+ = Cosmic Ray Composition Stéphane Coutu The Pennsylvania State University 3 rd rd School on Cosmic Rays and Astrophysics Arequipa,, Peru August 28-29, 29, 2008 1/ 30
Outline Cosmic Rays: Origin and Propagation; Composition, Spectrum, Secondary Particle; The CREAM Experiment: Instrument Design, Performance; Antarctic Campaigns 2004, 2005, 2007; First Results; Future Prospects. 2/ 30
The Cosmic Ray Spectrum Cosmic rays: high energy nuclei from H to Fe; 10 9 ev to >10 20 ev. The Knee: Limit to SN shock acceleration? The Ankle: Extragalactic component? >10 12 >10 16 >10 20 12 ev 16 ev ev: : 1 per (km 2 century sr) 20 ev Fluxes rescaled by E 2 ev: : 1 per (m 2 second sr) ev: : 1 per (m 2 year sr) E -2.65 E -3 Knee 1979-96 1979-83 1970s 1980s, 90s 1996-1997-98 1994-96 1990s 1990s 1990s Ankle 3/ 30
Cosmic Rays Production Acceleration (Crab) Propagation Interaction with ISM and fields Escape, Reacceleration, Diffusion δ Production of secondaries Solar Modulation Geomagnetic Cutoff Atmospheric Interactions Works only up to: E max β czebl (~10 15 ev knee? rigidity dependent?) 4/ 30
Direct Composition Near the Knee Under the SN shock acceleration scenario, expect charge-dependent knee, e.g., H spectrum knee at ~10 14 ev. H spectrum H He New Component Fe?? 5/ 30
Cosmic Ray Mass Composition Status Improved direct measurements can provide the foundation for studies at higher energies Indirect evidence highly model dependent Inferred fluxes can vary by factors of 2 or more UHE cosmic rays (Auger) extend a further 3 orders of magnitude in energy Direct measurements Indirect inferred from air showers Direct measurements Indirect inferred from air showers Direct measurements Indirect inferred from air showers p He Fe 6/ 30
Low Energy Cosmic Ray Abundances He and heavier, normalized to Si; CR 0.07 0.28 GeV/amu; CR 1 2 GeV/amu; Solar system abundances; Even-odd effect; He, CNO, NeMgSi,, Fe abundant species. LiBeB,, F, ScTiV not present as end products of stellar nucleosynthesis. Higher CR abundances, produced by spallation. 7/ 30
Direct Composition Measurements CREAM Missions (NASA) Direct composition measurements; Spectrum measurement from 10 12 10 15 ev; Elemental resolution; Antarctic Balloon missions; Redundant energy determination; Target: 200 days Antarctic exposure with a fully active instrument with geometric acceptance 2.2 m 2 sr. E -2.65 E -3 Knee 8/ 30
CREAM 100 TeV Fe nucleus (Cosmic Ray Energetics And Mass) TCD TRD Cherenkov TRD SCD Target Target Calorimeter S0/S1 S2 S3 Command data module 2.2 m 2 sr trigger aperture 9/ 30 71 (1.8 m)
CREAM Collaboration (Cosmic Ray Energetics And Mass) University of Maryland H. S. Ahn,, O. Ganel,, K.C. Kim, M. H. Lee, L. Lutz, A. Malinine,, E. S. Seo,, R. Sina,, J. Wu, Y. S. Yoon, S. Y. Zinn University of Chicago P. Boyle, S. Swordy,, S. Wakely Penn State University T. Anderson, N. B. Conklin, S. Coutu, M. Geske,, S. I. Mognet (B. Koger,, K. Rotz,, M. Stafford) Ohio State University P. Allison, J. J. Beatty,, T. Brandt University of Minnesota J. T. Childers, M. A. DuVernois University of Sienna & INFN, Italy M. G. Bagliesi,, G. Bigongiari,, P. Maestro, P. S. Marrocchesi,, R. Zei Ehwa Womans University, S. Korea J. H. Han, H. J. Hyun, J. A. Jeon,, J. K. Lee, S. W. Nam, I. H. Park, N. H. Park, J. Yang Northern Kentucky University S. Nutter Kent State University S. Minnick Kyungpook National University, S. Korea H. Park NASA Goddard; Grenoble,, France; U. Nacional Autonoma,, Mexico 10 / 30
TCD System Timing Charge Detector (TCD): 8 thin (5 mm) scintillators in 2 layers, 16 fast PMTs; Light pulse amplitude and time structure measured Q measured before albedo from calorimeter, 3-83 8 ns after incident particle; ; provide Z>3 trigger; 11 / 30 Charge accuracy ~0.2e for O, ~0.35e for Fe.
TRD System Plus Cherenkov Transition Radiation Detector (TRD): 512 thin-walled (100 µm) proportional tubes (2 cm diameter) in 16 layers in foam matrix; Filled with Xe(95%)-methane(5%); Hit pattern 3D track with σrms ~ 5 mm (ultimately 2 mm); 12 / 30 de/dx (+TR @ >1 TeV/n) yields E until saturation at γ ~ 20,000; sensitivity to Li and heavier.
