Search

Directed flow measurements for {Lambda} hyperons are presented and compared to those for protons produced in the same Au+Au collisions (2A, 4A, and 6AGeV; b

We have measured the sideward flow of neutral strange (K{sup 0}{sub s} ) mesons in 6A GeV Au +Au collisions. A prominent antiflow signal is observed for an impact parameter range (b(less-or-similar sign)7 fm ) which spans central and midcentral events. Since the K{sup 0}{sub s} scattering cross section is relatively small in nuclear matter, this observation suggests that the in-medium kaon vector potential plays an important role in high density nuclear matter. (c) 2000 The American Physical Society.

We present the first excitation function of ${\ensuremath{\pi}}^{\ensuremath{-}}$ intensity interferometry at Alternating Gradient Synchrotron (AGS) energies (2--8 A GeV). The sensitivity of the multidimensional correlation functions to the geometry and dynamics of the pion-emitting system provides a stringent test of transport models of heavy ion collisions. Detailed comparisons with a realistic transport model, both with and without an explicit nuclear mean field, suggest that the beam energy evolution in the reaction dynamics is different in the model than in the data. A significantly increased ${\ensuremath{\pi}}^{\ensuremath{-}}$ emission time scale, which has been suggested as a signal of the onset of the transition to quark-gluon plasma, is not observed.

We present a measurement and partial wave analysis of the final state ${K}_{L}{K}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\pi}}^{\ensuremath{\mp}}$ of $\overline{p}p$ annihilation at rest in liquid hydrogen. This reaction is important for the study of the $\overline{K}K$ decay mode of scalar resonances, in particular, the isovectors ${a}_{0}(980)$ and ${a}_{0}(1450).$ The determination of the ${a}_{0}(1450)$ production also fixes the $\overline{K}K$ coupling of the isoscalar ${f}_{0}(1500)$ which is discussed as a glueball. We find $B(\overline{p}\stackrel{\ensuremath{\rightarrow}}{p}{a}_{0}(1450)\ensuremath{\pi}{;a}_{0}(1450)\ensuremath{\rightarrow}\overline{K}K)=(8.88\ifmmode\pm\else\textpm\fi{}1.68)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ and hence $B(\overline{p}\stackrel{\ensuremath{\rightarrow}}{p}{f}_{0}(1500)\ensuremath{\pi}{;f}_{0}(1500)\ensuremath{\rightarrow}\overline{K}K)=(4.52\ifmmode\pm\else\textpm\fi{}0.36)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}.$ The mass and width of ${a}_{0}(1450)$ are $m=1480\ifmmode\pm\else\textpm\fi{}30\mathrm{MeV}{/c}^{2}$ and $\ensuremath{\Gamma}=265\ifmmode\pm\else\textpm\fi{}15\mathrm{MeV}{/c}^{2},$ respectively. For ${a}_{0}(980)$ we determine the relative ratio $B(\overline{p}\stackrel{\ensuremath{\rightarrow}}{p}{a}_{0}\ensuremath{\pi}{;a}_{0}\ensuremath{\rightarrow}\overline{K}K)/B(\overline{p}\stackrel{\ensuremath{\rightarrow}}{p}{a}_{0}\ensuremath{\pi}{;a}_{0}\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\eta})$ =0.23\ifmmode\pm\else\textpm\fi{}0.05 and its relative coupling, $\overline{K}K$ to \ensuremath{\pi}\ensuremath{\eta}, is $1.03\ifmmode\pm\else\textpm\fi{}0.14.$

Negative pion spectra emitted in the reactions of 775 MeV/nucleon [sup 139]La+[sup 12]C and [sup 139]La+[sup 139]La reactions have been measured in coincidence with the projectile fragments using the HISS spectrometer at the Bevalac. Prominent peaks near the beam velocity were observed in the pion spectra. Position and widths of the peaks were studied as a function of the sum charge'' of projectile fragments which is a good measure of impact parameter; the smaller the sum charge,'' the smaller the impact parameter. The peak position down shifts with the smaller sum charge.'' The pion peak is wider in the transverse than in the longitudinal direction, possibly mirroring the velocity dispersions of projectile fragments in the early stage of reactions.

