Efficiency corrected single ratios of neutron and proton spectra in central Sn112+112Sn and Sn124+124Sn collisions at 120 MeV/u are combined with double ratios to provide constraints on the density ...and momentum dependencies of the isovector mean-field potential. Bayesian analyses of these data reveal that the isoscalar and isovector nucleon effective masses, ms⁎−mv⁎ are strongly correlated. The linear correlation observed in ms⁎−mv⁎ yields a nearly independent constraint on the effective mass splitting Δmnp⁎=(mn⁎−mp⁎)/mN=−0.05−0.09+0.09δ. The correlated constraint on the standard symmetry energy, S0 and the slope, L at saturation density yields the values of symmetry energy S(ρs)=16.8−1.2+1.2 MeV at a sensitive density of ρs/ρ0=0.43−0.05+0.05.
In this work, two particular properties of the position-sensitive, thick silicon detectors (known as the “E” detectors) in the High Resolution Array (HiRA) are investigated: the thickness of the dead ...layer on the front of the detector, and the overall thickness of the detector itself. The dead layer thickness for each E detector in HiRA is extracted using a measurement of alpha particles emitted from a 212Pb pin source placed close to the detector surface. This procedure also allows for energy calibrations of the E detectors, which are otherwise inaccessible for alpha source calibration as each one is sandwiched between two other detectors. The E detector thickness is obtained from a combination of elastically scattered protons and an energy-loss calculation method. Results from these analyses agree with values provided by the manufacturer.
A 13F resonance was observed following a charge-exchange reaction between a fast 13O beam and a 9Be target. The resonance was found in the invariant-mass distribution of 3p + 10C events and probably ...corresponds to a 5/2+ excited state. The ground state was also expected to be populated, but was not resolved from the background. The observed level decays via initial proton emissions to both the ground and first 2+ state of 12O , which subsequently undergo 2p decay. In addition, there may also be a significant proton decay branch to the second 2+ level in 12O . The wave function associated with the observed level may be collectivized due to coupling to the continuum as is it located just above the threshold for proton decay to the 2+2 state of 12O .
Preliminary results of identical-particle correlations probing the geometric substructure of the particle-emitting source at RHIC are presented. An
m
T
-independent scaling of pion HBT radii from ...large (central Au+Au) to small (p+p) collision systems naively suggests comparable flow strength in all of them. Multidimensional correlation functions are studied in detail using a spherical decomposition method. In the light systems, the presence of significant long-range non-femtoscopic correlations complicates the extraction of HBT radii.
The geometric substructure of the particle-emitting source has been characterized via two-particle interferometry by the STAR collaboration for several energies and colliding systems at RHIC. In ...heavy ion collisions the mT dependence of femtoscopic radii has been observed for all particle types by several experiments at different collision energies. This dependence has been thought to arise from space-momentum correlations generated by collective flow. On the other hand, there are several reports of a similar mT dependence by experiments measuring elementary particle collisions. Here, quite different physical mechanisms – including resonances, strings, and uncertainty arguments – have been proposed to explain the dependence. Determining the differences or similarities in the space-time physics driving the signal in heavy ion versus p+p collisions requires a direct comparison of mT dependence of the radii. Such a comparison has, until now, been sorely lacking. STAR data allow, for the first time, such a direct comparison between A+A, d+A, and p+p collisions, at the same energy, measured in the same detector, and using the same analysis techniques. Surprisingly, our preliminary results indicate an mT-independent scaling of the femtoscopic radii with overall system size. Possible physics implications of these observations will be discussed, and the importance of long-range non-femtoscopic correlations for low multiplicity collisions will be emphasized.
Using the waveforms from a digital electronic system, an offline analysis technique on pulse shape discrimination (PSD) has been developed to improve the neutron-gamma separation in a bar-shaped ...NE-213 scintillator that couples to a photomultiplier tube (PMT) at each end. The new improved method, called the "valued-assigned PSD" (VPSD), assigns a normalized fitting residual to every waveform as the PSD value. This procedure then facilitates the incorporation of longitudinal position dependence of the scintillator, which further enhances the PSD capability of the detector system. In this article, we use radiation emitted from an AmBe neutron source to demonstrate that the resulting neutron-gamma identification has been much improved when compared to the traditional technique that uses the geometric mean (GM) of light outputs from both PMTs. The new method has also been modified and applied to a recent experiment at the National Superconducting Cyclotron Laboratory (NSCL) that uses an analog electronic system.
The study of low-energy reactions with radioactive-ion beams has been greatly enhanced by the recent use of active-target detectors, which have high efficiency and low thresholds to detect low-energy ...charged-particle decays. Both of these features have been used in experiments with the Prototype Active-Target Time-Projection Chamber to study α-cluster structure in unstable nuclei and 3-body charged-particle decays after implantation. Predicted α-cluster structures in 14C were probed using resonant α scattering and the nature of the 3-α breakup of the 02+ Hoyle state in 12C after the beta decay of 12N and 12B was studied. These experiments used in-flight radioactive-ion beams that were produced using the dual superconducting solenoid magnets TwinSol at the University of Notre Dame. Preliminary results from these experiments as well as the development of future radioactive beams to be used in conjunction with the PAT-TPC are presented.
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