SCD System Silicon Charge Detector 26 ladders, each with 7 silicon sensor modules, each with 16 cells ls 2.12 cm 2 ; Charge measurement, resolution ~0.1e; 13 / 30 Segmentation reduces back-scatter impact.
Hodoscope System Plus Graphite Targets 0.46 λ int Hodoscopes 640 2 22 2 mm 2 scintillating fibers arranged in 2 orthogonal planes (exc. S3); HPD readout (bundles of 64 fibers), PMT readout for S3; 14 / 30 Redundant charge measurement, plus trigger and tracking.
Calorimeter System Calorimeter stack 20 W plates, 3.5 mm thick, 1 X 0 ; 20 scintillating fiber layers, 1 cm wide ribbons (Moliere( radius 9 mm), 0.1 mm dia.. fibers; HPD readout (40 HPDs,, 2560 channels); fibers divided into low, mid, high energy 15 / readouts; 30 Tracking, energy measurement Z=1-26, E=~200 GeV-1000 TeV (45% resolution).
CERN Beam Tests TCD Response ~0.2e for O, ~0.35e for Fe Ethafoam In beam fragments 16 / 30 TRD Response vs Simulations
CERN Beam Tests Calorimeter response to electron beams SCD Response to In beam fragments 17 / 30
Overall Flight Configuration 18 / 30
Getting to Antarctica Christchurch McMurdo 19 / 30
Antarctica! 20 / 30
CREAM 2004/05 Flight 21 / 30
CREAM Flights CREAM1: Dec 15, 2004 Jan 26, 2005 3 Antarctic orbits, 42 days! NASA LDB flight duration record (32 days previous)! CREAM2: Dec 16, 2005 Jan 13, 2006 (28 days); CREAM3: Dec 19, 2007 Jan 16, 2008 (28 days); CREAM4: Planned for Dec 2008 flight. Estimated 10 TeV Fe nucleus CREAM1 22 / 30
Detector Performance in Flight 42 day flight; 40 million heavy nuclei; 0.4% atm.. Depth. Trigger Rate (Hz) Number of Triggers Number of Triggers Trigger Rate (Hz) Time since Launch (days) Giant solar flare (Jan 2005)! Solar flux increased by ~ 7000 23 / 30 Time since Launch (days)
ATIC 2000 Charge Distribution Not all corrections or event selection finalized Only indicative of charge resolution; relative intensities not meaningful yet. Preliminary 24 / 30
Energy Distribution Not all corrections or event selection finalized Energy deposited, conversion to total energy under way; Power-law apparent; Calorimeter energy deposit Events well above 100 TeV (0.45 TeV in CoM). TRD energy deposit E > 100 TeV Monte Carlo C, Calorimeter O, Calorimeter Cherenkov 25 / 30
P, He Spectra p Steeper proton source spectrum? High-energy protons depleted due to acceleration limit? Statistics will improve (CREAM1 only here); Better anchor point for higher-energy, energy, indirect studies. He 26 / 30
C, O Spectra Preliminary; arbitrary flux normalization for now; No atmospheric, instrumental corrections yet; Spectral shapes agree with HEAO and CRN data at low energy; CREAM data extend up to >100 TeV. Flux (m 2 s sr GeV) 1 Total Particle Energy (ev) 27 / 30 Total Particle Energy (ev)
Secondary/Primary Ratio Secondary/primary ratio (e.g., B/C) very sensitive to diffusion properties (e.g. diffusion constant δ,, possible reacceleration, etc). CR 0.07 0.28 GeV/amu; CR 1 2 GeV/amu; Solar system abundances; Source: E 2.1? 2.5? B E -2.65 Observed: E (2.1+ (2.1+δ) Knee Li, Be, B not made in stellar nucleosynthesis E -3 28 / 30
Secondary/Primary Ratio Secondary/primary ratio (e.g., B/C) very sensitive to diffusion properties (e.g. diffusion constant δ,, possible reacceleration, etc). Preliminary δ=0.3 CREAM before corrections HEAO (90) Simon (80) Mahel (77) Lezniak (78) Juliusson (74) Caldwell (77) Orth (78) CRN (90) Dwyer (87) δ=0.85 CREAM after inst. and atm. corrections δ ~ 0.6 δ ~ 0.6 29 / 51 29 / 30
Conclusions World s s largest set of high-energy, direct cosmic-ray measurements; unprecedented particle ID; Systems would have functioned well for >100 days (ULDB); Energy spectra of H, He, C, O up to ~200 TeV (eventually 900 TeV); He spectrum harder than H above 10 TeV? (first hint of accelerator limit on p s?); B/C measurements up to ~400 GeV/n favor δ~0.6 cosmic-ray source spectrum ~E 2.1 ; in-line with supernova shock acceleration models. 30 / 30