Mass-energy and angular distributions of fission fragments for the ${}^{48}\mathrm{Ca}+{}^{144,154}\mathrm{Sm}\to {}^{192,202}\mathrm{Pb}$, ${}^{40}\mathrm{Ca}+{}^{154}\mathrm{Sm}\to {}^{194}\mathrm{Pb}$ reactions have been measured. Fusion suppression and the presence of quasifission at energies near and below the Coulomb barrier have been observed for the reactions with the deformed target ${}^{154}\mathrm{Sm}$. In the case of the spherical ${}^{144}\mathrm{Sm}$ target no evidence of quasifission has been found. Quasifission cross sections have been extracted from total fission-like events by analysis of their mass and angular distributions.

We report measurements of double radiative capture in pionic hydrogen and pionic deuterium. The measurements were performed with the RMC spectrometer at the TRIUMF cyclotron by recording photon pairs from pion stops in liquid hydrogen and deuterium targets. We obtained absolute branching ratios of $[3.02\pm 0.27(\mathrm{stat}.)\pm 0.31(\mathrm{syst}.)]\times {10}^{-5}$ for hydrogen and $[1.42\pm {}_{0.12}^{0.09}(\mathrm{stat}.)\pm 0.11(\mathrm{syst}.)]\times {10}^{-5}$ for deuterium and relative branching ratios of double radiative capture to single radiative capture of $[7.68\pm 0.69(\mathrm{stat}.)\pm 0.79(\mathrm{syst}.)]\times {10}^{-5}$ for hydrogen and $[5.44\pm {}_{0.46}^{0.34}(\mathrm{stat}.)\pm 0.42(\mathrm{syst}.)]\times {10}^{-5}$ for deuterium. For hydrogen, the measured branching ratio and photon energy-angle distributions are in fair agreement with a reaction mechanism involving the annihilation of the incident ${\pi }^{-}$ on the ${\pi }^{+}$ cloud of the target proton. For deuterium, the measured branching ratio and energy-angle distributions are qualitatively consistent with simple arguments for the expected role of the spectator neutron. A comparison between our hydrogen and deuterium data and earlier beryllium and carbon data reveals substantial changes in the relative branching ratios and the energy-angle distributions and is in agreement with the expected evolution of the reaction dynamics from an annihilation process in $S$-state capture to a bremsstrahlung process in $P$-state capture. Lastly, we comment on the relevance of the double radiative process to the investigation of the charged pion polarizability and the in-medium pion field.

We present strange particle spectra and yields measured at midrapidity in $\sqrt{s}=200$ GeV proton-proton ($p+p$) collisions at the BNL Relativistic Heavy Ion Collider (RHIC). We find that the previously observed universal transverse mass ($m_T\equiv \sqrt{{p_T}^2+m^2}$) scaling of hadron production in $p+p$ collisions seems to break down at higher $m_T$ and that there is a difference in the shape of the $m_T$ spectrum between baryons and mesons. We observe midrapidity antibaryon to baryon ratios near unity for Λ and Ξ baryons and no dependence of the ratio on transverse momentum, indicating that our data do not yet reach the quark-jet dominated region. We show the dependence of the mean transverse momentum $\langle p_T\rangle$ on measured charged particle multiplicity and on particle mass and infer that these trends are consistent with gluon-jet dominated particle production. The data are compared with previous measurements made at the CERN Super Proton Synchrotron and Intersecting Storage Rings and in Fermilab experiments and with leading-order and next-to-leading-order string fragmentation model predictions. We infer from these comparisons that the spectral shapes and particle yields from $p+p$ collisions at RHIC energies have large contributions from gluon jets rather than from quark jets.

