Search

Inelastic {rho}{sup 0} photoproduction in the reaction {gamma}{ital p}{r_arrow}{rho}{sup 0}{pi}{sup +}{ital n} is observed in the peripheral region {vert_bar}{ital t}{sub {gamma},{rho}}{sup 0{prime}}{vert_bar}{lt}0.12 GeV{sup 2}. The data are consistent with the {rho}{sup 0} production being due to a double peripheral mechanism which conserves {ital s}-channel helicity. The {pi}{sup +}{ital n} produced in association with the {rho}{sup 0} is also consistent with the same mechanism, although there is a distortion of the expected angular distributions in the {pi}{sup +}{ital n} mass region of 1.3--1.5 GeV/{ital c}{sup 2}.

We examine the negative 3{pi} final state produced in association with {Delta}{sup ++}(1232) in the reaction {gamma}{ital p}{r arrow}{Delta}{sup ++}{pi}{sup +}{pi}{sup {minus}}{pi}{sup {minus}} at an incident photon energy of 19.3 GeV. The most prominent enhancement in the 3{pi} spectrum occurs at a mass and with a width consistent with the parameters of the {ital a}{sub 2}(1320). This identification is confirmed by the various angular distributions. The {ital a}{sub 2} production cross section, corrected for efficiencies and alternate {ital a}{sub 2} decay modes, is 0.45{plus minus}0.05 {mu}b.

We have used the Fermilab 30-in. bubble chamber--hybrid spectrometer to study the rapidities of produced particles'' in the interactions of 200-GeV/{ital c} protons and {pi}{sup +} and {ital K}{sup +} mesons with nuclei of gold, silver, and magnesium. The average rapidity decreases linearly with the number of projectile collisions {nu}{sub {ital p}} (up to {nu}{sub {ital p}}=5) with no {ital A} dependence and little beam dependence. The ratio {ital R} of normalized rapidity distributions for hadron-nucleus to hadron-proton interactions shows a plateau in the central region, and becomes much larger in the target region. However, the increase is significantly less than has been reported in previous experiments. As a function of {nu}{sub {ital p}}, the ratio {ital R} rises linearly in the target region, more gently in the central region, and decreases slowly in the projectile region, in all cases with no {ital A} dependence. Some discrepancies with a previous experiment are observed in the central region. Long-range rapidity correlations are observed in hadron-nucleus events, but not in hadron-proton events. For the former, it is shown that the correlations exist only for those events with multiple projectile collisions, as expected in the multichain dual parton model.

It is shown that the energy dependence of charge-exchange [ital a][sub 2][sup +] photoproduction ([gamma][ital p][r arrow][ital na][sub 2][sup +]) agrees with a one-pion exchange mechanism. No evidence for the photoproduction of the [ital a][sub 1][sup +](1260) is observed. If the dynamics of [ital a][sub 1] and [ital a][sub 2] photoproduction are assumed to be the same, the absence of evidence for the [ital a][sub 1] is shown to be consistent with either an extremely large [ital a][sub 1] hadronic width or with an [ital a][sub 1] of mass somewhat less than 1260 MeV.

We have studied the reactionspp→ppπ+π-,K+p→K+pπ+π−π, π+p→ π+,pπ+π− and π−p →π+π− at 147 GeV/c using the 30-inch Fermilab hybrid system. All four reactions were detected with the same apparatus and analyzed in the same way. The energy dependence of the channel cross section was found to beAp−0.6+B for thepp reaction andAp−1+B for the other three. About 90% of the cross section at 147 GeV/c can be accounted for by either beam or target diffraction. Some of the remaining cross section may come from double Pomeron exchange reactions which we tried to isolate. We have tested the hypothesis of a factorizable Pomeron and our data indicates a violation of this hypothesis. We show that the 3π mass enhancement in the mass region 1.2–1.4 GeV is diffractively produced in the π± beam reactions. Fourprong, four-constraint and six-prong, four-constraint cross sections are reported.

