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.