Nahee Park
Visiting researcher at the University of Maryland,<br />Ph.D. student at Ewha Womans University
Measuring the charge of high energy cosmic-ray particlesin the CREAM experiment
The Cosmic Ray Energetics And Mass (CREAM) balloon-borne
experiment is designed for direct measurement of high-energy cosmic-ray
particles. The science goal is to measure the single-element fluxes of
all cosmic-ray nuclei from hydrogen (protons) to iron with energies up
to the "knee," or spectral index change, near 1015 eV, observed in the
all-particle spectrum, The CREAM measurements in the sub-knee energy
region are expected observe a change in the elemental composition, and
perhaps a bend in the proton spectrum, if the knee is related to
rigidity dependent acceleration and propagation mechanisms.
The CREAM instrument is configured with redundant particle
detectors to measure the composition and spectra over the energy range
from ~1011 to ~1015
eV in a series of long-duration balloon flights. The first flight
(CREAM-I) took place in Antarctica from December 2004 - January 2005,
setting a duration record of 42 days. The second flight
(CREAM-II) collected data from December 2005 January 2006 over a
period of 28 days, for a total exposure of 70 days. Particle energy was
measured with a transition radiation detector (TRD) for Z > 3 nuclei
during the first flight and a sampling tungsten/scintillator
calorimeter
for Z ≥ 1 particles during both flights. Particle charge (Z) was
measured with a timing-based charge detector (TCD) and with a pixelated
single-layer silicon charge detector (SCD) for the first flight. In the
second flight, a second layer of silicon sensors was added to improve
further the SCD charge measurement. Flight performance and data
analysis for charge assignment will be presented, mainly for the SCD