Recent Results from the HiRes Air Fluorescence Experiment

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Recent Results from the HiRes Air Fluorescence Experiment

ÿÿ Physics of Ultra-High Energy Cosmic Rays (UHECR)Physics of Ultra-High Energy Cosmic Rays (UHECR)

ÿÿ Detection of Ultra-High Energy Cosmic RaysDetection of Ultra-High Energy Cosmic Rays

ÿÿ Description of the HiRes DetectorDescription of the HiRes Detector

ÿÿ Results from the HiRes DetectorResults from the HiRes Detector

TAUP2003

University of Washington September 7,2003

R. Wayne Springer University of Utah

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HiRes Collaboration HiRes Collaboration

J.A. Bellido, R.W. Clay, B.R. Dawson, K.M. Simpson

University of Adelaide

J. Boyer, S. Benzvi, B. Connolly, C. Finley, B. Knapp, E.J. Mannel, A. O’Neil, M. Seman, S. Westerhoff

Columbia University

J. Belz, M. Munro, M. Schindel

Montana State University

G. Martin, J.A.J. Matthews, M. Roberts

University of New Mexico

D. Bergman, L. Perera,

S. Schnetzer, G.B. Thomson, A. Zech

Rutgers University

N. Manago, M. Sasaki

University of Tokyo

T. Abu-Zayyad, J. Albretson, G. Archbold, J. Balling, K. Belov, Z. Cao, M. Dalton, A. Everett, J. Girard, R. Gray, W. Hanlon,

P. Hüntemeyer, C.C.H. Jui, D. Kieda, K. Kim, E.C. Loh, K. Martens, J.N. Matthews, A. McAllister, J. Meyer, S.A. Moore, P. Morrison, J.R. Mumford,

K. Reil,R. Riehle, P. Shen, J. Smith, P. Sokolsky, R.W. Springer, J. Steck,

B.T. Stokes, S.B. Thomas, T.D. Vanderveen, L. Wiencke

University of Utah

J. Amann, C. Hoffman, M. Holzscheiter, L. Marek, C. Painter, J. Sarracino,

G. Sinnis, N. Thompson, D. Tupa

Los Alamos National Laboratory

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UHECR Propagation through Universe UHECR Propagation through Universe

ÿ The Universe is filled with microwave photons (2.7K)

ÿPion-photoproduction exists for where

ÿ“Interaction length” of 50 Mpc for CMB density.

ÿThe observable universe is greater than 3000 Mpc

ÿIf sources of UHECR are of comological origin, THEN

But If GZK cutoff not observed

But If GZK cutoff not observed ËË NEW PHYSICS?NEW PHYSICS?

p

g m

E E

s = _GZK • ₂_.₇_K >

GZK Cutoff GZK Cutoff

(

^2.7

)

^Æ ⁺ ⁰

+g ^p p

p ^o K

eV E_GZK = 5¥10¹⁹

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Cosmic Ray Flux Cosmic Ray Flux

Limit to Supernova Limit to Supernova

Acceleration Mechanisms Acceleration Mechanisms

WhatWhat’’s this?s this?

FluxFlux

Energy Energy

LHC LHC Energy Energy

scale scale ÿÿFlux roughly followsFlux roughly follows

Power law Power law

ÿÿStructure in Spectrum.Structure in Spectrum.

ÿÿFlux varies by 32 orders ofFlux varies by 32 orders of magnitude over energy

magnitude over energy range 10

range 10⁸⁸ eV 10 eV 10²⁰²⁰eVeV

ÿÿCosmic Ray Particles withCosmic Ray Particles with energies extending beyond energies extending beyond 1010⁸⁸TeV???TeV???

ÿÿWhere does it stop?Where does it stop?

ÿAt energies above 10²⁰ eV the flux is extremely low!!!

Namely 1 particle/km1 particle/km²²-- steradian/century

steradian/century

Flux~E^-3.0

Long wait here!!!

