The TA and TALE Experiments Gordon Thomson Rutgers

The TA and TALE Experiments Gordon Thomson Rutgers University Workshop on Physics at the End of the Galactic Cosmic Ray Spectrum

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 < 6 x 1019 e. V if cosmic rays travel > 50 Mpc. – e+e- pair production: threshold ~ 4 x 1017 e. V, 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… Hi. Res observes the ankle; Has evidence for GZK suppression; Can not claim the second knee. Galactic/Extragalactic Transition: Hi. Res/MIA hybrid experiment, and Hi. Res Stereo results.

Best Evidence (cont’d) Second Knee at 1017. 6 e. V • Yakutsk, Akeno, Fly’s Eye Stereo, Hi. Res 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 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 e. V? Six points with chi squared 10. • Problem at 1017. 5 e. V? The second knee is too weak.

Interpretation of Extragalactic Spectrum • Pion-production pileup causes the bump at 1019. 5 e. V. • 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 e. V • Model: – Source density: constant multiplied by (1+z)m. – Power law cuts off at 1021 e. V. • 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 SDSS QSO density histograms: Croom et al. , Schneider et al. Lines: (1+z)3 QSO luminosity density, optical Boyle and Terlevich AGN luminosity density, 2 -8 ke. V X-rays. Barger et al.

What Do the Hi. Res Data Say? One Assumption: • Assume E 3 J is flat below the second knee.

Cosmology a la Hi. Res? • Adjust evolution to match QSO’s: – m=2. 6, z<1. 6 – Lower m, z>1. 6 • Hi. Res 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 e. V. .

Galactic Sources are Interesting! • Questions about Galactic sources: – What is the maximum energy they produce? – Is there anisotropy at 1018 e. V? • 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 x 2 better Xmax resolution than mono. • Paradoxical indication by Hi. Res-MIA and Hi. Res stereo: – “early” transition; i. e. , below the ankle. – “late” transition; i. e. , above supernova capability. • Need two new detectors: – stereo between TA and Hi. Res 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 Compositioncorrelated Spectrum Measurements • Magenta is Fe flux. – 1015 – 1017 e. V from Kascade. – 1017 – 1019. 4 e. V from Hi. Res/MIA, Hi. Res Stereo.

TA Aims • Solve the AGASA/Hi. Res 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 e. V. – Superior experiment for anisotropy studies at high energies.

TA Design • SA: 576 scintillation counters, each 3 m 2 area, 1. 2 km spacing. • 3 fluorescence stations, each covering 108 o in azimuth, looking inward. • Central laser facility. • Millard County, Utah, flat valley floor for SA, hills for fluorescence, low aerosols. • A 1020 e. V 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.

TA Progress (FD)

520 SD Sites have been staked. 18 counters have been deployed. Line of Sight to the “TOWER” checked

TA Time Line

What should be added to TA? • An extension of TA stereo coverage to measure spectrum and composition in ankle region; i. e. , move Hi. Res to Millard County: 6 km stereo with TA fluorescence detectors. • Arrange the Hi. Res detectors to extend the high energy fluorescence aperture of STA. • An extension of hybrid coverage to extend spectrum and composition measurements to below 1017 e. V; i. e. , a tower detector and infill array.

Observe the Ankle in Stereo Mode • Hi. Res stereo (12. 6 km separation) has rapidlychanging aperture below 1018. 5 e. V (Auger and STA stereo and hybrid are not better). • Flatten the aperture by having the two stereo detectors be closer: STA and Hi. Res fluorescence detectors 6 km apart. • Perform compositioncorrelated measurement of spectrum.

Increase the High Energy Fluorescence Aperture of TA by Factor of 3. 6 • Two Hi. Res detectors, moved to Millard Co. • One is a TA fluorescence detector (360 o azimuth). • 6 km stereo with Black Rock Mesa TA fluorescence detector. • Each detector has two rings. • High enegy instantaneous aperture of 18000 km 2 ster. • Increase high energy fluorescence aperture by factor of 3. 6 • Total high energy aperture of 3200 km 2 ster.

Lower-energy Limitations • Hi. Res observes elongation above 1018. 0 e. V clearly. • Hi. Res looks up to 31 o, can’t see Xmax for close-by (low energy) events. • Makes spectrum measurements difficult below 1017. 5 e. V. • Composition bias for E < 1018. 0 e. V. 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 3 x larger mirrors: – 750 cm radius of curvature. – Cluster box at 97% of focal length. – Use Hi. Res-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 Hi. Res mirrors. • Rings 3 -5 have 3 x larger mirrors and Winston cones. • Compare with Hi. Res 2 (data set 2). • Compare with a tower detector with standard Hi. Res mirrors throughout.

Lower Emin by order of magnitude. • Test tower detector design: MC ~ 2 mo running. – cover 90 o azimuthally. – 15 mirrors in rings 3 -5. – Hi. Res-size mirrors reach down ½ order of magnitude. – 3 x larger mirrors reach down full order of magnitude.

Tower Detector (events, track length, and psi resolution)

Noise Levels • Hi. Res prototype: all 5 rings have similar sky noise levels. • Larger mirrors √ 3 x more sky noise. • Bright stars also show up in our data: E-1 distribution 3 x more noise from this source. UV catalog at 275 nm, (Sadowski et al. )

TA/TALE Apertures

TA FD, Tower, Infill Array • 15 mirrors, 3 x. Hi. Res area, in rings 3, 4, 5. • 111 AGASA counters, spacing of 400 m, shown in red. Can see events hitting outside also. • 10 x Hi. Res/MIA hybrid aperture.

Shower Footprints

Summary • Build the TA/TALE experiment in Millard Co, UT. – TA being built by Japanese groups. – Add two 2 -ring detectors: reuse Hi. Res mirrors, phototubes, add new FADC readout. – Add tower detector, infill array. • • Resolve the Hi. Res/AGASA puzzle. Large high-energy aperture: 3200 km 2 ster. Powerful anisotropy engine. Observe the Ankle in stereo. Extend coverage down to 1016. 5 e. V. Perform composition-correlated spectrum measurement. Observe the galactic/extragalactic transition. Resolve astrophysics questions about second knee, 1019. 5 e. V regions.