5,786 research outputs found
Design considerations for high-power VHF radar transceivers: Phase matching long coaxial cables using a cable radar
The Poker Flat 49.92-MHz MST radar uses 64 phase-controlled transmitters in individual shelters distributed throughout the antenna array. Phase control is accomplished by sampling the transmitted pulse at the directional coupler of each transmitter and sending the sample pulse back to a phase-control unit. This method requires phase matching 64 long (256 meter) coaxial cables (RG-213) to within several electrical degrees. Tests with a time domain reflectometer showed that attenuation of high frequency components in the long RG-213 cable rounded the leading edge of the reflected pulse so that the cables could only be measured to within 50 cm (about 45 deg at 49.92 MHz). Another measurement technique using a vector voltmeter to compare forward and reflected phase required a directional coupler with unattainable directivity. Several other techniques were also found lacking, primarily because of loss in the long RG-213 cables. At this point it was realized that what was needed was a simple version of the phase-coherent clear-air radar, i.e., a cable radar. The design and operation of this cable are described
Design considerations for high-power VHF radar transceivers: The Poker Flat MST radar phase control system
Sixty-four separate 50-kW peak-power transmitters are distributed throughout the 200 x 200 meter Poker Flat MST radar antenna array. The relative phase of each transmitter is automatically controlled by a 64-channel unit located in the main building at the edge of the antenna. The phase control unit is described. In operation the RF pulse from a transmitter coupler is power divided and compared with the phase reference in a mixer. The mixer output is low-pass filtered and sampled near the center of the resulting video pulse by an amplifying sample-and-hold integrated circuit. Phase control is effected by maintaining the mixer output pulse near zero volts by amplifying the sample-and-hold output which then drives the voltage-controlled phase shifter in the direction to null the mixer output. The voltage-controlled shifter achieves over 360 deg phase shift in the range from 0.7 to 24 volts. When the voltage into the shifter tracks to either voltage limit the wrap-around control resets the voltage so that the shifter is always operating within its control range
Studies of the decays D^0 \rightarrow K_S^0K^-\pi^+ and D^0 \rightarrow K_S^0K^+\pi^-
The first measurements of the coherence factor R_{K_S^0K\pi} and the average
strong--phase difference \delta^{K_S^0K\pi} in D^0 \to K_S^0 K^\mp\pi^\pm
decays are reported. These parameters can be used to improve the determination
of the unitary triangle angle \gamma\ in B^- \rightarrow
decays, where is either a D^0 or a D^0-bar meson decaying to
the same final state, and also in studies of charm mixing. The measurements of
the coherence factor and strong-phase difference are made using
quantum-correlated, fully-reconstructed D^0D^0-bar pairs produced in e^+e^-
collisions at the \psi(3770) resonance. The measured values are R_{K_S^0K\pi} =
0.70 \pm 0.08 and \delta^{K_S^0K\pi} = (0.1 \pm 15.7) for an
unrestricted kinematic region and R_{K*K} = 0.94 \pm 0.12 and \delta^{K*K} =
(-16.6 \pm 18.4) for a region where the combined K_S^0 \pi^\pm
invariant mass is within 100 MeV/c^2 of the K^{*}(892)^\pm mass. These results
indicate a significant level of coherence in the decay. In addition, isobar
models are presented for the two decays, which show the dominance of the
K^*(892)^\pm resonance. The branching ratio {B}(D^0 \rightarrow
K_S^0K^+\pi^-)/{B}(D^0 \rightarrow K_S^0K^-\pi^+) is determined to be 0.592 \pm
0.044 (stat.) \pm 0.018 (syst.), which is more precise than previous
measurements.Comment: 38 pages. Version 3 updated to include the erratum information.
