Transmission length measurements: a “multi- wavelength” analysis from the OB data H Yepes IFIC (CSIC – Universitat de València) ANTARES Collaboration Meeting CERN, February 07 th -10 th, 2011

OUTLINEOUTLINE ANTARES Collaboration Meeting CERN, February 07 th -10 th 2 Status of transmission length measurements Experimental procedure (a brief reminder). The PMT calibration based on 40 K coincidences. Conclusions since the last collaboration meeting in Paris. The new “Multi-Wavelength Optical Beacon” Description of the new ANTARES instrument. Measurements of the LEDs spectrum.Results General comments Conclusions Status of transmission length measurements Experimental procedure (a brief reminder). The PMT calibration based on 40 K coincidences. Conclusions since the last collaboration meeting in Paris. The new “Multi-Wavelength Optical Beacon” Description of the new ANTARES instrument. Measurements of the LEDs spectrum.Results General comments Conclusions

Status of transmission length measurements ANTARES Collaboration Meeting CERN, February 07 th -10 th 3 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 R min, R max ) by means of an exponential function: To avoid the electronics dead time (related to R min ): region where the probability to get more than one photoelectron is negligible (i.e < 1 %). To avoid noise fluctuations at large distances (related to R max ): 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 40 K 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 40 K 40 Ca e - (  decay) Status of transmission length measurements ANTARES Collaboration Meeting CERN, February 07 th -10 th 4 THE PMT CALIBRATION BASED ON 40 K COINCIDENCES: Why?  Noise based efficiencies (old technique) are correlated with noise subtraction and they are sensitive to noise fluctuations along the line. 40 K is not affected by variations of the bioluminescence background in time. The light output of 40 K 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: R ij = R 0 * S i * S j where i, j =1, 2, 3 and R 0 is the nominal 40 K coincidence rate (R 0 =16 Hz, for a 0.3 pe ARS threshold). Using these formulas is possible to produce OM sensitivity tables based on any given 40 K + physics run.

Status of transmission length measurements ANTARES Collaboration Meeting CERN, February 07 th -10 th D Zaborov H Yepes Relative sensitivity 10*Floor+3.4*OM 1.First step (2 sub-steps): build 40 K 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 40 K 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 40 K coincidence rates. What if one OM was missing in a 40 K run? Remaining two OMs are set to the same efficiency. What if two OMs were missing in a 40 K 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 40 K sensitivities, after some codes exchanges between D Zaborov and H Yepes. 40 K sensitivities computations are under control (cross-checks performed with Dmitry).

Status of transmission length measurements ANTARES Collaboration Meeting CERN, February 07 th -10 th 6 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 = 400 nm. L = 54.4 ± 3.0 = 470 nm. L = 21.6 ± 1.2 = 532 nm. 3.The treatment of errors based on the “Student’s t” distribution and the PMT efficiencies based on the 40 K 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. MULTI-WAVELENGTH WHAT’S NEW  THE MULTI-WAVELENGTH OPTICAL BEACON (CHRISTMAS BEACON)

The Multi-Wavelength Optical Beacon ANTARES Collaboration Meeting CERN, February 07 th -10 th 7 THE NEW ANTARES INSTRUMENT: First tests at CPPM on November Integration until March Deployed on April Tested successfully in-situ on November 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 MODELVAOL- 5GUV8T4 HUVL B Ultrabright Pink HLMP-CB30- K000 HLMP-CB15- RSC00 HLMP-CE36- WZ000 SLA- 580ECT3F OB face (RC) [nm] FWHM [nm]

The Multi-Wavelength Optical Beacon ANTARES Collaboration Meeting CERN, February 07 th -10 th 8 Provided by the manufacturerMeasured at IFIC LEDMean [nm]FWHM [nm]Mean [nm]RMS [nm] VAOL-5GUV8T HUVL B Ultrabright Pink HLMP-CB30-K HLMP-CB15-RSC HLMP-CE36-WZ SLA-580ECT3F 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 Multi-Wavelength Optical Beacon ANTARES Collaboration Meeting CERN, February 07 th -10 th 9 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:

