Search

The transverse momentum dependent nuclear modification factors (NMF), namely $R_{CP}$, is investigated for protons produced in Au + Au at 1$A$ GeV within the framework of the isospin-dependent quantum molecular dynamics (IQMD) model. It is found that the radial collective motion during the expansion stage affects the NMF at low transverse momentum a lot. By fitting the transverse mass spectra of protons with the distribution function from the Blast-Wave model, the magnitude of radial flow can be extracted. After removing the contribution from radial flow, the $R_{CP}$ can be regarded as a thermal one and is found to keep unitary at transverse momentum lower than 0.6 GeV/c and enhance at higher transverse momentum, which can be attributed to Cronin effect., Comment: 8 pages, 5 figures; aceepted by Physics Letters B

Neutrinoless double-beta ($0\nu\beta\beta$) decay is a hypothesized lepton-number-violating process that offers the only known means of asserting the possible Majorana nature of neutrino mass. The Cryogenic Underground Observatory for Rare Events (CUORE) is an upcoming experiment designed to search for $0\nu\beta\beta$ decay of $^{130}$Te using an array of 988 TeO$_2$ crystal bolometers operated at 10 mK. The detector will contain 206 kg of $^{130}$Te and have an average energy resolution of 5 keV; the projected $0\nu\beta\beta$ decay half-life sensitivity after five years of live time is $1.6\times 10^{26}$ y at $1\sigma$ ($9.5\times10^{25}$ y at the 90% confidence level), which corresponds to an upper limit on the effective Majorana mass in the range 40--100 meV (50--130 meV). In this paper we review the experimental techniques used in CUORE as well as its current status and anticipated physics reach., Comment: 20 pages, 8 figures. Published in Advances in High Energy Physics, Volume 2015 (2015), Article ID 879871

Based on the framework of the Isospin-Dependent Quantum Molecular Dynamics (IQMD) model in which the initial neutron and proton densities are sampled according to the droplet model, the correlation between triton-to-$^{3}$He yield ratio (R(t/$^{3}$He)$=$Yield(t)/Yield($^{3}$He)) and neutron skin thickness (${\delta}_{np}$) in neutron-rich projectile induced reactions is investigated. By changing the diffuseness parameter of neutron density distribution in the droplet model for the projectile to obtain different ${\delta}_{np}$, the relationship between ${\delta}_{np}$ and the corresponding R(t/$^{3}$He) in semi-peripheral collisions is obtained. The calculated results show that R(t/$^{3}$He) has a strong linear correlation with ${\delta}_{np}$ for neutron-rich $^{50}$Ca and $^{68}$Ni nuclei. It is suggested that R(t/$^{3}$He) could be regarded as a good experimental observable to extract ${\delta}_{np}$ for neutron-rich nuclei because the yields of charged particles triton and $^{3}$He can be measured quite precisely., Comment: 7 pages and 6 figures

CUORE-0 is a cryogenic detector that uses an array of tellurium dioxide bolometers to search for neutrinoless double-beta decay of ^{130}Te. We present the first data analysis with 7.1 kg y of total TeO_2 exposure focusing on background measurements and energy resolution. The background rates in the neutrinoless double-beta decay region of interest (2.47 to 2.57 MeV) and in the {\alpha} background-dominated region (2.70 to 3.90 MeV) have been measured to be 0.071 \pm 0.011 and 0.019 \pm 0.002 counts/keV/kg/y, respectively. The latter result represents a factor of 6 improvement from a predecessor experiment, Cuoricino. The results verify our understanding of the background sources in CUORE-0, which is the basis of extrapolations to the full CUORE detector. The obtained energy resolution (full width at half maximum) in the region of interest is 5.7 keV. Based on the measured background rate and energy resolution in the region of interest, CUORE-0 half-life sensitivity is expected to surpass the observed lower bound of Cuoricino with one year of live time., Comment: 8 pages, 5 figures, version 2 as published in Eur. Phys. J. C

A comparative study of the nuclear Gamow-Teller response (GTR) within conceptually different state-of-the-art approaches is presented. Three nuclear microscopic models are considered: (i) the recently developed charge-exchange relativistic time blocking approximation (RTBA) based on the covariant density functional theory, (ii) the shell model (SM) with an extended "jj77" model space and (iii) the non-relativistic quasiparticle random-phase approximation (QRPA) with a Brueckner G-matrix effective interaction. We study the physics cases where two or all three of these models can be applied. The Gamow-Teller response functions are calculated for 208-Pb, 132-Sn and 78-Ni within both RTBA and QRPA. The strengths obtained for 208-Pb are compared to data that enables a firm model benchmarking. For the nucleus 132-Sn, also SM calculations are performed within the model space truncated at the level of a particle-hole (ph) coupled to vibration configurations. This allows a consistent comparison to the RTBA where ph+phonon coupling is responsible for the spreading width and considerable quenching of the GTR. Differences between the models and perspectives of their future developments are discussed., Comment: 9 pages, 2 figures, 1 table; to be published in Phys. Lett. B