Errors corrected in Eqs (25), (26), 28). Fit results updated accordingly, and
external inputs updated to latest best known values. Typo corrected in Eq(3)-
no other consequence
First Observation of barB0 to D*0 pi+pi+pi-pi- Decays
We report on the observation of B0bar -> D*0 pi+ pi+ pi- pi- decays. The
branching ratio is (0.30 +/- 0.07 +/- 0.06)%. Interest in this particular mode
was sparked by Ligeti, Luke and Wise who propose it as a way to check the
validity of factorization tests in B0bar -> D*+ pi+ pi- pi- pi0 decays.Comment: 11 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLNS, Version to appear in Phys. Rev.
Search for a Scalar Bottom Quark with Mass 3.5-4.5 GeV/
We report on a search for a supersymmetric meson with mass
between 3.5 and 4.5 GeV/ using 4.52 of integrated
luminosity produced at GeV, just below the threshold, and collected with the CLEO detector. We find no evidence
for a light scalar bottom quark.Comment: 10 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLN
Study of Charmless Hadronic B Meson Decays to Pseudoscalar-Vector Final States
We report results of searches for charmless hadronic B meson decays to
pseudoscalar(pi^+-,K^+-,Pi^0 or Ks^0)-vector(Rho, K* or Omega) final states.
Using 9.7 million BBbar pairs collected with the CLEO detector, we report first
observation of B^- --> Pi^-Rho^0, B^0 --> Pi^+-Rho^-+ and B^- --> Pi^-Omega,
which are expected to be dominated by hadronic b --> u transitions. The
measured branching fractions are (10.4+3.3-3.4+-2.1)x10^-6,
(27.6+8.4-7.4+-4.2)x10^-6 and (11.3+3.3-2.9+-1.4)x10^-6, respectively.
Branching fraction upper limits are set for all the other decay modes
investigated.Comment: 10 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLN
Observation of New States Decaying into
Using 13.7 fb^{-1} of data recorded by the CLEO detector at CESR, we
investigate the spectrum of charmed baryons which decay into Lambda_c^+ pi^-
pi^+ and are more massive than the Lambda_{c1} baryons. We find evidence for
two new states: one is broad and has an invariant mass roughly 480 MeV above
that of the Lambda_c^+; the other is narrow with an invariant mass of 596 +- 1
+- 2 MeV above the Lambda_c^+ mass. These results are preliminary.Comment: 11 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLN
Rate Measurement of and Constraints on Mixing
We present an observation and rate measurement of the decay D0 -> K+pi-pi0
produced in 9/fb of e+e- collisions near the Upsilon(4S) resonance. The signal
is inconsistent with an upward fluctuation of the background by 4.9 standard
deviations. We measured the rate of D0 -> K+pi-pi0 normalized to the rate of
D0bar -> K+pi-pi0 to be 0.0043 +0.0011 -0.0010 (stat) +/- 0.0007 (syst). This
decay can be produced by doubly-Cabibbo-suppressed decays or by the D0 evolving
into a D0bar through mixing, followed by a Cabibbo-favored decay to K+pi-pi0.
We also found the CP asymmetry A=(8 +25 -22)% to be consistent with zero.Comment: 10 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLN
First Measurement of Gamma(D*+) and Precision Measurement of m_D*+ - m_D0
We present the first measurement of the D*+ width using 9/fb of e+ e- data
collected near the Upsilon(4S) resonance by the CLEO II.V detector. Our method
uses advanced tracking techniques and a reconstruction method that takes
advantage of the small vertical size of the CESR beam spot to measure the
energy release distribution from the D*+ -> D0 pi+ decay. We find Gamma(D*+) =
96 +- 4 (Statistical) +- 22 (Systematic) keV. We also measure the energy
release in the decay and compute Delta m = m(D*+) - m(D0) = 145.412 +- 0.002
(Statistical) +- 0.012 (Systematic) MeV/c^2Comment: 24 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLNS, submitted to PR
A Search for Charmless Decays
We have studied two-body charmless decays of the meson into the final
states , , , , , , and
using only decay modes with charged daughter particles. Using 9.7 million pairs collected with the CLEO detector, we place 90% confidence level
upper limits on the branching fractions, , depending
on final state and polarization.Comment: 8 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLN
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