H Yepes, C Bigongiari, J Zuñiga, JdD Zornoza IFIC (CSIC - Universidad de Valencia) NEWS ON ABSORPTION LENGTH MEASUREMENT WITH THE OB SYSTEM ANTARES COLLABORATION MEETING FEBRUARY 2010, CERN (SWITZERLAND)

|| Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || OUTLINE A REMINDER OF THE EXPERIMENTAL PROCEDURE STATUS OF OPTICAL PROPERTY RUNS ACQUISITION ANALYSIS BASED ON GOLDEN RUNS: NEW MEASUREMENTS PERFORMED WITH UV LEDS CONCLUSIONS AND OUTLOOK

F2 EXPONENTIAL FIT 1. THE EXPERIMENTAL SETUP: One single top LED of the lowest optical beacon in the line flashes to the upper storeys and the collected charge (Q) can be plotted and fitted through an exponential function for hits or charge, once quality cuts are applied. The collected charge is a convolution of: Physics: Absorption length (L abs ) Scattering (L sca and  =  (  )) Detector: OB – OM relative orientation OM efficiency ARS token ring dead time Charge resolution To minimize the effects of the detector: Consider only OMs in the same line of the OB Consider only the region (R min, R max ) where signal < spe but well above background || Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || A REMINDER OF THE EXPERIMENTAL PROCEDURE 3

Q noise T max T min Q signal 2. TIME DISTRIBUTION: Determine the peak  Gaussian fit Choose a fixed time window [T min, T max ] and select the hits: T min = T peak – 3  T max = T peak ns Calculate their overall charge Q tot and the signal hits. 3. NOISE CONTRIBUTION: Fit a constant in the [-1000, -50] ns range (B level ) and substract the noise contribution (Q noise ): Q signal = Q tot – Q noise = Q tot – B level (T min - T max ) NOISE LEVEL Time distribution || Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || A REMINDER OF THE EXPERIMENTAL PROCEDURE 4

4. CHARGE LOSSES: Some hits are lost due to the electronic dead time from the readout of the ARSs. Consider only the region where the probability to get more than one photoelectron is negligible (i.e. < 1 %). Electronics dead time effects related to R min. 5. PMT EFFICIENCY CORRECTION BY NOISE: Assume that the Q noise ~  PMT Normalize PMTs signal charge to their own noise charge: Time distributionEfficiency correction by noise || Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || A REMINDER OF THE EXPERIMENTAL PROCEDURE 5

6. NOISE FLUCTUATIONS: To avoid noise fluctuations at large distances, signal greater than the noise is required  Maximum distance to fit R max. 7. MEASUREMENT OF ERRORS: Statistical and dispersion errors are considered for the data. 8. LOW EFFICIENCY OMs CLEANING: Low efficiency OMs are removed. Checked from noise plots  Compute hits projections, fit a Gaussian and consider only OMs between (  +3 ,  -3  ). 9. THE BACKGROUND “FLATNESS”: Efficiency correction by noise is affected by noise fluctuations along the line  A “flat” level noise along the line is required. GOLDEN RUN TOTAL RUNs126 GOLDEN53 The experience from the analysis has let the optimization of data taking: Golden runs taken by request, once conditions are met. No silver and copper runs taken anymore. Updated golden runs table until 01/02/2010: || Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || A REMINDER OF THE EXPERIMENTAL PROCEDURE 6

DATA ACQUISITION STATUS: Optical property runs are taken on request when background rates are low: USER Line 1-12 LED Beacon - Optical properties HI - V3.1 (L2F2) High intensity runs at 470 nm  Stability in time of results is confirmed USER Line 1-12 LED Beacon - Optical properties MI - V3.1 (L2F2) Medium intensity runs for testing USER Line 1-12 LED Beacon - L12 F2 KM3NeT LEDs - V3.1 (L12F2, UV!) First UV runs obtained (11 UV runs at present) USER Line 1-12 LED Beacon - only test (L4F2, L8F2, L2F9) Different lines/OBs/LEDs (L4F2, L8F2) to study systematic effects and influence of depth on absorption length (L2F9). || Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || STATUS OF OPTICAL PROPERTIES RUNS ACQUISITION 7

1.THE STABILITY FOR THE OPTICAL PARAMETER L : Last Collaboration Meeting (Gandia): Values for L obtained from different runs are stable provided that 1) a correction by efficiency is made (based on background rate), 2) high intensity runs are used and 3) phe level is required. High intensity runs  R min (H) = 135 m R max (H) = 275 m Value for L computed from the number of hits if the reference fit (0F, 0F) is moved: If R min decreases  We go out from the photoelectron region  L increases. If R min increases  Scattering effects are most remarkable  L decreases. Reference fit R max R min -2F (F10)-1F (F11)0F (F12)+1F (F13)+2F (F14) -1F (F20) F (F21) F (F22) || Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || ANALYSIS BASED ON GOLDEN RUNS 8

