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A Measurement of the UltraHigh Energy Cosmic Ray Flux with the HiRes FADC Detector

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Indirect Composition Measurement using depth of the shower maximum. ... Detection of longitudinal shower profile via UV fluorescence light. ... – PowerPoint PPT presentation

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Title: A Measurement of the UltraHigh Energy Cosmic Ray Flux with the HiRes FADC Detector


1
A Measurement of the Ultra-High Energy
Cosmic Ray Flux with the HiRes FADC Detector
  • PhD Defense Presentation
  • September 15th, 2004
  • Andreas Zech

2
Outline
  • A Brief Introduction to UHECR Physics
  • The HiRes Experiment
  • Unfolding the Cosmic Ray Spectrum
  • Results of the HiRes-2 Analysis
  • Conclusions

3
A Brief Introduction to Ultra-High Energy Cosmic
Ray Physics
4
Energy Spectrum
  • differential flux dN / (dE A O dt)
  • follows roughly E-3 power law
  • direct observation not possible above 1 PeV
  • three features
  • knee at 1015.5 eV
  • 2nd knee ( 1017.5 eV)
  • ankle at 1018.5 eV

5
Extensive Air Showers
  • main channels
  • p(-) µ(-) ?µ ( ?µ )
  • po 2 ?
  • main e.m. processes
  • bremsstrahlung
  • pair production
  • ionization

6
HiRes-2 Composition Measurement
  • Indirect Composition Measurement using depth of
    the shower maximum.
  • Shift from heavy to light composition at around
    1017 eV to 1018 eV.

7
HiRes-2 Skymap
  • UHECR arrival directions agree with isotropic
    distribution.
  • AGASA claims to see small-scale anisotropies
    (clusters of events) at ultra-high
    energies.

8
Propagation Effects
  • magnetic fields (galactic, extragalactic)
  • red-shifting
  • ee-- pair production with CMBR (at 1017.8 eV)
  • photo-spallation of cosmic ray nuclei
  • GZK effect with CMBR (at 1019.8 eV)
  • ? (2.7 K) p ?(1232) p
    n
  • ? (2.7 K) p ?(1232) p o
    p
  • Strong flux suppression for
    extra-galactic sources.

9
The HiRes Experiment
10
Air Fluorescence Detectors
  • Detection of longitudinal shower profile via UV
    fluorescence light.
  • Reconstruction of geometry from recorded shower
    track.
  • Using the atmosphere as a calorimeter.

11
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12
  • Mirror area 5 m2 .
  • 256 (16x16) PMT per mirror.
  • One PMT sees 1 degree of the sky.

13
1. Reconstruction of the shower-detector plane
  • project signal tubes onto sky
  • fit tube positions to a plane through the center
    of the detector
  • reject tubes that are off-track (and off in
    time) as noise
  • shower axis lies in the fitted shower-detector
    plane

14
2. Reconstruction of the geometry within the
s-d-plane (HiRes-2)
15
3. Shower Profile Energy Reconstruction
  • Reconstruct charged particle profile from
    recorded p.e.
  • Fit profile to G.H. function.
  • Subtract Cerenkov light.
  • Multiply by mean ionization loss rate ?
    calorimetric energy
  • Add missing energy (muons, neutrinos, nuclear
    excitations 10) total energy

16
Phototube Calibration
  • Relative calibration at the beginning and end of
    each nightly run.
  • using YAG laser.
  • optical fibers distribute the laser signal to all
    mirrors.
  • Conversion of recorded FADC signals to photon
    flux.
  • Absolute calibration using a portable
    light-source (RXF) of known intensity that is
    carried to both sites.

17
Atmospheric Calibration
  • attenuation of light by two main processes
  • Rayleigh (molecular) scattering
  • Mie (aerosol) scattering
  • Rayleigh contribution is quite stable and well
    known.
  • Aerosol profile of the atmosphere has to be
    monitored during the run.
  • Monitoring with an array of vertical Xenon
    flashers between the two detector sites.
  • Detailed monitoring with steerable lasers on
    both sites.
  • Additional vertical laser outside of Dugway
    (Terra).

18
Atmospheric Database
  • Atmospheric data of the selected nights in
    this analysis
  • 27 km
  • 0.035

19
Unfolding the Cosmic Ray Spectrum
20
Deconvolution of the UHECR Spectrum
  • We observe the spectrum convoluted with detector
    acceptance and limited resolution.
  • Deconvolution with help of a correction factor
  • D(Ei)S Rij T(Ej) T(Ei)
    Gmc(Ei)/Rmc(Ei) D(Ei)
  • We need M.C. to simulate acceptance (
    resolution) of our detectors
    for the flux measurement
  • This requires a simulation program that describes
    the shower development and detector
    response as realistically as possible.

21
HiRes Monte Carlo Simulation
22
CORSIKA Shower Library (proton iron)
  • Fit parameters scale with primary energy
  • Gaisser-Hillas fit to the shower profile

23
Data / Monte Carlo Comparisons
  • Testing how well we simulate our experiment...
  • HiRes-2 data shown from 12/99 until 09/01.
  • 531 hours of good weather data.
  • average atmosphere used for consistency with
    HiRes-1.
  • Statistics
  • rec. geometry 6262 events
  • after all cuts 2666 events
  • M.C. 5 x data statistics

24
Rp (Distance to shower axis)
25
of p.e. / degree of track
26
Energy Distribution Resolution
27
Acceptances Exposure
  • Rmc(Ei) / Gmc(Ei)
  • Acceptances from simulations broken up into
    3 datasets.

