The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search for weakly interacting massive particles (WIMPs) via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. CDMS data, accounting for the neutron background, give limits on the spin-independent WIMP-nucleon elastic-scattering cross section that exclude unexplored parameter space above 10 GeV͞c 2 WIMP mass and, at .75% C.L., the entire 3s allowed region for the WIMP signal reported by the DAMA experiment. Extensive evidence indicates that a large fraction of the matter in the universe is nonluminous, nonbaryonic, and "cold"-nonrelativistic at the time matter began to dominate the energy density of the universe [1][2][3]. Weakly interacting massive particles (WIMPs) are an excellent candidate for nonbaryonic, cold dark matter [2,4]. Minimal supersymmetry provides a natural WIMP candidate in the form of the lightest superpartner, with a typical mass M ϳ 100 GeV͞c 2 [5][6][7][8]. WIMPs are expected to have collapsed into a roughly isothermal, spherical halo within which the visible portion of our galaxy resides. WIMPs scatter off nuclei via the weak interaction, potentially allowing their direct detection [9,10]. The expected spectrum of recoil energies (energy given to the recoiling nucleus during the interaction) is exponential with a characteristic energy of a few to tens of keV [11]. The expected event rate is model dependent, but is generically 1 kg 21 d 21 or lower [10].This Letter reports new exclusion limits on the spinindependent WIMP-nucleon elastic-scattering cross section by the Cryogenic Dark Matter Search (CDMS). The rate of rare WIMP-nucleon interactions is constrained by extended exposure of detectors that discriminate WIMPinduced nuclear recoils from electron recoils caused by interactions of background particles [12,13].The ionization yield Y (the ratio of ionization production to recoil energy in a semiconductor) of a particle interaction differs greatly for nuclear and electron recoils. CDMS detectors measure phonon and electron-hole pair production to determine recoil energy and ionization yield for each event. The data discussed here were obtained with two types of detectors, Berkeley Large Ionization-and Phonon-mediated (BLIP) and Z-sensitive Ionization-and Phonon-mediated (ZIP) detectors [12][13][14][15][16][17][18]. For both types, the drift field for the ionization measurement is supplied by radially segmented electrodes on the faces of the disk-shaped crystals [19]. In BLIP detectors, phonon production is determined from the detector's calorimetric temperature change. In ZIP detectors, athermal phonons are collected to determine phonon production and xy position. Detector performance is discussed in detail elsewhere [14,[16][17][18][19][20].Photons cause most bulk electron recoils, while lowenergy electrons incident on the detector surfaces cause low-Y electron recoils in a thin surface layer ("surface events"). Neutron, photon, and electron sources ar...
The Gravity Probe B mission provided two new quantitative tests of Einstein’s theory of gravity, general relativity (GR), by cryogenic gyroscopes in Earth’s orbit. Data from four gyroscopes gave a geodetic drift-rate of −6601.8 ± 18.3 marc-s yr−1 and a frame-dragging of −37.2 ± 7.2 marc-s yr−1, to be compared with GR predictions of −6606.1 and −39.2 marc-s yr−1 (1 marc-s = 4.848 × 10−9 radians). The present paper introduces the science, engineering, data analysis, and heritage of Gravity Probe B, detailed in the accompanying 20 CQG papers.
In this paper, we discuss the timing system design and tests for the NASA/Stanford Gravity Probe B (GP-B) relativity mission. The primary clock of GP-B, called the 16fo clock, was an oven-controlled crystal oscillator that produced a 16.368 MHz master frequency. The 16fo clock and the 10 Hz data strobe, which was divided down from the 16fo clock, provided clock signals to all GP-B components and synchronized the data collection, transmission, and processing. The sampled data of science signals were stamped with the vehicle time, a counter of the 10 Hz data strobe. The time latency between the time of data sampling and the stamped vehicle time was compensated in the ground data processing. Two redundant global positioning system receivers onboard the GP-B satellite supplied an external reference for time transfer between the vehicle time and coordinated universal time (UTC), and the time conversion was established in the ground preprocessing of the telemetry timing data. The space flight operation showed that the error of time conversion between the vehicle time and UTC was less than 2 μs. Considering that the constant timing offsets were compensated in the ground processing of the GP-B science data, the time latency between the effective sampling time of GP-B science signals and the stamped vehicle time was verified to within 1 ms in the ground tests.
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