We report evidence for the Cabibbo-suppressed decay of the charm baryon Λ c + into the final state pK − K + . The analysis is performed on data collected by high energy photoproduction experiment E687 during the 1990–1991 Fermilab fixed target run. The branching ratio of the decay Λ c + → pK − K + relative to the non-suppressed Λ c + → pK − π + is measured to be BR( pK − K + / pK − π + ) = 0.096 ± 0.029 ± 0.010. The upper limit of the decay into pø relative to the inclusive pK − K + decay is measured to be BR( pø / pK − K + < 58% at the 90% confidence level.

Charged hadronic four-body decays of D 0 mesons have been studied in the E687 photoproduction experiment at Fermilab. Branching ratios relative to the D 0 → K − π + π + π − decay mode for the Cabibbo-suppressed decays D 0 → π − π + π − π + , D 0 → K − K + π − π + have been measured and the first evidence of the D 0 → K − K + K − π + decay mode is reported. An analysis of the D 0 → K − K + π − π + resonance structure is also presented.

Results for the Cabibbo suppressed semileptonic decays D 0 → π − e + ν and D 0 → π − μ + ν (charge conjugates are implied) are reported by Fermilab photoproduction experiment E687. We find 45.4 ± 13.3 events in the electron mode and 45.6 ± 11.8 in the muon mode. The relative branching ratio BR (D 0 →π − l + v) BR (D 0 →K − l + v) for the combined sample is measured to be 0.101 ± 0.020 (stat.) ± 0.003 (syst.) 14 .

We report measurements of charm particle production asymmetries from the Fermilab photoproduction experiment E687. An asymmetry in the rate of production of charm versus anticharm particles is expected to arise primarily from fragmentation effects. We observe statistically significant asymmetries in the photoproduction of D + , D ∗+ and D 0 mesons and find small (but statistically weak) asymmetries in the production of the D s + meson and the Λ c + baryon. Our inclusive photoproduction asymmetries are compared to predictions from nonperturbative models of charm quark fragmentation.

We report on the study of charm baryons decaying to Λ c + : Λ c ★+ (2625) → Λ c + π + π − , Λ c ★+ (2593) → Λ c + π + π − , Σ c 0 → Λ c + π − and Σ c ++ → Λ c + π + . We present a confirmation of the state Λ c ∗+ (2593) and determine its mass difference to be M ( Λ c ★+ (2593)) − M ( Λ c + ) = 309.2 ± 0.7 ± 0.3 MeV/ c 2 . We determine the lower limit on the resonant branching ratio to be BR (Λ c ★+ (2593) → Σ c π ± Λ c ★+ (2593) → Λ c + π + π − ) > 0.51 (90% c.l.). We also measure the mass differences M ( Σ c 0 ) − M ( Λ c + ) = 166.6±0.5±0.6 MeV/ c 2 and M ( Σ c ++ ) − M ( Λ c + ) = 167.6±0.6±0.6 MeV/ c 2 . Finally, we measure the relative photoproduction cross sections for Λ c ★+ and Σ c with respect to the (inclusive) photoproduction cross section for Λ c + .

Inclusive cross sections for π 0 , K s 0 , Λ 0 and Λ 0 production in 100, 200 and 360 GeV /c π − p interactions are presented and compared with data at other energies. Invariant cross sections for γ, K s 0 , Λ 0 and Λ 0 production are presented in terms of Feynman x , the rapidity y , and transverse momentum squared, p T 2 . A comparison of the observed γ spectrum is made with the spectra computed assuming that the π 0 momentum distribution is identical to that of the observed π + or π − .

The yields and average transverse momenta of pions, kaons, and antiprotons produced at the Fermilab p¯p collider at s=300, 540, 1000, and 1800 GeV are presented and compared with data from the energies reached at the CERN collider. We also present data on the dependence of average transverse momentum 〈pt〉 and particle ratios as a function of charged particle density dNcdη; data for particle densities as high as six times the average value, corresponding to a Bjorken energy density 6 GeV/fm3, are reported. These data are relevant to the search for quark-gluon phase of QCD.

