Aspen Galactic CR Workshop DISCUSSION GROUP BELOW THE KNEE Tues/4/26/05 – First Meeting Attendance: Folks associated with ground arrays balloon measurement (active and passive) space-based measurements R. Streitmatter

Aspen Galactic CR Workshop Discussion centered on What measurements would be most useful? What techniques would be most appropriate? What modalities (balloon or space) are right for which measurements? Most useful to which end? UNDERSTANDING THE KNEE Dominant, obvious feature in the all-particle spectrum Presumably carries with it broader understanding of CR

Aspen Galactic CR Workshop DIRECT MEASUREMENT Direct measurements to understand knee from data Direct measurements to help EAS people attain coherence e.g. KASCADE, Tibet Balloon measurements attain coherence, e.g. RUNJOB. JACEE

Aspen Galactic CR Workshop WHAT Direct Measurements? IDEALLY, Direct all-element energy spectra To energy ≈ eV Include Observable (?) bend in (at least) proton spectrum B/C ratios to “exhaustion” NOT REALISTIC FACTOID: In the foreseeable future (≈ 20 years) NO balloon measurements or space-based measurements are going to be able to observe the bend in the proton spectrum above ≈ Simple question of exposure, dictated by mass and time of flight: Subject to statistical quibble, invention of new technique.

Aspen Galactic CR Workshop Remedial Slide on Detector Characteristics TRD Useful for ≈ Z > 5. Can’t do protons, helium Can be pushed to Lorentz factor ≈ > Emax, carbon ≈ eV --> Emax, Fe ≈ 5 x eV “Light” --> large geometry factor Calorimeter Can measure Z > 1, i.e. protons, helium, iron “Heavy” --> lesser geometry factor Can’t do total absorption, --> “thin calorimeters” Question of interaction physics change at higher energy Need for calibration and simulation of response

Aspen Galactic CR Workshop So what (direct) measurements are both useful and can be done? (1) B/C Can be done by TRD or Cal, but TRD will have, for given mass, ≈ 5-10 x exposure Best done in space with no atmospheric overburden At what energy does atmospheric background overwhelm a balloon measurement? -- where errors in corrections exceed signal. (Check #)

Aspen Galactic CR Workshop So what (direct) measurements are both useful and can be done? (2) Measure individual element spectra to as high energy as feasible Provide composition “foundation” for EAS work What is minimum requirement of EAS folks “Everything helps” : We need a better answer

Aspen Galactic CR Workshop So what (direct) measurements are both useful and can be done? (2)-continued Would it make sense to Measure “lights” and “heavies” with entirely separate experiments? Measure heavies and all-particle, obtain lights by subtraction?

Aspen Galactic CR Workshop Extended discussion of instrumental limitations To be continued Electrons, positrons, antiprotons, isotopes and ultraheavies not mentioned yet, but they will be.