Gamma rays and, for the first time, conversion muons of [ital pt] fusion have been measured from liquid mixtures of protium, deuterium, and tritium. The rate [lambda][sub 10] for spin flip from the triplet to the singlet state of [ital t][mu](1[ital s]) was found to be [lambda][sub 10]=(1.06[plus minus]0.13)[times]10[sup 3][mu][ital s][sup [minus]1], the rate for muon-catalyzed [ital pt] fusion from the ([ital I]=1) nuclear-spin state to be [lambda][sub [ital p][ital t]][sup [ital f]]([ital I]=1) =0.067[plus minus]0.002[sub [minus]0.002][sup +0.005][mu][ital s][sup [minus]1], and the and the molecular formation rate to be [lambda][sub [ital p][ital t]][sup [ital m]]=(7.5[plus minus]0.3[sub [minus]0.3][sup +1.0])[mu][ital s][sup [minus]1] (all rates normalized to liquid hydrogen density).

We report on a first measurement of the polarized-target asymmetry of the pion-proton bremsstrahlung cross section ({pi}{sup +}{ital p}{r arrow}{pi}{sup {minus}}{ital p}{gamma}). As in previous cross section measurements the pion energy (298 MeV) and the detector geometry for this experiment was chosen to optimize the sensitivity to the radiation from the magnetic dipole moment of the {Delta}{sup ++}(1232) resonance {mu}{sub {Delta}}. Comparison to a recent isobar model for pion-nucleon bremsstrahlung yields {mu}{sub {Delta}}=(1.62{plus minus}0.18){mu}{sub {ital p}}, where {mu}{sub {ital p}} is the proton magnetic moment. Since the asymmetry depends less than the cross section on the choice of the other input parameters for the model, their uncertainties affect this analysis by less than the experimental error. However the theory fails to represent both the cross section and the asymmetry data at the highest photon energies. Hence further improvements in the calculations are needed before the model dependence of the magnetic moment analysis can be fully assessed. The present result agrees with bag-model corrections to the SU(6) prediction {mu}{sub {Delta}}=2{mu}{sub {ital p}}. As a by-product, the analyzing power for elastic {pi}{sup +}{ital p} scattering at 415 MeV/{ital c} was also measured. This second result is in good agreement with phase shiftmore » calculations.« less

The rate of nuclear muon capture by the proton has been measured using a new experimental technique based on a time projection chamber operating in ultra-clean, deuterium-depleted hydrogen gas at 1 MPa pressure. The capture rate was obtained from the dierence between the measured disappearance rate in hydrogen and the world average for the + decay rate. The target’s low gas density of 1% compared to liquid hydrogen is key to avoiding uncertainties that arise from the formation of muonic molecules. The capture rate from the hyperne singlet ground state of the p atom is measured to be S = 725:0 17:4 s 1 , from which the induced pseudoscalar coupling of the nucleon, g P (q 2 = 0:88m 2 ) = 7:3 1:1, is extracted. This result is consistent with theoretical predictions for gP that are based on the approximate chiral symmetry of QCD.

