Transcript Results from the High Resolution Fly`s Eye Experiment

Results from the HiRes
Experiment
Gordon Thomson
University of Utah
TeV Particle Astrophysics 2010
Outline
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•
Introduction
Some recent results
–
–
–
•
Spectrum
Composition
Anisotropy
Summary
High Resolution Fly’s Eye (HiRes)
Collaboration
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, B.T. Stokes, 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, J. Belz, D.R. Bergman, A. Blake, Z. Cao, W. Deng, W. Hanlon, P. Huentemeyer, C.C.H. Jui,
E.C. Loh, K. Martens,J.N. Matthews, D. Rodriguez, J. Smith, P. Sokolsky, R.W. Springer, B.T. Stokes, J.R. Thomas, S.B. Thomas,
G.B. Thomson, L. Wiencke
University of Utah
The Two HiRes Fluorescence
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).
Mirrors and Phototubes
• 4.2 m2 spherical mirror
• 16 x 16 array of phototubes, .96 degree pixels.
Reconstruction
•
ti
1.)
i
The trajectory of the EAS can be
determined in one of two ways:
1.
2.
Monocular reconstruction using the
arrival time of light signal at the
detector.
Stereo by intersecting the showerdetector planes (SDP) seen from the
two detector sites.
t0
ti  t0 

RP
tan i
c
2
2.)
Spectrum and Composition Method
• Spectrum: aperture varies with energy.
Must calculate with Monte Carlo method.
– Trigger and thresholds very important.
– Excellent accuracy is achievable.
• Composition: Monte Carlo simulations are
essential to understand Xmax studies.
Compare Data to Monte Carlo:
Judge success of simulation and
acceptance calculation.
Inputs to Monte Carlo:
Fly’s Eye stereo spectrum; HiRes/Mia and HiRes Stereo composition;
Library of Corsika showers.
Detailed nightly information on trigger logic and thresholds, live mirrors, etc.
Result: excellent simulation of the data,
and an accurate aperture calculation.
5σ Observation of the
Break in the Spectrum
• Broken Power Law Fits
– Two BP with extension
to test hypothesis that a
break is present.
• Expect 43 events
• Observe 13 events
• Poisson probability:
P(13;43) = 7x10-8,
which is 5.3s
– The break is
statistically
significant.
E-5.1
Break is at (5.6 ± 0.5) x 1019 eV;
GZK expected between 5 and 6 x 1019 eV.
The break is the true GZK cutoff.
Use Berezinsky’s E½ Method to Test
• E½ is the energy where the
integral spectrum falls
below the power-law
extension by a factor of 2.
• Berezinsky et al.: log10E½
= 19.72, for a wide range
of spectral slopes.
• Use 2 Break Point Fit with
Extension for the
comparison.
• log10E½ = 19.73 ± 0.07
• Passes the test.
Local Density of Sources
• Theoretical predictions for
spectrum shape agree with
HiRes measurements.
• Compare HiRes spectrum
slope above the GZK
energy to Berezinsky et al.
predictions:
– Line 1: constant density.
– Line 5: no sources within
10 Mpc.
– Line 2: double density
within 30 Mpc.
Berezinsky, Gazizov, and Grigorieva,
Phys. Rev. D74, 043005 (2006)
(uses older HiRes spectrum)
Local Density of Sources
•
Compare HiRes spectrum slope
above the GZK energy to
Berezinsky et al. predictions:
– Line 1: constant density.
– Line 5: no sources within 10
Mpc.
– Line 2: double density within
30 Mpc.
– Line 3: triple density within
30 Mpc.
– HiRes: E-5.1 fall-off.
•
E-5.1
More work is needed to make a
better comparison, but...
• Constant density of
sources is favored.
Berezinsky, Gazizov, and Grigorieva,
Phys. Rev. D74, 043005 (2006)
(uses older HiRes spectrum)
HiRes/Auger Spectra Comparison
Auger confirms all spectral features of HiRes spectrum
Spectrum Summary
• The GZK cutoff is present. The first
observation was by the HiRes experiment.
• All details of the spectrum indicate the
composition is protons.
– The energy of the GZK cutoff is as expected for protons.
– Highest energy extragalactic cosmic rays travel > 50 Mpc.
– The fall-off above the cutoff is evidence for a constant density of
sources. CR’s travel a long distance. Spallation breaks up all nuclei
at high energies  proton flux results.
– The ankle has been observed by HiRes, at 1018.65 eV. The spectral
index changes from -3.2 to -2.8
– Shape and energy of the ankle are consistent with e+e- production in
collisions between extragalactic protons and photons of the CMBR.
More Direct Composition Measurement:
use <Xmax>
• HiRes result on <Xmax>,
and on σ(Xmax), indicate
light composition.
• <Xmax> dependence is
logarithmic: halfway is
Be. Spallation at high
energies breaks up light
elements.
 Composition is
essentially all protons.
