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

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•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.

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 ≈ 105

• --> Emax, carbon ≈ 1015 eV•--> Emax, Fe ≈ 5 x 1015 eV

• “Light” --> large geometry factorCalorimeter

• 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.