We have studied the inclusive production of K/sup asteriskplus-or-minus/(890) and Y/sup asteriskplus-or-minus/(1385) in pp, ..pi../sup +/p, and K/sup +/p interactions at 147 GeV/c. The experiment used the Fermilab 30-inch hydrogen bubble chamber with the hybrid spectrometer system. Results are based on a sample of 1916 observed K/sub S/ and 932 observed ..lambda... Inclusive cross sections are given for K/sup asteriskplus-or-minus/ and Y/sup asteriskplus-or-minus/ production from the three beams, and comparisons are made with experiments at other energies. Feynman-x and transverse-momentum-squared distributions are also calculated. The results suggest that the K/sup asterisk-/ is entirely produced in the central region, while the K/sup asterisk+/ includes a component from beam fragmentation. Comparisons are made with the additive quark model.

The reaction ..gamma..p..-->..rho/sub fast//sup 0/p..pi../sup +/..pi../sup -/ has been studied with the linearly polarized 20-GeV monochromatic photon beam at the SLAC Hybrid Facility to test the prediction of s-channel helicity conservation in inelastic diffraction for t' ..p..pi../sup +/..pi../sup -/, and the p..pi../sup +/..pi../sup -/ mass distribution compares well and scales according to the vector dominance model with that produced in ..pi../sup + -/p..--> pi../sub fast//sup + -/p..pi../sup +/..pi../sup -/.

The gross features of the data are reviewed and the momentum tensor components, 〈S〉, and 〈T〉 are studied. Evidence for coplanarity effects is observed. A probabilistic method to search for jets is proposed. The jets found by this method are seen to be similar to highp T jets frompp interactionse + e − annihilations andvp interactions. The effect of subtracting the leading particles and the effect of lowp T diffractive and non diffractive components are investigated.

The Fermilab hybrid 30-in. bubble-chamber spectrometer was exposed to a tagged 147-GeV/c positive beam containing ..pi../sup +/, K/sup +/, and p. A sample of 3003 K/sup +/p, 19 410 pp, and 20 745 ..pi../sup +/p interactions is used to derive sigma/sub n/, , f/sub 2//sup tsc/c, and /D for each beam particle. These values are compared to values obtained at other, mostly lower, beam momenta. The overall dependence of on E/sub a/, the available center-of-mass energy, for these three reactions as well as ..pi../sup -/p and pp interactions has been determined.

The photoproduction of ${\ensuremath{\rho}}^{0}$ and ${\ensuremath{\rho}}^{\ensuremath{-}}$ mesons has been studied at 3 GeV in the reactions $\ensuremath{\gamma}d\ensuremath{\rightarrow}d{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\pi}}^{\ensuremath{-}}$, $\ensuremath{\gamma}d\ensuremath{\rightarrow}{p}_{s}n{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$, and $\ensuremath{\gamma}d\ensuremath{\rightarrow}{p}_{s}p{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$. For ${\ensuremath{\rho}}^{0}$ and ${\ensuremath{\rho}}^{\ensuremath{-}}$ production in these reactions we present the total and differential cross sections, the decay angular distributions, and the spin density matrix elements. The photoproduction of the ${\ensuremath{\rho}}^{0}$ is found to be consistent with $s$-channel helicity conservation and is dominated by natural-parity exchange. The ${\ensuremath{\rho}}^{\ensuremath{-}}$ meson production has approximately equal natural- and unnatural-parity-exchange contributions. The unnatural-parity-exchange contribution is consistent with one-pion exchange and is used to estimate the value of ${\ensuremath{\Gamma}}_{\ensuremath{\rho}\ensuremath{\pi}\ensuremath{\gamma}}$.

In an experiment with the 30-inch Hybrid Spectrometer at Fermilab we have obtained the inclusive and semi-inclusive production cross sections of the ϱ0 meson using a conventional background subtraction technique. Production cross sections for the ϱ0 are derived as a function of the Feynman scaling variablex, and the transverse variablespt2 andEt=(pt2+M2)1/2. The longitudinal distributions are compared with the (1−x) dependence of the proton and meson valence quark structure functions, using various forms of recombination and fragmentation models. The transverse distributions are compared with thermodynamic models. We give density matrix elements for the ϱ0 production from pions in the extreme forward region.

