QCD Corrections to Toponium Production at Hadron Colliders

Toponium production at future hadron colliders is investigated. Perturbative QCD corrections to the production cross section for gluon fusion are calculated as well as the contributions from gluon-quark and quark-antiquark collisions to the total cross section. The dependence on the renormalization and factorization scales and on the choice of the parton distribution functions is explored. QCD corrections to the branching ratio of $\eta_{t}$ into $\gamma\gamma$ are included and the two-loop QCD potential is used to predict the wave function at the origin. The branching ratio of $\eta_{t}$ into $\gamma Z$, $ZZ$, $HZ$ and $WW$ is compared with the $\gamma\gamma$ channel.Comment: 16 pages (latex) 9 figures (postscript) available upon request, TTP92-3

W and Z Polarization Effects in Hadronic Collisions

A Monte Carlo study of the polar and azimuthal angular distributions of the lepton pair arising from the decay of a $W$ or $Z$ boson produced at high transverse momentum in hadronic collisions is presented. In the absence of cuts on the final state leptons, the lepton angular distribution in the gauge boson rest frame is determined by the gauge boson polarization. Numerical results for the lepton angular distributions in the Collins--Soper frame with acceptance cuts and energy resolution smearing applied to the leptons are presented. In the presence of cuts, the lepton angular distributions are dominated by kinematic effects rather than polarization effects, however, some polarization effects are still observable on top of the kinematic effects. Polarization effects are highlighted when the experimental distributions are divided by the Monte Carlo distributions obtained using isotropic gauge boson decay.Comment: 23 pages (LaTeX) plus 13 postscript figures, MAD/PH/834, UCD--94--23. Figures are available from the authors or as a compressed tar file via anonymous ftp at phenom.physics.wisc.edu in directory ~pup/preprints/madph-94-834-figs.tar.

Hadronic ZγZ\gamma Production with QCD Corrections and Leptonic Decays

The process $p p \to Z \gamma + X \to \ell^- \ell^+ \gamma + X$, where $\ell$ denotes a lepton, is calculated to order $\alpha_s$. Total and differential cross sections, with acceptance cuts imposed on the leptons and photon, are given for the Tevatron and LHC center of mass energies. In general, invariant mass and angular distributions are simply scaled up in magnitude by the QCD radiative corrections, whereas in transverse momentum distributions, the QCD radiative corrections increase with the transverse momentum.Comment: 16 pages + 9 figures, UCD-94-29. A postscript version and 9 postscript figures are available via anonymous ftp to UCDHEP.UCDAVIS.EDU in the directory [.ohnemus.ucd-94-29

Soft gluon effects on lepton pairs at hadron colliders

With a large integrated luminosity expected at the Tevatron, a next-to-leading order (NLO) calculation is no longer sufficient to describe the data which yield the precision measurement of $M_W$, etc. Thus, we extend the Collins-Soper-Sterman resummation formalism, for on-shell vector boson production, to correctly include the effects of the polarization and the width of the vector boson to the distributions of the decay leptons. We show how to test the rich dynamics of the QCD multiple soft gluon radiation, for example, by measuring the ratio $R_{CSS} \equiv \frac{\sigma (Q_T>Q_T^{\min})}{\sigma _{Total}}$. ($Q_T$ is the transverse momentum of the vector boson.) We conclude that both the total rates and the distributions of the lepton charge asymmetry predicted by the resummed and the NLO calculations are different when kinematic cuts are applied.Comment: 50 pages, REVTeX, 16 figures (27 eps files

Re-evaluation of the LHC potential for the measurement of Mw

We present a study of the LHC sensitivity to the W boson mass based on simulation studies. We find that both experimental and phenomenological sources of systematic uncertainties can be strongly constrained with Z measurements: the lineshape is robustly predicted, and its analysis provides an accurate measurement of the detector resolution and absolute scale, while the differential cross-section analysis absorbs most of the strong interaction uncertainties. A sensitivity \delta Mw \sim 7 \MeV for each decay channel (W --> e nu, W --> mu nu), and for an integrated luminosity of 10 fb-1, appears as a reasonable goal

