The production and event topology of three-jet events produced in $p\overline{p}$ collisions at $\sqrt{s}=1.8\mathrm{}$ TeV have been studied with the Collider Detector at Fermilab at the Tevatron Collider. The distributions of the three-jet angular variables (${\psi }^{*}$ and $cos{\theta }^{*}$) and of the variables describing the energy sharing between jets ($x_3$ and $x_4$) are found to agree well with tree-level QCD calculations. These distributions are predicted to have different shapes for different initial-state subprocesses (quark-antiquark, quark-gluon, and gluon-gluon). The data are consistent with the small expected contribution from quark-antiquark initial states, in agreement with theoretical expectations.

Kinematic properties of four-jet events produced in $p\overline{p}$ collisions at $\sqrt{s}=1.8\mathrm{}$ TeV have been studied using data with an integrated luminosity of 325 ${\mathrm{nb}}^{-1\mathrm{}}$ collected using the Collider Detector at Fermilab during the 1988-1989 Fermilab Collider run. The individual jet $p_T$ spectra and the angles between each jet pair are compared to the predictions of leading-order quantum chromodynamics for the double gluon bremsstrahlung process and good agreement is observed. In addition, a search for double parton scattering has been undertaken using variables sensitive to the topology of four-jet events. A small double parton content provides the best description of the data. We find $\frac{N_{\mathrm{DP}}}{N_{\mathrm{DB}}}={5.4}_{-2.0\mathrm{}}^{+1.6\mathrm{}}\%$, where $N$ represents the number of events attributed to each process. We measure ${\sigma }_{\mathrm{DP}}={63}_{-28\mathrm{}}^{+32\mathrm{}}$ nb for jets having $p_T>25\mathrm{}$ GeV/c in the pseudorapidity interval $\left|\eta \right|<\mathrm{}3.5\mathrm{}$.

Inclusive J/ψ and ψ(2S) production has been studied in p¯p collisions at √s =1.8 TeV using 2.6±0.2 ${\mathrm{pb}}^{\mathrm{-}1}$ of data taken with the Collider Detector at Fermilab. The products of production cross section times branching fraction were measured as functions of ${\mathit{P}}_{\mathit{T}}$ for J/ψ→${\mathrm{\mu }}^{+}$ ${\mathrm{\mu }}^{\mathrm{-}}$ and ψ(2S)→${\mathrm{\mu }}^{+}$ ${\mathrm{\mu }}^{\mathrm{-}}$. In the kinematic range ${\mathit{P}}_{\mathit{T}}$>6 GeV/c and ‖η‖≤0.5 we get σ(p¯p→J/ψ X)B(J/ψ→${\mathrm{\mu }}^{+}$ ${\mathrm{\mu }}^{\mathrm{-}}$) =6.88±0.23(stat${)}_{\mathrm{-}1.08}^{+0.93\mathrm{}}$(syst) nb, and σ(p¯p→ψ(2S)X)B(ψ(2S)→${\mathrm{\mu }}^{+}$ ${\mathrm{\mu }}^{\mathrm{-}}$) =0.232±0.051(stat${)}_{\mathrm{-}0.032}^{+0.029\mathrm{}}$(syst)nb. From these values we calculate the inclusive b-quark production cross section.

We present measurements of the pseudorapidity ($\eta$) distribution of charged particles ($\frac{d{N}_{\mathrm{ch}}}{d\eta }$) produced within $\left|\eta \right|\le 3.5$ in proton-antiproton collisions at $\sqrt{s}$ of 630 and 1800 GeV. We measure $\frac{d{N}_{\mathrm{ch}}}{d\eta }$ at $\eta =0\mathrm{}$ to be 3.18±0.06(stat)±0.10(syst) at 630 GeV, and 3.95±0.03 (stat)±0.13(syst) at 1800 GeV. Many systematic errors in the ratio of $\frac{d{N}_{\mathrm{ch}}}{d\eta }$ at the two energies cancel, and we measure 1.26±0.01±0.04 for the ratio of $\frac{d{N}_{\mathrm{ch}}}{d\eta }$ at 1800 GeV to that at 630 GeV within $\left|\eta \right|\le 3$. Comparing to lower-energy data, we observe an increase faster than $\ln \mathrm{}\left(s\right)\mathrm{}$ in $\frac{d{N}_{\mathrm{ch}}}{d\eta }$ at $\eta =0\mathrm{}$.

Measurements of inclusive transverse-momentum spectra for charged particles produced in proton-antiproton collisions at √2 of 630 and 1800 GeV are presented and compared with data taken at lower energies.