International Journal of Modern Physics A

The first physics run of the superconducting Tevatron Collider at Fermilab ended this morning. I will present a status report on the progress of the small angle elastic scattering and total cross section experiment, E710. The goals of this experiment are to measure the total proton-antiproton cross section from √s=300 to 2000 GeV, the slope of the diffraction peak and ρ, the ratio of the real to imaginary part of the forward scattering amplitude, at these energies.

The decays W → eν, Z → e⁺e^- have been studied using the UA2 detector at the CERN Collider. Measurements of the Standard Model parameters from a sample of 251 W decays and 39 Z decays are compared with expectations of the Standard Electroweak Model. An upper limit on the number of light neutrino species is deduced from the cross — section ratio σ(W → eν)/σ(Z → e⁺e^-). A signal of the hadronic decay mode, , is observed above the background of QCD produced di-jets.

The TRISTAN e⁺e⁻ collider came into operation in the last October. The first beam collision was confirmed with the VENUS detector on November 19, '86. Then we have observed 56 Bhabha events and 16 hadronic events for the integrated luminosity of 93 nb⁻¹ at . R-value obtained by a preliminary quick analysis is 5.7±1.6. Here we report the present status and the results of the VENUS experiment.

The experimental status of mixing is reviewed. The ARGUS experiment has recently reported evidence for substantial mixing in the system. UA1 has also reported evidence for mixing, but this cannot be unambiguously interpreted to yield a measurement of the amount of mixing in the system. The CLEO, Mk. II, and JADE experiments have all reported upper limits, and the MAC experiment a lower limit, which are compatible with the ARGUS and UA1 results.

Bhabha scattering and multi-hadronic e⁺e⁻ annihilation events have been observed in the AMY detector at √s=500 GeV at the TRISTAN e⁺e⁻ storage ring. Here we report the results of a preliminary analysis of the properties of these events. Of particular note is one event that contains a high energy, isolated gamma ray together with a large amount of missing momentum that penetrates the fiducial volume of the detector.

We survey recent developments in techniques for searching for the Standard Model Higgs boson. We also discuss theories that go beyond the Standard Model, and illustrate the extent to which Higgs search strategies must be altered, with respect to the Standard Model approaches, in order to probe the associated Higgs sectors.

Various issues pertaining to the search for the high mass Higgs boson (m_H~800 GeV) in the purely leptonic decays of Z pairs are studied. In addition, the usability of a high luminosity SSC (L= 10³⁴/(cm²−s)) in this context is assessed.

Requirements for detecting H→Z⁰Z⁰→ℓ⁺ℓ⁻ℓ⁺ℓ⁻ at the SSC with m_H=800GeV are explored. It is found a luminosity of 10³⁴cm⁻²sec⁻¹ is needed but that the detector can have only a fast electromagnetic calorimeter plus a muon detector. Such a detector should be feasible at the required luminosity.

The observability of the heavy Higgs boson (m_H>2m_W) through pure leptonic decays of Z pairs from Higgs and continuum processes is studied. A bump hunt in m_ZZ is possible for m_H<600 GeV. For mH > 600 GeV, precise knowledge of the background rate is essential. The following is a progress report of the Heavy Higgs Working Group for the July 1987 Workshop on Experiments, Detectors and Experimental Areas for the Supercollider to be held in Berkeley, CA.

It is shown that for intermediate Higgs masses, in the range 0.3– 0.6 TeV, the contribution σ_T of the transversely polarized gauge bosons (V) to the process qq→qqVV→qqH, in the leading log (LL) Equivalent Vector Boson Approximation (EVBA) is comparable to the contribution σ_L of the longitudinal ones. As a result the LL EVBA for σ=σ_L+σ_T overestimates the exact total cross-section by ~100–200 % at the q₁q₂ centre of mass energies of interest for SSC; viz. 5–10 TeV. An improved formulation of the EVBA leads to modified vector boson densities. These densities lead to an EVBA estimate, including the transverse contributions, which agrees with the exact calculation, for m_H as low as 0.3 TeV, within 20–30 % upto quark energies ~5–10 TeV.