We present a short overview of our recent theoretical developments aiming at the description of exotic nuclear phenomena to be reached and studied at the next-generation radioactive beam facilities. Applications to nuclear shell structure and response of nuclei at the limits of their existence, with a special focus on the physics cases of astrophysical importance, are discussed., Comment: Invited talk at EURISOL topical meeting 2013 "Going to the limits of mass, temperature, spin and isospin with heavy Radioactive Ion Beams"

The isoscalar giant monopole resonance (ISGMR) in Sn isotopes and other nuclei is investigated in the framework of the isospin-dependent quantum molecular dynamics (IQMD) model. The spectrum of GMR is calculated by taking the root-mean-square (RMS) radius of a nucleus as its monopole moment. The peak energy, the full width at half maximum (FWHM), and the strength of GMR extracted by a Gaussian fit to the spectrum have been studied. The GMR peak energies for Sn isotopes from the calculations using a mass-number dependent Gaussian wave-packet width $\sigma_r$ for nucleons are found to be overestimated and show a weak dependence on the mass number compared with the experimental data. However, it is found that experimental data of the GMR peak energies for $^{56}$Ni, $^{90}$Zr, and $^{208}$Pb as well as Sn isotopes can be nicely reproduced after taking into account the isospin dependence in isotope chains in addition to the mass number dependence of $\sigma_r$ for nucleons in the IQMD model calculation., Comment: 9 pages, 12 figures; accepted by Phys. Rev. C

Recent observations of current-induced magnetization switching at ferromagnet/normal-conductor interfaces have important consequences for future magnetic memory technology. In one interpretation, the switching originates from carriers with spin-dependent scattering giving rise to a relativistic anti-damping spin-orbit torque (SOT) in structures with broken space-inversion symmetry. The alternative interpretation combines the relativistic spin Hall effect (SHE), making the normal-conductor an injector of a spin-current, with the non-relativistic spin-transfer torque (STT) in the ferromagnet. Remarkably, the SHE in these experiments originates from the Berry phase effect in the band structure of a clean crystal and the anti-damping STT is also based on a disorder-independent transfer of spin from carriers to magnetization. Here we report the observation of an anti-damping SOT stemming from an analogous Berry phase effect to the SHE. The SOT alone can therefore induce magnetization dynamics based on a scattering-independent principle. The ferromagnetic semiconductor (Ga,Mn)As we use has a broken space-inversion symmetry in the crystal. This allows us to consider a bare ferromagnetic element which eliminates by design any SHE related contribution to the spin torque. We provide an intuitive picture of the Berry phase origin of the anti-damping SOT and a microscopic modeling of measured data., Comment: Send to: ajf1006@cam.ac.uk

Thermodynamic and transport properties of nuclear fireball created in the central region of heavy-ion collisions below 400 MeV/nucleon are investigated within the isospin-dependent quantum molecular dynamic (IQMD) model. These properties including the density, temperature, chemical potential, entropy density ($s$) and shear viscosity ($\eta$), are calculated by a generalized hot Thomas Fermi formulism and a parameterized function, which was developed by Danielewicz. As the collision goes on, a transient minimal $\eta/s=5/4\pi-10/4\pi$ occurs in the largest compression stage. Besides, the relationship of $\eta/s$ to temperature ($T$) in the freeze-out stage displays a local minimum which is about 9-20 times $1/4\pi$ around $T$ = 8-12 MeV, which can be argued as indicative of a liquid gas phase transition. In addition, the influences of nucleon-nucleon (NN) cross section ($\sigma_{NN}$) and symmetry energy coefficient ($C_{s}$) are also discussed, and it is found that the results are sensitive to $\sigma_{NN}$ but not to $C_{s}$., Comment: 10 pages, 13 figures; Phys. Rev. C (in press) (x-axis of Fig.1 is corrected)

