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.