Recently the HADES Collaboration has published the invariant mass spectrum of $e^{+}{e}^{-}$ pairs, $\mathit{dN}/{\mathit{dM}}_{e^{+}{e}^{-}}$, produced in C + C collisions at 2$A$ GeV. Using electromagnetic probes, one hopes to get information from this experiment on hadron properties at high density and temperature. Simulations show that firm conclusions on possible in-medium modifications of meson properties will only be possible when the elementary meson production cross sections, especially in the $\mathrm{pn}$ channel, as well as production cross sections of baryonic resonances are better known. Presently one can conclude that (i) simulations overpredict by far the cross section at $M_{e^{+}{e}^{-}}\approx M_{\omega }^0$ if free production cross sections are used and that (ii) the upper limit of the η decay into $e^{+}{e}^{-}$ is smaller than the present upper limit of the Particle Data Group. This is the result of simulations using the isospin quantum molecular dynamics approach.

A theoretical formalism leading to elegant derivation of formulas for all spin observables is outlined for photoproduction of mesons with arbitrary spin-parity $s^{\pi }$. The salient features of this formalism, based on irreducible tensor techniques, are (i) the number of independent irreducible tensor amplitudes is $4(2s+1)$, (ii) a single compact formula is sufficient to express these amplitudes in terms of allowed electric and magnetic multipole amplitudes, and (iii) all the spin observables, including beam analyzing powers as well as the differential cross section, are expressible in terms of bilinear irreducible tensors of rank 0 to $2(s+1)$. The relationship between the irreducible tensor amplitudes and the helicity amplitudes is elucidated in general and explicit expressions for the helicity amplitudes are given in terms of the irreducible tensor amplitudes in the particular cases of pseudoscalar and vector meson photoproduction. The connection between the irreducible tensor amplitudes introduced here and the well-known Chew-Goldberger-Low-Nambu amplitudes for photoproduction of pseudoscalar mesons is also established.

We have developed a novel technique for measurements of low-energy $(p,\alpha )$ reactions using heavy-ion beams and a differentially pumped windowless gas target. We applied this new approach to study the 183 keV resonance in the ${}^{17}\mathrm{O}$($p,\alpha$)${}^{14}\mathrm{N}$ reaction. We report a (center-of-mass) resonance energy of $E_r=183.5\genfrac{}{}{0ex}{}{+0.1}{-0.4}$ keV and a resonance strength of $\omega {\gamma }_{p\alpha }=(1.70\pm 0.15)$ meV, and we set an upper limit (95% confidence) on the total width of the state of $\Gamma <0.1$ keV. This resonance is important for the ${}^{17}\mathrm{O}$($p,\alpha$)${}^{14}\mathrm{N}$ reaction rate, and we find that ${}^{18}\mathrm{F}$ production is significantly decreased in low-mass ONeMg novae but less affected in more energetic novae. We also report the first determination of the stopping power for oxygen ions in hydrogen gas near the peak of the Bragg curve ($E=193$ keV/u) to be $(63\pm 1)\times {10}^{-15}$ eV cm${}^2$.

The high-spin levels in the neutron-rich ${}^{143}\mathrm{La}$ nucleus have been investigated from the study of prompt γ rays in the spontaneous fission of ${}^{252}\mathrm{Cf}$ with the Gammasphere detector array. A new level scheme with spin up to 27/2 ħ has been established, and the collective bands have been identified for the first time. A set of opposite-parity bands connected by $\Delta I=1E1$ crossing transitions gives evidence for octupole correlations. The results of $B(E1)/B(E2)$ branching ratios indicate that the octupole correlations in ${}^{143}\mathrm{La}$ are strong. The reflection-asymmetry shell model is applied to calculate the levels of the octupole bands of ${}^{143}\mathrm{La}$, and the calculated results are in good agreement with the experimental ones.

The decay of ${}^{10}\mathrm{C}$ excited states to the $2p+2\alpha$ exit channel has been studied using an $E/A=10.7$ MeV ${}^{10}\mathrm{C}$ beam inelastically scattered from a ${}^9\mathrm{Be}$ target. Levels associated with two-proton decay to the ground state of ${}^8\mathrm{Be}$ have been observed. These include states at 5.18 and 6.54 MeV which decay by sequential two-proton emission through the long-lived ground state of ${}^9\mathrm{B}$. In addition, states at 5.3 and 6.57 MeV were found in which there is no long-lived intermediate state between the two proton emissions. For the 6.57 MeV state, the two protons are preferably emitted on the same side of the decaying ${}^{10}\mathrm{C}$ fragment.