QGSJetII Protons Look Like Our Data
(points=data, histogram=MC)
MC protons
MC iron
Data (points) vs. QGSJet-II MC (histogram)
Energy Bins: 18.3, 18.5
Energy Bins: 18.7, 18.9
Energy Bins: 19.1, 19.3
Energy Bins: 19.5, 19.7
Composition Summary
• The most direct indicator of composition is
<Xmax>.
• Our <Xmax> data indicate a light
composition, and favor protons.
• This is consistent with all of our spectrum
information.
The Search for Anisotropy:
• Aim is to identify UHECR sources.
• Two methods:
– Make a sky plot and look for bumps.
– Look for correlations with known astronomical object
types.
• All cosmic ray results are of marginal significance:
– Sky plots: AGASA doublets/triplet at 40 EeV
– Correlations: BL Lac’s at 10 EeV & AGN’s at 57 EeV
AGN Correlations
• Auger events’ correlations with AGN’s (south)
– Early data set: scanned in (Emin, θ, zmax) using VeronCetty+Veron catalog, found best correlations at (57
EeV, 3.1°, .018).
– Tested correlation with later data set, found 8/13 events
correlated, chance probability of 0.002 (2.9σ).
• Not an “observation”: PRL requires 5σ.
Require confirmation.
• Auger test using later data:
42 events, 12 correlated,
expect 8.8 random, 1σ.
 no effect.
HiRes Test of AGN
Correlations (north)
• Choose Auger optimum point, same catalog.
– 2/13 events correlated (expect 3 randomly)
– chance probability of 0.23  no effect.
• Scan the HiRes data
– best point is (15.8 EeV, 2.5°, 0.016), 46/198
correlated.
– chance probability of 0.29  no effect.
Test of Correlations with
Local Large Scale Structure
• All results extragalactic, point source; energies of
10 (BL Lac), 40 (clusters), 57 EeV (AGN).
• Matter is not distributed uniformly within the
horizon of 57 EeV protons
 Search for correlations with local large scale
structure for high energy events with relatively
close horizons. A priori choice: 10, 40, 57 EeV.
Also choose, a priori, to quote 95% CL.
HiRes Stereo Data
• HiRes complete
stereo data set,
angular resolution
~0.8°
• Events not within
10° of galactic
plane:
– 10 above 57 EeV
– 27 above 40 EeV
– 310 above 10 EeV
• 6636 events in all
Local LSS Model
• Based on 2 Micron All-Sky
Redshift Survey (2MRS)1, a
flux-limited sample of galaxies
with m ≤ 11.25
– Remove galactic plane (|b| < 10°)
and objects within 5 Mpc.
– Transform to a volume-limited
sample by weighting.
– Result is 15,508 galaxies
between 5 and 250 Mpc.
– Assume distribution is isotropic
beyond 250 Mpc.
1. J. Huchra, L. Macri, T. Jarrett, et al., in
preparation.
Procedure: set of MC events coming from LSS
• Start with local LSS model.
• Modify using HiRes aperture.
• Simulate the data set; find average
predicted event density.
• Two parameters:
57 EeV
– Minimum energy
– Angular smearing to simulate
magnetic fields
• Expect ~1°, extragalactic fields, for
E≥40 EeV1
• Expect 2°-4°, galactic fields.
40 EeV
• Perform K-S test between data and
expectation from LSS.
• Repeat starting with an isotropic
galaxy distribution.
1. T. Kashti and E. Waxman, JCAP 0805, 006 (2008).
10 EeV
Smearing angle of 6°
10 EeV
Sky Plots
40 EeV
57 EeV
Results
• Choose 95% c.l.
exclusion to quote, a
priori.
• For isotropic model,
get good agreement.
• For local LSS model
get poor agreement.
• Exclude correlation at
95% c.l. for θs < 10°,
E ≥ 40 EeV
LSS Conclusions
• We have searched for correlations between the pointing
directions of HiRes stereo high energy events and local large
scale structure.
• There are none at the 95% confidence level for magnetic
smearing angles < 10°.
• This is very surprising.
– One expects to see correlations.
– One expects magnetic field smearing at the 4°-5° level.
– With limited statistics we are able to place very significant limits.
– Are the sources not in galaxies? Are magnetic field estimates wrong?
• This result should be confirmed by a future experiment (north).
• The Telescope Array Experiment is now collecting data. It has
statistics equal to HiRes stereo (see TA talk, Yuichiro Tameda).
Summary
• HiRes made the first observation of the GZK
cutoff.
– It occurs at (5.6 ± 0.5 ± 0.9) x 1019 eV.
– Flux α E-5.1 ± 0.7 above the cutoff.
• We see the “ankle” at 1018.6 eV.
– E-3.3 below and E-2.8 above.
• The composition is very light, probably protons
• No AGN correlations are observed.
• Correlations with local large scale structure are
very weak; magnetic fields may be larger than
previously thought.