the high resolution fly’s eye

JNM Dec. 2001 Annecy, France

The High Resolution Fly’s Eye

John MatthewsUniversity of Utah

Department of Physics and

High Energy Astrophysics Institute


Outline

• Questions• Detector• Calibration• Atmosphere• Capabilities


UHECR Questions

• Energy Spectrum• Sources, Anisotropy• Composition• Search for neutrinos


The Cosmic Ray Spectrum

Direct Observation below about 1014 eV

Indirect Observation at higher energies

HiRes is optimized for stereo observations above 3x1018 eV


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….


The Atmosphere as Detector

• The cosmic ray initiates an extensive air shower when it hits the atmosphere

• Measure the resulting fluorescence light


The High Resolution Fly’s Eye (HiRes)

• Spherical Mirrors: Area = 5.1 m2

• 256 PMT pixels/mirror: 1 degree resolution


Stereo Observation

• Viewing the shower from two sites allows for precise measurement of geometry as well as a measurement of the energy resolution


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


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


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


Detector Calibration


Atmospheric Transmission

• Need to know the atmospheric quality– Clouds

– Haze

– General transmission (horizontal extinction length and vertical scale height)


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


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


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


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


Measurement of the UHECR Spectrum and its Structure

John MatthewsUniversity of Utah

Department of Physics and

High Energy Astrophysics Institute


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


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


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)


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


HiRes-I Event Display


HiRes-I Event Profile Fit


HiRes-I: Raw Energy Distribution


Impact Parameter Resolution


MC Impact Parameter Resolution


Stereo Impact Parameter Resolution


MC Plane Angle Resolution


Stereo Plane Angle Resolution


MC Energy Resolution


Stereo Energy Resolution


Energy Resolution Comparision


Energy Correction


Energy Distribution


HiRes-I Energy Spectrum


HiRes-I Spectrum Atm Effects


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.


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


HiRes-II Event


HiRes-II Data/MC Comparisons


HiRes-II Flux


HiRes-II Energy Spectrum


HiRes-I Spectrum


Fly’s Eye Stereo Spectrum


HiRes-I/HiRes-II Joint Spectra


Energy Spectra


Stereo Event


Preliminary Stereo Results


Preliminary Stereo Spectrum


Preliminary Anisotropy Results


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.

the high resolution fly’s eye

Documents

hires sitesbetter

flys eyeenergy resolution

gmcm2angular resolution

xmax resolution

hrs data

cosmic ray air shower

kma hires eventexample

deg azimuth3