The ratio of hadronic π+/π− production has been studied in the target fragmentation region of π+ p, π− p,K + p andp p collisions at 147 GeV/c beam momentum. The difference between this ratio in the π+ p and π− p data is less than at lower energies but still present. No difference exists anymore for the π+/π− ratio at this energy betweenK + p andpp collisions. Exclusion of diffraction dissociation and resonance production does not change the main conclusions. The energy dependence of the ratio for π+ p and π− p collisions gives evidence for a universal asymptotic ratio for all beams. Thep t -dependence at low-p t is in agreement with the expectation from geometrical correlation of the valence quarks.

The production of ..pi../sup +/..pi../sup -/..pi../sup 0/ events allows the study of pure I=1 exchange without the complicating presence of the ..delta.. (1236) which appears with proton targets. A total of 4218 events, corresponding to 8.5 events/..mu..b, were analyzed from an exposure of the SLAC 82-inch deuterium bubble chamber. The low-mass resonances (eta, ..omega.., A/sub 2/, and ..omega.. (1675)) are clearly observed. In addition, enhancements due to possible higher-mass resonances are observed by using the technique of p/sub perpendicular/ cuts.

Eleven neutral and nine charged decays of charmed particles have been observed in a sample of 205 000 hadronic interactions in a 1.2-million-picture exposure of the SLAC Hybrid Facility bubble chamber to a 20-GeV/c backward-scattered laser beam. The charged and neutral lifetimes were determined to be ${8.2}_{\ensuremath{-}2.5}^{+4.5}$\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ and ${6.7}_{\ensuremath{-}2.0}^{+3.5}$\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ sec, respectively, with a ratio of ${1.2}_{\ensuremath{-}0.5}^{0.9}$.

A large lead glass shower detector containing 204 lead glass blocks and 250 finger hodoscope elements has been constructed and operated in a photoproduction experiment at the SLAC Hybrid facility. An energy resolution of σ E /E = (0.84+4.8/E 1 2 )% has been achieved for electron energies between 4 and 16 GeV. Details of the apparatus, its stability monitoring system, and its use in triggering the bubble chamber are presented. The performance of the detector in electron identification and π0 reconstruction is discussed.

Results are reported based on a study of π − p interactions at 147 GeV/ c in the FERMILAB 30-inch Proportional Wire Hybrid Bubble Chamber System. We have measured the topological cross sections and separated two-prong elastic and inelastic channels. In addition, we have extracted leading particle cross sections using the increased momentum resolution of the downstream proportional wire chambers. We have compared our results with experiments and predictions of a simple fragmentation hyphothesis.

We present data on inclusive and semi-inclusive ϱ 0 production in 147 GeV/ c π − p interactions. We find a total cross section of 7.3 ± 1.3 mb. Most of this cross section is found in the lower topology events (⩽ 10 prongs), and in the central and forward rapidity regions. The P T 2 dependence of ϱ 0 production, 〈: n > ϱ 0 per event, and the ϱ 0 / π + ratios are also discussed.

Results are presented from a study of inclusive neutral strange particle production by a 147 GeV/c tagged π+/K+/p beam in the Fermilab 30-inch hydrogen bubble chamber. The experiment made use of the proportional hybrid spectrometer system. Results are based on 995 KS0, 485 Λ, and 83 Λ found in a sample of 132 000 pictures. Cross sections are given for inclusive production of these particles by each of the three beam particles, and comparisons are made with measurements at other energies. Topological cross sections are also calculated, and KNO multiplicity scaling is investigated. Distributions are presented of invariant cross sections as functions of the Feynman scaling variable x and c.m. rapidity y. The transverse momentum-squared distributions with their fitted slopes are also given. Comparisons are made of the production characteristics for the three beam types.

The energy dependence of the average of the charged multiplicity and its dispersion in π + /K + /p interaction on protons at 147 GeV/ c is found to be the same as in e + e − annihilations if an “effective energy” variable is used instead of the total energy. The effective energy S eff is defined as the invariant mass of all secondaries left after the two leading particles have been removed. Fitting the expression aS eff b to the average charge multiplicity 〈 n ch 〉, we find the power b to be in good agreement with the value of 0.25 predicted by Fermi's statistical model and by Landau's hydrodynamical model.

