Search

This report provides a comprehensive overview of the prospects for B physics at the Tevatron. The work was carried out during a series of workshops starting in September 1999. There were four working groups: 1) CP Violation, 2) Rare and Semileptonic Decays, 3) Mixing and Lifetimes, 4) Production, Fragmentation and Spectroscopy. The report also includes introductory chapters on theoretical and experimental tools emphasizing aspects of B physics specific to hadron colliders, as well as overviews of the CDF, D0, and BTeV detectors, and a Summary., Comment: 583 pages. Further information on the workshops, including transparencies, can be found at the workshop's homepage: http://www-theory.lbl.gov/Brun2/. The report is also available in 2-up http://www-theory.lbl.gov/Brun2/report/report2.ps.gz or chapter-by-chapter http://www-theory.lbl.gov/Brun2/report/

We examine how mixing between the Standard Model(SM) Higgs boson, $h$, and the radion of the Randall-Sundrum model modifies the expected properties of the Higgs boson. In particular, we demonstrate that the total and partial decay widths of the Higgs, as well as the $h\to gg$ branching fraction, can be substantially altered from their SM expectations, while the remaining Higgs branching fractions are modified less than $\lsim 5%$ for most of the parameter region., Comment: 3 pgs, Contributed to the APS/DPF/DPB Summer Study on the Future of Particle Physics (Snowmass 2001), Snowmass, Colorado, 30 Jun - 21 Jul 2001

We examine the unitarity properties of spontaneously broken non-commutative gauge theories. We find that the symmetry breaking mechanism in the non-commutative Standard Model of Chaichian et al. leads to an unavoidable violation of tree-level unitarity in gauge boson scattering at high energies. We then study a variety of simplified spontaneously broken non-commutative theories and isolate the source of this unitarity violation. Given the group theoretic restrictions endemic to non-commutative model building, we conclude that it is difficult to build a non-commutative Standard Model under the Weyl-Moyal approach that preserves unitarity., Comment: 31 pages

A calibration source using gamma-rays from 16N (t_1/2 = 7.13 s) beta-decay has been developed for the Sudbury Neutrino Observatory (SNO) for the purpose of energy and other calibrations. The 16N is produced via the (n,p) reaction on 16O in the form of CO2 gas using 14-MeV neutrons from a commercially available Deuterium-Tritium (DT) generator. The 16N is produced in a shielding pit in a utility room near the SNO cavity and transferred to the water volumes (D2O or H2O) in a CO2 gas stream via small diameter capillary tubing. The bulk of the activity decays in a decay/trigger chamber designed to block the energetic beta-particles yet permit the primary branch 6.13 MeV gamma-rays to exit. Detection of the coincident beta-particles with plastic scintillator lining the walls of the decay chamber volume provides a tag for the SNO electronics. This paper gives details of the production, transfer, and triggering systems for this source along with a discussion of the source gamma-ray output and performance., Comment: Accepted for publication in NIM-A. 25 total pages, including 10 figures and 1 Table

The TESLA Technical Design Report Part III: Physics at an e+e- Linear Collider, Comment: 192 pages, 131 figures. Some figures have reduced quality. Full quality figures can be obtained from http://tesla.desy.de/tdr. Editors - R.-D. Heuer, D.J. Miller, F. Richard, P.M. Zerwas

Recent theoretical results have demonstrated that non-commutative geometries naturally appear within the context of string/M-theory. One consequence of this possibility is that QED takes on a non-abelian nature due to the introduction of 3- and 4-point functions. In addition, each QED vertex acquires a momentum dependent phase factor. We parameterize the effects of non-commutative space-time co-ordinates and show that they lead to observable signatures in several $2\to 2$ QED processes in $e^+e^-$ collisions. In particular, we examine pair annihilation, Moller and Bhabha scattering, as well as $\gamma\gamma\to\gamma\gamma$ scattering and show that non-commutative scales of order a TeV can be probed at high energy linear colliders., Comment: 51 pages, 23 figures, typos corrected, figure and references added

