transmission length measurements: a “multi- wavelength” analysis from the ob data h yepes ific...

Transmission length measurements: a Transmission length measurements: a “multi-wavelength” analysis from the OB “multi-wavelength” analysis from the OB

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Transmission length measurements: a Transmission length measurements: a “multi-wavelength” analysis from the OB “multi-wavelength” analysis from the OB

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H Yepes H Yepes IFIC (CSIC – Universitat de València)IFIC (CSIC – Universitat de València)

ANTARES Collaboration Meeting ANTARES Collaboration Meeting

CERN , February 07CERN , February 07thth-10-10thth, 2011, 2011

OUTLINEOUTLINEOUTLINEOUTLINE

ANTARES Collaboration Meeting ANTARES Collaboration Meeting CERN, CERN, FebruaryFebruary 07 07thth-10-10thth2

Status of transmission length Status of transmission length measurementsmeasurements

• Experimental procedure (a brief reminder).• The PMT calibration based on 40K coincidences.• Conclusions since the last collaboration meeting in Paris.

The new “Multi-Wavelength Optical The new “Multi-Wavelength Optical Beacon”Beacon”

• Description of the new ANTARES instrument.• Measurements of the LEDs spectrum.

ResultsResultsGeneral commentsGeneral commentsConclusionsConclusions


• Experimental procedure (a brief reminder).• The PMT calibration based on 40K coincidences.• Conclusions since the last collaboration meeting in Paris.

The new “Multi-Wavelength Optical The new “Multi-Wavelength Optical Beacon”Beacon”

• Description of the new ANTARES instrument.• Measurements of the LEDs spectrum.

ResultsResultsGeneral commentsGeneral commentsConclusionsConclusions




EXPERIMENTAL PROCEDURE (BRIEF REMINDER):

1.One single top LED of the lowest OB in the line flashes upwards.

2.Signal hits are plotted and fitted (between Rmin, Rmax) by means of an exponential function:

•To avoid the electronics dead time (related to Rmin): region where the probability to get more than one photoelectron is negligible (i.e < 1 %).

•To avoid noise fluctuations at large distances (related to Rmax): region where the signal will be greater than the noise.

•Low efficiency OMs cleaning: from the noise hits projections, only those between (+3, -3) are considered.

•Low background rates (top, middle, bottom): BKG < 100 kHz.

Remarks:

1)The PMT efficiencies are computed from 40K coincidences analysis.

2)The total error assigned is computed by means of “Student’s t”.

3)Transmission length (L) is a lower limit of the absorption length (not scattering effects considered).

F2

γ

40K

40Ca

e- ( decay)




THE PMT CALIBRATION BASED ON 40K COINCIDENCES:

• Why? Noise based efficiencies (old technique) are correlated with noise subtraction and they are sensitive to noise fluctuations along the line.

• 40K is not affected by variations of the bioluminescence background in time.

• The light output of 40K per unit volume is constant over depth .

• Our new efficiencies are computed as Dmitry Zaborov has performed them:

OM SENSITIVITIES COMPUTATION:

The relative sensitivities of the three OMs in a triplet S i can be computed by solving the system of 3 equations:

Rij = R0 * Si * Sj where i, j =1, 2, 3

and R0 is the nominal 40K coincidence rate (R0=16 Hz, for a 0.3 pe ARS threshold).

Using these formulas is possible to produce OM sensitivity tables based on any given 40K + physics run.




------ D Zaborov

------ H Yepes

Rel

ativ

e se

nsiti

vity

10*Floor+3.4*OM

1. First step (2 sub-steps): build 40K coincidence histograms for each run and pair of OMs/ARSs; compute event rates and dead time (XOFF/HRV) corrections.

2. Second step: fit each of the 40K histograms and apply the dead time corrections.

3. Third step: Choose the “best runs” (7) of the day (low background, enough events…).

4. Fourth step: Run a sensitivity computation script for each of the selected run series.

5. Fifth step: Computations of OM efficiencies based on the measured 40K coincidence rates.

• What if one OM was missing in a 40K run?Remaining two OMs are set to the same efficiency.

• What if two OMs were missing in a 40K run?Efficiencies are set to 0 for that floor.

