The Telescope Array
Low Energy Extension
(TALE)
Pierre Sokolsky
University 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 <Xmax>
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
It is important than we establish a
– The Second Knee
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.
TA-FD
From HiRes
Middle Drum
New FDs
Long Ridge
7
Black Rock Mesa
Example stereo hybrid event
BRM CAMERA8
LR CAMERA7 BRM CAMERA7
Absolute Energy Calibration in situ by 40 MeV electron beam
released 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
o
24 telescopes (3-31 elevation) – “ring 1 & 2”
o
 15 large area Tower telescopes (31-73 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 ~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
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 patches64
underground scintillation counters each):
HiRes Prototype/MIA Hybrid
TALE Tower Fluorescence Detector:
3 additional rings of mirrors, 31° – 72º
Each mirror 3x HiRes mirror area
Left: TALE-1 site, showing 3rd 4th and
5th rings
Right: Prototype 4th ring 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 Xmax 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


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
Infill Array
TALE Methods:

1017 eV showers, 30° zenith at TA ground
(CORSIKA/EPOS)
TALE: Underground Muon
Detectors

Preferred design, if
BLM permits
 Reduced
cost
 Simpler

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.