time calibration of amanda three variations on a theme of t 0 kael d. hanson department of physics...

Time Calibration of AMANDATime Calibration of AMANDA

Three Variations on a Theme of TThree Variations on a Theme of T00

Kael D. HansonKael D. HansonDepartment of Physics & Astronomy

University of Pennsylvania

For the AMANDA CollaborationFor the AMANDA Collaboration

[email protected]@hep.upenn.edu

March 27, 2002 K. Hanson - Calor2002 – Pasadena, CA

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The AMANDA CollaborationThe AMANDA CollaborationThe AMANDA CollaborationThe AMANDA Collaboration7 US and 9 European institutions, about 110 current members:

1. Bartol Research Institute, University of Delaware, Newark, USA2. BUGH Wuppertal, Germany3. Universite Libre de Bruxelles, Brussels, Belgium4. DESY-Zeuthen, Zeuthen, Germany5. Dept. of Technology, Kalmar University, Kalmar, Sweden6. Lawrence Berkeley National Laboratory, Berkeley, USA7. Dept. of Physics, UC Berkeley, USA 8. Institute of Physics, University of Mainz, Mainz, Germany9. University of Mons-Hainaut, Mons, Belgium10. University of California, Irvine, CA11. Dept. of Physics and Astronomy, University of Pennsylvania, Philadelphia, USA12. Physics Department, University of Wisconsin, River Falls, USA13. Physics Department, University of Wisconsin, Madison, USA14. Division of High Energy Physics, Uppsala University, Uppsala, Sweden15. Fysikum, Stockholm University, Stockholm, Sweden16. Vrije Universiteit Brussel, Brussel, Belgium


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The AMANDA DetectorThe AMANDA Detector

• Currently operating AMANDA-II, 677 OMs, 20 Megaton geometric volume.

• Several artificial light sources deployed for calibrating AMANDA:– Nd:YAG surface laser

• Timing• Geometry

– N2 (UV) in situ lasers– UV LED ‘flashers.’


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Timing is Critical to Timing is Critical to AMANDA Event AMANDA Event Reconstruction!Reconstruction!

• Muon/cascade particle id and reconstruction depend crucially on relative timing in the OMs.

• Studies of reconstruction per-formance indicate 10 - 20 ns resolution sufficient for muon track reco (Biron, AIR-20001101).

tcoefficien Timewalk

offset timing Relative

04171 slope TDC

0

0

T

TTDCtADCHIT

.


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Dealing with Discriminator Dealing with Discriminator WalkWalk

• Electrical signals suffer large amount of dispersion in cables pulse risetime corrections necessary.

• Timewalk effect is deter-ministic: pulse risetimes at surface are up to 100’s of ns but jitter is still at ns level.

• Pulse risetimes only signi-ficant for electrical channels; optical channels

Cable Type Risetime (typ.)

Coaxial 100 ns

Twisted pair 50 ns

Optical fiber 10 ns


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Variation 1: Laser TVariation 1: Laser T00

• T0 measures the signal propagation time from OM to TDC– Cable prop. time– Front-end electronics

• Amplifiers (SWAMPs)

• Discriminators

• High power pulsed Nd:YAG laser at surface delivers 532 nm light via optical fibers to OM.


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Laser TLaser T00 (continued) (continued)

• Acrylic “diffuser ball” at OM isotropizes laser light.– Each OM on strings 1-4 and

strings 11-19 equipped with diffuser ball.

– Only even OMs on strings 5-10 have diffuser ball: neighboring OM used for those lacking diffuser.

• Fiber lengths determined separately using OTDR equipment.


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Laser Calibration AnalysisLaser Calibration Analysis

• YAG intensity controlled via ND filters and optical atten-uators. Sample T0 in range of 1 – 5 photo-electrons.

• TDC leading edge plotted vs. 1/SQRT(ADC) – Y intercept is T0

– Slope is timewalk coefficient

• Fiber lengths must be sub-tracted to obtain signal propagation time.

• Precision of laser cal esti-mated at ~ 5 ns.


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Stability of AMANDA T0’sStability of AMANDA T0’s

• Q: Is annual calibration sufficient?– Station closed for winter.– No HW changes unless

catastrophic failure of equipment

– Electronics in ice static– TDCs use crystal

oscillator: very stable.

• A: YES!


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Laser TLaser T00 Summary Summary

• Laser T0 remains the default AMANDA time calibration method.

• Very labor-intensive: full detector calibration done annually requires 1000 man-hours!