• Do we have to applied a cut in the number of OMs per storey for the fit?

SINCE NOVEMBER 2010 IFIC has been used its own self-computed 40K sensitivities, after some codes exchanges between D Zaborov and H Yepes. 40K sensitivities computations are under control (cross-checks performed with Dmitry).




CONCLUSIONS SINCE THE LAST COLLABORATION MEETING IN PARIS:

1.The optical properties data taking is optimized for different optical beacons at different heights and different wavelengths.

2.The transmission length at three wavelengths has been measured and confirmed its stability in time:

• L = 36.5 ± 1.0 m @ = 400 nm.

• L = 54.4 ± 3.0 m @ = 470 nm.

• L = 21.6 ± 1.2 m @ = 532 nm.

3.The treatment of errors based on the “Student’s t” distribution and the PMT efficiencies based on the 40K coincides rates, have pointed out to a better quality fits.

4.The transmission length experimental procedure has given confidence to extract the absorption length using the “R technique” (based on the information of the single scattering of light) once the data/MC agreement will be checked.

WHAT’S NEW THE MULMULTI-WTI-WAVEAVELELENGNGTHTH OPTICAL BEACON (CHRISTMAS BEACON)

The Multi-Wavelength Optical The Multi-Wavelength Optical BeaconBeacon



THE NEW ANTARES INSTRUMENT:

• First tests at CPPM on November 2009.• Integration until March 2010. • Deployed on April 2010.• Tested successfully in-situ on November 2010.• The Multi-Wavelength OB is placed on L6F2.• Three LEDs per face pointing up-wards.• LEDs control (DAQ reference):

Central LED TOP group.Left LED MIDDLE group.Right LED FOUR group.

• One different wavelength on each face, except face 4:Central LED CB30 LED model for testing (460 nm).Left/Right LEDs CB15 ANTARES LED model (470 nm).• Assure to check LEDs systematics.

LED MODEL VAOL-5GUV8T4

HUVL400-520B

Ultrabright Pink

HLMP-CB30-K000

HLMP-CB15-RSC00

HLMP-CE36-WZ000

SLA-580ECT3F

OB face (RC) 1 2 3 4 4 5 6

[nm] 385 400 440 460 472 505 518

FWHM [nm] 5 20 - 35 35 30 35




Provided by the manufacturer Measured at IFIC

LED Mean [nm] FWHM [nm] Mean [nm] RMS [nm]

VAOL-5GUV8T4 385 5 384 9

HUVL400-520B 400 20 400 10

Ultrabright Pink 440 - 447 13

HLMP-CB30-K000 460 35 458 19

HLMP-CB15-RSC00 472 35 469 13

HLMP-CE36-WZ000 505 30 494 18

SLA-580ECT3F 518 35 518 25

MEASUREMENTS OF THE LEDs SPECTRUM:•Multi-wavelength LED spectrum has been measured with a high res calibrated spectrometer from Ocean Optics.

• Light sources already installed: Standard LOB. Laser Beacon.• A total of 8 wavelengths are available for analysis.•Only measurements with TOP LEDs has been performed.




THE EFFECT OF THE PROPAGATION PATH ON THE WAVELENGTH:• The width of the sources is not monochromatic (as the Laser is), then the LED source spectrum could be affected due to absorption along the light propagation path.

• It is an effect we have to take into account because we work at photoelectron level (~120 m for high intensity regime).

•A way to check Convolution of LED source spectrum with the absorption length spectrum and to test at different distances:




•This effect has to be corrected in our analysis Take the correct spectrum at the distance which we work (120 m).• The effect is more “evident” for extreme values of the LEDs spectrum.• No appreciable effect is seen for the narrow spectrum of the Laser.

LOW

+ Photons

- Absorption

HIGH

- Photons

+ Absorption

ResultsResultsResultsResults


TRANSMISSION LENGTH DEPENDENCE ON WAVELENGTHS:

EXPONENTIAL FIT AT DIFFERENT WAVELENGTHS:

Exponential fit to the number of hits for the different wavelengths available in ANTARES:

• Availability of wavelengths for analysis in ANTARES:

Standard OB (1).

Modified OB in L12F2 with UV and KM3NeT prototype LEDs (1)

Laser Beacon (1).

