Search

We report on the measurement of the beam asymmetry Σ for the reactions → γ p → p η and → γ p → p η ′ from the GlueX experiment using an 8.2–8.8-GeV linearly polarized tagged photon beam incident on a liquid hydrogen target in Hall D at Jefferson Laboratory. These measurements are made as a function of momentum transfer − t with significantly higher statistical precision than our earlier η measurements and are the first measurements of η ′ in this energy range. We compare the results to theoretical predictions based on t -channel quasiparticle exchange. We also compare the ratio of Σ η to Σ η ′ to these models as this ratio is predicted to be sensitive to the amount of s ¯ s exchange in the production. We find that photoproduction of both η and η ′ is dominated by natural parity exchange with little dependence on − t .

The η → π 0 γγ rare decay was measured at the AGS with the Crystal Ball photon spectrometer and its relative branching ratio was extracted to be B 1 =(8.3±2.8±1.4)×10 −4 , based on the analysis of 3×10 7 detected η mesons. This leads to a lower partial width for this eta channel than past measurements and is in line with chiral perturbation theory calculations.

Precise new data for the reaction K−p→π0Λ are presented in the c.m. energy range 1565 to 1600 MeV. Our analysis of these data sheds new light on claims for the Σ(1580) 3 2 − resonance, which (if it exists with the specified quantum numbers) must be an exotic baryon because of its very low mass. Our results show no evidence for this state.

We measured the cross section and response functions for the quasielastic 16O(e,e'p) reaction for missing energies 25< or =E(m)< or =120 MeV at missing momenta P(m)< or =340 MeV/c. For 25

We have measured the cross section for quasielastic 1p -shell proton knockout in the {sup 16}O( e, e{sup '}p) reaction at {omega}=0.439 GeV and Q{sup 2}=0.8 (GeV/c){sup 2} for missing momentum P{sub miss}{

The ratio of the proton's elastic electromagnetic form factors was obtained by measuring the transverse and longitudinal polarizations of recoiling protons from the elastic scattering of polarized electrons with unpolarized protons. The ratio of the electric to magnetic form factor is proportional to the ratio of the transverse to longitudinal recoil polarizations. The ratio was measured over a range of four-momentum transfer squared between 0.5 and 3.5 GeV-squared. Simultaneous measurement of transverse and longitudinal polarizations in a polarimeter provides good control of the systematic uncertainty. The results for the ratio of the proton's electric to magnetic form factors show a systematic decrease with increasing four momentum squared, indicating for the first time a marked difference in the spatial distribution of charge and magnetization currents in the proton.

The 1 H(e, e′K + )Λ and 1 H(e,e′K + )Σ 0 reactions were studied as a function of the squared four-momentum-transfer, Q 2 , and the virtual photon polarization, e, thus enabling the separation of the longitudinal and transverse parts of the cross section. The existence of a sizable longitudinal component for the 1 H(e,e′K + )Λ reaction seems to be indicated by these data.

Differential and total cross sections for ${\mathrm{\ensuremath{\pi}}}^{+}$ absorption on $^{6}\mathrm{Li}$, leading to the pp${+}^{4}$${\mathrm{He}}_{\mathrm{g}.\mathrm{s}.}$, pp${+}^{4}$${\mathrm{He}}^{\mathrm{*}}$, and pp+X final states, are presented at incident pion energies of 100 and 165 MeV. We conclude that most of the cross section is confined to the level of coplanarity expected from quasideuteron absorption in the nuclear environment and that the contributions of nonquasideuteron absorption mechanisms are small. \textcopyright{} 1996 The American Physical Society.

