Lifetime of the Bose Gas with Resonant Interactions

We study the lifetime of a Bose gas at and around unitarity using a Feshbach resonance in lithium~7. At unitarity, we measure the temperature dependence of the three-body decay coefficient $L_{3}$. Our data follow a $L_3 {=} \lambda_{3} / T^{2}$ law with \lambda_{3} = 2.5(3)_{stat}_(6)_{sys} 10^{-20} (\mu K)^2 cm^6 s^{-1} and are in good agreement with our analytical result based on the zero-range theory. Varying the scattering length $a$ at fixed temperature, we investigate the crossover between the finite-temperature unitary region and the previously studied regime where $|a|$ is smaller than the thermal wavelength. We find that $L_{3}$ is continuous across resonance, and over the whole $a {<} 0$ range our data quantitatively agree with our calculation

Longitudinal Momentum Fraction X_L for Two High P_t Protons in pp->ppX Reaction

We present an analysis of new data from Experiment E850 at BNL. We have characterized the inclusive cross section near the endpoint for pp exclusive scattering in Hydrogen and in Carbon with incident beam energy of 6 GeV. We select events with a pair of back-to-back hadrons at large transverse momentum. These cross sections are parameterized with a form $\frac{d \sigma}{d X_{L}}$ $\sim(1-X_{L})^{p}$, where ${X_{L}}$ is the ratio of the longitudinal momentum of the observed pair to the total incident beam momentum. Small value of $p$ may suggest that the number of partons participating in the reaction is large and reaction has a strong dependence on the center-of-mass energy. We also discuss nuclear effects observed in our kinematic region.Comment: 4 pages, 2 figures, to be published in Proceedings of CIPANP2000, Quebec, May 22-28, 2000, requires aipproc.sty(included

Telephone conversation impairs sustained visual attention via a central bottleneck

Recent research has shown that holding telephone conversations disrupts one's driving ability. We asked whether this effect could be attributed to a visual attention impairment. In Experiment 1, participants conversed on a telephone or listened to a narrative while engaged in multiple object tracking (MOT), a task requiring sustained visual attention. We found that MOT was disrupted in the telephone conversation condition, relative to single-task MOT performance, but that listening to a narrative had no effect. In Experiment 2, we asked which component of conversation might be interfering with MOT performance. We replicated the conversation and single-task conditions of Experiment 1 and added two conditions in which participants heard a sequence of words over a telephone. In the shadowing condition, participants simply repeated each word in the sequence. In the generation condition, participants were asked to generate a new word based on each word in the sequence. Word generation interfered with MOT performance, but shadowing did not. The data indicate that telephone conversation disrupts attention at a central stage, the act of generating verbal stimuli, rather than at a peripheral stage, such as listening or speaking

Metastability in spin polarised Fermi gases and quasiparticle decays

We investigate the metastability associated with the first order transition from normal to superfluid phases in the phase diagram of two-component polarised Fermi gases.We begin by detailing the dominant decay processes of single quasiparticles.Having determined the momentum thresholds of each process and calculated their rates, we apply this understanding to a Fermi sea of polarons by linking its metastability to the stability of individual polarons, and predicting a region of metastability for the normal partially polarised phase. In the limit of a single impurity, this region extends from the interaction strength at which a polarised phase of molecules becomes the groundstate, to the one at which the single quasiparticle groundstate changes character from polaronic to molecular. Our argument in terms of a Fermi sea of polarons naturally suggests their use as an experimental probe. We propose experiments to observe the threshold of the predicted region of metastability, the interaction strength at which the quasiparticle groundstate changes character, and the decay rate of polarons

Energy Dependence of Nuclear Transparency in C(p,2p) Scattering

The transparency of carbon for (p,2p) quasi-elastic events was measured at beam energies ranging from 6 to 14.5 GeV at 90 degrees c.m. The four momentum transfer squared q*q ranged from 4.8 to 16.9 (GeV/c)**2. We present the observed energy dependence of the ratio of the carbon to hydrogen cross sections. We also apply a model for the nuclear momentum distribution of carbon to normalize this transparency ratio. We find a sharp rise in transparency as the beam energy is increased to 9 GeV and a reduction to approximately the Glauber level at higher energies.Comment: 4 pages, 2figures, submitted to PR

Measurement of quasi-elastic 12C(p,2p) scattering at high momentum transfer

We measured the high-momentum quasi-elastic 12C(p,2p) reaction (at center of mass angle near 90 degrees) for 6 and 7.5 GeV/c incident protons. The three-momentum components of both final state protons were measured and the missing energy and momentum of the target proton in the nucleus were determined. The validity of the quasi-elastic picture was verified up to Fermi momenta of about 450 MeV/c, where it might be questionable. Transverse and longitudinal Fermi momentum distributions of the target proton were measured and compared to independent particle models which do not reproduce the large momentum tails. We also observed that the transverse Fermi distribution gets wider as the longitudinal component increases in the beam direction, in contrast to a simple Fermi gas model.Comment: 4 pages including 3 figure