DISCUSSION GROUP BELOW THE KNEE Tues/4/26/05 – First Meeting Attendance: Folks associated with

1. 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

2. 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

3. 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

4. WHAT Direct Measurements? • IDEALLY, Direct all-element energy spectra • To energy ≈ 1015eV • 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 ≈ 1014 • Simple question of exposure, dictated by mass and time of flight: Subject to statistical quibble, invention of new technique.

5. Remedial Slide on Detector Characteristics • TRD • • Useful for ≈ Z > 5. • Can’t do protons, helium • • Can be pushed to Lorentz factor ≈ 105 • • --> Emax, carbon ≈ 1015 eV • --> Emax, Fe ≈ 5 x 1015 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

6. 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 #)

7. 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

8. 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?

9. Extended discussion of instrumental limitations • To be continued • Electrons, positrons, antiprotons, isotopes and ultraheavies • not mentioned yet, but they will be.