Experimental study of the reactionse+e−→

M. Derrick

¹

,

K. K. Gan

²

,

P. Kooijman

³

et al.

Abstract

This paper reports measurements of the differential cross sections for the reactions e+e -+e+e {Bhabha scattering) and e e~yy {y-pair production). The reactions are studied at a center-ofmass energy of 29 GCV aud in the polar-angular region I cos8 I & 0.55. A direct cross-section comparison between these two reactions provides a sensitive test of the predictions of quantum electrodynamics (QED) to order n . When the ratio of y-pair to Bhabha experimental cross sections, integrated over I cose I &0.55, is divided by the same ratio predicted from n QED theory, the result is 1.007+0.009%0.008. The 95%-confidence limits on the QED-cutoff parameters are A+ y 154 GeV and A~220 GeV for Bhabha scattering, and A+ g 59 GeV and A~59 GeV for y-pair production.

Testing Lorentz-symmetry violation via electroweak decays

“…In the SM electroweak processes are generally harder to detect than pure electromagnetic ones due to the presence of inverse powers of the large mass of the mediating bosons in the scattering amplitudes. In well-measured processes, such as Bhabha scattering [14,15], QED effects are responsible for the leading contributions, whereas electroweak effects amount to only a few percent at energies already close to the Z pole [16]. Since at low energies W -and Z-mediated processes are strongly suppressed relative to photon-mediated ones, we are going to focus on purely electroweak interactions.…”

Lorentz violation bounds on Bhabha scattering

“…Our choice to study Bhabha scattering was motivated, in addition to the questions outlined in the introduction, by practical reasons, i.e, the experimental data on precision tests for this kind of scattering in QED are readily available in Ref. [30]. In the experiment reported in that paper, the measurements of the differential cross sections for e + e − → e + e − and e + e − → γγ scatterings were evaluated at a center-ofmass energy of 29 GeV and in the polar-angular region |cos θ| < 0.55.…”

“…Moreover, Bhabha scattering is one of the most fundamental reactions in QED processes and has been extensively studied in colliders [27][28][29]. It is particularly important since it is used to determine the luminosity of the e + e − collisions [30,31]. This fact motivated us to evaluate and analise the behavior of the differential cross section for Bhabha scattering in the presence of nonminimal couplings and to directly obtain upper bounds on LV coefficients.…”

Lorentz Violation, Möller Scattering, and Finite Temperature

“…The dependence of the cross section on the secondorder Lorentz-violating parameters has been obtained also in other scatterings, such as Bhabha scattering and pair annihilation in the presence of a CPT-odd nonminimal coupling [18,19] and electron-positron scattering with nonminimal CPTeven coupling term [20]. Good upper bounds for Lorentzviolating parameters have been obtained using experimental data from [36].…”

“…In addition, the result obtained here may be compared with the nonrelativistic result; see (36). Let us consider the following comparisons: (i) = 0 and ̸ = 0-in this case, there are corrections due to temperature effects that become relevant in the high temperature limit since the estimates defined in (34) become large.…”