International Journal of Modern Physics A

Based on the easy availability of highly polarized electron beams, we revisit the need for an early realization of a TeV electron-electron collider. Most EWSB searches can be performed in unique ways at this facility, and the tunable "exotic" quantum numbers of the e^-e^- initial states can be used as powerful probes for a vairety of forays beyond the Standard Model. There are no accelerator. interaction region, or detector issues that would not compatibly function in the e⁺e^- and e^-e^- configurations.

I argue that it would be crucial to have as many channels as possible to understand the physics of electroweak symmetry breaking (EWSB) in next-generation collider experiments. A historic example of the parity violation and the V-A interaction is used to make this point. An e^-e^- option offers us a new channel in this respect. The usefulness of this channel is exemplified for the case of supersymmetry and of the strongly coupled EWSB sector.

Parity violating left–right scattering asymmetries at future high energy e⁺e^- and e^-e^- colliders are examined. The utility of two polarized beams for precision measurements is pointed out. Sensitivity to "new" short–distance physics is briefly discussed. Electroweak radiative corrections due to the running of sin²θ_W·(q²) are exhibited.

In this talk I summarize the capability of future lepton colliders to indirectly discover a new Z′ and to determine its couplings to the fermions of the Standard Model. The physics associated with sitting on the Z′-pole is also briefly discussed. This analysis is based on the results presented in the Snowmass 1996 New Gauge Boson Working Group report.

We discuss the production of the standard Higgs scalar in the reaction e^-e^-→e^-e^-X mediated by ZZ or γγ fusion. It provides even sensitivity for a wide band of scalar masses .

The theoretical structure of the Higgs sector of the Minimal Supersymmetric Standard Model (MSSM) is briefly described. An outline of Higgs phenomenology at future lepton colliders is presented, and some opportunities for probing the physics of the MSSM Higgs sector at an e^-e^- collider are considered.

I review extended Higgs sectors and constraints thereon arising from ρ=1, gauge-coupling unification and b→sγ. The couplings and decays of the Higgs boson eigen-states are outlined for triplet representations. Direct experimental probes of exotic Higgs bosons are reviewed with a focus on the important role that would be played by an e^-e^- or μ^-μ^- collider.

I present the basic formulae for slepton production in e⁺e^- and e^-e^- collisions in an especially simple form, using a helicity basis. This parametrization introduces the useful neutralino functions to connect the neutralino eigenstates to observable cross sections.

The effect of CP-odd supersymmetric phases on slepton pair production are considered. It is shown that CP-even observables in e⁺e^- and e^-e^- collisions, such as the total selectron cross section, can depend on CP-odd supersymmetric phases through interference between different tree level amplitudes. Left handed selectron pair production in e^-e^- collisions is particularly sensitive to the relative phase between the bino and wino masses. This sensitivity is not limited to any kinematic regime and extends over all of neutralino parameter space. The relative phase between the bino and wino masses is a renormalization group invariant at one-loop, and therefore provides a clean probe for operators which violate gaugino universality at the messenger scale.

Advantages of the e^-e^- option at linear colliders for the study of supersymmetry are highlighted. The fermion number violating process provides unique opportunities for studies of slepton masses and flavor mixings. In particular, slepton mass measurements at the 100 MeV level through threshold scans of scalar pair production may be possible. Such measurements are over an order of magnitude better than those possible in e⁺e^- mode, require far less integrated luminosity, and may lead to precise, model-independent measurements of tan β. Implications for studying gauginos and the importance of accurate beam polarimetry are also discussed.

Measurements of supersymmetric particle couplings provide important verification of supersymmetry. If some of the superpartners are at the multi-TeV scale, they will escape direct detection at planned future colliders. However, such particles induce nondecoupling corrections in processes involving the accessible superparticles through violations of the supersymmetric equivalence between gauge boson and gaugino couplings. These violations are analogous to the oblique corrections in the electroweak sector of the Standard Model, and can be parametrized in terms of super-oblique parameters. The e^-e^- collision mode of a future linear collider is shown to be an excellent environment for such high precision measurements of these SUSY parameters, which will provide an important probe of superparticles beyond reachable energies.

We study the possible experimental signatures resulting from a strongly-interacting electroweak sector at e^-e^- colliders, emphasizing the signal enhancement by high beam polarization. We also discuss the unique role for operating the collider in e^-γ mode to produce a heavy isosinglet vector state ω_T.

Theoretical background for bileptonic gauge bosons is reviewed, both the SU(15) GUT model and the 3-3-1 model. Then the mass limits for bileptons are discussed coming from e⁺e^- scattering, polarized muon decay and muonium-antimuonium conversion. A consequence of precision electroweak data on the masses is mentioned. Discovery in e^-e^- at a linear collider is emphasised.

In this talk I summarize the capability of future lepton colliders to discover leptoquarks and to determine their electroweak quantum numbers. This analysis is an updated discussion based on the results presented in the Snowmass 1996 New Phenomena Working Group report as well as some more recent work that has appeared in the literature as a result of the HERA high-Q² excess.

We discuss the process e^-e^-→W^-W^- mediated by heavy Majorana neutrino exchange in the t- and u channel. In our model the cross section for this reaction is a function of the masses (m_N) of the heavy Majorana neutrinos and mixing parameters (U_eN) originating from mixing between the ordinary left-handed standard model neutrinos and additional singlet right-handed neutrino fields. Taking into account the standard model background and constraints from low energy measurements, we present discovery limits in the plane. We also discuss how to measure in principle the CP violating phases, i.e., the relative phases between the mixing parameters.

