10,004 research outputs found
Single Z Production at the Tevatron
The production of single bosons has been studied at Fermilab's Tevatron
by the CDF and D0 collaborations. Measurements include the weak mixing angle,
vector and axial-vector couplings between bosons and light quarks, and
angular coefficients in electronic decays which are sensitive to the spin of
the gluon. The collaborations have looked for and indication of new physics
above the mass scale that can be directly produced at the Tevatron by studying
the interference between and photon propagators. All measurements are
consistent with Standard Model expectations.Comment: XLVIIth Rencontres de Moriond Electroweak conference paper; 5 pages,
5 figure
A multi-photon magneto-optical trap
We demonstrate a Magneto-Optical Trap (MOT) configuration which employs
optical forces due to light scattering between electronically excited states of
the atom. With the standard MOT laser beams propagating along the {\it x}- and
{\it y}- directions, the laser beams along the {\it z}-direction are at a
different wavelength that couples two sets of {\it excited} states. We
demonstrate efficient cooling and trapping of cesium atoms in a vapor cell and
sub-Doppler cooling on both the red and blue sides of the two-photon resonance.
The technique demonstrated in this work may have applications in
background-free detection of trapped atoms, and in assisting laser-cooling and
trapping of certain atomic species that require cooling lasers at inconvenient
wavelengths.Comment: 10 pages, 5 figure
Measurements of noise in Josephson-effect mixers
We present new heterodyne receiver results obtained at 100 GHz using resistively-shunted Nb and NbN tunnel junctions. In addition, we have carried out accurate measurements of the available noise power of these devices at the L-band (1.5 GHz) IF frequency. Both the heterodyne and the output noise measurements show that the noise of these devices can be a factor of five or more higher than that predicted by the simple current-biased RSJ model. The noise approaches the appropriate thermal or thermal and shot noise limits for bias voltages where the nonlinearity is not strong (i.e., V>ICRN), but as expected from the RSJ model, can be significantly higher at the low voltages where the mixers are typically biased. The bias voltage dependence of the noise shows structure which is associated with resonances in the RF embedding circuit. Surprisingly, we find that changes in the high-frequency (100 GHz) impedance presented to the junction can dramatically affect the magnitude and voltage dependence of the low-frequency (1.5 GHz) noise. This emphasizes the necessity of very closely matching the junction to free space over a wide frequency range
The Alignment of the Magnetic Field and Collimated Outflows in Star-forming Regions: the Case of NGC 2071
The magnetic field is believed to play a crucial role in the process of star
formation. From the support it provides during the initial collapse of
molecular clouds to the creation of strong collimated jets responsible for
large mass losses, current theories predict its importance in many different
stages during the formation of stars. Here we report on observational evidence
which tests one aspect that can be inferred from these theories: the alignment
between the local magnetic field and collimated bipolar outflows in such
environments. There is good evidence of an alignment in the case of NGC 2071.Comment: 11 pages, 4 figure
- …