AN UPDATE ON ABSORPTION LENGTH MEASUREMENT WITH THE OB SYSTEM ANTARES Collaboration Meeting Paris (France), September 20th-24th H Yepes, J Barrios IFIC (CSIC – Universitat de València)

A BRIEF REMINDER OF THE EXPERIMENTAL PROCEDURE DATA TAKING STATUS DATA ANALYSIS STATUS: (I) Multi-wavelength analysis and (II) OB systematic effects studies CONCLUSIONS OUTLINEOUTLINE ANTARES Collaboration Meeting Paris, September 20th-24th 2

THE EXPERIMENTAL PROCEDURE ANTARES Collaboration Meeting Paris, September 20th-24th 3 Experimental method: 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. F2 3. Quality cuts applied: 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 and flat level noise along the line is required (<100 kHz). 1.A BRIEF REMINDER OF THE EXPERIMENTAL PROCEDURE: Remarks: 1) The efficiencies for the OMs are computed from the normalization of the signal hits to their own noise hits. 2) The total error assigned is computed as the quadratic sum of the statistical and dispersion errors. 3) Transmission length is a lower limit of the absorption length. ANTPLOT-CALI

DATA TAKING STATUS I ANTARES Collaboration Meeting Paris, September 20th-24th 4 The experience from the analysis has let the optimization of data taking: Golden runs taken by request, once conditions are met: LOW AND FLAT LEVEL SHAPE OF THE NOISE along the line required. Different lines/OBs/LEDs/LEDs intensities (L4F2, L4F9, L8F2, L8F9, L2F2 all faces) to study MAINLY systematic effects and influence of depth on absorption length (L2F9, L8F9). Runs at three different wavelengths have been taken. Number of Golden runs (maximum LED intensity) Collaboration Meeting Clermont-Ferrand 42 Collaboration Meeting Paris +59 TOTAL101 GOLDEN RUN [nm] Golden runs 470 (blue) (UV) (green)30 TOTAL101 Updated until 16/08/2010

DATA ANALYSIS STATUS I ANTARES Collaboration Meeting Paris, September 20th-24th 5 TREATMENT OF ERRORS (since the last CM): Assign one signal intensity per storey computed as the average of the 3 OMs. Compute error by means of Student’s t. t follows Student’s distribution: In order to have 68.27% errors, the one-side tail of the cumulative Student function must be 84.13% and thus t = 1.32 (for n=3) or t = 1.83 (for n=2). If only one OM in the storey do not use that storey in the fit. CHANGING TO 40 K EFFICIENCIES: Noise based efficiencies are correlated with noise subtraction. Noise based efficiencies 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 described clearly in the Collaboration Meeting Marseille April 2009, based on 40 K coincidences.

DATA TAKING STATUS I ANTARES Collaboration Meeting Paris, September 20th-24th 6 NEW MEASUREMENTS PERFORMED AT = 532 nm by means of the laser beacon: Reference fit criterion (R min ): Take distances where the probability to get more than one phe is negligible: x = number of signal hits reaching the OM  = number of signal hits / number of flashes Laser beacon runs selection: Standard laser beacon runs at maximum polarizer voltage value. Low and flat level shape along the line. N flashes >= 100k. High intensity at 532 nm LED intensityR min [m]R max [m]P(phe>1) H (blue, 470 nm) % H (UV, 400 nm) % H (green, 532 nm) %

DATA ANALYSIS STATUS I ANTARES Collaboration Meeting Paris, September 20th-24th 7 Bad fits? Increasing rates in time? Time distributions? Blue UV Green Blue UV Green TRANSMISSION LENGTH RESULTS: One UV run. Six L2 runs batch. Some under-over flows not shown.

DATA ANALYSIS STATUS I ANTARES Collaboration Meeting Paris, September 20th-24th 8 ANOMALOUS CASES: UV  Overflows values are due to extreme and strange small error assignment in some points. Blue  Six L2 runs batch displaced: Not similar effects on error assignment. Not due to noise fluctuations along the line/time. Deepest analysis is being performed.

DATA ANALYSIS STATUS I ANTARES Collaboration Meeting Paris, September 20th-24th 9 Some drawbacks have been corrected casually during the below cross-checks performed (i.e F14-F17):  EMPTY BINS effect which have a strong dependence on the noise subtraction: a time cut is performed OM0 OM1 OM2

DATA ANALYSIS STATUS I ANTARES Collaboration Meeting Paris, September 20th-24th 10 If the unexplained runs batch are removed: Blue UV Green Blue UV Green

DATA ANALYSIS STATUS I ANTARES Collaboration Meeting Paris, September 20th-24th 11 Blue UV Green Blue UV Green

DATA ANALYSIS STATUS I ANTARES Collaboration Meeting Paris, September 20th-24th 12 The mean value of the distribution of the L errors from the fits shows an agreement with the RMS of the transmission length distribution: UV  1.0 m Vs 1.5 m Green  1.1 m Vs 1.0 m Blue  3.0 m Vs 2.9 m. The time stability and the RMS distribution confirms the showed results in the latest Collaboration Meetings, except for the anomalous six runs batch (a deeper analysis is being performed). Blue UVGreen

DATA ANALYSIS STATUS I ANTARES Collaboration Meeting Paris, September 20th-24th 13 [nm] Entrie s L ± RMS[m] Average σ fit (RMS) [m] Mean Prob (  2 )RMS Prob (  2 )Entries with Prob (  2 ) < 1% 470 (Blue) ± (1.0) (UV)2036.5± (1.0) (Green) ± (0.4) SUMMARY: BLUE: Reasonable fit probabilities Variability of L ~ 5% (RMS/L): RMS of L in agreement with average σ fit : 3.0 m vs. 2.9 m Change of L with time not much larger than statistical Somewhat high probabilities: few entries close to 1. UV: Good fit probabilities Variability of L around 3% (RMS/L): RMS of L distribution in agreement with average σ fit :1.0 m vs. 1.5 m. Green: Good fit probabilities Variability of L around 6% (RMS/L): RMS of L distribution in agreement with average σ fit :1.2 m vs. 1.0 m. Mean Prob (  2 )  should be 0.5 RMS Prob (  2 )  should be 1/√12 = 0.29 STABILITY IN TIME IS CONFIRMED FOR DIFFERENT WAVELENGTHS * If we assume the fluctuation of the measurements is statistical (not yet clear) the errors for the three wavelengths would be ±0.2m (√entries).