As part of an experimental study of the {pi}{ital NN} system, the pion-deuteron breakup reaction {pi}{sup +}{ital {rvec d}}{r_arrow}{ital pn}{pi}{sup +} was investigated at intermediate energies. Distributions of the vector analyzing power {ital iT}{sub 11} versus outgoing proton momentum {ital P}{sub {ital p}} are presented for 36 {pi}{ital p} angle pairs in the range of scattering angles 20{degree}{le}{theta}{sub {ital p}}{le}51{degree}, 62{degree}{le}{theta}{sub {pi}}{le}124{degree} at 228 and 134 MeV. These include 7 previously unmeasured angle pairs at 228 MeV and 20 new pairs at 134 MeV. In all regions of overlap with previous measurements, there is excellent agreement. There is generally excellent agreement with relativistic Faddeev predictions, except in the {ital np} final-state interaction region at 228 MeV. This is in contrast to the cross-section measurements, which are not well described by the theory.

Differential and total cross sections for {pi}{sup +} absorption on {sup 6}Li leading to the {ital pp}+{sup 4}He{sub g.s} final state are presented at incident pion energies of 100 and 165 MeV. The narrow width of the {ital pp} angular correlation is observed and reported.

Angular distributions of the differential cross sections and analyzing powers have been measured for the [sup 3]He([ital [rvec p]],[pi][sup +]) [sup 4]He and [sup 4]He([ital [rvec p]],[pi][sup +])[sup 5]He reactions at proton bombarding energies between 240 and 507 MeV. These new results provide a comprehensive set of data spanning the region of the [Delta][sub 1232] resonance and are compared with a phenomenological model that incorporates the amplitudes for the [ital pp][r arrow][ital d][pi][sup +] reaction, and with calculations from a microscopic ([ital p],[pi][sup +]) model. A [sup 5]He final state interaction calculation based upon the low energy [ital n]+[alpha] elastic phase shifts indicates that the [sup 4]He([ital p],[pi][sup +])[sup 5]He spectra are nearly independent of pion angle and proton energy. Comparisons made with the time reversed charge symmetric reaction [sup 3]H([ital n],[pi][sup [minus]])[sup 4]He reaction indicate substantial Coulomb effects are still present at 300 MeV.

The [sup 3]He([gamma],[ital pp])[ital n] reaction was investigated in the photon energy range 200--500 MeV using the spectrometer TAGX, which has a solid angle for protons of [pi] sr. Two types of photon absorption, one by two protons and the other by three nucleons, were observed by looking at the undetected neutron momentum distributions. The total cross section for photon absorption by two protons shows that this process is consistent with the [ital E]2 transition.

Three-body $^{3}\mathrm{He}$ photodisintegration was measured in the photon energy range (${\mathit{E}}_{\ensuremath{\gamma}}$) of 145--425 MeV. The total cross section for photon absorption on the np pairs in $^{3}\mathrm{He}$, \ensuremath{\sigma}${(}^{3}$He(\ensuremath{\gamma},np)${\mathit{p}}_{\mathrm{sp}}$), where ${\mathit{p}}_{\mathrm{sp}}$ is a spectator proton, is reported here for the first time. The ${\mathit{E}}_{\ensuremath{\gamma}}$ dependence of the \ensuremath{\sigma} is found to scale to that of \ensuremath{\sigma}${(}^{2}$H(\ensuremath{\gamma},np)), and the ratio is determined to be \ensuremath{\sigma}${(}^{3}$He(\ensuremath{\gamma},np)${\mathit{p}}_{\mathrm{sp}}$)/\ensuremath{\sigma}${(}^{2}$H(\ensuremath{\gamma},np))=1.24\ifmmode\pm\else\textpm\fi{}0.,26.

3 He(γ, pπ ± ) reactions are simultaneously measured for tagged photon energies of 380 ⩽ Eγ ⩽ 700 MeV. The yield ratio for the two channels, under the same kinematical and dynamical conditions, is found to be 0.90±0.07. Implications of this ratio in terms of the delta component in the ground state of 3He are examined. An alternate interpretation of this ratio as due to an admixture of isospin T = 1 2 and 3 2 transition amplitudes in a pure isovector interaction is also presented.

