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Workshop on Physics at the End of the Galactic Cosmic Ray Spectrum
The TA and TALE Experiments
Gordon Thomson
Rutgers University
Outline
• TA/TALE physics motivation: Study ALL the physics in the UHECR regime.
• The TA Experiment: aims and detectors.
• The TALE Experiment: aims and detectors.
What Spectral Features Does One Expect to see in the UHE Regime?
• CMBR photons interact with cosmic ray protons: – Pion production makes the GZK suppression: E < 6x1019 eV if cosmic
rays travel > 50 Mpc.– e+e- pair production: threshold ~ 4x1017 eV, excavates the ankle.
• Pair production pileup + galactic/extragalactic transition: the second knee.
• One should see three spectral features in the UHE regime.• But NO single experiment has done so: the exact energies
(even the relative energies) are not known; i.e., basic information is in doubt.
• The field needs an experiment with WIDE energy coverage!! Good resolution!! and good systematics!!
Physics in the UHECR Regime: Best Evidence so far…
HiRes observes the ankle; Has evidence for GZK suppression;Can not claim the second knee.
Galactic/Extragalactic Transition:HiRes/MIA hybrid experiment, and HiRes Stereo results.
Best Evidence (cont’d)Second Knee at 1017.6 eV
• Yakutsk, Akeno, Fly’s Eye Stereo, HiRes Prototype/MIA all saw flat spectrum followed by a steepening in the power law. The break is called the second knee.
• Correct for varying energy scales: all agree on location of the second knee.
• There are THREE spectral features in the UHE regime.
• But location of second knee is unknown.
• The ULTIMATE experiment is one which would see the three UHE cosmic ray features with good statistics!
Fitting the Spectrum
• It is important to fit the spectrum to a model that incorporates known-physics.– Position of the ankle is
important for determining the distance to sources.
– Regions of poor fit quality indicate where the model may break down.
• Problem near 1019.5 eV? Six points with chi squared 10.
• Problem at 1017.5 eV? The second knee is too weak.
Interpretation of Extragalactic Spectrum
• Pion-production pileup causes the bump at 1019.5
eV.• e+e- pair production
excavates the ankle.• Pileup at location of second
knee.• Fractionation in distance
and energy; e.g., z=1 dominates at second knee.
• Can cosmic ray physicists see evolution of sources?
• Can we do cosmology?
The Problem at 1017.5 eV
• Model: – Source density: constant
multiplied by (1+z)m.– Power law cuts off at 1021
eV.
• Second knee is too weak in the model:– Are extragalactic sources
too strong? Is different evolution needed for z > 1?
– Galactic sources weaker? Different shape?
• Need better data on:– Flux at lower energies to tie
down the fit; long lever arm: need wide energy range.
– Composition to improve the model.
Cosmology with QSO’s and AGN’s
QSO density histograms: Croom et al., Schneider et al.
QSO luminositydensity, optical Boyle and Terlevich
AGNluminosity density, 2-8 keV X-rays. Barger et al.
SDSS
Lines: (1+z)3
Cosmology a la HiRes?
• Adjust evolution to match QSO’s: – m=2.6, z<1.6– Lower m, z>1.6
• HiRes has a hard time doing cosmology.
• Must extend spectrum measurement lower by an order of magnitude.
• TA/TALE aim: measure spectrum from 1016.5 to over 1020 eV..
Galactic Sources are Interesting!
• Questions about Galactic sources:– What is the maximum energy they produce?– Is there anisotropy at 1018 eV?
• TA/TALE aim: attack these questions:– Measure spectrum and composition at lower energies where
galactic contribution is larger.– Search for anisotropy along galactic plane, and just above the
galactic center.
• The next experiment needs a WIDE energy range.
Observe the Galactic-Extragalactic Transition through Composition Change
• Xmax is the variable that discriminates between p and Fe primaries.• Fluorescence gives direct observation best technique.• Choose stereo and hybrid: each has x2 better Xmax resolution than
mono.• Paradoxical indication by HiRes-MIA and HiRes stereo:
– “early” transition; i.e., below the ankle.– “late” transition; i.e., above supernova capability.
• Need two new detectors: – stereo between TA and HiRes fluorescence detectors.– hybrid between a tower detector and infill array.
• Kascade is moving up in energy using a 100% different technique; test the two methods.
Current Status of Composition-correlated Spectrum Measurements
• Magenta is Fe flux.– 1015 – 1017 eV
from Kascade.
– 1017 – 1019.4 eV from HiRes/MIA, HiRes Stereo.
TA Aims• Solve the AGASA/HiRes puzzle.