Brookhaven-AGS. Measuerment of the spectra of charged pions over nearly full rapidity coverage from target to beam rapidity in the centrality range 0-5pct in AU-AU collisions at beam energies from 2 to 8 A GeV/nucleon. The rapidity densities are extracted using a thermal paramatrization model to fit the transverse mass spectra.. Numerical values supplied by J Klay.. This part (1) covers the data at 2 GeV/nucleon. Brookhaven-AGS. Measuerment of the spectra of charged pions over nearly full rapidity coverage from target to beam rapidity in the centrality range 0-5pct in AU-AU collisions at beam energies from 2 to 8 A GeV/nucleon. The rapidity densities are extracted using a thermal paramatrization model to fit the transverse mass spectra.. Numerical values supplied by J Klay.. This part (2) covers the data at 4 GeV/nucleon. Brookhaven-AGS. Measuerment of the spectra of charged pions over nearly full rapidity coverage from target to beam rapidity in the centrality range 0-5pct in AU-AU collisions at beam energies from 2 to 8 A GeV/nucleon. The rapidity densities are extracted using a thermal paramatrization model to fit the transverse mass spectra.. Numerical values supplied by J Klay.. This part (3) covers the data at 6.0 GeV/nucleon. Brookhaven-AGS. Measuerment of the spectra of charged pions over nearly full rapidity coverage from target to beam rapidity in the centrality range 0-5pct in AU-AU collisions at beam energies from 2 to 8 A GeV/nucleon. The rapidity densities are extracted using a thermal paramatrization model to fit the transverse mass spectra.. Numerical values supplied by J Klay.. This part (4) covers the data at 8.0 GeV/nucleon. Brookhaven-AGS. Measurement of the spectra of charged pions over nearly full rapidity coverage from target to beam rapidity in the centrality range 0-5pct in AU-AU collisions at beam energies from 2 to 8 A GeV/nucleon. The rapidity densities are extracted using a thermal paramatrization model to fit the transverse mass spectra.. Numerical values supplied by J Klay.. This part (5) covers the data Rapidiy density data.

Rapidity distributions of protons from central ${}^{197}\mathrm{Au}{+}^{197}\mathrm{Au}$ collisions measured by the E895 Collaboration in the energy range from $(2--8)A\mathrm{GeV}$ at the Brookhaven AGS are presented. Longitudinal flow parameters derived using a thermal model including collective longitudinal expansion are extracted from these distributions. The results show an approximately linear increase in the longitudinal flow velocity, $〈\ensuremath{\beta}\ensuremath{\gamma}{〉}_{L}$, as a function of the logarithm of beam energy.

We report on a measurement of the branching ratio of the rare decay $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\omega}}\ensuremath{\eta}\ensuremath{\gamma}$ relative to the well known decay $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\omega}}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}.$ The \ensuremath{\omega}'s are produced in $p\overline{p}\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\omega}$ and $p\overline{p}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\omega}.$ Eigenstate mixing and interference effects of the \ensuremath{\omega} and ${\ensuremath{\rho}}^{0}$ are taken into account, as well as coherent interference with the background. We find evidence for the non-resonant annihilation channel $B(p\overline{p}\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\eta}\ensuremath{\gamma})=(3.5\ifmmode\pm\else\textpm\fi{}1.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ and limit the value of $B(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\omega}}\ensuremath{\eta}\ensuremath{\gamma})$ to the range of $(0.7\mathrm{to}5.5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ depending on the degree of coherence with the background.

High rates for mesomolecular processes were found in a study of neutron spectra from muon-catalyzed $\mathrm{dt}$ fusion in low-density D/T mixtures. An interpretation is given in terms of a reaction-kinetics model which includes hyperfine effects. The hyperfine components of the $d\ensuremath{\mu}t$ formation rates, first separated in this experiment, are large from 30 to 300 K. An unexpected temperature dependence for the transition rate between $\ensuremath{\mu}t$ hyperfine states is found.

The spin relaxation of the positive muon in copper has been measured below 5 K in zero applied magnetic field. The results are well described by the theory of Kubo and Toyabe with a temperature-independent dipolar width. It is concluded that neither trapping nor changes in the muon site with temperature explain the increased mobility below 5 K.

