Luminosity spectrum reconstruction at linear colliders

A good knowledge of the luminosity spectrum is mandatory for many measurements at future $\mathrm {e}^{+}\mathrm {e}^{-}$ colliders. As the beam-parameters determining the luminosity spectrum cannot be measured precisely, the luminosity spectrum has to be measured through a gauge process with the detector. The measured distributions, used to reconstruct the spectrum, depend on Initial State Radiation, cross-section, and Final State Radiation. To extract the basic luminosity spectrum, a parametric model of the luminosity spectrum is created, in this case the spectrum at the 3 TeV compact linear collider. The model is used within a reweighting technique to extract the luminosity spectrum from measured Bhabha event observables, taking all relevant effects into account. The centre-of-mass energy spectrum is reconstructed within 5 % over the full validity range of the model. The reconstructed spectrum does not result in a significant bias or systematic uncertainty in the exemplary physics benchmark process of smuon pair production.     

Monte Carlo generator photon jets used for luminosity at e+e- colliders

A Monte-Carlo Generator Photon Jets(MCGPJ)to simulate Bhabha scattering as well as produc-tion of two charged muons and two photons events is discussed.The theoretical precision of the cross sections with radiative corrections(RC)is estimated to be smaller than 0.2%.The Next Leading Order(NLO)radia-tive corrections proportional to α are treated exactly,whereas the all logarithmically enhanced contributions,related to photon jets emitted in the collinear region,are taken into account in frame of the Structure Function approach.Numerous tests of the MCGPJ as well as a detailed comparison with other MC generators are presented.     

Supersymmetric left-right model and its tests in linear colliders

We investigate phenomenological implications of a supersymmetric left-right model based on SU(2)_L × SU(2)_R × U(1)_B–L gauge symmetry testable in the next generation linear colliders. We concentrate in particular on the doubly charged SU(2)_R triplet higgsino , which we find very suitable for experimental search. We estimate its production rate in e⁺e⁻, e⁻e⁻, e⁻γ and γγ collisions and consider its subsequent decays. These processes have a clear discovery signature with a very low background from other processes.     

Novel final focus design for future linear colliders

The length, complexity, and cost of the present final focus designs for linear colliders grow very quickly with the beam energy. In this Letter, a novel final focus system is presented and compared with the one proposed for the Next Linear Collider (NLC Zeroth-Order Design Report, edited by T. O. Raubenheimer, SLAC Report No. 474, 1996). This new design has fewer optical elements and is much shorter, nonetheless achieving better chromatic properties. Moreover, the new system is more suitable for operation over a larger energy range.     

Virtual effects of split-SUSY in Higgs productions at linear colliders

In split supersymmetry, gauginos and higgsinos are the only supersymmetric particles possibly accessible at foreseeable colliders like the CERN Large Hadron Collider (LHC) and the International Linear Collider (ILC). In order to account for the cosmic dark matter measured by WMAP, these gauginos and higgsinos are stringently constrained and could be explored at the colliders through their direct productions and/or virtual effects in some processes. The clean environment and high luminosity of the ILC render the virtual effects at percent level meaningful in unraveling the new physics effects. In this work we assume split supersymmetry and calculate the virtual effects of the WMAP-allowed gauginos and higgsinos in the Higgs productions e⁺e^-→Zh and e⁺e^-→ν_eν̄_eh through WW fusion at the ILC. We find that the production cross section of e⁺e^-→Zh can be altered by a few percent in some part of the WMAP-allowed parameter space, while the correction to the WW fusion process e⁺e^-→ν_eν̄_eh is below 1%. Such virtual effects are correlated with the cross sections of chargino pair productions and can offer complementary information in probing split supersymmetry at the colliders. PACS 14.80.Ly; 95.35.+d     

Effects of new neutral currents at linear electron-positron colliders

Effects that are induced by contact four-fermion interactions in the processes e ⁺ e ^? → μ ⁺ μ ^?, $\bar bb$ , and $\bar cc$ at $\sqrt s = 0.5$ TeV linear electron-positron colliders are investigated for the case of longitudinally polarized initial beams. This analysis employs new integrated observables constructed from the polarized cross sections for the scattering of final fermions into the forward (σ _F) and the backward (σ _B) hemisphere in such a way that they single out the helicity cross sections for the processes in question. This property of the observables makes it possible to perform, in the most general form, a model-independent analysis of contact four-fermion interactions and to set constraints on their parameters. It is also shown that the sensitivity of new polarization observables to contact interactions is noticeably higher than the corresponding sensitivity of canonical observables like σ, A _FB, A _LR, and A _LR,FB.     

