title: First observation of the Greisen-Zatsepin-Kuzmin suppression.
abstract: The High Resolution Fly's Eye (HiRes) experiment has observed the Greisen-Zatsepin-Kuzmin suppression (called the GZK cutoff) with a statistical significance of five standard deviations. HiRes' measurement of the flux of ultrahigh energy cosmic rays shows a sharp suppression at an energy of 6 x 10(19) eV, consistent with the expected cutoff energy. We observe the ankle of the cosmic-ray energy spectrum as well, at an energy of 4 x 10(18) eV. We describe the experiment, data collection, and analysis and estimate the systematic uncertainties. The results are presented and the calculation of the statistical significance of our observation is described.
authors: Department of Physics, University of Utah, Salt Lake City, Utah 84112, USA.
authors: R U
authors: RU
authors: Abbasi
authors: T
authors: T
authors: Abu-Zayyad
authors: M
authors: M
authors: Allen
authors: J F
authors: JF
authors: Amman
authors: G
authors: G
authors: Archbold
authors: K
authors: K
authors: Belov
authors: J W
authors: JW
authors: Belz
authors: S Y
authors: SY
authors: Ben Zvi
authors: D R
authors: DR
authors: Bergman
authors: S A
authors: SA
authors: Blake
authors: O A
authors: OA
authors: Brusova
authors: G W
authors: GW
authors: Burt
authors: C
authors: C
authors: Cannon
authors: Z
authors: Z
authors: Cao
authors: B C
authors: BC
authors: Connolly
authors: W
authors: W
authors: Deng
authors: Y
authors: Y
authors: Fedorova
authors: C B
authors: CB
authors: Finley
authors: R C
authors: RC
authors: Gray
authors: W F
authors: WF
authors: Hanlon
authors: C M
authors: CM
authors: Hoffman
authors: M H
authors: MH
authors: Holzscheiter
authors: G
authors: G
authors: Hughes
authors: P
authors: P
authors: Hüntemeyer
authors: B F
authors: BF
authors: Jones
authors: C C H
authors: CC
authors: Jui
authors: K
authors: K
authors: Kim
authors: M A
authors: MA
authors: Kirn
authors: E C
authors: EC
authors: Loh
authors: M M
authors: MM
authors: Maestas
authors: N
authors: N
authors: Manago
authors: L J
authors: LJ
authors: Marek
authors: K
authors: K
authors: Martens
authors: J A J
authors: JA
authors: Matthews
authors: J N
authors: JN
authors: Matthews
authors: S A
authors: SA
authors: Moore
authors: A
authors: A
authors: O'Neill
authors: C A
authors: CA
authors: Painter
authors: L
authors: L
authors: Perera
authors: K
authors: K
authors: Reil
authors: R
authors: R
authors: Riehle
authors: M
authors: M
authors: Roberts
authors: D
authors: D
authors: Rodriguez
authors: N
authors: N
authors: Sasaki
authors: S R
authors: SR
authors: Schnetzer
authors: L M
authors: LM
authors: Scott
authors: G
authors: G
authors: Sinnis
authors: J D
authors: JD
authors: Smith
authors: P
authors: P
authors: Sokolsky
authors: C
authors: C
authors: Song
authors: R W
authors: RW
authors: Springer
authors: B T
authors: BT
authors: Stokes
authors: S B
authors: SB
authors: Thomas
authors: J R
authors: JR
authors: Thomas
authors: G B
authors: GB
authors: Thomson
authors: D
authors: D
authors: Tupa
authors: S
authors: S
authors: Westerhoff
authors: L R
authors: LR
authors: Wiencke
authors: X
authors: X
authors: Zhang
authors: A
authors: A
authors: Zech