The Telescope Array and its Low Energy Extension (TA/TALE)

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The Telescope Array and its Low Energy Extension
(TA/TALE)

• J.N. Matthews
• University of Utah

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Outline

• Objective and Motivation for TA/TALE
• TA Construction and Status
• TALE 6km Stereo Fluorescence
• TALE Fluorescence Tower
• TALE Infill Array
• TALE Muon Array
• Summary

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Spring 2008

• Spectral Shape
• The GZK Cut-off is there!
• 1st Observation by the HiRes group Announced at
  the 2001 ICRC/Hamburg, PRL in print
• Recent confirmation by Auger
• Ankle Clearly Observed by Flys Eye and HiRes
• Second Knee Observed by HiRes-MIA among others
  energy not well known
• Structure Physics
• Composition
• heavy at 1017 eV, turning light at 1018 eV,
  constant to highest energies
• Anisotropy No Clear Signs
• Experiment
• HiRes AGASA triplet?, BL-Lacs?, Galactic
  Anticenter deficit?, no correlation with AGNs, No
  sign of Autocorrelation
• AGASA doublets, triplet, BL-Lacs?, Galactic
  Center excess? Anticenter deficit?, Positive
  Autocorrelation
• Auger AGNs?, No excess at Galactic Center,
  Positive Autocorrelation

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Theres Work to be done!

• Understand the spectral shape it tells us about
  sources, their distribution, and propagation
• Look at changes in composition in conjunction
  with the spectrum try to figure out the end of
  the Galactic Spectrum and separate it from the
  Extra-Galactic part
• As always, search for sources/anisotropy

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TALE Goal Reach 1016.5 eV

• Study the Transition Region from Galactic to
  Extra-galactic cosmic ray flux
• Extend the overall coverage of the TA experiment
  to include all three cosmic ray spectral features
  in the ultrahigh energy regime
• The GZK Suppression
• The Ankle
• The Second Knee

It is important than we establish a single
unified energy scale for the measurement of all
three features
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Xmax Tells Us Composition

• Measuring ltXmaxgt gives us our best handle on
  composition.
• Need to extend Xmax measurements down to 1016.5
  eV to see the galactic/extragalactic transition
  with good lever arm.

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TA Stage-1

• The energy region gt 1019 eV is well-covered by
  the existing TA detectors
• Ground Array becomes fully efficient at 5x1018
  eV
• The three FD stations
• TA-FD0 at Black Rock Mesa
• TA-FD1 at Long Ridge
• TA-FD2 at Middle Drum
• provide 100 coverage of the ground array at
  1019 eV and above

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Below 1019 eV

• However, Stage-1 of TA was not designed for
  physics below 1019 eV.
• There is no overlap at all in the aperture of the
  three fluorescence detectors at 1018 eV
• The ground array efficiency drops quickly in the
  1018-1019 eV decade

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HiRes Stereo

• HiRes Stereo aperture falls too rapidly through
  the ankle region to extend flux measurements much
  below 3?1018eV.
• There are two primary reasons for this
• The 12.6 km separation of the two stations is too
  large the overlap between the two shrinks very
  quickly below 3?1018eV
• HiRes-1 only covers elevation angles up to 17?,
  which further limits the aperture near and below
  the ankle itself

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TALE 6km Stereo Detector

• TALE will deploy a 2-ring, 24 mirror detector
  (using HiRes FADC detectors) on Long Ridge, 6 km
  from TA-FD1.
• Site separation of 6km State trust land (SITLA)
  site available at the location shown (more
  flexibility in land-use than BLM land)
• Available SITLA locations near BRM are too close
  to archaeological sites and to scenic landmarks

Top view projection of the viewing solid angles
of the TALE telescopes
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Stereo Overlap

• Aperture is much flatter than the HiRes stereo
  aperture.
• Aperture at 1018 eV is 6? that of HiRes stereo.
• Stereo detection over the ankle region provides
  better resolution than monocular
• Stereo is better than hybrid redundant
  measurement of shower properties (e.g. E and
  Xmax) which allows DIRECT validation of MC

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TALE 6km detector Housing

• Construct two (2) 6-bay buildings similar to the
  Middle Drum structure (which has 7 bays)
• Each bay holds one ring-1 (3-17 ?) and one ring-2
  (17-31?) telescope
• For 24 telescopes you need two buildings in order
  not to have the telescopes obscure one another
• HiRes2 mirrors, PMT cameras and mirror stands
  will provide these 24 telescopes.

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Zero in on the Ankle

• The energy, angular, and Xmax resolutions of the
  6km stereo pair is expected to be similar to that
  of the HiRes stereo pair, except that the
  aperture is flattened in the decade of energy
  containing the ankle.
• Will provide stereo composition measurement down
  to 1018 eV, where we expect the elongation rate
  to begin to changeoverlapping with the Tower
  hybrid detector.

