PHYSICAL REVIEW D VO LUM E 13, NUMB ER 7 1 APRIL 1976 Theoretical estimates for photoproduction and leptoproduction of neutral vector bosons* R. W. Brown, ~ Leon B. Gordon, ~ and J. Smith Institute for Theoretical Physics, State University of New York at Stony Brook, Stony Brook, ¹w York 11794 Karnig O. Mikaelian~ Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802 (Received 28 July 1975) We give estimates for the production of neutral vector bosons in several reactions. These reactions involve the collisions of photons and leptons (electrons, muons, and neutrinos) with protons. The possible mechanisms considered are diffraction, parton (constituent) scattering, and electromagnetic recoil through the boson's anomalous moments. We address ourselves to both the case when the boson is a hadron and the case when it is not, although the emphasis is on the latter. I. INTRODUCTION Some important aspects of elementary-particle physics revolve around two families of massive vector bosons. One family is predicted, along with other spin states, in the charm version of the quark model. ' The other consists of the gauge bosons needed in unified theories (e.g. , the Wein- berg-Salam model') of weak and electromagnetic interactions. Proof of the existence of either family would be major progress. Precisely this kind of progress seems to be at hand. The exciting Brookhaven' and Stanford' dis- coveries may be compatible with a charm-anti- charm picture, particularly in view of the recent photoproduction experiments at Fermilab and SLAC' where the size and the diffractive nature of the cross section indicate that these narrow states are hadrons. The discovery of weak neutral cur- rents' gives hope for the existence of a triplet of charged and neutral intermediate vector bosons, hinting in turn that gauge theories could be accu- rate pictures of the world. Thus members of the first family and indirect effects of the second family may have already been seen. Much experimental effort will now go into new production modes for the J (g) particles as well as the continued search for the weak bosons. We consider in this paper some reactions of interest in the production of the neutxa/ members and give some crude estimates of their rates. 7 The types of estimates that we have in mind will complement our earlier work on weak-vector-boson produc- tion. We begin in See. II with the photoproduction of vector bosons on proton targets. With rather large minimum momentum transfers, coherent scatter- ing oif nuclear targets may be ignored. (This is also true for the lepton-induced reactions). For the weak-boson case, we apply the phenomenologi- cal form factor model and the quark-parton mod- el' used earlier in charged-boson studies. A dif- fractive mechanism is also compared where, as input, the information gleaned from the P-produc- tion experiments' is put to use. We next consider muon (and electron) beams and proton targets in Sec. III. Projectile fragmenta- tion (weak bremsstrahlung by the charged lepton) in such an experiment has already been studied for weak bosons'; the interest here is in target fragmentation, where the photoproduction models of the previous section are put to use. Lastly, neutrino-proton collisions round out the reactions and are discussed in Sec. IV. We once again look at the photoproduction models men- tioned above. For weak neutral bosons, there is an added inhibition: We can have no lowest-order electromagnetic recoil if the bosons are self-con- jugate, so only some sort of hadronie emission after a weak excitation is imaginable. But if such bosons are not self-conjugate and have anomalous moments, electromagnetic recoil is possible. We calculate the rates for this possibility. Final re- marks comparing the various estimates are col- lected together in Sec. V. II. PHOTOPRODUCTION A division into the two cases where the vector boson is a hadron and where it is not is made be- low and in later sections. For the sake of con- venience, we shall use the labels "strong boson V"' and "weak boson Z"' for these cases, re- spectively. The reader should be warned that the emphasis is, for the most part, on the strong- boson case as &&Put into the weak-boson calcula- tions. A. Strong boson Vo We wish to extract some information from known experimental results for later use. The starting point is the consideration of vector- meson V' pho- 1856