A measurement of the neutron lifetime ${\tau }_n$ performed by the absolute counting of in-beam neutrons and their decay protons has been completed. Protons confined in a quasi-Penning trap were accelerated onto a silicon detector held at a high potential and counted with nearly unit efficiency. The neutrons were counted by a device with an efficiency inversely proportional to neutron velocity, which cancels the dwell time of the neutron beam in the trap. The result is ${\tau }_n=(886.3\pm 1.2[\mathrm{stat}]\pm 3.2[\mathrm{sys}])s$, which is the most precise measurement of the lifetime using an in-beam method. The systematic uncertainty is dominated by neutron counting, in particular, the mass of the deposit and the ${}^6\mathrm{Li}$$(n,t)$ cross section. The measurement technique and apparatus, data analysis, and investigation of systematic uncertainties are discussed in detail.

We provide an analysis of vector meson photoproduction in the channel of the vector meson decaying into a pseudoscalar meson plus a photon (i.e., $V\to P\gamma$). It is shown that nontrivial kinematic correlations arise from the measurement of the $P\gamma$ angular distributions in the overall c.m. system in comparison with those in the vector meson rest frame. The implication of such kinematic correlations in the measurement of polarization observables is discussed in terms of the vector meson density matrix elements. For ω meson production, because of its relatively large branching ratios for $\omega \to {\pi }^0\gamma$, additional events from this channel may enrich the information about the reaction mechanism and improve the statistics of the recent measurement of polarized beam asymmetries by the GRAAL Collaboration. For $\varphi \to \eta \gamma ,\rho \to \pi \gamma$, and $K^{*}\to K\gamma$, we expect that additional information about the spin structure of the vector meson production vertex can be derived.

The Coulomb interaction between two protons is included in the calculation of proton-deuteron elastic scattering, radiative proton-deuteron capture, and two-body electromagnetic disintegration of ${}^3\mathrm{He}$. The hadron dynamics is based on the purely nucleonic charge-dependent (CD) Bonn potential and its realistic extension CD Bonn $+\Delta$ to a coupled-channel two-baryon potential, allowing for single virtual $\Delta$-isobar excitation. Calculations are done using integral equations in momentum space. The screening and renormalization approach is employed for including the Coulomb interaction. Convergence of the procedure is found at moderate screening radii. The reliability of the method is demonstrated. The Coulomb effect on observables is seen at low energies for the entire kinematic regime. In proton-deuteron elastic scattering at higher energies the Coulomb effect is confined to forward scattering angles; the $\Delta$-isobar effect found previously remains unchanged by the Coulomb effect. In electromagnetic reactions the Coulomb effect competes with other effects in a complicated way.

We address a recent comment by Alam et al. [Phys. Rev. C 71, 059802 (2005)], on our work of thermal photon emission rates from hadronic matter. Specifically, we explain how t-channel ω exchange in the $\pi \rho \to \pi \gamma$ reaction arises as a dominant contribution to the rates at high energy and why hadronic form factors cannot be neglected in this assessment.

We have used the $(d,{}^2\mathrm{He})$ reaction to obtain the GT${}^{+}$ strength distribution for ${}^{116}\mathrm{Sn}\to {}^{116}\mathrm{In}$ transitions. Here, ${}^{116}\mathrm{In}$ is the intermediate nucleus in the second-order perturbative description of ${}^{116}\mathrm{Cd}$ double beta $(\beta \beta )$ decay. In this paper we will review what is known about the nuclear matrix elements for the ${}^{116}\mathrm{Cd}$ $2\nu \beta \beta$ decay, discuss the single-state dominance hypothesis and combine our new data with other existing data from charge-exchange reactions to obtain a $2\nu \beta \beta$-decay half-life. The deduced value $T_{1/2}=(4\pm 1)\times {10}^{19}$y compares well with the one known from direct counting experiments.

