Aspen 4/28/05 Physics at the End of the Galactic Cosmic Ray Spectrum - “Below the Knee” Working Group

“Below the Knee” Working Group Report - Day 3Binns, Hörandel, Mitchell, Moskalenko, Müller, Streitmatter, Takita, Vacchi, Yodh, et al.

Issues directly bearing on measurements to knee energies:1. Combined spectral measurement approaching 1015 eV

• Calorimeter at high mountain altitude measures surviving protons• TRD balloon instrument measures heavy composition

2. L/M measurements - Propagation• B/C to highest possible energy to determine energy dependent pathlength.• TRD on balloon or in space

3. High Energy electrons above ~1 TeV • Identify local sources• Local diffusion coefficient to high energy• Calorimeters or synchrotron X-ray detectors

Note: Should not abandon high precision space instrument too quickly. Years invested in study. TRD/Calorimeter (ACCESS) could achieve listed goals.

Aspen 4/28/05 Physics at the End of the Galactic Cosmic Ray Spectrum - “Below the Knee” Working Group

Technical Issues:How realistic are proposed techniques? - 1

High mountain altitude, large-area proton calorimeter:– Measures unaccompanied (uninteracted primary) protons– Area required ~100 m2 (depends on run time)– To veto showers, requires large “carpet” of veto counters and/or Cherenkov

telescope with extremely large FOV.• Even non-interacting events will have accompanying electrons• Cherenkov telescope would limit efficiency by requiring night operation

– Absolute flux (not slope) requires ~3% p/air cross-sections for 15% accuracy.

• How well can instrument itself measure cross-sections using inclined measurements?

• Mainly issue of statistics.• May drive area/run time.

– What fraction of interacting events mimic non-interacting primaries?

Aspen 4/28/05 Physics at the End of the Galactic Cosmic Ray Spectrum - “Below the Knee” Working Group

Technical Issues:How realistic are proposed techniques? - 2

Large-area TRD balloon instrument– Measures to ~105 for ~Z≥5. – Easily calibrated in electron beam.– Area required to reach 1015 eV in 10 LDB flights ~30 m2

• Weight?• Launch logistics

– 10 LDB flights may require 15-20 years.– What is energy limit of B/C ratio measurement due to atmospheric

secondaries?• Atmosphere above balloon comparable to galactic grammage traversed at ~1 TeV

(check)

– Event by event energy resolution?

TRD space instrument– Limitation to B/C only B statistics and energy resolution

Aspen 4/28/05 Physics at the End of the Galactic Cosmic Ray Spectrum - “Below the Knee” Working Group

Techniques - High Energy Electrons

• Measurements must extend well beyond ~1 TeV.• Need ~1.5m2 sr yr exposure.• Calorimeters:

– PAMELA to fly October 2005• Si/W imaging calorimeter with self-trigger mode - 600 cm2sr. • Measurements to ~2 TeV

– Other calorimeters - e.g. Japanese proposal for JEM flight.

• Synchrotron radiation in magnetic field of Earth– Detect fan of hard X-radiation– Does not need to directly detect incident electron - large collecting power– CREST (Cosmic Ray Electron Synchrotron Telescope)

• Balloon instrument. • Full instrument ~4m2 measures >2 TeV in single ULDB flight.

– AMS?

Aspen 4/28/05 Physics at the End of the Galactic Cosmic Ray Spectrum - “Below the Knee” Working Group

Complementary Measurements

• Precision proton and elemental spectra from magnetic-rigidity spectrometers (BESS-TeV, AMS?).– Provide precise reference up to about 1 TeV.

• Air Cherenkov measurements down to ~1014 eV.– Primary pulse gives charge, shower gives energy– May be able to connect to highest energy direct measurements.

• Positrons and antiprotons.– Secondaries from protons probe propagation– Antiprotons propagate over great distances (small cross-section)

• Trace average proton spectrum• In combination with measured (local) proton spectrum can indicate

local fluctuations• Simultaneous measurement by magnet spectrometers (e.g.

BESS/BESS-Polar, HEAT, CAPRICE, IMAX, PAMELA, AMS?)

– No existing techniques to measure antiprotons above ~50 GeV

Aspen 4/28/05 Physics at the End of the Galactic Cosmic Ray Spectrum - “Below the Knee” Working Group

“Classical” Cosmic Ray Measurements

• Very important for understanding of knee even if measured at lower energy– Indicate sources– Probe propagation– Important clues to stellar environments in which CR originate

• Radioactive isotopes– Confinement time– Time to acceleration– Matter distribution in path

• Secondary/primary ratios - pathlength distribution• Ultra-heavies - probe source, e.g. sample of OB association

material/WR stars• Others already mentioned (e+, p-bar, element spectra)