So now that the community planning meeting of Snowmass is over, I thought I'd take the chance to highlight one (of the many) interesting topics that came up that could make this Snowmass different than other recent studies - the Energy Frontier(EF)! 1/n

The EF is normally associated with searching for new particles and mega projects like the LHC. A question the field is dealing with is what is next? There's a whole host of great projects ILC, CLIC, FCC-ee, FCC-hh, CEPC, SPPC, etc and some critics even say let's opt for none! 2/n

What I'd like to explore in this thread, is that maybe there will be a new direction coming out of Snowmass!First, where does the cornucopia of existing potential projects come from? Physics drivers of course! The last prioritization of the field "P5" laid out these well 3/n

P5 had a few drivers related to this: Using the Higgs as a tool for discovery, dark matter, and exploring the unknown! This also plays well with how CPM grouped the various projects into Higgs factories, intermediate energy leptons and discovery machines 4/n

However, a lot of these projects are based on realizing the physics potential by scaling up tried and true options the field has been doing for many years. If you want energy build a hadron collider, if you want precision build an electron collider (linear or circular)5/n

Since Snowmass provides input for P5 to prioritize projects, early on I made a figure to emphasize both aspects of R&D and physics potential, since given the enormous timescales and costs involved, both are important for vibrancy of the field/spinoffs/physics results! 6/n

Obviously not everyone is happy with this figure, but it's just meant to be illustrative not the final word, an attempt to get people to think a bit more out of the box! The cool R&D factor matters if we want both young people in our field, and the public to support us! 7/n

I'm a theorist, not an exp or accel physicist,but even in theory because some *perceive* the LHC to have maxed out its potential(not true) and w/o a def future project, many young people have moved to Dark Matter rather than the EF,so it's important to optimize multiple axes. 8/n

Now on top of that figure only having two qualitative not quantitative axes, of course an important missing axis is cost! So why this long preamble?Because what I want to lay out in this thread is that there may be a collider that optimizes it all including physics potential! 9/n

Going back to the physics drivers, using the Higgs is one of the most exciting - despite some people thinking its discovery was the end of the SM(it wasn't). Which is why you hear a lot about Higgs factories as the next step beyond the LHC 10/n

It's also a solid foundation to build on, since it's a particle we know is there. It's harder to argue for exploration for it's own sake when the costs are so large (personally I think it's always a good idea, but I prefer Star Trek to Star Wars-so my take is unsurprising) 11/n

Why is there still a lot to do with the Higgs?Beyond being the most confusing/unique particle of the SM it's also the lynchpin.After LHC there still will be a lot of missing info about how it couples to matter and how it couples to *itself*,i.e. we need to *complete* the SM 12/n

Okay you already said there were Higgs factories so what's your point? Actually to complete the SM we need both precision *and* energy, the low energy Higgs factories only focus on the former-which is why it's normally thought of a 2 collider program e.g. FCC-ee then hh 13/n

Of course the ancillary benefit of needing a separate high energy collider to complete the SM, is it also serves as a discovery machine at the same time! Drawback? Cost. So again what if there was an all in one machine? Enter the high energy lepton colliders! 14/n

A high energy lepton collider can potentially provide a clean environment for precision(unlike hadron colliders), huge Higgs production, and great discovery reach(beyond 100 TeV hadrons) all in one once you get to energies in the 10-30 TeV scale! 15/n

Why don't we hear about them more? Snarky answer, last P5 didn't have a lot of foresight, but tbh a lot has been demonstrated since then. More to the point they're *definitely* not just scaling up what we've done before to get the physics out. 16/n

To get to these high energies for lepton colliders you have two options. With electrons you'd need new acceleration techniques implemented by e.g. plasma Wakefields! The other option is a freaking muon collider! Both super cool and they address that R&D axis from before. 17/n

So there you have it, a collider that optimizes on the physics, R&D, and cost(you only need one collider) all in one. Obvious case right?Well there's still a lot of work to do, but just the chance that it could all work and end the energy/precision dichotomy is pretty cool!18/n

So the last Snowmass we though quite a bit about the 100 TeV hadron colliders and Higgs factories, but maybe there is a new even more exciting direction to explore this time around. We'll see what tech comes to fruition sooner, it looks like muons are closer for now. 19/n

Regardless of the lepton flavor, it would be great to get a concrete proposal out of Snowmass so studies could be compared on similar footing to all the other amazing projects out there for P5. For now I'll just advertise there's lots of recent muon pheno work on the arxiv. 20/n

Including in the not too distant future the muon-smasher's guide captained by Captain Craig @physics_nate and joined by lots of others that I'll share when it makes to the arXiv but for now a picture and spam tags for who I know is on twitter so far ( @isobelo9 @shomiller2 ) 21/n

Okay that's it, high energy lepton colliders in way too many tweets, although there's still more to say.Sometimes bureaucratic field wide exercises can be soul-sapping, but there also can be novel things that come of them, and hopefully this is one of them from last week! 22/n

PS something that was cost effective, required new R&D/tech, and had great physics reach in a smaller footprint sure sounds like a great potential next step for @Fermilab after DUNE @Nigel_Lockyer if not elsewhere...