Jet Physics

Recent measurements of the inclusive jet cross section, dijet cross section, dijet invariant mass distributions and strong coupling constant at TEVATRON, HERA and LEP colliders are presented in this paper. The comparisons with NLO perturbative QCD predictions are shown. In general consistency with QCD predictions is observed for a variety of processes and energy ranges. The observed discrepancies can be accommodated by the modiications of parton distribution functions. The inclusive jet cross section measured by CDF at p s = 1800 GeV in the 1992-1993 data agrees with the NLO QCD prediction up to a jet E t of 250 GeV. For E t above 250 GeV the measured cross section is higher than the NLO QCD prediction 1). An independent measurement from 1994-1995 data connrmed the high E t excess (Fig. 1, Left). The inclusive jet cross section, measured by DD experiment in 1994-1995 (Fig. 1,Right) shows no signiicant excess above NLO QCD prediction at high E t 2). For the NLO QCD predictions CDF used EKS 3) with renormalization and factorization scale = E Jet t f, while DD used JETRAD 4) with = E Leading Jet t f, where f is a multiplicative factor usually chosen as 0.25-2.0. EKS and JETRAD use diierent approaches in the calculations but provide essentially the same result, since both of them are based on the same NLO matrix element calculations. Both experiments selected central jets, CDF in jj range 0.1-0.7, DD | in the range jj <0.5. DD also measured the inclusive jet cross section in the CDF range for direct comparison of results.