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Energy spectra of both protons and deuterons emitted following the capture of negative muons by [sup 3]He nuclei have been measured for energies above 15 MeV. A limited number of proton-neutron pairs emitted in coincidence were also observed. A simple plane wave impulse approximation (PWIA) model calculation yields fair agreement with the measured proton energy spectra, but underpredicts the measured rate of deuteron production above our energy threshold by a large factor. A more sophisticated PWIA calculation for the two-body breakup channel, based on a realistic three-body wave function for the initial state, is closer to the deuteron data at moderate energies, but still is significantly lower near the kinematic end point. The proton-neutron coincidence data also point to the presence of significant strength involving more than one nucleon in the capture process at high energy transfer. These results indicate that additional terms in the capture matrix element beyond the impulse approximation contribution may be required to explain the experimental data. Specifically, the inclusion of nucleon-nucleon correlations in the initial or final state and meson exchange current contributions could bring calculations into better agreement with our data. A fully microscopic calculation would thus open the possibility for a quantitative testmore » of multinucleon effects in the weak interaction.« less

Spectra of energetic protons and deuterons emitted following negative muon capture from rest in $^{3}\mathrm{He}$ have been measured for the first time. Significant capture strength is observed at high energy transfers (${\mathit{m}}_{\mathrm{\ensuremath{\mu}}}$-${\mathit{E}}_{\ensuremath{\nu}}$g60 MeV) for the two-body and three-body breakup channels, indicative of the importance of nucleon-nucleon correlations and meson exchange currents in the capture process. A simple plane wave impulse approximation calculation reproduces the proton spectrum reasonably well, but underpredicts the deuteron rate at the highest energies by a large factor.

Particle production of identified charged hadrons, ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}},{K}^{\ifmmode\pm\else\textpm\fi{}},p$, and $\overline{p}$ in Au+Au collisions at $\sqrt{{s}_{\mathit{NN}}}=$ 200 GeV, has been studied as a function of transverse momentum and collision centrality at $y=0$ and $y~1$ by the BRAHMS experiment at Brookhaven National Laboratory's Relativistic Heavy-Ion Collider. Significant collective transverse flow at kinetic freeze-out has been observed in the collisions. The magnitude of the flow rises with the collision centrality. Proton and kaon yields relative to the pion production increase strongly as the transverse momentum increases and also increase with centrality. Particle yields per participant nucleon show a weak dependence on the centrality for all particle species. Hadron production remains relatively constant within one unit around midrapidity in Au+Au collisions at $\sqrt{{s}_{\mathit{NN}}}=$ 200 GeV.

We have measured rapidity densities dN/dy of pi+/- and K+/- over a broad rapidity range (-0.1 < y < 3.5) for central Au + Au collisions at square root(sNN) = 200 GeV. These data have significant implications for the chemistry and dynamics of the dense system that is initially created in the collisions. The full phase-space yields are 1660 +/- 15 +/- 133 (pi+), 1683 +/- 16 +/- 135 (pi-), 286 +/- 5 +/- 23 (K+), and 242 +/- 4 +/- 19 (K-). The systematics of the strange to nonstrange meson ratios are found to track the variation of the baryochemical potential with rapidity and energy. Landau-Carruthers hydrodynamics is found to describe the bulk transport of the pions in the longitudinal direction.

We report on a study of the transverse momentum dependence of nuclear modification factors ${R}_{d\mathrm{A}\mathrm{u}}$ for charged hadrons produced in $\mathrm{\text{deuteron}}\text{ }\text{ }+\text{ }\text{ }\mathrm{\text{gold}}$ collisions at $\sqrt{{s}_{NN}}=200\text{ }\text{ }\mathrm{G}\mathrm{e}\mathrm{V}$, as a function of collision centrality and of the pseudorapidity ($\ensuremath{\eta}=0$, 1, 2.2, 3.2) of the produced hadrons. We find a significant and systematic decrease of ${R}_{d\mathrm{A}\mathrm{u}}$ with increasing rapidity. The midrapidity enhancement and the forward rapidity suppression are more pronounced in central collisions relative to peripheral collisions. These results are relevant to the study of the possible onset of gluon saturation at energies reached at BNL RHIC.