The flux of cosmic rays beyond the GZK cutoff ($\sim 10^{20}$ eV) may be explained through their production by ultra high energy cosmic neutrinos, annihilating on the relic neutrino background, in the vicinity of our galaxy. This process is mediated through the production of a $Z$ boson at resonance, and is generally known as the $Z$-Burst mechanism. We show that a similar mechanism can also contribute to the super-GZK spectrum at even higher, ultra-GZK energies, where the particles produced at resonance are the Kaluza-Klein gravitons of weak scale mass and coupling from the Randall-Sundrum (RS) hierarchy model of localized gravity model. We call this mechanism Gravi-Burst. We discuss the parameter space of relevance to Gravi-Bursts, and comment on the possibility of its contribution to the present and future super-GZK cosmic ray data and place bounds on the RS model parameters. Under certain assumptions about the energy spectrum of the primary neutrinos we find that cosmic ray data could be potentially as powerful as the LHC in probing the RS model., Comment: 18 pages, 2 figs, LaTex

There are many low-energy models of supersymmetry breaking parameters which are motivated by theoretical and experimental considerations. Here, we discuss some of the lesser-known theories of low-energy supersymmetry, and outline their phenomenological consequences. In some cases, these theories have more gauge symmetry or particle content than the Minimal Supersymmetric Standard Model. In other cases, the parameters of the Lagrangian are unusual compared to commonly accepted norms (e.g., Wino LSP, heavy gluino LSP, light gluino, etc.). The phenomenology of supersymmetry varies greatly between the different models. Correspondingly, particular aspects of the detectors assume greater or lesser importance. Detection of supersymmetry and the determination of all parameters may well depend upon having the widest possible view of supersymmetry phenomenology., Comment: 78 pages, 49 figures, to appear in the Proceedings of the Tevatron Run II SUSY/Higgs Workshop. Editor: J. F. Gunion; BTMSSM Convenors: M. Chertok, H. Dreiner, G. Landsberg, J. F. Gunion, J.D. Wells

The (g-2) of the muon is well known to be an important model building constraint on theories beyond the Standard Model. In this paper, we examine the contributions to $(g-2)_\mu$ arising in the Randall-Sundrum model of localized gravity for the case where the Standard Model gauge fields and fermions are both in the bulk. Using the current experimental world average measurement for $(g-2)_\mu$, we find that strong constraints can be placed on the mass of the lightest gauge Kaluza-Klein excitation for a narrow part of the allowed range of the assumed universal 5-dimensional fermion mass parameter, $\nu$. However, employing both perturbativity and fine-tuning constraints we find that we can further restrict the allowed range of the parameter $\nu$ to only one fourth of its previous size. The scenario with the SM in the RS bulk is thus tightly constrained, being viable for only a small region of the parameter space., Comment: 16 pages, 2 figs, LaTex, Additional discussion added

The phenomenology of the Randall-Sundrum model of localized gravity is analyzed in detail for the two scenarios where the Standard Model (SM) gauge and matter fields are either confined to a TeV scale 3-brane or may propagate in a slice of five dimensional anti-deSitter space. In the latter instance, we derive the interactions of the graviton, gauge, and fermion Kaluza-Klein (KK) states. The resulting phenomenological signatures are shown to be highly dependent on the value of the 5-dimensional fermion mass and differ substantially from the case where the SM fields lie on the TeV-brane. In both scenarios, we examine the collider signatures for direct production of the graviton and gauge KK towers as well as their induced contributions to precision electroweak observables. These direct and indirect signatures are found to play a complementary role in the exploration of the model parameter space. In the case where the SM field content resides on the TeV-brane, we show that the LHC can probe the full parameter space and hence will either discover or exclude this model if the scale of electroweak physics on the 3-brane is less than 10 TeV. We also show that spontaneous electroweak symmetry breaking of the SM must take place on the TeV-brane., Comment: 62 pages, Latex, 22 figures

We explore the consequences of placing the Standard Model gauge fields in the bulk of the recently proposed localized gravity model of Randall and Sundrum. We find that the Kaluza Klein excitations of these fields are necessarily strongly coupled and we demonstrate that current precision electroweak data constrain the lowest states to lie above $\simeq 23$ TeV. Taking the weak scale to be $\sim 1$ TeV, the resulting implications on the model parameters force the bulk curvature, $R_5$, to be larger than the higher dimensional Planck scale, $M$, violating the consistency of the theory. In turn, to preserve $|R_5|\lsim M^2$, the weak scale must be pushed to $\gsim 100$ TeV. Hence we conclude that it is disfavored to place the Standard Model gauge fields in the bulk of this model as it is presently formulated., Comment: Improved results, 14 pages, Latex file