An analysis is presented of the production of jets in low-ptπ±p,k+p,pp collisions at 147 GeV/c collected at Fermilab in the rapid cycling hydrogen bubble chamber hybrid spectrometer. It is shown that selected events are more planar than predicted by a cylindrical phase space, but that 3-jet and 4-jet like structures seen in the momentum flows are reasonably reproduced by the cylindrical phase space events subjected to the same mathematical manipulation required to build momentum flows.

A study of charged particle production in 147 GeV/c π − p collisions yields no evidence for an electrically neutral central region or corresponding rapidity plateau. The results do indicate that electric charge and transverse momentum may be locally conserved over small intervals on the rapidity axis. These results support a picture in which the observed hadrons are emitted in clusters whose quantum numbers vary as a function of rapidity and reflect the incident channel quantum numbers at the extremes of the rapidity scale.

The low-mass ..omega pi../sup 0/ enhancement in ..gamma..p..-->..p..omega pi../sup 0/ has been of considerable interest in the past due to its suggested vector nature and possible role in the spectroscopy of the rho-meson radial recurrences. We have measured the properties of this photoproduced ..omega pi../sup 0/ system using the SLAC Hybrid Facility. The experimental data consists of 306 785 usable hadronic events for which excellent ..gamma..-ray detection is provided by the large lead-glass array located behind the bubble-chamber. The photon beam had a 52% polarization. We have examined in detail the angular distributions of the 274 events from the reaction ..gamma..p..-->..p..omega pi../sup 0/. The angular distribution of the production plane relative to the polarization vector shows a structure inconsistent with an s-channel helicity-conserving process. We have extracted the moments of the decay angular distribution. Our data favors a B(1235) interpretation of the ..omega pi../sup 0/ state over a vector-meson interpretation.

In this paper we present new data for the reactions π−p→pslow+X− and π−p→πfast− + X+ at 147 GeV/c. This is the first time that experimental information on these two processes has been obtained using the same apparatus at Fermilab energies. The triple-Regge formalism is applied to the differential cross sections dσ/dMx2 of both reactions using all the data at present available in the literature. A good description of the data is obtained when parameters from a triple-Regge fit of the reaction pp → p + X are used, together with the assumption of factorization of the pomeron and the reggeons. The equality of the dσ/dMx2 distributions of the two reactions may be explained in terms of an interesting assumption in the framework of the independent quark model and imposes an additional relation between the triple-Regge terms.

We report the results of a study of \ensuremath{\rho} and \ensuremath{\omega} production in ${\ensuremath{\pi}}^{+}$p interactions at 15.7 GeV/c. The SLAC hybrid bubble-chamber facility was used to study reactions in which neutral particles are produced. Three tantalum plates inside the 40-in. bubble chamber and a large array of lead glass downstream of the chamber provided photon detection over a large solid angle. Final states with two neutral particles have been isolated with kinematic fits in which neutral pions were reconstructed in the plates and lead glass. Data from an earlier untriggered ${\ensuremath{\pi}}^{+}$p bubble-chamber experiment at 15 GeV/c were used to obtain samples of events in channels which did not trigger the hybrid system. Cross sections for \ensuremath{\rho} and \ensuremath{\omega} production are given for several exclusive final states. Relative \ensuremath{\rho} and \ensuremath{\omega} production rates are studied. The ratio of nondiffractive \ensuremath{\omega} to ${\ensuremath{\rho}}^{0}$ production is measured to be \ensuremath{\omega}/${\ensuremath{\rho}}^{0}$=0.44\ifmmode\pm\else\textpm\fi{}0.07. We estimate the inclusive \ensuremath{\omega} cross section to be 1.9\ifmmode\pm\else\textpm\fi{}0.3 mb. The results are compared to the Lund model of low-${p}_{T}$ hadronic reactions.

We have studied inclusive production of ${K}_{S}^{0}$, $\ensuremath{\Lambda}$, and $\overline{\ensuremath{\Lambda}}$ particles in 20-GeV $\ensuremath{\gamma}p$ interactions and have found features similar to those observed in both hadronic and leptonic interactions. The production cross sections, charged-particle multiplicities, and average $\ensuremath{\Lambda}$ polarization are reported. Inclusive distributions of $x$ and ${p}_{T}$ are shown and discussed in terms of quark fragmentation models. Production cross sections for ${K}^{*}(890)$ and ${\ensuremath{\Sigma}}^{*}(1385)$ are also reported.

