Search

The branching ratios Γ(η → 3π 0 ) Γ(η → π + π − π 0 ) = 1.44 ± 0.09 ± 0.10 and Γ(η → γγ) Γ(η → π + π − π 0 ) = 1.78 ± 0.10 ± 0.13 have been determined using the Crystal Barrel detector at LEAR. The latter ratio yields a partial width of Γ ( η → π + π − π 0 ) = 0.26 ± 0.03 keV using the known value for Γ ( η → γγ ). The η → π + π − π 0 ) Dalitz plot is compared to the predictions of chiral perturbation theory.

The decay of the η-meson into three pions plays an important role as a test of low-energy QCD calculations in the framework of chiral perturbation theory. Previous experiments show results that are inconclusive or even contradictory. The Crystal Barrel experiment at LEAR has determined the braching ratiosΓ(η→3π0)/Γ(η→π+π−π0)=1.47±0.09±0.15 andΓ(η→γγ)/Γ(η→π+π−π0)=1.88±0.10±0.17 using its unique features to detect charged particles as well as neutral particles. The value for the first ratio agrees nicely with the theoretical predictions and solves previous experimental uncertainties. The second value, which yields a partial width ofΓ(η→π+π−π0)=(0.24±0.03) keV, shows that the same next-to-leading order chiral perturbation theory calculations still have some problems.

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.

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.

Source imaging analysis was performed on two-pion correlations in central Au + Au collisions at beam energies between 2 and 8$A$ GeV. We apply the imaging technique by Brown and Danielewicz, which allows a model-independent extraction of source functions with useful accuracy out to relative pion separations of about 20 fm. We found that extracted source functions have Gaussian shapes. Values of source functions at zero separation are almost constant across the energy range under study. Imaging results are found to be consistent with conventional source parameters obtained from a multidimensional HBT analysis., Talk given at Bologna 2000 - Structure of the Nucleus at the Dawn of the Century, Bologna, Italia, May 29 - June 3, 2000

Bose-Einstein correlations of negative pions in heavy ion collisions have been investigated for the reaction [sup 139]La+[sup nat]La[r arrow]2[pi][sup [minus]][ital X] at 12.6 GeV/nucleon at two acceptances, centered at laboratory observation angles of approximately 0[degree] and 45[degree] with respect to the beam axis. A scintillation counter array downstream of the target was used to sample the charged particle multiplicity of each event and hence give some information on the impact parameter of the collision. Including results from previous experiments, space-time dimensions of the pion source are now available for mass-symmetric collisions in the mass range of [ital A]=40 to 139. The sources are oblate for nearly all systems, except for La+La central collisions viewed near 45[degree] in the laboratory (90[degree] in the center of mass) where the source is spherical. The perpendicular radius [ital R][sub [perpendicular]] is never less than 4 fm, regardless of the centrality of the La+La collision. Furthermore, [ital R][sub [perpendicular]] seems independent of the mass of the collision system.

The method of two-pion interferometry was used to obtain source-size and lifetime parameters for the pions produced in heavy ion collisions. Two acceptances (centered at approximately 0\ifmmode^\circ\else\textdegree\fi{} and approximately 90\ifmmode^\circ\else\textdegree\fi{}, in the center of mass) were used for each of three systems, 1.70 GeV/nucleon $^{56}\mathrm{Fe}$+Fe, 1.82 GeV/nucleon $^{40}\mathrm{Ar}$+KCl, and 1.54 GeV/nucleon $^{93}\mathrm{Nb}$+Nb, allowing a search for dependences on nuclear mass and viewing angle. The correlation functions were calculated by comparing data samples to event-mixed reference samples. The effect of the particle correlations on the reference samples was corrected by weighting the events appropriately to remove the residual correlation effect. The source parameters, in the nucleus-nucleus center-of-mass frame, show an oblate source (i.e., ${\mathit{R}}_{\mathrm{\ensuremath{\perp}}}$g${\mathit{R}}_{\mathrm{\ensuremath{\parallel}}}$) for the lighter systems and an approximately spherical source for the heaviest system. The dependence on nuclear mass shows that ${\mathit{R}}_{\mathrm{\ensuremath{\perp}}}$ is essentially constant (under both viewing angles), whereas ${\mathit{R}}_{\mathrm{\ensuremath{\parallel}}}$ for the 90\ifmmode^\circ\else\textdegree\fi{} (c.m.) data increases with the nuclear mass. No evidence was found for a dependence of the source size on the pion momentum.