We explore the phenomenology associated with the recently proposed localized gravity model of Randall and Sundrum where gravity propagates in a 5-dimensional non-factorizable geometry and generates the 4-dimensional weak-Planck scale hierarchy by an exponential function of the compactification radius, called a warp factor. The Kaluza-Klein tower of gravitons which emerge in this scenario have strikingly different properties than in the factorizable case with large extra dimensions. We derive the form of the graviton tower interactions with the Standard Model fields and examine their direct production in Drell-Yan and dijet events at the Tevatron and LHC as well as the KK spectrum line-shape at high-energy linear \epem colliders. In the case where the first KK excitation is observed, we outline the procedure to uniquely determine the parameters of this scenario. We also investigate the effect of KK tower exchanges in contact interaction searches. We find that present experiments can place meaningful constraints on the parameters of this model., Comment: 14 pages, LaTex, 3 figs

We present an outlook for possible discovery of supersymmetry with broken R-parity at Run II of the Tevatron. We first present a review of the literature and an update of the experimental bounds. In turn we then discuss the following processes: 1. Resonant slepton production followed by R-parity violating decay, (a) via $LQD^c$ and (b) via $LLE^c$. 2. How to distinguish resonant slepton production from $Z'$ or $W'$ production. 3. Resonant slepton production followed by the decay to neutralino LSP, which decays via $LQD^c$. 4. Resonant stop production followed by the decay to a chargino, which cascades to the neutralino LSP. 5. Gluino pair production followed by the cascade decay to charm squarks which decay directly via $L_1Q_2D^c_1$. 6. Squark pair production followed by the cascade decay to the neutralino LSP which decays via $L_1Q_2D^c_1$. 7. MSSM pair production followed by the cascade decay to the LSP which decays (a) via $LLE^c$, (b) via $LQD^c$, and (c) via $U^cD^cD^c$, respectively. 8. Top quark and top squark decays in spontaneous R-parity violation., Comment: 39 pages, 51 figures, LaTex, reqires aipproc2.sty and axodraw.sty. To be published in the Physics at Run II Workshop: Supersymmetry/Higgs. Text has been edited by H. Dreiner. Author list on front page has been corrected

A recent suggestion that quantum gravity may become strong near the weak scale has several testable consequences. In addition to probing for the new large (submillimeter) extra dimensions associated with these theories via gravitational experiments, one could search for the Kaluza Klein towers of massive gravitons which are predicted in these models and which can interact with the fields of the Standard Model. Here we examine the indirect effects of these massive gravitons being exchanged in fermion pair production in \epem annihilation and Drell-Yan production at hadron colliders. In the latter case, we examine a novel feature of this theory, which is the contribution of gluon gluon initiated processes to lepton pair production. We find that these processes provide strong bounds, up to several TeV, on the string scale which are essentially independent of the number of extra dimensions. In addition, we analyze the angular distributions for fermion pair production with spin-2 graviton exchanges and demonstrate that they provide a smoking gun signal for low-scale quantum gravity which cannot be mimicked by other new physics scenarios., Comment: Corrected typos, added table and references

The principle components of the Standard Model and the status of their experimental verification are reviewed. Lectures given at TASI97: Supersymmetry, Supergravity, and Supercolliders}, Boulder, CO, June 1997., Comment: 83 pgs

Single $s$-channel production of sleptons, such as $\tilde \tau$'s and/or $\tilde \nu_\tau$, with their subsequent decay into purely leptonic or dijet final states is possible in hadronic collisions via R-parity violating couplings. We examine the impact of slepton production on bump searches in both the Drell-Yan and dijet channels and examine whether the lepton charge asymmetry in the $\ell\nu$ channel provides for additional search sensitivity. As a consequence, search reaches in the slepton mass-R-parity violating coupling plane are obtained for both the Tevatron and LHC. The possibility of using the leptonic angular distributions and the lepton charge asymmetry to distinguish slepton resonances from new gauge bosons is also analyzed., Comment: 5 pages, 9 figures. To appear in the "Proceedings of the XXIX International Conference on High Energy Physics", Vancouver, CA, 23-29 July 1998