DATA ANALYSIS STATUS I ANTARES Collaboration Meeting Paris, September 20th-24th 14 Distribution of relative errors  Looking for the optimal assignment of errors: Histogram entries correspond to those storeys used in fit for each wavelength, for all golden runs selected. PATHOLOGICAL CASES ARE UNDER STUDY Blue UV Green  Gaussian distributions suggest an error assignment around 6 %.

DATA ANALYSIS STATUS I ANTARES Collaboration Meeting Paris, September 20th-24th 15 Pulls distributions  Evidence of BIAS and verification of error coverage Blue UVGreen For Blue and UV pulls distributions, the fitted function parameters are slightly in agreement to the expected center in 0 and width unit gaussian distributions. For pulls distributions in the green, a deeper analysis is being carried out to determine the origin of BIAS.

DATA ANALYSIS STATUS I ANTARES Collaboration Meeting Paris, September 20th-24th 16 Having in mind that we have to be at photoelectron region, we consider a P(phe>1) ≈ 0.3%. Being consistent with such requirement, we can take one storey before to begin the fit P(phe>1) ≈ 0.5%: Blue UV Green Blue UVGreen

DATA ANALYSIS STATUS I ANTARES Collaboration Meeting Paris, September 20th-24th 17 Blue UV Green Blue UVGreen

DATA ANALYSIS STATUS I ANTARES Collaboration Meeting Paris, September 20th-24th 18 [nm] Entrie s L ± RMS[m] Average σ fit (RMS) [m] Mean Prob (  2 )RMS Prob (  2 )Entries with Prob (  2 ) < 1% 470 (Blue) ± (0.9) (UV)2037.3± (0.6) (Green) ± (0.4) Mean Prob (  2 )  should be 0.5 RMS Prob (  2 )  should be 1/√12 = 0.29

DATA ANALYSIS STATUS: SYSTEMATICS ANTARES Collaboration Meeting Paris, September 20th-24th 19 OPTICAL BEACON FACES: LED SYSTEMATICS There are 6 LEDs placed over the 6 LED Beacon faces. Optical Beacon chosen for analysis  L2F2. A batch of six runs, one per LED Beacon face, have been performed in different periods to study the influence of LED flashing -- different OM orientation, shadowing, etc. Bad runs batch, just for this study GOLDEN RUN SILVER RUN

DATA ANALYSIS STATUS: SYSTEMATICS ANTARES Collaboration Meeting Paris, September 20th-24th 20 Amount of light collected by the OMs at different periods of time using all LOB faces: medium light intensity region ( F12, used in fit): For medium light intensity region in the line, a dependence to the LED seems not to be found. The amount of light percentage collected by one particular OM is higher /lower than the other ones:  Different angle between OB – OM ? Try angular acceptance correction? GOLDEN RUN

DATA ANALYSIS STATUS: SYSTEMATICS ANTARES Collaboration Meeting Paris, September 20th-24th 21 Amount of light collected by the OMs at different periods of time using all LOB faces: ( F15, used in fit): GOLDEN RUN When the distance to the source is more larger, some hint of LED systematics begins to disappear. LED flashing – OM orientation dependence.

DATA ANALYSIS STATUS: SYSTEMATICS ANTARES Collaboration Meeting Paris, September 20th-24th 22 Amount of light collected by the OMs at different periods of time using all LOB faces: low light intensity region ( F18, used in fit): For low light intensity region the systematics are not so evident since there is low statistics. Next step: correction by alignment based on angular acceptance studies? The obtained value for the transmission length doesn't show large fluctuations without taking into account the angular aceptance -> should we to perform such correction?  A SECOND ORDER CORRECTION. GOLDEN RUN

CONCLUSIONSCONCLUSIONS ANTARES Collaboration Meeting Paris, September 20th-24th 23 1.The optical properties data taking is optimized: several runs covering different optical beacons at different heights and different lines, likewise as “multi-faces” LED beacon runs and “multi- wavelength” runs, have been taken systematically. 2.A new value for the transmission length in the green sets a value L ~ 21 m. 3.The stability in time for the transmission length at different wavelengths is confirmed. Some particular cases have been revisited and taken under study. 4.The new treatment of errors and the new 40 K efficiencies based on noise coincidence rates, pointed out to a better quality fits. 5.A preliminary study on the influence of LED flashing - different OM orientation, shadowing, etc, suggests that a possible correction by alignment based on angular acceptance studies could not give enough changes in the stability of transmission length. 6.Being the transmission length a lower limit for the absorption length, the experimental procedure has been developed, gives confidence for the extraction of the absorption length using the “delta R” technique based on the information of scattered photons (SEE NEXT TALK BY J RUIZ-RIVAS).

BACKUPBACKUP ANTARES Collaboration Meeting Paris, September 20th-24th 24 NOISE SUBTRACTION: RATE OF CORRELATED COINCIDENCES: 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 )