Speaker
Description
A gravity-aligned vertical electron-positron linear collider is proposed as a concept to break the cost-and-scale impasse that confronts conventional horizontal Higgs factories [KEK Preprint 2026-16, arXiv:2607.24179]. The accelerating axis is oriented along the local gravitational field inside a single deep vertical shaft with a depth of ~3 km. Positrons are injected downward from the surface while electrons are accelerated upward from the bottom, the two beams meeting at an interaction point located deep underground. Targeting a staged center-of-mass energy in the Higgs factory range (250 - 500 GeV), this concept assumes high-gradient, high-efficiency, normal-conducting accelerating structures operated at cryogenic temperature together with a two-beam power-delivery scheme. It can be designed to reuse the existing KEK/SuperKEKB accelerator complex in the KEK Tsukuba Campus. We discuss the advantages of the vertical orientation, namely a small surface footprint, intrinsic azimuthal symmetry of the gravity load, deep vibration isolation of the collision point, a natural vertical alignment reference, a cosmically quiet deep interaction point, a unique opportunity and value in social/industrial evaluation, as well as the principal disadvantages and challenges, including the required high accelerating gradient and the construction of a kilometers-deep shaft. This presentation is deliberately concept-level and is intended to motivate technological innovation and feasibility studies.