Proton-neutron, neutron-neutron and proton-proton momentum correlation functions ($C_{pn}$, $C_{nn}$, $C_{pp}$) are systematically investigated for $^{15}$C and other C isotopes induced collisions at different entrance channel conditions within the framework of the isospin-dependent quantum molecular dynamics (IDQMD) model complemented by the CRAB (correlation after burner) computation code. $^{15}$C is a prime exotic nucleus candidate due to the weakly bound valence neutron coupling with closed-neutron shell nucleus $^{14}$C. In order to study density dependence of correlation function by removing the isospin effect, the initialized $^{15}$C projectiles are sampled from two kinds of density distribution from RMF model, in which the valence neutron of $^{15}$C is populated on both 1$d$5/2 and 2$s$1/2 states, respectively. The results show that the density distributions of valence neutron significantly influence nucleon-nucleon momentum correlation function at large impact parameter and high incident energy. The extended density distribution of valence neutron largely weakens the strength of correlation function. The size of emission source is extracted by fitting correlation function using Gaussian source method. The emission source size as well as the size of final state phase space is larger for projectiles sampling from more extended density distribution of valence neutron corresponding 2$s$1/2 state in RMF model. Therefore momentum correlation function can be considered as a potential valuable tool to diagnose the exotic nuclear structure such as skin and halo., Comment: 8 pages, 9 figures, 1 table

We measure electrically detected ferromagnetic resonance in microdevices patterned from ultra-thin Co/Pt bilayers. Spin pumping and rectification voltages are observed and distinguished via their angular dependence. The spin-pumping voltage shows an unexpected increase as the cobalt thickness is reduced below 2 nm. This enhancement allows more efficient conversion of spin to charge current and motivates a theory modelling the dependence of impurity scattering on surface roughness.

In this article we describe the background challenges for the CUORE experiment posed by surface contamination of inert detector materials such as copper, and present three techniques explored to mitigate these backgrounds. Using data from a dedicated test apparatus constructed to validate and compare these techniques we demonstrate that copper surface contamination levels better than 10E-07 - 10E-08 Bq/cm2 are achieved for 238U and 232Th. If these levels are reproduced in the final CUORE apparatus the projected 90% C.L. upper limit on the number of background counts in the region of interest is 0.02-0.03 counts/keV/kg/y depending on the adopted mitigation technique., Comment: 10 pages, 6 figures, 6 tables

Motivated by the prospects of increased measurement bandwidth, improved signal to noise ratio and access to the full complex magnetic susceptibility we develop a technique to extract microwave voltages from our high resistance (10 k{\Omega}) (Ga,Mn)As microbars. We drive magnetization precession with microwave frequency current, using a mechanism that relies on the spin orbit interaction. A capacitively coupled lambda/2 microstrip resonator is employed as an impedance matching network, enabling us to measure the microwave voltage generated during magnetisation precession., Comment: (4 pages)

We report the results of a search for axions from the 14.4 keV M1 transition from Fe-57 in the core of the sun using the axio-electric effect in TeO2 bolometers. The detectors are 5x5x5 cm3 crystals operated at about 10 mK in a facility used to test bolometers for the CUORE experiment at the Laboratori Nazionali del Gran Sasso in Italy. An analysis of 43.65 kg d of data was made using a newly developed low energy trigger which was optimized to reduce the detectors energy threshold. An upper limit of 0.63 c kg-1 d-1 was established at 95% C.L.. From this value, a lower bound at 95% C.L. was placed on the Peccei-Quinn energy scale of fa >= 0.76 10**6 GeV for a value of S=0.55 for the flavor-singlet axial vector matrix element. Bounds are given for the interval 0.15 < S < 0.55., Comment: 14 pages, 6 figures, submitted to JCAP

We collected 19.4 days of data from four 750 g TeO2 bolometers, and in three of them we were able to set the energy threshold around 3 keV using a new analysis technique. We found a background rate ranging from 25 cpd/keV/kg at 3 keV to 2 cpd/keV/kg at 25 keV, and a peak at 4.7 keV. The origin of this peak is presently unknown, but its presence is confirmed by a reanalysis of 62.7 kg.days of data from the finished CUORICINO experiment. Finally, we report the expected sensitivities of the CUORE0 (52 bolometers) and CUORE (988 bolometers) experiments to a WIMP annual modulation signal., Comment: 9 pages, 10 figures

