The UHECR Spectrum observed with HiRes in monocular mode

1
The UHECR Spectrum observed with HiRes in
monocular mode

• Andreas Zech
• (LPNHE, Paris)
• Seminar at UNM
• Albuquerque, 03/29/05

2
Outline

• Ultra-High Energy Cosmic Ray Physics
• The HiRes Experiment
• Unfolding the Cosmic Ray Spectrum
• Fits to the Spectrum
• Summary
• The Future of HiRes TA TALE

3
Ultra-High Energy Cosmic Ray Physics
4
Energy Spectrum

• differential flux dN / (dE A ? dt)
• follows roughly E-3 power law
• direct observation not possible above 1 PeV
• two widely observed features
• knee at 1015.5 eV
• ankle at 1018.5 eV

5
Propagation Effects

• magnetic fields (galactic, extragalactic)
• red-shifting
• ee-- pair production with CMBR (at 1017.8 eV)
• photo-spallation of cosmic ray nuclei
• GZK effect with CMBR (at 1019.8 eV)
• ? (2.7 K) p ?(1232) ?
  n
• ? (2.7 K) p ?(1232) ?o
  p
• Strong flux suppression expected
  for extra-galactic sources.

6
Extensive Air Showers

• main channels
• ?(-) ?(-) ?? ( ?? )
• ?o 2 ?
• K(-) ?(-) ?? ( ?? )
• ? 2 ?
• main e.m. processes
• bremsstrahlung
• pair production
• ionization

7
Ground Arrays (Surface Detectors)

• Detection of lateral particle profile on ground.
• Reconstruction of geometry from pulse time
  information.
• Reconstruction of energy by model comparisons.

• Pro 100 duty cycle, low cost, low
  maintenance, good geometry reconstr., nearly
  constant aperture
• Contra Energy reconstr. is model dependent,
  uncertainties due to fluctuations in lateral
  profile.

8
Air Fluorescence Detectors

• Detection of longitudinal shower profile via UV
  fluorescence light.
• Reconstruction of geometry from recorded shower
  track.
• Using the atmosphere as a calorimeter.

• Pro Direct measurement of cosmic ray energy and
  shower maximum, good geometry energy
  reconstruction.
• Contra 10 duty cycle, higher cost
  maintenance, energy dependent aperture,
  atmospheric uncertainties

9
UHECR Composition

• depth of shower maximum ( Xmax ) depends on
  energy cosmic ray species
• indirect composition measurement
• comparison of Xmax with simulation allows
  bi-modal determination of c.r. composition in a
  statistical way.

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The HiRes (High Resolution Flys Eye) Experiment
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The HiRes Collaboration

• 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

• 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. ONeil, 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, G. Hughes,
• S. Stratton, D. Ivanov,
• S. Schnetzer, G.B. Thomson, A. Zech
• Rutgers University

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• Mirror area 5 m2 .
• 256 (16x16) PMT per mirror.
• One PMT sees 1 degree of the sky.

14
Measuring the Energy Spectrum with HiRes

• Stereo observation of the cosmic ray flux
  yields a better resolution in geometry and energy
  than monocular.

• Analyzing our data in monocular mode has
  also some advantages, though
• better statistics at the high energy end due to
  longer lifetime of HiRes-1.
• extension of the spectrum to lower energies due
  to greater elevation coverage and better time
  resolution of HiRes-2.

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1. Reconstruction of the shower-detector plane

• project signal tubes onto sky
• fit tube positions to a plane through the center
  of the detector
• reject tubes that are off-track (and off in
  time) as noise
• shower axis lies in the fitted shower-detector
  plane

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2. Reconstruction of the geometry within the
shower-detector-plane
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3. Shower Profile Energy Reconstruction

• Reconstruct charged particle profile from
  recorded p.e.s .
• Fit profile to G.H. function.
• Subtract Cerenkov light.
• Multiply by mean energy loss rate ?
  calorimetric energy
• Add missing energy (muons, neutrinos, nuclear
  excitations 10) total energy

18
Phototube Calibration

• Relative calibration at the beginning and end
  of each nightly run.
• using YAG laser
• optical fibers distribute the laser signal to all
  mirrors.

• Absolute calibration using a portable
  light-source (RXF), that is carried to both
  sites about once a month.
• calibration of RXF in the lab using HPDs.
• /- 10 uncertainty in energy scale.

19
Atmospheric Calibration

• Rayleigh contribution is quite stable and well
  known.
• Aerosol profile of the atmosphere has to be
  monitored during the run.
• 0.04 /- 0.02
• /- 15 in J(E)

• Detailed monitoring with steerable lasers at
  both sites.
• Additional vertical laser outside of Dugway
  (Terra).
• Shoot the Shower

20
Unfolding the Cosmic Ray Spectrum
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Deconvolution of the UHECR Spectrum

• We observe the spectrum convoluted with detector
  acceptance and limited resolution.
• Deconvolution with help of a correction factor
• D(Ei)? Rij T(Ej) T(Ei)
  Gmc(Ei)/Rmc(Ei) D(Ei)
• We need M.C. to simulate acceptance (
  resolution) of our detectors
  for the flux measurement

• This requires a simulation program that describes
  the shower development and detector response as
  realistically as possible.

