A study of the AMANDA detector using atmospheric muons

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A study of the AMANDA detector using atmospheric
muons

• Julio Rodriguez Martino
• Fysikum, Stockholm University, Sweden

Institut de Física d'Altes Energies,
Barcelona May 16th, 2003
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Seminar summary

• Short info about AMANDA
• Why atmospheric muons ?
• Photomultiplier test facility
• WLS
• PMT tests
• Tests at South Pole
• Detector characterization
• Ice properties
• Individual OM response

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The AMANDA-II detector

• 677 OMs
• Between 1000 and
• 2350 m below ice surface
• Analog and digital signal measurement
• High or low energy threshold (multiplicity or
  string trigger)
• Technology tested and understood for ICECUBE

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Why atmospheric muons ?

• Free and rather well known calibration source
• Allows to calibrate/study all OMs at the same
  time (specially useful for ICECUBE)
• We measure them anyway
• Disadvantages
• Hard to select a single energy
• Still big error in the flux and spectrum
  measurements

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Photomultiplier test facility

• Water Cherenkov detector
• Used to test PMTs and for educational purposes
• Use one OM for tests and the other as monitor
• All possible OM orientations
• Black lining
• Muon telescope made of scintillators

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Associated electronics
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Tests

• ADC and TDC calibrated with pulse generator
• PMTs gain (single PE spectra)
• PMT linear response (using two polarimeters)
• Spectral response of lampmonochromator system.

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Wavelength shifters

• The OM sensitivity has a cut-off at about 300 nm
  (glass, gel and PMT window)
• A lot of Cherenkov light is lost (1/l2 spectrum)
• A WLS could help increase the amount of light
  collected and thus the efficiency of each OM
• Required good time properties and small
  absorption in the visible range

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Measurements

• No water in the tank (too high absorption in UV)
• Same electronics, but replacing the muons by a UV
  lamp
• WLS compounds dissolved in dichloromethane.
  Paraloid binder added for mechanical support.
  Painted over the OM surface by hand
• Compare the collected charge in the same OM with
  and without WLS, as a function of wavelength
• Measure LE and TE distribution to study time
  properties

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Time properties
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Results
Nucl. Inst. Meth. A443 (2000) 136-147
J. Rodriguez Martino A Photomultiplier
Test Facility at Fysikum Construction,
calibration and Studies for the Improvement of
the AMANDA/ICECUBE Detectors, Licenciat Thesis,
USIP Report 99-04
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PMT gain test

• Problem OMs in strings 11, 12 and 13 showed a
  lower gain value in 1998 than the one measured
  when deployed
• We tried to reproduce the gain decay in the lab
• Several types of OMs tested inside a freezer over
  a period of more than a year
• High gain values (HV) and LEDs to increase the
  pulse rate

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Time evolution
AMANDA
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Conclusions

• Same behaviour in the lab and at South Pole
• Fast decay followed by a long period of stability
• The result is independent of the OM type (batch),
  the base type or the induced rate
• Some component in the PMTs base is producing the
  decay
• The long term monitoring at South Pole, even in
  the new strings, shows that the detector is
  stable and this problem does not affect its
  normal operation
• OMs in strings 11-13 are different

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Tests at South Pole

• Amplification
• OM pulse quality

AMANDA-II
Skiway
Dome

• Trigger system
• New trigger in 2000

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Track length calculation

• Extend the regular reconstruction method to get
  the track length
• Allows to get the stopping point of the muon
• Could be used to measure contained events

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Track length calculation accuracy

• Analysis done with AMANDA B-10 data (with event
  quality cuts)
• Compare the real track length (from MC
  simulated events) with the calculated length
• Use nearly vertical muon tracks (zenith 5)

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3-D detector map

• Determine the active volume of AMANDA B-10
• Count the number of muon tracks passing
  vertically through different areas
• Find a plateau in the number of tracks

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Effective area and volume

• Detector efficiency (e)