The ratio of the shear viscosity ($\eta$) to entropy density ($s$) for the intermediate energy heavy-ion collisions has been calculated by using the Green-Kubo method in the framework of the quantum molecular dynamics model. The theoretical curve of $\eta/s$ as a function of the incident energy for the head-on Au+Au collisions displays that a minimum region of $\eta/s$ has been approached at higher incident energies, where the minimum $\eta/s$ value is about 7 times Kovtun-Son- Starinets (KSS) bound (1/4$\pi$). We argue that the onset of minimum $\eta/s$ region at higher incident energies corresponds to the nuclear liquid gas phase transition in nuclear multifragmentation., Comment: 6 pages, 8 figures

The reduced transition probability B(E2;0 ->2+) for 28S was obtained experimentally using Coulomb excitation at 53 MeV/nucleon. The resultant B(E2) value 181(31) e2fm4 is smaller than the expectation based on empirical B(E2) systematics. The double ratio |M_n/M_p|/(N/Z) of the 0+ ->2+ transition in 28S was determined to be 1.9(2) by evaluating the M_n value from the known B(E2) value of the mirror nucleus 28Mg, showing the hindrance of proton collectivity relative to that of neutrons. These results indicate the emergence of the magic number Z=16 in the |T_z|=2 nucleus 28S., Comment: 10 pages, 3 figures. Published in Phys. Rev. Lett (http://link.aps.org/doi/10.1103/PhysRevLett.108.222501)

Hard photons emitted from energetic heavy ion collisions are very interesting since they do not experience nuclear interaction, and therefore they are useful to explore properties of nuclear matter. We investigated hard photon production and its properties in intermediate energy heavy-ion collisions with the help of the Blotzmann-Uehling-Ulenbeck model. Two components of hard photons are discussed: direct and thermal. The positive directed flow parameter and negative elliptic flow parameter of direct photons are demonstrated and they are anti-correlated to the flows of free protons. The dependencies of hard photon production and anisotropic parameters on impact parameter, beam energy, nuclear equation of state and symmetry energy are also discussed. Furthermore, we investigated the two-photon momentum correlation function from which the space-time structure information of the photon source could be extracted as well as the two-photon azimuthal correlation which could provide another good method to determine the elliptic flow parameter $v_{2}$ of direct hard photons., Comment: 13 pages, 18 figures

We present a study of the sensitivity and discovery potential of CUORE, a bolometric double-beta decay experiment under construction at the Laboratori Nazionali del Gran Sasso in Italy. Two approaches to the computation of experimental sensitivity for various background scenarios are presented, and an extension of the sensitivity formulation to the discovery potential case is also discussed. Assuming a background rate of 10^-2 cts/(keV kg y), we find that, after 5 years of live time, CUORE has a 1 sigma sensitivity to the neutrinoless double-beta decay half-life of T_1/2(1 sigma) = 1.6 \times 10^26 y and thus a potential to probe the effective Majorana neutrino mass down to 40-100 meV; the sensitivity at 1.64 sigma, which corresponds to 90% C.L., will be T_1/2(1.64 sigma) = 9.5 \times 10^25 y. This range is compared with the claim of observation of neutrinoless double-beta decay in 76Ge and the preferred range of the neutrino mass parameter space from oscillation results., Comment: 14 pages, 6 figures, revision for new submission to Astroparticle Physics

The CUORE Crystal Validation Runs (CCVRs) have been carried out since the end of 2008 at the Gran Sasso National Laboratories, in order to test the performances and the radiopurity of the TeO$_2$ crystals produced at SICCAS (Shanghai Institute of Ceramics, Chinese Academy of Sciences) for the CUORE experiment. In this work the results of the first 5 validation runs are presented. Results have been obtained for bulk contaminations and surface contaminations from several nuclides. An extrapolation to the CUORE background has been performed., Comment: 11 pages, 8 figures

The ratio of shear viscosity ($\eta$) to entropy density ($s$) for an equilibrated system is investigated in intermediate energy heavy ion collisions below 100$A$ MeV within the framework of the Boltzmann-Uehling-Uhlenbeck (BUU) model . After the collision system almost reaches a local equilibration, the temperature, pressure and energy density are obtained from the phase space information and {$\eta/s$} is calculated using the Green-Kubo formulas. The results show that {$\eta$}/$s$ decreases with incident energy and tend towards a smaller value around 0.5, which is not so drastically different from the BNL Relativistic Heavy Ion Collider results in the present model., Comment: 5 pages, 4 figures