Transverse momentum spectra and rapidity densities, dN/dy, of protons, antiprotons, and net protons (p-p) from central (0%-5%) Au+Au collisions at square root of S(NN)=200 GeV were measured with the BRAHMS experiment within the rapidity range 0

We present spectra of charged hadrons from $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ and $d+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{{s}_{NN}}=200\text{ }\mathrm{G}\mathrm{e}\mathrm{V}$ measured with the BRAHMS experiment at RHIC. The spectra for different collision centralities are compared to spectra from $p+\overline{p}$ collisions at the same energy scaled by the number of binary collisions. The resulting ratios (nuclear modification factors) for central $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions at $\ensuremath{\eta}=0$ and $\ensuremath{\eta}=2.2$ evidence a strong suppression in the high ${p}_{T}$ region ($g2\text{ }\text{ }\mathrm{G}\mathrm{e}\mathrm{V}/c$). In contrast, the $d+\mathrm{A}\mathrm{u}$ nuclear modification factor (at $\ensuremath{\eta}=0$) exhibits an enhancement of the high ${p}_{T}$ yields. These measurements indicate a high energy loss of the high ${p}_{T}$ particles in the medium created in the central $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions. The lack of suppression in $d+\mathrm{A}\mathrm{u}$ collisions makes it unlikely that initial state effects can explain the suppression in the central $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions.

We present ratios of the numbers of charged antihadrons to hadrons (pions, kaons, and protons) in Au+Au collisions at sqrt[s(NN)]=200 GeV as a function of rapidity in the range y=0-3. While the ratios at midrapidity are approaching unity, the K(-)/K(+) and p;/p ratios decrease significantly at forward rapidities. An interpretation of the results within the statistical model indicates a reduction of the baryon chemical potential from mu(B) approximately 130 MeV at y=3 to mu(B) approximately 25 MeV at y=0.

We present charged-particle multiplicities as a function of pseudorapidity and collision centrality for the ${}^{197}\mathrm{Au}{+}^{197}\mathrm{Au}$ reaction at $\sqrt{{s}_{\mathrm{NN}}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}200\mathrm{GeV}$. For the $5%$ most central events we obtain ${\mathrm{dN}}_{\mathrm{ch}}/d\ensuremath{\eta}{|}_{\ensuremath{\eta}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}625\ifmmode\pm\else\textpm\fi{}55$ and ${N}_{\mathrm{ch}}{|}_{\ensuremath{-}4.7\ensuremath{\le}\ensuremath{\eta}\ensuremath{\le}4.7}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}4630\ifmmode\pm\else\textpm\fi{}370$, i.e., $14%$ and $21%$ increases, respectively, relative to $\sqrt{{s}_{\mathrm{NN}}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}130\mathrm{GeV}$ collisions. Charged-particle production per pair of participant nucleons is found to increase from peripheral to central collisions around midrapidity. These results constrain current models of particle production at the highest RHIC energy.

Measurements, with the BRAHMS detector, of the antiproton-to-proton ratio at midrapidities and forward rapidities, are presented for Au+Au reactions at s{sub NN}=130 GeV , and for three different collision centralities. For collisions in the 0%--40% centrality range, we find N({bar p})/N(p)=0.64{+-} 0.04{sub (stat)}{+-}0.06{sub ( syst)} at y{approx}0 , 0.66{+-}0.03{+-}0.06 at y{approx}0.7 , and 0.41{+-}0.04{+-}0.06 at y{approx}2 . The ratios are found to be nearly independent of collision centrality and transverse momentum. The antiproton and proton rapidity densities vary differently with rapidity, and indicate a significant degree of collision transparency, although a net-baryon free midrapidity plateau (Bjorken limit) is not yet reached.

The pionic x-ray energies of the $4f\ensuremath{-}3d$ transition in $\ensuremath{\pi}$-P and the $5f\ensuremath{-}4d$ transition in $\ensuremath{\pi}$-Ti were measured with a bent-crystal spectrometer at the Nevis synchrocyclotron; and a new value of the pionic mass is deduced to be 139 567.5\ifmmode\pm\else\textpm\fi{}0.9 keV, leading to an improved value for the $\ensuremath{\mu}$-neutrino mass of ${{m}_{{\ensuremath{\nu}}_{\ensuremath{\mu}}}}^{2}$=0.102\ifmmode\pm\else\textpm\fi{}0.119 ${\mathrm{MeV}}^{2}$; ${m}_{{\ensuremath{\nu}}_{\ensuremath{\mu}}}l0.52$ MeV, at 90% confidence level.