It is observed that, if multinucleon absorption of slow antiprotons occurs with reasonable frequency in complex nuclei, the occurrence of annihilations with two A0 in the final state may occur as often as ∼ 10-5 per p annihilation.

Sixty-two charm events have been observed in an exposure of the SLAC Hybrid Facility to a backward scattered laser beam. Based on 22 neutral and 21 charged decays we have measured the charmed-meson lifetimes to be tau/sub D//sup 0/ = (6.8/sub -1.8//sup +2.3/)= x 10/sup -13/ sec, tau/sub D//sup + -/ = (7.4/sub -2.0//sup +2.3/) x 10/sup -13/ sec and their ratio tau/sub D//sup + -//tau0 = 1.1/sub -0.3/ /sup +0.6/. The inclusive charm cross section at a photon energy of 20 GeV has been measured to be 56/sub -/23/sup +24/ nb. Evidence is presented for a non-DD-bar component to charm production, consistent with (35 +- 20)% ..lambda../sub c//sup +/ production and some D/sup asteriskplus-or-minus/ production. We have found no unambiguous F decays.

Seventy-one events containing charmed-particle decays have been observed in an experiment using the SLAC Hybrid Facility exposed to a backward-scattered photon beam. Several improvements were made to the apparatus since the previous experiment on charm photoproduction. Results for the charmed-meson lifetimes are consistent with the published results from the previous experiment and the two data samples have been combined yielding a total sample of 136 charm events. After imposing rigorous cuts, 50 neutral, 48 charged, and 2 charged/neutral ambiguous decays remain. From these, the charmed-meson lifetimes are measured to be tau/sub D/ = (8.6 +- 1.3/sub -0.3/ /sup .7/) x 10 T sec, tau/sub D/ = (6.1 +- 0.9 +- 0.3) x 10 T sec, and their ratio tau/sub D/ /tau0 = 1.4 +- 0.3/sub -/ /sub 0.1//sup +0.2/. The total charm cross section at a photon energy of 20 GeV has been measured to be (62 +- 8/sub -/10 V) nb. There is evidence for both DD-barX and D-bar /sub c/ X production with sigma/sub D/ /sub c/ X/sigma/sub charm/ = (71 +- 11 +- 6)%.

High energy neutrino interactions in a heavy liquid bubble chamber were classified by the presence or absence of dark tracks (stubs) at the interaction vertices. Quark distributions, σ ( x ), were compared in the two groups of data. Those with dark tracks, presumably indicative of an interaction with a deeply bound nucleon, show an enhanced nuclear effect.

Diffraction dissociation of both the beam and target particles has been observed in 150-GeV/c ..pi../sup -/p interactions in the Fermilab 30-in.-bubble-chamber--proportional-wire-chamber hybrid spectrometer. The dissociations are observed as recoil systems opposite leading particles, the signals of which are separated from background where appropriate by a variant of the Van Hove sector cut, thus allowing the high-mass portion of the spectrum to be observed. Pion dissociation has a cross section of 1758 +- 105 ..mu..b, divided among two-, four-, and six-prong events; some rho/sup 0/ production is seen and comes primarily from the ..pi../sup -/ ..-->.. 2..pi../sup -/..pi../sup +/ channel. The proton dissociation cross section is 1726 +- 100 ..mu..b, again divided among two-, four-, and six-prong events. The final state contains a neutron more frequently than a proton in the two- and six-prong events, a proton more frequently in the four-prong events. Production of ..delta../sup + +/ is observed in the p ..-->.. p..pi../sup +/..pi../sup -/ dissociations.

From a study of 8-GeV/c ..pi../sup -/p interactions, the various two-pion and four-pion decay channels available to the g/sup -/ meson have been investigated. Our results indicate that the dominant 4..pi.. decay modes involve intermediate rho and ..omega.. production without significant A/sub 2/ formation.