Extensive calculations on isoscaling behavior with the sequential-decay model gemini are performed for the medium-to-heavy nuclei in the mass range A = 60-120 at excitation energies up to 3 MeV/nucleon. The comparison between the products after the first-step decay and the ones after the entire-steps decay demonstrates that there exists a strong sequential decay effect on the final isoscaling parameters and the apparent temperature. Results show that the apparent symmetry energy coefficient $\gamma_{app}$ does not reflect the initial symmetry energy coefficient $C_{sym}$ embedded in the mass calculation in the present GEMINI model., Comment: 4 pages, 3 figures, 1 table

The $^{150}$Nd($^3$He,$t$) reaction at 140 MeV/u and $^{150}$Sm($t$,$^3$He) reaction at 115 MeV/u were measured, populating excited states in $^{150}$Pm. The transitions studied populate intermediate states of importance for the (neutrinoless) $\beta\beta$ decay of $^{150}$Nd to $^{150}$Sm. Monopole and dipole contributions to the measured excitation-energy spectra were extracted by using multipole decomposition analyses. The experimental results were compared with theoretical calculations obtained within the framework of Quasiparticle Random-Phase Approximation (QRPA), which is one of the main methods employed for estimating the half-life of the neutrinoless $\beta\beta$ decay ($0\nu\beta\beta$) of $^{150}$Nd. The present results thus provide useful information on the neutrino responses for evaluating the $0\nu\beta\beta$ and $2\nu\beta\beta$ matrix elements. The $2\nu\beta\beta$ matrix element calculated from the Gamow-Teller transitions through the lowest $1^{+}$ state in the intermediate nucleus is maximally about half of that deduced from the half-life measured in $2\nu\beta\beta$ direct counting experiments and at least several transitions through $1^{+}$ intermediate states in $^{150}$Pm are required to explain the $2\nu\beta\beta$ half-life. Because Gamow-Teller transitions in the $^{150}$Sm($t$,$^3$He) experiment are strongly Pauli-blocked, the extraction of Gamow-Teller strengths was complicated by the excitation of the $2\hbar\omega$, $\Delta L=0$, $\Delta S=1$ isovector spin-flip giant monopole resonance (IVSGMR). However, the near absence of Gamow-Teller transition strength made it possible to cleanly identify this resonance, and the strength observed is consistent with the full exhaustion of the non-energy-weighted sum rule for the IVSGMR., Comment: 18 pages, 13 figures, 2 tables

The detailed analysis of wide excitation function of nuclear stopping has been studied within a transport model, Isospin-dependent Quantum Molecular Dynamics model (IQMD) and an overall good agreement with the INDRA and FOPI experimental data has been achieved. It is found that mean value of isotropy in central Heavy-Ion Collision (HIC) reaches a minimum near Fermi energy and approaches a maximum around 300 - 400$A$ MeV. This suggests that, in statistical average, the equilibration is far from being reached even in central HIC especially near Fermi energy. A hierarchy in stopping of fragments, which favors heavy fragments to penetrate, provides a robust restriction on the global trend of nuclear stopping and could serve as a probe for nuclear equation of state., Comment: 7 pages, 7 figures

We demonstrate a scalable new ferromagnetic resonance (FMR) technique based on the spin-orbit interaction. An alternating current drives FMR in uniform ferromagnetic structures patterned from the dilute magnetic semiconductors (Ga,Mn)As and (Ga,Mn)(As,P). This allows the direct measurement of magnetic anisotropy coefficients and damping parameters for individual nano-bars. By analysing the ferromagnetic resonance lineshape, we perform vector magnetometry on the current-induced driving field, observing contributions with symmetries of both the Dresselhaus and Rashba spin-orbit interactions., Comment: 4 figures

The reaction dynamics of axisymmetric deformed $^{24}$Mg + $^{24}$Mg collisions have been investigated systematically by an isospin-dependent quantum molecular dynamics (IDQMD) model. It is found that different deformations and orientations result in apparently different properties of reaction dynamics. We revealed that some observables such as nuclear stopping power ($R$), multiplicity of fragments, and elliptic flow are very sensitive to the initial deformations and orientations. There exists an eccentricity scaling of elliptic flow in central body-body collisions with different deformations. In addition, the tip-tip and body-body configurations turn out to be two extreme cases in central reaction dynamical process., Comment: 5 pages, 7 figures, to appear in Physical Review C (Rapid Communication)

