Results are reported concerning the charged-particle multiplicity distribution obtained in an exposure of the high-resolution hydrogen bubble chamber LEBC to a beam of 800 GeV protons at the Fermilab MPS. This is the first time that such data have been available at this energy. The distribution of the number n ch of charged particles produced in inelastic interactions obeys KNO-scaling. The average multiplicity is 〈 n ch 〉 = 10.26±0.15. For n ch ⩾8 the data can be well fitted to a negative binomial. The difference between the overall experimental multiplicity distribution and that resulting from the latter fit is in agreement with the contribution expected from diffractive processes.
We have used the spin-precession technique to measure the Σ− magnetic moment (μΣ). A Σ− beam with a polarization of 22% was produced by a 400-GeV proton beam striking a Cu target at nominal production angles of ±3 mrad. We simultaneously recorded 21 000 Σ−→ne−ν¯ decays and 650 000 Σ−→nπ− decays at Σ− beam momenta of 253 and 308 GeV/c. We find μΣ=−1.166±0.014±0.010 nuclear magnetons, where the quoted errors are statistical and systematic, respectively.
We present results on the production of hadrons in collisions of 400-GeV/c protons with beryllium, copper, and tungsten nuclei. The data cover the region from 5.6 to 8.0 GeV/c in the transverse momentum of the final-state hadron and from 73° to 102° in the proton-nucleon center-of-momentum frame production angle theta*. The restriction of the data to values of xT (xT=2pT/ √s ) greater than 0.4 enriches the sample with hard collisions of valence quarks. Asymmetries about theta*=90° reflect the presence of neutrons in the target nuclei. The variation of the atomic-weight dependence parameter α with production angle is discussed in the context of the phenomenology of nucleonic structure within nuclei. We also extrapolate our measurements to a ‘‘deuteron’’ target to minimize nuclear effects and compare the result to QCD calculations.
In a beam-dump experiment at Fermilab the cross section for charm-particle production has been deduced from a measurement of the prompt neutrino flux. The reaction cross section, if we assume only DD¯ and the dependence on atomic weight A0.75, is 57.2 ± 2.9 ± 8.5 μb/nucleon and the dependence on Feynman x and transverse momentum is EDd3σdpD3∝(1−x)3.2e−1.5p⊥ (p⊥ in GeV/c). The data are consistent with as much as 40% diffractive production of ΛcD¯.
Experimental multiplicity distributions scaled in the Koba-Nielsen-Olesen (KNO) form for hadron-nucleus interactions show clear deviations from the scaling distribution observed for hadron-hadron interactions. The deviations become larger as A increases. Our data can be described by a model which invokes the hypothesis that KNO scaling is valid for hadron-nucleus interactions at a fixed impact parameter. In this model, the A dependence of the multiplicity distributions results from the convolution of scatterings at various impact parameters.
The production of φ-meson pairs has been observed in 400-GeV/c proton-nucleon interactions at the Fermilab multiparticle spectrometer in the inclusive reaction pN→φφ+X, where each φ decays to a K+K− pair. A fast (200 nsec) high-level processor was used to selectively trigger on events containing two pairs of oppositely charged kaons having low invariant masses. The experimental apparatus and trigger processor are described. The cross section for φφ production and an upper limit for ηc production are presented.
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.
We have measured the production polarization of 265- and 310-GeV/c Σ− in the inclusive reaction p+Cu→Σ−+X using 400-GeV/c protons. The polarization was analyzed via the asymmetry in the weak decay Σ−→n+π−, and has typical values of +0.20 with respect to the direction of the cross product of the incident-proton and Σ− momenta. Using the spin-precession technique, we have determined the Σ− magnetic moment to be -1.23±0.03±0.03 nuclear magnetons, where the statistical and systematic errors are shown separately.
The cross section for the reaction p¯N→μ+μ−X with muon pairs in the mass range 4<M<9 GeV/c2 and xF>0 was measured to be σ=0.104±0.005±0.008 nb/nucleon. The distributions dσdxF and M3dσdM were compared to the QCD-improved Drell-Yan model and to calculations including first-order QCD corrections, with use of deep-inelastic structure functions. Excellent agreement with the data was obtained if the calculations were multiplied by factors of 2.45 and 1.41, respectively.
Hadronic production of charmed particles in association with muons from their semileptonic decay has been observed in a high-resolution streamer-chamber experiment performed at Fermilab. A miss-distance analysis of the pictures gives a signal of 17.3±4.7 events. Depending on the production model this corresponds to a range of neutron-nucleon cross sections from 8 to 50 μb, assuming an A23 dependence.