• Effective area
• Aeff e . Ageom

• Effective volume
• Veff e . Vgeom

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Effective area and volume

• Get the number of incident muons

• Get the live time of the measurement

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Effective area and volume
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Stopping muons

• Check the number of tracks stopping within the
  detector volume
• For each slice (25 m) count the number of
  vertical tracks stopping in that slice

• The same procedure is applied to data and MC
  simulations
• Good agreement between data and MC

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Energy calibration
-dE/dx a b E

• The energy of a stopping muon can be estimated
• Response of the detector to different energies
  (track lengths)
• Only valid for vertical tracks (gets better in
  A-II)

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Individual OM sensitivity

• Probability of having at least one hit in a given
  OM, as a function of the track parameters
• Full reconstruction with quality cuts
  (AMANDA-II). Selection of events close (lt 35 m)
  to that OM
• Partial reconstruction of the selected events,
  using all OMs but the selected one
• Same calculation for each one of the 677 Oms
• Bin the 5 different variables

P Nhit / Ntot
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Ice properties

• The probability as a function of the distance can
  be fitted as an exponential decay
• I e-a.d
• The parameter a includes absorption and
  scattering (attenuation length)
• Cut on the theta angle to select photons arriving
  almost horizontally to the OM
• The dust layers in the ice can be measured with
  muons

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Multidimensional probability map

• Simulation uses photon tables to avoid
  propagating every single Cherenkov photon
• The tables are generated once and re-used (2
  programs PTD and Photonics)
• The same could be done with data
• Get an accurate representation of the photon
  behaviour for the simulation
• On-going work lots of statistics needed

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Summary and conclusions

• Different parts of the detector have been tested
  (in the lab and at South Pole)
• A photomultiplier test facility has been built
  (many other capabilities)
• WLS could increase the OM sensitivity with
  negligible time delay
• Method to get the end-point of the track
• 3-D map of the detector
• Effective area and volume
• Individual OM sensitivity
• Ice properties
• Probability map
• More geometrical calibrations

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ADDITIONAL PLOTS
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Detection Method for nm

• Cherenkov photons are detected by array of PMTs
• Tracks are reconstructed by maximum likelihood
  method of photon arrival times

5
6
2
3
4
1
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String trigger threshold
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PMT gain
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UV lamp spectrum
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Tap water transmission spectrum
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PPO gain
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ADC spectrum
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Typical pulse after amplification
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DMAD
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DMAD connection
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Quality cuts

• Time window TDCgt4500 ns (1998) and with TDCgt7500
  ns (2000) removed. A large TDC value usually
  indicates a noise hit, that is not related to the
  real event registered
• Isolated hits more than 70 m or more than 500 ns
• Cross-talk Hits with 75ltTOTlt2000 ns or
  5ltTOTlt2000, depending on the type of OM, are
  removed
• Direct hits given a reconstructed track, the
  expected arrival time of a hit to an OM can be
  calculated, assuming that the photons did not
  scatter in the ice. The difference between the
  real recorded time and this expected time is
  known as ''residual''. Direct hits of type a
  (ndira) have a residual in the interval
• -15 ns 25 ns and those of type b (ndirb)
  have a residual in the interval
• -15 ns 75 ns
• Cerenkov length the direct path length of a
  Cerenkov photon (ckvlength) is calculated from
  the reconstructed track to the hit OM, assuming
  an emission angle of 42. Length lt 50 m
• Smoothness it tests the consistency of the
  observed hit pattern with the hypothesis of
  constant light emission by a relativistic muon. A
  value close to 1 or -1 indicates a clustering of
  hits at the beginning or the end of the track,
  which possibly indicates a misreconstructed track
  due to muon bremsstrahlung
• Bad OMs Filter unstable/dead OMs

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Optical properties of ice
Detailed measurement of optical properties ?
strong light scattering ? dust layers ? low
absorption (in particular in UV !!)
Scattering coefficient (1/m) vs. depth