Dynamical dipole $\gamma$-ray emission in heavy-ion collisions is explored in the framework of the quantum molecular dynamics model. The studies are focused on systems of $^{40}$Ca bombarding $^{48}$Ca and its isotopes at different incident energies and impact parameters. Yields of $\gamma$ rays are calculated and the centroid energy and dynamical dipole emission width of the $\gamma$ spectra are extracted to investigate the properties of $\gamma$ emission. In addition, sensitivities of dynamical dipole $\gamma$-ray emission to the isospin and the symmetry energy coefficient of the equation of state are studied. The results show that detailed study of dynamical dipole $\gamma$ radiation can provide information on the equation of state and the symmetry energy around the normal nuclear density., Comment: 5 pages, 6 figures

We study the relation between neutron removal cross section ($\sigma_{-N}$) and neutron skin thickness for finite neutron rich nuclei using the statistical abrasion ablation (SAA) model. Different sizes of neutron skin are obtained by adjusting the diffuseness parameter of neutrons in the Fermi distribution. It is demonstrated that there is a good linear correlation between $\sigma_{-N}$ and the neutron skin thickness for neutron rich nuclei. Further analysis suggests that the relative increase of neutron removal cross section could be used as a quantitative measure for the neutron skin thickness in neutron rich nuclei., Comment: 4 pages, 3 figures

The fragment production cross sections for 140 MeV/nucleon $^{48,40}$Ca$+^{9}$Be reactions have been calculated by the Heavy Ion Phase Space Exploration (HIPSE) model. Isoscaling behavior is observed. The isoscaling parameters $\alpha$ and $\beta$ for both heavy and light fragments from HIPSE model calculations are in good agreement with the experiment data. Studies show that the potential parameters in the HIPSE model have very small effect on the isoscaling parameters. The effect of the excitation energy and evaporation on the isoscaling behavior has also been discussed., Comment: 5 pages, 5 figures

The behaviour of the cross-sectional polarization field is explored for thin nanowires of barium titanate from first-principles calculations. Topological defects of different winding numbers have been obtained, beyond the known textures in ferroelectric nanostructures. They result from the inward accommodation of the polarization patterns imposed at the surface of the wire by surface and edge effects. Close to a topological defect the polarization field orients out of the basal plane in some cases, maintaining a close to constant magnitude, whereas it virtually vanishes in other cases., Comment: 4 pages, 3 figures

The dependence between neutron-to-proton yield ratio ($R_{np}$) and neutron skin thickness ($\delta_{np}$) in neutron-rich projectile induced reactions is investigated within the framework of the Isospin-Dependent Quantum Molecular Dynamics (IQMD) model. The density distribution of the Droplet model is embedded in the initialization of the neutron and proton densities in the present IQMD model. By adjusting the diffuseness parameter of neutron density in the Droplet model for the projectile, the relationship between the neutron skin thickness and the corresponding $R_{np}$ in the collisions is obtained. The results show strong linear correlation between $R_{np}$ and $\delta_{np}$ for neutron-rich Ca and Ni isotopes. It is suggested that $R_{np}$ may be used as an experimental observable to extract $\delta_{np}$ for neutron-rich nuclei, which is very significant to the study of the nuclear structure of exotic nuclei and the equation of state (EOS) of asymmetric nuclear matter., Comment: 7 pages, 5 figures; accepted by Phys. Lett. B

The cross sections of fragments produced in 140 $A$ MeV $^{40,48}$Ca + $^9$Be and $^{58,64}$Ni + $^9$Be reactions are calculated by the statistical abration-ablation(SAA) model and compared to the experimental results measured at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. The fragment isotopic and isotonic cross section distributions of $^{40}$Ca and $^{48}$Ca, $^{58}$Ni and $^{64}$Ni, $^{40}$Ca and $^{58}$Ni, and $^{48}$Ca and $^{64}$Ni are compared and the isospin dependence of the projectile fragmentation is studied. It is found that the isospin dependence decreases and disappears in the central collisions. The shapes of the fragment isotopic and isotonic cross section distributions are found to be very similar for symmetric projectile nuclei. The shapes of the fragment isotopic and isotonic distributions of different asymmetric projectiles produced in peripheral reactions are found very similar. The similarity of the distributions are related to the similar proton and neutron density distributions inside the nucleus in framework of the SAA model., Comment: 7 pages, 4 figures; to be published in Phys Rev C

