“Above the Kneepcap” Working Group Report

C. C. H. Jui

April 27, 2005

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

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

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

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?

Second Knee

• Considerable interest expressed concerning the second knee:

• Experimental evidence: energy adjustments required

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

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

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.