Attenuation measurement with all 4 frozen-in SPATS strings Justin Vandenbroucke Freija Descamps IceCube Collaboration Meeting, Utrecht, Netherlands September

Attenuation measurement with all 4 frozen-in SPATS strings

Justin VandenbrouckeFreija Descamps

IceCube Collaboration Meeting, Utrecht, NetherlandsSeptember 15, 2008

Outline

• Motivation and background• Data set• Method• Amplitude vs. distance• Best fit and confidence regions• Attenuation length lower limit• Systematics

Justin Vandenbroucke Utrecht, Netherlands September 15, 2008

Motivation

• Two types of attenuation analyses– Inter-string: frozen-in sensors & transmitters– Pinger: frozen-in sensors & retrievable pinger in water

• Last year’s 3-string inter-string analyses inconclusive• Last year’s pinger analyses inconclusive• Improve with 4-string inter-string?• Now enough strings for single-transmitter analysis, to reduce systematics


• Is attenuation length at least a few hundred meters?

Background

Significantly improved inter-string data set taken

• 4 strings (D with improved transmitters and sensors)• Each sensor records 200 seconds @ 200 kHz• 40 Hz transmitter repetition: 8,000 pulses per T-S

combination! cf. 726 pulses previously• Optimized parameters

– Sampling frequency– RAM disk size– Transmitter repetition rate– Steering amplitude


Geometry: D transmitter to ABC sensors, all at 320 m depth


Data subset for this analysis

• Single depth (320 m) transmitters & sensors, to reduce systematics

• One transmitter only, to reduce systematics• All 3 ABC string sensors recording• All 3 channels per module recording• Select only the first 10 s: for longer duration we need

more precision in clock drift determination


Pulse averaging algorithm


(1) Stretch times according to clock drift(2) Wrap and re-sort by time(3) Re-bin at chosen sampling frequency

- all samples wrapped and sorted- average pulse after binning at 200 kHz

Azimuthal variation of transmitter?


transmittersensor

sensor

sensor

19°

29°

We use a small range of azimuths:

Analysis method

• Frozen-in transmitter removes many systematics plaguing the pinger analyses

• Single level to minimize systematics• String D transmitter (good quality)• Use amplitudes directly (no ratios assuming

negligible angular variation)• Determine clock drift by scanning over assumed drift

values, maximize Vpp, check Vmax and Vmin peak at same drift value

• Apply full confidence level treatment


Peak to peak amplitude vs. distance (linear scale)


Ln(amplitude * distance) vs. distance


“statistical” errors: std. dev. of avg. pulse Vpp

• pulse to pulse signal variation• pulse to pulse noise variation• residual clock drift

Attenuation coefficient confidence region


Best fit and sigma of each parameter from analytical methodEllipses from numerical method• best fit- best fit +/- 1 sigma- delta-chi-square = 1 (tangents contain 68.3% of either parameter alone)- delta-chi-square = 2.3 (contains 68.3% of parameter space jointly)

Attenuation length confidence region


Best fit: 1055 m

Attenuation coefficient PDF (Gaussian)


Attenuation length: probability distribution function


Attenuation length cumulative PDF and lower limit


Attenuation length > 363 m @ 68.3 % CL• statistical errors only• without constraining lambda positive

Adding 100% systematic error to the statistical error


Lower limit with 100% systematic error and lambda constrained positive


68.3% CL: attenuation length > 269 m90% CL: attenuation length > 168 m

Systematic effects


Effect Present? Comment

S chan. to chan. variation Accounted

Dominant systematic error: ~100% ?

IceCube cable shadowing Yes Effectively changes S sens. or T. azim.

Hole ice quality Yes Would appear as chan. to chan. S variation

Clock drift Small Removed, but sufficiently?

T azimuth response Small All S in roughly same direction

Background noise No Automatically in statistical uncertainty

T zenith response No Single depth

S zenith response No Single depth

S azimuth response No Each sensor channel used once

T module to module variation

No Single transmitter

Reflections interference No Frozen hole column

Transmission coef. with angle No Frozen hole column: no transmission coef.

Shear waves No No variation in fraction going to S waves

Saturation No None of these runs saturated

Variation in waveform shape No No pinger motion

T = transmitter S = sensor

Conclusions

• We now have high quality optimized 4-string inter-string data set• First analysis complete• Confidence interval and lower limit in addition to best fit• “Direct” method, complementary to “ratio” method• Claim: this analysis is least affected by systematics, of all (inter-string or

pinger) attenuation analyses to date• Is it good enough? No. We need improved pinger runs (see Delia’s talk) and

more inter-string analysis• To do

– Verify amplitude determination (clock drift correction algorithm)– Verify systematic error estimate– New data for few combinations with sufficient online drift determination– Repeat with transmitters at other depths on D (also ABC?)– Frequency domain analysis?


Cross check: Two independent amplitude determinations


Justin Freija

Ratio analysis: in progress


Pulse averaging improves signal to noise


- single raw pulse- average pulse

Pulse averaging: Effect of chosen re-binning sampling frequency on average pulse


- 200 kHz- 6 MHz

• after stretching times, wrapping, and re-sorting• BT6 to AS5-0; 3000 pulses

Documents

Attenuation measurement with all 4 frozen-in SPATS strings Justin Vandenbroucke Freija Descamps IceCube Collaboration Meeting, Utrecht, Netherlands September