We synthesized Sr-doped $La_{0.85}Sr_{0.15}OFeAs$ sample with single phase, and systematically studied the effect of oxygen deficiency in the Sr-doped LaOFeAs system. It is found that substitution of Sr for La indeed induces the hole carrier evidenced by positive thermoelectric power (TEP), but no bulk superconductivity is observed. The superconductivity can be realized by annealing the as-grown sample in vacuum to produce the oxygen deficiency. With increasing the oxygen deficiency, the superconducting transition temperature ($T_c$) increases and maximum $T_c$ reaches about 26 K the same as that in La(O,F)FeAs. TEP dramatically changes from positive to negative in the nonsuperconducting as-grown sample to the superconducting samples with oxygen deficiency. While $R_H$ is always negative for all samples (even for Sr-doped as grown sample). It suggests that the $La_{0.85}Sr_{0.15}O_{1-\delta}FeAs$ is still electron-type superconductor., Comment: 4 pages, 4 figures

We synthesized the samples $Ba_{1-x}M_xFe_2As_2$ (M=La and K) with $ThCr_2Si_2$-type structure. These samples were systematically characterized by resistivity, thermoelectic power (TEP) and Hall coefficient ($R_H$). $BaFe_2As_2$ shows an anomaly in resistivity at about 140 K. Substitution of La for Ba leads to a shift of the anomaly to low temperature, but no superconducting transition is observed. Potassium doping leads to suppression of the anomaly in resistivity and induces superconductivity at 38 K as reported by Rotter et al.\cite{rotter}. The Hall coefficient and TEP measurements indicate that the TEP is negative for $BaFe_2As_2$ and La-doped $BaFe_2As_2$, indicating n-type carrier; while potassium doping leads to change of the sign in $R_H$ and TEP. It definitely indicates p-type carrier in superconducting $Ba_{1-x}K_xFe_2As_2$ with double FeAs layers, being in contrast to the case of $LnO_{1-x}F_xFeAs$ with single FeAs layer. A similar superconductivity is also observed in the sample with nominal composition $Ba_{1-x}K_xOFe_2As_2$., Comment: 4 pages, 4 figures

The magnetic fluctuations associated with a quantum critical point (QCP) are widely believed to cause the non-Fermi liquid behaviors and unconventional superconductivities, for example, in heavy fermion systems and high temperature cuprate superconductors. Recently, superconductivity has been discovered in iron-based layered compound $LaO_{1-x}F_xFeAs$ with $T_c$=26 K\cite{yoichi}, and it competes with spin-density-wave (SDW) order\cite{dong}. Neutron diffraction shows a long-rang SDW-type antiferromagnetic (AF) order at $\sim 134$ K in LaOFeAs\cite{cruz,mcguire}. Therefore, a possible QCP and its role in this system are of great interests. Here we report the detailed phase diagram and anomalous transport properties of the new high-Tc superconductors $SmO_{1-x}F_xFeAs$ discovered by us\cite{chenxh}. It is found that superconductivity emerges at $x\sim$0.07, and optimal doping takes place in the $x\sim$0.20 sample with highest $T_c \sim $54 K. While $T_c$ increases monotonically with doping, the SDW order is rapidly suppressed, suggesting a QCP around $x \sim$0.14. As manifestations, a linear temperature dependence of the resistivity shows up at high temperatures in the $x<0.14$ regime, but at low temperatures just above $T_c$ in the $x>0.14$ regime; a drop in carrier density evidenced by a pronounced rise in Hall coefficient are observed, which mimic the high-$T_c$ cuprates. The simultaneous occurrence of order, carrier density change and criticality makes a compelling case for a quantum critical point in this system., Comment: 10 pages, 4 figures

Since the discovery of high-transition temperature ($T_c$) superconductivity in layered copper oxides, extensive efforts have been devoted to explore the higher $T_c$ superconductivity. However, the $T_c$ higher than 40 K can be obtained only in the copper oxide superconductors so far. The highest reported value of $T_c$ for non-copper-oxide bulk superconductivity is 39 K in $MgB_2$.\cite{jun} The $T_c$ of about 40 K is close to or above the theoretical value predicted from BCS theory.\cite{mcmillan} Therefore, it is very significant to search for non-copper oxide superconductor with the transition temperature higher than 40 K to understand the mechanism of high-$T_c$ superconductivity. Here we report the discovery of bulk superconductivity in samarium-arsenide oxides $SmFeAsO_{1-x}F_x$ with ZrCuAiAs type structure. Resistivity and magnetization measurements show strong evidences for transition temperature as high as 43 K. $SmFeAsO_{1-x}F_x$ is the first non-copper oxide superconductor with $T_c$ higher than 40 K. The $T_c$ higher than 40 K may be a strong argument to consider $SmFeAsO_{1-x}F_x$ as an unconventional superconductor., Comment: 8 pages, 4 figures