Multi-wavelength Beacon (6).

TOTAL: 8 wavelengths(UV L12 LED and UV L6 LED are equal)

F2



TRANSMISSION LENGTH DEPENDENCE WITH THE OPTICAL BEACON (L2F2 HI and MI):



TRANSMISSION LENGTH DEPENDENCE WITH THE OPTICAL BEACON (L4F2 and L4F9 HI):



TRANSMISSION LENGTH DEPENDENCE WITH THE OPTICAL BEACON (L6F2):

• THE NEW MULTI-WAVELENGTH BEACON BEHAVES MORE BETTER THAN WE CAN EXPECTED.

• New runs are needed and they will be included in our new policy of data taking.

• L386 ~ 31 m, L403 ~ 36 m, L449 ~ 50 m, L460 ~ 53 m, L490 ~ 50 m, L491 ~ 48 m.

• L distributions in next slides for all wavelengths.

Not ’s at 470 and 532 are drawn



Entries

L ± RMS[m]

Average σfit (RMS) [m]

Mean Prob (2)

RMS Prob (2)

Entries with Prob (2) < 1%

RMS/L

L1F2 5 - - - - - -

L2F2 36 54.7±2.3 2.1 (0.7) 0.7 0.3 2 0.04

L2F9 9 56.4±3.4 1.9 (0.8) 0.5 0.4 2 0.06

L4F2 15 56.9±3.5 4.1 (0.9) 0.7 0.2 0 0.06

L4F9 6 53.2±2.8 2.3 (0.7) 0.5 0.4 1 0.05

L6F2 29 * - - - - -

L8F0 49 21.4±1.0 0.8 (0.3) 0.6 0.3 3 0.05

L8F2 9 56.0±2.9 2.5 (1.2) 0.8 0.3 1 0.05

L8F9 7 57.9±4.2 3.0 (1.0) 0.1 0.3 4 0.07

L12F2 12 36.4±1.4 1.2 (0.6) 0.8 0.2 1 0.04

L2F2 MI 11 55.7±2.7 2.8 (0.6) 0.8 0.3 0 0.05

SUMMARY:

• Particular cases with low statistics have to be checked and also to take more data.

• Variability of L < 5 % in most of the cases, except for L1F2, L2F9, L4F2 (RMS/L ~ 6%), L8F9 (RMS/L ~ 7%).

• RMS of L in agreement with average σfit in most of the cases, except L2F9.

• Change of L with time not much larger than statistical.

• L Vs depth: No appreciable effect is seen (L2F2-L2F9, L4F2-L4F9, L8F2-L8F9), MORE statistics is needed, and runs with OB in F15.

• L Vs : stability in time for the new measurements with the multi-wavelength optical beacon is kept.

Mean Prob (2) should be 0.5 RMS Prob (2) should be 1/√12 = 0.29

* Next slide



TRANSMISSION LENGTH DISTRIBUTIONS AT DIFFERENT WAVELENGTHS:

[nm] 385 400 440 460 472 505

L [m] 31.1 36.0 50.4 53.3 55.3 49.6

RMS [m] 0.8 1.6 2.2 2.4 3.4 2.0

518 532

48.0 21.4

1.6 1.0



TRANSMISSION LENGTH SPECTRUM (DATA) VS ABSORPTION LENGTH SPECTRUM (KM3 MC):



STABILITY IN TIME FOR DIFFERENT WAVELENGTHS AT THE ANTARES SITE:

The stability in time is confirmed once again for all wavelengths available in ANTARES.

It is the first plot of Neutrino Telescope which shows the stability in time of the transmission length measurements at deep sea water for different wavelengths.

