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The pre-equilibrium deexcitation process for (particle, $\mathrm{xn} \mathrm{yp} \gamma$) reactions induced by medium energy (40-120 MeV) light ions was studied by measuring singles $\gamma$-ray spectrum. The neutron multiplicity $x$ following these reactions was identified by discrete $\gamma$ rays characteristic of the (particle, $\mathrm{xn} \mathrm{yp} \gamma$) reaction residues. The neutron multiplicity distribution was found to depend on the projectile mass number. It suggests that the decaying neutrons depend on the initial exciton number at the pre-equilibrium phase. The median spin $I_m$ of the yrast levels populated by the (particle, $\mathrm{xn} \mathrm{yp}$) reactions was found to be nearly constant in a wide range of the bombarding energy. The $K$-isomer population ratio for the ${}_{}{}^{172}{}_{}{}^{}\mathrm{Hf}$ and ${}_{}{}^{174}{}_{}{}^{}\mathrm{Hf}$ depends on the projectile mass. The neutron multiplicity distribution was analyzed in terms of a simple two phase deexcitation model. The pre-equilibrium temperature, the number of particles emitted at the pre-equilibrium phase, and the exciton particle number at the preequilibrium phase (local mass) were deduced.

NUCLEAR REACTIONS ${}_{}{}^{175}{}_{}{}^{}\mathrm{Lu}(p, xn)$, $x=2-5\mathrm{}$, $E=40\mathrm{}$ MeV; ${}_{}{}^{176}{}_{}{}^{}\mathrm{Yb}({}_{}{}^3{}_{}{}^{}\mathrm{He}, \mathrm{xn} yp)$ $x=5-11\mathrm{}$, $y=0-1\mathrm{}$, $E=65-100\mathrm{}$ MeV; ${}_{}{}^{174,176}{}_{}{}^{}\mathrm{Yb}(\alpha , xn)$, $x=2-11\mathrm{}$, $E=50-120\mathrm{}$ MeV; measured $E_{\gamma }$, $I_{\gamma }$; deduced median spin values, $K$-isomer population ratio. Enriched targets, HPGe, Ge(Li) detectors. Two phase deexcitation model analysis.

The ${}_{}{}^3{}_{}{}^{}\mathrm{He}(\gamma ,pp)n$ reaction was investigated in the photon energy range 200-500 MeV using the spectrometer TAGX, which has a solid angle for protons of $\pi$ sr. Two types of photon absorption, one by two protons and the other by three nucleons, were observed by looking at the undetected neutron momentum distributions. The total cross section for photon absorption by two protons shows that this process is consistent with the $E2\mathrm{}$ transition.

Cross sections have been measured for ${\pi }^{+}$ and ${\pi }^{\mathrm{-}}$ inelastic scattering to the $2_1^{+}$ levels of ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$, ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$, ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}$, and ${}_{}{}^{34}{}_{}{}^{}\mathrm{S}$. The data are used to infer neutron and proton quadrupole-matrix elements for these transitions. The matrix elements extracted from the pion data are in good agreement with their corresponding electromagnetic matrix elements. These results indicate that the use of the distorted-wave impulse-approximation is a valid procedure for this class of transition.

Analyzing powers of the continuum energy spectra from the reactions ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$, ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$($p_{\mathrm{pol}}, p^{\prime }X$) and ($p_{\mathrm{pol}}, \mathrm{dX}$) at 65 MeV have been measured. The analyzing powers of the continuum spectra were found to be small at forward angles and to be very large and positive at backward angles. These features indicate the importance of the spin-dependent interaction in the understanding of the continuum spectra.

Fast-neutron emission from the giant quadrupole resonance in ${}_{}{}^{119}{}_{}{}^{}\mathrm{Sn}$ was studied for the first time by measuring the deexciting neutrons in coincidence with the inelastic ${\alpha }^{\prime }$ from the reaction ${}_{}{}^{119}{}_{}{}^{}\mathrm{Sn}(\alpha , {\alpha }^{\prime })$. The neutron time-of-flight spectrum shows both the slow evaporation component corresponding to the spreading process and the fast component corresponding to the direct escape leading to single-hole states in the residual nucleus ${}_{}{}^{118}{}_{}{}^{}\mathrm{Sn}$.

