“Above the Kneepcap” Working Group Report

1. “Above the Kneepcap” Working Group Report C. C. H. Jui April 27, 2005

2. General Discussion on Apr.26 • Working Group had a ~1 hr discussion on the following topics: • The desirability of covering multiple spectral features (knee, second knee, ankle, GZK?) with a single technique, if not a single experiment (Akeno 1km2 is cited as an example to be inspired by). • The second knee • Separation of Galactic and Extra-Galactic cosmic rays

3. A Single Technique to Measure Them All • It was pointed out that the Akeno example is not without its challenages: • Ne-to-energy conversion varies with energy. • The systematics of the measurement probably also varies strongly over 4 decades of energy • Composition measurement is especially challenging: • Current Shower Models predict too few muons at higher energies. • Yesterday: example of too many muons in Shower Models

4. Techniques • RHIC results suggest that muon production should be even lower than the Shower Models predict • Forward calorimeters at LHC will be analyzed against air Shower Models • this will help to reduce many of the theoretical systematic uncertainties, including perhaps the muons problem

5. Techniques • It was also pointed out that the Xmax technique has not been cross-calibrated • FLASH thick-target experiment has demonstrated that light yielded follows shower size • Possibility of using RHIC for further thick target studies?

6. Second Knee • Considerable interest expressed concerning the second knee: • Experimental evidence: energy adjustments required

7. Nature of the Second Knee? • Question: What is the Second Knee:? • Several Theoretical Presentations will address whether the Second Knee is a source- or propagation effect • Need to separate out Galactic/Super-Galactic cosmic rays

8. Galactic Cosmic Rays • Recent Hess observation of hard TeV gamma sources and the consistency of their spectral indices suggest that shock acceleration does indeed occur around SNR (at least of electrons) • Can the Upper Limit of this mechanism be determined experimentally from the TeV gamma ray experiments? • Stay tuned for Rowell Presentation

9. Galactic Cosmic Rays • Several Presentations on the topic of the origin of the galactic cosmic rays • The separation of galactic/super-galactic components will likely depend on composition-tagged anisotropy studies • Some reservation expressed about the suitability of fluorescence detectors for this given the variable seasonal exposure • Not clear how well a ground array can measure the composition given the uncertainty of muon yield.