Heavy flavor production at high energyep colliders

The total production rates for heavy quark pairs due to gauge boson fusion processes at high energyep colliders are evaluated. At HERA,b \(\bar t\) production dominates overt \(\bar t\) production form _t ≧60 GeV and is observable up tom _t ?80(90)GeV where the number of expectedb \(\bar t\) events is about 15(10) for ∝L=200pb^?1. Including the contributions fromep→WX→btX the total number of expectedbt events amounts to about 50 events form _t ?80GeV. The influence of thresholds for heavy quark pair production is also studied for the relevant structure functionsF _i (x,Q ²) and shown to contribute to the measured scaling violations. All these effects are sensitive to the heavy quark massesand to the shape of the gluon distribution which can thus be tested experimentally by analyzing heavy quark pair signals.     

Testing Higgs self-couplings at e^+e^- linear colliders

To establish the Higgs mechanism sui generis experimentally, the self-energy potential of the Higgs field must be reconstructed. This task requires the measurement of the trilinear and quadrilinear self-couplings, as predicted, for instance, in the Standard Model or in supersymmetric theories. The couplings can be probed in multiple Higgs production at high-luminosity linear colliders. Complementing earlier studies to develop a coherent picture of the trilinear couplings, we have analyzed the production of pairs of neutral Higgs bosons in all relevant channels of double Higgs-strahlung, associated multiple Higgs production and WW/ZZ fusion to Higgs pairs. Received: 3 March 1999 / Published online: 15 July 1999     

Radiated energy loss due to beamstrahlung in high-energy electron-positron linear colliders

We studyT-odd andCP-odd triple momentum correlations in exclusive semi-leptonic charm meson decaysDK ^*(K)lv _l . We define asymmetry ratios that measure the trueCP-violating effects, andT-odd triple momentum correlation effects from unitarity contributions. Possible newCP-violating contributions are parametrized in terms of an effective four-fermion Hamiltonian whereCP-violating effects should come from new non-standard sources. A detailed analysis of the left-right model and the Weinberg Higgs-boson model ofCP-violation is carried out.Supported by Bundesministerium für Forschung und Technologie (BMFT), FRG     

Cone electrostatic energy analyser of high luminosity

It is proved that the conical electrostatic potential Φ=−ln(tg(γ/2)) is the only axisymmetric Laplace potential which depends only on γ—the angular coordinate of the cylindrical coordinate system (z,r,γ). It is also shown that, thanks to the meridional beam broadening which is inherent in Φ, the analyser based on such a potential can have a resolution several times better than that of the well-known 42.3° cylindrical mirror analyser (CMA), their luminocities being equal. The main electron-optical parameters of the hypothetical analysers based on the potential Φ are described in detail in the case of the narrow inner field-forming electrode. This case is considered to be interesting in electron spectroscopy practice.     

Vector resonances from a strong electroweak sector at linear colliders

We explore the usefulness of very energetic lineare ⁺ e ^? colliders in the TeV range in studying an alternative scheme of electroweak symmetry breaking based on a strong interacting sector. The calculations are performed within the BESS model which contains new vector resonances. If the massM _V of the new boson multiplet lies not far from the maximum machine energy, or if it is lower, such a resonant contribution would be quite manifest. A result of our analysis is that also virtual effects are important. It appears that annihilation into a fermion pair in such machines, at the considered luminosities, would improve only marginally on existing limits if polarized beams are available and left-right asymmetries are measured. On the other hand, the process ofW-pair production bye ⁺ e ^? annihilation would allow for sensitive tests of the hypothesized strong sector, especially if theW polarizations are reconstructed from their decay distributions, and the more so the higher the energy of the machine. Ane ⁺ e ^? collider with c.m. energy \(\sqrt s = 500\) GeV could improve the limits on the model for the range 500<M _V (GeV)<1000 whenW polarization is not reconstructed. IfW polarizations are reconstructed, then the bounds improve for the entire expected range ofM _V . These bounds become more stringent for larger energy of the collider. We have also studied the detectability of the new resonances through the fusion subprocesses, but this channel does not seem to be interesting even for a collider with a c.m. energy \(\sqrt s = 2\) TeV.