An isovector $M6\mathrm{}$ transition is observed for the first time in a ($p, n$) reaction. A prominent peak was seen at $E_x=5.545\mathrm{}\pm 0.025$ MeV in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Al}$ in the study of the reaction ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}(p, n){}_{}{}^{24}{}_{}{}^{}\mathrm{Al}$ at $E_p=35\mathrm{}$ MeV. This state is interpreted as the "stretched" particle-hole state with $J^{\pi }=6^{-}$, $T=1\mathrm{}$, which corresponds to the 15.13-MeV state in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$. Distorted-wave Born approximation analysis gives a result consistent with those for ($p, p^{\prime }$) and ($e, e^{\prime }$) reactions, indicating that at least 50% of the isovector $M6\mathrm{}$ strength is missing.

We report a virtual Compton scattering study of the proton at low c.m. energies. We have determined the structure functions $P_{LL}-P_{TT}/ϵ$ and $P_{LT}$, and the electric and magnetic generalized polarizabilities (GPs) ${\alpha }_E(Q^2)$ and ${\beta }_M(Q^2)$ at momentum transfer $Q^2=0.92$ and $1.76{\mathrm{G}\mathrm{e}\mathrm{V}}^2$. The electric GP shows a strong falloff with $Q^2$, and its global behavior does not follow a simple dipole form. The magnetic GP shows a rise and then a falloff; this can be interpreted as the dominance of a long-distance diamagnetic pion cloud at low $Q^2$, compensated at higher $Q^2$ by a paramagnetic contribution from $\pi N$ intermediate states.

Virtual Compton scattering (VCS) on the proton has been studied at the Jefferson Laboratory using the exclusive photon electroproduction reaction $ep\to ep\gamma$. This paper gives a detailed account of the analysis which has led to the determination of the structure functions $P_{LL}-P_{TT}/\epsilon$ and $P_{LT}$ and the electric and magnetic generalized polarizabilities (GPs) ${\alpha }_E\left(Q^2\right)$ and ${\beta }_M\left(Q^2\right)$ at values of the four-momentum transfer squared $Q^2=0.92$ and 1.76 GeV${}^2$. These data, together with the results of VCS experiments at lower momenta, help building a coherent picture of the electric and magnetic GPs of the proton over the full measured $Q^2$ range and point to their nontrivial behavior.

Asymmetries $A_y$ for ${\pi }^{+}$ and ${\pi }^{-}$ elastic scattering from polarized ${}^3$He were measured at incident energies passing through the $\pi$ nucleon $P_{33},$ or $\Delta$(1232), resonance. The data were taken at the Clinton P. Anderson Meson Physics Facility using the high-energy pion channel $P^3$ and a large acceptance spectrometer to detect the scattered pions. The polarized ${}^3$He target, originally developed at TRIUMF, was modified for these experiments by the addition of diode lasers. Completely unexpected negative asymmetries were observed at and below the resonance in ${\pi }^{+}$ scattering near $50°$–60$°$, which cannot be reproduced by multiple scattering theory and Faddeev wave functions. A hybrid model, which adds a $\Delta$-neutron spin-spin interaction term to the conventional calculations, provides a good description of the ${\pi }^{+}$ data. For ${\pi }^{-}$ scattering this term predicts a negligible effect on $A_y$ and the data do not show the anomalous $A_y$ seen with ${\pi }^{+}$.

The missing mass spectroscopy of the ${}_{\mathrm{\Lambda }}{}^7\mathrm{He}$ hypernucleus was performed using the ${}^7\mathrm{Li}(e,e^{\prime }{K}^{+}){}_{\mathrm{\Lambda }}{}^7\mathrm{He}$ reaction at the Thomas Jefferson National Accelerator Facility Hall C. The $\mathrm{\Lambda }$-binding energy of the ground-state ($1/2^{+}$) was determined with a smaller error than that of the previous measurement, being $B_{\mathrm{\Lambda }}=5.55\pm 0.{10}^{\mathrm{stat}.}\pm 0.{11}^{\mathrm{sys}.}\mathrm{MeV}$. The experiment also provided new insight into charge symmetry breaking in $p$-shell hypernuclear systems. Finally, a peak at $B_{\mathrm{\Lambda }}=3.65\pm 0.{20}^{\mathrm{stat}.}\pm 0.{11}^{\mathrm{sys}.}\mathrm{MeV}$ was observed and assigned as a mixture of $3/2^{+}$ and $5/2^{+}$ states, confirming the “gluelike” behavior of $\mathrm{\Lambda }$, which makes an unstable state in ${}^6\mathrm{He}$ stable against neutron emission.

