Summary of Recent Results from HiRes

Tareq AbuZayyadUniversity of Utah

High Resolution Fly’s Eye Collaboration:

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

Columbia University

J.F.Amman, M.D.Cooper, C.M.Hoffman, M.H. Holzscheiter, C.A.Painter, J.S.Sarracino, G.Sinnis, T.N.Thompson, D.Tupa

Los Alamos National Laboratory

J. Belz, M. Kirn

University of Montana

J.A.J. Matthews, M. Roberts

University of New Mexico

D.R. Bergman, G. Hughes, D. Ivanov, S.R. Schnetzer, L.. Scott, S. Stratton, G.B. Thomson, A. Zech

Rutgers University

N. Manago, M. Sasaki

University of Tokyo

R.U.Abbasi, T.Abu-Zayyad, G.Archbold, K.Belov, O.Brusova, S.A..Blake, C. Cannon, Z.Cao, W.Deng, R.C.Gray, W.Hanlon, Y.Fedorova, P.Huentemeyer, B.F Jones, C.C.H.Jui, E.C.Loh, M.M.Maestas, K.Martens, J.N.Matthews, S.A.Moore, K.Reil, R.Rehile, D.Rodriguez,,P.Shen, J.Smith, P.Sokolsky, R.W.Springer, B.T.Stokes, J.R.Thomas,

S.B.Thomas, L.Wiencke

University of Utah

HiRes HiRes is located on the U.S. Army’s Dugway Proving Ground, ~2 hours SW of The University of Utah

The two fluorescence detector sites are located 12.6 km apart at Little Granite Mountain and Camel’s Back Ridge

The Two HiRes Detectors

HiRes1: atop Five Mile Hill 21 mirrors, 1 ring

(3<altitude<17 degrees). Sample-and-hold electronics

(pulse height and trigger time).

HiRes2: Atop Camel’s Back Ridge

12.6 km SW of HiRes1. 42 mirrors, 2 rings

(3<altitude<31 degrees). FADC electronics (100 ns

period).

Typical HiRes Event

~21019 eV event seen in 1999 (3× vertical scale)

Measured Shower Profile

Event by event: Xmax in g/cm2; Total energy of the primary

particle: Arrival direction

Statistically: Mass composition p-air inelastic cross-section

Measured shower parameters.

HiRes Topics: Spectrum Chemical Composition Anisotropy proton-air Cross-section (Talk by K.Belov) Neutrinos (Talks by K. Martens & L. Scott)

High Resolution Fly’s Eye (HiRes) Experiment:Has the World’s Highest Exposure (5xAGASA)

HiRes1 Collected data from May 1997 to April 2006 HiRes2 Collected data from Dec 1999 to April 2006 HiRes Collected data on moonless nights: about 10%

duty factor. Mono: wider energy range (1017.2 < E < 1020.5 eV), best

statistics. Stereo: best resolution, 1018.5 < E < 1020.5 eV, fewer

events.

Physics with HiRes Data HiRes-1

monocular data began ~3 years earlier: largest statistics,

HiRes-2 monocular: can reach down to as low as 1017.2eV,

Stereo data: best resolution, optimized for E>31018eV

HiRes-2 mono

HiRes-1 monoHiRes stereo

Tandem Stereo Study

Energy Spectrum

Spectral Shape Almost featureless spectrum at lower energies However, the GZK Cutoff was predicted in 1966 by

K. Greisen, G. Zatsepin, and V. Kuzmin. Photons of CMBR interact with cosmic ray protons

of extragalactic origin. Photoproduction of ’s via Δ resonance Pion carries away 20% of proton’s energy strong

energy-loss mechanism for protons, that travel > 50 Mpc.

Should occur at about 6x1019 eV (10J) causing a strong break in the spectrum

Previous Experiments Several smaller experiments

saw one super-GZK event each: Volcano Ranch, Haverah Park, Yakutsk, Fly’s Eye.

Akeno Giant Air Shower Array (AGASA) was the first experiment to be large enough to measure the spectrum at the GZK energy; they didn’t see the cutoff.

AGASA main evidence: 11 events above 1020 eV.

This led some to question whether the GZK cutoff exists, and how it might be evaded.

5σ Observation of the GZK Suppression Broken Power Law Fits

No Break Point 2/DOF = 162/39

One BP 2/DOF = 62.9/37 BP = 18.65

Two BP’s 2/DOF = 39.5/35 1st BP = 18.65 2nd BP = 19.75 2 difference=>4.5

Two BP with Extension Expect 39 events Observe 13 events Poisson probability:

P(13,39) = 4.8

Confidence Building Tests:

Geometry/Energy Reconstruction Aperture Composition Dependence Atmosphere (Avg vs Hourly) Aperture High Energy Efficiency/Aperture

Mono versus Stereo Energy Measurements

The HiRes monocular energy is in excellent agreement with stereoscopic measurements !

HiRes-1 mono vs. stereo

Add the HiRes Stereo Spectrum(absolutely normalized)

Spectrum with Systematic Uncertainty from Composition

Composition determines whether <Xmax> is in HiRes’ field of view, or above.

