Ice Cube Calibration Overview Kurt Woschnagg University of
Ice. Cube Calibration Overview Kurt Woschnagg University of California, Berkeley MANTS 2009 Berlin, September 25 4800 identical sensors in ultraclean, stable ice
Database timing charge High level Low level ice properties: scattering, absorption, hole ice event energy track pointing g geometry efficiency m n
Calibration instrumentation • LED flasher boards • “Standard Candles” • Dust loggers • Bubble cameras • Transmissometers • Pressure sensors • Thermistors • Golden DOMs • • • other 6 5 c
Geometry calibration Stage 1 water surface tower base plate Where on the surface? well depth pressure sensors bottom DOM (defines string depth) string depth in water How deep? How straight?
Geometry calibration Stage 2 Relative depth adjustments Gaussian fit t 0 = a - b·d t (ns) Distance between DOMs [m] d. D L z=0 Hyperbola fit z [m] Unscattered photon timing with interstring flasher data
Geometry calibration Requirement: position of every DOM known to 1 m
Timing calibration Requirement: single-photon timing resolution < 5 ns RAPcal – run by DAQ every few seconds – synchronizes local clocks with master clock for 76 OMs monitored for every run: In-ice DOMs Ice. Top
Timing calibration: verification with flashers
Timing calibration: verification with muons Muon time residuals Reconstruct muon tracks without DOM i. Look at time residuals for DOM i for nearby (<10 m) tracks:
Charge calibration Translate digitized waveform signal (V) to number of photo-electrons (pe) DOMcal – DOM-resident calibration software – runs regularly (once per month) • PMT gain as function of HV • Analog frontend gains and offsets • Discriminator thresholds • Digitizer sampling speed • PMT transit time • Baselines
Charge calibration: PMT linearity & saturation Pre-deployment lab measurements (at low gain) Saturation curves measured in-situ with flasher data Need DOM-specific saturation curves
PMT and DOM efficiency Lab measurements & Golden DOMs PMT DOM High-QE DOMs for Deep. Core:
Understanding the ice “Three feet of ice does not result from one day of cold weather” Chinese proverb The deepest Ice. Cube ice is 100, 000 years old
Understanding the ice What is the scattering/absorption length? “Answer the question, jerk!” John Mc. Enroe
Understanding the ice What is the scattering/absorption length? “Answer the question, jerk!” John Mc. Enroe “You can not be serious!” John Mc. Enroe
Ice properties ↔ dust concentration ↔ climate South Pole (US) Dome Fuji (Japan) Vostok (Russia)
Understanding the ice Extrapolation beyond AMANDA depths has been done with ice core data on dust concentration: Will be updated with flasher measurements
Understanding the ice: Dust Loggers
Understanding the ice: Dust Loggers The dust layers are not completely horizontal
Understanding the ice There may be shear in the deep ice – Geometry changes over time Temperature profile Ice flow model “hole ice” (trapped bubbles) The “hole ice” is different from the “bulk ice” – Air bubbles make acceptance more isotropic in-situ lasers, “bubble cameras”, transmissometers, water/ice muon data
Energy calibration Energy estimators are getting refined Ntop/Nbottom to handle depth dependences due to ice properties vertical diagonal horizontal
Energy calibration: Standard Candles • Nitrogen laser (337 nm) • Calibrated output (~10%) • Cherenkov cone
Energy calibration overlapping energy region useful for cross-calibration depends on brightness setting, # of LEDs, pulse width flashers SC II cascade energy* Ge. V Te. V *applying rule-of-thumb: 105 photons/Ge. V Pe. V Ee. V
Pointing accuracy “calibration” 1. Ice. Top coincidences Mismatch angle between Ice. Top and in-ice reconstructed track 2. Moon shadow [talk by L. Gladstone]
Ice. Cube calibration summary Low-level calibrations • Geometry, timing – mature, understood (lots of experience from AMANDA) • Waveforms/charge – basics (SPE) understood – more work needed as complex NPE waveforms included • Ice – need mapping of deep ice properties – non-trivial to implement in simulation High-level calibrations • Energy calibration – have special devices, depends on low-level calibration
- Slides: 25