A O t Rmc(Ei) / Gmc(Ei)
Smoothed exposure
(in 104 km2 sr s).
28
Results of the HiRes-2 Analysis
29
The HiRes-2 UHECR Spectrum
30
The HiRes monocular UHECR Spectra
31
Systematic Uncertainties
  • Systematic uncertainties in the energy scale
  • absolute calibration of phototubes /- 10
  • fluorescence yield /- 10
  • correction for misssing energy /- 5
  • aerosol concentration
  • uncertainty in energy scale /- 16
  • atmospheric uncertainty in aperture
  • total uncertainty in the flux /- 31

What are the uncertainties due atmospheric
variations and due to the MC input composition ?
32
Systematics due to MC Input Composition
  • Detector acceptance at low energies depends on
    c.r. composition.
  • MC uses HiRes/MIA measurement as input
    composition.
  • Relevant uncertainties
  • detector calibration
  • atmosphere
  • fit to HiRes/MIA data
  • /-5 uncertainty in proton fraction

33
Systematics due to Atmospheric Variations
  • Repeated HiRes-2 analysis using the atmospheric
    database.
  • Regular Analysis
  • 25 km, 0.04
  • in MC generation
  • in data MC reconstr.
  • Systematics Check
  • HAL VAOD from database (hourly entries)
  • in MC generation
  • in data MC reconstr.

34
Fits to the HiRes-2 Spectrum
J E -3.33/-0.01
J E -2.81/-0.02
35
Spectrum Fit
  • Fit to the HiRes monocular spectra assuming
  • galactic extragalactic components
  • all propagation effects (ee-, red-shift,
    GZK)
  • Details of the fit procedure
  • Float normalization, input spectral slope (g) and
    m
  • Extragalactic component
  • 45 protons at 1017 eV
  • 80 protons at 1017.85 eV
  • 100 protons at 1020 eV
  • Use binned maximum likelihood method

36
HiRes and Flys Eye
37
HiRes and Haverah Park
38
HiRes and Yakutsk
39
HiRes and AGASA
40
Conclusions
41
  • We have measured the UHECR spectrum from
    1017.2 eV to the highest energies with HiRes-2 in
    monocular mode.
  • A simulation of the exact data taking conditions
    was used to determine the acceptance and
    resolution of the detector.
  • The simulation was tested in detailed data-MC
    comparisons and proven to be realistic.
  • Systematic uncertainties due to atmospheric
    variations and MC input composition were shown to
    be small.

42
  • We observe the ankle in the HiRes-2 spectrum
    at 1018.5 eV.
  • The HiRes-2 result is in close agreement with
    HiRes-1 and Flys Eye.
  • The HiRes-2 spectrum is consistent with the
    second knee and GZK flux suppression.
  • The combined monocular HiRes spectra show
    evidence for a break above 1019.8 eV. The Poisson
    probability for continuation of the spectrum with
    unchanged slope from the HiRes monocular data is
    1 x 10-4 .

43
The HiRes Collaboration
THANK YOU !
  • N. Manago, M. Sasaki
  • University of Tokyo
  • T. Abu-Zayyad, J. Albretson, G. Archbold,
  • J. Balling, K. Belov, Z. Cao, M. Dalton,
  • A. Everett, J. Girard, R. Gray, W. Hanlon,
    P. Hüntemeyer, C.C.H. Jui, D. Kieda,
    K. Kim, E.C. Loh, K. Martens,
    J.N. Matthews, A. McAllister, J. Meyer,
    S.A. Moore, P. Morrison, J.R. Mumford,
    K. Reil,R. Riehle, P. Shen, J. Smith,
    P. Sokolsky, R.W. Springer, J. Steck,
    B.T. Stokes, S.B. Thomas,
    T.D. Vanderveen, L. Wiencke
  • University of Utah
  • J. Amann, C. Hoffman, M. Holzscheiter,
    L. Marek, C. Painter, J. Sarracino,
    G. Sinnis, N. Thompson, D. Tupa
  • Los Alamos National Laboratory
  • J.A. Bellido, R.W. Clay, B.R. Dawson,
  • K.M. Simpson
  • University of Adelaide
  • J. Boyer, S. Benzvi, B. Connolly,
    C. Finley, B. Knapp, E.J. Mannel,
    A. ONeil, M. Seman, S. Westerhoff
  • Columbia University
  • J. Belz, M. Munro, M. Schindel
  • Montana State University
  • G. Martin, J.A.J. Matthews, M. Roberts
  • University of New Mexico
  • D. Bergman, L. Perera, G. Hughes,
  • S. Stratton, D. Ivanov,
  • S. Schnetzer, G.B. Thomson, A. Zech
  • Rutgers University

44
The Truth about Ultra-High Energy Cosmic Rays
  • Weve established a clear link between UHECR
    program related activities and evildoers
    in Iraq.
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