– Is the GZK cutoff present?– Do clusters/sources exist?– Is there an enhancement along the galactic plane?
• Method chosen:– Build SA 8 x AGASA in size, similar technology (scintillators).– Build fluorescence detectors overlooking the SA.
• Observe in hybrid and in stereo at high energies.• Cross calibrate SA against fluorescence detector.
• Result:– Direct comparison with same techniques and events.– Excellent resolution, statistics, and systematics above 1019 eV.– Superior experiment for anisotropy studies at high energies.
TA Design• SA: 576 scintillation counters,
each 3 m2 area, 1.2 km spacing.• 3 fluorescence stations, each
covering 108o in azimuth, looking inward.
• Central laser facility.• Millard County, Utah, flat
valley floor for SA, hills for fluorescence, low aerosols.
• A 1020 eV event (on a night when the moon is down) will be seen by SA and all three fluorescence detectors.
• A powerful detector for hybrid and stereo cross correlation with SA.
What should be added to TA?
• An extension of TA stereo coverage to measure spectrum and composition in ankle region; i.e., move HiRes to Millard County: 6 km stereo with TA fluorescence detectors.
• Arrange the HiRes detectors to extend the high energy fluorescence aperture of STA.
• An extension of hybrid coverage to extend spectrum and composition measurements to below 1017 eV; i.e., a tower detector and infill array.
Observe the Ankle in Stereo Mode
• HiRes stereo (12.6 km separation) has rapidly-changing aperture below 1018.5 eV (Auger and STA stereo and hybrid are not better).
• Flatten the aperture by having the two stereo detectors be closer: STA and HiRes fluorescence detectors 6 km apart.
• Perform composition-correlated measurement of spectrum.
Increase the High Energy Fluorescence Aperture of TA by Factor of 3.6
• Two HiRes detectors, moved to Millard Co.
• One is a TA fluorescence detector (360o azimuth).
• 6 km stereo with Black Rock Mesa TA fluorescence detector.
• Each detector has two rings.• High enegy instantaneous
aperture of 18000 km2 ster.• Increase high energy
fluorescence aperture by factor of 3.6
• Total high energy aperture of 3200 km2 ster.
Lower-energy Limitations
• HiRes observes elongation above 1018.0 eV clearly.
• HiRes looks up to 31o, can’t see Xmax for close-by (low energy) events.
• Makes spectrum measurements difficult below 1017.5 eV.
• Composition bias for E < 1018.0 eV.
Before bracketing and Cerenkov cuts
Observe the Second Knee in Hybrid Mode with a Tower Detector
• Two methods of lowering the minimum energy:– Use bigger mirrors.– Look higher up.
• Tower detector with 3x larger mirrors:– 750 cm radius of curvature.– Cluster box at 97% of focal
length.– Use HiRes-type phototubes
with Winston cones.– Collect 2.88 times as much
light.
Tower Detector
• Simulate a five-ring detector.
• Rings 1 and 2 have standard HiRes mirrors.
• Rings 3-5 have 3x larger mirrors and Winston cones.
• Compare with HiRes2 (data set 2).
• Compare with a tower detector with standard HiRes mirrors throughout.
Lower Emin by order of magnitude.
• Test tower detector design: MC ~ 2 mo running. – cover 90o azimuthally.
– 15 mirrors in rings 3-5.
– HiRes-size mirrors reach down ½ order of magnitude.
– 3x larger mirrors reach down full order of magnitude.
Noise Levels
• HiRes prototype: all 5 rings have similar sky noise levels.
• Larger mirrors √3x more sky noise.
• Bright stars also show up in our data: E-1 distribution 3x more noise from this source.
UV catalog at 275 nm, (Sadowski et al.)
TA FD, Tower, Infill Array
• 15 mirrors, 3xHiRes area, in rings 3,4,5.
• 111 AGASA counters, spacing of 400m, shown in red. Can see events hitting outside also.
• 10 x HiRes/MIA hybrid aperture.
Summary
• Build the TA/TALE experiment in Millard Co, UT.– TA being built by Japanese groups.– Add two 2-ring detectors: reuse HiRes mirrors, phototubes, add
new FADC readout.– Add tower detector, infill array.
• Resolve the HiRes/AGASA puzzle.• Large high-energy aperture: 3200 km2 ster.• Powerful anisotropy engine.• Observe the Ankle in stereo.• Extend coverage down to 1016.5 eV.• Perform composition-correlated spectrum measurement.• Observe the galactic/extragalactic transition. • Resolve astrophysics questions about second knee, 1019.5
eV regions.