The photon spectra in the capture of stopped pions on $^{14}\mathrm{N}$ and $^{10}\mathrm{B}$ were measured in the 50-150-MeV region with a high-resolution pair spectrometer. The total radiative capture branching ratios are 2.13\ifmmode\pm\else\textpm\fi{}0.21 and 2.27\ifmmode\pm\else\textpm\fi{}0.22%, respectively. The spectrum corresponding to the first 13 MeV excitation in each of the residual nuclei $^{14}\mathrm{C}$ and $^{10}\mathrm{Be}$ is dominated by the transition to the analog of a giant $M1$ state of the target nucleus. The ground state transitions in both nuclei are resolved experimentally. The measured branching ratio for the extremely weak $^{14}\mathrm{C}$(g.s.) transition is (3\ifmmode\pm\else\textpm\fi{}2) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}5}$. There is evidence for selective excitation of the analogs of the giant dipole spin-isospin states of $^{14}\mathrm{N}$, of which the ${3}^{\ensuremath{-}}$ component appears to be the strongest. In $^{10}\mathrm{B}$ the transition strength to the giant resonance region is more fragmented. An analysis is presented that employs an impulse-approximation Hamiltonian with amplitudes taken directly from the fundamental process on the nucleon, ${\ensuremath{\pi}}^{\ensuremath{-}}+p\ensuremath{\rightarrow}n+\ensuremath{\gamma}$, and shell-model wave functions obtained using realistic interactions in the $1s$, $1p$, and $2s\ensuremath{-}1d$ shells. Also, a calculation for the $^{14}\mathrm{C}$(g.s.) transition from $1s$ capture using the "elementary-particle soft-pion" ansatz is presented.

An application of intensity interferometry to relativistic heavy ion collisions is reported. The correlation between two like-charged pions is used to study the reactions Ar+KC1..-->..2..pi../sup + -/+X and Ne+NaF..-->..2..pi../sup -/+X, both at an incident beam energy of 1.8A GeV. Source sizes and lifetimes are measured and compared to the predictions of simple geometric models and of Monte Carlo cascade calculations. There appears to be a substantial coherent component of the pion source, although measurement is complicated by the presence of final state interactions. A detailed discussion of the techniques of intensity interferometry is also presented. The generation of uncorrelated background events is discussed, along with the influence of the correlation on the background and the prescription for its removal. The statistical errors in the background spectrum are examined and found to have nontrivial implications for the analysis. The effect of the mutual Coulomb repulsion of the two pions, and of the pion-nuclear Coulomb interaction, on the two-pion correlation function is analyzed. The impact parameter bias resulting from a two-pion trigger is calculated and found to be substantial. Finally, a simple model for the interpretation of Gaussian source parameters is presented and compared to the predictions of Monte Carlo cascade calculations.

Doubly differential cross sections for the production of ${\ensuremath{\pi}}^{+}$ and ${\ensuremath{\pi}}^{\ensuremath{-}}$ near the velocity of the incident beam for pion laboratory angles from 0 to 20 degrees are presented. Beams of $^{20}\mathrm{Ne}$ with $\frac{E}{A}=280, 380, \mathrm{and} 480$ MeV and $^{40}\mathrm{Ar}$ with $\frac{E}{A}=535$ MeV incident on C, NaF, KCl, Cu, and U targets were used. A sharp peak in the ${\ensuremath{\pi}}^{\ensuremath{-}}$ spectrum and a depression in the ${\ensuremath{\pi}}^{+}$ spectrum is observed at 0\ifmmode^\circ\else\textdegree\fi{} near the incident projectile velocity. The effect is explained in terms of Coulomb interactions between pions and fragments of the incident beam. Least squares fits to the data using the Coulomb correction formulas of Gyulassy and Kauffmann and an effective projectile fragment charge are made. The relationship between these data and previously measured projectile fragmentation data is discussed and a simple parametrization of projectile mass, target mass, and beam energy dependence of the differential cross sections is given.NUCLEAR REACTIONS C, NaF, Cu, U $(^{20}\mathrm{Ne},{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}})X$, $\frac{E}{A}=280\ensuremath{-}480$ MeV; C, KCl $(^{40}\mathrm{Ar},{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}})X$, $\frac{E}{A}=535$ MeV; measured $\ensuremath{\sigma}({E}_{\ensuremath{\pi}},{\ensuremath{\theta}}_{\ensuremath{\pi}})$, ${\ensuremath{\theta}}_{\ensuremath{\pi}}=0\ifmmode^\circ\else\textdegree\fi{}\ensuremath{-}20\ifmmode^\circ\else\textdegree\fi{}$, $\ensuremath{\pi}$ velocity near beam velocity; deduced projectile fragment charges, Coulomb effects.