We give explicit formulas for the decays of the Higgs bosons of the minimal supersymmetric model to neutralinos and charginos. The important features of these decays are illustrated and their phenomenological implications discussed. When phase space allowed, this class of two-body decays is at least as important as, and often dominates, other types of Higgs decay modes, such as WW or ZZ and heavy fermion anti-fermion channels.

We examine the possibility of finding charged Higgs bosons (H^±) at the SSC. The charged Higgs boson is produced with a top quark via a gluon+bottom quark interaction (g+b→H+t). For the two Higgs doublet models, H^± decays predominantly into t+b. Since the background from QCD processes will be very severe for this decay mode, we studied the H^±→τ+ν decay mode. Even for this mode, background from the processes pp→W+t+spectators→ℓ+ν_ℓ+t+spectators will be very high. In the two Higgs doublet models, it is very difficult to extract the charged Higgs signal for reasonable values of the ratio of the two vacuum expectation values (tan β=v₁/v₂).

We calculate the joint production of W^± and top quarks via the leading order diagrams and bg→Wt. Although the latter contribution is O(α_s) we find it to be sizeable and to subtract from the leading order . The calculations are of interest as they represent the dominant background in the search of charged Higgs particles in the minimal SUSY model. With this in mind we also present results for the p_T distribution of the top and the dilepton invariant mass resulting from leptonic decay of both particles in the Wt final state.

The system of interacting Higgs and longitudinal gauge bosons, when the Higgs mass M_H varies above 1 TeV, is studied using dispersion relations (N/D method). Models satisfying unitarity and analyticity constraints are constructed and solved exactly. For M_H≲0.6 TeV the dispersive and perturbative (tree level) amplitudes are similar. For M_H≳1.5 TeV, however, they much differ in structure. For M_H≃1.5, in ZZ→ZZ the dispersive amplitudes exceed the perturbative ones by factors 2~4. There are indications of strong interaction effects: In HH→HH there is an ℓ=0 bound state, which can be taken as the Higgs itself; in fact, for M_H≃2.5 there is an almost self-consistent solution with respect to the mass, and very roughly with respect to the coupling. There is also some indication of a resonance in ZZ→ZZ, as well as in HH→HH.

We examine the allowed mass range of the charged Higgs field H⁺ in a minimal left-right symmetric model. We find that the mass of this Higgs is nearly degenerate with the mass of the flavor-changing neutral Higgs, and this implies M_H+≳5~10 TeV. We examine a number of solutions, but fail to evade this restriction. If this constraint can not be avoided, the H⁺ (and very likely all other left-right extended Higgs particles) would be virtually undetectable at all experimental facilities, including the SSC.

A summary is given of the results obtained by the Superstring working group. New physics phenomena arising from superstring models that might be detected at the SSC as well as their possible backgrounds were investigated. Topics examined were models with extra Z bosons and right handed W bosons, detection of Winos, Zinos and gluinos and production of heavy squarkonium.

The prospect for the detection of supersymmetry from the trileptonic signal arising from the final state in PP collisions at SSC is examined. The most severe background arises from the leptonic modes coming from final state decays. In addition a new phenomenon emerges at SSC energies in that normally hadronically quiet events are associated with considerable background hard jet activity. Cuts are proposed to drastically reduce the background. Preliminary estimates indicate that the supersymmetric trileptonic signal should be detectable for Wino mass up to 80 GeV over a wide range of the t-quark mass.

We study the production of heavy bound states of squarks at the SSC and analyse their decays into longitudinal W’s and Z’s. In some situations a squarkonium state can be detected through its decay into a pair of W’s.

