Challenges for FCC-ee luminosity monitor design

For cross section measurements, an accurate knowledge of the integrated luminosity is required. The FCC-ee physics programme at and around the Z pole sets the ambitious precision goal of $$10^{-4}$$ 10 - 4 on the absolute luminosity measurement and one order of magnitude better on the relative measurement between energy scan points. The luminosity is determined from the rate of Bhabha scattering, $$\mathrm {e^+e^- \rightarrow e^+e^-}$$ e + e - → e + e - , where the final state electrons and positrons are detected in dedicated monitors covering small angles from the outgoing beam directions. The constraints on the luminosity monitors are multiple: (i) they are placed inside the main detector volume only about 1 m from the interaction point; (ii) they are centred around the outgoing beam directions and do not satisfy the normal axial detector symmetry; (iii) their coverage is limited by the beam pipe, on the one hand, and by the requirement to stay clear of the main detector acceptance, on the other; (iv) the steep angular dependence of the Bhabha scattering process imposes a precision on the acceptance limits at about 1 $$\upmu $$ μ rad, corresponding to an absolute geometrical precision of $${\mathcal {O}}(1\,\upmu \text {m})$$ O ( 1 μ m ) on the monitor radial dimensions; and v) the very high bunch-crossing rate of 50 MHz during the Z-pole operation calls for fast readout electronics. Inspired by second-generation LEP luminosity monitors, which achieved an experimental precision of $$3.4 \times 10^{-4}$$ 3.4 × 10 - 4 on the absolute luminosity measurement (Abbiendi et al. in Eur Phys J C 14:373–425, 2000), a proposed ultra-compact solution is based on a sandwich of tungsten-silicon layers. A vigorous R&D programme is needed in order to ensure that such a solution satisfies the more challenging FCC-ee requirements.

Constraints on antisymmetric tensor fields from Bhabha scattering

Antisymmetric tensor fields are a compelling prediction of string theory. This makes them an interesting target for particle physics because antisymmetric tensors may couple to electromagnetic dipole moments, thus opening a possible discovery opportunity for string theory. The strongest constraints on electromagnetic dipole couplings would arise from couplings to electrons, where these couplings would contribute to Møller and Bhabha scattering. Previous measurements of Bhabha scattering constrain the couplings to $${\tilde{M}}_e m_C>7.1\times 10^4\,{\mathrm {GeV}}^2$$ M ~ e m C > 7.1 × 10 4 GeV 2 , where $$m_C$$ m C is the mass of the antisymmetric tensor field and $${\tilde{M}}_e$$ M ~ e is an effective mass scale appearing in the electromagnetic dipole coupling.

Study of theoretical luminosity precision for electron colliders at higher energies

We present an estimation of the theoretical precision of low angle Bhabha scattering at the proposed future ILC collider at 500 GeV. The analysis is an extension of the previous analysis done for the FCCee collider at $$\sqrt{s}=M_Z$$ s = M Z . As the state-of-the-art and the reference point we use the Monte Carlo event generator. Based on the current precision status of for LEP analysis, we estimate how various error components evolve from the LEP to ILC setups. The conclusion of our work is that for the ILC the precision of the current version of 4.04 deteriorates to 0.5%, by more than an order of magnitude w.r.t. the present precision for LEP. With the expected future improvements, the precision of can change to 0.016%, nearly as good as for the FCCee at the $$M_Z$$ M Z setup (0.01%). Based on the developed methodology we present also results for ILC$$_{1000}$$ 1000 , FCCee$$_{350}$$ 350 and CLIC$$_{3000}$$ 3000 setups.

Analytic results for two-loop planar master integrals for Bhabha scattering

We analytically evaluate the master integrals for the second type of planar contributions to the massive two-loop Bhabha scattering in QED using differential equations with canonical bases. We obtain results in terms of multiple polylogarithms for all the master integrals but one, for which we derive a compact result in terms of elliptic multiple polylogarithms. As a byproduct, we also provide a compact analytic result in terms of elliptic multiple polylogarithms for an integral belonging to the first family of planar Bhabha integrals, whose computation in terms of polylogarithms was addressed previously in the literature.

Bhabha scattering in very special relativity at finite temperature

In this paper the differential cross section for Bhabha scattering in the very special relativity (VSR) framework is calculated. The main characteristic of the VSR is to modify the gauge invariance. This leads to different types of interactions appearing in a non-local form. In addition, using the Thermo Field Dynamics formalism, thermal corrections for the differential cross section of Bhabha scattering in VSR framework are obtained.

Simulating hard photon production with Whizard

One of the important goals of the proposed future $$\hbox {e}^{+}\hbox {e}^{-}$$e+e- collider experiments is the search for dark matter particles using different experimental approaches. The most general search approach is based on the mono-photon signature, which is expected when production of the invisible final state is accompanied by a hard photon from initial state radiation. Analysis of the energy spectrum and angular distributions of those photons can shed light on the nature of dark matter and its interactions. Therefore, it is crucial to be able to simulate the signal and background samples in a uniform framework, to avoid possible systematic biases. The Whizard program is a flexible tool, which is widely used by $$\hbox {e}^{+}\hbox {e}^{-}$$e+e- collaborations for simulation of many different “new physics” scenarios. We propose the procedure of merging the matrix element calculations with the lepton ISR structure function implemented in Whizard. It allows us to reliably simulate the mono-photon events, including the two main Standard Model background processes: radiative neutrino pair production and radiative Bhabha scattering. We demonstrate that cross sections and kinematic distributions of mono-photon in neutrino pair-production events agree with corresponding predictions of the $$\mathcal{KK}$$KK MC, a Monte Carlo generator providing perturbative predictions for SM and QED processes, which has been widely used in the analysis of LEP data.

Radion Effects on Bhabha Scattering

In this article, we have considered the possible signatures of radion through Bhabha scattering. The numerical results show that the total cross section with radion effects are about 1.43-19.70 pb. This could have important implications for radion searches and for the measurement of the cross-section of the Bhabha scattering.