The High Resolution Fly’s Eye
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Transcript of The High Resolution Fly’s Eye
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JNM Dec. 2001 Annecy, France
The High Resolution Fly’s Eye
John MatthewsUniversity of Utah
Department of Physics and
High Energy Astrophysics Institute
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Outline
• Questions• Detector• Calibration• Atmosphere• Capabilities
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UHECR Questions
• Energy Spectrum• Sources, Anisotropy• Composition• Search for neutrinos
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The Cosmic Ray Spectrum
Direct Observation below about 1014 eV
Indirect Observation at higher energies
HiRes is optimized for stereo observations above 3x1018 eV
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Anisotropy and Composition
• Relatively isotropy– Slight anisotropy observed by Fly’s Eye and possible sources observed by
AGASA
• Composition– In the 1012 – 1015 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 5x1018 eV
• Neutrino Search– Search for deeply penetrating or upward going events….
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The Atmosphere as Detector
• The cosmic ray initiates an extensive air shower when it hits the atmosphere
• Measure the resulting fluorescence light
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The High Resolution Fly’s Eye (HiRes)
• Spherical Mirrors: Area = 5.1 m2
• 256 PMT pixels/mirror: 1 degree resolution
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Stereo Observation
• Viewing the shower from two sites allows for precise measurement of geometry as well as a measurement of the energy resolution
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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
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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 1998
• 2947 hrs data, 2314 hrs good weather
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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
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Detector Calibration
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Atmospheric Transmission
• Need to know the atmospheric quality– Clouds
– Haze
– General transmission (horizontal extinction length and vertical scale height)
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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
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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
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A HiRes EventExample of a cosmic ray air shower as observed by HiRes-I:
Up = North
Right = East
Center of Circle = Zenith (UP)
Outer Circle = Horizon
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Capabilities of the HiRes Experment
• Stereo instantaneous aperture grows to 10,000 km2-str at 1020 eV. Factor of ten over Fly’s Eye
• Energy resolution 10%
• Xmax resolution 30 gm/cm2
• 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
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Measurement of the UHECR Spectrum and its Structure
John MatthewsUniversity of Utah
Department of Physics and
High Energy Astrophysics Institute
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The HiRes-I Data Set
• Collected June 1997- May 2001• 2947 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
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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
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HiRes-I Monocular Fitting
• Profile Constrained Fit (assumed a Gaisser-Hillas parameterization)
• Assumed– x0 = 40 gm/cm2 (shower initiation)
= 70 gm/cm2 (elongation rate)
• Allowed xmax to vary 680 < xmax < 900 gm/cm2, 35 gm/cm2 steps (expected range for p - Fe primaries)
• Stepped through in 1 deg steps (angle of shower in the plane)
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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/cm2 (highest
elevation)• Inplane shower angle, < 120 degrees (avoid
events with significant Cerenkov light)• No more than 1 bin with >25% Cerenkov light• 5,264 events remain
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HiRes-I Event Display
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HiRes-I Event Profile Fit
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HiRes-I: Raw Energy Distribution
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Impact Parameter Resolution
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MC Impact Parameter Resolution
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Stereo Impact Parameter Resolution
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MC Plane Angle Resolution
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MC Plane Angle Resolution
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Stereo Plane Angle Resolution
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MC Energy Resolution
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MC Energy Resolution
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Stereo Energy Resolution
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Energy Resolution Comparision
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Energy Correction
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Energy Distribution
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HiRes-I Energy Spectrum
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HiRes-I Spectrum Atm Effects
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HiRes-II Data
• Good weather data Dec. 1999 – 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.
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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
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HiRes-II Event
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HiRes-II Data/MC Comparisons
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HiRes-II Data/MC Comparisons
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HiRes-II Data/MC Comparisons
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HiRes-II Data/MC Comparisons
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HiRes-II Flux
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HiRes-II Energy Spectrum
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HiRes-I Spectrum
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Fly’s Eye Stereo Spectrum
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HiRes-I/HiRes-II Joint Spectra
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Energy Spectra
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Stereo Event
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Preliminary Stereo Results
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Preliminary Stereo Spectrum
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Preliminary Anisotropy Results
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Preliminary Anisotropy Results
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Preliminary Anisotropy Results
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Preliminary Anisotropy Results
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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.