The Telescope Array Low Energy Extension (TALE)
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The Telescope Array Low Energy Extension
(TALE)
Pierre SokolskyUniversity of Utah
Spectrum: Ankle and Cutoff
Ankle Pair production? Galactic to
extragalactic transition?
Cutoff GZK feature Sources getting
tired?
Spectrum: Second Knee Left: Cosmic ray
spectra measured by the Fly’s Eye, HiRes/MIA, Akeno, and Yakutsk experiments.
Right: Aligning the flat parts of the spectra from the four experiments, a “second knee” appears
The energy and origin of the feature is unknown – needs to be measured with other features
Composition
Changes in composition and how they correlate with changes in spectral shape tell us about the sources – width and <X
max>
HiRes-MIA data imply a change from heavy to light from 1017 – 1018 eV
HiRes data imply a constant light composition for E>1018 eV
TALE Goal: Reach 1016.5 eV
Study the Transition Region from Galactic to Extra-galactic cosmic ray flux
Extend the 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
Telescope Array – High Energy
The High Energy component of Telescope Array – 507 scintillator surface detectors and 28 fluorescence telescopes at 3 stations is
complete and operational as of 1/2008.
7
Long Ridge Black Rock Mesa
Middle Drum
TA-FDFrom HiRes
New FDs
Example stereo hybrid event
BRM CAMERA7
BRM CAMERA8
LR CAMERA7
Absolute Energy Calibration in situ by 40 MeV electron beamreleased vertically into the sky.
TA Stage-1 The energy region > 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
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
Low Energy Extension to TA
4th Fluorescence Station - 6 km separation 24 telescopes (3-31o elevation) – “ring 1 & 2” 15 large area Tower telescopes (31-73o elevation)
Infill scintillator array 111 detectors at 400 m Graded muon array – 25 detectors, buried 3 m
Lessons from HiRes Stereo
HiRes Stereo aperture falls too rapidly through the ankle region to extend flux measurements much below ~31018eV.
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 31018eV
– HiRes-1 only covers elevation angles up to 17, which further limits the aperture near and below the ankle itself
6 km Stereo and Tower
•24 low elevation (ring 1 & 2) telescopes; mirrors the same effective area as HiRes and Auger
•15 higher elevation (rings 3-5) telescopes; mirrors 3x larger area
Aperture
The 6 km stereo provides
• a much flatter stereo aperture than HiRes
• a 10x increase in aperture at 1018 eV
HiRes Prototype 92-96 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 patches64 underground scintillation counters each):
HiRes Prototype/MIA Hybrid
Left: TALE-1 site, showing 3rd 4th and 5th rings
Right: Prototype 4th ring detector
3 additional rings of mirrors, 31° – 72º Each mirror 3x HiRes mirror area
TALE Tower Fluorescence Detector:
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.
Tower helps with <Xmax
> Bias
Comparison of <Xmax
> (solid
line) measured by the HiRes and HiRes-MIA experiments and the distribution of X
max of HiRes
events (2-D box histogram), demonstrating the trigger bias (towards light composition) inherent in a “2-ring” fluorescence detectors like those used by HiRes and PAO.
need the Tower to cover this region, which contains the Second Knee Structure
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
1017 eV showers, 30° zenith at TA ground(CORSIKA/EPOS)
TALE Methods:
TALE: Underground Muon Detectors
Preferred design, if BLM permitsReduced costSimpler
Reclamation, reseeding required
/e ratio signal for transition in log(E) = 17 decade
Conclusion:
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.
TALE will have two orthogonal composition measurements in galactic/extragalactic transition region: FD shower profile and /e ratio.
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