Final commentsFinal commentsFinal commentsFinal comments


Detector covered range for transmission length

measurements

ACQUISITION STATUS:

Run setups available for optical properties studies:

USER Line 1-12 LED Beacon - Optical Properties HI L1F2 - Nov2010; USER Line 1-12 LED Beacon - Optical Properties HI L2F2 - Nov2010USER Line 1-12 LED Beacon - Optical Properties HI L2F9 - Nov2010; USER Line 1-12 LED Beacon - Optical Properties HI L4F2 - Nov2010USER Line 1-12 LED Beacon - Optical Properties HI L4F9 - Nov2010; USER Line 1-12 LED Beacon - Optical Properties HI L6F2 - Nov2010USER Line 1-12 LED Beacon - Optical Properties HI L8F2 - Nov2010; USER Line 1-12 LED Beacon - Optical Properties HI L8F9 - Nov2010USER Line 1-12 LED Beacon - Optical Properties HI L12F2 - Nov2010; USER Line 1-12 Laser Beacon Nov2010



MAIN STATISTICS:

• Total run setups available 9 for LED + 1 for LASER.• Total golden runs availability 211 runs.• Runs at low and medium intensity have begun to be taken, in order to find a way to reduce the scattering effects Not enough statistics now.



NEW POLICY FOR OPTICAL PROPERTIES RUNS:

1. Many of runs for some beacons which confirm the measurement they give No more data taking with them.

2. The need of more statistics with other beacons: L6F2 (Multi-wavelength beacon), OBs placed on storeys 9 (high intensity) and 15 (low intensity).

3. Interest on L Vs LED Intensity and L Vs Depth (F15 LI) plots.

ConclusionsConclusionsConclusionsConclusions


• We have started our 40K calibration. Cross-checks performed with Dmitry gives us confidence that this kind of calibration is under control.

• Depth dependence on transmission length has not an appreciable effect, however more statistics in needed.

• The new Multi-wavelength beacon is working and the stability in time is kept, and the quality of the cuts seems to be OK but more statistics is needed. Preliminary values set:

• Possible second order corrections as angular acceptance and alignment are in the “to –do list”.

• The stability in time is kept for all optical beacons considered, including the Multi-Wavelength Optical Beacon, a quality fit studies require more statistics in this case.

• Is it the moment to write a brief NIM paper or internal note (NESTOR has already published something)?

• Please, take a look on the new Wikipage section for optical calibration updates (it is almost fulfilled). Suggestions and comments are welcome:

http://antares.in2p3.fr/internal/dokuwiki/doku.php?id=calibration

• We have started our 40K calibration. Cross-checks performed with Dmitry gives us confidence that this kind of calibration is under control.

• Depth dependence on transmission length has not an appreciable effect, however more statistics in needed.

• The new Multi-wavelength beacon is working and the stability in time is kept, and the quality of the cuts seems to be OK but more statistics is needed. Preliminary values set:

• Possible second order corrections as angular acceptance and alignment are in the “to –do list”.

• The stability in time is kept for all optical beacons considered, including the Multi-Wavelength Optical Beacon, a quality fit studies require more statistics in this case.

• Is it the moment to write a brief NIM paper or internal note (NESTOR has already published something)?

• Please, take a look on the new Wikipage section for optical calibration updates (it is almost fulfilled). Suggestions and comments are welcome:


[nm] 385 400 440 460 472 505 518 532

Mean [m] 31.1 36.0 50.4 53.3 55.3 49.6 48.0 21.4

RMS [m] 0.8 1.6 2.2 2.4 3.4 2.0 1.6 1.0



BACKUPBACKUPBACKUPBACKUP


NOISE SUBTRACTION:

RATE OF CORRELATED COINCIDENCES (40K):

Defined as the integral under the coincidence peak (excluding pedestal) normalized to the effective duration of observation period, and properly corrected for dead time of the electronics and data acquisition. Gaussian fit to compute the rate. Average value ~ 14 Hz (R0). R0 may include the loss of glass transparency due to biofouling (if any) and similar effects, so it may be less than for "ideal" Monte Carlo OM. OM angular acceptance can be constrained by the 40K measurements.

NOISE LEVEL

Fit a constant in the [-1000, -50] ns range (B level) and substract the noise contribution (Qnoise, Nnoise):

Nsignal = Nhits(tot)– Nnoise = Ntot – Blevel (Tmin - Tmax)

= Ntot – <n>Nbins (Tmin - Tmax)



(nm) 10 V 17 V 23 V ΔV

385 383 383 383 0

400 400 399 399 1

440 447 446 445 2

470 461 458 455 6

505 507 497 493 14

518 541 540 537 4

transmission length measurements: a “multi- wavelength” analysis from the ob data h yepes ific...

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