An experimental search for bound systems of {pi}{sup {minus}}'s and neutrons (pineuts) was made in collisions of {sup 40}Ar (1.8{ital A} GeV) and {sup 139}La (1.3{ital A} GeV) projectiles on a {sup 238}U target. Five candidate events survived the selection criteria but--in view of their marginal systematic consistency--they are not taken as valid evidence for pineuts. Upper limits for production cross sections are derived for singly and doubly charged systems on the order of 4{times}10{sup {minus}35} cm{sup 2}/sr(MeV/{ital c}).

First data are presented for the polarized-target asymmetry in the reaction {pi}{sup +}{ital p}{r arrow}{pi}{sup +}{ital p}{gamma} at an incident pion energy of 298 MeV. The geometry was chosen to maximize the sensitivity to the radiation of the magnetic dipole moment {mu}{sub {Delta}} of the {Delta}{sup ++}(1232 MeV). A fit of the asymmetry in the cross section {ital d}{sup 5}{sigma}/{ital d}{Omega}{sub {pi}} {ital d}{Omega}{sub {gamma}} {ital dk} as a function of the photon energy {ital k} to predictions from a recent isobar-model calculation with {mu}{sub {Delta}} as the only free parameter yields {mu}{sub {Delta}}=1.64({plus minus}0.19exp{Delta},{plus minus}0.14 theor){mu}{sub {ital p}}. Though this value agrees with bag-model corrections to the SU(6) prediction {mu}{sub {Delta}}=2{mu}{sub {ital p}}, further clarifications on the model dependence of the result are needed, in particular since the isobar model fails to describe both the cross section and the asymmetry at the highest photon energies.

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.

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.

The cross section and angular distribution for the reaction 13C(π+, γ)13N(g.s.) have been measured from 37 to 85° in the laboratory, at a pion energy of 115.5 MeV. The observed cross section ranges from 320 to 660 nbsr. These results do not show the large magnitude and wide-angle peaking expected if pre-critical effects due to nascent pion condensation were present. In addition, the observed cross section is less than one-half of the predictions of available theoretical calculations which do not include the pre-critical effect. Data on the reaction 1H(π−, γ)n at Tπ = 116.6 MeV were also obtained for calibration purposes. These data agree with expectations based on knowledge of the inverse reaction and previous measurements.

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.

Differential cross-section measurements for π−p → γn, consisting of three angular distributions at 618, 676 and 718 MeV/c, and the energy dependence at θγ = 90° for seven incident pion momenta between 502 and 888 MeV/c, are presented. Our data qualitatively support recent multipole analyses. Agreement with the Scheffler et al. results for the inverse reaction, γn → π−p, using a (π−-recoil p) coincidence technique is good excluding a large violation of time reversal invariance. The agreement with γn → π−p data obtained using the R(π−/π+) ratio technique or a deuterium bubble chamber is only qualitative.

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 +/.

The differential energy distributions of neutrons from the reaction π − + p → π o + π o + n were measured at four different neutron lab angles. Fitting the distributions with the Chew-Mandelstam solution for π − π phase shift, we obtain a value a SO = (0.28 ± 0.21) μ −1 for the S-wave π − π scattering length.

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.)

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: ${{M}_{\ensuremath{\mu}}}^{+}=206.3\ifmmode\pm\else\textpm\fi{}0.3 {m}_{e}.$

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.

