Co-Conveners: Alexander Valishev (Fermilab), Mark Palmer (BNL), Nadia Pastrone (INFN/Torino) , Jingyu Tang (IHEP)

For the past 50 years Particle Colliders have been at the forefront of scientific discoveries in high energy physics. This working group will focus on potential machine routes, R&D requirements, and possible timelines to deliver colliders that could operate in the 1-100 TeV center-of-mass energy range (or beyond). The topics that we will address include:

• Connections between the physics needs and accelerator types
• Detailed machine requirements to achieve the community's physics goals
• Exploration of the various types of colliders that may play a future role at the energy frontier:
  • Very high energy proton-proton machines
  • Multi-TeV electron-positron machines
  • Muon colliders
  • Other very high energy machine concepts (e.g. gamma-gamma, high energy electron-ion, and others)
• Common issues at the very high energy scale such as energy efficiency and cost

The first two topics above, will be explored in conjunction with the relevant Snowmass 2021 physics working groups. For each of the machine concepts, we are soliciting a set of Letters of Intent from the accelerator community that individually address:

1. The machine concept
2. The R&D needs to deliver a potential future capability
3. The connections of the technology to existing facilities (e.g. to provide potential facility construction and/or R&D pathways)

A more detailed request for these LOIs will be circulated shortly after the APS April Meeting 2020. A schedule for both joint meetings and AF4 discussions will also be developed at that point.

Many relevant publications can be found at: https://www.nature.com/collections/cajfiddcee , https://www.nature.com/collections/heigibehfc, https://arxiv.org/abs/1910.11775

Here is the list of submitted LOIs to this topic. First index before “/” corresponds to the primary frontier used for the submission.