The Telescope Array and its

Low Energy Extension (TA/TALE)

J.N. MatthewsUniversity of Utah

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

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 Fly’s 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

There’s 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

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:1. The GZK

Suppression

2. The Ankle

3. The Second Knee

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

Xmax Tells Us Composition

• Measuring <Xmax> 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.

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

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:1. The 12.6 km separation of

the two stations is too large: the overlap between the two shrinks very quickly below 31018eV

2. HiRes-1 only covers elevation angles up to 17, which further limits the aperture near and below the ankle itself

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

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

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.

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 change…overlapping with the “Tower” hybrid detector.

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 >50% 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

“31° Bias”: Can’t 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 (<31 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

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 patches64 underground scintillation counters each):

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 can’t 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.

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 < 1016.5 eV.• Use scaled-up ~F1.1 optics identical to HiRes• Re-use PMTs from HiRes telescopes• Use Winston cones for light collection

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

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.

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

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

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

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/ ratio.

HiRes: 5σ 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(13;43) = 5.3

Break is at (5.6 ± 0.5) x 1019 eV;GZK expected at 6 x 1019 eV.

The break is the GZK cutoff!

E-5.1

HiRes and Other Experiments

HiRes and Auger(2007)HiRes, AGASA, Auger(2005)

A New Detector in the North!

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

Telescope Array

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

Surface Detectors

LR

MD

BRM

CLF

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

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