Within a transport model we search for potential probes of the isospin dependence of the in-medium nucleon-nucleon (NN ) cross sections. Traditional measures of the nuclear stopping power are found to be sensitive to the magnitude but they are ambiguous for determining the isospin dependence of the in-medium NN cross sections. It is shown that isospin tracers, such as the neutron/proton ratio of free nucleons, at backward rapidities and angles in nuclear reactions induced by radioactive beams in inverse kinematics are a sensitive probe of the isospin dependence of the in-medium NN cross sections. At forward rapidities and angles, in contrast, they are more sensitive to the density dependence of the symmetry energy. Measurements of the rapidity and angular dependence of the isospin transport in nuclear reactions will enable a better understanding of the isospin dependence of in-medium nuclear effective interactions.

The characteristics of intermediate mass fragments (IMFs: $3\le Z\le 20)$ produced in midperipheral and central collisions are compared. We compare IMFs detected at midvelocity with those evaporated from the excited projectilelike fragment (PLF${}^{*}$). On average, the IMFs produced at midvelocity are larger in atomic number, exhibit broader transverse velocity distributions, and are more neutron rich as compared to IMFs evaporated from the PLF${}^{*}$. These characteristics of midvelocity fragments are consistent with the low-density formation of the fragments. We present in the different kinematical regions studied, the $\langle E_{\perp }\rangle$ for isotopically identified IMFs. For a given $Z,\langle E_{\perp }\rangle$ is either constant or decreases slightly with increasing A, in contradiction with a mass-dependent collective expansion in which all IMFs are emitted on average at the same time. Neutron-deficient isotopes of even Z elements manifest higher kinetic energies than heavier isotopes of the same element for both PLF${}^{*}$ and midvelocity emission. This result may be because of the charged-particle decay of long-lived excited states.

We explore the possibility of extrapolating state of the art lattice QCD calculations of nucleon form factors to the physical regime. We find that the lattice results can be reproduced using the light front cloudy bag model by letting its parameters be analytic functions of the quark mass. We then use the model to extend the lattice calculations to large values of $Q^2$ of interest to current and planned experiments. These functions are also used to define extrapolations to the physical value of the pion mass, thereby allowing us to study how the predicted zero in $G_E(Q^2)/G_M(Q^2)$ varies as a function of quark mass.

We report on the first measurement of exclusive ${\Xi }^{-}(1321)$ hyperon photoproduction in $\gamma p\to K^{+}{K}^{+}{\Xi }^{-}$ for $3.2<E_{\gamma }<3.9$ GeV. The final state is identified by the missing mass in $p(\gamma ,K^{+}{K}^{+})X$ measured with the CLAS detector at Jefferson Laboratory. We have detected a significant number of the ground state ${\Xi }^{-}(1321){\frac{1}{2}}^{+}$ and have estimated the total cross section for its production. We also have strong evidence for the first excited state ${\Xi }^{-}(1530){\frac{3}{2}}^{+}$. Photoproduction provides a copious source of Ξ's. We discuss the possibilities of a search for the recently proposed ${\Xi }_5^{-}$ and ${\Xi }_5^{+}$ pentaquarks.

We measured the cross sections of the ${}^2\mathrm{H}(p,\mathit{pp})n$ breakup reaction at $E_p=16\text{MeV}$ in three kinematical configurations: the np final-state interaction (FSI), the coplanar star (CST), and an intermediate-star (IST) geometry. The cross sections are compared with theoretical predictions based on the CD Bonn potential alone and combined with the updated 2π-exchange Tucson-Melbourne three-nucleon force (TM99'), calculated without inclusion of the Coulomb interaction. The resulting excellent agreement between data and pure CD Bonn predictions in the FSI testifies to the smallness of three-nucleon force (3NF) effects as well as the insignificance of the Coulomb force for this particular configuration and energy. The CST also agrees well whereas the IST results show small deviations between measurements and theory seen before in the pd breakup space-star geometries which point to possible Coulomb effects. An additional comparison with effective field theory (EFT) predictions (without 3NF) up to order $\mathrm{N}{}^3\mathrm{LO}$ shows excellent agreement in the FSI case and a rather similar agreement as for CD Bonn in the CST and IST situations.

