University of Maryland
Atlantic Building, Room 2400 4:30 PM Monday, November 6, 2006
Coffee, Tea & Snacks 4:15-4:30 PM

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