Differential cross sections for K{sup -} radiative capture in flight on the proton, leading to the gammaLAMBDA and gammaSIGMA{sup 0} final states, have been measured at eight K{sup -} momenta between 514 and 750 MeV/c. The data were obtained with the Crystal Ball multiphoton spectrometer installed at the separated K/pi beam line C6 of the BNL Alternating Gradient Synchrotron. The results substantially improve the existing experimental data available for studying radiative decays of excited hyperon states. An exploratory theoretical analysis is performed within the Regge-plus-resonance approach. According to this analysis, the gammaSIGMA{sup 0} final state is dominated by hyperon-resonance exchange and hints at an important role for a resonance in the mass region of 1700 MeV. In the gammaLAMBDA final state, in contrast, the resonant contributions account for only half the strength, and the data suggest the importance of a resonance in the mass region of 1550 MeV.

Measured values of the differential cross sections for pion-nucleon charge exchange, ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}n$, are presented for ${\ensuremath{\pi}}^{\ensuremath{-}}$ momenta of $103,112,120,130,139,152$, and $178$ MeV/$c$. Complete angular distributions were obtained by using the Crystal Ball detector at the Alternating Gradient Synchrotron at Brookhaven National Laboratory. Statistical uncertainties of the differential cross sections vary from $3$ to $6%$ in the backward angle region and from $6$ to about $20%$ in the forward region with the exception of the two most forward angles. The systematic uncertainties are estimated to be about $3%$ for all momenta.

Differential cross sections and hyperon polarizations have been measured for ${\overline{K}}^{0}n$, ${\ensuremath{\pi}}^{0}\ensuremath{\Lambda}$, and ${\ensuremath{\pi}}^{0}{\ensuremath{\Sigma}}^{0}$ production in ${K}^{\ensuremath{-}}p$ interactions at eight ${K}^{\ensuremath{-}}$ momenta between 514 and 750 MeV/$c$. The experiment detected the multiphoton final states with the Crystal Ball spectrometer using a ${K}^{\ensuremath{-}}$ beam from the BNL Alternating Gradient Synchrotron. The results provide significantly greater precision than the existing data, allowing a detailed reexamination of the excited hyperon states in our energy range.

We report the first measurements of the total cross section of the reaction K{sup -}p{yields}{sigma}{sup 0}{gamma} at eight beam momenta from 514 to 750 MeV/c. The data were obtained at the Alternating Gradient Synchrotron (AGS) at Brookhaven National Laboratory using the Crystal Ball detector consisting of 672 NaI crystals. All charged particles were vetoed by a barrel of plastic scintillators, resulting in a study of only the neutral decays of the {sigma}{sup 0}. The prompt photon and the photons from the decay products of {sigma}{sup 0} were detected for each reconstructed event; the neutron was also detected in a small fraction of the events.

Angular distributions of the analyzing powers have been measured for the $^{3}\mathrm{He}$(p\ensuremath{\rightarrow},${\mathrm{\ensuremath{\pi}}}^{+}$${)}^{4}$He reaction at proton bombarding energies of 300, 416, and 507 MeV. These results, together with existing measurements at 178, 198, and 800 MeV, provide a comprehensive set of data spanning the region of the ${\mathrm{\ensuremath{\Delta}}}_{1232}$ resonance. The results are compared with a phenomenological model that incorporates the amplitudes for the pp\ensuremath{\rightarrow}d${\mathrm{\ensuremath{\pi}}}^{+}$ reaction and calculations from a microscopic (p,${\mathrm{\ensuremath{\pi}}}^{+}$) model.

The first spin-transfer observables for the {pi}{bold d}{r arrow}{bold p}{ital p} reaction have been measured at a number of energies spanning the {Delta} resonance in this system. These parameters correspond to {ital K}{sub {ital S}{ital L}} and {ital K}{sub {ital S}{ital S}} of the {ital p}{bold p}{r arrow}{bold d}{pi} reaction for incident proton energies ranging from 600 to 800 MeV. Such data can provide an important constraint on the determination of the partial-wave amplitudes describing this fundamental reaction. The discrepancies between our data, theoretical predictions, and values calculated from published partial-wave amplitudes demonstrate the need for further work in this area.

