JNM Dec Annecy, France The High Resolution Fly’s Eye John Matthews University of Utah Department of Physics and High Energy Astrophysics Institute

JNM Dec Annecy, France Outline Questions Detector Calibration Atmosphere Capabilities

JNM Dec Annecy, France UHECR Questions Energy Spectrum Sources, Anisotropy Composition Search for neutrinos

JNM Dec Annecy, France The Cosmic Ray Spectrum  Direct Observation below about eV  Indirect Observation at higher energies  HiRes is optimized for stereo observations above 3x10 18 eV

JNM Dec Annecy, France Anisotropy and Composition Relatively isotropy –Slight anisotropy observed by Fly’s Eye and possible sources observed by AGASA Composition –In the – eV energy range, direct measurements are available. The composition is: ~50% protons ~25% alpha particles ~13% C/N/O nuclei <1% electrons –At higher energies, Fly’s Eye observed a composition which was heavy (iron-like) transitioning to lighter (proton-like) around 5x10 18 eV Neutrino Search –Search for deeply penetrating or upward going events….

JNM Dec Annecy, France The Atmosphere as Detector The cosmic ray initiates an extensive air shower when it hits the atmosphere Measure the resulting fluorescence light

JNM Dec Annecy, France The High Resolution Fly’s Eye (HiRes) Spherical Mirrors: Area = 5.1 m PMT pixels/mirror: 1 degree resolution

JNM Dec Annecy, France Stereo Observation Viewing the shower from two sites allows for precise measurement of geometry as well as a measurement of the energy resolution

JNM Dec Annecy, France Utah’s West Desert HiRes is located in Utah’s West Desert at the Dugway Proving Ground The two sites are separated by 12.6 km

JNM Dec Annecy, France HiRes-I: Little Granite Mountain 22 mirrors viewing –~360 deg azimuth –3-17 deg elevation S&H electronics (5.6  s integration time) Began data collection in 1997, completed hrs data, 2314 hrs good weather

JNM Dec Annecy, France HiRes-II: Camel’s Back Ridge 42 mirrors viewing ~360 deg azimuth and 3-31 deg in elevation FADC electronics with 100ns integration time Completed in Aug. 1999

JNM Dec Annecy, France Detector Calibration

JNM Dec Annecy, France Atmospheric Transmission Need to know the atmospheric quality –Clouds –Haze –General transmission (horizontal extinction length and vertical scale height)

JNM Dec Annecy, France Atmospheric Instrumentation Two Steerable YAG Lasers –Located at each of the HiRes sites –Computer/GPS controlled –Operated nightly One Steerable Mobile YAG Laser –Computer/GPS controlled –Operated as needed 10 Vertical Xenon Flashers –Arrayed between the two HiRes sites

JNM Dec Annecy, France Better than Standard Desert The “Standard Desert” Model uses an aerosol horizonal extinction length of 12 km and vertical scale height of 1.2 km. Optical Depth: OD=VS/HE = 1.2/12 = 0.10 Dugway Atmosphere is, on average, cleaner with an aerosol horizontal extinction length of 25 km and 1.0 km vertical scale height. Optical Depth: OD=VS/HE = 1.0/25 = 0.04 In addition, the molecular part of the atmosphere has a horizontal extinction length of 18 km

JNM Dec Annecy, France A HiRes Event Example of a cosmic ray air shower as observed by HiRes-I: Up = North Right = East Center of Circle = Zenith (UP) Outer Circle = Horizon

JNM Dec Annecy, France Capabilities of the HiRes Experment Stereo instantaneous aperture grows to 10,000 km 2 -str at eV. Factor of ten over Fly’s Eye Energy resolution 10% X max resolution 30 gm/cm 2 Angular resolution better than 0.4 degreees Measure Spectrum, Composition, and Anisotropy. Search for Neutrino flux Expect to collect at least 5 years of data

JNM Dec Annecy, France Measurement of the UHECR Spectrum and its Structure John Matthews University of Utah Department of Physics and High Energy Astrophysics Institute

JNM Dec Annecy, France The HiRes-I Data Set Collected June May hours of monocular data 2314 hours of good weather data selected for this analysis Containing 119M triggers (mostly noise and atmospheric monitoring ie laser shots) 4.54M downward “track-like” events selected for further processing

