High-energy photon collisions at the LHC – dream or reality?

Abstract

In this review, we motivate these studies beyond the famous quote from Genesis 1, 3-4, where God said: 'Let there be light,' and there was light. God saw that the light was good, and he separated the light from the darkness. We first discuss the legacy of past photoproduction experiments at LEP and HERA and the gold-plated channels proposed for a photon collider at the ILC. We then present the emerging experimental results from RHIC and the Tevatron and three promising channels at the LHC: exclusive vector-meson production, measurements of possibly anomalous electroweak gauge-boson or top-quark couplings, and slepton production. We close with an outlook on other channels that might be interesting to study further in the future. Photon physics at lepton collidersAt circular lepton accelerators such as LEP and the electron-ring at HERA, spacelike, almost real bremsstrahlung photons are exchanged during the hard collision. At a future ILC, large particle bunch densities are needed to reach high luminosities. Then additional beamstrahlung photons will be created before the hard interaction by the coherent action of the electromagnetic field of one bunch on the opposite one. If the electron beams are collided with additional highenergy laser beams, real photons can be producedWe discuss the potential of high-energy photon collisions at the LHC for improving our understanding of QCD and studying the physics beyond the Standard Model. After reviewing briefly the legacy of past photoproduction experiments at LEP and HERA, we examine the gold-plated channels proposed for a photon collider at the ILC for their potential in a hadron collider environment. We stress that initial-state photon interactions have indeed been observed at RHIC and at the Tevatron. Three promising channels at the LHC are then presented in some detail: exclusive vector-meson production, measurements of possibly anomalous electroweak gauge-boson or top-quark couplings, and slepton production.

Pair production of the T-odd leptons at the LHC

“…Although the contributions of the γγ fusion mechanism to pair production of the T-odd lepton pairs at the LHC are much smaller than those for the Drell-Yan process, for M 200 GeV, its production cross-section can only reach 26.4 fb. However, due to the absence of the proton remnants, this production process has clean experimental conditions and well-defined final states, which can be selected and precisely reconstructed [25]. The SM backgrounds coming from the partonic interactions, such as P P → W + W − , ZZ, and τ τ , can be significantly omitted by using the large rapidity gap technique and the dedicated very forward detectors [26].…”

Pair Production of the Doubly Charged Leptons via Electroweak Vector Boson Fusion at the Large Hadron Collider

“…It is well known that, due to the absence of the proton remants, the 𝛾𝛾 fusion production processes generally have clean experimental conditions and well defined final states, which can be selected and precisely reconstructed. [21] However, the production cross section for the subprocess 𝛾𝛾 → 𝑋 ++ 𝑋 −− is very small, which is smaller than 6 fb in all of the parameter space and is challenging for its detection at the LHC.…”