Hard photon emitted from energetic heavy ion collisions is of very interesting since it does not experience the late-stage nuclear interaction, therefore it is useful to explore the early-stage information of matter phase. In this work, we have presented a first calculation of azimuthal asymmetry, characterized by directed transverse flow parameter $F$ and elliptic asymmetry coefficient $v_2$, for proton-neutron bremsstrahlung hard photons in intermediate energy heavy-ion collisions. The positive $F$ and negative $v_2$ of direct photons are illustrated and they seem to be anti-correlated to the corresponding free proton's flow., Comment: 7 pages, 4 figures; accepted by Physics Letters B

Anisotropic flows ($v_1$, $v_2$, $v_3$ and $v_4$) of light fragments up till the mass number 4 as a function of rapidity have been studied for 25 MeV/nucleon $^{40}$Ca + $^{40}$Ca at large impact parameters by Quantum Molecular Dynamics model. A phenomenological scaling behavior of rapidity dependent flow parameters $v_n$ (n = 1, 2, 3 and 4) has been found as a function of mass number plus a constant term, which may arise from the interplay of collective and random motions. In addition, $v_4/{v_2}^2$ keeps almost independent of rapidity and remains a rough constant of 1/2 for all light fragments., Comment: 4 pages, 5 figures

Isoscaling behavior of the statistical emission fragments from the equilibrated sources with $Z$ = 30 and $N$ = 30, 33, 36 and 39, resepectively, is investigated in the framework of isospin dependent lattice gas model. The dependences of isoscaling parameters $\alpha$ on source isospin asymmetry, temperature and freeze-out density are studied and the "symmetry energy" is deduced from isoscaling parameters. Results show that "symmetry energy" $C_{sym}$ is insensitive to the change of temperature but follows the power-law dependence on the freeze-out density $\rho$. The later gives $C_{sym}$ = 30$(\rho/\rho_0)^{0.62}$ if the suitable asymmetric nucleon-nucleon potential is taken. The effect of strength of asymmetry of nucleon-nucleon interaction potential on the density dependence of the "symmetry energy" is dicussed., Comment: 5 pages, 4 pages

We investigate the cross sections of the elastic electron or positron scattering from $^{208}$Pb, $^{12}$C, $^{12,16}$O and $^{28, 32}$S by the relativistic partial-wave expansion method using the static charge density distribution from the self-consistent relativistic mean field model and also calculate the charge form factor for $^{12, 16}$O and $^{28, 32}$S. The numerical results are compared with the available data. Calculations indicate that the extended charge density distributions of $^{12}$O and $^{28}$S have observable effects on the cross sections of the electron or positron scattering as well as the charge form factors., Comment: 4 pages, 5 figures

Elliptic flow ($v_2$) and hexadecupole flow ($v_4$) of light clusters have been studied in details for 25 MeV/nucleon $^{86}$Kr + $^{124}$Sn at large impact parameters by Quantum Molecular Dynamics model with different potential parameters. Four parameter sets which include soft or hard equation of state (EOS) with/without symmetry energy term are used. Both number-of-nucleon ($A$) scaling of the elliptic flow versus transverse momentum ($p_t$) and the scaling of $v_4/A^{2}$ versus $(p_t/A)^2$ have been demonstrated for the light clusters in all above calculation conditions. It was also found that the ratio of $v_4/{v_2}^2$ keeps a constant of 1/2 which is independent of $p_t$ for all the light fragments. By comparisons among different combinations of EOS and symmetry potential term, the results show that the above scaling behaviors are solid which do not depend the details of potential, while the strength of flows is sensitive to EOS and symmetry potential term., Comment: 5 pages, 5 figures

The longitudinal momentum distribution (P_{//}) of fragments after one-proton removal from ^{23} Al and reaction cross sections (\sigma_R) for ^{23,24} Al on carbon target at 74A MeV have been measured. The ^{23,24} Al ions were produced through projectile fragmentation of 135 A MeV ^{28} Si primary beam using RIPS fragment separator at RIKEN. P_{//} is measured by a direct time-of-flight (TOF) technique, while \sigma_R is determined using a transmission method. An enhancement in \sigma_R is observed for ^{23} Al compared with ^{24} Al. The P_{//} for ^{22} Mg fragments from ^{23} Al breakup has been obtained for the first time. FWHM of the distributions has been determined to be 232 \pm 28 MeV/c. The experimental data are discussed by using Few-Body Glauber model. Analysis of P_{//} demonstrates a dominant d-wave configuration for the valence proton in ground state of ^{23} Al, indicating that ^{23} Al is not a proton halo nucleus.