In developing theories of nuclear binding energy such as density-functional theory, the effort required to make a fit can be daunting because of the large number of parameters that may be in the theory and the large number of nuclei in the mass table. For theories based on the Skyrme interaction, the effort can be reduced considerably by using the singular value decomposition to reduce the size of the parameter space. We find that the sensitive parameters define a space of dimension four or so, and within this space a linear refit is adequate for a number of Skyrme parameters sets from the literature. We find no marked differences in the quality of the fit among the SLy4, the BSk4, and SkP parameter sets. The root-mean-square residual error in even-even nuclei is about 1.5 MeV, half the value of the liquid drop model. We also discuss an alternative norm for evaluating mass fits, the Chebyshev norm. It focuses attention on the cases with the largest discrepancies between theory and experiment. We show how it works with the liquid drop model and make some applications to models based on Skyrme energy functionals. The Chebyshev norm seems to be more sensitive to new experimental data than the root-mean-square norm. The method also has the advantage that candidate improvements to the theories can be assessed with computations on smaller sets of nuclei.

The properties of nuclei belonging to the newly observed α-decay chain starting from ${}^{287}115$ have been studied. The axially deformed relativistic mean field calculation with the force NL-Z2 has been performed in the blocked BCS approximation. Some ground state properties such as average binding energies, deformations, spins, and parities as well as $Q$ values of the α decay for this decay chain have been calculated and compared with known experimental data. Good agreement is found. The study of the single-particle spectrum in ${}^{287}115$ shows that after $Z=100$ the magic numbers appear at $Z=116,114$ and smaller gaps at $Z=(110),(106)$ and (122), (126), (128). For neutrons, the gaps appear at $N=174,(172),(168),(162),(160),(186)$. Because of the neutron-deficient character of superheavy nuclei, there is some probability that protons could be distributed at positive levels, which form the resonance continuum; this is worth further investigation. The α-decay lifetimes in the ${}^{287}115$ decay chain are evaluated by different formulas and compared with experimental data. The methods that give better agreement with the data are selected.

The production rates of ultracold neutrons (UCN) from cold neutrons on gaseous, liquid, and solid deuterium targets have been measured. The comparison of the measured and calculated UCN production on gaseous ${}^2{H}_2$ is used to calibrate the simulated target extraction and transport efficiencies of the experimental apparatus. The production cross section in solid ${}^2{H}_2$ at 8 K for UCN with energies between 0 and 250 neV is $R_{\mathrm{solid},8\hspace{1em}K}={\sigma }_{\mathrm{solid},8\hspace{1em}K}^{\mathrm{CN}\to \mathrm{UCN}}\hspace{1em}\rho =(1.11\pm 0.23)\times {10}^{-8}{\mathrm{cm}}^{-1}$. This value is consistent with other experiments in which UCN had been extracted from ${}^2{H}_2$. The value also agrees with calculations using the incoherent approximation and a simple Debye model and corroborates predictions for UCN densities expected at the high-intensity UCN source at the Paul Scherrer Institut. The temperature dependence of the UCN production in solid ${}^2{H}_2$ down to 8 K can be explained within the same model when multiple-phonon excitation is included.

In order to test the ${}^{16}\mathrm{C}$ internal wave function, we perform microscopic coupled-channels (MCC) calculations of the ${}^{16}\mathrm{C}(0_1^{+}\to 2_1^{+})$ inelastic scattering by a ${}^{208}\mathrm{Pb}$ target at $E/A=52.7\mathrm{MeV}$ using the antisymmetrized molecular dynamics (AMD) wave functions of ${}^{16}\mathrm{C}$, and compare the calculated differential cross sections with the measured ones. The MCC calculations with AMD wave functions reproduce the experimental data fairly well, although they slightly underestimate the magnitude of the cross sections. The absolute magnitude of calculated differential cross sections is found to be sensitive to the neutron excitation strength. We prove that the MCC method is a useful tool for connecting the inelastic scattering data with the internal wave functions.