The trouble with neutrinoless doble beta decay is not its non-observation up to the present time: the trouble is caused by the misinterpretation of this negative result. We show that the existence of heavy Majorana neutrinos in the TeV mass range is not precluded by present evidence.

The ability of high energy lepton and photon colliders to probe the gauge couplings of the top-quark is summarized.

Linear colliders offer a unique possibility to study γγ and γe interactions at the energies 0.1–2 TeV. This option is now included in design reports of NLC, JLC and TESLA/SBLC. This paper includes: status of photon colliders, new possibilities in study of Higgs boson, ways to achieve high luminosities.

The feasibility of a measurement of the partial decay width of the intermediate-mass Higgs boson(M_H=120 GeV) into two photons at a photon-photon collider is studied by a simulation. It is found that the two-photon decay width can be measured with the statistical error of 7.6% with the integrated luminosity of 10fb^-1. We also discussed a possibility toward further improvement with sophisticated b-quark tagging technique.

The advent of a next linear e^±e^- collider and back-scatterd laser beams will allow the study of a vast array of high energy processes of the Standard Model through the fusion of real and virtual photons and other gauge bosons. As examples, I discuss virtual photon scattering γ*γ*→X in the region dominated by BFKL hard Pomeron exchange and report the predicted cross sections at present and future e^±e^- colliders. I also discuss exclusive γγ reactions in QCD as a measure of hadron distribution amplitudes and a new method for measuring the anomalous magnetic and quadrupole moments of the W and Z gauge bosons to high precision in polarized electron-photon collisions.

TESLA is one of the projects for a next generation TeV linear collider. Emphasis is on e⁺e^--Physics at an initial center of mass energy of 500 GeV and a luminosity above 5·10³³cm^-2s^-1. Different to other approaches, TESLA has chosen superconducting acceleration structures operated at 1.3 GHz. In this report, the TESLA project is briefly described and some aspects of a possible e^-e^--mode are discussed.

In this paper, we discuss some operational aspects of electron-electron collisions at the Next Linear Collider (NLC) and estimate the luminosity attainable in such a machine. We also consider the use of two future technologies which could simplify the operation and improve the luminosity in an e^-e^- collider: polarized rf guns and plasma lenses.

The joint ECFA/DESY Study "Physics and Detectors for a Linear Collider" has worked out a proposal for a detector for a next generation TeV e⁺e^- linear collider. In this report, the principle design and layout of the proposed detector with emphasis on the TESLA version is reviewed. Examples of reference reactions studied to demonstrate the detector performance are given.

Background sources at a 1 TeV Linear Collider are discussed along with ideas on how to limit their effect on the detector. With modest shielding and an adequate solenoidal field, we find that detector backgrounds are minimal and that the experimental environment should be similar to that which one normally associates with e⁺e^- colliders.

Effects that limit the luminosities of a general purpose linear collider or GLC capable of , and incident channels are discussed together with potential mitigations. The relative characteristics of such channels and their luminosities are predicted based on differing assumptions – including those for the current configurations for the NLC at and 1.0 TeV. Disadvantages related to the increased complexity of linear colliders can be offset by broader design constraints that seek to optimize the generalized luminosity. Decreased disruptions and bunch charges are effective and can be used in combination with feasable charge compensation schemes to predict higher luminosities and power conversion efficiencies. The incremental costs of additional channels is modest compared to the cost of any one by itself or potential gains in the integrated luminosity.

In this paper, we discuss practical issues that must be addressed to reconfigure an e⁺e^- linear collider for e^-e^-operation and argue that modest steps should be taken during the design stage to preserve this operation.

Disruption effects in e^-e^- collisions at a future linear collider affect the attainable luminosity; the angular spread of the disrupted beam particles may present a background in a detector. In this paper, I present simulations of the beam-beam interaction with the simulation code CAIN of relevance for these questions.

The SLC operates with electron beams having a polarization of ~ 80%. The physics opportunities for future colliders will be greatly enhanced if the beam polarization can be significantly higher. The prospects for achieving electron single-beam polarizations > 95% are discussed. A complimentary achievement would be to use two-beam polarization.

An electron beam polarization of 80% or greater will be a key feature of a 1 TeV Linear Collider. Accurate measurements of the beam polarization will therefore be needed. We discuss design considerations and capabilities for a Compton-scattering polarimeter located in the extraction line from the Interaction Point. Polarization measurements with 1% accuracy taken parasitic to collision data look feasible, but detailed simulations are needed. Polarimeter design issues are similar for both electron-positron and electron-electron collider modes, though beam disruption creates more difficulties for the electron-electron mode.

A 3-km long high-gradient W-band switched matrix linac may, in parallel channels, accelerate multiple electron and positron bunches to an energy of 2.5 TeV, with a tight control on the intra-bunch energy spread. In this report, we describe a final-focus system for such an accelerator, whose length is restrained by eliminating chromatic correction. The interaction point (IP) spot size is limited by synchrotron radiation in the last quadrupole (Oide effect). The energy loss due to beamstrahlung is optionally suppressed by combining bunches of opposite charge and colliding the neutral beams. We present two different high-luminosity multiple-collision schemes, which can provide a luminosity of up to 10³⁵cm^-2s^-1, with only about 1 MW average beam power. In the first scheme, batches of equally-charged bunches are combined into superbunches which, possibly after charge compensation, are collided head-on with the opposing beam. In the second scheme, 25 charge-neutral electron-positron bunch pairs of one beam are each collided with 25 neutral bunch pairs of the other beam. These multiplexed collisions are facilitated by a crossing angle and by crab cavities upstream of the electron-positron combiner; however they also require focusing channels (e.g., a crystal) preserving IP beam size between the collision points, a difficult if not impossible construct. We describe the challenges posed by each approach.