The hadronic production of charmed states was studied in a two-arm spectrometer using a 205-GeV/c negative-pion beam incident upon a beryllium target. One arm, filled with dense absorber, triggered the detectors upon the passage of a muon with a moderate transverse momentum and a total momentum of at least 4 GeV/c. The other arm was an open-geometry magnetic spectrometer which had both neutral- and charged-particle identification capabilities. The apparatus, the data, and an invariant-mass-plot search for evidence of charmed-meson production through several charged-particle decay modes are described. The Kπ, Kππ, and Kπππ mass plots fail to reveal significant D-meson signals. Based upon the Kπ mass plots, the 95%-confidence upper limit on the DD¯ production cross section is found to be less than 51 μb per nucleon for the production models tested. A search for evidence of charged-D* production yields 30±16 combinations above background in association with the expected trigger muon charge. Interpreted as a D* signal, this excess corresponds to a model-dependent inclusive DD¯ production cross section of 34±18−9+14 μb per nucleon. Model-dependent upper limits on the ratio of the F to D cross sections are also presented.

Experiment E735 searched for evidence of the transition to quark-gluon plasma in p p collisions at √ s = 1.8 TeV. Using data from a high statistics run in 1988–1989, results are presented on multiplicity distributions, hyperon and phi production, and Bose-Einstein correlations. Some data were also taken at lower collision energies and results will be compared to previous experiments.

The transverse-momentum spectra of lambdas (Λ0, Λ¯0) produced in the central region has been measured in p¯p collisions at s=1.8 TeV at the Fermilab Collider. We find that the average transverse momentum of the lambdas increases more rapidly with center-of-mass energy than that of charged particles, and the ratio of lambdas to charged particles increases as a function of center-of-mass energy.

The production ofK0, Λ and\(\bar \Lambda \) particles is studied in the E665 muon-nucleon experiment at Fermilab. The average multiplicities and squared transverse momenta are measured as a function ofxF andW2. Most features of the data can be well described by the Lund model. Within this model, the data on the K0/π± ratios and on the averageK0 multiplicity in the forward region favor a strangeness suppression factors/u in the fragmentation process near 0.20. Clear evidence for QCD effects is seen in the average squared transverse momentum ofK0 and Λ particles.

We have measured cross sections for forward neutron production from a variety of targets using proton beams from the Fermilab Main Injector. Measurements were performed for proton beam momenta of 58 GeV/c, 84 GeV/c, and 120 GeV/c. The cross section dependence on the atomic weight (A) of the targets was found to vary as $A^(alpha)$ where $\alpha$ is $0.46\pm0.06$ for a beam momentum of 58 GeV/c and 0.54$\pm$0.05 for 120 GeV/c. The cross sections show reasonable agreement with FLUKA and DPMJET Monte Carlos. Comparisons have also been made with the LAQGSM Monte Carlo.

Using data from Fermilab fixed-target experiment E769, we have measured particle-antiparticle production asymmetries for Lambda0 hyperons in 250 GeV/c pi+-, K+- and p -- nucleon interactions. The asymmetries are measured as functions of Feynman-x (x_F) and p_t^2 over the ranges -0.12<=x_F<=0.12 and 0<=p_t^2<=3 (GeV/c)^2 (for positive beam) and -0.12<=x_F<=0.4 and 0<=p_t^2<=10 (GeV/c)^2 (for negative beam). We find substantial asymmetries, even at x_F around zero. We also observe leading-particle-type asymmetries. These latter effects are qualitatively as expected from valence-quark content of the target and variety of projectiles studied.

The reaction π−N→KS0KS0π−N′ at 200 GeV/c has been observed with a sensitivity of 450±150 events/μb. The KS0KS0π− system exhibits substantial K*−(890)K0 production. Also produced are f0(1270)π−, f′(1515)π−, and K*−(1430)K0 final states. These resonances occur predominantly at threshold. The diffractive KS0KS0π− cross section is 3.4±1.1 μb. An enhancement near the A3−(1680) is observed in the KS0KS0π− invariant-mass distribution.