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 $\ensuremath{\Gamma}({\ensuremath{\tau}}^{\ensuremath{'}})=(1.71\ifmmode\pm\else\textpm\fi{}0.07)%$.

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.

The intensity interferometry method has been used to measure pion-source parameters in the reaction 1.70A-GeV /sup 56/Fe+Fe..-->..2..pi../sup -/+X. The parameters show an oblate source for a narrow-acceptance spectrometer near either 0/sup 0/ or 90/sup 0/ with respect to the beam axis in the center-of-mass frame. Intranuclear-cascade--model predictions show similar behavior and are compared to the experimental results.

Doubly differential cross sections for producing ..pi../sup +/ and ..pi../sup -/ were measured for several target-projectile combinations. They were /sup 40/Ar+C, Ca, and U at 1050A MeV and /sup 20/Ne+Be and NaF at 655A MeV. The ..pi../sup -//..pi../sup +/ ratios are smaller than those expected from several Coulomb effect calculations. The Ne+NaF..--> pi../sup -/ data exhibit a peak at 90/sup 0/ in the center of mass and p/sub ..pi../ = 0.4m/sub ..pi../c.

The central question to be addressed in this article is: What can be learned about nuclear structure by stopping negatively charged pions in targets of nuclei from various regions of the periodic table and examining the emitted photon spectra between 50 and 150 MeV with a resolution of ≲ 2 MeV? The two processes which account for nearly all photons in this energy interval are radiative capture, $$ \pi ^ - + A_i \to A_f + \gamma $$ (1a) $$ \to \left( {A - 1} \right)_f + n + \gamma $$ (1b) $$\begin{array}{*{20}c} { \to \left( {A - 2} \right)_f + n + n + \gamma } \\ \vdots \\ \end{array} $$ (1c) and charge exchange, $$ \pi ^ - + A_i \to A_f + \mathop {\pi ^0 }\limits_{\mathop |\limits_{ \to 2\gamma } } $$ (2) The latter has been observed only with hydrogen and 3He targets. Measurements of the photon spectra from hydrogen and deuterium targets in the early 1950s helped determine basic properties of the pion, such as its mass, odd intrinsic parity, and the π-N coupling constant. In recent years targets ranging up to A = 209 have been studied and much of the interest has turned to the use of radiative pion capture as a probe of nuclear structure.

Using neutron time-of-flight techniques, the pi /sup -/ mass was determined to be 272.4 plus or minus 1.1 and the mass difference of pi /sup -/ and pi /sup 0/ to be 8.991 plus or minus 0.020 m/sub e/. These values agree favorably with determinations by other groups. (C.J.G.)

We have completed an experiment at the Berkeley 184 inch-cy-clotron set up to study radiative capture of pions on nuclei, i.e. the process π−N(A,Z) -4- γN*(A,Z-1).

Publisher Summary This chapter discusses the photon spectra from pion absorption on 3He and 6Li+ and the preliminary results of a high-resolution study of the photon spectra in the 50–150 MeV regions associated with stopped п− absorption on 3He and 6Li. The measurements are performed at the Berkeley l84-in. cyclotron. The principal modifications have been to replace the optical spark chambers of the pair spectrometer with a set of three wire spark chambers and to increase the solid angle by a factor of 2. A liquid hydrogen target was employed in the calibration. The branching ratio for the direct transition to 6He(g.s.) was determined by fitting the instrumental line shape, obtained from the hydrogen spectrum, to the high energy region of the observed peak.

The He/sup 3/ and H/sup 3/ spectra resulting from collisions of 740Mev protons with deuterium were measured. Results are shown in figures and tables. The anomalous bump found previously in the He/sup 3/ spectra and assumed to correspond to double pion production was clearly evident. It was concluded that the anomaly must be assigned an isotopic spin I = 0. (M.C.G.)

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.)