The experimentally determined average charged-particle multiplicities, , of the systems, X, produced in the following reactions for 147 GeV/c incident pion momentum are presented as functions of the square of the invariant mass of X, M/sub x//sup 2/, and of *t*: ..pi../sup -/p ..-->.. ..pi../sup -//sub fast/X, ..pi../sup -/p ..-->.. pX, ..pi../sup -/p ..-->.. ..delta../sup + +/X, ..pi../sup -/p ..-->.. (..pi../sup -/..pi../sup +/)/sub rho//sup 0/X, and ..pi../sup -/p ..-->.. ..lambda../sup 0/X. Details of the analysis are discussed. These data can be fit by the expression = A + BlnM/sub X//sup 2/ + C*t* and the coefficients obtained for B are equal within their uncertainties. C is significantly different from zero only for ..pi../sup -/p ..-->.. ..pi../sup -//sub fast/X.

Results from a high-statistics experiment involving an exposure of the SLAC 82-in. hydrogen bubble chamber to a beam of 8-GeV/c ..pi../sup -/ yielding a final state of ..pi../sup -/..pi../sup +/..pi../sup -/p are presented. Copious production of rho, ..delta../sup + +/, and f is found. Considerable quasi-two-body production in which one particle decays to one of the above resonances is also observed. Some double-resonance production involving baryon and meson resonances is also seen. The production properties of rho, ..delta../sup + +/, and f mesons are well described by a double-Regge model.

From a study of 15-GeV/c ${\ensuremath{\pi}}^{+}$-deuterium interactions obtained in an 890 000-picture exposure in the SLAC 82-inch bubble chamber, evidence is presented for at least two broad dipion states beyond the $g(1680)$ region. These states appear in the spectrum representing highly peripheral interactions, and in the spectra obtained by eliminating those interactions for which the transverse momentum of each pion is less than a specified minimum value. Further, examination of the ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\mathrm{MM}$ (missing mass) spectrum from the reaction ${\ensuremath{\pi}}^{+}n\ensuremath{\rightarrow}p{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}(\mathrm{MM})$ indicates that agreement with the previously obtained branching ratios is possible only if higher-mass dipion states are present. Evidence is also presented which suggests a finite decay probability of the $g$ (or a state of similar mass) into ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\eta}$ and/or ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\eta}}^{\ensuremath{'}}$.

We report on the interactions of an incident 200 GeV / c beam composed of 33% protons, 16% kaons, and 48% pions on targets of silver and gold mounted in the Fermilab 30″ bubble chamber. Within our limited statistics, we find the total cross sections and average multiplicities to agree with previously published data. We find the KNO scaling distribution curve to be broader for heavy nuclei than for hydrogen. We present the first data for V0 production on gold and silver. We also present, for the first time, evidence for a positive charge excess among the sample of relativistic tracks from interactions on gold and silver. We observe a trend where the positive charge excess increases with target atomic number and with increasing charged particle multiplicity. We find the charge excess to exist among the sample of particles having greater than 2 GeV / c momentum and to persist in the sample with momentum greater than 4 GeV / c.

The SLAC 40-inch bubble chamber augmented by an array of lead-glass detectors was used to study the reaction ..pi../sup +/p..--> delta../sup + +/..pi../sup 0/..pi../sup 0/ at 15.7 GeV/c. No new high-mass neutral mesons are seen at a sensitivity of 14.2 events/..mu..b. A moments and amplitude analysis indicates that only S and D waves contribute to the ..pi../sup +/..pi../sup -/..--> pi../sup 0/..pi../sup 0/ cross section. A one-pion-exchange-model calculation is performed using phase-shift measurements from other experiments. The older phase shifts from Estabrooks and Martin are in better agreement with our data than are the more recent ones of Biswas et al.