Author(s): Truol, Peter; Baer, Helmet W.; Bistirlich, James A.; Crowe, Kenneth M.; Botton, Nico de; Helland, Jerome A.

The photon spectrum from the pion capture reaction ..pi../sup -/ + t ..-->.. 3n + ..gamma.. was measured with a high-resolution pair-spectrometer to study the A = 3 system in a pure T = 3/2 state. The measured branching ratio (..pi../sup -/t ..-->.. nn..gamma..)/(..pi../sup -/t ..-->.. nnn..gamma.. or nnn) is 4.5 +- 0.8 percent. The shape of the photon spectrum is in satisfactory agreement with theoretical calculations which include final state interactions among the three neutrons. No evidence for a bound trineutron is found.

We have measured the fivefold differential cross section ${d}^{5}$\ensuremath{\sigma}/d${\ensuremath{\Omega}}_{\ensuremath{\pi}}$d${\ensuremath{\Omega}}_{\ensuremath{\gamma}}$${\mathrm{dE}}_{\ensuremath{\gamma}}$ for the process ${\ensuremath{\pi}}^{+}$p\ensuremath{\rightarrow}${\ensuremath{\pi}}^{+}$p\ensuremath{\gamma} with incident pions of energy 299 MeV. The angular regions for the outgoing pions (55\ifmmode^\circ\else\textdegree\fi{}\ensuremath{\le}${\ensuremath{\theta}}_{\mathrm{lab}{}^{\ensuremath{\pi}}\mathrm{\ensuremath{\le}}95}$\ifmmode^\circ\else\textdegree\fi{}), and photons (${\ensuremath{\theta}}_{\mathrm{lab}{}^{\ensuremath{\gamma}}=241\mathrm{\ifmmode^\circ\else\textdegree\fi{}}\ifmmode\pm\else\textpm\fi{}10}$\ifmmode^\circ\else\textdegree\fi{}) in coplanar geometry are selected to maximize the sensitivity to the radiation from the magnetic dipole moment of the ${\ensuremath{\Delta}}^{++}$(1232) resonance. At low photon energies, the data agree with the soft-photon approximation to pion-proton bremsstrahlung. At forward pion angles the data agree with older data and with the latest theoretical calculations for 2.3${\ensuremath{\mu}}_{p}$\ensuremath{\le}${\ensuremath{\mu}}_{\ensuremath{\Delta}}$\ensuremath{\le}3.3${\ensuremath{\mu}}_{p}$. However at more backward pion angles where no data existed, the predictions fail.

The photon spectrum of the pion capture reaction /sup 14/C(..pi../sup -/,..gamma..)/sup 14/B was measured with a resolution of 0.9 MeV full width at half maximum. A single strong transition is observed with ..gamma..-ray energy 115.70 +- 0.17 MeV, corresponding to a state in /sup 14/B at 2.15 +- 0.17-MeV excitation. Comparisons with previous experiments and theoretical calculations identify this as the second T = 2,2/sup -/ state in mass-14 nuclei. The single strong transition has a measured branching ratio (11.1 +- 3.0) x 10/sup -4/, which equals one-fifth of the shell-model prediction. The total radiative capture branching ratio is 0.68 +- 0.16%, which is a factor of 2 to 3 smaller than for other 1-p-shell nuclei.

The photon spectrum from /sup 20/Ne(0/sup -/,..gamma..)/sup 20/F has been measured. The branching ratio to /sup 20/F(1/sup +/,1.06 MeV) is compared to the analogous M1 decay width /sup 20/Ne(1/sup +/,11.24 MeV)..-->../sup 20/Ne(g.s.). This determines the relative importance of spin and orbital magnetization in the transition amplitude. The M1 amplitude is found to contain only (47 +- 16)% spin flip, in agreement with shell-model calculations. Excitation of 2/sup -/ states by /sup 20/Ne(..pi../sup -/,..gamma..) is also observed.