Cross sections were measured for the production of electrons with kinetic energies from 50 to 150 keV by heavy-ion-atom collisions. Beams of 40- and 70-MeV nickel and 70- and 120-MeV bromine ions were incident on targets of carbon, nickel, potassium bromide, silver, and gold. Electron energies were measured using a steering electron spectrometer capable of 7% transmission and 4-keV resolution. The observed cross sections exceed the plane-wave-Born-approximation predictions by factors of 2 to 10 with deviation becoming more pronounced at high electron energy.

Neutron spectra identified by final nuclear states have been measured for stopped ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ capture in $^{165}\mathrm{Ho}$. Neutron time of flight, with a resolution of 20% at 100 MeV, was collected in coincidence with the rotational \ensuremath{\gamma}-ray transitions in the even-even Dy isotopes. The inclusive spectrum was also measured in coincidence with pionic x rays, and agrees with previous singles measurements. The neutron spectra for individual final states show sharp cutoffs at characteristic energies, and, in some cases, the structure in the high energy component of the spectra is resolved. A Monte Carlo program based on the hybrid exciton model was developed, suitable for computing the inclusive and exclusive neutron spectra. The program gives a good fit to the measured inclusive spectrum. A different set of model parameters had to be used to reproduce the features of the spectra identified by the final nuclear states, and the fit was less satisfactory, indicating the need for an improvement in the preequilibrium approach which was not apparent in the past application to the inclusive spectra.

Reanalysis of our experimental results on /sup 12/B and /sup 12/N provides shape factors that yield (a/sub -//sup 0/ - a/sub +//sup 0/)/sub exp/ = + (0.86 +- 0.24) % MeV/sup -1/, still in good agreement with the theoretical prediction of (a/sub -//sup 0/ - a/sub +//sup 0/)/sub theo/ = + 0.86% MeV/sup -1/. The experimental evidence for the conserved-vector-current theory as manifested in the mass-12 traid is on no less firm ground than it was at the time of our previous publication.

$\ensuremath{\gamma}$-ray linear polarization measurements have been used to locate negative parity states in the even-odd isotopes $^{99,101,103}\mathrm{Pd}$. A Compton polarimeter based on two Ge(Li) coaxial detectors was used. Collective bands ($I={\frac{11}{2}}^{\ensuremath{-}}, {\frac{15}{2}}^{\ensuremath{-}}, {\frac{19}{2}}^{\ensuremath{-}}, \dots{}$) built on ${\frac{11}{2}}^{\ensuremath{-}}$ states were observed in $^{101}\mathrm{Pd}$ and $^{103}\mathrm{Pd}$. Many negative parity states were also observed in $^{99}\mathrm{Pd}$, but they do not appear to be part of a similar collective band. These polarization measurements also confirm many angular momentum assignments which previously had been made using systematic arguments.NUCLEAR REACTIONS $^{90,92,94}\mathrm{Zr}(^{12}\mathrm{C}, 3n)$, $E=48\ensuremath{-}56$ MeV; measured linear polarization of $\ensuremath{\gamma}$ rays; parities and multipole mixing ratios in $^{99,101,103}\mathrm{Pd}$ transitions deduced.

The linear polarization of ..gamma.. rays from the deexcitation of Cd isotopes A = 105 through 109 following (/sup 16/O,xn) reactions were measured using a Ge(Li) Compton polarimeter. The linear polarizations are used with ..gamma..-ray angular distributions to make unique-parity assignments and to remove ambiguity in angular-momentum values. With these measurements it is possible to identify many states in /sup 105hyphen109/Cd which are similar to states in Pd nuclei that have been interpreted as having one, two, or three quasiparticles coupled to a slightly deformed rotating core.