The ratio of the proton elastic electromagnetic form factors, $G_{\mathit{Ep}}/G_{\mathit{Mp}}$, was obtained by measuring $P_t$ and $P_{\ell }$, the transverse and longitudinal recoil proton polarization components, respectively, for the elastic $\overrightarrow{e}p\to e\overrightarrow{p}$reaction in the four-momentum transfer squared range of 0.5 to $3.5\text{GeV}{}^2$. In the single-photon exchange approximation, $G_{\mathit{Ep}}/G_{\mathit{Mp}}$ is directly proportional to $P_t/P_{\ell }$. The simultaneous measurement of $P_t$ and $P_{\ell }$ in a polarimeter reduces systematic uncertainties. The results for $G_{\mathit{Ep}}/G_{\mathit{Mp}}$ show a systematic decrease with increasing $Q^2$, indicating for the first time a definite difference in the distribution of charge and magnetization in the proton. The data have been reanalyzed and their systematic uncertainties have become significantly smaller than those reported previously.

We propose a quantum chromodynamics (QCD) based many-body model for the nucleus where the strong coupling regime is controlled by a three-body string force, and the weak coupling regime is dominated by a pairing force. This model operates effectively with a quark-gluon Lagrangian containing a pairing force from instantons, and a baryonic string term which contains a confining potential. The unified model for weak and strong coupling regimes is, however, only consistent at the border of perturbative QCD. The baryonic string force is necessary, as a stability and compressibility analysis shows, for the occurrence of the phases of nuclear matter. The model exhibits a quark deconfinement transition and chiral restoration, which are ingredients of QCD and give qualitatively correct numerics. The effective model is shown to be isomorphic to the Nambu–Jona-Lasinio model and exhibits the correct chirality provided that the chiral fields are identified with the two-particle strings, which are natural in a QCD framework. Moreover, the model is able to reconcile qualitatively such aspects of hadronic physics as saturation density and binding energy of nuclear matter, surface density of finite nuclei, mass of the scalar particle, medium range NN interaction, and $f_{\pi }$ value in vacuum.

Several possible background sources determine the detectability of pep and CNO solar neutrinos in organic liquid scintillator detectors. Among such sources, the cosmogenic ${}^{11}\mathrm{C}$ nuclide plays a central role. ${}^{11}\mathrm{C}$ is produced underground in reactions induced by the residual cosmic muon flux. Experimental data available for the effective cross section for ${}^{11}\mathrm{C}$ by muons indicate that ${}^{11}\mathrm{C}$ will be the dominant source of background for the observation of pep and CNO neutrinos. ${}^{11}\mathrm{C}$ decays are expected to total a rate 2.5 (20) times higher than the combined rate of pep and CNO neutrinos in Borexino (KamLAND) in the energy window preferred for the pep measurement between 0.8 and 1.3 MeV. This study examines the production mechanism of ${}^{11}\mathrm{C}$ by muon-induced showers in organic liquid scintillators with a novel approach: for the first time, we perform a detailed ab initio calculation of the production of a cosmogenic nuclide, ${}^{11}\mathrm{C}$, taking into consideration all relevant production channels. Results of the calculation are compared with the effective cross sections measured by target experiments in muon beams. This article also discusses a technique for reduction of background from ${}^{11}\mathrm{C}$ in organic liquid scintillator detectors, which allows to identify on a one-by-one basis and remove from the data set a large fraction of ${}^{11}\mathrm{C}$ decays. The background reduction technique hinges on an idea proposed by Martin Deutsch, who suggested that a neutron must be ejected in every interaction producing a ${}^{11}\mathrm{C}$ nuclide from ${}^{12}\mathrm{C}$. ${}^{11}\mathrm{C}$ events are tagged by a threefold coincidence with the parent muon track and the subsequent neutron capture on protons.