JNM Dec Annecy, France HiRes-I Data Cuts Events were also required to: >25 p.e./PMT (on average) – for reliable shower profile reconstruction – avoid Poisson fluctuation problems angular speed < 3.33 deg/ms (5 km for vertical tracks) 10,683 events selected for reconstruction

JNM Dec Annecy, France HiRes-I Monocular Fitting Profile Constrained Fit (assumed a Gaisser-Hillas parameterization) Assumed –x 0 = 40 gm/cm 2 (shower initiation) – = 70 gm/cm 2 (elongation rate) Allowed x max to vary 680 < x max < 900 gm/cm 2, 35 gm/cm 2 steps (expected range for p - Fe primaries) Stepped through  in 1 deg steps (angle of shower in the plane)

JNM Dec Annecy, France HiRes-I: More Data Cuts Assuming the profile fit converged, additional cuts were made. Events were required to have: > 8 deg of track length First observation < 1000 gm/cm 2 (highest elevation) In  plane shower angle,  < 120 degrees (avoid events with significant Cerenkov light) No more than 1 bin with >25% Cerenkov light 5,264 events remain

JNM Dec Annecy, France HiRes-I Event Display

JNM Dec Annecy, France HiRes-I Event Profile Fit

JNM Dec Annecy, France HiRes-I: Raw Energy Distribution

JNM Dec Annecy, France Impact Parameter Resolution

JNM Dec Annecy, France MC Impact Parameter Resolution

JNM Dec Annecy, France Stereo Impact Parameter Resolution

JNM Dec Annecy, France MC Plane Angle Resolution

JNM Dec Annecy, France MC Plane Angle Resolution

JNM Dec Annecy, France Stereo Plane Angle Resolution

JNM Dec Annecy, France MC Energy Resolution

JNM Dec Annecy, France MC Energy Resolution

JNM Dec Annecy, France Stereo Energy Resolution

JNM Dec Annecy, France Energy Resolution Comparision

JNM Dec Annecy, France Energy Correction

JNM Dec Annecy, France Energy Distribution

JNM Dec Annecy, France HiRes-I Energy Spectrum

JNM Dec Annecy, France HiRes-I Spectrum Atm Effects

JNM Dec Annecy, France HiRes-II Data Good weather data Dec – May 2000 Due to longer tracks (two rings of mirrors) and greater timing information (FADC), HiRes-II events can be reconstructed using timing information alone.

JNM Dec Annecy, France HiRes-II Data Cuts Required: Downward, track-like events Angular speed < 11 deg./  s Track-length > 10 deg. (ring 2 events) Track-length > 7 deg. (ring 1 events) Zenith angle < 60 degrees Shower maximum observed < 60% of signal Cerenkov light subtraction  781 Events remain

JNM Dec Annecy, France HiRes-II Event

JNM Dec Annecy, France HiRes-II Data/MC Comparisons

JNM Dec Annecy, France HiRes-II Data/MC Comparisons

JNM Dec Annecy, France HiRes-II Data/MC Comparisons

JNM Dec Annecy, France HiRes-II Data/MC Comparisons

JNM Dec Annecy, France HiRes-II Flux

JNM Dec Annecy, France HiRes-II Energy Spectrum

JNM Dec Annecy, France HiRes-I Spectrum

JNM Dec Annecy, France Fly’s Eye Stereo Spectrum

JNM Dec Annecy, France HiRes-I/HiRes-II Joint Spectra

JNM Dec Annecy, France Energy Spectra

JNM Dec Annecy, France Stereo Event

JNM Dec Annecy, France Preliminary Stereo Results

JNM Dec Annecy, France Preliminary Stereo Spectrum

JNM Dec Annecy, France Preliminary Anisotropy Results

JNM Dec Annecy, France Preliminary Anisotropy Results

JNM Dec Annecy, France Preliminary Anisotropy Results

JNM Dec Annecy, France Preliminary Anisotropy Results

JNM Dec Annecy, France Summary Mono HiRes-I and HiRes-II spectra have the same slope and amplitude as the stereo Fly’s Eye data… They show the same structure with a kink at ~3E18 eV. This structure is a good cross-calib point. There is a disagreement with AGASA as to the location of this kink. The first stereo and anisotropy results are coming soon (preliminary results shown here) Five years of STEREO data to come – proposal submitted to US NSF.