Improved parametrization of the transparency parameter in Kox and Shen models of total reaction cross sections

The total reaction cross section is an essential quantity in particle and heavy-ion transport codes when determining the mean free path of a transported particle. Many transport codes determine the distance a particle is transported before it collides with the target or is stopped in the target material, with the Monte Carlo (MC) method using semiempirical parametrization models for the total reaction cross sections. In order to improve the well-known Kox and Shen models of total reaction cross sections and allow the models to be used at energies below 30 MeV/nucleon, we propose a modified parametrization of the transparency parameter. We also report that the Kox and Shen models have a projectile-target asymmetry and should be used so that the lighter nucleus is always treated as the projectile

Hall coefficient and Hc2 in underdoped LaFeAsO0.95F0.05

The electrical resistivity and Hall coefficient of LaFeAsO0.95F0.05 polycrystalline samples were measured in pulsed magnetic fields up to m0H = 60 T from room temperature to 1.5 K. The resistance of the normal state shows a negative temperature coefficient (dr/dT < 0) below 70 K for this composition, indicating insulating ground state in underdoped LaFeAsO system in contrast to heavily doped compound. The charge carrier density obtained from Hall effect can be described as constant plus a thermally activated term with an energy gap DE = 630 K. Upper critical field, Hc2, estimated from resistivity measurements, exceeds 75 T with zero-field Tc = 26.3 K, suggesting an unconventional nature for superconductivity.Comment: 12 pages and 4 figure

Field-induced Bose-Einstein Condensation of triplons up to 8 K in Sr3Cr2O8

Single crystals of the spin dimer system Sr3Cr2O8 have been grown for the first time. Magnetization, heat capacity, and magnetocaloric effect data up to 65 T reveal magnetic order between applied fields of Hc1 ~ 30.4 T and Hc2 ~ 62 T. This field-induced order persists up to ~ 8 K at H ~ 44 T, the highest observed in any quantum magnet where Hc2 is experimentally-accessible. We fit the temperature-field phase diagram boundary close to Hc1 using the expression Tc = A(H-Hc1)^v. The exponent v = 0.65(2), obtained at temperatures much smaller than 8 K, is that of the 3D Bose-Einstein condensate (BEC) universality class. This finding strongly suggests that Sr3Cr2O8 is a new realization of a triplon BEC where the universal regimes corresponding to both Hc1 and Hc2 are accessible at He-4 temperatures.Comment: 4 pages, 3 figures, accepted by PR

Nuclear transparencies for nucleons, knocked-out under various semi-inclusive conditions

Using hadron dynamics we calculate nuclear transparencies for protons, knocked-out in high-$Q^2$, semi-inclusive reactions. Predicted transparencies are, roughly half a standard deviation above the NE18 data. The latter contain the effects of binned proton missing momenta and mass, and of finite detector acceptances. In order to test sensitivity we compare computed transparencies without restrictions and the same with maximal cuts for missing momenta and the electron energy loss. We find hardly any variation, enabling a meaningful comparison with data and predictions based on hadron dynamics. Should discrepancies persist in high-statistics data, the above may with greater confidence be attributed to exotic components in the description of the outgoing proton.Comment: 13 pages + 3 figsin appended PS file, report # WIS-94/43/Oct-P

Weak anisotropy of the superconducting upper critical field in Fe1.11Te0.6Se0.4 single crystals

We have determined the resistive upper critical field Hc2 for single crystals of the superconductor Fe1.11Te0.6Se0.4 using pulsed magnetic fields of up to 60T. A rather high zero-temperature upper critical field of mu0Hc2(0) approx 47T is obtained, in spite of the relatively low superconducting transition temperature (Tc approx 14K). Moreover, Hc2 follows an unusual temperature dependence, becoming almost independent of the magnetic field orientation as the temperature T=0. We suggest that the isotropic superconductivity in Fe1.11Te0.6Se0.4 is a consequence of its three-dimensional Fermi-surface topology. An analogous result was obtained for (Ba,K)Fe2As2, indicating that all layered iron-based superconductors exhibit generic behavior that is significantly different from that of the high-Tc cuprates.Comment: 4 pages, 4 figures, submit to PR

Pion interferometry with pion-source-medium interactions

An extended pion source, which can be temporarily created by a high energy nuclear collision, will also absorb and distort the outgoing pions. We discuss how this effect alters the interferometric pattern of the two-pion momentum correlation function. In particular, we show that the two-pion correlation function decreases rapidly when the opening angle between the pions increases. The opening-angle dependence should serve as a new means of obtaining information about the pion source in the analysis of experimental data.Comment: 14 pages (revtex) and 9 figures (uuencoded), Caltech preprint MAP-175, Indiana Univ. preprint IU/NTC 914-1

Magnetic and Dielectric Properties in Multiferroic Cu3Mo2O9 under High Magnetic Fields

The magnetic and dielectric properties under high magnetic fields are studied in the single crystal of Cu3Mo2O9. This multiferroic compound has distorted tetrahedral spin chains. The effects of the quasi-one dimensionality and the geometrical spin frustration are expected to appear simultaneously. We measure the magnetoelectric current and the differential magnetization under the pulsed magnetic field up to 74 T. We also measure the electric polarization versus the electric field curve/loop under the static field up to 23 T. Dielectric properties change at the magnetic fields where the magnetization jumps are observed in the magnetization curve. Moreover, the magnetization plateaus are found at high magnetic fields.Comment: 6 pages, 3 figures, in press in JPS Conf. Proc. as a part of SCES2013 Proceeding

The Earliest Optical Observations of GRB 030329

We present the earliest optical imaging observations of GRB 030329 related to SN 2003dh. The burst was detected by the HETE-2 satellite at 2003 March 29, 11:37:14.67 UT. Our wide-field monitoring started 97 minutes before the trigger and the burst position was continuously observed. We found no precursor or contemporaneous flare brighter than $V=5.1$ ($V=5.5$) in 32 s (64 s) timescale between 10:00 and 13:00 UT. Follow-up time series photometries started at 12:51:39 UT (75 s after position notice through the GCN) and continued for more than 5 hours. The afterglow was $Rc= 12.35\pm0.07$ at $t=74$ min after burst. Its fading between 1.2 and 6.3 hours is well characterized by a single power-law of the form $f{\rm(mJy)} = (1.99\pm0.02{\rm (statistic)}\pm0.14{\rm (systematic)}) \times (t/1 {\rm day})^{-0.890\pm 0.006 {\rm (statistic)}\pm 0.010 {\rm (systematic)}}$ in $Rc$-band. No significant flux variation was detected and upper limits are derived as $(\Delta f/f)_{\rm RMS} = 3-5$% in minutes to hours timescales and $(\Delta f/f)_{\rm RMS} = 35-5$% in seconds to minutes timescales. Such a featureless lightcurve is explained by the smooth distribution of circumburst medium. Another explanation is that the optical band was above the synchrotron cooling frequency where emergent flux is insensitive to the ambient density contrasts. Extrapolation of the afterglow lightcurve to the burst epoch excludes the presence of an additional flare component at $t<10$ minutes as seen in GRB 990123 and GRB 021211.Comment: ApJL, in pres