Jet Definition Research Articles

Next-to-leading-order QCD corrections to jet cross sections and jet rates in deeply inelastic electron-proton scattering.

Jet cross sections in deeply inelastic scattering in the case of transverse photon exchange for the production of (1+1) and (2+1) jets are calculated in next-to-leading order QCD (here the `+1' stands for the target remnant jet, which is included in the jet definition for reasons that will become clear in the main text). The jet definition scheme is based on a modified JADE cluster algorithm. The calculation of the (2+1) jet cross section is described in detail. Results for the virtual corrections as well as for the real initial- and final state corrections are given explicitly. Numerical results are stated for jet cross sections as well as for the ratio $\sigma_{\mbox{\small (2+1) jet}}/\sigma_{\mbox{\small tot}}$ that can be expected at E665 and HERA. Furthermore the scale ambiguity of the calculated jet cross sections is studied and different parton density parametrizations are compared.

Measurement of the dijet mass distribution in pp-bar collisions at sqrt s =1.8 TeV.

The dijet invariant mass distribution has been measured in the region between 120 and 1000 GeV/[ital c][sup 2], in 1.8-TeV [ital p[bar p]] collisions. The data sample was collected with the Collider Detector at Fermilab (CDF). Data are compared to leading order (LO) and next-to-leading order (NLO) QCD calculations using two different clustering cone radii [ital R] in the jet definition. A quantitative test shows good agreement of data with the LO and NLO QCD predictions for a cone of [ital R]=1. The test using a cone of [ital R]=0.7 shows less agreement. The NLO calculation shows an improvement compared to LO in reproducing the shape of the spectrum for both radii, and approximately predicts the cone size dependence of the cross section.

QCD radiative decay of the top quark produced in hadron collisions.

The discovery of the top-quark and the analysis of its decay products is an important test of the standard model. We consider the effects of final-state QCD radiation on the determination of the top-quark mass for $t\overline{t}$ pairs produced at the Superconducting Super Collider, CERN Large Hadron Collider, and Fermilab Tevatron. We also examine the polarization of the $W$ boson produced from a heavy-top-quark decay. We calculate the rate for gluon bremsstrahlung in the charged-current decay $t\ensuremath{\rightarrow}b{W}^{+}g$ of a heavy top quark. The effect of $b$ tagging and jet definition on the determination of these observables is discussed.

One-jet inclusive cross section at order alpha s3: Quarks and gluons.

The next-to-leading order inclusive jet cross section is calculated including both quarks and gluons. The general structure of the dependence of the cross section on the explicit jet definition and on the choice of the renormalization scale ${\mathrm{\ensuremath{\mu}}}^{2}$ is found to be very similar to the case of gluons only, calculated earlier. The resulting cross section is shown to involve a much reduced theoretical uncertainty compared to the lowest-order result. First comparisons with experimental data are also exhibited.

One-jet inclusive cross section at order alpha s3: Gluons only.

The next-to-leading-order jet cross section is calculated for the simplified case in which there are only gluons. The general structure of the differences from the lowest-order cross section are described. The important new effects at this order are the explicit dependence on the definition of the jet and the reduced dependence on the choice of the renormalization scale ${\ensuremath{\mu}}^{2}$. While only the purely glue results are discussed here, we expect that the dependence on the jet definition and on ${\ensuremath{\mu}}^{2}$ will be quite similar in the complete calculation, which we are now undertaking.

Experimental investigation of the energy dependence of the strong coupling strength

The energy dependence of the relative production rate of three-jet events is studied in hadronic e+e− annihilation events at center of mass energies between 22 and 46.7 GeV. Three-jet events are defined by a jet finding algorithm which is closely related to the definition of resolvable jets used in O(αs2) perturbative QCD calculations, where the relative production rate of three-jet events is roughly proportional to the size of the strong coupling strength. The production rates of three-jet events in the data decrease significantly with increasing centre of mass energy. The experimental rates, which are independent of fragmentation model calculations, can be directly compared to theoretically calculated jet production rates and are in good agreement with the QCD expectations of a running coupling strength. The hypothesis of an energy independent coupling constant can be excluded with a significance of four standard derivations.

A new approach to the Sterman-Weinberg jet formula

A new way to define a Sterman-Weinberg jet is described. The fraction of hadronic final states frome + e − annihilation consisting of 2 jets is obtained exactly to order α s Q 2 in QCD perturbation theory using two opposed cones along the thrust axis. Conditions on the parton phase space are discussed in detail. The deviation of the jet angular distribution from 1+cos2 θ is also obtained. In contrast to some previously proposed 2 jet definitions we find no restriction of the range of applicability by a relation between the Sterman-Weinberg parameters ɛ and δ. This definition allows a very easy comparison with experimental data. A rough estimate of the fragmentation effects on the fraction of 2 jet events is also presented.

Large-p T jet production on nuclei

Large-pT jet production on nuclei is studied in the frame-work of the hard-scattering parton model including multiple-scattering corrections. Attention is paid to the possibility of multijet contamination to single-jet events. This phenomenon is due to the experimental definition of jet and is proved to explain the bulk of the anomalous nuclear enhancement observed experimentally. The possibility of getting deeper insight into the incoming-hadron structure is indicated.

Jet production in high-energy hadron-proton collisions

We present experimental details from a study of hadron jet production at high transverse momentum (p⊥) in 130 and 200 GeV hadron-proton collisions. Jet definition and acceptance of the apparatus are discussed thoroughly. Jet cross sections are measured for p, π−, π+, K−, K+, andp incident on a liquid hydrogen target. These cross sections depend strongly on the number of valence quarks in the beam. The p⊥ dependence of the jet cross section is measured to be significantly flatter than that for single particles. We show that a model based on quantum chromodynamics (QCD) is able to qualitatively explain both the large jet cross section and the event structure on the trigger and away sides. We present evidence for scale breaking; higher transverse momentum jets are seen to be composed of a greater number of lower momentum particles. The average momentum (<k⊥>) of these particles transverse to the jet direction is observed to increase with increasing jet p⊥. Charged particle correlations on both the trigger and away sides are given for both pion and proton beams.

Equipartitioned Jets: New Tests of Quantum Chromodynamics

We propose a modified definition of hadronic jets in quantum chromodynamics which is more selective than the Sterman-Weinberg criterion. It prohibits any two jet streams from having appreciably different energies. Our more restrictive definition provides new tests of quantum chromodynamics in high-energy experiments. We illustrate this idea for two-"quark"-jet configurations in ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\mathrm{hadrons}$ and for two-"gluon"-jet production. The necessity of exponentiating perturbative jet predictions is also discussed.

Production of jets and single particles at high p⊥ in 200 GeV hadron-beryllium collisions

We present results from an experiment studying the production of single particles and jets (groups of particles) with high p⊥ (transverse momentum) in 200 GeV/ c interactions on a beryllium target. We give a detailed discussion of the ambiguities in the jet definition. The jet and single-particle cross sections have a similar shape but the jet cross section is over two orders of magnitude larger. The events show evidence for the coplanar structure suggested by constituent models, and the momentum distributions of charged particles give strong support to a simple quark-quark scattering model.