an update on absorption length measurement with the ob system

AN UPDATE ON ABSORPTION AN UPDATE ON ABSORPTION LENGTH MEASUREMENT WITH THE LENGTH MEASUREMENT WITH THE

OB SYSTEMOB SYSTEM

AN UPDATE ON ABSORPTION AN UPDATE ON ABSORPTION LENGTH MEASUREMENT WITH THE LENGTH MEASUREMENT WITH THE

OB SYSTEMOB SYSTEM

ANTARES Collaboration ANTARES Collaboration Meeting Meeting

Paris (France), September Paris (France), September 20th-24th20th-24th

H Yepes, J Barrios H Yepes, J Barrios IFIC (CSIC – Universitat de València)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 AND MILESTONES

OUTLINEOUTLINEOUTLINEOUTLINE

ANTARES Collaboration Meeting ANTARES Collaboration Meeting Paris, September 20th-Paris, September 20th-24th24th

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THE EXPERIMENTAL PROCEDURETHE EXPERIMENTAL PROCEDURETHE EXPERIMENTAL PROCEDURETHE EXPERIMENTAL PROCEDURE


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Experimental method:

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.

F2

3. Quality cuts applied:

• 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 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-2010-

001

DATA TAKING STATUS IDATA TAKING STATUS IDATA TAKING STATUS IDATA TAKING STATUS I


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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.

Updated until 16/08/2010

Number of Golden runs(maximum LED intensity)

Collaboration Meeting Clermont-Ferrand

42

Collaboration Meeting Paris

+59

TOTAL 101

GOLDEN RUN

[nm] Golden runs

470 (blue) 51

400 (UV) 20

532 (green) 30

TOTAL 101

DATA ANALYSIS STATUS IDATA ANALYSIS STATUS IDATA ANALYSIS STATUS IDATA ANALYSIS STATUS I


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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.

n

ii

n

ii

xxn

s

xn

x

1

22

1

)(1

1

1

n

st

s

xt

2/)1(2 )/1()2/(

)2/)1(()(

ttf

CHANGING TO 40K EFFICIENCIES:

• Noise based efficiencies are correlated with noise subtraction.

• Noise based efficiencies 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 described clearly in the Collaboration Meeting Marseille April 2009, based on 40K coincidences.

DATA TAKING STATUS IDATA TAKING STATUS IDATA TAKING STATUS IDATA TAKING STATUS I


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NEW MEASUREMENTS PERFORMED AT = 532 nm by means of the laser beacon:

Reference fit criterion (Rmin): 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.

• Nflashes >= 100k.

ex

xPx

!),(

High intensity at 532 nm

LED intensity Rmin [m] Rmax [m] P(phe>1)

H (blue, 470 nm) 140 235 0.2 %

H (UV, 400 nm) 125 220 0.3 %

H (green, 532 nm) 200 280 0.2 %



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• Bad fits?

• Increasing rates in time?

• Time distributions? Blue

UV

Green

BlueUV Green

TRANSMISSION LENGTH RESULTS:

• One UV run.

• Six L2 runs batch.

• Some under-over flows not shown.



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ANOMALOUS CASES:

UV 47696

Over-underflows values are due to extreme and strange small error assignment in some points.

Blue 50370

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: a mystery which has not been solved.



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• 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



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If the unexplained runs batch are removed:

Blue

UV

Green

BlueUV Green



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Blue

UV

Green

BlueUV Green



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• 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).

BlueUV Green



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[nm] Entries

L ± RMS[m]

Average σfit (RMS) [m]

Mean Prob (2) RMS Prob (2)

Entries with Prob (2) < 1%

470 (Blue)

45 54.4±3.0 2.9 (1.0) 0.68 0.31 2

400 (UV)

20 36.5±1.0 1.5 (1.0) 0.74 0.29 1

532 (Green)

30 21.6±1.2 1.0 (0.4) 0.53 0.30 3

SUMMARY:

BLUE:

• Reasonable fit probabilities

• Variability of L ~5% (RMS/L):

RMS of L in agreement with average σfit : 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 σfit :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 σfit :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).



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• 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.

student

studentr

PATHOLOGICAL CASES ARE BEING STUDIED NOW

Blue UV Green

Gaussian distributions suggest an error assignment around 6 %.



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• Pulls distributions Evidence of BIAS and verification of error coverage

Blue UV Green

student

student fitPull

• 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.



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For an error assignment of 6%, we obtain:



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• Most of low 2 probabilities are focused to UV and green runs.

• An equal error assignment for all runs should be revisited since student’s t value gives the flatter 2 probability.



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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

BlueUV Green



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Blue

UV

Green

BlueUV Green



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[nm] Entries

L ± RMS[m]

Average σfit (RMS) [m]

Mean Prob (2) RMS Prob (2)

Entries with Prob (2) < 1%

470 (Blue)

45 55.7±2.3 2.3 (0.9) 0.68 0.32 3

400 (UV)

20 37.3±1.0 1.2 (0.6) 0.49 0.30 1

532 (Green)

30 21.8±1.1 0.8 (0.4) 0.50 0.31 3

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

DATA ANALYSIS STATUS: DATA ANALYSIS STATUS: SYSTEMATICSSYSTEMATICS



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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 are performed by day for different periods in time to study the influence LED flashing – different OM orientation and light collected, shadowing, etc.

Bad runs batch, just for this study




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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:

OM dependent .

Angle between photon – OM ? Angular acceptance not used. mean

meani

OM

OMOMDeviation




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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.

• At high distances, a correction by angular acceptance could carry out.

Next step: correction by alignment based on angular acceptance studies.

The obtained value for the transmission length doesn’t has large changes , without to take into account the angular aceptance, then, should we to perform such analysis? A SECOND ORDER CORRECTION.

CONCLUSIONS AND MILESTONESCONCLUSIONS AND MILESTONESCONCLUSIONS AND MILESTONESCONCLUSIONS AND MILESTONES


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Being the transmission length, a lower limit for the absorption length …

BACKUPBACKUPBACKUPBACKUP


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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 (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)

an update on absorption length measurement with the ob system

Documents

noise fluctuations

flat level noise

noise subtraction

noise hits projections

signal intensity

students t

new efficiencies

line flashes