Different apertures for Corsika/QGSJet protons and iron; leads to systematic uncertainty below 1018 eV, which is larger than statistical uncertainty.

HiRes can’t say much about the second knee.

The field needs an experiment, with wide enough energy range, which would see all three UHE cosmic ray features with good statistics!

ATM and the Aperture

Ratio of Apertures:

numerator:

MC w/ATM database

Reconstruction w/

database

denominator:

MC gen w/database

Reconstruction using

Average ATM

log (E)

Aperture Check HiRes-2 Data:

Artificially cut the data so that you are certain of the aperture.

Cut data with an impact parameter > 15 km

>10 km

Excellent agreement! Confidence in aperture calculation

Phase SpaceSpace at High Energies

Compare data with high energy MC phase space relations.

Super GZK events are just like those at lower energies.

No surprises HiRes aperture calculation is accurate.

HE Aperture Test

HiRes 1

HiRes 2

Terra (Laser)

Shower~30 EeV

Laser tests the reach of our HE aperture - 34 km from HiRes-2 Detector.

Light production equivalent to ~6x1019 - 1020 eV air shower

Detectors have no trouble seeing this laser under good to worse than acceptable viewing conditions.

GZK CutoffGZK Cutoff

30 EeV Shower

Terra Laser

profiles recorded by HR2

NP

E/2

De

g

Composition

Stereo HiRes Elongation RateWidth is constant from ~1018 eV up

Width and Xmax (elongation) imply constant composition in this energy range

- QGSjet (1) prefers ~80% “protons”

- Sybil prefers ~60%

Application of radio-sonde data (SLC) will move the HiRes Xmax up ~10 gm/cm2 on average, thus lighter

Model-independent break in slope at about 1018 eV.Heavy (galactic) nuclei decrease, give way to light (extragalactic) composition.Galactic/extragalactic transition is complete by about 1018 eV.

•Astrophysical Journal 622 (2005) 910-926

Composition: Xmax Distribution Width Predictions

Protons: deeper and wider

The distributions overlap

Thus not an event by event measurement

MC with E = 1018 – 1019 eV

Composition: All-Energy Xmax Distribution

Solid Line: DataSolid Line: Data

Heavy Dots: QGSJet Heavy Dots: QGSJet

Light Dots: SIBYLLLight Dots: SIBYLL

Data v Proton Models Data v Iron Nuclei Models

Stereo Data:Stereo Data:~800 Events ~800 Events 11/1999 – 9/200111/1999 – 9/2001

Some of the Additional Data Previous result runs out of statistics near 30 EeV Analyze “golden events” above 8 EeV to

increase statistical reach “golden events” are events where Xmax is

clearly observed by HR 2 as determined by manual scan

80% of data above 10 EeV falls into this category

Scan bias is believed to be small

Open circles: previous HiRes publication

Filled circles: new HiRes “golden events”

Composition appears to remain light approaching 1020 eV

Student’s Thesis on this is taking shape and expect an updated result this summer

Log10(E)

XmaxExtending the Analysis

A first look:

HiRes Anisotropy Results: BL Lac Correlations

Correlations between UHE cosmic rays’ pointing directions, and BL Lac sources have been found individually in AGASA, Yakutsk, and HiRes stereo data, by P.Tinyakov, I.Tkachev, D.Gorbunov, S. Troitsky et al.

HiRes stereo result: BL with m<18: 10-4 chance probability. Add HP sources: 10-5 chance probability.

The HiRes result should not exist, since the ~0.5o resolution is smaller than expected magnetic deflections.

This is a northern-hemisphere effect, since many fewer sources are known in the southern hemisphere.

More Northern Hemisphere Anisotropy

The Quartet: AGASA triplet + HiRes stereo high energy event; in Ursa Major.

Dip near galactic anticenter, observed by AGASA and HiRes at lower energies.

HiRes-1 Anisotropy

• HiRes-1 mono ang. resolution: ~8° within the SD plane.

• Asymmetric error ellipses but with area comparable to AGASA angular resolution

• 2 publications in 2004

Autocorrelation functions (histogram of cos between all possible pairs) for HiRes-1 monocular (left) and AGASA (right) events above ~4x1019eV Astropart. Phys. 22, 139 (2004)

HiRes-1 mono AGASA

Cen. A

=0.020.06

Galactic Ctr.

=0.010.05

M87

=0.010.05

Search for dipole enhancement in the direction of nearby a-priori sources: null results for the Galactic Center, Centaurs A, and M87 Astropart. Phys. 21, 111 (2004)

Summary Spectrum

The UHECR Spectrum clearly shows structure (ankle, GZK suppression) – there is physics here

Chemical Composition Xmax AND Width important to measuring composition Changing heavy to light - light and constant above ~1018 eV Transition apparently complete BEFORE the Ankle

Anisotropy Tantalizing hints of BL-Lac correlation – needs verification with

independent data Possible Point source with AGASA Triplet