• Useful for debugging detector (channel mapping errors) after hardware work.

• Very easy to piggyback crosstalk mapping.• Only method that currently obtains timewalk

coefficients.


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Variation 2: Using CR MuonsVariation 2: Using CR Muons

• AMANDA-II receives ample supply (~100 Hz) of downgoing muons.

• If T0’s known well enough to give track reco then possible to iteratively refine T0 guesses.

• Premise: shift in T0 will appear as offset in timing residual

Timing residual = Measured hit time – Hit time expected from track

parameters


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Outline of AlgorithmOutline of Algorithm

1. Reconstruct muon tracks using best knowledge of T0 calibration constants.

2. Accumulate time residuals from tracks.3. Determine time offset from residual

distribution.4. Apply offset as correction to T0 constant.

5. Go to step #1. Repeat until T0 converges to a fixed point.


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Offset DeterminationOffset Determination

• Timing residuals have complex structure: some suggestions for getting the ‘zero’ point:1. Take maximum of distribution,2. Fit gaussian around max,3. Cross-correlation with template

• We chose 3 since it was overall most robust.

• Fast implementation using FFTs.


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ConvergenceConvergence

• Convergence is monitored by plotting width of distri-bution of offsets for each iteration.

• Applying only a fraction of offset at each iteration seems to stabilize method against oscillations:

)()()( nnn TTT 001

0

• Terminal value of this width gives rough estimate of precision of calibration.

• Still not clear how close initial guess must be in order to ensure convergence.


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Testing Muon-TTesting Muon-T00

• Take standard AMANDA T0 constants and shift by known amount (black line in figure).

• Run 25 iterations of muon-T0 procedure.

• Corrections shown as red points.


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Muon-T0 SummaryMuon-T0 Summary

• Systematic drift over string hampers adoption by AMANDA as primary calibration – however it has been used in conjunction with laser T0:– Incorrect laser T0’s (fiber lengths incorrectly measured),– Fibers leaking at OM optical penetrator,– Can quickly check validity of T0’s for any given run period

throughout the year or even previous years’ data!– 2001 calibration done using muon-T0 to determine which

offsets have changed: only run laser cal on those channels (~50 as opposed to 700).

• No special runs necessary (eliminates 1000 man-hour task in favor of 25 man-hour task).

• Does not (yet) calibrate timewalk coefficients.• Eventually hope to use improved muon calibration.


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Variation 3: IceCube Clock Variation 3: IceCube Clock SynchronizationSynchronization

• Baseline technology for IceCube is DOM:– Waveforms digitized in situ, stamped

with local DOM time, and sent to surface as digital packet.

– Each DOM (~5000 total) has independent clock oscillator.

– Surface clocks are synchronized to GPS clock using high precision rubidium clock

• RAPCal (Reciprocal Active Pulsing Calibration) method:

– Surface electronics sends pulse on communication line at time T1,

– DOM digitizes pulse /w/ local timestamp T2, sends mirror pulse at time T3,

– Surface electronics digitizes pulse /w/ timestamp T4

.


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RAPCal Waveform AnalysisRAPCal Waveform Analysis

• Pulses sent at time clock is latched,

• Received pulses arrive asynchronously, must fit WF to get higher precision than 33 MHz clock.

• Linear fit to leading edge extrapolated to baseline.

TTarrivalarrival


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RAPCal (continued)RAPCal (continued)

• RAPCal calibrates:– Cable propagation delay (T0!)

– Ratio of clock frequencies fSURF/fDOM

• RAPCal/DOM technology being tested now in AMANDA-II (18th string DOMs)

• String 18 RAPCal done approximately 0.1 Hz, achieves time resolution of approx. 5 ns RMS.

12340

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2

11

1

21

:nCalculatio Delay Cable

:nCalculatio Ratio Clock

TTTff

Tf

T

TTTT

ff

DOM

SURF

SURF

nn

nn

DOM

SURF)()(

)()(


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RAPCal SummaryRAPCal Summary

• Hardware built into DOM and DOMHub (front-end surface electronics).

• Software runs as application in DOMHub.• RAPCal must run in realtime: IceCube trigger

depends on globally time-ordered hits. Simple linear fits currently implemented seem adequate to achieve desired time resolution of ~ ns.

• RAPCal in IceCube eliminates need for explicit T0 calibration.

time calibration of amanda three variations on a theme of t 0 kael d. hanson department of physics...

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