Search Results (14 total)

It is shown that in reaction γγ→ℓ⁺ℓ^-+ν’s at sqrt[s]>200  GeV with polarized photons, large and well observable differences arise in the distribution of positive and negative charged leptons (ℓ=μ^±, e^±) (charge asymmetry). The modification due to the contribution of the cascade processes with intermediate τ lepton in γγ→W^±ℓ^∓+ν’s reaction is taken into account. This charge asymmetry is potentially sensitive to effects of physics beyond the standard model at the anticipated luminosity of the photon collider mode of the future international linear collider.

We discuss the extrema of the two-Higgs-doublet model with different physical properties. We have found necessary and sufficient conditions for realization of the extrema with different properties as the vacuum state of the model. We found explicit equations for extremum energies via parameters of potential if it has explicitly CP conserving form. These equations allow to pick out extremum with lower energy—vacuum state and to look for change of extrema (phase transitions) with the variation of parameters of potential. Our goal is to find a general picture here to apply it for description of the early Universe.

We use the invariance of a physical picture under a change of Lagrangian, the reparameterization invariance in the space of Lagrangians and its particular case—the rephrasing invariance—for analysis of the two-Higgs-doublet extension of the standard model. We found that some parameters of theory like tan⁡β are reparameterization dependent and therefore cannot be fundamental. We use the Z₂ symmetry of the Lagrangian, which prevents a ϕ₁↔ϕ₂ transition, and the different levels of its violation, soft and hard, to describe the physical content of the model. In general, the broken Z₂ symmetry allows for a CP violation in the physical Higgs sector. We argue that the two-Higgs-doublet model with a soft breaking of Z₂ symmetry is a natural model in the description of electroweak symmetry breaking. To simplify the analysis, we choose among different forms of Lagrangian describing the same physical reality a specific one, in which the vacuum expectation values of both Higgs fields are real. A possible CP violation in the Higgs sector is described by using a two-step procedure with the first step identical to a diagonalization of the mass matrix for CP-even fields in the CP-conserving case. We find a very simple, necessary, and sufficient condition for a CP violation in the Higgs sector. We determine the range of parameters for which CP violation and flavor-changing neutral current effects are naturally small—it corresponds to a small dimensionless mass parameter ν=Rem₁₂²/(2v₁v₂). We show that for small ν some Higgs bosons can be heavy—with mass up to about 0.6 TeV—without violating of the unitarity constraints. If ν is large, all Higgs bosons except one can be arbitrarily heavy. We discuss, in particular, main features of this case, which corresponds for ν→∞ to a decoupling of heavy Higgs bosons. In the model II for Yukawa interactions we obtain the set of relations among the couplings to gauge bosons and to fermions which allows us to analyze different physical situations (including CP violation) in terms of these very couplings, instead of the parameters of Lagrangian.

We obtain tree-level unitarity constraints for the most general Two-Higgs-Doublet Model (2HDM) with explicit CP-violation. We briefly discuss correspondence between possible violation of tree-level unitarity limitation and physical content of the theory.

We describe the status of our effort to realize a first neutrino factory and the progress made in understanding the problems associated with the collection and cooling of muons towards that end. We summarize the physics that can be done with neutrino factories as well as with intense cold beams of muons. The physics potential of muon colliders is reviewed, both as Higgs factories and compact high-energy lepton colliders. The status and time scale of our research and development effort is reviewed as well as the latest designs in cooling channels including the promise of ring coolers in achieving longitudinal and transverse cooling simultaneously. We detail the efforts being made to mount an international cooling experiment to demonstrate the ionization cooling of muons.

If the next generations of heavy quarks and leptons exist within the standard model (SM), they can manifest themselves in Higgs boson production at the Fermilab Tevatron and the CERN LHC, before being actually observed. This generation leads to an increase of the Higgs boson production cross section via gluon fusion at hadron colliders by a factor 6–9. So, the study of this process at the Tevatron and LHC can finally fix the number of generations in the SM. Using the WW^* Higgs boson decay channel, the studies at the upgraded Tevatron will answer the question about the next generation for mass values 135 GeV ≲M_H≲190 GeV. Studying the ττ̅ channel we show its large potential for the study of the Higgs boson at the LHC even in the standard case of three generations. At the Tevatron, studies in this channel could explore the mass range 110–140 GeV.