Hadronic final states in deep-inelastic scattering with Sherpa

We extend the multi-purpose Monte-Carlo event generator Sherpa to include processes in deeply inelastic lepton-nucleon scattering. Hadronic final states in this kinematical setting are characterised by the presence of multiple kinematical scales, which were up to now accounted for only by specific resummations in individual kinematical regions. Using an extension of the recently introduced method for merging truncated parton showers with higher-order tree-level matrix elements, it is possible to obtain predictions which are reliable in all kinematical limits. Different hadronic final states, defined by jets or individual hadrons, in deep-inelastic scattering are analysed and the corresponding results are compared to HERA data. The various sources of theoretical uncertainties of the approach are discussed and quantified. The extension to deeply inelastic processes provides the opportunity to validate the merging of matrix elements and parton showers in multi-scale kinematics inaccessible in other collider environments. It also allows to use HERA data on hadronic final states in the tuning of hadronisation models.Comment: 32 pages, 22 figure

A measurement of the W boson mass using large rapidity electrons

We present a measurement of the W boson mass using data collected by the D0 experiment at the Fermilab Tevatron during 1994--1995. We identify W bosons by their decays to e-nu final states where the electron is detected in a forward calorimeter. We extract the W boson mass, Mw, by fitting the transverse mass and transverse electron and neutrino momentum spectra from a sample of 11,089 W -> e nu decay candidates. We use a sample of 1,687 dielectron events, mostly due to Z -> ee decays, to constrain our model of the detector response. Using the forward calorimeter data, we measure Mw = 80.691 +- 0.227 GeV. Combining the forward calorimeter measurements with our previously published central calorimeter results, we obtain Mw = 80.482 +- 0.091 GeV

Structure Functions of the Nucleon and their Interpretation

The current status of measurements of the nucleon structure functions and their understanding is reviewed. The fixed target experiments E665, CCFR and NMC and the HERA experiments H1 and ZEUS are discussed in some detail. The extraction of parton momentum distribution functions from global fits is described, with particular attention paid to much improved information on the gluon momentum distribution. The status of alpha_s measurements from deep inelastic data is reviewed. Models and non-perturbative approaches for the parton input distributions are outlined. The impact on the phenomenology of QCD of the data at very low values of the Bjorken x variable is discussed in detail. Recent advances in the understanding of the transition from deep inelastic scattering to photoproduction are summarised. Some brief comments are made on the recent HERA measurements of the ep NC and CC cross-sections at very high Q2.Comment: 196 pages, 79 figures, uses ijmpa.sty and psfig.tex (included

Forward jet production in deep inelastic ep scattering and low-x parton dynamics at HERA

Differential inclusive jet cross sections in neutral current deep inelastic ep scattering have been measured with the ZEUS detector. Three phase-space regions have been selected in order to study parton dynamics where the effects of BFKL evolution might be present. The measurements have been compared to the predictions of leading-logarithm parton shower Monte Carlo models and fixed-order perturbative QCD calculations. In the forward region, QCD calculations at order alpha_s^1 underestimate the data up to an order of magnitude at low x. An improved description of the data in this region is obtained by including QCD corrections at order alpha_s^2, which account for the lowest-order t-channel gluon-exchange diagrams, highlighting the importance of such terms in parton dynamics at low x.Comment: 25 pages, 4 figure

Isospin Violation in tau -> 3 pi nu_tau

Isospin violating signals in the tau -> 3 pi nu_tau decay mode are discussed. For the tau -> pi^- pi^- pi^+ nu_tau decay mode, isospin violation arises from the vector current contribution in the tau -> omega pi nu_tau decay with the subsequent isospin violating omega decay into pi^+ pi^-. We demonstrate that such effects may be observed in presently available data through the measurement of the interference effects of these vector current contributions with the dominating axial vector current, i.e. through a measurement of the structure functions W_F,W_G,W_H and W_I. In the case of the tau -> pi^0 pi^0 pi^- nu_tau decay mode, a vector current contribution is generated by eta pi mixing in the decay chain tau -> eta rho nu_tau -> pi^0 pi^0 pi^- nu_tau. We find that this effect is rather small, the magnitude of the associated interference terms being too low for present statistics.Comment: LaTex, 16 pages, 5 figures. The complete paper is also available via anonymous ftp at ftp://ttpux2.physik.uni-karlsruhe.de/ , or via www at http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints