A measurement of continuum dimuon production in proton-copper collisions at 800-GeV incident energy is presented. The dimuons observed in this experiment cover the mass range from 6.5 to 18 GeV near y=0 in the proton-nucleon center-of-momentum frame. Scaling forms of the cross section for the continuum are compared with the results of other experiments in the context of the parton model and quantum chromodynamics. The present limitations of such scaling comparisons are discussed.
Experimental results on the production of dimuons by 800-GeV protons incident on a copper target are presented. The results include measurements of both the continuum of dimuons and the dimuon decays of the three lowest-mass ϒ S states. A description of the apparatus, data acquisition, and analysis techniques is included. A comparison of the results with data taken at lower incident energies indicates a scaling behavior of the continuum dimuon yields.
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.
Results of high-transverse-momentum charged-hadron production in 400-GeV/c proton-proton and proton-deuteron collisions and 800-GeV/c proton-proton collisions are presented. The transverse-momentum range of the data is from 5.2 to 9.0 GeV/c for the 400-GeV/c collisions and from 3.6 to 11.0 GeV/c for the 800-GeV/c collisions; the data are centered around 90° in the proton-nucleon center-of-momentum system. Single-pion invariant cross sections and particle ratios were measured at both energies. The results are compared to previous experiments and the Lund model.
The production of neutrons carrying at least 20% of the proton beam energy ($\xl > 0.2$) in $e^+p$ collisions has been studied with the ZEUS detector at HERA for a wide range of $Q^2$, the photon virtuality, from photoproduction to deep inelastic scattering. The neutron-tagged cross section, $e p\to e' X n$, is measured relative to the inclusive cross section, $e p\to e' X$, thereby reducing the systematic uncertainties. For $\xl >$ 0.3, the rate of neutrons in photoproduction is about half of that measured in hadroproduction, which constitutes a clear breaking of factorisation. There is about a 20% rise in the neutron rate between photoproduction and deep inelastic scattering, which may be attributed to absorptive rescattering in the $\gamma p$ system. For $0.64 < \xl < 0.82$, the rate of neutrons is almost independent of the Bjorken scaling variable $x$ and $Q^2$. However, at lower and higher $\xl$ values, there is a clear but weak dependence on these variables, thus demonstrating the breaking of limiting fragmentation. The neutron-tagged structure function, ${{F}^{\rm\tiny LN(3)}_2}(x,Q^2,\xl)$, rises at low values of $x$ in a way similar to that of the inclusive \ff of the proton. The total $\gamma \pi$ cross section and the structure function of the pion, $F^{\pi}_2(x_\pi,Q^2)$ where $x_\pi = x/(1-\xl)$, have been determined using a one-pion-exchange model, up to uncertainties in the normalisation due to the poorly understood pion flux. At fixed $Q^2$, $F^{\pi}_2$ has approximately the same $x$ dependence as $F_2$ of the proton.
We report on a sample of Jψ mesons coming from secondary vertices, a characteristic of heavyquark decay, detected in the Fermilab Meson West spectrometer. Based on eight signal events in which a Jψ emerges from a secondary vertex occurring in an air-gap region, we obtain an inclusive bb¯ cross section of 75 ± 31 ± 26 nb/nucleon. This result is compared to recent QCD predictions. We have also observed several events in the exclusive decay modes B±→Jψ+K± and B0→Jψ+K0* in which the B mass is fully reconstructed.
We report on χc1 and χc2 production in the Feynman-x range 0.1
We have studied the production of J/ψ and ψ(2S) charmonium mesons in 515 GeV/c π−Be collisions in the Feynman-x range 0.1
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We report on the production of J/psi mesons in 530 and 800 GeV/c proton - Be collisions in the Feynman-x range 0.0 < xf < 0.6. The J/psi mesons were detected via decays into opposite sign muon pairs. Differential distributions for J/psi production have been measured as functions of xf, pT^2, and cosine of the Gottfried-Jackson decay angle. These distributions are compared with results on J/psi production obtained in 515 GeV/c pion - Be collisions, measured by the same experiment, as well as with results from other experiments using incident protons.
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