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The "Toward" Region

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The above figure shows the data the average number of "toward" region charged particles compared with the QCD Monte-Carlo model predictions of HERWIG, ISAJET, and PYTHIA. This plot is very similar to the average number of charged particles within the leading jet. At PTJ1 = 20 GeV/c the "toward" region contains, on the average, about 8.7 charged particles with about 6.9 of these charged particles belonging to the leading charged jet.
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We expect the "toward" region to be dominated by the leading charged particle jet. This is clearly the case for ISAJET as can be seen in the above figure, where the predictions of ISAJET for the "toward" region are divided into three categories: charged particles that arise from the break-up of the beam particles ("beam-beam remnants"), charged particles that arise from initial-state radiation, and charged particles that result from the outgoing jets plus final-state radiation. For PTJ1 values below 5 GeV/c the "toward" region charged multiplicity arises mostly from the "beam-beam remnants", but as PTJ1 increases the contribution from the outgoing jets plus final state-radiation quickly begins to dominate. The bump in the "beam-beam remnant" contribution at low PTJ1 is caused by leading jets composed almost entirely from the "remnants". Of course, the origin of an outgoing particle ("beam-beam remnant" or "initial-state radiation") is not an experimental observable. Experimentally one cannot say where a given particle comes from. However, we do know the origins of particles generated by the QCD Monte-Carlo models and this figure shows the composition of the "toward" region as modelled by ISAJET.
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