Artist's view of a Higgs event at ILC

Detector & Physics in Zeuthen for a Linear Collider

Physics > Electroweak studies

Electroweak studies

ILD event

High precision studies of electroweak processes offer a window to physics at higher energy scales than the one available at the ILC. The sensitivity to the new physics comes either via higher order loop corrections that are usually suppressed by the coupling constant or the new processes contribute directly to the process under study, but because of the high mass of the new particles they are suppressed by s/M2, where s is the squared centre of mass energy and M the mass of the new particles.

Mainly three types of processes were studied in this context:

To all three points significant contributions to the TESLA TDR and ILC RDR have been produced in Zeuthen. Special emphazis was put to studies which exploit the posibility of polarized beams.

Studies of W-pair production in electron-positron and photon-photon collisions

In case that no light Higgs exists electroweak interactions amongst gauge bosons become strong at the TeV scale, eventually violating unitarity. In this case deviations from the Standard Model predictions in W-pair productions should be visible at ILC. In the figure above a simulated e+e-→ννWW→ννqqqq event in the ILD is shown.

Studies of the properties of the Z-boson, running close to the peak of the Z-resonance (Giga-Z).

The usefulness of these studies has already been proven at LEP and SLD. From measurements of the decay rates of the Z and the effective weak mixing angle already in 1993 the mass of the top quark could be predicted with high accuracy, prior to its discovery at the TEVATRON. At present these data make us believe that the Higgs boson is light and in the reach of ILC. ILC offers the possibility to increase the LEP statistics by two orders of magnitude with polarised electron and positron beams. With this data sample the weak mixing angle could be measured a factor 10 better than now. Depending on the scenario of electroweak symmetry breaking, realised in nature, with this precision parameters of supersymmetric theories can be constrained or a non-standard Higgs sector can be tested.

Precision measurement of fermion pair production at high energies.

Away from the Z-resonance interactions mediated by new heavy particles are suppressed by a factor s/M2. Effects of these particles may be seen if the precision of the cross sections and distributions of fermion pairs is high enough. Possible effects of additional heavy Z-bosons or different types of models containing extra space dimensions have been studied. In all cases ILC is sensitive to mass scales of several TeV, often higher than the LHC, presently being built at CERN. However, since the LHC measures masses of the new particles directly while ILC measures the couplings of the new particles to fermion divided by the mass of the new particles only the combination of ILC and LHC can establish the model of new physics once deviations from the Standard Model predictions are found.