An excited superdeformed band in ${}^{194}\mathrm{Hg}$, observed to decay directly to both normal-deformed and superdeformed yrast states, is proposed to be a $K^{\pi }{=2\mathrm{}}^{-}$ octupole vibrational band, based on its excitation energies, spins, and likely parity. The transition energies are identical to those of the yrast superdeformed band in ${}^{192}\mathrm{Hg}$, but originate from levels with different spins and parities. The evolution of transition energies with spin suggests that cancellations between pairing and particle alignment are partly responsible for the identical transition energies.

A Comment on the Letter by L. G. Moretto et al., Phys. Rev. Lett. 75, 4186 (1995). The authors of the Letter offer a Reply.

A Reply to the Comment by B. B. Back, D. J. Hofman, and V. Nanal.

Using coherent bremsstrahlung at MAMI (Mainz), the beam asymmetry of the differential cross sections for coherent $\pi °$ photoproduction on ${}^4\mathrm{He}$ has been measured in the energy interval from 200 to 500 MeV at an angle of ${\theta }_{\mathrm{lab}}=37\mathrm{}°$. The coherent ( $\gamma ,\pi °$) reaction is used as a precise linear polarimeter for the first time. Agreement with predictions has been obtained on a $\gtrsim 3\%$ level of precision.

The capture cross section of the reaction ${}^{16}\mathrm{O}(p,\gamma {)}^{17}\mathrm{F}$ was measured in the energy range from $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=200\mathrm{}–3750\mathrm{keV}$ using the windowless gas target facility Rhinoceros. The low-energy $S$ factor that is dominated by the transition to the $1/2^{+}$ first excited state in ${}^{17}\mathrm{F}$ increases strikingly with decreasing energy. This behavior is explained by the halo properties of this $1/2^{+}$ state within the framework of the direct capture model.

The relativistic Hartree Bogoliubov model is applied in the self-consistent mean-field approximation to the description of the neutron halo in the mass region above the $s-d$ shell. Pairing correlations and the coupling to particle continuum states are described by finite range two-body forces. Finite element methods are used in the coordinate space discretization of the coupled system of Dirac-Hartree-Bogoliubov integro-differential eigenvalue equations, and Klein-Gordon equations for the meson fields. Calculations are performed for the isotopic chains of Ne and C nuclei. We find evidence for the occurrence of neutron halo in heavier Ne isotopes. The properties of the $1f-2p$ orbitals near the Fermi level and the neutron pairing interaction play a crucial role in the formation of the halo. Our calculations display no evidence for the neutron halo phenomenon in C isotopes.

The ${}^{28}\mathrm{Si}(\alpha {,}^8\mathrm{He}{)}^{24}\mathrm{Si}$ reaction has been used to measure the energies of the first two excited states in ${}^{24}$Si. The excitation energies were found to be $1.879\pm 0.011$ and $3.441\pm 0.010\mathrm{MeV}$. These data allow for the first time the calculation of the stellar reaction rate of ${}^{23}\mathrm{Al}(p,\gamma {)}^{24}\mathrm{Si}$ on the basis of experimental information. This reaction is of considerable interest, since it might lead to a decrease of the ${}^{22}$Na production in nova explosions, and solve the discrepancy between the ${}^{22}$Na yield predictions of nova models and recent COMPTEL observations. We show, however, that the temperatures and densities required for a significantly reduced ${}^{22}$Na yield are not reached in current nova models.

The $({\pi }^{+},{\pi }^{-})$ reaction on the isoscalar, doubly magic nuclei ${}^{16}\mathrm{O}$ and ${}^{40}\mathrm{Ca}$ has been measured in the energy range $T_{\pi }=45\mathrm{}–90\mathrm{MeV}$. The forward angle cross sections of the ground state transitions (GST) show a very pronounced resonancelike energy dependence. The observed energy and angle dependences are well described by the recent hypothesis of the formation of a $\pi \mathrm{NN}$ resonance in the course of the double charge exchange process. The deduced spreading widths are in accordance with estimates of the $d^{\prime }$ collision damping in the nuclear medium. In the reaction on ${}^{16}\mathrm{O}$ in addition to the GST the transition to a $0^{+}$ state at $E_x=2.1\mathrm{}\left(2\right)\mathrm{MeV}$ in ${}^{16}\mathrm{Ne}$ has been observed, which is interpreted as the quadruple isobaric analog state (QIAS) of the $0_2^{+}$ state in ${}^{16}\mathrm{C}$ at $E_x=3.03\mathrm{}\mathrm{MeV}$.