Coherent photoproduction of the neutral-pion and $\eta$-meson on the deuteron, $\gamma d\to {\pi }^0\eta d$, was experimentally studied at incident photon energies ranging from the reaction threshold to 1.15 GeV. The total cross section demonstrates a rapid rise below 1 GeV. The data are underestimated by the existing theoretical calculations based on quasifree ${\pi }^0\eta$ photoproduction on the nucleon followed by deuteron coalescence. At the same time, the data are rather well reproduced by the calculations taking into account the final-state interaction. We also measured for the first time the differential cross sections: the ${\pi }^0\eta$ invariant-mass distribution $d\sigma /d{M}_{\pi \eta }$, the ${\pi }^{0}d$ invariant-mass distribution $d\sigma /d{M}_{\pi d}$, the $\eta d$ invariant-mass distribution $d\sigma /d{M}_{\eta d}$, and the distribution over the deuteron emission angle $d\sigma /d{\mathrm{\Omega }}_d$ in the overall center-of-mass frame. The measured cross section $d\sigma /d{\mathrm{\Omega }}_d$ does not exhibit strongly backward-peaking behavior predicted by the calculations. At all incident energies, an increase in $d\sigma /d{M}_{\eta d}$ near the $\eta d$ threshold is observed, which indicates a bound or virtual $\eta d$ state resulting from a strong attraction between $\eta$ and a deuteron. The possibilities of using coherent ${\pi }^0\eta$ photoproduction on a nucleus to study the $\eta$-nuclear interaction are also discussed.

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.

We have studied the $({\pi }^{-},K^{+})$ reaction on a silicon target to investigate the sigma-nucleus potential. The inclusive spectrum was measured at a beam momentum of $1.2\mathrm{G}\mathrm{e}\mathrm{V}/c$ with an energy resolution of 3.3 MeV (FWHM) by employing the superconducting kaon spectrometer system. The spectrum was compared with theoretical calculations within the framework of the distorted-wave impulse approximation, which demonstrates that a strongly repulsive sigma-nucleus potential with a nonzero size of the imaginary part reproduces the observed spectrum.

The angular distribution of gravitational-wave power from persistent sources may exhibit anisotropies arising from the large-scale structure of the Universe. This motivates directional searches for astrophysical and cosmological gravitational-wave backgrounds, as well as continuous-wave emitters. We present results of such a search using data from the first observing run through the first portion of the fourth observing run of the LIGO-Virgo-KAGRA Collaborations. We apply gravitational-wave radiometer techniques to generate skymaps and search for both narrowband and broadband persistent gravitational-wave sources. Additionally, we use spherical harmonic decomposition to probe spatially extended sources. No evidence of persistent gravitational-wave signals is found, and we set the most stringent constraints to date on such emissions. For narrowband point sources, our sensitivity estimate to effective strain amplitude lies in the range $(0.03–8.4)\times {10}^{-24}$ across all-sky and frequency range ($20-160$) Hz. For targeted sources—Scorpius X-1, SN 1987A, the Galactic Center, Terzan 5, and NGC 6397—we constrain the strain amplitude with best limits ranging from $\sim 1.1\times {10}^{-25}$ to $6.5\times {10}^{-24}$. For persistent broadband sources, we constrain the gravitational-wave flux $F_{\alpha ,\widehat{n}}^{95\%,\mathrm{UL}}(25\mathrm{Hz})<(0.008–5.5)\times {10}^{-8}\mathrm{erg}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}{\mathrm{Hz}}^{-1}$, depending on the sky direction $\widehat{n}$ and spectral index $\alpha =0,2/3$, 3. Finally, for extended sources, we place upper limits on the angular power spectrum $C_{\ell }^{1/2}<(0.63–17)\times {10}^{-10}{\mathrm{sr}}^{-1}$.