The nucleon direct-semidirect (DSD) capture cross sections are obtained by calculating a transition amplitude to the Hartree-Fock-BCS bound states. The radial matrix elements in the DSD amplitudes are calculated from the radial part of the single-particle wave functions. For deformed nuclei the single-particle states are expanded in the cylindrical harmonic-oscillator basis and then projected on the spherical harmonic-oscillator basis. The pairing correlations are treated in the BCS approach and the calculated spectroscopic factors are in fairly good agreement with experimental data in the even tin isotopes from ${}^{116}\mathrm{Sn}$ to ${}^{124}\mathrm{Sn}$. The resulting DSD cross sections for the neutron capture by ${}^{208}\mathrm{Pb}$ and ${}^{238}\mathrm{U}$ are found to be in good agreement with the available experimental data. The calculations are also performed for the neutron capture on ${}^{122}\mathrm{Sn}$ and ${}^{132}\mathrm{Sn}$ isotopes that are important for the r-process in astrophysics.

A maximum of the $S(E)$ factor is evidence for an onset of sub-barrier fusion hindrance and it can be well described by a radius-of-curvature expression near the maximum. The systematics of this radius of curvature has been studied over a wide range of projectile-target combinations. It follows a tentative general trend as a function of the parameter $\zeta =Z_1{Z}_2\sqrt{\mu }$, and is strongly affected by effects associated with the nuclear structure of the nuclei in the entrance channel. It also explains the reason why the $S$ factor maximum is not easily recognized visually for lighter, astrophysically interesting fusion systems.

The subthreshold photoproduction of ϕ mesons from heavy nuclear targets has been suggested as a candidate to search for the ϕ-$N$ bound state, a quantum chromodynamics molecular state. In this Brief Report, we present detailed Monte Carlo studies to demonstrate the feasibility of this technique. Further, we show that proton-induced subthreshold production of ϕ meson from heavy nuclear targets is also suitable for such a search.

We investigate how the unitary correlation operator method (UCOM), developed to explicitly describe the strong short-range central and tensor correlations present in the nuclear many-body system, relates to the similarity renormalization group (SRG), a method to band-diagonalize Hamiltonians by continuous unitary transformations. We demonstrate that the structure of the UCOM transformation, originally motivated from the physically intuitive picture of correlations in coordinate space, arises naturally from the SRG flow equation. Apart from formal considerations we show that the momentum space matrix elements of the effective interactions obtained in both schemes agree extremely well.

We use the Peierls-Yoccoz projection method to study the motion of a relativistic system of nucleons interacting with sigma and omega mesons, generalizing a method developed for the alpha particle. The nuclear system is described in a mean-field Hartree approach, including explicitly the meson contribution. The formalism is applied to ${}^4\mathrm{He}$, ${}^{16}\mathrm{O},$ and ${}^{40}\mathrm{Ca}$. The center-of-mass correction makes the system too much bounded. It turns out that a new set of model parameters is needed when the center-of-mass motion is consistently treated with respect to the traditional approaches. An appropriate refitting of the model brings the radii and binding energies to reasonable values for the oxygen and calcium.

Emission-energy distributions for cross sections as well as analyzing powers were investigated for ($\overrightarrow{p},{}^3\mathrm{He}$) reactions on ${}^{59}\mathrm{Co}$ and ${}^{93}\mathrm{Nb}$ to the continuum from a threshold of $\sim$40 MeV up to the kinematic limit at incident energies of 130 and 160 MeV. A range of scattering angles from 15$°$ to 140$°$ (laboratory) was explored. The experimental distributions were compared with a multistep direct theory in which a reaction mechanism based on deuteron pickup is employed. Reasonable agreement between experimental double differential cross sections and analyzing powers and the theoretical expectation was obtained. This work, together with published results for the same reaction and targets at a lower projectile energy of 100 MeV, allowed the incident-energy dependence of the cross section and analyzing power distributions to be explored.

