Several approaches to QCD with two massless quarks at finite temperature $T$ and baryon chemical potential $\mu$ suggest the existence of a tricritical point on the boundary of the phase with spontaneously broken chiral symmetry. In QCD with massive quarks there is then a critical point at the end of a first order transition line. We discuss possible experimental signatures of this point, which provide information about its location and properties. We propose a combination of event-by-event observables, including suppressed fluctuations in $T$ and $\mu$ and, simultaneously, enhanced fluctuations in the multiplicity of soft pions.

We present the first results of a calculation of the differential cross section and of polarization observables for proton-deuteron elastic scattering at 10 MeV proton laboratory energy, for the Paris potential. The method used is the “screening and renormalization approach” which allows one to correctly take into account the Coulomb repulsion between the two protons. Comparison is made with the precise experimental data of Sagara et al. [Phys. Rev. C 50, 576 (1994)] and of Sperison et al. [Nucl. Phys. A422, 81 (1984)].

The ratio of the exclusive production cross sections for $\phi$ and $\omega$ mesons has been measured in $\mathrm{pp}$ reactions at $T_{\mathrm{beam}}=2.85\mathrm{GeV}$. The observed $\phi /\omega$ ratio is $(3.7\pm {0.7}_{-0.9\mathrm{}}^{+1.2\mathrm{}})\times {10}^{-3\mathrm{}}$. After phase space corrections, this ratio is about a factor of 10 enhanced relative to naive predictions based upon the Okubo-Zweig-Iizuka rule, in comparison to an enhancement by a factor of $\sim 3$ previously observed at higher energies. The modest increase of this enhancement near the production threshold is compared to the much larger increase of the $\phi /\omega$ ratio observed in specific channels of $\overline{p}p$ annihilation experiments.

The first measurements of the differential cross section for the $d(\gamma ,p)n$ reaction up to 4.0 GeV were performed at the Continuous Electron Beam Accelerator Facility (CEBAF) at Thomas Jefferson Laboratory. We report the cross sections at the proton center-of-mass angles of 36°, 52°, 69°, and 89°. These results are in reasonable agreement with previous measurements at lower energy. The 89° and 69° data show constituent-counting-rule behavior up to 4.0 GeV photon energy. The 52° and 36° data disagree with the counting-rule behavior. The quantum chromodynamics (QCD) model of nuclear reactions involving reduced amplitudes disagrees with the present data.

The fusion of ${}^6\mathrm{He}$ with a ${}^{209}\mathrm{Bi}$ target has been studied at energies near to and below the Coulomb barrier. Despite the weak binding of the valence neutrons in ${}^6\mathrm{He}$, little evidence is found for suppression of fusion due to projectile breakup. Instead, a large enhancement of sub-barrier fusion is observed. It is suggested that this enhancement may arise from coupling to positive $Q$ value neutron transfer channels, resulting in “neutron flow” between the projectile and the target.

A Comment on the Letter by N. Majumdar et al., Phys. Rev. Lett. 77, 5027 (1996). The authors of the Letter offer a Reply.

A Comment on the Letter by N. Majumdar et al., Phys. Rev. Lett. 77, 5027 (1996). The authors of the Letter offer a Reply.

A Reply to the Comment by J. P. Lestone et al. and D. J. Hinde et al.

Variational Monte Carlo wave functions, obtained from a realistic Hamiltonian consisting of the Argonne $v_{18}$ two-nucleon and Urbana-IX three-nucleon interactions, are used to calculate the ${}^6\mathrm{Li}$ ground-state longitudinal and transverse form factors as well as transition form factors to the first four excited states. The charge and current operators include one- and two-body components, leading terms of which are constructed consistently with the two-nucleon interaction. The calculated form factors and radiative widths are in good agreement with available experimental data.

We have measured lifetimes of $\Lambda$ hypernuclei over a broad mass range explicitly identifying $\Lambda$ hypernuclear production in the $\left({\pi }^{+}{,K}^{+}\right)$ reaction. The obtained results are $\tau {(}_{\Lambda }^{12}\mathrm{C})=231\mathrm{}\pm 15\mathrm{ps}$, $\tau {(}_{\Lambda }^{28}\mathrm{Si})=206\mathrm{}\pm 12\mathrm{ps}$, and $\tau {(}_{\Lambda }\mathrm{Fe})=215\mathrm{}\pm 14\mathrm{ps}$. The lifetimes of $\Lambda$ hypernuclei over the mass region from carbon to iron are found almost constant at about 80% of that of free $\Lambda$ within the statistical uncertainties. The short-range nature of the nonmesonic weak decay process, which is dominant in heavy $\Lambda$ hypernuclei, is possibly responsible for the observed weak hypernuclear mass dependence.

The excited states of the “halo” nucleus, ${}^{11}\mathrm{Li}$, have been investigated by means of the pion capture reaction, ${}_{}{}^{14}{}_{}{}^{}C({\pi }^{-},pd{)}^{11}\mathrm{Li}$. Excited states have been identified at $1.02\pm 0.07$, $2.07\pm 0.12$, and $3.63\pm 0.13\mathrm{MeV}$. The continuum part of the ${}^{11}\mathrm{Li}$ missing mass spectrum is found to contain a major component which is consistent with ${}^{11}\mathrm{Li}$ breakup into one of the ${}^9\mathrm{Li}$ excited states and two strongly correlated neutrons.

