Comparison of Air Fluorescence and Ionization Measurements of E'M' Shower Depth Profiles

1

• Comparison of Air Fluorescence and Ionization
  Measurements of E.M. Shower Depth Profiles
• Guey-Lin Lin
• CosPA and National Chiao-Tung University
• for the FLASH collaboration
• Annual PSROC meeting at Taipei, Jan. 18, 2006

2
Collaborators
J. Belz1,2, D. R. Bergman5, Z.Cao2, S.
Cavanaugh5, F.Y. Chang4, P.Chen3, C.C. Chen4,
C.W. Chen4, C. Field3, A. Goldammer1, D. Guest1,
C. Hast3, P. Huntemeyer2, M.A. Huang4, W-Y. P.
Hwang4, R.Iverson3, C.C.H. Jui2, G.L. Lin4, E.C.
Loh2, K. Martens2, J.N. Matthews2,W.R. Nelson3,
J.S.T. Ng3, A. Odian3, L. Perera5, K. Reil3, S.
Schnetzer5, J.D. Smith2, P. Sokolsky2, R. W.
Springer2, S.B. Thomas2, G.B. Thomson5, H.
Vincke3, D. Walz3, and A. Zech5 1 University
of Montana, Missoula, Montana 2 University of
Utah, Salt Lake City, Utah 3 Stanford Linear
Accelerator Center, Stanford University, CA 4
Center for Cosmology and Particle Astrophysics
(CosPA), Taiwan 5 Rutgers University, Piscataway,
New Jersey
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The Motivation For FLASH

• The ultra-high energy cosmic ray (UHECR) spectra
  measured by HiRes (fluorescence) and AGASA
  (scintillation counter ground array) differ
  significantly in slope for E1020 eV.
• This discrepancy can be possibly accounted for
  by a systematic difference in the energy scale
  (25)

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The Detection of UHECR
Air Fluorescence Detector HiRes
AGASA Detector
5
The Energy Reconstruction of UHECR in the
Fluorescence Technique
D. J. Bird et al., APJ 424, 491-502,(1994)
Fitted from the atmospheric scintillation
processmodel independent!

• How well do we know the fluorescence efficiency?
• Can the fluorescence yield really map out the
  longitudinal
• profile Ne(X)?

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The Existing Air Fluorescence Yield
MeasurementsWithout Showers

• Kakimoto et al., NIM A372 (1996)
• Nagano et al., Astroparticle Physics 20, 293-309
  (2003)
• Belz et al., to appear in Astroparticle Physics
  astro-ph/0506741
• Huentemeyer et al., presented at ICRC 05

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Thick Target RunWith Showers

• The shower age S3X/(X2Xmax) determines the
  electron spectrum. Mean electron energies near
  the shower maximum are very similar for 30 GeV
  electrons and 1019 eV protonssuperposition at
  works! SLAC is a right place as 3?1010 eV?5 ?
  1081019 eV.
• Vindicate the hypothesis that nitrogen
  fluorescence is proportional to the deposited
  ionization energya key in the fluorescence
  technique.

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The Strategy

• Produce a shower in the lab with a similar
  characteristics to the EM shower in the air.
• Measure dE/dt (from the fluorescence yield) and
  charged particle profile (with the ion chamber).

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Thick Target Fluorescence Vessel and Ion Chamber

• The shower parameters of Al2O3 close to those of
  air
• Fluorescence light collected from the thin
  vessel charged particle profile measured by the
  ion chamber
• PMTs shielded from ionizing radiation by two 90
  degree reflections
• Drop-in mechanical shutter (for studying
  background) and filter holder (for studying
  fluorescence spectra).

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Thick Target Vessel Design
PMT 2 5 permanently hooded to sample background
signals from ionizing radiation
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Thick Target Fluorescence Chamber in situ
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Direct Detection of Shower Particles Ion Chamber

• Direct measurement of ionization produced by beam
  particles.
• Use helium gas at 1 atm and apply an 140 V/mm
  voltage

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Lateral Profile Measurement
Cr doped alumina screen

• Scintillation Screen and CCD Camera for
  measuring the shower lateral profilea test of
  the shower simulation code.

mirror
CCD camera
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Fluorescence Signal and Background

• PMT ADC Counts vs. Beam Charge (blue)
• Background subtraction (red)
• Fit slope in linear region
• Note3x107 30 GeV electrons 1018 eV airshower!

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Light Yield vs Shower Depth

• Five series of runs overlaid on this plot
• Very stable results
• 0.8 at 6 r.l.
• 7 at 14 r.l.

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Light Yield vs Shower Depth

• Results given by 3 different PMTs.

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Comparison to EGS4

• A comparison between the light yield and the
  energy deposit simulation. Geant3 gives a
  consistent result.
• Effects of aluminum boxes accounted for by
  scaling the Al2O3 density
• RMS deviation from the unity is only 1.7!

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Ion Chamber Results

• Plot of ion chamber signal against beam toroid
  signal at 6 R.L.
• The correlation tested with polynomial fits from
  1st to 3rd orders
• Coefficients of the linear terms taken as
  proportional to the ionization events in the ion
  chamber

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Ion Chamber Results

• Ion chamber depth profile and EGS4 simulated
  depth profile both normalized with the sum of
  points equal to unity.
• Shower profiles averaged from 3 electronic
  configurations
• Geant3 simulation gives a consistent result

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Comparison to EGS4

• The discrepancies between two results are within
  4 for all shower depths.
• The RMS deviation of the ratio values is only
  1.9!

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Lateral Profile Result

• The comparison of profiles from the scintillation
  screen and the EGS4 simulation at 10 R.L.
• The agreement is satisfactory for purposes of
  this work.

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The Vindication of Fluorescence Technique

• Comparison of fluorescence and ionization
  longitudinal profiles. The sum of points in each
  profile is independently normalized to unity.
• The ion chamber data points correspond to
  slightly larger radiation lengths.

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• Using band-pass filters, we can isolate the
  contributions of several different wavelength
  bands to the overall light yield.
• Shape of fluorescence profile unchanged

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Conclusions

• The atmospheric fluorescence technique is
  validated through simultaneous measurements of
  fluorescence light yield and shower longitudinal
  profiles.
• Band-pass filter data indicates that the above
  energy deposition proportionality to the
  fluorescence yield is wavelength-independent.
• The shower longitudinal profile simulation (EGS4
  and Geant3) is validated as well. The agreement
  between simulation and measurement is better than
  2.
• Our result is also very important for the next
  generation of UHECR experiments, such as Auger
  and Telescope Array.
• Paper to appear in Astroparticle Physics.
  Available from astro-ph/0510375.