New results on the rare, doubly radiative decay {eta}{yields}{pi}{sup 0}{gamma}{gamma} have been obtained from a revised analysis of the Crystal Ball experiment performed at the AGS. The analysis yields the first information on the dependence of the decay width, {gamma}({eta}{yields}{pi}{sup 0}{gamma}{gamma}), on the two-photon invariant mass squared, m{sup 2}({gamma}{gamma}). A re-evaluation of the branching ratio is also made, BR({eta}{yields}{pi}{sup 0}{gamma}{gamma})=(2.21{+-}0.24{sub stat}{+-}0.47{sub syst})x10{sup -4}; it implies that the decay width is {gamma}({eta}{yields}{pi}{sup 0}{gamma}{gamma})=0.285{+-}0.031{sub stat}{+-}0.061{sub syst} eV. These results are close to predictions based on chiral perturbation theory with vector-meson dominance.

We present a measurement of the spin-dependent cross sections for the \vec{^3He}(\vec{e},e')X} reaction in the quasielastic and resonance regions at four-momentum transfer 0.1 < Q^2< 0.9 GeV^2. The spin-structure functions have been extracted and used to evaluate the nuclear Burkhardt--Cottingham and extended GDH sum rules for the first time. Impulse approximation and exact three-body Faddeev calculations are also compared to the data in the quasielastic region., Final version

The reaction K{sup -}p{yields}{sigma}{sup 0}{pi}{sup 0}{yields} neutrals was studied with the Crystal Ball detector at the BNL Alternating Gradient Synchrotron for beam momenta between 514 and 750 MeV/c. The photons from {sigma}{sup 0} and {pi}{sup 0} decays were detected, as well as the neutron in a small fraction of the events. The differential cross section and the {sigma}{sup 0} polarization are reported at eight momenta and nearly the full angular range. Total cross sections are derived from Legendre polynomial fits to the data. The measurements presented are of considerably higher precision than previous results.

Double differential and total cross sections of the ({pi}{sup {minus}},{ital pd}), ({pi}{sup {minus}},{ital dp}), and ({pi}{sup {minus}},{ital dd}) reactions on {sup 12}C were measured over a wide angular range at an incident pion kinetic energy of 165 MeV. The shape of the angular distributions of the differential cross sections of these reactions is in most cases similar to that of the {sup 12}C({pi}{sup {minus}},{ital pp}){ital X} reaction. These similarities seem to indicate a pickup mechanism in certain regions of phase space following three-nucleon absorption. Contributions from both three-nucleon absorption and two-step processes are found to be important for the above type of reactions.

We measured angular distributions of differential cross section, beam analyzing power, and recoil polarization for neutral pion electroproduction at Q(2)=1.0 (GeV/c)(2) in 10 bins of 1.17 M-Delta. We performed a multipole analysis that adjusts suitable subsets of center dot(pi) Delta quadrupole ratios are not negligible. Parabolic fits to the W dependence around M-Delta for the multiple analysis gives values for Re(S1+/M1+)=(-6.61 +/- 0.18)% and Re(E1+/M1+)=(-2.87 +/- 0.19)% for the p pi(0) channel at W=1.232 GeV and Q(2)=1.0 (GeV/c)(2) that are distinctly larger than those from the Legendre analysis of the same data. Similarly, the multipole analysis gives Re(S0+/M1+)=(+7.1 +/- 0.8)% at W=1.232 GeV, consistent with recent models, while the traditional Legendre analysis gives the opposite sign because its truncation errors are quite severe.