The direct excitation of a “sea” of two-phonon configurations above 15 MeV from the ground state is considered. It is concluded that these configurations form a flat physical background in photoexcitation cross sections and Coulomb excitation in heavy ion reactions at relativistic energies. The contribution of the background to the total cross section in Coulomb excitation of ${}^{208}\mathrm{Pb}$ in the double giant dipole resonance (DGDR) energy region is about 15%. It should be considered while drawing conclusions on anharmonicity effects for the DGDR.

We present results of a search for strange quark matter (strangelets) in $11.5A\mathrm{GeV}/c\mathrm{Au}+\mathrm{Pb}$ collisions from the 1994 and 1995 runs of experiment E864 at Brookhaven's Alternating Gradient Synchrotron. We observe no strangelet candidates and set a 90% confidence level upper limit of approximately $3\times {10}^{-8\mathrm{}}$ per 10% central interaction for the production of $|Z|=1\mathrm{}$ and $|Z|=2\mathrm{}$ strangelets over a large mass range and with metastable lifetimes of about 50 ns or more. These results place constraints primarily on quark-gluon plasma based production models for strangelets.

We present the first results from the E864 Collaboration on the production of antiprotons in 10% central $11.5A\mathrm{GeV}/\mathrm{c}\mathrm{Au}+\mathrm{Pb}$ nucleus collisions at the Brookhaven Alternating Gradient Synchrotron. We report invariant multiplicities for antiproton production in the kinematic region $1.4<y<\mathrm{}2.2\mathrm{}$ and $50<\mathrm{}{p}_T<300\mathrm{MeV}/c$, and compare our data with a first collision scaling model and previously published results from the E878 Collaboration. The differences between the E864 and E878 antiproton measurements and the implications for antihyperon production are discussed.

We have measured total nuclear disintegration cross sections for ${}^{208}\mathrm{Pb}$ ions at 33 TeV $\left(160-\mathrm{GeV}A\right)$ colliding with C, Si, Cu, Sn, and Pb. Using well established theory, we calculate the nuclear electromagnetic, electron electromagnetic, and the hadronic contributions and find that their sum underestimates the measured cross sections. An additive correction term linear in target $Z_T$ (i.e., ${120Z}_T\mathrm{mb}$) is necessary to bring agreement between theory and experiment. The source of this additional term is unknown.

A Comment on the Letter by P. F. Mastinu et al., Phys. Rev. Lett. 76, 2646 (1996).

A Comment on the Letter by Aldo Bonasera and Akira Iwamoto, Phys. Rev. Lett. 78, 187 (1997). The authors of the Letter offer a Reply.

A Reply to the Comment by George F. Bertsch and Aurel Bulgac.

A new technique based on barium phosphate glass detectors was used in searching for Dirac pointlike magnetic monopoles with $n\ge 2$ in ultrarelativistic heavy ion collisions. No candidates were found in $1.05\times {10}^9$ and $3.08\times {10}^{10}$ interactions of $11A\mathrm{GeV}$ Au nuclei and $1.46\times {10}^{10}$ interactions of $160A\mathrm{GeV}$ Pb nuclei with Pb targets. The upper limits, on order of nb, on the production cross sections for Dirac magnetic monopoles and other hypothetical highly ionizing objects are well below those predicted via the Drell-Yan mechanism.

Utilizing the Langevin equation for the linear $\sigma$ model we investigate the interplay of friction and white noise on the evolution and stability of collective pionic fields in energetic heavy ion collisions. We find that the smaller the volume, the more stable transverse (pionic) fluctuations become on a homogeneous disoriented chiral field background (the average transverse mass $〈m_t^2〉$ increases). On the other hand the variance of $m_t^2$ increases even more, so for a system thermalized in an initial volume of $10\mathrm{fm}{}^3$ about $96\%$ and even in $1000\mathrm{fm}{}^3$ about $60\%$ of the individual trajectories enter into unstable regions ( $m_t^2<0\mathrm{}$) for a while during a rapid one-dimensional expansion ( ${\tau }_0=1\mathrm{fm}/c$). In contrast the ensemble averaged solution in this case remains stable. This result supports the idea of looking for disoriented chiral condensate (DCC) formation in individual events.

A Comment on the Letter by G. Casini et al., Phys. Rev. Lett. 78, 828 (1997). The authors of the Letter offer a reply.

A Reply to the Comment by S. Chattopadhyay.

We use the auxiliary fields Monte Carlo method for the shell model in the complete $\left({pf+0g}_{9/2}\right)$ shell to calculate level densities. We introduce parity projection techniques which enable us to calculate the parity dependence of the level density. Results are presented for ${}^{56}\mathrm{Fe}$, where the calculated total level density is found to be in good agreement with the experimental level density. The parity-projected densities are well described by a backshifted Bethe formula, but with significant dependence of the single-particle level-density and backshift parameters on parity. We compare our exact results with those of the thermal Hartree-Fock approximation.