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Additional Benefits of TALE-6km

• The TALE-FD (6km telescopes) will also extend the
  both the monocular and stereo coverage of TA at
  the highest energies we will have total
  time-averaged FD aperture gt50 that of the ground
  array
• We will also have improved stereo-hybrid (2 FD
  in coincidence with ground array) coverage
  essentially 2/3 stereo-hybrid coverage of the
  ground array above 1019 eV

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31 Bias Cant Measure Xmax Below 1018 eV

• Xmax measurements below 1018 eV are beyond the
  scope of HiRes and Auger. TA is only a little
  better.
• Two-ring (lt31? elevation) configuration
  introduces significant trigger bias toward low
  Xmax (heavy composition) showers

TALE will need additional elements to cover this
region, which contains the Second Knee Structure
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Previous Attempt HiRes prototype-Mia (1993-1996)

• 14 (HiRes-1) 4 (HiRes-2) mirror prototype
  detector operated between 1992 and 1996
• HiRes-1 field of view up to 70?.
• HiRes-1 operated in hybrid mode with the MIA muon
  array (16 patches?64 underground scintillation
  counters each)

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HiRes-MIA TALE Designs

• HiRes-MIA was a experiment of opportunity and was
  not optimized for the overlap region
• Used the 0.25km2 CASA-MIA array (CASA was used
  only for triggering) limited by limited flux
  over such a small (but dense) ground array
• MIA was designed as a hadronic event veto and
  cannot actually count muons
• Due to a longitudinal bias, HiRes-size mirrors
  cant measure Xmax below 1017 eV
• The TALE solution is an improvement on the
  HiRes-MIA hybrid design. Deploy larger mirrors
  in rings 3-5, plus a larger infill surface array
  covering 40 km2 with 400m spacing
• 3x larger mirrors in to extend the lowest
  energy physics threshold to 1016.5 eV.
• Dedicated muon detector with counting capability.

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Tower Fluorescence Detector

• Use 4 m diameter mirrors to triple the
  collection area over those of the re-deployed
  HiRes mirrors in the 6km stereo detector.
• Lowers bias to E lt 1016.5 eV.
• Use scaled-up F1.1 optics identical to HiRes
• Re-use PMTs from HiRes telescopes
• Use Winston cones for light collection

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Tower FD

• The TALE Tower FD consists of 15 telescopes in
  its top three rings
• 6 (3) at 31-45?
• 5 (3) at 45-59?
• 4 (4) at 59-73?
• in parenthesis shows the number of mirrors in
  the HiRes tower prototype at the same elevation
• The 6km telescopes also provide 16 telescopes
  directly below the top three rings compared to
  only 4 in the HiRes-prototype
• Stereo overlap with TA-FD1 at Long Ridge for
  direct validation of MC resolutions

Top view projection of the viewing solid angles
of the TALE telescopes
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Improved Sensitivity

• The increased mirror size will improve
  substantially the sensitivity of TALE in the
  1016.5-1017.5 eV energy decade
• Note the gain in sensitivity comes from the
  improvement in signal.
• The HiRes trigger scheme is not S/N limited, but
  limited by having enough signal to reconstruct a
  reliable shower profile.

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Hybrid Operation

• The tower can operate in monocular mode, but
  limited to Xmax resolution of 50 g/cm2.
• Stereo overlap with Long Ridge FD site is too
  small to have large enough stereo aperture (but
  enough for direct MC validation of resolutions
• Need infill array for hybrid operation
• Simulations show 400 m spacing and 4km x 4km
  array to be the optimal solution for hybrid
  operation the 1016.5-1019 eV energy range

Part of the main ground array northeast of
TALE-FD site suitable for infill AND muon array.
Sensitive plant species are found south of that
location
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Infill Array

• Will place 111 additional surface array counters
  overlapping with main ground array 4km x 4km
• 16 of the counters in the main ground array will
  form part of the infill
• One possibility re-use the AGASA scintillators
  and PMTs for the infill array

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Muon Array

• One of the goals of TALE is to find where the
  (heavy) Galactic flux gives way to the (light)
  extra-galactic flux
• An orthogonal composition measurement (in
  addition to shower profile) will be a valuable
  addition to TALE
• Measure the e/µ ratio.
• Propose a 25 detector array placed in the inner
  corner of the infill array.
• The current plan is to bury the counters under 3m
  of packed soil
• Negotiations under way with BLM to collaborate

This 2.5km x 2.5km graded array is designed to
work at 1016.5-1018 eV
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Summary

• TA/TALE will bring together four different
  detector systems with overlapping energy ranges
  to give continuous coverage from 1016.5 eV
  to the highest energies.
• The cost will be shared between U.S., Japan,
  South Korea, and Russia.
• TA/TALE will be able to study all three spectral
  features in the UHE regime and measure the
  composition in each energy range.
• In the energy region of the Second Knee where we
  suspect Galactic/Extragalactic transition to
  occur, we will have two orthogonal composition
  measurements FD shower profile e/m ratio.

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HiRes 5s Observation of the GZK 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(1343) 5.3s

E-5.1
Break is at (5.6 0.5) x 1019 eV GZK expected
at 6 x 1019 eV. The break is the GZK cutoff!
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HiRes and Other Experiments
HiRes and Auger(2007)
HiRes, AGASA, Auger(2005)
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A New Detector in the North!

• The Telescope Array was approved first by the
  Japanese government in 2003

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Telescope Array
MD
CLF
Surface Detectors
LR
BRM

• Surface Detector Stations covering (blue
  diamonds) 800 km2 square grid with 1.2km
  spacing 3.0 m2 plastic scintillation detectors
• Three fluorescence Stations 12 x 3m dia. mirrors
  each at Black Rock Mesa and Long Ridge, 14x 2m
  dia. Mirrors at Middle Drum
• Central Laser Facility atmospheric monitoring
  laser seen by all 3 FD

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A New Detector in the North!

• The University of Utah and began site procurement
  with help from the University of Utah and the
  State of Utah
• Construction of the Black Rock Fluorescence
  Detector began in 2004

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A New Detector in the North!

• The University of Utah and began site procurement
  with help from the U and State
• Construction of the Black Rock Fluorescence
  Detector began in 2004
• Phase-1 Approval by US NSF in 2006

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