We present results on two-particle angular correlations in proton-proton collisions at center-of-mass energies of 200 and 410 GeV. The PHOBOS experiment at the BNL Relativistic Heavy Ion Collider has a uniquely large coverage for charged particles, giving the opportunity to explore the correlations at both short- and long-range scales. At both energies, a complex two-dimensional correlation structure in $\Delta \eta$ and $\Delta \varphi$ is observed. In the context of an independent cluster model of short-range correlations, the cluster size and its decay width are extracted from the two-particle pseudorapidity correlation function and compared with previous measurements in proton-proton and proton-antiproton collisions, as well as PYTHIA and HIJING predictions.

We calculate the bulk viscosity of color-superconducting quark matter in the color-flavor-locked (CFL) phase. We assume that the lightest bosons are the superfluid mode $H$ and the kaons $K^0$ and $K^{+}$, and that there is no kaon condensate. We calculate the rate of strangeness-equilibrating processes that convert kaons into superfluid modes, and the resultant bulk viscosity. We find that for oscillations with a timescale of milliseconds, at temperatures $T<1$ MeV, the CFL bulk viscosity is much less than that of unpaired quark matter, but at higher temperatures the bulk viscosity of CFL matter can become larger.

A parton and hadron cascade model, PACIAE, is applied to follow the particle transport in partonic and the hadronic stages in 0–5% most central Au+Au collisions at energies from SPS to RHIC. We have determined the specific heat of hadron matter (${\pi }^{+}+{\pi }^{-}$) in the hadronic final state and the specific heat of quark-gluon matter ($u+d+g$) in the partonic initial state in Au+Au collisions as a function of the reaction energy (excitation function). It turns out that the quark-gluon matter (QGM) specific heat is hard to survive the hadronization and there is not a peak structure in the specific heat excitation functions in studied energy region.

A high-resolution (${\sigma }_{\mathrm{instr}.}=1.5$ MeV) search for narrow states ($\Gamma <10$ MeV) with masses of $M_x\approx 1500–1850$ MeV in $\mathit{ep}\to e^{\prime }{K}^{+}X,e^{\prime }{K}^{-}X$, and $e^{\prime }{\pi }^{+}X$ electroproduction at small angles and low $Q^2$ was performed. These states would be candidate partner states of the reported ${\Theta }^{+}(1540)$ pentaquark. No statistically significant signal was observed in any of the channels at 90% C.L. Upper limits on forward production were determined to be between 0.8% and 4.9% of the $\Lambda (1520)$ production cross section, depending on the channel and the assumed mass and width of the state.

Penning trap mass measurements of the super-allowed β emitter ${}^{38}\mathrm{Ca}$ and of ${}^{37}\mathrm{Ca}$ have been performed using the low-energy beam and ion trap facility at the coupled cyclotron facility of the National Superconducting Cyclotron Laboratory. Both isotopes were produced by fast-beam fragmentation and in-flight separation. The mass of ${}^{38}\mathrm{Ca}$ ($T_{1/2}=440$ ms) was determined with a precision of $\delta m=280$ eV, corresponding to a relative mass uncertainty of $\delta m/m\approx 8\times {10}^{-9}$. A mass excess value of ME $=-22508.52(28)$ was obtained. ${}^{38}\mathrm{Ca}$ is a $0^{+}\to 0^{+}$ emitter, and the improved mass value makes it a new candidate for testing the conserved vector current hypothesis. For ${}^{37}\mathrm{Ca}$ ($T_{1/2}=180$ ms), a mass excess value of ME $=-13135.7(1.4)$ was measured. Using the quadratic form of the isobaric mass multiplet equation and the improved ${}^{37}\mathrm{Ca}$ mass value, a precise prediction of the excitation energy of the ${}^{37}\mathrm{Ar}$ isobaric analog state was obtained.