The ability of present and future experiments to test the Standard Model in the $B$ meson sector is described. We examine the loop effects of new interactions in flavor changing neutral current $B$ decays and in $Z\to b\bar b$, concentrating on supersymmetry and the left-right symmetric model as specific examples of new physics scenarios. The procedure for performing a global fit to the Wilson coefficients which describe $b\to s$ transitions is outlined, and the results of such a fit from Monte Carlo generated data is compared to the predictions of our two sample new physics scenarios. A fit to the $Zb\bar b$ couplings from present data is also given., Comment: 18 pages, LaTex, Based on presentations given at the Workshop on Physics Beyond the Standard Model: Beyond the Desert: Accelerator and Nonaccelerator Approaches, Tegernsee, Germany, June 8-14, 1997; 20th Anniversary Symposium: Twenty Beautiful Years of Bottom Physics, Chicago, IL, June 29 - July 2, 1997; and the 7th International Symposium on Heavy Flavor Physics, Santa Barbara, CA, July 7-11, 1997

The ability of high energy lepton and photon colliders to probe the gauge couplings of the top-quark is summarized., Comment: 10 pages, LaTex, to appear in the Proceedings of the 2nd International Workshop on e-e- Interactions at TeV Energies, Santa Cruz, CA, 22-24 September 1997

The ability of high energy $e^+e^-$ colliders to indirectly probe the existence of heavy new charged gauge bosons via their exchange in the reaction $e^+e^-\to \nu\bar\nu\gamma$ is investigated. It is shown that examination of the resulting photon energy spectrum with polarized beams can extend the $W'$ search reach above the center of mass energy. [ To appear in the Proceedings of the 1996 DPF/DPB Summer Study on New Directions for High Energy Physics - Snowmass96, Snowmass, CO, 25 June - 12 July 1996.], Comment: 4 pages, LaTex2e

The effects of light, long-lived gluinos on $2\to 2$ processes at hadron colliders are examined. Such particles can mediate single squark resonant production via $q\glu\to\sq\to q\glu$ which would significantly modify the dijet data sample. We find that squark masses in the range $130

Fermion compositeness and other new physics can be signalled by the presence of a strong four-fermion contact interaction. Here we present a study of $\ell\ell qq$ and $\ell\ell\ell'\ell'$ contact interactions using the reactions: $\ell^+ \ell^- \to \ell'^+\ell'^-,b\bar b, c\bar c$ at future $e^+e^-$ linear colliders with $\sqrt s=0.5-5$ TeV and $\mu^+\mu^-$ colliders with $\sqrt s=0.5,4$ TeV. We find that very large compositeness scales can be probed at these machines and that the use of polarized beams can unravel their underlying helicity structure., Comment: 12 pg, to appear in the {\it Proceedings of the 1996 DPF/DPB Summer Study on New Directions for High Energy Physics - Snowmass96}, Snowmass, CO, 25 June - 12 July, 1996

We determine the ability of future experiments to observe supersymmetric contributions to the rare decays $B \to X_s \gamma$ and $B \to X_s l^+l^-$. A global fit to the Wilson coefficients which contribute to these decays is performed from Monte Carlo generated data. This fit is then compared to supersymmetric predictions for several different patterns of the superpartner spectrum., Comment: Talk given at the 28th International Conference on High Energy Physics, Warsaw, Poland, July 1996

We summarize the indirect effects of new physics in a variety of processes. We consider precision electroweak measurements, the $g-2$ of the muon, rare decays, meson mixing, CP violation, lepton number violating interactions, double beta decay, and the electric dipole moments of atoms, molecules, and the neutron. We include discussions of both model independent and dependent analyses where applicable., Comment: 100 pgs + 27 figures (not included here). Complete postscript file available on SLAC-SPIRES web pages. To appear in {\it Electroweak Symmetry Breaking and Beyond the Standard Model}, ed. T. Barklow, S. Dawson, H. Haber, and S. Siegrist

Signals for new, non-supersymmetric physics at hadron colliders are reviewed. We focus on extended gauge sectors and new matter particles. {Presented at the {\it 10th Topical Workshop on Proton-Antiproton Collider Physics}, Batavia, IL, 9-13 May, 1995}}, Comment: 11 pages, uuencoded postscript file

Rare $B$ decays provide an opportunity to probe for new physics beyond the Standard Model. In this paper, we propose to measure the tau polarization in the inclusive decay $B\to X_s\tau^+\tau^-$ and discuss how it can be used, in conjunction with other observables, to completely determine the parameters of the flavor-changing low-energy effective Hamiltonian. Both the Standard Model and several new physics scenarios are examined. This process has a large enough branching fraction, $\sim {\rm few}\times 10^{-7}$, such that sufficient statistics will be provided by the B-Factories currently under construction., Comment: 11 pages, LaTex file with psfig. Figures included via uufiles. Lengthened version. Includes new calculation of Monte Carlo fit to Wilson coefficients

