andλs • Results • λa = 52 -> 49 m and rms = 6 m • λs = 59 -> 55 m and rms = 8 m

  31. Backup

  32. Changing Eta (MC templates) Eta 0.4 Eta 0.15 Large eta more scattering at large angle Photons from peak region go to tail region Scattering and eta are connected => Difficult to disentangle

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