The $3p-1s$ x-ray line of pionic hydrogen was measured with a reflecting bent crystal spectrometer. The strong interaction energy level shift and the total decay width of the $1s$ state, obtained from the transition energy and the linewidth, are ${\varepsilon }_{1s}=-7.127\mathrm{}\pm 0.028\left(\mathrm{stat}\right)\pm 0.036\left(\mathrm{syst}\right)\mathrm{eV}$ (attractive) and ${\gamma }_{1s}=0.97\mathrm{}\pm 0.10\left(\mathrm{stat}\right)\pm 0.05\left(\mathrm{syst}\right)\mathrm{eV}$. The corresponding hadronic $\pi N$ s-wave scattering lengths for elastic scattering and single charge exchange are $a_{{\pi }^{-}p\to {\pi }^{-}p}^h=0.0885\mathrm{}\pm {0.0009m}_{\pi }^{-1\mathrm{}}$ and $a_{{\pi }^{-}p\to {\pi }^{0}n}^h=-0.136\mathrm{}\pm {0.010m}_{\pi }^{-1\mathrm{}}$.

We have investigated particle production using a zero degree two-segment focusing beam-line spectrometer, examining $2\times {10}^{12}\mathrm{Au}+\mathrm{Au}$ interactions at a beam momentum of $10.8A\mathrm{GeV}/c$. We have measured invariant cross sections for protons, various light nuclei (through $A=6\mathrm{}$), antiprotons, and have set upper limits on the production of heavier nuclei, antideuterons, and strangelets. There is no evidence, within the sensitivity of our measurements, for the formation of new particles having lifetimes $>100\mathrm{ns}$

A previously unexploited experimental observable is used to explore emission times for intermediate mass fragments relative to directly emitted ${}^2\mathrm{H}$ and ${}^3\mathrm{H}$ particles. Small-angle correlations are reported in central collisions for $34A\mathrm{MeV}$ ${}^{40}\mathrm{Ar}{+}^{\mathrm{nat}}\mathrm{Ag}$. High-velocity ${}^3\mathrm{H}$ and ${}^2\mathrm{H}$ particles follow a direct emission scenario with mean lifetime $\tau \sim 30-60\mathrm{fm}/c$. Fragmentation to Li is characterized by $\tau \sim 120\mathrm{fm}/c$. Current model calculations suggest a delay time of $\sim 100-200\mathrm{fm}/c$ for expansion of the central collision zone prior to the onset of “freeze-out” into fragments. But the observed velocity difference spectra limit the delay time to $\lesssim 50\mathrm{fm}/c$ for expansion between direct emission and fragmentation.

The global correlation in the observed variation with mass number of the $E2\mathrm{}$ and summed $M1\mathrm{}$ transition strengths is examined for rare-earth nuclei. It is shown that a theory of correlated $S$ and $D$ fermion pairs with a simple pairing plus quadrupole interaction leads naturally to this universality. Thus a unified and quantitative description emerges for low-lying quadrupole and dipole strengths.

A measurement of $B\left(E3\mathrm{}\right)$ in the two-proton nuclide ${}^{134}\mathrm{Te}$ was made, giving the first empirical value of the effective proton octupole charge in the neutron rich doubly closed shell region at ${}^{132}\mathrm{Sn}$. It is demonstrated that the effective $E2\mathrm{}$ and $E3\mathrm{}$ charges can be used to derive the core phonon strengths in ${}^{132}\mathrm{Sn}$ and ${}^{208}\mathrm{Pb}$. The octupole charge and the corresponding phonon strength were found to be substantially lower at ${}^{132}\mathrm{Sn}$ than at ${}^{208}\mathrm{Pb}$, thus confirming long standing theoretical predictions of a weak octupole collectivity in the heavy Sn region.

Two-proton correlation functions for central collisions of ${}^{36}\mathrm{Ar}{+}^{45}\mathrm{Sc}$ at $E/A=80\mathrm{}$, 120, and 160 MeV are compared to calculations with the Boltzmann-Uehling-Uhlenbeck (BUU) transport model. Agreement is found at $E/A=80\mathrm{}\mathrm{MeV}$, but the model predicts too large correlations at $E/A=120\mathrm{}$ and 160 MeV. The discrepancy may be due to delayed emission of protons from particle-unstable states not modeled in BUU.

Intermediate-mass fragments (IMF) from the ${}^{209}{\mathrm{B}\mathrm{i}+}^{136}\mathrm{Xe}$ reaction at $E_{\mathrm{lab}}/A=28\mathrm{}\mathrm{MeV}$ have been measured in coincidence with other reaction products, using a highly efficient $4\pi$ detector setup. Their emission patterns exhibit features consistent with dynamical fragmentation of a neck zone between the reaction partners, in addition to sequential statistical emission. In peripheral collisions with an average of 0.3 GeV of dissipated kinetic energy, the dynamical process accounts for 0.24 of the observed IMF multiplicity of 0.33.

Considering the propagation of off-shell particles in the framework of thermal field theory, we present the general formalism for the calculation of the production rate of soft photons and dileptons from a hot plasma. This approach is first illustrated with an electrodynamic plasma. The photon production rate from strongly interacting quarks in the quark-gluon plasma, which might be formed in ultrarelativistic heavy ion collisions, is also calculated. We utilize an effective field theory incorporating dynamical chiral symmetry breaking and obtain results in the previously inaccessible regime of photon energies of the order of the plasma temperature.

