Stephen Anthony Minnick

New measurement of the cosmic-ray positron fraction from 5 to 15 GeV

We present a new measurement of the cosmic-ray positron fraction at energies between 5 and 15 GeV with the balloon-borne HEAT-pbar instrument in the spring of 2000. The data presented here are compatible with our previous measurements, obtained with a different instrument. The combined data from the three HEAT flights indicate a small positron flux of nonstandard origin above 5 GeV. We compare the new measurement with earlier data obtained with the HEAT-e(+/-) instrument, during the opposite epoch of the solar cycle, and conclude that our measurements do not support predictions of charge sign dependent solar modulation of the positron abundance at 5 GeV.

Measurement of the Cosmic-Ray Antiproton-to-Proton Abundance Ratio between 4 and 50 GeV

We present a new measurement of the antiproton-to-proton abundance ratio, pbar/p, in the cosmic radiation. The HEAT-pbar instrument, a balloon borne magnet spectrometer with precise rigidity and multiple energy loss measurement capability, was flown successfully in Spring 2000, at an average atmospheric depth of 7.2 g/cm(2). A total of 71 antiprotons were identified above the vertical geomagnetic cutoff rigidity of 4.2 GV. The highest measured proton energy was 81 GeV. We find that the pbar/p abundance ratio agrees with that expected from a purely secondary origin of antiprotons produced by primary protons with a standard soft energy spectrum.

Performance of a Dual Layer Silicon Charge Detector During CREAM Balloon Flight

The balloon-borne cosmic-ray experiment CREAM (Cosmic Ray Energetics And Mass) has completed two flights in Antarctica, with a combined duration of 70 days. One of the detectors in the payload is the SCD (silicon charge detector) that measures the charge of high energy cosmic rays. The SCD was assembled with silicon sensors. A sensor is a 4 × 4 array of DC-coupled PIN diode pixels with the total active area of 21 × 16 mm2. The SCD used during the first flight (December 2004-January 2005) was a single layer device, then upgraded to a dual layer device for the second flight (December 2005-January 2006), covering the total sensitive area of 779 × 795 mm2. Flight data demonstrated that adding a second layer improved SCD performance, showing excellent particle charge resolution. With a total dissipation of 136 W for the dual layer system, special care was needed in designing thermal paths to keep the detector temperature within its operational range. As a consequence, flight temperatures of the SCD, even at diurnal maximum were kept below 38°C. The SCD mechanical structure was designed to minimize the possibility of damage to the sensors and electronics from the impacts of parachute deployment and landing. The detector was recovered successfully following the flight and is being refurbished for the next flight in 2007. Details of construction, operation, and performance are presented for the dual-layered SCD flown for the second CREAM flight.

COSMIC RAY ENERGETICS AND MASS (CREAM): CALIBRATING A COSMIC RAY CALORIMETER

CREAM is slated to fly as the first NASA Ultra Long Duration Balloon (ULDB) payload in late 2003. On this 60-plus-day flight CREAM is expected to collect more direct high-energy cosmic ray events than the current world total. With three such flights CREAM is expected to have a proton energy reach above 5x1Ol4 eV, probing near 100 TeV for the predicted kink in the cosmic-ray proton spectrum. With a Transition Radiation Detector (TRD) above a sampling tungsten/scintillator calorimeter, an in-flight cross-calibration of the absolute energy scale becomes possible with heavy ions. We report on results from a 2001 beam test of the calorimeter in an SPS beam at the European High Energy Physics lab (CERN) and on the planned in-flight calibration.

New measurement of the altitude dependence of the atmospheric muon intensity

We present a new measurement of atmospheric muons made during an ascent of the High Energy Antimatter Telescope balloon experiment. The muon charge ratio {mu}{sup +}/{mu}{sup -} as a function of atmospheric depth in the momentum interval 0.3-0.9 GeV/c is presented. The differential {mu}{sup -} intensities in the 0.3-50 GeV/c range and for atmospheric depths between 4-960 g/cm{sup 2} are also presented. We compare these results with other measurements and model predictions. We find that our charge ratio is {approx}1.1 for all atmospheric depths and is consistent, within errors, with other measurements and the model predictions. We find that our measured {mu}{sup -} intensities are also consistent with other measurements, and with the model predictions, except at shallow atmospheric depths.