The ratio of the proton elastic electromagnetic form factors, GEp/GMp, was obtained by measuring Pt and P, the transverse and longitudinal recoil proton polarization components, respectively, for the elastic epepreaction in the four-momentum transfer squared range of 0.5 to 3.5 GeV2. In the single-photon exchange approximation, GEp/GMp is directly proportional to Pt/P. The simultaneous measurement of Pt and P in a polarimeter reduces systematic uncertainties. The results for GEp/GMp show a systematic decrease with increasing Q2, 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. (Less)

We report a virtual Compton scattering study of the proton at low c.m. energies. We have determined the structure functions P(LL)-P(TT)/epsilon and P(LT), and the electric and magnetic generalized polarizabilities (GPs) alpha(E)(Q2) and beta(M)(Q2) at momentum transfer Q(2)=0.92 and 1.76 GeV2. The electric GP shows a strong falloff with Q2, and its global behavior does not follow a simple dipole form. The magnetic GP shows a rise and then a falloff; this can be interpreted as the dominance of a long-distance diamagnetic pion cloud at low Q2, compensated at higher Q2 by a paramagnetic contribution from piN intermediate states.

We report a new measurement of the ${\ensuremath{\pi}}^{\ensuremath{-}}\stackrel{\ensuremath{\rightarrow}}{p}3{\ensuremath{\pi}}^{0}n$ total cross section from threshold to ${p}_{\ensuremath{\pi}}=0.75\mathrm{GeV}/c.$ The cross section near the $N(1535){\frac{1}{2}}^{\ensuremath{-}}$ resonance is only a few $\ensuremath{\mu}\mathrm{b}$ after subtracting the large $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\eta}}3{\ensuremath{\pi}}^{0}$ background associated with ${\ensuremath{\pi}}^{\ensuremath{-}}\stackrel{\ensuremath{\rightarrow}}{p}\ensuremath{\eta}n.$ A simple analysis of our data results in the estimated branching fraction $\mathcal{B}[{S}_{11}\ensuremath{\rightarrow}\ensuremath{\pi}N(1440){\frac{1}{2}}^{+}]=(8\ifmmode\pm\else\textpm\fi{}2)%.$ This is the first such estimate obtained with a three-pion production reaction.

The first results obtained in 1998 by the Crystal Ball collaboration from a measurement of the total and differential cross sections for the reaction pi(-)p --> etan are presented.These new experimental results for the total cross sections are compared with the predictions of the K-matrix model for pion- nucleon scattering.The angular distribution at momenta near the reaction threshold (685 MeV/c) is determined by the S-wave contribution.The P-wave contribution begins to manifest itself from a momentum of 720 MeV/c.

We present measurements of the differential and total cross sections and the {Lambda} polarization for the reaction K{sup -}p{yields}{eta}{Lambda} from threshold to p{sub K}-=770 MeV/c, with much better precision than previous measurements. Our cross-section data show a remarkable similarity to the SU(3) flavor-related {pi}{sup -}p{yields}{eta}n cross-section results. The reaction K{sup -}p{yields}{eta}{Lambda} at threshold is dominated by formation of the intermediate {Lambda}(1670)1/2- state.

The first $(\stackrel{\ensuremath{\rightarrow}}{e}{,e}^{\ensuremath{'}}\stackrel{\ensuremath{\rightarrow}}{p})$ polarization transfer measurements on a nucleus heavier than deuterium have been carried out at Jefferson Laboratory. Transverse and longitudinal components of the polarization of protons ejected in the reaction ${}^{16}\mathrm{O}(\stackrel{\ensuremath{\rightarrow}}{e}{,e}^{\ensuremath{'}}\stackrel{\ensuremath{\rightarrow}}{p})$ were measured in quasielastic perpendicular kinematics at a ${Q}^{2}$ of 0.8 $(\mathrm{GeV}{/c)}^{2}.$ The data are in good agreement with state of the art calculations.

Differential and total cross sections for π+ absorption on 12C are presented at incident pion energies of 100 and 165 MeV. This is the first time that this reaction has been measured with a combination of good energy and angle information over an extensive region of phase space. Results are compared to extensive Monte Carlo simulations in order to investigate the role of two- and multinucleon absorption processes in this nucleus. Signatures of ISI and FSI in the pion absorption process are also investigated, in order to explain the complex reaction mechanism implied by the data. Nuclear Physics A

The angular distributions of the differential cross sections and analyzing powers are presented for the /sup 12/C(p,..pi../sup +/)/sup 13/C( reaction leading to the ground state of /sup 13/C as well as some of the /sup 13/C( low-lying excited states. The analyzing powers for some of the transitions exhibit a considerable energy dependence while for other transitions they remain relatively unchanged, thus indicating a dynamic sensitivity of the analyzing power dependent on nuclear structure. Comparisons of theoretical predictions for A/sub N/0 and dsigma/d..cap omega.., based on microscopic two-nucleon models, with our results indicate that substantial differences between theory and experiment still exist for A(p,..pi../sup +/)A+1 type of reactions.

