Title: 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
2Collaborators
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
3The 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)
4The Detection of UHECR
Air Fluorescence Detector HiRes
AGASA Detector
5The 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)?
-
6The 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
7Thick 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.
8The 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).
9Thick 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).
10Thick Target Vessel Design
PMT 2 5 permanently hooded to sample background
signals from ionizing radiation
11Thick Target Fluorescence Chamber in situ
12Direct 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
13Lateral 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
14Fluorescence 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!
15Light 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.
16Light Yield vs Shower Depth
- Results given by 3 different PMTs.
17Comparison 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!
18Ion 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
19Ion 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
20Comparison 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!
21Lateral 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.
22The 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.
23- Using band-pass filters, we can isolate the
contributions of several different wavelength
bands to the overall light yield. - Shape of fluorescence profile unchanged
24Conclusions
- 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.