Novel results were obtained for the spin dispersion parameter, which demonstrate the influence of the nucleon pairing correlations and shell effects in nuclei. The volume and surface parameters of the level density parameter, as well as the shell-damping factor, were determined as $a_v=0.076\mathrm{}\pm 0.009{\mathrm{MeV}}^{-1\mathrm{}}$, $a_s=0.180\mathrm{}\pm 0.047{\mathrm{MeV}}^{-1\mathrm{}}$, and ${\gamma }_0=0.47\mathrm{}\pm 0.04{\mathrm{MeV}}^{-1\mathrm{}}$, respectively. The effective nucleon mass at the Fermi surface is found to be enhanced and its value is $m^{*}/m=1.09\mathrm{}\pm 0.13$. These findings are in excellent agreement with the theoretical estimates of Shlomo and Natowitz.

The production of neutral pions in $158A\mathrm{GeV}$ ${}^{208}\mathrm{Pb}{+}^{208}\mathrm{Pb}$ collisions has been studied in the WA98 experiment at the CERN Super Proton Synchrotron (SPS). Transverse momentum spectra are studied for the range $0.3\le m_T{-m}_0\le 4.0\mathrm{GeV}/c$. The results for central collisions are compared to various models. The centrality dependence of the neutral pion spectral shape and yield is investigated. An invariance of the spectral shape and a simple scaling of the yield with the number of participating nucleons is observed for centralities with greater than about 30 participating nucleons. This is most naturally explained by assuming an equilibrated system.

Ratios of hadronic abundances are analyzed for $\mathrm{pp}$ and nucleus-nucleus collisions at $\sqrt{s}\approx 20\mathrm{GeV}$ using the microscopic ultrarelativistic quantum molecular dynamics transport model. Secondary interactions significantly change the primordial hadronic composition of the system. A strong dependence on rapidity is predicted. Without assuming thermal and chemical equilibrium, predicted hadron yields and ratios agree with many of the data ( $\pi /p$, $d/p$, $\overline{p}/p$, $\overline{\Lambda }/\Lambda$, $\overline{\Xi }/\overline{\Lambda }$, etc.).

The lifetime of a disoriented chiral condensate formed within a heat bath of pions is calculated assuming temperatures and densities attainable at present and future heavy-ion colliders. A generalization of the reduction formula to include coherent states allows us to derive a formula for the decay rate. We predict the half-life to be between 4 and $7\mathrm{fm}/c$, depending on the assumed pion density. We also calculate the lifetime in the presence of higher resonances and baryons, which shortens the lifetime by at most $20\%$.

In deep-inelastic collisions of 8 MeV/nucleon ${}^{76}\mathrm{Ge}$ projectiles with ${}^{198}\mathrm{Pt}$, we have found a $T_{1/2}=0.25\mathrm{}\left(3\right)\mu \mathrm{s}$ isomer in ${}^{71}\mathrm{Cu}$ which decays through a $\gamma$-ray cascade of 133-495-939-1189 keV to the $\pi p_{3/2}$ ground state. The detector setup records the $\gamma$ rays of the isomeric decay as well as data on the fragment which provide its isotopic assignment. The new ${}^{71}\mathrm{Cu}$ levels are firmly assigned as the five yrast states of the $\nu g_{9/2}^2\pi p_{3/2}$ configuration; a parameter-free shell model calculation using the two-body residual interactions as observed in ${}^{70}\mathrm{Cu}$ and ${}^{70}\mathrm{Ni}$ predicts the ${}^{71}\mathrm{Cu}$ data with excellent accuracy.

The fundamental structure of the full set of solutions of the BCS ${}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$ pairing problem in neutron matter is established. The relations between different spin-angle components in these solutions are shown to be practically independent of density, temperature, and the specific form of the pairing interaction. The spectrum of pairing energies is found to be highly degenerate.

A Comment on the Letter by J. Toke et al., Phys. Rev. Lett. 77, 3514 (1996).

The odd-even staggering of nuclear masses was recognized in the early days of nuclear physics. Recently, a similar effect was discovered in other finite fermion systems, such as ultrasmall metallic grains and metal clusters. It is believed that the staggering in nuclei and grains is primarily due to pairing correlations (superconductivity), while in clusters it is caused by the Jahn-Teller effect. We find that, for light- and medium-mass nuclei, the staggering has two components. The first originates from pairing while the second, comparable in magnitude, has its roots in the deformed mean field.

The attenuation factor $F$ responsible for the decay out of a superdeformed (SD) band is calculated with the help of a statistical model. This factor is given by $F=(1+{\Gamma }^{\downarrow }/{\Gamma }_S{)}^{-1\mathrm{}}$. Here, ${\Gamma }_S$ is the width for the collective $E2\mathrm{}$ transition within the superdeformed band, and ${\Gamma }^{\downarrow }$ is the spreading width which describes the mixing between a state in the SD band and the normally deformed (ND) states of equal spin. The attenuation factor $F$ is independent of the statistical $E1\mathrm{}$ decay widths ${\Gamma }_N$ of the ND states provided that ${\Gamma }_N\gg {\Gamma }^{\downarrow }$, ${\Gamma }_S$. This condition is generically met. Previously measured values of $F$ are used to determine ${\Gamma }^{\downarrow }$.