The linear polarization of $\ensuremath{\gamma}$ rays in $^{129}\mathrm{Ba}$ produced by the reaction $^{120}\mathrm{Sn}(^{12}\mathrm{C},3n)$ was measured using a Compton polarimeter made of two Ge(Li) coaxial detectors. The results establish unambiguously the ${h}_{\frac{11}{2}}$ band structure and its separation into the $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\Omega}}=j=\frac{11}{2}$ and $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\Omega}}=j\ensuremath{-}1=\frac{9}{2}$ level subsystems. The existence of the ${g}_{\frac{7}{2}}$ band is shown for the first time in the mass region $A\ensuremath{\approx}130$.[NUCLEAR REACTIONS $^{120}\mathrm{Sn}(^{12}\mathrm{C},3n)$, $E=52$ MeV; measured linear polarization of $\ensuremath{\gamma}$ rays; deduced spins and parities of levels and multipole mixing ratios of transitions in $^{129}\mathrm{Ba}$; triaxial shape.]

A newly designed, large-aperture and high-resolution bent-crystal spectrometer has been used to observe high-intensity sources of pionic x rays. The pionic x-ray source was a target of natural titanium which was placed adjacent to a copper pion-production target in the external beam of the Nevis synchrocyclotron. The energy difference between the 5g ..-->.. 4f and 5f ..-->.. 4d transitions in pionic titanium was measured to be 87.6 +- 1.8 eV. Comparison with the prediction of the Klein-Gordon equation is made.

A precise measurement of the beta spectra of B/sup 12/ and N/sup 12/ was made as an experimental confirmation of the conserved vector current (CVC) theory. Great care was taken as to the precision of the results. End-point energies obtained from the Curie plots of the BETA rays are 13.373 ction in DDT-C/ 0.04 and 16.43 ction in DDT-C/ 0.10 Mev for B/sup 12/ and N/sup 12/, respectively. Thus investigation confirms that the deviations from the allowed shape of the observed beta spectra for B/sup 12/ and N/sup 12/ have the correct magnitude and sign due to a weak magnetism term. This unique relation between the beta interaction and electrodynamics strongly supports the CVC theory. (C.E.S.)

The lifetime of the second excited levels in Ni/sup 60/ and Ti/sup 46/ was measured by beta-gamma delayed coincidence method employimg a time-to- amplitude converter. The centroid shift of the beta-gamma delayed time distribution was measured with respect to the prompt time distribution due to a prompt gamma-gamma cascade that is present in each isotope. Simultaneous accumulation of the delayed and prompt time distribution on a split memory of a multichannel analyzer was made possible by the use of a third sorting detector. An upper limit of 5., 10/sup -12/ sec was established for the mean life of both Ni/sup 60/ and Ti/sup 46/. The mean life of the first excited state of Pb/sup 207/ was also measured to be (1.60 plus or minus 0.1) x 10/sup -10/ sec from the slope of the delayed time distribution. (auth)

A search for the internal conversion line in O/sup 16/ was made. The line was found to be sharp enough to have its energy determined and its intensity estimated. The line provided a check on the theoretically predicted ratio of internal conversion to internal pair creation in the 6.052-Mev 0/sup +/ min gave no sig 0/sup +/ transition in O/sup 16/. Agreement between the experimental points and the theoretical curves was very satisfactory. (C.E.S.)

The Zeeman transition between the $M=\ifmmode\pm\else\textpm\fi{}1$ and $M=0$ states of orthopositronium in its ground state has been observed in a solid for the first time, when positrons were stopped in a $\ensuremath{\gamma}$-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ powder pellet, thus providing strong evidence that essentially free orthopositronium exists in $\ensuremath{\gamma}$-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$. The value for the positronium fine-structure interval is $\ensuremath{\Delta}\ensuremath{\nu}(\ensuremath{\gamma}\ensuremath{-}{\mathrm{Al}}_{2}{\mathrm{O}}_{3})=203.308\ifmmode\pm\else\textpm\fi{}0.024$ GHz (120 ppm). The difference $\ensuremath{\Delta}\ensuremath{\nu}(\mathrm{free}\mathrm{Ps})\ensuremath{-}\ensuremath{\Delta}\ensuremath{\nu}(\ensuremath{\gamma}\ensuremath{-}{\mathrm{Al}}_{2}{\mathrm{O}}_{3})$ is 88 \ifmmode\pm\else\textpm\fi{} 25 MHz.