We present the first measurement of two-particle momentum correlations in jets produced in p$\bar{p}$ collisions at center of mass energy of 1.96 TeV. A comparison of the experimental data to theoretical predictions obtained for partons within the framework of resummed perturbative QCD (Next-to-Leading Log Approximation) shows that the predicted parton momentum correlations survive the hadronization stage of jet fragmentation and are present at the hadron level. We also present the measurement of the intrinsic transverse momenta of particles with respect to jet axis (kT). Experimental data is compared to the theoretical predictions obtained for partons within the framework of Modified Leading Log Approximation and Next-to-Modified Leading Log Approximation, and shows good agreement in the range of validity of the theoretical predictions. The results of both measurements indicate that the perturbative stage of the jet formation must be dominant and give further support to the hypothesis of Local Parton-Hadron Duality.

Jet fragmentation properties have been studied in collisions of protons and antiprotons at a center-of-mass energy of 1.8 TeV, using the Collider Detector at Fermilab (CDF). The fractional momentum distribution of charged particles within jets is presented and compared with Monte-Carlo predictions. With increasing di-jet invariant mass from 60 to 200 GeV/c2 the fragmentation is observed to soften as predicted by scale breaking effects in Quantum Chromodynamics (QCD). The charged multiplicity in the jet core is observed to rise with di-jet invariant mass. 57 refs.

ABSTRACT: We present the first measurement of two-particle momentum correlations in jets produced in proton-antiproton collisions at center of mass energy of 1.96 TeV. A comparison of the experimental data to theoretical predictions obtained for partons within the framework of resummed perturbative QCD (Next-to-Leading Log Approximation) shows that the predicted parton momentum correlations survive the hadronization stage of jet fragmentation and are present at the hadron level. We also present the measurement of the intrinsic transverse momenta of particles with respect to jet axis (k [subscript T]). Experimental data is compared to the theoretical predictions obtained for partons within the framework of Modified Leading Log Approximation and Next-to-Modified Leading Log Approximation, and shows good agreement in the range of validity of the theoretical predictions. The results of both measurements indicate that the perturbative stage of the jet formation must be dominant and give further support to the hypothesis of Local Parton-Hadron Duality.

ABSTRACT: We report the first model independent measurement of charged particle multiplicities in quark and gluon jets, Nq_ and Ng_, produced at the Tevatron in proton-antiproton collisions with center-of-mass energy 1.8 TeV and recorded by the Collider Detector at Fermilab. The measurements are made for jets with average energies 41 and 53 GeV by counting charged particle tracks in cones with opening angle of thetac_=0.28, 0.36, and 0.47 rad around the jet axis. The corresponding jet hardness Q=Ej_et*thetac_ varies in the range from 12 GeV to 25 GeV. At Q=19.2 GeV, the ratio of multiplicities r=Ng_/Nq_ is found to be 1.64"0.17, where statistical and systematic uncertainties are added in quadrature. The results are in agreement with re-summed perturbative QCD calculations and are consistent with recent ee− measurements.

Production of heavy quark flavors in proton-antiproton collisions with a center-of-mass energy of 1.8 $\times$ 10$\sp{12}$ electron volts is studied for events containing hadronic jets with a nearby muon track, where both the jet and the muon are produced at large angles from the incident beams. The muon tracking system and pattern recognition are described. Detailed calculations of the muon background due to meson decay and hadron noninteractive punchthrough are presented, and other background sources are evaluated. Distributions of muon transverse momentum relative to the beam and the jet axis agree with QCD expectations for semileptonic charm and beauty decay. Muon identification cuts and background subtraction leave 57.5 $\pm$ 17.1 muon-jet pairs, a rate consistent with the established production cross sections for charm and beauty quarks and the acceptance for minimum ionizing particles overlapping with nearby jets. A small dimuon sample clarifies the muon signature. No signatures of undiscovered phenomena are observed in this new energy domain.

The production of jets in association with a Z/?* boson is an example of an important class of processes at hadron colliders, namely vector boson + jet (V + jet) production. Comparisons of measurements of this class of processes with theory predictions constitute an important, fundamental test of the Standard Model of particle physics, and of the theory of QCD in particular. While having a smaller cross section than other V +jet processes, Z/?*(→ e+e-) + jets production, with Z/?* → e+e-/?+?-, has a distinct experimental signature allowing for measurements characterized by low backgrounds and a direct, precise measurement of the properties of the decay products of the Z/?* boson. In this thesis, several new measurements of the properties of jets produced in association with a Z/?* boson in p$ar{p}$ collisions at √s = 1.96 TeV are presented. The cross section for Z/?*(→ e+e-) + N jet production (N ≤ 3) is measured, differential in the transverse momentum of the Nth jet in the event, normalized to the inclusive Z/?* cross section. Also, the cross section for Z/?*(→e+e-) + N jets (N ≥ 1) is measured, differential in the difference in azimuthal angle between the di-electron system and any jet in the event, normalized to unity. The data used in the measurements were collected by the D0 experiment located at the Tevatron Collider of the Fermi National Accelerator Laboratory and correspond to an integrated luminosity of 1.04 fb-1. The measured jet transverse momentum spectra are compared with the predictions of perturbative calculations at the next-to-leading order in the strong coupling constant. Given the low sensitivity of the calculations to model parameters, these comparisons represent a stringent test of perturbative QCD. One of the main goals currently being pursued in particle physics is the discovery of the only particle predicted by the Standard Model which has so far no been detected experimentally, namely the Higgs boson. It is assumed that the ATLAS and CMS experiments located at the Large Hadron Collider (LHC), a proton-proton collider at √s = 14 TeV, will be able to detect the Higgs boson, or rule out its existence, within the next few years. The collisions delivered by the LHC will also be used to perform a long range of searches for other new particles, for instance particles predicted by models based on the principle of supersymmetry. The associated production of vector bosons with jets has relatively large production rates at the LHC and can produce a long list of different final states which can include charged leptons, missing transverse energy, as well as light- and heavy-flavour jets. This makes V + jet production a major source of background events to many searches for new particles. Most techniques used for estimating the expected number of background events to searches rely on passing the stable final-state particles of simulated hadron collisions generated using a so-called event generator code, through a simulation of the experimental detector system. The development of event generators which are capable of reliably predicting the properties of jets produced in association with a core process, e.g. the production of a vector boson, has been the subject of a large amount of research activity during the last ten years. These efforts have led to the appearance of the CKKW and MLM algorithms which are implemented in several event generators, among them SHERPA and ALPGEN + PYTHIA. The large data sample collected by the D0 experiment during Run II offers an excellent opportunity for validating these new event generators against experimental measurements of V + jet production. As argued above, the Z/?*(→ e+e-) + jets process offers the combination of a clean experimental signature and large production rates, making it the process of choice for these studies.