CCHJ Apr-30- 2000 Results from the High Resolution Fly’s Eye Charles Jui HiRes Collaboration University of Utah APS Meeting, Long Beach April 30, 2000
Dec 28, 2015
CCHJ Apr-30-2000
Results from the High Resolution Fly’s Eye
Charles Jui
HiRes CollaborationUniversity of Utah
APS Meeting, Long Beach
April 30, 2000
CCHJ Apr-30-2000
Introduction to Cosmic Rays
• Cosmic Rays were discovered in 1912 by Victor Hess, carrying electroscopes aboard a balloon to 17,500 feet (without oxygen!)
• Hess found increased radiation levels at higher altitudes: named them Cosmic Radiation
CCHJ Apr-30-2000
Cosmic Rays
Cosmic Rays are:• Atomic particles (electrons,
nuclei), radiation (gamma rays), and exotic short lived particles of extra-terrestrial origin.
• At 1012-1015 eV range:~50% protons
~25% alpha particles
~13% C/N/O nuclei
<1% electrons
<0.1% gammas
CCHJ Apr-30-2000
Cosmic Ray Spectrum
• Cosmic Rays with energies in excess of 1020 eV have been reported:
• Over the full range 109-1020 eV, the spectrum follows roughly a single power law of spectral index ~3
• changes of slope appear at:~1015 eV (Knee)
~5x1018 eV (Ankle)
CCHJ Apr-30-2000
Cosmic Ray Spectrum
CCHJ Apr-30-2000
Ultra-High Energy (UHE) Cosmic Rays
• Cosmic Rays @ E > 1018 eV are referred to as “Ultra-High Energy (UHE) Cosmic Rays”.
CCHJ Apr-30-2000
Mystery of UHE Cosmic Rays
• What are they?
Apparent shift from heavy to light composition at the “ankle”*.
• Where do they come from? Apparently nowhere in particular: no point sources or significant anisotropy have been observed**.
• How are they made / accelerated?
Some plausible theories: but it takes some fine tuning to achieve ~10-100 EeV energies.
BUT: any serious model must explain power law and index ~3.
CCHJ Apr-30-2000
Acceleration Mechanism
• Fermi (1949): Stochastic collisions between particles and magnetic clouds in the interstellar medium:– Particles lose energy in “rear-end”
collisions, gain energy in “head-on” collisions (more probable).
– Leads naturally to power-law spectrum. But spectral index depends on local details…does not lead naturally to a universal index.
CCHJ Apr-30-2000
Acceleration Mechanisms
CCHJ Apr-30-2000
Acceleration Mechanisms
• Diffusive Shock Acceleration (1st Order Fermi Acceleration):– Particles repeatedly crossing a
shock front: collisions are always “head-on”
– More efficient acceleration– leads to “universal” spectral index
of 2.0
CCHJ Apr-30-2000
(a) Shock front traveling at speed U
(b) seen in rest frame of shock front
CCHJ Apr-30-2000
(c) rest frame of downstream medium
(d) rest frame of upstream medium
CCHJ Apr-30-2000
Possible Sources
• Diffusive shock acceleration (Fermi) in extended objects:– Lobes of radio galaxies
(Biermann)– Galaxy cluster accretion shocks
(Kang, et. al)– Collisions of galaxies (Cesarsky)– Motion of galaxies in ISM
• Acceleration in strong fields associated with accretion disks and compact rotating galaxies (Colgate)
CCHJ Apr-30-2000
Possible Sources
• Cosmic rays with energies up to ~1015-16 eV might be generated in supernovae. (observation of non-thermal X-rays from SN1006 by ASCA)
CCHJ Apr-30-2000
Possible Sources
• Production of UHE cosmic rays require larger, more energetic objects: e.g. colliding galaxies
CCHJ Apr-30-2000
Possible Sources
AGN(Active Galactic Nuclei): A class of galaxies (~10%) which eject massive amounts
of energy from their centers. Many astronomers believe super-massive black holes may lie at the center of these galaxies and power their explosive energy output.
CCHJ Apr-30-2000
Exotic Mechanisms
• “Top-Down” Models: Decay or annihilation of some super-heavy particles or cosmological relics:– e.g. topological defects, relic
magnetic monopoles.
• Acceleration in Catastrophic events:– GRB’s
• New Physics?
CCHJ Apr-30-2000
Detection of Cosmic Rays
• For E < 1014 eV, flux is large enough to allow DIRECT measurement:– magnetic spectrometers, calorimeters
on balloons, satellites, shuttle missions.
• At E > 1015 eV, flux < 10-5/m2 Sr s:– 1 m2, 2 Sr. detector: < 2000 events/yr.:
direct measurement is difficult!!!
• At E > 1017 eV, flux < 10-10/m2 Sr s:– 1 m2, 2 Sr. detector: < 1 event/50 yrs.:
direct measurement is impractical!!!
• One Possible Solution: measure extensive air showers (EAS)– Use the Earth’s atmosphere as part of
your detector system!!!
CCHJ Apr-30-2000
Pierre Auger:
Discovered Extensive Air Showers
CCHJ Apr-30-2000
The Fluorescence Technique
• The particle shower leaves a faint glow in its trail: like a 100 W, ultra-violet light- bulb moving at the speed of light.
• This flash lasts only a few microseconds.
• This faint glow can be seen by fast, sensitive electronic cameras on clear, moonless nights.
CCHJ Apr-30-2000
The Fluorescence Technique
The fluorescence technique was first investigated as a means for estimating yields of atmospheric nuclear tests.
CCHJ Apr-30-2000
Cornell, 1967
CCHJ Apr-30-2000
The Fly’s Eye in Utah
The original Fly’s Eye experiment (1981-1993):– Site 1 (FE1): 67 mirrors– Site 2 (FE2): 34 mirrors– 12-14 pixels (PMT) per mirror– Each pixel covers 5 deg x 5 deg portion of the sky
CCHJ Apr-30-2000
Evading the GZK Cut-off
Representative Physical Models:• Astrophysical sources < 50 Mpc.
– AGN + radio-jets (Bierman + Streittmatter, 1987)
– No obvious viable sources within error box (Elbert and Sommers, 1995)
• Annihilation of UHE neutrino on relic massive neutrinosclustered in Super-galactic halo (Weiler, 1997)– predicts high gamma rates!!!
• Cold Dark Matter with super-massive X particles (Berezinsky, Kachelriess, Vilenkiu, 1998) in galatic halo:– MX ~ 1013 - 1016 eV, X--> hadrons
– also predicts high gamma rates!!!
CCHJ Apr-30-2000
Kinematic Evasion ModelsKinematic Evasion Models
• Supersymmetric S0 (uds-gluino) particles (Chung, Ferrar, Kolb, 1998):
– M ~ 2 GeV: raises the kinematic threshold for photo-pion production.
• Anomalously large intergalatic magnetic fields: ~ G (Ferrar 1999?)
– the photonic emissions died long ago!!!
• Fe nuclei do no photospallate as much as previously expected (Stecker & Salamon, 1998)
• Violation of Special Relativity at UHE (Coleman & Glashow, 1998)
– Reduction in CM energy for proton-CMBR photon collisions: raises cut-off.
– Anomalously long neutron lifetimes.