Dilepton mass edge measurement in SUSY events with CMS

Within the mSUGRA model, the observability of the decay of the next to lightest neutralino into leptons and the lightest neutralino has been studied using a full simulation of the CMS detector. The final state signature consists of two opposite sign leptons, several hard jets and missing transverse energy. The expected precision of the measurement of the dilepton mass edge is reported for 1 fb^-1 of data, including systematic and statistic uncertainties, comparing two benchmark points with different signatures.Comment: 4 pages, 6 figures, Proceedings of the XLIVth Recontres de Moriond on Electroweak Interactions and Unified Theories, La Thuile, March 200

Nucleosynthesis of 92^{92}Nb and the relevance of the low-lying isomer at 135.5 keV

Background: Because of its half-life of about 35 million years, 92Nb is considered as a chronometer for nucleosynthesis events prior to the birth of our sun. The abundance of 92Nb in the early solar system can be derived from meteoritic data. It has to be compared to theoretical estimates for the production of 92Nb to determine the time between the last nucleosynthesis event before the formation of the early solar system. Purpose: The influence of a low-lying short-lived isomer on the nucleosynthesis of 92Nb is analyzed. The thermal coupling between the ground state and the isomer via so-called intermediate states affects the production and survival of 92Nb. Method: The properties of the lowest intermediate state in 92Nb are known from experiment. From the lifetime of the intermediate state and from its decay branchings, the transition rate from the ground state to the isomer and the effective half-life of 92Nb are calculated as a function of the temperature. Results: The coupling between the ground state and the isomer is strong. This leads to thermalization of ground state and isomer in the nucleosynthesis of 92Nb in any explosive production scenario and almost 100% survival of 92Nb in its ground state. However, the strong coupling leads to a temperature-dependent effective half-life of 92Nb which makes the 92Nb survival very sensitive to temperatures as low as about 8 keV, thus turning 92Nb at least partly into a thermometer. Conclusions: The low-lying isomer in 92Nb does not affect the production of 92Nb in explosive scenarios. In retrospect this validates all previous studies where the isomer was not taken into account. However, the dramatic reduction of the effective half-life at temperatures below 10 keV may affect the survival of 92Nb after its synthesis in supernovae which are the most likely astrophysical site for the nucleosynthesis of 92Nb.Comment: 5 pages, 3 figures; Phys. Rev. C, accepted for publicatio

Total reaction cross section σreac\sigma_{\rm{reac}} of α\alpha-induced reactions from elastic scattering: the example 140^{140}Ce(α\alpha,α\alpha)140^{140}Ce

Angular distributions of elastic $^{140}$Ce($\alpha$,$\alpha$)$^{140}$Ce scattering are analyzed in the framework of the optical model from low energies around the Coulomb barrier up to about 40\,MeV. From the local fits the total reaction cross section $\sigma_{\rm{reac}}$ is extracted. This procedure requires experimental scattering data with small uncertainties. The results for $\sigma_{\rm{reac}}$ are compared to predictions of different systematic global potentials. It is found that the total reaction cross section $\sigma_{\rm{reac}}$ is well predicted from all global potentials under study although the reproduction of the angular distributions is not perfect in all cases. In addition, the lower energy limit for the extraction of $\sigma_{\rm{reac}}$ from elastic scattering angular distributions is analyzed. Finally, the potentials under study are used to calculate the $^{143}$Nd(n,$\alpha$)$^{140}$Ce cross section, and the predictions are compared to experimental data.Comment: 11 pages, 7 figures, Phys. Rev. C, accepted for publicatio

Unexpected properties of the 33^{33}S(α\alpha,p)36^{36}Cl reaction cross section at low energies