2.THE REFERENCE FIT FOR UV RUNS:  Take distances where the probability to get more than one phe is negligible: x = number of signal reaching the OM  = number of signal hits / number of flashes High intensity runs ( 470 nm )  R min (H) = 135 m R max (H) = 275 m High intensity runs ( 400 nm )  R min (H) = 135 m R max (H) = 275 m LED intensityR min (m)P(phe > 1) H (blue)1350.2% H (UV)1350.5% High intensity at 470 nm (blue) High intensity at 400 nm (UV) || Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || ANALYSIS BASED ON GOLDEN RUNS 9

3.RESULTS BY LED WAVELENGTH: L (470 nm) L8, L2, L4, L1 L (400 nm) L12 || Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || ANALYSIS BASED ON GOLDEN RUNS 10

|| Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || ANALYSIS BASED ON GOLDEN RUNS 11

4.RESULTS BY LINES: || Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || ANALYSIS BASED ON GOLDEN RUNS 12 No hint of a dependence of L on line or OB

5.RELATIONSHIP BETWEEN L AND THE ABSORPTION LENGTH ( abs ): MC PRODUCTION Water model: Partic abs = 60 m fixed  = 0.17, 0.05 scat = 30, 40, 50, 60, 70 m    L 1000 IS A LOWER LIMIT FOR THE abs  abs MC input L obtained from Data || Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || ANALYSIS BASED ON GOLDEN RUNS 13 L obtained from MC The difference abs - L depends on scat and  ↔  (  )

6. THE  R TECHNIQUE: || Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || ANALYSIS BASED ON GOLDEN RUNS 14 The effect of scattering is to increase the photon path length in ΔR on average. Perform the exponential fit using ( mean photon path ), R + ΔR instead of R. R ΔRΔR R+ΔR ΔR should be proportional to the scattering. Exponential fit with R + ΔR will be more insensitive to scattering since the greater the scattering the greater the delay and viceversa, making the L parameter closer to the real absorption length. ΔR can be extracted from time distributions !!! tt

|| Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || ANALYSIS BASED ON GOLDEN RUNS PARAMETERIZATION OF  R FOR DATA AND MC SIMULATIONS: Correlation between R+  R for data (golden runs) Correlation between R+  R for MC The values of the above slopes are then related to the Rayleigh scattering (  ). MC simulations can give an idea about the scattering contribution, from the relationship between R +  R and R.  R +  R =  R (  depends on scattering) R [m] R +  R [m] PRELIMINARY R [m] R +  R [m] PRELIMINARY

|| Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || ANALYSIS BASED ON GOLDEN RUNS 16  scat, eff PRELIMINARY Relationship scat, eff and  (differents  )  MC 8.DEPENDENCE OF  ON THE EFFECTIVE SCATTERING LENGTH ( scat, eff )

|| Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || ANALYSIS BASED ON GOLDEN RUNS 16 L parameter using  R parameterization  MC L parameter using  R parameterization  DATA Fit of L to seems to “recover” abs VERY PRELIMINARY  Needs cross-checks !!! 9.RESULTS OF THE  R TECHNIQUE ON MC AND DATA: PRELIMINARY

|| Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || CONCLUSIONS AND OUTLOOK The new runs confirm the stability of L for high intensity runs in the blue (470 nm). New UV (470 nm) runs have been taken. L (≈38 m ) is also stable (good agreement with the old run of the previous L12F2 OB  collaboration meeting Marseille). L does not seem to depend on OB, LED or line. Depth dependence being currently studied. Systematic errors have to be revisited. Monte Carlo simulations indicate that L is a lower limit of abs. However,  = abs ­ L depends on scat and on the angular distribution  (  ) and these are poorly known (to say the least). An educated guess indicates  ≈ 5-10 m for 470 nm. A first attempt has been made to extract information for scat and  (  ) from the time distribution at different distances. Assuming that scattering changes absorption length only through the increase of the effective travelled distance, the fit is made to R + ΔR (instead of R) where ΔR is extracted from data. Preliminary Monte Carlo results are encouraging ( L is much closer to abs ), but still a lot of work to be done to check the range of applicability of the procedure. Take new low intensity runs → distance OB-OM shorter → effect of scat smaller→ L should approach abs. This is indeed roughly seen, but the few low intensity runs that we have are poorly understood, the exponential seems to change slope (an indication?). Integration of new multi-wavelength OB in line 6 has taken place. Hopefully new data at different wavelengths soon.

BACKUP SLIDES

|| Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || BACKUP SLIDES THE BACKGROUND FLATNESS AS A QUALITY FACTOR Noise efficiency correction is affected by noise fluctuations along the line  A “flat” level noise along the line is required. The background level flat shape along the line is correlated with low rates  Special runs request at low mean background rates: E-LOG entry: 4126 USER Line 1-12 LED Beacon - Optical properties MI - V3.1 USER Line 1-12 LED Beacon - Optical properties HI - V3.1

|| Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || BACKUP SLIDES DEPENDENCE OF P1 (a) ON SEVERAL WATER PARAMETERS

|| Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || BACKUP SLIDES

|| Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || BACKUP SLIDES

|| Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || BACKUP SLIDES

|| Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || BACKUP SLIDES

|| Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || BACKUP SLIDES

|| Harold Yepes || ANTARES Collaboration Meeting, February 2010, CERN || BACKUP SLIDES