Calibration of NT200+ with the external Laser

Antipin Konstantin MEPhI (Moscow)

Zeuthen, 19.09.2006

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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 ~1013 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

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• Analysis 2005: Indications that lowest channels on strings (5th, 6th) 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

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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

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• 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

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Amplitude analysisChannel selection

81617132644

95101119205863

11711114269672

16317715959601

12111087

ChannelPosition

Amplitudes on 2ndstring

Amplitude distribution (ch #1 position 1)

2nd 3rd

4 th

5th

1st

Overflow

excluded

1 2

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Checking of channel linearityExcluded : ch #7, small amplitudes on ch #11, #16, #17

Not expected

Unexpected amplitudes: 2nd string, 4th laser position. …

screened ?

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Amplitude analysisAngular dependence of laser Intensity

α < 50˚ quasi isotropic

α > 50˚ Intensity significantly decreases

I = A*R2*eR/L/f(cosθ)

1st string

2nd string

3rd string

Laser is nonisotropic source of light

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• t = tshift + β*tcode • Arrival time difference

Δtki= tk – ti

<Δt> σΔt One reference channel

per string

Time ResponseReference channel

Δτ = <Δtki>theor - <Δtki>exper

Deviation from expected direct light difference

Imagine laser as isotropic high intensity source of light( i.e. all channel see direct light)

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Time ResponseDeviation from expected times

Big deviation only for:2nd String Intensities >= 3Lowest 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

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Time ResponseTime 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

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• 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

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The end