Photon spectra from radiative capture of stopped negative pions captured by /sup 13/C and /sup 19/F nuclei have been measured with a high resolution pair spectrometer. In the bound region transitions have been observed to /sup 13/B(g.s.), /sup 13/B(3.5 MeV), /sup 19/O(g.s.), /sup 19/O(4.9 MeV), and /sup 19/O(6.3 MeV). In addition, strong transitions to narrow states above the neutron separation threshold were observed in both cases. The results for /sup 13/C are in agreement with detailed shell model calculations of this process. Major strength is observed for states formed by coupling extra nucleons or holes to the spin-quadrupole d/sub 5/2/ and d/sub 3/2/, J/sup ..pi../ = 2/sup -/ states in /sup 16/O. The /sup 13/C(..pi../sup -/,..gamma..)/sup 13/B/sub g.s./ branching ratio is shown to be consistent with beta decay and electroexcitation data, through a combined phenomenological analysis. The observed transition strengths are accounted for by matrix elements of the spin-density operators (sigma x Y/sub 0/)/sup 1/t/sup +/ and (sigma x Y/sub 1/)t/sup +/.

A study is made of p-d reactions in which He/sup 3/ + pi /sup O/, He/ sup 3/ + omega /sup O/, He/sup 3/ + pi /sup +/ + pi /sup -/, He/sup 3/ + pi / sup O/ + pi /sup O/O, H/sup 3/ I pi /sup +/, H/sup 9/ + omega +, and H/sup 3/ + pi /sup +/ + pi /sup 9/ are produced. The omega is an assumed particle with a mass between 1 and 2.8 times that of the pi meson. An anomalous peak is found in the He3 spectra that behaves kinematically like a resonance of mass 310 Mev. It is shown that this resonance may be explained as a strong S-wave pi - pi attractive mode in the 1 = 0 state, or as an He/sup 3/- pi final state interaction. (T.F.H.)

Total cross sections of ${K}^{\ensuremath{-}}$ mesons in hydrogen and deuterium were measured over the momentum range 630 to 1100 Mev/c. The ${K}^{\ensuremath{-}}\ensuremath{-}n$ total cross sections were obtained from deuterium and hydrogen data. A well-defined resonance appeared in the ${K}^{\ensuremath{-}}\ensuremath{-}p$ total cross section at about 1000 Mev/c. Two high-resolution velocity-selecting \ifmmode \check{C}\else \v{C}\fi{}erenkov counters were used to select ${K}^{\ensuremath{-}}$ mesons. The momentum resolution was within 1% to 2%, and the momentum intervals chosen were very closely spaced.

The helicity of the electron and positron from muon decay was measured by determining the sense of circular polarization of their bremsstrahlung by the method of absorption in iron magnetized against or along the direction of motion of the particles. The positron is found to be right-handed and the electron left- handed. The results are consistent with the two-component neutrino theory, which assumes (V,A) interaction, conservation of leptons, and left-handed neutrinos. (auth)

An attempt was made to determine the spin and parity of the I = 0 anomaly by detecting charged pions and gamma rays in coincidence with He/sup 3/. The results are consistent with the interpretation that the predominant mode of decay is into two pions with a charged-to-neutral ratio of 2/1, indicating a state of spin 0 and even parity. (auth)

A measurement has been made of the differential cross section for the elastic scattering of positive and negative pions of energies 51, 60, 68, and 75 MeV scattered from helium. The experiment is discussed and a phase-shift analysis is presented. An optical-model analysis has been used to extract the pion electromagnetic radius, yielding 2.96\ifmmode\pm\else\textpm\fi{}0.43 F. There remain uncertainties in this application of the model, which are discussed.