We consider the prospect of using the charm system as a laboratory for probing new physics. The theoretical expectations for rare charm meson decays, $D^0-bar D^0$ mixing, and charm quark asymmetries in $Z$ decays are examined in the Standard Model. The effects of new physics from several classes of non-standard dynamical models are summarized for these phenomena. {Presented at {\it Lafex International School on High Energy Physics (LISHEP95)}, Rio de Janeiro, Brazil, February 6-22, 1995}, Comment: 13 pages, LaTex file with worldsci and psfig. Figures included via uufiles

Constraints placed on physics beyond the Standard Model from the recent CLEO observation of the inclusive decay $B\to X_s\gamma$ are summarized. Further searches for new physics using the process $B\to X_s\ell^+\ell^-$ are discussed. {Presented at the {\it International Workshop on B Physics: Physics Beyond the Standard Model at the B Factory}, Nagoya, Japan, October 26-28, 1994}, Comment: 7 pages, LaTex file with worldsci and psfig. Figures included via uufiles

We examine the indirect effects of new physics on a variety of processes in the $B$ system, such as the $Z\to b\bar b$ vertex, the decays $B\to X_s \gamma$ and $B\to X_s\ell^+\ell^-$, and CP violation. {Presented at the 4th International Conference on Physics Beyond the Standard Model, Lake Tahoe, CA, December 13-18, 1994}, Comment: 11 pages, LaTex file with worldsci and psfig. Figures included via uufiles

The charm physics program accessible to a Tau-Charm Factory is summarized. Semileptonic, leptonic, hadronic, rare and forbidden charm decay modes are discussed, as well as \dmix\ mixing and CP violation in the charm sector. The theoretical expectations in the Standard Model and beyond as well as the experimental capabilities of a Tau-Charm Factory are examined for each of the above processes. {To appear in {\it The Tau-Charm Factory in the Era of B-Factories and CESR}, Stanford, CA, August 15-16, 1994}, Comment: 21 pg + 6 figures (available from author by request), latex (uses worldsci.sty), SLAC-PUB-6695

The possibility of using the charm system to search for new physics is addressed. Phenomena such as $D^0-\bar D^0$ mixing and rare decays of charmed mesons are first examined in the Standard Model to test our present understanding and to serve as benchmarks for signals from new sources. The effects of new physics from various classes of non-standard dynamical models on $D^0-\bar D^0$ mixing are investigated., Comment: 5 pg (Presented at DPF'94, Albuquerque, NM, August, 1994), SLAC-PUB-6674

The radiative decay b to s gamma is examined in the Standard Model and in nine classes of models which contain physics beyond the Standard Model. The constraints which may be placed on these models from the recent results of the CLEO Collaboration on both inclusive and exclusive radiative $B$ decays is summarized. Reasonable bounds are found for the parameters in some cases., Comment: 21 pages (LaTex, figures obtainable by request), SLAC-PUB-6521

We explore the production of vector leptoquarks ($V$) at the Tevatron, LHC, and SSC through both quark-antiquark and gluon fusion: $q \bar q, gg \to VV$. The cross sections are found to be somewhat larger than for scalar leptoquarks of the same mass implying enhanced search capabilities. Contributed to the Workshop on Physics at Current Accelerators and the Supercollider, Argonne National Lab, June 1993., Comment: 8 pg (including 5 figures, available by request to hewett@anlhep), ANL-HEP-CP-93-52, UH-511-775-93, SCIPP-93/36

We explore the possibility that $Z'$ couplings can be probed using decay modes which involve neutrinos once Standard Model backgrounds are directly determined by the data itself. For some models, sufficient statistics are available at either the SSC or LHC to render these modes useful for coupling determinations, provided the mass of the $Z'$ is not much larger than 1 TeV, if we assume other new physics background sources are absent., Comment: 8 pages (including 3 figures, available by request), LaTex, contributed to the Workshop on Physics at Current Accelerators and the Supercollider, Argonne, IL, June 1993, ANL-HEP-CP-93-51

Signatures of extended gauge models at high energy \epem\ linear colliders are summarized. Talk presented at the Workshop on Physics and Experiments with Linear \epem\ Colliders, Waikoloa, Hawaii, April 1993., Comment: 24 pages (figures + text, figures available by request), LaTex, ANL-HEP-CP-93-68