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The Air Fluorescence Technique The Air Fluorescence Technique

Shower Shower Development Development

Atmospheric Atmospheric Monitoring Monitoring Detector Response

Detector Response and Calibration and Calibration

Need to understand Need to understand

ÿÿShower DevelopmentShower Development

ÿÿAtmospheric MonitoringAtmospheric Monitoring

ÿÿDetector Response and CalibrationDetector Response and Calibration Need to Need to KnowKnow

FluorescenceYield FluorescenceYield

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HiRes Event Reconstruction HiRes Event Reconstruction Determination of shower profile Determination of shower profile

_HiRes-I binning

_1.5 degree angular bins

_Ray tracing to determine detector acceptance

_HiRes-II binning

_Time based binning

_Measure intensity and direction of light spot every 100ns

_Ray tracing to determine detector acceptance

_Profile fit

_Signal fit to shower profile function

_Cerenkov correction calculated based on geometry.

_dE/dX determined from fit

_Primary particle total energy calculated using “standard” relationship between

EM and total energy.... Depth [g/cm²]

Signal

Integral of shower profile Integral of shower profile determines energy of UHECR determines energy of UHECR

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The HiRes Detector Volume The HiRes Detector Volume

Photograph of the “Camels’ back” site (HiRes2) looking Northeast…

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Description of the HiRes Detector Description of the HiRes Detector

ÿ Sites

ÿ Two “eyes” separated by 12.6 km

ÿ “Eyes” located ~500 feet above Desert floor.

ÿ Located in West Desert of UTAH, elevation ~4800 feet (870 g/cm²). Excellent visibility

ÿ Aperture ~10,000 km²-sr for E>10²⁰eV

ÿ Duty Cycle ~ 10%

ÿ Viewing Distance up to 30+ km

ÿ Detector Components

ÿ 5.1 m²mirrors (21 @ HiRes1 covering 3-15 deg) (42 @ HiRes2 covering 3-31 deg)

ÿ PMT field of view 1 x 1 degree (arranged in ~ 16 x 16 cluster at focal plane of each mirror for a total of 16128 PMTs)16128 PMTs

ÿ Readout Electronics

ÿHiRes1: Sample and Hold ÿHiRes2: FADC 100ns clock

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Stereoscopic Event Reconstruction Stereoscopic Event Reconstruction Determination of Shower Geometry Determination of Shower Geometry

The geometry of the air shower is determined simply by finding the intersection of the shower-

detector planes

Reduced Uncertainty in Energy Determination

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What can HiRes determine about What can HiRes determine about

Ultra High Energy Cosmic Rays (UHECR) Ultra High Energy Cosmic Rays (UHECR) ÿ ÿ Energy Spectrum (Flux vs. Energy) Energy Spectrum (Flux vs. Energy)

ÿ ÿ Composition Composition ( (

on a statistical basison a statistical basis

, ,

also including neutrino andalso including neutrino and gamma searches)

gamma searches)

ÿ ÿ Arrival Directions Arrival Directions

Charged Particle Astronomy for E>10

¹⁹

eV?

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The Measurement of the Energy Spectrum The Measurement of the Energy Spectrum

Important to understand the following…

ÿEnergy Measurement

ÿ Detector Calibration

ÿShower Geometry (STEREO HELPS!!)

ÿAtmospheric Conditions

ÿAperture

ÿDetector Calibration

ÿTrigger Thresholds

ÿReconstruction

ÿAtmospheric Conditions Note that the atmosphere has greatest effect on the aperture at enegies below 10 EeV!!!!

Need to ensure that there are no tails in Energy distribution!!!!

Fractional Resolution %

Stereo Energy Resolution 15.5 %

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Ideally we would have a Ideally we would have a 1010¹⁸¹⁸ eV proton accelerator eV proton accelerator

In geo-synchronous orbit over In geo-synchronous orbit over Utah…Utah….But.But……..