It is shown that, for a wide range of parameters, the dominant decays of gluinos with mass ≳500 GeV contain gauge bosons, W^± and Z, among their decay products. The pair production of heavy gluinos at the SSC is thus characterized by events with 3–4 hard jets and pairs of gauge bosons. The cleanest signature comes from the case where both gluinos decay into Z followed by which leads to ~50–100 4-lepton + multijet events annually at the SSC. In addition, 1600 trilepton + multijet and about 6000 dilepton + multijet events may be expected from WZ and WW sources. The backgrounds to these signals are estimated to be small.

We give explicit formulas for the decays of the neutralinos and charginos of the minimal model of supersymmetry into other neutralinos and charginos plus a W, Z, or Higgs boson. The important features of these decays are illustrated and their phenomenological implications discussed. In general, this class of two-body decays is dominant for the heaviest charginos and neutralinos.

We consider the production of an extra U(1) gauge boson (Z₂) (at the SSC) and its decay to a pair of zinos. The subsequent decays of these zinos will give rise to four charged leptons with high p_t, and will be an interesting signal for supersymmetry.

We report on the decays of a heavy neutral gauge boson Z₂ into W⁺W⁻, the Z and a Higgs boson, or two Higgs bosons in superstring-inspired electroweak models with an extra U(1) gauge group, two Higgs doublets and a Higgs singlet. The branching ratios for these processes are generally similar and two boson decay modes of Z₂ must exist at the few percent level if kinematically accessible, although the bosonic modes which dominate in any given scenario depend on the U(1) quantum numbers and mixing in the Higgs sector.

We investigate the signatures of leptoquarks or diquarks of the rank 5 E₆ superstring model produced in and pp machines. Leptoquark decays are characterized by lack of e, μ universality and diquark decays by quark flavor non-conservation (e.g., ). If the top quark is heavier than one of the scalar superpartners , then it may decay dominantly by two body modes (e.g., or ), invalidating the usual signatures. Two body gluino decays may swamp its conventional signatures.

We examine the possibility that heavy lepton pair production can be significantly enhanced by the existence of a new neutral gauge boson, Z’, at SSC energies. We find that in some models, the heavy lepton production cross section resulting from this mechanism exceeds that from production via other scenarios.

We consider the phenomenological implications for the Superconducting Super Collider of a new supersymmetric left-right symmetric model, motivated by E₆ compactification in superstring theories.

This is a summary report of the working group on Heavy Flavors. Discussions at the workshop were centered on B physics and on the signals for heavy quarks and leptons at the SSC. The Working Group Members were: V. Barger, H.-U. Bengtsson, C. Buchanan, I. Bigi, M. Block, B. Cox, N. Glover, J. Hewett, W.Y. Keung, B. Margolis, T. Rizzo, M. Suzuki, A. Soni, D. Stork, and S. Willenbrock.

We note that the combination of a vertex detector with a J/Ψ trigger should enable one to measure the masses and lifetimes of various beauty baryons and heavy beauty mesons at the SSC or Tevatron II.

A simple technique for selecting top quark events and reconstructing the quark mass is given for 100<M_t<200 GeV. Using a charged lepton with large p_T to trigger the event, simple attempts to reconstruct the quark mass from jets indicate that the quark mass may be measured to O(10%).

Decays of fourth generation t′-quarkonium states are examined. Although b′-quarkonium decays are hard to see, the η_t′→γγ decay is enhanced by a factor of 16 relative to the η_b′→γγ decay. Provided the fourth generation quark mass splitting is small, O(few GeV), the decay η_t′→γγ leads to a rate of two photon events that is observable above the continuum background in high luminosity pp collisions at for M_t′<O(250 GeV).

Four topics related to horizontal symmetries and composite models are discussed: a model of horizontal interactions avoiding FCNC constraints, the production of scalar leptoquarks, production and decay of excited quarks, and the sensitivity of pp colliders for measuring the ZWW vertex in ZW production.

Composite models generally predict the existence of excited quark and lepton states. We consider the production and experimental signatures of excited quarks Q* of spin and isospin 1/2 at hadron colliders and estimate the background for those channels which are most promising for Q* identification. Multi-TeVpp-colliders will give access to such particles with masses up to several TeV.