The momentum spectra of ${\mathrm{He}}^{3}$ and ${\mathrm{H}}^{3}$ nuclei produced in $p+d$ collisions have been measured with high resolution. Data were obtained at several angles and incident proton energies of about 745 MeV. Each spectrum exhibits a peak due to single pion production and a continuum due to double pion production. An anomalous bump has been observed in the ${\mathrm{He}}^{3}$ spectra which we interpret as an $I=0$ virtual di-pion with a scattering length of 2 \ensuremath{\Elzxh}/\ensuremath{\mu}c. In this series of four papers we summarize the data obtained over a series of three cyclotron runs. The first paper deals with the experiment and techniques, and the second with the results of the measurements on single-pion production. Next we describe an experiment to determine the spin and parity of the anomalous bump, and finally we discuss its interpretation.

The gamma-ray spectrum of the reaction ${\ensuremath{\pi}}^{\ensuremath{-}}+p\ensuremath{\rightarrow}n+\ensuremath{\gamma}$ has been remeasured with an improved design of the high-energy pair spectrometer. This design has taken advantage of one of the focusing properties of a 90-degree wedge-shaped magnetic field to minimize the effect on the resolving power of multiple scattering of the pair fragments in the converter. The theory of the spectrometer is developed in detail. The accuracy of the energy scale depends on magnetic field measurements and the calculation of orbits, aberrations, and resolving power. By the determination of the mesonic absorption gamma-ray energy, a precise mass value for the negative pion has been found: ${{M}_{\ensuremath{\pi}}}^{\ensuremath{-}}=272.7\ifmmode\pm\else\textpm\fi{}0.3{m}_{e}.$From the ${\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{-}{\ensuremath{\pi}}^{0}$ mass differences already obtained by Panofsky, Aamodt, and Hadley (PAH), by Chinowsky, Sachs, and Steinberger (CSS), and the ${\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{-}{\ensuremath{\mu}}^{\ensuremath{-}}$ mass difference obtained by Lederman, Tinlot, and Booth (LTB), it is possible to improve the mass values for the ${\ensuremath{\pi}}^{0}$ and the ${\ensuremath{\mu}}^{\ensuremath{-}}$ mesons. $\mathrm{From} {\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{-}{\ensuremath{\pi}}^{0} (\mathrm{PAH}): {{M}_{\ensuremath{\pi}}}^{0}=262.2\ifmmode\pm\else\textpm\fi{}2.0{m}_{e};$ $\mathrm{from} {\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{-}{\ensuremath{\pi}}^{0} (\mathrm{CSS}): {{M}_{\ensuremath{\pi}}}^{0}=263.9\ifmmode\pm\else\textpm\fi{}0.7{m}_{e};$ $\mathrm{from} {\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{-}{\ensuremath{\mu}}^{\ensuremath{-}} (\mathrm{LTB}): {{M}_{\ensuremath{\mu}}}^{\ensuremath{-}}=206.7\ifmmode\pm\else\textpm\fi{}3.0{m}_{e}.$ If one assumes that the positive and negative pions have the same mass, the mass of the positive muon can also be deduced from the work of Birnbaum, Smith, and Barkas: ${{M}_{\ensuremath{\mu}}}^{+}=206.3\ifmmode\pm\else\textpm\fi{}0.3 {m}_{e}.$

Author(s): Hague, J.F.; Rothberg, J.E.; Schenck, A.; Williams, D.L.; Williams, R.W.; Young, K.K.; Crowe, K.M.

The photon spectrum from the reaction $^{6}\mathrm{Li}({\ensuremath{\pi}}^{\ensuremath{-}},\ensuremath{\gamma})$ was measured with high resolution in the 50- to 150-MeV region by using an electron-positron pair spectrometer. The total fraction of pions absorbed radiatively is 4.4 \ifmmode\pm\else\textpm\fi{} 0.6% with branching ratios to the $^{6}\mathrm{He}$ ground state of 0.31 \ifmmode\pm\else\textpm\fi{} 0.04% and to the 1.8-MeV state of 0.15 \ifmmode\pm\else\textpm\fi{} 0.03%, in disagreement with previous experimental results, but in qualitative agreement with theoretical predictions. Evidence for higher excitations is observed in addition to quasifree capture accompanied by neutron emission.