The vector analyzing power ${\mathit{A}}_{\mathit{y}}$(θ) of the ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(p→,p${)}^2$H scattering has been measured at ${\mathit{E}}_{\mathit{p}}$=5, 6, 6.5, 7, 8, 8.5, 9, 10, 12, 14, 16, and 18 MeV with a typical statistical accuracy of 0.0009 and an uncertainty in the beam polarization of less than 0.7%. The differential cross section σ(θ) of the ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(p,p${)}^2$H scattering has also been measured with a typical uncertainty of 0.8% using unpolarized beams of the same energies and of 2, 2.5, 3, and 4 MeV. A large discrepancy of about 25% between the experiment and the Faddeev calculation with the Paris NN potential is observed at the maximum of ${\mathit{A}}_{\mathit{y}}$(θ) around ${\mathrm{\theta }}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$=120°. This discrepancy is shown to be reduced by modifying LS force in the NN potential, though a discrepancy still remains in the energy dependence of the ${\mathit{A}}_{\mathit{y}}$(θ) maximum. At the minimum of σ(θ) around ${\mathrm{\theta }}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$=120°, a large discrepancy ranging from -19% at 2 MeV to +24% at 18 MeV is observed between the experiment and the calculations with either of the original and the LS-modified NN potentials. This indicates that an improvement is also necessary in the scalar part of the potential. The difference in the ${\mathit{A}}_{\mathit{y}}$(θ) maximum between the p→+d and the n→+d scatterings is discussed.

Hypernuclear mass spectra of ${\mathrm{}}_{\mathrm{\Lambda }}^{10}$B, ${\mathrm{}}_{\mathrm{\Lambda }}^{12}$C, ${\mathrm{}}_{\mathrm{\Lambda }}^{28}$Si, ${\mathrm{}}_{\mathrm{\Lambda }}^{89}$Y, ${\mathrm{}}_{\mathrm{\Lambda }}^{139}$La, and ${\mathrm{}}_{\mathrm{\Lambda }}^{208}$Pb were measured by the (${\mathrm{\pi }}^{+}$,${\mathit{K}}^{+}$) reaction with an energy resolution of 2 MeV (FWHM). The experiment was carried out with a 1.06 GeV/c ${\mathrm{\pi }}^{+}$ beam from the KEK 12-GeV PS and with the superconducting kaon spectrometer (SKS). For light hypernuclei, core-excited states were resolved for the first time. For heavy hypernuclei, peak structure reflecting Λ shell structure was observed. © 1996 The American Physical Society.

We present a search for gravitational waves from inspiraling, planetary-mass ultracompact binaries using data from the first part of the fourth observing run of LIGO, Virgo, and KAGRA. Finding no evidence of such systems, we determine the maximum distance reach for such objects and their merger rate densities. Then, we identify classes of primordial black hole mass distributions for which these rate limits can be translated into relevant constraints on the mass distribution of primordial black holes, assuming that they are all composed of dark matter, in the mass range $[{10}^{-6},{10}^{-3}]M_{\odot }$. Our constraints for the class of primordial black hole mass distribution functions $f(m)$ we consider reach down to $f(m)\sim 0.1$. They are consistent with existing microlensing results in the planetary-mass range, provide a complementary probe to subsolar mass objects, and are publicly available [1].

Stretched particle-hole states of a 0ħω (π${\mathit{d}}_{5/2}$,ν${\mathit{d}}_{5/2}^{\mathrm{-}1}$${)}_5^{+}$ type were observed as low-lying isolated peaks in the high-resolution (p,n) reactions on ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$ and ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$ at ${\mathit{E}}_{\mathit{p}}$=35 MeV. Angular distributions of the differential cross sections have been successfully interpreted, especially at large angles, or in high-momentum transfer regions (q∼2 ${\mathrm{fm}}^{\mathrm{-}1}$), by microscopic distorted-wave Born approximation calculations using shell-model wave functions and the M3Y interaction. No quenching of the (p,n) cross sections has been observed for these 0ħω stretched transitions in light nuclei.

The polarization of quasifree Λ hyperons produced by the (${\mathrm{\pi }}^{+}$${\mathit{K}}^{+}$) reaction on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and on the deuteron was measured for the first time. The asymmetry of pions from weak decay of the Λ hyperon was used to determine the polarization. The polarization for the deuterium target was found to be consistent with that for the elementary n(${\mathrm{\pi }}^{+}$,${\mathit{K}}^{+}$)Λ reaction. The polarization of the Λ produced by the quasifree process from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ is consistent with that for the elementary reaction, which demonstrates that the spin characteristics of the elementary reaction are not modified by the nuclear medium.

Asymmetries for ${\pi }^{+}$ elastic scattering from polarized ${}^3\mathrm{He}$ were measured across the $\Delta$(1232) $\pi$-nucleon resonance region at incident energies $T_{\pi }=142\mathrm{}$, 180, and 256 MeV. Large discrepancies were found between the data and calculations that use the multiple scattering formalism and Faddeev wave functions. Inclusion of a $\Delta$-neutron spin-spin interaction term in the calculations gives a greatly improved representation of the data.