22
HiRes Monte Carlo Simulation
23
CORSIKA Shower Library (proton iron)

• Fit parameters scale with primary energy

• Gaisser-Hillas fit to the shower profile

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Data / Monte Carlo Comparisons

• Testing how well we understand and
• simulate our experiment...
• HiRes-1
• data shown from 06/1997 to 02/2003.
• 6920 events in final event sample
• HiRes-2
• data shown from 12/1999 until 09/2001.
• 2685 events in final event sample
• Measurement of average atmosphere used
• M.C. 5 x data statistics

25
HiRes-2 light ( p.e. / deg of track)
26
HiRes 2 ?2/d.o.f. of time vs. angle fit
27
Energy Distribution Resolution
? 18
28
HiRes-1 distance to shower core
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HiRes-1 Energy Resolution
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Instant Apertures
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The HiRes-2 UHECR Spectrum
32
HiRes and Flys Eye
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HiRes and Haverah Park
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HiRes and Yakutsk
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HiRes and AGASA
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Systematic Uncertainties

• Systematic uncertainties in the energy scale
• absolute calibration of phototubes /- 10
• fluorescence yield /- 10
• correction for misssing energy /- 5
• aerosol concentration 9
• uncertainty in energy scale /- 17
• atmospheric uncertainty in aperture
• total uncertainty in the flux /- 31

37
Systematics due to MC Input Composition

• Detector acceptance at low energies depends on
  c.r. composition.
• MC uses HiRes/MIA measurement as input
  composition.
• Relevant uncertainties
• detector calibration
• atmosphere
• fit to HiRes/MIA data
• /-5 uncertainty in proton fraction

38
Systematics due to Atmospheric Variations

• Repeated HiRes-2 analysis using the atmospheric
  database.
• Regular Analysis
• 25 km, 0.04
• in MC generation
• in data MC reconstr.
• Systematics Check
• HAL VAOD from database (hourly entries)
• in MC generation
• in data MC reconstr.

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Fits to the Spectrum
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Power Law Fits Observation of Ankle and Evidence
for High Energy Break

• fit without break points ?2 / d.o.f 114 / 37
• fit with one break point ?2 / d.o.f. 46.0 /35,
  logE18.45/-0.03 eV
• fit with two break points ?2 / d.o.f. 30.1 /
  33, logE18.47/-0.06 eV
  19.79/-0.09eV ?3.32/-0.04 2.86/-0.04
  5.2/-1.3
• In case of unchanged spectrum above 2nd break
  point, wed expect 28.0 events where we see 11
• Poisson prob. 2.4 E-4

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Fit with Toy Model

• Fit to the HiRes monocular spectra assuming
• galactic extragalactic components
• all propagation effects (ee-, red-shift,
  GZK)
• Details of the fit procedure
• Float normalization, input spectral slope (g) and
  m
• uniform source density evolving with (1z) m
• Extragalactic component
• 45 protons at 1017 eV
• 80 protons at 1017.85 eV
• 100 protons at 1020 eV
• Use binned maximum likelihood method

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Interpretation

• Pion-production pileup causes the bump at 1019.5
  eV.
• ee- pair production excavates the ankle.
• Fractionation in distance and energy e.g., z1
  dominates at second knee.

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The Future of HiRes TA / TALE
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TA - the Telescope Array

• SD 576 scintillation counters, each 3 m2 area,
  1.2 km spacing.
• 3 fluorescence stations, each covering 108o in
  azimuth, looking inward.
• Central laser facility.
• Millard County, Utah, flat valley floor for SD,
  hills for fluorescence, low aerosols.
• A 1020 eV event (on a night when the moon is
  down) will be seen by SD and all three
  fluorescence detectors.
• A powerful detector for hybrid and stereo cross
  correlation with SD.

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Ideas for Recyling HiRes

• Two HiRes detectors, moved to Millard Co.
• 6 km stereo with TA fluorescence detectors.
• Each HiRes detector has two rings, 270o azimuthal
  coverage.
• Aperture of 16000 km2 ster.
• Increase fluorescence aperture from 500 to 1,780
  km2 ster, including 10 duty cycle. (TA SD1400).
• Increase in fluorescence aperture of x 3.6

46
TA Low energy ExtensionTower of Power
Infill Array

• 15 mirrors, 3xHiRes area, in rings 3,4,5 ( 3o -
  71o )
• good coverage down to logE 16.5 eV
• 111 AGASA counters, spacing of 400m, shown in
  red.
• 10 x HiRes/MIA hybrid aperture.
• observation of spectrum composition around
  second knee

