CCHJ Apr Results from the High Resolution Fly’s Eye Charles Jui HiRes Collaboration University of Utah APS Meeting, Long Beach April 30, 2000

CCHJ Apr 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 Cosmic Rays Cosmic Rays are: Atomic particles (electrons, nuclei), radiation (gamma rays), and exotic short lived particles of extra-terrestrial origin. At eV range: ~50% protons ~25% alpha particles ~13% C/N/O nuclei <1% electrons <0.1% gammas

CCHJ Apr Cosmic Ray Spectrum Cosmic Rays with energies in excess of eV have been reported: Over the full range eV, the spectrum follows roughly a single power law of spectral index ~3 changes of slope appear at: ~10 15 eV (Knee) ~5x10 18 eV (Ankle)

CCHJ Apr Cosmic Ray Spectrum

CCHJ Apr Ultra-High Energy (UHE) Cosmic Rays Cosmic E > eV are referred to as “Ultra-High Energy (UHE) Cosmic Rays”.

CCHJ Apr 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 ~ EeV energies. BUT: any serious model must explain power law and index ~3.

CCHJ Apr 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 Acceleration Mechanisms

CCHJ Apr 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 (a) Shock front traveling at speed U (b) seen in rest frame of shock front

CCHJ Apr (c) rest frame of downstream medium (d) rest frame of upstream medium

CCHJ Apr 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 Possible Sources Cosmic rays with energies up to ~ eV might be generated in supernovae. (observation of non-thermal X-rays from SN1006 by ASCA)

CCHJ Apr Possible Sources Production of UHE cosmic rays require larger, more energetic objects: e.g. colliding galaxies

CCHJ Apr 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 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 Detection of Cosmic Rays For E < eV, flux is large enough to allow DIRECT measurement: –magnetic spectrometers, calorimeters on balloons, satellites, shuttle missions. At E > eV, flux < /m 2 Sr s: –1 m 2, 2  Sr. detector: < 2000 events/yr.: direct measurement is difficult!!! At E > eV, flux < /m 2 Sr s: –1 m 2, 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 Pierre Auger: Discovered Extensive Air Showers

CCHJ Apr 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 The Fluorescence Technique The fluorescence technique was first investigated as a means for estimating yields of atmospheric nuclear tests.

CCHJ Apr Cornell, 1967

CCHJ Apr The Fly’s Eye in Utah The original Fly’s Eye experiment ( ): –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 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: –M X ~ eV, X--> hadrons –also predicts high gamma rates!!!

CCHJ Apr Kinematic Evasion Models Supersymmetric S 0 (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.