[en] The cross section for charmed meson production at √(s)=4.03 and 4.14 GeV has been measured with the Beijing Spectrometer. The measurement was made using 22.3 pb^-1 of e⁺e^- data collected at 4.03 GeV and 1.5 pb^-1 of e⁺e^- data collected at 4.14 GeV. Inclusive observed cross sections for the production of charged and neutral D mesons and momentum spectra are presented. Observed cross sections were radiatively corrected to obtain tree level cross sections. Measurements of the total hadronic cross section are obtained from the charmed meson cross section and an extrapolation of results from below the charm threshold. (c) 2000 The American Physical Society

[en] We point out a dramatic new experimental signature for a class of theories with extra dimensions, where quarks and leptons are localized at slightly separated parallel ''walls'' whereas gauge and Higgs fields live in the bulk of the extra dimensions. The separation forbids direct local couplings between quarks and leptons, allowing for an elegant solution to the proton decay problem. We show that scattering cross sections for collisions of fermions which are separated in the extra dimensions vanish exponentially at energies high enough to probe the separation distance. This is because the separation puts a lower bound on the attainable impact parameter in the collision. We present cross sections for two body high energy scattering and estimate the power with which future colliders can probe this scenario, finding sensitivity to inverse fermion separations of order 10-70 TeV. (c) 2000 The American Physical Society

[en] The elementary particles of the standard model may reside in more than 3+1 dimensions. We study the consequences of large compactified dimensions on scattering and decay observables at high-energy colliders. Our analysis includes global fits to electroweak precision data, indirect tests at high-energy electron-positron colliders (CERN LEP2 and NLC), and direct probes of the Kaluza-Klein resonances at hadron colliders (Fermilab Tevatron and CERN LHC). The present limits depend sensitively on the Higgs sector, both the mass of the Higgs boson and how many dimensions it feels. If the Higgs boson is trapped on a (3+1)-dimensional wall with the fermions, large Higgs boson masses (up to 500 GeV) and relatively light Kaluza-Klein mass scales (less than 4 Tev) can provide a good fit to precision data. That is, a light Higgs boson is not necessary to fit the electroweak precision data, as it is in the standard model. If the Higgs boson propagates in higher dimensions, precision data prefer a light Higgs boson (less than 260 GeV) and a higher compactification scale (greater than 3.8 TeV). Future colliders can probe much larger scales. For example, a 1.5 TeV electron-positron linear collider can indirectly discover Kaluza-Klein excitations up to 31 TeV if 500 fb^-1 integrated luminosity is obtained. (c) 1999 The American Physical Society

[en] The theoretical merits of longitudinal polarization asymmetries of electron-positron annihilation into two final fermions at future colliders are examined, using a recently proposed theoretical description. A number of interesting features, valid for searches of virtual effects of new physics, is underlined, that is reminiscent of analogous properties valid on top of Z resonance. As an application to a concrete example, we consider the case of a model with triple anomalous gauge couplings and show that the additional information provided by these asymmetries would lead to a drastic reduction of the allowed domain of the relevant parameters. copyright 1997 The American Physical Society

[en] The structure of hadronic jets depends not only on the dynamics of QCD but also on the details of the jet finding algorithm and the physical process in which the jet is produced. To study these effects in more detail we calculate the jet cross section and the internal jet structure in e⁺e^- annihilations and compare them to the results found in hadronic collisions using the same jet definition, the cone algorithm. The different structures of the overall events in the two cases are evident in the comparison. For a given cone size and jet energy, the distribution of energy inside the cone is more concentrated near the center for jets from e⁺e^- collisions than for jets from hadronic collisions. copyright 1997 The American Physical Society

[en] I examine the determination of the QCD color factor ratio C_A/C_F from the scale evolution of particle multiplicity in e⁺e^- three jet events. I fit an analytic expression for the multiplicity in three jet events to event samples generated with QCD multihadronic event generators. I demonstrate that a one parameter fit of C_A/C_F yields the expected result C_A/C_F=2.25 in the limit of asymptotically large energies if energy conservation is included in the calculation. In contrast, a two parameter fit of C_A/C_F and a constant offset to the gluon jet multiplicity, proposed in a recent study, does not yield C_A/C_F=2.25 in this limit. I apply the one parameter fit method to recently published data of the DELPHI experiment at the e⁺e^- collider LEP at CERN and determine the effective value of C_A/C_F from this technique, at the finite energy of the Z⁰ boson, to be 1.74±0.03±0.10, where the first uncertainty is statistical and the second is systematic. (c) 2000 The American Physical Society

[en] We have made a detailed study of the signals expected at CERN LEP 2 from charged scalar bosons whose dominant decay channels are into four fermions. The event rates as well as kinematics of the final states are discussed when such scalars are either pair produced or are generated through a tree-level interaction involving a charged scalar, the W, and the Z. The backgrounds in both cases are discussed. We also suggest the possibility of reconstructing the mass of such a scalar at LEP 2. copyright 1997 The American Physical Society

[en] Gravity can become strong at the TeV scale in the theory of extra dimensions. An effective Lagrangian can be used to describe the gravitational interactions below a cutoff scale. In this work, we study the diphoton production in γγ, pp(bar sign), and e⁺e^- collisions in the model of low scale gravity. Since in the standard model photon-photon scattering only occurs via box diagrams, the cross section is highly suppressed. Thus, photon-photon scattering opens an interesting opportunity for studying the new gravity interaction, which allows tree-level photon couplings. In addition, we also examine the diphoton production at hadronic and e⁺e^- colliders. We derive the limits on the cutoff scale from the available diphoton data and also estimate the sensitivity reach in run II at the Fermilab Tevaton and at the future linear e⁺e^- colliders. (c) 1999 The American Physical Society

[en] A new treatment of Bose-Einstein correlations is incorporated in a space-time parton-shower model for e⁺e^- annihilation into hadrons. Two alternative algorithms are discussed, and we use a simple calculable model to demonstrate that they reproduce successfully the size of the hadron emission region. One of the algorithms is used to calculate two-pion correlations in e⁺e^-→Z⁰→hadrons and e⁺e^-→W⁺W^-→hadrons. Results are shown with and without resonance decays, for correlations along and transverse to the thrust jet axis in these two classes of events. (c) 2000 The American Physical Society

[en] In the PQCD analyses of the exclusive production of higher generation hadrons, the quark distribution amplitude of the heavy quark system has often been approximated by a δ function from the nonrelativistic consideration. Going beyond the peaking approximation, the factorization of the covariant hard scattering amplitude from the nonperturbative quark distribution amplitude is no longer valid. We therefore use the light-cone time-ordered perturbation theory which is the step prior to the usual factorization formula and calculate the form factor of a pseudoscalar meson composed of a heavy quark and antiquark. However, we find that the numerical results for the cross section of exclusive heavy meson pair production in e⁺e^- annihilation are not much different from those of the peaking approximation. copyright 1997 The American Physical Society