47
for more informationwww.cosmic-ray.orgwww.phy
sics.rutgers.edu/aszech
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Fit with Toy Model

• Fit to the HiRes monocular spectra assuming
• galactic extragalactic components
• all propagation effects (ee-, red-shift,
  GZK)
• Details of the fit procedure
• Float normalization, input spectral slope (g) and
  m
• uniform source density evolving with (1z)3
• Extragalactic component
• 45 protons at 1017 eV
• 80 protons at 1017.85 eV
• 100 protons at 1020 eV
• Use binned maximum likelihood method

? 2.32/-0.01
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Summary
50

• We have measured the UHECR spectrum from
  1017.2 eV to the highest energies with the HiRes
  detectors in monocular mode.
• A simulation of the exact data taking conditions
  was used to determine the acceptance and
  resolution of the detector, and tested in detail
  against data.
• We observe the ankle in the HiRes-2 spectrum
  at 1018.5 eV.
• The combined monocular HiRes spectra show
  evidence for a break above 1019.8 eV. The Poisson
  probability for continuation of the spectrum with
  unchanged slope from the HiRes monocular data is
  2.4 10-4 .

51
Cosmology with TA/TALE ?

• Adjust evolution to match QSOs
• m2.6, z
• Lower m, z1.6
• Must extend spectrum measurement lower by an
  order of magnitude.

52
Mono versus Stereo Energy Measurements
HiRes-1 mono vs. stereo

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

53
Calibration Correction

• Problems with the HiRes-2 calibration due to
  limited access to Dugway.
• We adopted HiRes-1 calibration for the absolute
  energy scale.
• Correction factors for each dataset were
  determined from comparisons of stereo
  events.

54
Varying Detection Parameters

• Weather
• strict cuts based on hourly observation
• Aerosols
• atmospheric database from laser shots
• average values were used for this analysis
• Light pollution
• Average for each data set

• Trigger logic
• data divided into 3 datasets
• Trigger gains
• Dead mirrors
• Live-time
• Nightly Database
• Atmospheric Density
• Seasonal variations

55
Noise assisted triggering

• Track angle distribution shows a deficit in the
  MC for nearly vertical tracks.

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Noise assisted triggering
Adding noise to the MC increases the number of
nearly vertical tracks. This effect is caused
by an inefficiency in the HiRes-2 trigger.

• Additional sky noise
• (high amplitude)
• is added to the M.C. to
• get agreement with
• data of a certain period.

Ambient noise (low amplitude) is added to each
channel in the MC. It is measured from the
variances taken from snapshots.
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Fits to the HiRes-2 Spectrum
J ? E -3.33/-0.01
J ? E -2.81/-0.02
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Atmospheric Database

• Atmospheric data of the selected nights in
  this analysis
• 27 km
• 0.035

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Acceptances Aperture

• Rmc(Ei) / Gmc(Ei)
• Acceptances from simulations broken up into
  3 datasets.

• A? Rmc(Ei) / Gmc(Ei)
• Average instant aperture
• (in km2 sr) for all 3 datasets.

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Exposure
A? t Rmc(Ei) / Gmc(Ei) Exposure
(in 104 km2 sr s) with fit.
A? t Rmc(Ei) / Gmc(Ei)
Smoothed exposure
(in 104 km2 sr s).
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• We observe the ankle in the HiRes-2 spectrum
  at 1018.5 eV.
• The HiRes-2 result is in close agreement with
  HiRes-1 and Flys Eye.
• The HiRes-2 spectrum is consistent with the
  second knee and GZK flux suppression.
• The combined monocular HiRes spectra show
  evidence for a break above 1019.8 eV. The Poisson
  probability for continuation of the spectrum with
  unchanged slope from the HiRes monocular data is
  2.4 10-4 .

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HiRes-2 Composition Measurement

• We can extend composition analysis down to
  about 1017.5 eV with HiRes-2 data.

63
HiRes vs. Auger FD

• 2 eyes, 22 / 42 spherical mirrors
• azimuth 360, elevation 3 - 17 / 3-31
• mirror radius 1.3 m
• 16x16 PMT per mir.
• Pixel size 1 x 1
• UV filter
• SampleHold / FADC _at_ 10 MHz

• 2 eyes (so far), 6 spherical mirrors each
• azim. 180, el. 28.6
• Schmidt optics
• mirror radius 3.4 m
• 20 x 22 PMT per mir.
• pixel size 1.5 x 1.5
• UV filter, Winston cones
• FADC _at_ 10 MHz

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Phototube Calibration

• pe qe ce A ?
• ? G pe
• ? G v(?pe)
• pe ? (?/?) 2
• Relative calibration at the beginning and end of
  each nightly run.
• using YAG laser
• optical fibers distribute the laser signal to all
  mirrors.

• Absolute calibration using a portable
  light-source (RXF), that is carried to both
  sites.
• calibration of RXF in the lab using HPDs.
• /- 10 uncertainty in energy scale.