Charm production by muons and its role in scale noninvariance

Abstract

Interactions of 209 GeV muons in the Multimuon Spectrometer at Fermi lab have yielded more than 8xl0 4 e'vents with two muons in the final state. After reconstruction and cuts, the data contain 20 072 events with (81±10)% attributed to the diffractive production of charmed states decaying to muons. The cross section for diffractive charm +1•9 muoproduction is 6.9_ 1 • 4 nb where the error includes systematic uncertainties. Extrapolated to Q 2 =0 with o(Q 2)=o(O)(l+Q2JA2)-2, the effective cross +180 +200 section for 178 (100) GeV photons is 750_130 (560-120) nb and the parameter A is 3.3±0.2 (2.9±0.2) GeV/c. The \! dependence of the cross section is similar to that of the photon-gluon-fusion model. Okubo-Zweig-Iizuka selection rules and unitarity allow the muon data to set a 90% confidence lower limit on the ~N total cross section of 0.9 mb. A first determination of the structure function F 2 (cc) for diffractive charm production indicates that charm accounts for approximately 1/3 of the scale-noninvariance observed in inclusive muon-nucleon scattering at low Bjorken x.

Muon Scattering

“…The Q2 dependence for open charm production, similar to 1ft/; produc tion, is rather weak and characterized again by a (Q2 + M;)-2 dependence with Mv � 3.9 ±O.1 GeV (47) for the EMC data. As for the 1ft/; data the BFP (43) values are systematically lower. Using these dependences, cross sections for Q2 = 0 can be extracted and these are shown for the data fr om the two groups in Figure 22.…”

“…A much larger fraction of the total cross section is in the form of the open charm production (42)(43)(44)(45)(46)(47), which is of the order of 1-1 ,ub. Detection here is via the semileptonic decay of one or both of the produced charmed particles resulting in a di-or trimuon final state with missing undetected energy corresponding to the neutrino(s) energy.…”

“…The MMS attempted to achieve these aims with a repeated structure of iron plates that were at one and the same time the target modules and the detector modules of the iron core magnet. The apparatus (38,43,51,66) is illustrated in Figure 6.…”

Open Charm Production in Deep Inelastic Scattering at Next-to-Leading Order at HERA

“…Early measurements of open charm production in neutral current DIS, performed by the Berkeley-Fermilab-Princeton (BFP) [1] and European Muon Collaboration (EMC) [2] experiments, touched upon the topics relevant for HERA today: production mechanism, charm fragmentation, gluon parton distribution function extraction, and charm contribution to the proton structure function. See [3] for a review of these experiments.…”

“…The coefficient functions in the large momentum transfer limit are a necessary ingredient for constructing the variable flavor number schemes mentioned in the introduction. Exact analytic formulae for the d (1) k,i together with analytic formulae for the coefficient functions c…”