1. Velocity of light in water
Simple Method MC
Data

2. Method (Led run)

3. Method From Led run (time and position for each OM)
Time = Peak (highest bin, bin size=0.5 ns)
Position = nominal OM position
Eliminate not significant peak
(Noise>Peak-5*sqrt(peak))
Time versus distance
Fit y=ax+b

4. Plot MC Take time from bin with maximal hits = Timepeak
Timepeak versus distance
n=v_vacuum/v_measured

5. MC (Led) Run Absorption Scattering Fit range n delta n
Inf

6. MC (Laser) Led and Laser runs slightly dependent from fit range
Run Absorption Scattering Fit range n delta n
Led and Laser runs slightly dependent from fit range
Fit over full range no dependence of absorption and scattering
Led run n =
Laser run n =
Ciro put in the MC:
Led run n =
Laser run n =
Ciro can you please generate MC with n=1.3 and n=1.5 ???

7. MC (different Lines)

8. Thinking about errors Laser (full width 0.8 ns) Led (full width 4 ns)
=> early photon effect maximum 4 ns
Walk effect (is smaller than 4ns)
Binning in histogram 0.5ns
Positioning (possible 20 cm = 1ns)
We measure times of 1000 ns => accuracy of the measurement around 0.5%

9. Data (Do we crosscheck Pacos timing calibration?)

10. Data (different fit range)
Error in t=2 ns, error in position x=1m
Run fit rang[m] n delta n chi/ndf
/38
/19
/17

11. Data (Different Lines) We crosscheck Pacos timing calibration)

12. Data (different Lines)
Run Line n delta n chi/ndf
/38
/49
/47
/39

13. Data (different runs) Run Line n delta n chi/ndf
/38
/38
/36
/38
/35
/43
/41
/39
/42
36063UV /30

14. Is this useful? Only cross check of Pacos work?
Improvement:Take real OM positions
Define fit range (systematic bias)
Method ok?
Have a look to Laser runs

15. Early photon effect (MC)
Introduce cut to minimize early photon effect:
Ciros cut: charge per hit < 1.5p.e. => minimal distance 100m

16. Early photon effect (MC and Data)

17. Method From Led run (time and position for each OM)
Time = Peak (highest bin, bin size=0.5 ns)
Position = nominal OM position
Eliminate not significant peak
(Noise>Peak-5*sqrt(peak))=>defines max. fit value
Charge per hit < 1.5 p.e=>defines min. fit value
Time versus distance
Fit y=ax+b

18. MC Measured refraction index
MC Input n= (at 470nm)
Run Absorption Scattering Fit range n delta n
Inf
Conclusion: Small model dependence about 0.5%
Laser MC run: MC Input n= (at 532nm)
MC measured n=

19. Stability against cuts
(Noise>Peak-5*sqrt(peak))=>defines max. fit value
Charge per hit < 1.5 p.e=>defines min. fit value
Change charge per hit to 5.0 => 0.2%
Change charge per hit to 1.2 => 0.2%
Change Peak-10*sqrt(peak) => 0.5%
Conclusion: Small cut dependence about 0.5%

20. Data at 470 nm
N= (+-0.5%)

21. Conclusion Method stable against cuts +-0.5%
Method stable against different assumption for absorption and scattering +-0.5%
Measurement at lambda=470 nm (Led) n= %(stat.)+-0.5%(exp.)+-0.5%(theo.)
=>n=