The first results are presented from a new experiment, APEX, designed to study the previously reported sharp lines in sum-energy spectra of positrons and electrons produced in collisions of very heavy ions. Data were collected for ${}^{238}$U $+$${}^{181}$Ta at 5.95, 6.10, and 6.30 MeV/u and ${}^{238}$U $+$${}^{232}$Th at 5.95 MeV/u. In none of our analyses is any evidence found for sharp sum-energy lines. For the specific case of the isolated decay of a neutral particle of mass 1.4–2.1 MeV/ $c^2$, the upper limits on cross sections obtained from the present data are significantly less than the previously reported cross sections.

A systematic study of energy spectra for light particles emitted at midrapidity from $\mathrm{Au}+\mathrm{Au}$ collisions at $E=$ (0.25–1.15) $A$ GeV reveals a significant nonthermal component consistent with a collective radial flow. This component is evaluated as a function of bombarding energy and event centrality. Comparisons to quantum molecular dynamics and Boltzmann-Uehling-Uhlenbeck models are made for different equations of state.

We consider charge-symmetry violations in the nucleon-nucleon force that result from isospin-violating meson-baryon coupling constants. The isospin violations arise from the difference in the up and down constituent quark masses. We show that a class IV charge-symmetry-breaking potential exists in the resulting $\omega$ exchange contribution to the $\mathrm{NN}$ force. The magnitude of this contribution is consistent with that phenomenologically required by the measured difference of $n$ and $p$ analyzing powers in elastic $\overrightarrow{n}-\overrightarrow{p}$ scattering at 183 MeV.

The collective yrast band of the nucleus ${}^{48}\mathrm{Cr}$ is studied using the spherical shell model and the Hartree-Fock-Bogoliubov (HFB) method. Both approaches produce basically the same axially symmetric intrinsic state up to the—accurately reproduced—observed backbending. Agreement between both calculations extends to most observables. The only significant discrepancy comes from the static moments of inertia and can be attributed to the need of a more refined treatment of pairing correlations in the HFB calculation.

The neutron-rich ${}^{106}$Mo nucleus has been studied by prompt γ-ray spectroscopy following the spontaneous fission of ${}^{248}$Cm. The characteristics of the rotational band built on a state at 1435 keV identifies the band head as the best candidate for a harmonic double-phonon $K^{\pi }{=4\mathrm{}}^{+}$ γ-vibrational state observed so far.

We propose a new approach which allows us to obtain analytical expressions for the angular momentum dependence of the intermediate-state transition rates in the exciton model. Using this approach we deduce the condition for the equilibration of the angular momentum distribution of $n$-exciton states. We also calculate the isomeric ratio in the ${}^{111}\mathrm{Cd}(p,2n)$ reaction using the solutions of the master equation for each value of the total angular momentum of the composite system. We obtain good agreement with experimental data for proton energy of about $\epsilon \le 50\mathrm{MeV}$.

We investigate experimentally the issue of selecting classes of multiple particle decay events in nucleus-nucleus collisions at intermediate energy taking into account the fluctuations of global observables. We show that observed binomial-like multiplicity distributions do not necessarily imply evidence of reducibility to an elementary binary emission probability.

A Comment on the Letter by A. K. Mohanty and S. K. Kataria, Phys. Rev. Lett. 73 1994. The authors of the Letter offer a Reply.

A Reply to the Comment by B. K. Nayak and Zafar Ahmed.

Exclusive measurements have been made of Au $+$Au reactions with beam energies ranging from 0.25 $A$ to 1.15 $A$ GeV. We present measurements of directed collective flow averaged over all light fragments with masses up to alphas, as well as separate measurements for protons, deuterons, tritons, ${}^3$He, ${}^4$He, and Li. The results show a strong increase of the directed flow with fragment mass at all energies measured. Experimental results are compared with a quantum molecular dynamics model. We find that neither the “soft” nor the “hard” equation of state can describe the data over the entire range of beam energies.

In bombardments of ${}^{238}$U targets with 186-MeV ${}^{34}$S projectiles we discovered the $\alpha$-decaying nuclide ${}^{267}$108 with a half-life of ${19}_{-10\mathrm{}}^{+29\mathrm{}}$ ms, $E_{\alpha }=9.74\mathrm{}$ to 9.87 MeV, and a production cross section of about 2.5 pb. The new nuclide was identified by measuring correlations in energy, time, and position to establish genetic links between its implantation in a position-sensitive silicon detector and subsequent $\alpha$ decay followed by $\alpha$ decays of known descendant nuclides.

Charge symmetry breaking in $\mathrm{np}$ elastic scattering at 347 MeV has been measured with high precision. From fits of the measured asymmetry curves over the angular range $53.4°\le {\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}\le 86.9°$, the difference in the center-of-mass zero-crossing angles of the analyzing powers was determined to be $0.438°\pm 0.054°\left(\mathrm{stat}\right)\pm 0.051°\left(\mathrm{syst}\right)$. Using the experimentally determined slope of the analyzing power, $\mathrm{dA}/d\theta =(-1.35\mathrm{}\pm 0.05)\times {10}^{-2\mathrm{}}{\mathrm{deg}}^{-1\mathrm{}}$, this is equivalent to $\Delta A=[59\pm 7(\mathrm{stat})\pm 7(\mathrm{syst})\pm 2(\mathrm{syst}\left)\right]\times {10}^{-4\mathrm{}}$. Predictions of nucleon-nucleon interaction models based on meson exchange agree well with this result.