Energy Scale Calibration

We perform piece-wise We perform piece-wise

calibration of optics, PMTs and electronics calibration of optics, PMTs and electronics

also perform end-to-end calibration using laser beam also perform end-to-end calibration using laser beam……

Simulate shower development Simulate shower development using HEP inspired Monte using HEP inspired Monte Carlo Simulation code

Carlo Simulation code……

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Determination of Stereoscopic Aperture

__Use Simulation to generate eventsUse Simulation to generate events

_

_Reconstruct these MC events usingReconstruct these MC events using standard reconstruction software to standard reconstruction software to determine aperture

determine aperture

_Calculated for “average atmospheric conditions” of VSH=1.0km and

HAL=25.0km

_76% Proton 24% Iron mixture

Aperture exceeds

10,000 km2-sr above 100 EeV

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HiRes Stereo Flux Measurement HiRes Stereo Flux Measurement

Energy Distributions Energy Distributions

_The energy distribution of stereo_The energy distribution of stereo events after all cuts. The line is the events after all cuts. The line is the predicted number of events using a predicted number of events using a Fly’Fly’s Eye spectrum with no GZKs Eye spectrum with no GZK cutoff

cutoff

_Only considering energies above_Only considering energies above 3 x 10

3 x 10¹⁸¹⁸ eV at this time because of eV at this time because of sensitivity of aperture to details of sensitivity of aperture to details of atmosphere, calibration, trigger atmosphere, calibration, trigger settings.

settings.

_Will push on to lower energies_Will push on to lower energies with better understanding of with better understanding of detector....

detector....

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Determination of Flux for Stereo Events Determination of Flux for Stereo Events

t A

E E

N E

Exposure

E ents Numberofev

E J

Flux W D

D

= D

=

= ( )

) (

) ) (

(

Stereo Energy Distribution Stereo Aperture

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Stereo UHECR Energy Spectrum

Flux * 10Flux * 10

2929 m m

-2-2 ss

-1-1 steradiansteradian

Log E Log E

Spectral index = -2.95+/-0.09 Spectral index = -2.95+/-0.09 Agrees with HiRes mono spectrum Agrees with HiRes mono spectrum

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Stereo UHECR Flux

Red = HR1 Mono Red = HR1 Mono Blue = HR2 Mono Blue = HR2 Mono

Black = Stereo Black = Stereo Good Agreement!!

Good Agreement!!

33 EE * Flux * Flux

Log E Log E

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Systematic Uncertainties Systematic Uncertainties

Energy Scale and Atmosphere Energy Scale and Atmosphere

ÿ

Detector calibration: 10%

ÿ

Fluorescence yield: 10%

ÿ

Unobserved energy: 5%

ÿ

Atmospheric absorption: most sensitive to vertical aerosol optical depth (VAOD)

_ Mean VAOD = 0.04 ; VAOD RMS = 0.02

_ Modify MC and analysis programs to use VAOD = 0.02 and 0.06, reanalyze.

_ J(E) changes by 15% ; Energy changes by ~ 15%

_ Total systematic uncertainty on energy Scale = 21%

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Systematic Uncertainties Systematic Uncertainties

ÿ Need to propagate uncertainty into spectrum measurement.

ÿ If only Energy is modified. Easy to deal with by just multiplication …

ÿ But Aperture is also modified. Need to utilize

hundreds of years of VAX 11/780 CPU equivalent to generate Simulated events…

ÿ Beware when manipulating others data....

Ú

=

Xearth

em EC X N x dx

E

0 0

) (

] )

/[(

)

(x DetSig Y T R QE T G

N = ¥ _filter ¥ _mirror ¥ ¥ _atmos ¥

126 . 0 0

0963 . 0 9437 . 0

-

˜¯ Á ˆ

Ë - Ê

= EeV

em

em E E

E E

t A

E E

E N

J W D

D

= D ( ) )

(

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HiRes Monocular Spectrum HiRes Monocular Spectrum

_ More data from HiRes-I ==> greater exposure

(started operation in 1997)

_ HiRes-II monocular reconstruction has lower energy threshold than stereo

(stereo needs shower to be close enough to BOTH sites)

_ Monocular Analysis of HiRes data is still

useful!!!!

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HiRes Monocular Spectra HiRes Monocular Spectra

• Fit: E^-2.8 from 18.7 to 19.8; Predicts 29.8 events, logE>19.8; See 11. Probability = 7.3 x 10^-5

GZK cutoff???