Possible anomalous couplings of the top-quark to on-shell photons and gluons are constrained by the recent results of the CLEO Collaboration on both inclusive and exclusive radiative $B$ decays. We find that the process \bsg\ can lead to reasonable bounds on both the anomalous electric and magnetic dipole moments of the top-quark, while essentially no limits are obtained on the corresponding chromoelectric and chromomagnetic moments, which enter the expression for the decay rate only through operator mixing., Comment: 10 pages plus 6 figures (available by request), LaTex, ANL-HEP-PR-93-37

We present the bounds that can be obtained on the charged Higgs sector in two-Higgs-Doublet Models from measurements at LEP of the decay $B\to D\tau\nu$, and from searches by CLEO for the inclusive decay $b\to s\gamma$., Comment: 4 pages (+ 3 figures, available by request), LaTex, ANL-HEP-CP-92-125, Presented at the 1992 Meeting of the DPF, Fermilab, November 1992

We study the effects of virtual leptoquark exchange on charged current and neutral current processes at HERA, on di-lepton production at the Tevatron, and on quark pair production at LEP II. We present the areas of parameter space that can be excluded at these colliders by searching for deviations from Standard Model expectations., Comment: 4 pages (+ 2 figures, available by request), LaTex, Presented at the 1992 Meeting of the DPF, Fermilab, November 1992, ANL-HEP-CP-92-126

We show that the present limit from CLEO on the inclusive decay $b\to s\gamma$ provides strong constraints on the parameters of the charged Higgs sector in two-Higgs-Doublet-Models. Only a slight improvement in the experimental bound will exclude the region in the Supersymmetric Higgs parameter space which is inaccessible to collider searches., Comment: 8 pages plus 3 figures (available by request), latex, ANL-HEP-PR-92-110. Substantial revision to text, results unchanged

We investigate the possibility of a multi-Higgs doublet model where the lightest neutral Higgs boson ($h^0$) decouples from the fermion sector. We are partially motivated by the four $\ell^+\ell^-\gamma\gamma$ events with $M_{\gamma\gamma}\simeq60$\,GeV recently observed by the L3 collaboration, which could be a signal for $Z\to (Z^*\to \ell^+\ell^-)+(h^0\to \gamma\gamma)$. Collider signatures for the additional physical Higgs bosons present in such models are discussed., Comment: 8 pages (plus 2 figures, available by request), latex, ANL-HEP-PR-92-102

We examine how the abilities of an SDC-like detector to discover and identify the origin of a new neutral gauge boson are affected by $Z_1-Z_2 $ mixing and by variations in detector parameters such as lepton pair mass resolution, particle identification efficiency, and rapidity coverage. Also examined is the sensitivity of these results to variations in structure function uncertainties and uncertainties in the machine integrated luminosity. Such considerations are of importance when dealing with the issues of detector descoping and design., Comment: 17 pages, 4 figures (available by request), phyzzx, ANL-HEP-PR-92-34

We examine the possibility of using rare, 3-body decays of a new neutral gauge boson, \ztwo, to probe its gauge couplings at hadron colliders. Specifically, we study the decays $\ztwo\to W\ell\nu$ and $\ztwo\to Z\nu\bar\nu$ and find that much knowledge of the \ztwo\ properties can be obtained from these processes. In particular, these decay modes can yield valuable information on the amount of $Z_1-Z_2$ mixing, on the generation dependence of the \ztwo\ couplings, on the properties of the new generator associated with the \ztwo, as well as being used to distinguish between possible extended models. The analogous 3-body decays into a new, heavy charged gauge boson, $\ztwo\to W_2^\pm\ell^\mp\nu$, are also investigated in models where this can occur., Comment: 23 pages, 9 figures (available by request), phyzzx, ANL-HEP-PR-92-33, revised version (expanded reference list)

We study the effects of virtual leptoquarks on charged current and neutral current processes at the $ep$ collider HERA. We present the areas of parameter space that can be excluded at HERA by searching for deviations from Standard Model expectations. The best results are obtained by examining the ratio of neutral current to charged current cross sections, $R=\sigma_{NC}/\sigma_{CC}$, where, with $200\inpb$ of integrated luminosity for unpolarized $e^-$ and $e^+$ beams, HERA can search for leptoquarks with masses up to $\sim 800\gev$, with leptoquark coupling strengths of order $\alpha_{em}$., Comment: 14 pages, 6 figures (not included)