We examine the single and pair production of scalar leptoquarks (S) in pp and collisions. The signals and backgrounds for leptoquark production are discussed. We find that the discovery limits for pair production are M_S≃40 GeV at the CERN collider, 120 GeV at the Tevatron, and 1.7 TeV at the proposed SSC. The limits in the case of single S production are found to be model dependent.

A brief overview of signatures at hadron colliders to be expected from horizontal symmetries, gauge as well as global, is given. Several other exotic possibilities and their possible signatures at hadron colliders are also considered. In particular; leptoquarks, stable leptons or quarks with funny charges, color excitation with integer charged unconfined quarks are discussed.

We present production cross-sections for additional gauge bosons W′ and Z′ of Sp_L(6)×U(1) Gauge Group at the SSC.

Following a brief survey of nongauge interactions of composite W and Z from a theoretical viewpoint, we point out some of conspicuous signatures of compositeness at supercolliders, in particular, W^γ and Z^γ productions through by interactions of dimension six. In these processes, a suppression factor 1/Λ² due to compositeness scale Λ is largely compensated by longitudinal polarizations of W and Z, allowing us to probe up to high values of Λ.

A model is presented in which quarks and leptons are composites of three spin-½ preons and a scalar preon. The model is an extension of the rishon model and consists of two spin-½ preons T, V and a scalar preon S as the fundamental building blocks of matter. Assuming distinguishability of states due to the order assigned to the preons in forming the quark and lepton states, the concepts of flavour, colour and generation number acquire meaning only at the level of compositeness. The model predicts four generations of conventional quarks and leptons.

For three generations of fermions, Sp_L(6)×U_Y(1) is proposed as the flavor gauge group which unifies the electroweak and horizontal interactions. The existence of another set of light (~ 1 TeV), left-handed weak bosons is suggested.

The status of Monte Carlo and other perturbative QCD calculations for signals and backgrounds in hadronic collisions is reviewed, and possibilities for improvements are discussed.

Some non-trivial features of the QCD-improved parton model relevant to applications on heavy particle production and semi-hard (small-x) processes of interest to collider physics are reviewed. The underlying ideas are illustrated by a simple example. Limitations of the naive parton formula as well as first order corrections and subtractions to it are dis-cussed in a quantitative way. The behavior of parton distribution functions at small x and for heavy quarks are discussed. Recent work on possible impact of unconventional small-x behavior of the parton distributions on small-x physics at SSC and Tevatron are summarized. The Drell-Yan process is found to be particularly sensitive to the small x dependence of parton distributions. Measurements of this process at the Tevatron can provide powerful constraints on the expected rates of semi-hard processes at the SSC.

The problem of incorporating exact 2→3 QCD cross sections into Monte Carlo models for hadron-hadron scattering is examined, and a simple, branching weight formalism which retains all the information of the 2→3 processes is presented. The connection of this prescription with the angle-ordered soft gluon results of Ellis, Marchesini and Webber is explored in detail. Possible unresolved questions for the procedure are also noted.

We examine the integrated rates and differential cross-sections for b-quark pair production and Drell-Yan processes at the SSC and the Tevatron colliders, and we determine their sensitivity to a range of possible small x behaviors for the parton distribution functions (PDF’s). We find that both the integrated rates and the differential distributions for the Drell-Yan process are very sensitive to the unknown small x behavior of the PDF’s; whereas, only the integrated rates can distinguish various input PDF’s in the b-pair production process. Experiments at the Tevatron can provide very useful information on small x physics if these two processes, especially Drell-Yan, can be measured.

The way to evaluate multi-parton cross-sections systematically is discussed. In the leading-double-log approximation in QCD, the successive emission of soft gluons is at successively smaller angles. The angular ordering, however, is violated in the next-to-leading order.

The author, a novice user of the CERN detector simulation package GEANT¹⁾, offers a very brief summary of some of the strengths and weaknesses the program, along with some indications of what must be done to implement a useful detector simulation for the SSC energy scale.