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

2. 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.

3. 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 50 Mpc. –e + e - pair production: threshold ~ 4x10 17 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!!

4. 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.

5. Best Evidence (cont’d) Second Knee at 10 17.6 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!

6. 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 10 19.5 eV? Six points with chi squared 10. Problem at 10 17.5 eV? The second knee is too weak.

7. Interpretation of Extragalactic Spectrum Pion-production pileup causes the bump at 10 19.5 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?

8. The Problem at 10 17.5 eV Model: –Source density: constant multiplied by (1+z) m. –Power law cuts off at 10 21 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.

9. Cosmology with QSO’s and AGN’s QSO density histograms: Croom et al., Schneider et al. QSO luminosity density, optical Boyle and Terlevich AGN luminosity density, 2-8 keV X-rays. Barger et al. SDSS Lines: (1+z) 3

10. What Do the HiRes Data Say? One Assumption: Assume E 3 J is flat below the second knee.

11. 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 10 16.5 to over 10 20 eV..

12. Galactic Sources are Interesting! Questions about Galactic sources: –What is the maximum energy they produce? –Is there anisotropy at 10 18 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.

13. Observe the Galactic-Extragalactic Transition through Composition Change X max is the variable that discriminates between p and Fe primaries. Fluorescence gives direct observation  best technique. Choose stereo and hybrid: each has x2 better X max 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.

14. Current Status of Composition- correlated Spectrum Measurements Magenta is Fe flux. –10 15 – 10 17 eV from Kascade. –10 17 – 10 19.4 eV from HiRes/MIA, HiRes Stereo.

15. 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 10 19 eV. –Superior experiment for anisotropy studies at high energies.

16. 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 10 20 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.

17. TA Progress (FD)

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

19. TA Time Line

20. 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 10 17 eV; i.e., a tower detector and infill array.

21. Observe the Ankle in Stereo Mode HiRes stereo (12.6 km separation) has rapidly- changing aperture below 10 18.5 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.

22. 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 (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.

23. Lower-energy Limitations HiRes observes elongation above 10 18.0 eV clearly. HiRes looks up to 31 o, can’t see X max for close-by (low energy) events. Makes spectrum measurements difficult below 10 17.5 eV. Composition bias for E < 10 18.0 eV. Before bracketing and Cerenkov cuts

24. 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.

25. 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.

26. Lower E min by order of magnitude. Test tower detector design: MC ~ 2 mo running. –cover 90 o 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.

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

28. 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.)

29. TA/TALE Apertures

30. 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.

31. Shower Footprints

32. 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 km 2 ster. Powerful anisotropy engine. Observe the Ankle in stereo. Extend coverage down to 10 16.5 eV. Perform composition-correlated spectrum measurement. Observe the galactic/extragalactic transition. Resolve astrophysics questions about second knee, 10 19.5 eV regions.