Neutron-induced reaction cross sections on unstable nuclei are inherently difficult to measure due to target activity and the low intensity of neutron beams. In an alternative approach, named the “surrogate” technique, one measures the decay probability of the same compound nucleus produced using a stable beam on a stable target to estimate the neutron-induced reaction cross section. As an extension of the surrogate method, in this paper we introduce a new technique of measuring the fission probabilities of two different compound nuclei as a ratio, which has the advantage of removing most of the systematic uncertainties. This method was benchmarked in this report by measuring the probability of deuteron-induced fission events in coincidence with protons, and forming the ratio $P[{}^{236}\mathrm{U}(d,\mathrm{pf})]/P[{}^{238}\mathrm{U}(d,\mathrm{pf})]$, which serves as a surrogate for the known cross section ratio of ${}^{236}\mathrm{U}(n,f)/{}^{238}\mathrm{U}(n,f)$. In addition, the $P[{}^{238}\mathrm{U}(d,d^{\text{'}}f)]/P[{}^{236}\mathrm{U}(d,d^{\text{'}}f)]$ ratio as a surrogate for the ${}^{237}\mathrm{U}(n,f)/{}^{235}\mathrm{U}(n,f)$ cross section ratio was measured for the first time in an unprecedented range of excitation energies.

Incoherent ${\pi }^0$ photoproduction from nuclei is evaluated via a multicollisional intranuclear cascade framework. In-medium modifications are taken into account, including a realistic dynamical treatment of multiple $\pi N$ and $\Delta N$ scattering processes throughout the cascade. This time-dependent analysis yields structures in the ${}^{12}\mathrm{C}{\pi }^0$ differential cross section both in the $\Delta$ region and in the photon energy range from 5 to 6 GeV, with the former in very nice agreement with recent results from Mainz Microton. For heavy nuclei, however, such structures disappear because of a more effective Fermi motion and a relatively higher final state interaction of the produced pions as they exit the nucleus. The calculation of the incoherent part of the total ${\pi }^0$ photoproduction propitiates a clean and powerful kinematical separation from competitive (electromagnetic/nuclear) production processes, which currently is a theoretical challenge for the PrimEx experiment at the Jefferson Lab.

The ${}^8\mathrm{Li}(n,\gamma ){}^9\mathrm{Li}$ reaction plays an important role in both the r-process nucleosynthesis and the inhomogeneous big bang models. Its direct capture rates can be extracted from the ${}^8\mathrm{Li}(d,p){}^9\mathrm{Li}$ reaction, indirectly. We have measured the angular distribution of the ${}^8\mathrm{Li}(d,p){}^9\mathrm{Li}{}_{g.s.}$ reaction at $E_{c.m.}\hspace{1em}=\hspace{1em}7.8$ in inverse kinematics using coincidence detection of ${}^9\mathrm{Li}$ and the recoil proton, for the first time. Based on distorted wave Born approximation (DWBA) analysis, the ${}^8\mathrm{Li}(d,p){}^9\mathrm{Li}{}_{g.s.}$ cross section was determined to be 7.9 ± 2.0 mb. The single particle spectroscopic factor $S_{1,3/2}$ for the ground state of ${}^9\mathrm{Li}={}^8\mathrm{Li}\otimes n$ was derived to be $0.68\pm 0.14$, and then used to calculate the direct capture cross sections for the ${}^8\mathrm{Li}(n,\gamma ){}^9\mathrm{Li}{}_{g.s.}$ reaction at energies of astrophysical interest. The astrophysical ${}^8\mathrm{Li}(n,\gamma ){}^9\mathrm{Li}{}_{g.s.}$ reaction rate for the direct capture was found to be $3970\pm 950{\mathrm{cm}}^3{\mathrm{mole}}^{-1}{s}^{-1}$ at $T_9=1.$ This presents the first experimental constraint for the ${}^8\mathrm{Li}(n,\gamma ){}^9\mathrm{Li}$ reaction rates of astrophysical relevance.