The Multi-Wavelength Optical Beacon ANTARES Collaboration Meeting CERN, February 07 th -10 th 10 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

ResultsResults ANTARES Collaboration Meeting CERN, February 07 th -10 th 11 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

ResultsResults ANTARES Collaboration Meeting CERN, February 07 th -10 th 12 TRANSMISSION LENGTH DEPENDENCE WITH THE OPTICAL BEACON (L2F2 HI and MI):

ResultsResults ANTARES Collaboration Meeting CERN, February 07 th -10 th 13 TRANSMISSION LENGTH DEPENDENCE WITH THE OPTICAL BEACON (L4F2 and L4F9 HI):

ResultsResults ANTARES Collaboration Meeting CERN, February 07 th -10 th 14 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. L 386 ~ 31 m, L 403 ~ 36 m, L 449 ~ 50 m, L 460 ~ 53 m, L 490 ~ 50 m, L 491 ~ 48 m. L distributions in next slides for all wavelengths. Not ’s at 470 and 532 are drawn

ResultsResults ANTARES Collaboration Meeting CERN, February 07 th -10 th 15  Entrie s L ± RMS[m] Average σ fit (RMS) [m] Mean Prob (  2 )RMS Prob (  2 )Entries with Prob (  2 ) < 1% RMS/L L1F L2F ± (0.7) L2F9956.4± (0.8) L4F ± (0.9) L4F9653.2± (0.7) L6F229 * L8F ± (0.3) L8F2956.0± (1.2) L8F9757.9± (1.0) L12F ± (0.6) L2F2 MI1155.7± (0.6) 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 σ fit 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

ResultsResults ANTARES Collaboration Meeting CERN, February 07 th -10 th 16 TRANSMISSION LENGTH DISTRIBUTIONS AT DIFFERENT WAVELENGTHS: [nm] L [m] RMS [m]

ResultsResults ANTARES Collaboration Meeting CERN, February 07 th -10 th 17 TRANSMISSION LENGTH SPECTRUM (DATA) VS ABSORPTION LENGTH SPECTRUM (KM3 MC):

ResultsResults ANTARES Collaboration Meeting CERN, February 07 th -10 th 18 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 comments ANTARES Collaboration Meeting CERN, February 07 th -10 th 19 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 - Nov2010 USER Line 1-12 LED Beacon - Optical Properties HI L2F9 - Nov2010; USER Line 1-12 LED Beacon - Optical Properties HI L4F2 - Nov2010 USER Line 1-12 LED Beacon - Optical Properties HI L4F9 - Nov2010; USER Line 1-12 LED Beacon - Optical Properties HI L6F2 - Nov2010 USER Line 1-12 LED Beacon - Optical Properties HI L8F2 - Nov2010; USER Line 1-12 LED Beacon - Optical Properties HI L8F9 - Nov2010 USER Line 1-12 LED Beacon - Optical Properties HI L12F2 - Nov2010; USER Line 1-12 Laser Beacon Nov2010

Final comments ANTARES Collaboration Meeting CERN, February 07 th -10 th 20 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.

Final comments ANTARES Collaboration Meeting CERN, February 07 th -10 th 21 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.

ConclusionsConclusions ANTARES Collaboration Meeting CERN, February 07 th -10 th 22 We have started our 40 K 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: We have started our 40 K 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] Mean [m] RMS [m]

BACKUPBACKUP ANTARES Collaboration Meeting CERN, February 07 th -10 th 23 NOISE SUBTRACTION: RATE OF CORRELATED COINCIDENCES ( 40 K): 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 (R 0 ). R 0 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 40 K measurements. NOISE LEVEL Fit a constant in the [-1000, -50] ns range (B level ) and substract the noise contribution (Q noise, N noise ): N signal = N hits(tot) – N noise = N tot – B level (T min - T max ) = N tot – N bins (T min - T max )

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