New experimental data for the $^{33}$S($\alpha$,p)$^{36}$Cl reaction show a very unusual energy dependence. Contrary to common findings for many other $\alpha$-induced reactions, statistical model calculations underestimate the measured cross sections at very low energies. The relatively huge cross sections at these low energies require a significant amount of single-particle strength in the measured energy range which exceeds by far 100% as soon as the additional strength from the competing $^{33}$S($\alpha$,n)$^{36}$Ar reaction is taken into account. In addition, the new data deviate from a general trend for the energy dependence of $\alpha$-induced reaction cross sections.Comment: 5 pages, 4 figures, Phys. Rev. C, accepted as Brief Report; misprint (overestimate -> underestimate) "in "Note added in proof" replace

alpha-cluster states in intermediate mass nuclei

Properties of intermediate mass nuclei have been investigated within the framework of the alpha-cluster model in combination with systematic double-folding potentials. Previously, this alpha-cluster model has been widely applied to light nuclei, in particular to 8Be = alpha \otimes alpha, 20Ne = 16O \otimes alpha, and 44Ti = 40Ca \otimes alpha, and to heavy nuclei, in particular to 212Po = 208Pb \otimes alpha. In the present work a wide range of nuclei is investigated with the magic neutron number N = 50 in the mass range around A \approx 80 - 100: (A+4,N=52) = (A,N=50) \otimes alpha. It is found that excitation energies, decay properties, and transition strengths can be described successfully within this model. The smooth and small variation of the underlying parameters of the alpha-nucleus potential may be used for extrapolations to predict experimentally unknown properties in the nuclei under study.Comment: 9 pages, 7 figures, TONPPJ, accepte

Photon-induced Nucleosynthesis: Current Problems and Experimental Approaches

Photon-induced reactions play a key role in the nucleosynthesis of rare neutron-deficient p-nuclei. The paper focuses on (gamma,alpha), (gamma,p), and (gamma,n) reactions which define the corresponding p-process path. The relation between stellar reaction rates and laboratory cross sections is analyzed for photon-induced reactions and their inverse capture reactions to evaluate various experimental approaches. An improved version S_C(E) of the astrophysical S-factor is suggested which is based on the Coulomb wave functions. S_C(E) avoids the apparent energy dependence which is otherwise obtained for capture reactions on heavy nuclei. It is found that a special type of synchrotron radiation available at SPring-8 that mimics stellar blackbody radiation at billions of Kelvin is a promising tool for future experiments. By using the blackbody synchrotron radiation, sufficient event rates for (gamma,alpha) and (gamma,p) reactions in the p-process path can be expected. These experiments will provide data to improve the nuclear parameters involved in the statistical model and thus reduce the uncertainties of nucleosynthesis calculations.Comment: 13 pages, 6 figures, EPJA, accepte

Optical Turbulence Measurements and Models for Mount John University Observatory

Site measurements were collected at Mount John University Observatory in 2005 and 2007 using a purpose-built scintillation detection and ranging system. $C_n^2(h)$ profiling indicates a weak layer located at 12 - 14 km above sea level and strong low altitude turbulence extending up to 5 km. During calm weather conditions, an additional layer was detected at 6 - 8 km above sea level. $V(h)$ profiling suggests that tropopause layer velocities are nominally 12 - 30 m/s, and near-ground velocities range between 2 -- 20 m/s, dependent on weather. Little seasonal variation was detected in either $C_n^2(h)$ and $V(h)$ profiles. The average coherence length, $r_0$, was found to be $7 \pm 1$ cm for the full profile at a wavelength of 589 nm. The average isoplanatic angle, $\theta_0$, was $1.0 \pm 0.1$ arcsec. The mean turbulence altitude, $\bar{h_0}$, was found to be $2.0\pm0.7$ km above sea level. No average in the Greenwood frequency, $f_G$, could be established due to the gaps present in the \vw\s profiles obtained. A modified Hufnagel-Valley model was developed to describe the $C_n^2(h)$ profiles at Mount John, which estimates $r_0$ at 6 cm and $\theta_0$ at 0.9 arcsec. A series of $V(h)$ models were developed, based on the Greenwood wind model with an additional peak located at low altitudes. Using the $C_n^2(h)$ model and the suggested $V(h)$ model for moderate ground wind speeds, $f_G$ is estimated at 79 Hz.Comment: 14 pages; accepted for publication in PAS