The inclusive production of the ${\ensuremath{\Delta}}^{++}(1232)$ resonance in ${\ensuremath{\pi}}^{\ensuremath{-}}p$ collisions at 147 GeV/c has been studied. The ${\ensuremath{\Delta}}^{++}$ is found to be produced in comparable amounts in four-, six-, eight-, and ten-prong events. The Feynman-$x$, ${t}^{\ensuremath{'}}$, ${{P}_{T}}^{2}$, and the decay angular distributions of the ${\ensuremath{\Delta}}^{++}$ are found to be consistent with the predictions of a one-pion-exchange model with absorption. Essentially all of the ${\ensuremath{\Delta}}^{++}$ are found to be associated with a ${\ensuremath{\Delta}}^{++}$${\ensuremath{\pi}}^{\ensuremath{-}}$ low-mass enhancement. The ${\ensuremath{\Delta}}^{++}$ cross section is approximately constant from 11 to 205 GeV/c, which could indicate that the ${\ensuremath{\Delta}}^{++}$ is a decay product of a target-fragmentation object. While the one-pion-exchange character of the ${\ensuremath{\Delta}}^{++}$ production and the target-fragmentation character of the ${\ensuremath{\Delta}}^{++}{\ensuremath{\pi}}^{\ensuremath{-}}$ low-mass enhancement can both be described in terms of a Deck-type diagram, a Monte Carlo study indicates that any mechanism that produces particles with limited transverse momentum will yield a ${\ensuremath{\Delta}}^{++}{\ensuremath{\pi}}^{\ensuremath{-}}$ low-mass enhancement.

The yield and energy distribution of electrons emitted from absorptions of stopping ${K}^{\ensuremath{-}}$ mesons in nuclear emulsions have been measured. In the electron energy range from 20-70 keV, the yield in the heavy elements Ag and Br has been analyzed to consist of 14% background electrons contributed by radioactivity, and 24% contributed by the radiationless Auger process in the $K$-mesonic atom. This Auger yield is considerably less than would be expected theoretically from existing conventional analyses of the ${K}^{\ensuremath{-}}$-mesonic atom cascade in Ag and Br. A possible explanation of the discrepancy is given in terms of a description involving Stark mixing in highly excited mesonic states. This gives rise to nuclear capture from the $f$ and $d$ angular momentum substates of highly excited levels. The probable effect of such a capture mechanism on the rate of multinucleon captures in nuclei is briefly discussed. Further experimental results are given on electron emission from $\ensuremath{\pi}$-mesonic atoms, and other data on $\ensuremath{\mu}$-mesonic and $\ensuremath{\Sigma}$-hyperonic atoms are also reviewed.

Nuclear scattering of K- mesons of an average energy of 21 MeV has been measured inG5 nuclear emulsion. An optical model calculation of the differential and total reaction cross-sections has been performed. Comparison of experiment and theory supports the conclusion reached at higher K- meson energies that the nuclear optical potential is attractive.

From a study of stopping K− meson interactions in a variety of elements located in a hydrogen bubble chamber, we find evidence for the existence of a substantial neutron halo in the periphery of heavy nuclei.

A diffractively produced $3\ensuremath{\pi}$ enhancement is observed with mass \ensuremath{\sim}1.1 GeV and width \ensuremath{\sim}0.35 GeV. There is no structure observed in the peak in either the mass or angular distributions. The system is predominantly $s$-wave $\ensuremath{\pi}\ensuremath{\rho}$ with a $3\ensuremath{\pi}$ ${0}^{\ensuremath{-}}$ admixture which is essentially constant in percentage and relative phase across the peak.

Examination of the available experimental evidence on mesic atoms suggests that the nuclear capture of K− mesons may well be less peripheral than is commonly supposed. This conclusion tends to vitiate recent results, obtained in a study of K− meson nuclear absorptions, that indicate a neutron halo on the surface of heavy nuclei.

A study of internally converted electron-positron pairs associated with K− neon absorption at rest reveals that 0.67 ± 0.15 γ-rays are emitted per nuclear absorption, indicating a large probability for residual nuclear excitation following K− absorption.

From the interaction of 3.29 GeV/cπ+ mesons with deuterium the production and decay of the f0 meson has been studied. The production is highly collimated in the forward direction. Under the assumption that the f0 is a spin 2 meson, measurement of the decay angular distributions yield values for the f0 spin density matrix elements. Only qualitative agreement with the one-pion exchange model is observed, the implication being that absorptive corrections and interference effects are required.

From a study of stopping antiprotons in a variety of elements located in a hydrogen bubble chamber, we find evidence for the existence of a neutron fringe in heavy nuclei.