Cloud-Chamber Study of the Production and Decay of Strange Particles

Out of 1242 decay events observed in a magnetic cloud chamber array triggered on penetrating showers, a total of 54 associated V-particle pairs has been obtained. All the associations observed are consistent with the "strangeness" selection rules. A statistical analysis of the numbers of double and single events has been used to obtain rough estimates of the fractions of neutral K particles and neutral hyperons which decay by "invisible" modes, and of the relative frequencies of occurrence of various production processes. The main uncertainties in the resulting values are discussed in detail

Cloud-Chamber Investigation of Charged V Particles

An analysis of 84 charged V events obtained during two years of operation of a vertical magnetic cloud-chamber array is presented. The particular features of interest which are studied in detail are the distribution of P*, the momentum of the charged secondary in the rest system of the primary, and the possible existence of a component of short lifetime (i.e., τ<5×10^-10 sec). The P* distribution from 19 slow, accurately measurable positive events is shown to imply that the large majority of these events arise from one or more two-body decays from primaries of mass approximately equal to that of the τ meson. One case turns out to be inconsistent with this interpretation, and is presumed to represent a three-body decay. The P* distribution from 6 slow, accurately measurable negative events is consistent with a single two-body decay having a P* value of about 200 Mev/c. This suggests the existence of a negative counterpart to the well-known θ0 particle, though the statistics are much too poor to permit any strong conclusion. The lifetime analysis provides strong evidence for the existence of a negative component of lifetime equal to or less than (1.3±0.6)×10^-10 sec. The transverse momentum distribution for these short-lived events is shown to suggest a two-body decay with a P* value of 201±12 Mev/c

Linear Air Trough

The construction and operation of a linear air trough, a device for floating small rectangular blocks (called gliders) on an air film, is described. The apparatus is useful for demonstrations and laboratory study of one-dimensional particle mechanics. The very small friction that is present is due to the viscosity of the air film, and causes the speed of a glider to decay with a time constant of the order of a few hundred seconds. A type of bumper has been designed which yields a coefficient of restitution greater than 0.99. Ten of these air troughs have been used in a student laboratory for a year, and have proved quite successful in experiments involving Newton's laws, collisions, damped harmonic motion, and motion on an incline

Cloud Chamber Investigation of Anomalous θ^0 Particles

Eighteen anomalous θ^0, (θ^0_(anom)), decay events observed in the California Institute of Technology magnet cloud chambers have been analyzed. Many of these decays are dynamically inconsistent with the τ^0→π^++π^−+π^0 scheme, but most are consistent with the decay processes: θ^0_(anom)→π^++π^−+γ, π^±+μ^∓+ν, and π^±+e^∓+ν. However, at least one event is inconsistent with each decay scheme. From the locations of the decays in the cloud chamber, the lifetime is found to be significantly longer than that of the normal θ^0 particle, called here the θ^0_(π2) particle. Other differences in the behavior of the θ0anom and θ^0_(π2) particles were also observed in the (a) momentum distributions, (b) origin locations, (c) relative numbers of θ^0_(anom) and θ^0_(π2) particles traveling upward, and (d) the types of V particles produced in association with the θ^0_(anom) and θ^0_(π2). It is concluded that not all the θ^0_(anom) decays can result from alternate decay modes of the θ^0_(π2). Moreover, many decays can be neither τ^0 decays nor alternate decays of the θ^0_(π2). The characteristics of the θ^0_2 particle proposed by Gell-Mann and Pais are consistent with those of the θ^0_(anom) particle, with the possible exception of the observed types of associations. An estimate was made of the relative number of θ^0_(anom) to θ^0_(π2) particles observed to decay in the cloud chamber. If all θ^0_(anom) decays are assumed to arise from decays of the θ^0_2 particle, then a lower limit for the θ^0_2 lifetime is found to be about 10^(−9) sec

Pinholes May Mimic Tunneling

Interest in magnetic-tunnel junctions has prompted a re-examination of tunneling measurements through thin insulating films. In any study of metal-insulator-metal trilayers, one tries to eliminate the possibility of pinholes (small areas over which the thickness of the insulator goes to zero so that the upper and lower metals of the trilayer make direct contact). Recently, we have presented experimental evidence that ferromagnet-insulator-normal trilayers that appear from current-voltage plots to be pinhole-free may nonetheless in some cases harbor pinholes. Here, we show how pinholes may arise in a simple but realistic model of film deposition and that purely classical conduction through pinholes may mimic one aspect of tunneling, the exponential decay in current with insulating thickness.Comment: 9 pages, 3 figures, plain TeX; submitted to Journal of Applied Physic

