Experimental observation of the Σ hypernuclei, ΣH and ΣC

The hypernuclei _Σ⁶H and _Σ¹⁶C were observed by the (K⁻, π⁺) reaction on targets of ⁶Li and liquid O, respectively, at 713 MeV/c incident K⁻ momentum. Structure is seen in _Σ⁶H which may be interpreted in terms of particle-hole excitations similar to the previously observed states in _Λ⁶Li. The inablitity to resolve individual Σ hypernuclear levels in _Σ¹⁶C, due in part to the excitation of non-coherent states as a result of the large momentum transfer of about 130 MeV/c, precludes the extraction of the Σ-nucleus spin-orbit potential strength. The Σ-nucleus well depth appears to be 7 to 10 MeV less than that for the Λ.     

Reflection of plane waves from the boundary of a pre-stressed compressible elastic half-space

The effect of pre-stress on the propagation and reflection ofplane waves in an incompressible isotropic elastic half-spacehas been examined recently by the authors (Ogden & Sotiropoulos,1997). In the present paper the corresponding analysis for compressiblematerials is detailed. In the two-dimensional context consideredfor incompressible materials the (homogeneous) plane waves werenecessarily shear waves. By contrast, in the compressible contextpure shear waves can propagate only in specific directions inthe considered principal plane and, in a general direction,a quasi-shear wave may be accompanied by a quasi-longitudinalwave, as is the case in the anisotropic linear theory. The dependenceof the (in-plane) slowness section on the pre-stress (and finitedeformation) and on the choice of constitutive law is elucidated.This information is used to determine the reflection coefficientsfor reflection of either a (quasi-) shear wave or a (quasi-)longitudinal wave from the boundary of the half-space and tocharacterize the different cases which arise depending on thegeometry of the slowness section. The theoretical results are illustrated by numerical calculationsfor the range of possible types of behaviour with referenceforms of strain-energy function and different states of finitedeformation and to the question of stability of the half-space.     

Design and preliminary test results of Daya Bay RPC modules

Resistive Plate Chamber (RPC) modules will be used as one part of the cosmic muon veto system in the Daya Bay reactor neutrino experiment. A total of 189 RPC modules will cover the three water pools in the experiment. To achieve track reconstruction and high efficiency, each module consists of 4 layers, each of which contains two sizes of bare chambers. The placement of bare chambers is reversed in different layers to reduce the overlapping dead areas. The module efficiency and patch efficiency were studied both in simulation and test of the data analysis. 143 modules have been constructed and tested. The preliminary study shows that the module and patch 3 out of 4 layers efficiency reaches about 98%.     

Exotic meson decay to omegapi0pi-

A partial-wave analysis of the mesons from the reaction pi(-)p --> pi(+)pi(-)pi(-)pi(0)pi(0)p has been performed. The data show b(1)pi decay of the spin-exotic states pi(1)(1600) and pi(1)(2000). Three isovector 2(-+) states were seen in the omegarho(-) decay channel. In addition to the well known pi(2)(1670), signals were also observed for pi(2)(1880) and pi(2)(1970).