X(1835): A Natural Candidate of η′\eta^\prime's Second Radial Excitation

Recently BES collaboration observed one interesting resonance X(1835). We point out that its mass, total width, production rate and decay pattern favor its assignment as the second radial excitation of $\eta^\prime$ meson very naturally

Field-induced structure transformation in electrorheological solids

We have computed the local electric field in a body-centered tetragonal (BCT) lattice of point dipoles via the Ewald-Kornfeld formulation, in an attempt to examine the effects of a structure transformation on the local field strength. For the ground state of an electrorheological solid of hard spheres, we identified a novel structure transformation from the BCT to the face-centered cubic (FCC) lattices by changing the uniaxial lattice constant c under the hard sphere constraint. In contrast to the previous results, the local field exhibits a non-monotonic transition from BCT to FCC. As c increases from the BCT ground state, the local field initially decreases rapidly towards the isotropic value at the body-centered cubic lattice, decreases further, reaching a minimum value and increases, passing through the isotropic value again at an intermediate lattice, reaches a maximum value and finally decreases to the FCC value. An experimental realization of the structure transformation is suggested. Moreover, the change in the local field can lead to a generalized Clausius-Mossotti equation for the BCT lattices.Comment: Submitted to Phys. Rev.

Effects Of A Borehole Environment And Residual Hydrocarbon On Stoneley Wave Amplitude And Reflectivity

In recent years, borehole Stoneley wave amplitude and reflectivity have been used for estimating formation permeability based on the strong correlation between Stoneley wave attenuation, reflectivity and formation fluid conductivity. There are other factors, however, that may cause substantial Stoneley attenuation and reflection in a borehole environment. To make better use of Stoneley measurements for formation permeability estimation, it is desirable to identify and quantify those causes of Stoneley attenuation and reflection that do not directly result from formation permeability. In this study, a simplified Biot-Rosenbaum model developed by Tang et at. (1991) is adopted to systematically model Stoneley attenuation and reflection in various borehole environments and formation configurations. By changing pore fluid, formation porosity, lithology, bed boundaries and thickness in the modeling, the sensitivity of Stoneley wave propagation to these conditions are quantitatively assessed. It is found that the presence of a light hydrocarbon in the formation, especially a natural gas residual in the immediate vicinity of the borehole wall, even with only 5% contained in pore fluid, may also cause substantial Stoneley attenuation and reflection. This phenomenon, on the other hand, can be used to evaluate a nonfractured, low permeability gas reservoir when combined with shear wave velocity data. For the full gas-saturated zone, Stoneley wave reflection may be observed even when the permeability is as low as a few milliDarcies. Compared to the effects of pore fluid, the effects due to lithology contrasts at the boundaries and the changes of nonfracture porosity are insignificant in the cases studied here. For a residual gas-bearing zone of moderate permeability, Stoneley wave attenuation and reflection may be observed if the zone is thicker than 0.5 meter.Massachusetts Institute of Technology. Borehole Acoustics and Logging ConsortiumERL/nCUBE Geophysical Center for Parallel ProcessingUnited States. Dept. of Energy (Contract DE-FG02-86ER13636

Probing the electron-phonon coupling in ozone-doped graphene by Raman spectroscopy

We have investigated the effects of ozone treatment on graphene by Raman scattering. Sequential ozone short-exposure cycles resulted in increasing the $p$ doping levels as inferred from the blue shift of the 2$D$ and $G$ peak frequencies, without introducing significant disorder. The two-phonon 2$D$ and 2$D'$ Raman peak intensities show a significant decrease, while, on the contrary, the one-phonon G Raman peak intensity remains constant for the whole exposure process. The former reflects the dynamics of the photoexcited electrons (holes) and, specifically, the increase of the electron-electron scattering rate with doping. From the ratio of 2$D$ to 2$D$ intensities, which remains constant with doping, we could extract the ratio of electron-phonon coupling parameters. This ratio is found independent on the number of layers up to ten layers. Moreover, the rate of decrease of 2$D$ and 2$D'$ intensities with doping was found to slowdown inversely proportional to the number of graphene layers, revealing the increase of the electron-electron collision probability

Catastrophic Photo-z Errors and the Dark Energy Parameter Estimates with Cosmic Shear

We study the impact of catastrophic errors occurring in the photometric redshifts of galaxies on cosmological parameter estimates with cosmic shear tomography. We consider a fiducial survey with 9-filter set and perform photo-z measurement simulations. It is found that a fraction of 1% galaxies at z_{spec}~0.4 is misidentified to be at z_{phot}~3.5. We then employ both chi^2 fitting method and the extension of Fisher matrix formalism to evaluate the bias on the equation of state parameters of dark energy, w_0 and w_a, induced by those catastrophic outliers. By comparing the results from both methods, we verify that the estimation of w_0 and w_a from the fiducial 5-bin tomographic analyses can be significantly biased. To minimize the impact of this bias, two strategies can be followed: (A) the cosmic shear analysis is restricted to 0.5<z<2.5 where catastrophic redshift errors are expected to be insignificant; (B) a spectroscopic survey is conducted for galaxies with 3<z_{phot}<4. We find that the number of spectroscopic redshifts needed scales as N_{spec} \propto f_{cata}\times A where f_{cata}=1% is the fraction of catastrophic redshift errors (assuming a 9-filter photometric survey) and A is the survey area. For A=1000 {deg}^2, we find that N_{spec}>320 and 860 respectively in order to reduce the joint bias in (w_0,w_a) to be smaller than 2\sigma and 1\sigma. This spectroscopic survey (option B) will improve the Figure of Merit of option A by a factor \times 1.5 thus making such a survey strongly desirable.Comment: 25 pages, 9 figures. Revised version, as accepted for publication in Ap

Doubly heavy baryon production at polarized photon collider

We study the inclusive production of doubly heavy baryon $\Xi_{cc}$ at polarized photon collider. Our results show that proper choice of the initial beam polarizations may increase the production rate of $\Xi_{cc}$ approximately 10%.Comment: 9 pages, 5 figure