The diffractive dissociation of a 200-GeV/c π− beam into KS0KS0π+π−π− has been observed. The diffractive KS0KS0π+π−π− cross section is 1.59±0.78 μb. The ratio of the diffractive KS0KS0π+π−π− cross section to the diffractive KS0KS0π− cross section is 0.40±0.13, which is in good agreement with a diffractive-fragmentation-model prediction of 0.36. There is evidence for simultaneous production of K*− and K*+ in the diffractive KS0KS0π+π−π− sample. The K*+−KS0π−+ mass distribution shows an enhancement near 1.95 GeV.

For the reaction π−N→V0X, where V0 is a Ks0, Λ, and Λ¯ and X are charged particles, we measured the transverse- and longitudinal-momentum distributions, and inclusive cross sections for the V0 and for K*±(892), Σ±(1385), and Ξ±(1321). We compare our results with predictions of quark-counting rules, and conclude that valence quarks play an important role in strange-particle production.

>From a sample of $2722 \pm 78$ $\Lambda_c~+$ decaying to the $pK~-\pi~+$ final state, we have observed, in the hadroproduction experiment E791 at Fermilab, $143 \pm 20$ $\Sigma_c~0$ and $122 \pm 18$ $\Sigma_c~{++}$ through their decays to $\Lambda_c~+ \pi~{\pm}$. The mass difference $M(\Sigma_c~0) - M(\Lambda_c~+$) is measured to be $(167.38\pm 0.29\pm 0.15)\,\mbox{MeV}$; for $M(\Sigma_c~{++}) - M(\Lambda_c~+)$, we find $(167.76\pm 0.29\pm0.15)\,\mbox{MeV}$. The rate of $\Lambda_c~+$ production from decays of the $\Sigma_c$ triplet is $(22\pm 2\pm 3)\,\mbox{\%}$ of the total $\Lambda_c~+$ production assuming equal rate of production from all three, as measured for $\Sigma_c~0$ and $\Sigma_c~{++}$. We do not observe a statistically significant $\Sigma_c$ baryon-antibaryon production asymmetry. The $x_F$ and $p_t~2$ spectra of $\Lambda_c~+$ from $\Sigma_c$ decays are observed to be similar to those for all $\Lambda_c~+$'s produced.

We present a measurement of asymmetries in the production of $\Lambda_c^+$ and $\Lambda_c^-$ baryons in 500 GeV/c $\pi^-$--nucleon interactions from the E791 experiment at Fermilab. The asymmetries were measured as functions of Feynman x ($x_F$) and transverse momentum squared ($p_T^2$) using a sample of $1819 \pm 62$ $\Lambda_c$'s observed in the decay channel $\Lambda_c \to pK^-\pi^+$. We observe more $\Lambda_c^+$ than $\Lambda_c^-$ baryons, with an asymmetry of $(12.7\pm3.4\pm1.3) %$ independent of $x_F$ and $p_T^2$ in our kinematical range $(-0.1 < x_F < 0.6$ and $0.0 < p_T^2 < 8.0 (GeV/c)^2$). This $\Lambda_c$ asymmetry measurement is the first with data in both the positive and negative $x_F$ regions.

This paper presents measurements of the production of Ds- mesons relative to Ds+ mesons as functions of x_F and square of p_t for a sample of 2445 Ds decays to phi pi. The Ds mesons were produced in Fermilab experiment E791 with 500 GeV/c pi- mesons incident on one platinum and four carbon foil targets. The acceptance-corrected integrated asymmetry in the x_F range -0.1 to 0.5 for Ds+- mesons is 0.032 +- 0.022 +- 0.022, consistent with no net asymmetry. The results, as functions of x_F and square of p_t, are compared to predictions and to the large production asymmetry observed for D+- mesons in the same experiment. These comparisons support the hypothesis that production asymmetries come from the fragmentation process and not from the charm quark production itself.

Using data from Fermilab fixed-target experiment E791, we have measured particle-antiparticle production asymmetries for lambda zero, cascade minus, and omega minus hyperons in pi minus-nucleon interactions at 500 GeV/c. The asymmetries are measured as functions of Feynman-x (x_F) and pt^2 over the ranges of -0.12 GE x_F LE 0.12 and 0 GE pt^2 LE 4 (GeV/c)^2. We find substantial asymmetries, even at x_F = 0. We also observe leading-particle- type asymmetries which qualitatively agree with theoretical predictions.