Four telescopes of three (2-ΔE, 1-E) silicon surface barrier detectors each, mounted in the focal plane of a magnetic spectrometer, have been used to detect positive pions in the energy range from 4.7–17.9 MeV and negatice pions from 14.1–17.9 MeV. Positive pions from 4.7–12.7 MeV were stopped in the third detector while positive and negative pions from 14.1–17.9 MeV were detected in transmission. For energies greater than 7.4 MeV aluminum moderators were placed in front of the first detector to degrade the pion energy. Energy spectra show well resolved pion peaks with extremely low background. Double differential cross sections for the 12C(e, π+)12B, e′ reaction have been measured.

Differential cross sections for the /sup 12/C(p, ) /sup 13/C/sup */ reaction at T/sub p/ = 250, 354, and 489 MeV are presented and compared with previously published data taken at other energies in the /sub 1232/ resonance region. At fixed four momentum transfers greater than 0.4 GeVS/cS, the differential cross sections exhibit a maximum near the invariant mass of the /sub 1232/. This energy dependence is similar to that shown by the pp d reaction at equivalent energy, and provides strong evidence of a NN NN process in the (p, ) reaction mechanism. The total cross section for each transition exhibits a maximum at an energy about 100 MeV lower than that expected from the /sub 1232/ invariant mass. This energy dependence could be the result of an interplay between the increase in cross section due to the role of the /sub 1232/ in the (p, ) reaction mechanism, and the decrease in cross section due to the large momentum transfers that the reaction is restricted to at higher energies.

Angular distributions of the tensor analyzing powers T/sub 20/ and tau/sub 21/ have been measured for ..pi..d elastic scattering, in a single scattering experiment employing a tensor polarized deuteron target. Measurements of T/sub 20/ were obtained for pion bombarding energies of 134, 151, 180, 220, and 256 MeV. Measurements of tau/sub 21/ were obtained for pion bombarding energies of 134, 180, and 220 MeV. The results are compared with three-body calculations where effects relating to pion absorption are seen to play an important role.

The tensor polarization ${t}_{20}$ in ${\ensuremath{\pi}}^{+}d$ elastic scattering has been measured as a function of energy at 15\ifmmode^\circ\else\textdegree\fi{} (laboratory) over the energy range ${T}_{\ensuremath{\pi}}=118 \mathrm{to} 148$ MeV. The angular distributions at 135 and 142 MeV between 15\ifmmode^\circ\else\textdegree\fi{} and 35\ifmmode^\circ\else\textdegree\fi{} were also measured. The ${t}_{20}$ values are negative for all energies and angles investigated and are consistent with the data of Holt et al. and Ungricht et al., resolving the previous discrepancy with the results of Ulbricht et al., Gr\"uebler et al., and Konig et al. As there are no significant rapid variations in ${t}_{20}$, our data do not lend support to the existence of dibaryon resonance effects at these kinematic ranges.

Single arm spectrometer measurements of the differential cross sections and analyzing powers of the pp pn reaction have been performed at 400 and 450 MeV incident proton energy. The measurements covering an angular range from 46 to 90 (lab) spanned pion energies corresponding to production of the np system with relative energies between 0 and 30 MeV, a region where the influence of the np final state interaction is particularly important. The trend of the measured analyzing power is very similar to that of the pp d reaction, and is well explained by calculations that use this latter data as input. Dominance of the triplet pn final state is implied by these results.