If a heavy Dirac monopole exists, the light-to-light scattering below the monopole production threshold is enhanced due to the strong coupling of monopoles to photons. At the Next Linear Collider with an electron beam energy of 250 GeV this photon pair production could be observable at monopole masses less than 2.5–6.4 TeV in the e⁺e^- mode or 3.7–10 TeV in the γγ mode, depending on the monopole spin. At the upgraded Fermilab Tevatron such an effect is expected to be visible at monopole masses below 1–2.5 TeV. The strong dependence on the initial photon polarizations allows us to find the monopole spin in experiments at e⁺e^- and γγ colliders. We consider the Zγ production and the 3γ production at e⁺e^- and pp or pp̅ colliders via the same monopole loop. The possibility to discover these processes is significantly lower than that of the γγ case.

The status of the research on muon colliders is discussed and plans are outlined for future theoretical and experimental studies. Besides work on the parameters of a 3–4 and 0.5 TeV center-of-mass (COM) energy collider, many studies are now concentrating on a machine near 0.1 TeV (COM) that could be a factory for the s-channel production of Higgs particles. We discuss the research on the various components in such muon colliders, starting from the proton accelerator needed to generate pions from a heavy-Z target and proceeding through the phase rotation and decay (π→μν_μ) channel, muon cooling, acceleration, storage in a collider ring, and the collider detector. We also present theoretical and experimental R&D plans for the next several years that should lead to a better understanding of the design and feasibility issues for all of the components. This report is an update of the progress on the research and development since the feasibility study of muon colliders presented at the Snowmass '96 Workshop [R. B. Palmer, A. Sessler, and A. Tollestrup, Proceedings of the 1996 DPF/DPB Summer Study on High-Energy Physics (Stanford Linear Accelerator Center, Menlo Park, CA, 1997)].

We discuss the potentialities of the nonstandard interaction study via the Higgs boson production at photon (γγ and eγ) colliders. We estimate the scale of new physics phenomena beyond the SM that can be seen in the experiments with Higgs boson production. In particular, the effect of new heavy particles within the SM is shown to be quite observable.

Dimuonium (the bound system of two muons, the μ⁺μ^--atom system) has not been observed yet. In this paper we discuss the electromagnetic production of dimuonium at RHIC and LHC in relativistic heavy ion collisions. The production of parastates is analyzed in the equivalent photon approximation. For the treatment of orthostates, we develop a three-photon formalism. We determine the production rates at RHIC and LHC with an accuracy of a few percent and discuss problems related to the observation of dimuonium.

If a heavy Dirac monopole exists, the light to light scattering below the monopole production threshold is enhanced due to the strong coupling of monopoles to photons. This effect could be observable in the collision of virtual photons at proton colliders. At the Fermilab Tevatron it will be seen as pair production of photons with energies 200–400 GeV and roughly compensated transverse momenta 100–400 GeV/c. This effect could be seen at monopole masses of about 1–2.5 TeV at the upgraded Tevatron and 7.4–19 TeV at the CERN Large Hadron Collider depending on the monopole spin.

We consider two coupled problems. We study the dependence on the photon virtuality Q² for the semihard quasi-elastic photoproduction of neutral vector mesons on a quark, gluon, or real photon [at s≫p_⊥², Q²; p_⊥²≫μ²≈(0.3 GeV)²]. To this end we calculate the corresponding amplitudes (in an analytical form) in the lowest nontrivial approximation of perturbative QCD. It is shown that the amplitude for the production of a light meson varies very rapidly with the photon virtuality near Q²=0. We estimate the bound of the PQCD validity region for such processes. For a real incident photon the obtained bound for ρ meson production is very high. This bound decreases fast with the increase of Q², and we expect that the virtual photoproduction at DESY HERA will give us the opportunity to test the PQCD results. The signature of this region is discussed. For the hard Compton effect PQCD should work well at not too high p_⊥, and this effect seems measurable at HERA.

The cross sections for processes with the production of Z and pairs of leptons or quarks in the γγ collisions are calculated. They are large enough to give an important background for Higgs boson hunting at future photon colliders if the Higgs boson mass is about 100 GeV and they are small for the production of two Z. The equivalent electron approximation for the polarized photon beams is presented.

We consider radiation caused by the collective electromagnetic field of one beam deflecting particles of the other. We find the number of photons for a single collision is dN_γ≊N₀ dE_γ/E_γ in the energy range E_γ<E_c=4ħcγ²<l, where l is the length of the bunch. At the Superconducting Super Collider, for example, N₀=50 and E_c=6 keV. Specific features of this radiation can be used for a fast control over collisions and for measuring beam parameters. A background due to synchrotron radiation in the magnetic field of a collider is estimated.