We have studied precession of polarized positive muons in quartz and silicon in transverse magnetic fields, via the asymmetric decay. We observed free muon precession and two-frequency muonium precession, as well as two anomalous precession frequencies apparent only in silicon.

A measurement of the rates ${K}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}+{\ensuremath{\pi}}^{+}$, ${K}^{+}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\pi}}^{0}\ensuremath{\nu}$, and ${K}^{+}\ensuremath{\rightarrow}{e}^{+}+{\ensuremath{\pi}}^{0}+\ensuremath{\nu}$ with respect to ${K}^{+}\ensuremath{\rightarrow}\ensuremath{\mu}+\ensuremath{\nu}$ has been made by using a magnetic spectrometer and spark chambers. Both the range and momentum of the charged decay product are measured and compared with a Monte Carlo calculation. The decay in flight of the ${K}^{+}$ mesons and the scattering of pions into the apparatus are rejected by a decay-time requirement. The results of the branching-ratio measurement are $\ensuremath{\Gamma}({K}_{\ensuremath{\mu}2})=(65.0\ifmmode\pm\else\textpm\fi{}0.9)%$, $\ensuremath{\Gamma}({K}_{\ensuremath{\pi}2})=(19.8\ifmmode\pm\else\textpm\fi{}1.1)%$, $\ensuremath{\Gamma}({K}_{\ensuremath{\mu}3})=(3.5\ifmmode\pm\else\textpm\fi{}0.6)%$, and $\ensuremath{\Gamma}({K}_{e3})=(4.4\ifmmode\pm\else\textpm\fi{}0.4)%$, on the assumptions $\ensuremath{\Gamma}(\ensuremath{\tau})=(5.57\ifmmode\pm\else\textpm\fi{}0.03)%$ and $\ensuremath{\Gamma}({\ensuremath{\tau}}^{\ensuremath{'}})=(1.71\ifmmode\pm\else\textpm\fi{}0.07)%$.

Positive muons from the Berkeley 184-in. synchrocyclotron were stopped in various materials and the asymmetry of positrons from their decay was determined by using a magnetic spectrometer method. The measurements of the polarization are in agreement with that predtcted by the two-component neutrino theory. The product of the muon beam polarization and of from tests in , the parameter of the two-component neutrino theory, was measured as 0.89 the J-57 engin O.09. (auth)

Measurements have been made on the relative cross section of positive pions made by 350-Mev bremsstrahlung for deuterium and hydrogen for laboratory angles between 30\ifmmode^\circ\else\textdegree\fi{} and 90\ifmmode^\circ\else\textdegree\fi{}. The ratio of the differential cross sections is essentially a constant to about \ifmmode\pm\else\textpm\fi{}5%. The mean pion laboratory energy of 75\ifmmode\pm\else\textpm\fi{}5 Mev was held constant for the different angles. The results compare qualitatively with those obtained from Watson's phenomenological theory for photopion production.

In a previous publication (Abashian et al., Phys. Rev. Letters, 5: 258(1960)) measurements were reported on the momentum spectra of He/sup 3/ and H/ sup 3/ nuclei produced in collisions of 740-Mev protons with deuterons. The He/ sup 3/ spectrum exhibited an anomaly in the form of a peak in the region corresponding to double pion production. For reactions resulting in He/sup 3/, the two pions (or particle) can be in isotopic spin states 0 or 1; if a R/sup 3/ nucleus results, only 1 = 1 is allowed. The experiment was repeated with a new arrangement which enabled both the He/sup 3/ and the H/sup 3/ spectra to be measured with improved resolution and accuracy. It is concluded that the anomaly must be assigned an isotopic spin I = O. (L.T.W.)