Double differential cross sections at six angles ranging from 45° to 143° have been measured for the 12C(e,p)e′ reaction. The proton energy ranged from 15.6 to 17.2 MeV at an incident electron energy of 200 MeV. At the backward angles our results are in good agreement with data reported by Vysotskaya and Afanas'ev but for forward angles the results are lower.

The analyzing power angular distributions A/sub y/(THETA) for the /sup 10/Be/sub g.s./ as well as the /sup 10/Be(/sub 3.37/ state transitions from the /sup 9/Be(p, /sup +/)/sup 10/Be reaction are reported as a function of incident proton energy from 200 to 250 MeV. Instead of the dramatic dependence on energy characterizing the /sup 12/C(p>, ..pi../sup +/)/sup 13/C reaction, the analyzing power for the present reaction shows little variation with energy. At energies above 200 MeV the analyzing power angular distibutions exhibited by the (p>, /sup +/) reactions on /sup 9/Be and /sup 12/C are markedly different, unlike the earlier observations at 200 MeV where the distribution was essentially the same.

Angular correlations of the 12 C(π - , pp)X reaction cross sections were measured over a wide angular range at an incident pion kinetic energy of 165 MeV and the results were compared to published data. A broad peak was observed in the angular distribution of the differential cross section that deviates from the angular distribution expected from a three-body phase space calculation for the two detected protons. The observed angular correlation disagrees with correlations previously reported in the literature.

Angular distributions of the 6 Li (π + , 3 He ) 3 He differential cross section are presented for incident pion beam energies of 60, 80 and 100 MeV, together with a few values at 140 MeV. The results are compared with previously published data and two theoretical predictions. The 60, 80 and 100 MeV data, and previously published results for 15.4 MeV, were fit to Legendre polynomials. The fitted coefficients, which allow the energy dependence of the total and differential cross sections at a fixed c.m. angle to be determined, are also presented. These coefficients show the increasing importance of higher-order partial-waves with increasing pion energy.

Angular distributions for near threshold electroproduction of positive pions from /sup 12/C are reported and compared to theory. These data provide tests of recently developed second-order optical potentials and of the nuclear response to electroproduction in the giant resonance region.

Angular distributions of the ..pi../sup -//..pi../sup +/ ratio for 15.8 and 17.9 MeV pions have been measured from the /sup 12/C(e,e'..pi../sup + -/)X reaction at incident electron energy of 200 MeV. The results show a structure with a minimum at theta/sub ..pi../approx. =100/sup 0/. Calculations based on the partial conservation of axial-vector current hypothesis and realistic optical potentials fail to reproduce the experimental structure.

Angular distributions of the differential cross sections for the pionic fission 6 Li (π + , 3 He ) 3 He have been measured at pion energies of 60 and 80 MeV. The differential cross section is found to decrease monotonically with cos 2 θ ∗ and is compared with a theoretical prediction.

The energy dependence of the (p,..pi../sup -/) and (p,..pi../sup +/) reactions on /sup 13/C leading to isobaric analog states of /sup 14/O and /sup 14/C has been measured at a fixed four-momentum transfer at proton lab energies of 250, 354, and 489 MeV. Unlike the (p,..pi../sup +/) reactions, which show an enhancement of the differential cross section near the invariant mass of the ..delta../sub 1232/ similar to that observed for the pp..-->..d..pi../sup +/ reaction at an equivalent center of mass energy and momentum transfer, the differential cross section of the (p,..pi../sup -/) reactions decrease with increasing energy through this region. This difference is consistent with an interpretation of the (p,..pi../sup -/) reaction mechanism as a NN..-->..NN..pi../sup -/ process in which nonresonant amplitudes are dominant in this region

Analyzing power measurements of the pp..--> pi../sup +/d reaction have been made at proton bombarding energies of 400 and 450 MeV, over the angular range from 76--119/sup 0/ center of mass. The data at 400 MeV confirm older measurements; no previous data at 450 MeV have been reported. A comparison of these data with theoretical predictions of Niskanen reveals generally good agreement, although the data tend to exhibit slightly greater asymmetry about 90/sup 0/ than predicted by theory.