The Geometry of Entanglement Sudden Death

In open quantum systems, entanglement can vanish faster than coherence. This phenomenon is usually called sudden death of entanglement. In this paper sudden death of entanglement is discussed from a geometrical point of view, in the context of two qubits. A classification of possible scenarios is presented, with important known examples classified. Theoretical and experimental construction of other examples is suggested as well as large dimensional and multipartite versions of the effect.Comment: 6 pages, 2 figures, references added, initial paragraph corrected, sectioning adopted, some parts rewritten; accepted by New J. Phy

Phase-transition induced giant negative electrocaloric effect in a lead-free relaxor ferroelectric thin film

The electrocaloric (EC) effect has been widely investigated during the past decade due to the potential applications in commercial solid state refrigeration devices. The positive EC effect in lead-based materials has been significantly enhanced from 12 K to 40 K since it is observed in 2006, but the negative EC effect still stays at a very low level of about −10 K, which limits further enhancement of cooling efficiency, especially when we attempt to combine both negative and positive EC effect in one cooling cycle. Due to the toxicity of lead, lead-free materials are always sought after to replace lead-containing materials. In this study, a giant negative EC effect (maximum ΔT ∼ −42.5 K) comparable to the best positive EC effects reported so far is demonstrated for 0.5(Ba0.8Ca0.2)TiO3–0.5Bi(Mg0.5Ti0.5)O3 lead-free relaxor ferroelectric thin films prepared by using a sol–gel method. An electric-field induced structural phase transition (nanoscale tetragonal and orthorhombic to rhombohedral) along the out-of-plane [111] direction plays a key role in developing the giant negative EC effect. This breakthrough will pave the way for practical applications of next-generation refrigeration devices with high cooling efficiency in one cycle by utilizing and combining both the giant negative and positive EC effects

Λ0-Fragment Decay in a Cloud Chamber

The decay in flight of a heavy nuclear fragment is described. The event is most reasonably interpreted as the decay of a Λ0 particle bound to a He3 nucleus, and is similar to examples previously observed in nuclear emulsions. The lifetime of the excited fragment in this single example is 5.4±0.6×10^-10 sec, and the binding energy of the Λ0 to He3 is probably less than 2 Mev

The Role of Corpus Callosum Development in Functional Connectivity and Cognitive Processing

The corpus callosum is hypothesized to play a fundamental role in integrating information and mediating complex behaviors. Here, we demonstrate that lack of normal callosal development can lead to deficits in functional connectivity that are related to impairments in specific cognitive domains. We examined resting-state functional connectivity in individuals with agenesis of the corpus callosum (AgCC) and matched controls using magnetoencephalographic imaging (MEG-I) of coherence in the alpha (8–12 Hz), beta (12–30 Hz) and gamma (30–55 Hz) bands. Global connectivity (GC) was defined as synchronization between a region and the rest of the brain. In AgCC individuals, alpha band GC was significantly reduced in the dorsolateral pre-frontal (DLPFC), posterior parietal (PPC) and parieto-occipital cortices (PO). No significant differences in GC were seen in either the beta or gamma bands. We also explored the hypothesis that, in AgCC, this regional reduction in functional connectivity is explained primarily by a specific reduction in interhemispheric connectivity. However, our data suggest that reduced connectivity in these regions is driven by faulty coupling in both inter- and intrahemispheric connectivity. We also assessed whether the degree of connectivity correlated with behavioral performance, focusing on cognitive measures known to be impaired in AgCC individuals. Neuropsychological measures of verbal processing speed were significantly correlated with resting-state functional connectivity of the left medial and superior temporal lobe in AgCC participants. Connectivity of DLPFC correlated strongly with performance on the Tower of London in the AgCC cohort. These findings indicate that the abnormal callosal development produces salient but selective (alpha band only) resting-state functional connectivity disruptions that correlate with cognitive impairment. Understanding the relationship between impoverished functional connectivity and cognition is a key step in identifying the neural mechanisms of language and executive dysfunction in common neurodevelopmental and psychiatric disorders where disruptions of callosal development are consistently identified