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UHECR Spectra

Monocular HiRes and AGASA

Agasa sees 10 events above 10 Agasa sees 10 events above 10^{20 eV}^{20 eV}

No GZK cutoff No GZK cutoff

HiRes Monocular sees 2 events HiRes Monocular sees 2 events

CONTROVERSY!

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HiRes Stereo Composition Measurement

Elongation Rate

HiRes Stereo:

Range 1 x 10¹⁸ to 3 x 10¹⁹ eV ER = 54.5 +/- 6.5 (stat) +/- 4.5 (syst) gm/cm2 per decade energy

HiRes Prototype/MIA:

Range 1x10¹⁷ to 1x10¹⁸ eV

ER = 93.0 +/- 8.5 (stat) +/- 10.5 (syst) gm/cm2 per decade energy

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Composition Conclusions

ÿ Systematic uncertainties are significantly smaller than the proton/Fe separation

ÿ HiRes Stereo measurement consistent with unchanging, light composition above 10¹⁸ eV ÿ Stereo HiRes and HiRes Prototype-MIA

measurements are consistent in overlap region

ÿ HiRes Prototype-MIA Hybrid result consistent with changing composition (Heavy to Light) between 10¹⁷ and 10¹⁸ eV

ÿ No significant information near GZK region yet

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HiRes-I Monocular Data, E > 10

^19.5

eV

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AGASA

Exposure HiRes

Exposure

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Global Dipole Searches

• Galactic Center — possible effects observed by AGASA and Fly’s Eye

• CEN-A — suggested as a potential source of a dipole effect (Farrar and Piran)

• M87 — possible weak effects (Biermann)

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Dipole source models:

• Arrival directions of cosmic rays possess a

number density n=1+acosq (q is the angle w.r.t.

dipole source).

galactic dipole model, a=1 galactic dipole model, a=-1

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Dipole Functions for an Isotropic Source Model and HiRes-I Data

Isotropic source model HiRes Data

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HiRes-I Anisotropy Search Conclusions

HiRes-I Anisotropy searches have yielded null results:

• Flux upper limit of 0.33 events/km²*Yr (90% c.l.) on pointlike sources with E > 10^18.5 eV in northern hemisphere

• Flux upper limit of 1.2 x 10^-18 events/cm²*sec (90% c.l.) on pointlike sources with E > 10¹⁸ eV centered at Cygnus X-3

• Dipole analyses consistent with isotropy for sources at galactic center, Centaurus A, M-87

• No clustering observed in highest energy events. Upper limit of 4 doublets (90% c.l.) in HiRes-I monocular dataset.

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HiRes Stereo Data Set (>10

¹⁹

eV)

• 228 well-

reconstructed events above 10¹⁹ eV

• RMS energy resolution for these events better than 20%

• Angular resolution

better than 0.7º

Equatorial Coordinates

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Stereo Autocorrelation

Two-Point

Correlation Function:

• Count number of

events separated by _

• Perform same count on Monte Carlo data sets with same event number and similar exposure.

• Clustering would show up as excess over fluctuations at small angular scales

w(_) = N(_) / N_MC(_) - 1 Two-point correlation for HiRes Stereo Events > 10¹⁹ eV

RMS fluctuations

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Stereo Autocorrelation Scan

HiRes Results:

• Strongest clustering signal:

1. N = 97 , _ = 1.2°

( E = 1.76_10¹⁹ eV )

1. n_pairs = 4

2. P_min= 1.1%

• However, there is a statistical penalty for scanning

• True significance is chance probability for scan of Monte Carlo data to have lower

minimum:

• P_chance = 39%

• No significant clustering signal

observed Scan of HiRes Stereo Events > 10¹⁹ eV

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Conclusions

ÿ The two HiRes detectors continue to collect data.

ÿ Measured flux agrees with Fly’s Eye experiment.

ÿ We see spectral features.

ÿ Our monocular spectra supports the existence of the GZK cutoff

ÿ HiRes Stereo measurement consistent with unchanging, light composition above 10¹⁸ eV ÿ HiRes-I Anisotropy searches have yielded null

results

ÿ No significant clustering signal observed in stereo Autocorrelation scan

ÿ Need more statistics and study of systematics