1. Calibration of NT200+ with the external Laser Antipin Konstantin MEPhI (Moscow) Zeuthen, 19.09.2006

2. 2 Laser is used for: Calibration –Time (time offsets) –Verification of amplitude calibration Water parameters crosscheck Global performance test HE shower reconstruction (10-500 PeV) Main properties : High power ~10 13 phot/pulse Short pulse duration ~1 ns 5 Intensities per Run (PC-controlled attenuator) Laser installed in April 2005 with NT200+ Successfully used in 2005 Laser in Baikal experiment

3. 3 Analysis 2005: Indications that lowest channels on strings (5 th, 6 th) see possible non-direct light. -> Effect on time offset. Laser Experiment on 08.04.2006 –4 Runs with 4 different laser z-positions –NT200+ not yet with standard HV/Thresholds –Setup and calibration was carried out during next two weeks –No precision calibration available (Thresholds, Ampl.). Calibration for standard mode used. –5 channels with only 1 OM operates Laser in standard position since 10.04.2006 Measurement of laser’s isotropy for lower hemisphere (zenith angle > 90˚) α Dedicated Laser Experiment in April 2006

4. 4 Two analysis ways : Amplitude Time vs laser angle (α) External Laser and outer strings (NT+) Search for indication of laser nonisotropy at α > 90˚ Aim of the experiment View from above

5. 5 4 Runs with NT+ (3 strings) Standard data preprocessing Preliminary calibration Ntuple Analysis under Root efficiency = 99,9 % Laser event selection: Nch > 10 time tagging Amplitutde vs. runtime ~13 min I1 > I2 > I3 > I4 > I5 For 3 runs – 2998 laser events 3000 events expected (3 runs) x (5 intensities) x (200 pulse) Data analysis

6. 6 Amplitude analysis Channel selection 81617132644 95101119205863 11711114269672 16317715959601 12111087 ChannelPosi tion Amplitudes on 2 nd string Amplitude distribution (ch #1 position 1) 2 nd 3 rd 4 th 5 th 1 st Overflow excluded 1 2 3 Checking of channel linearity Excluded : ch #7, small amplitudes on ch #11, #16, #17 Not expected Unexpected amplitudes: 2 nd string, 4 th laser position. … screened ?

7. 7 Amplitude analysis F(R) A = I* e -R/L *f(cosθ)/R 2 F(R) = ln(A*R 2 /f(cosθ)) = -R/L + const

8. 8 Amplitude analysis Angular dependence of laser Intensity α < 50˚ quasi isotropic α > 50˚ Intensity significantly decreases I = A*R 2 *e R/L /f(cosθ) 1 st string 2 nd string 3 rd string Laser is nonisotropic source of light

9. 9 t = t shift + β*tcode Arrival time difference Δt ki = t k – t i  σ Δt One reference channel per string Time Response Reference channel Light scattering in water Difference on mean arrival times vs Intensity σ δ13-3 I1 > I2 > I3 > I4 > I5 Time delay up to 8.5 ns Scattering – playing role only on big distances Channel #13 – far from laser

10. 10 t = t shift + β*t code Arrival time difference Δt ki = t k – t i  σ Δt One reference channel per string Time Response Reference channel Δτ = theor - exper Deviation from expected direct light difference Imagine laser as isotropic high intensity source of light ( i.e. all channel see direct light)

11. 11 Normalizing on first position : Δt theor – Δt exper = 0  Study in detail : Δτ = theor - exper Deviation from expected direct light difference Experimental data Data from model Δt ki Chan 1 - 2 Δt ki Chan 8 - 7 Time Response Expected times vs experiment values Imagine laser as isotropic high intensity source of light ( i.e. all channel see direct light)

12. 12 Time Response Deviation from expected times Big deviation only for: 2 nd String Intensities >= 3 Lowest channel #11, #12 (α > 110˚) All deviation due to 4th laser position (abrupt amplitude decreasing) Typical deviation < 2 ns Direct light detected for most channels

13. 13 Time Response Time delay versus amplitude Water scattering only Screening ? Chan #11 and #12 are closer to the laser than ch #13 Water scattering contribution should be lower Shadowing ? Reference ch = #13

14. 14 Analysis of the amplitude information –α < 50˚ quasi isotropic –α > 50˚ Intensity decreases –α ~ 120˚ Intensity decreases on factor 5 –Laser is nonisotropic source of light Analysis based on time information –Scattering process in water and angular dependence of laser intensity don’t influence on arrival times for high amplitudes –Laser can be used as calibration tool for NT200 + Array geometry verification by simultaneous fit of coordinates + Δt. Compare to laser data in standard operation (with full calibration) Possible upgrade of Laser design –Change to lower z-position ? –Locate diffusor sphere outside glass housing ? Design and test in progress Summary

15. 15 The end