LISTSERV 16.5 - SNOWMASS-EF Archives

hi everyone,

As you can imagine, we're fighting length and nuance. We apologize if we went too far in shortening and then going below what you suggested as the threshold for the VLHC. We've gone back and forth about calling out the muon collider explicitly, and decided against it but we've tried to come up with an approach to take Cecilia's valid concerns into account.

My personal concern is that there is always an overall fascination with higher energy. Remember, I have been a proponent and lost that battle years ago. But I would hate for Snowmass to appear to have suddenly fallen in love over 9 days with this old flame at the expense of really important and hair-on-fire programs that we already cannot support. And I don't think that's where you guys are. So it's tricky rhetorical spot, right? We've tried to take into account comments that have come in from Liantao, Meena, Rick, Graham, Ashutosh, Tom, Markus, and Ron. Here is where it stands now.

We have to complete this and Michael and I will try to talk about 8pm EDT this evening. So please have your (final?) reactions to us by about 6pm EDT?

thanks

Michael and Chip

Here we go:

Energy Frontier. The mysteries of the newly discovered Higgs boson were a major theme at Snowmass. The properties of the Higgs boson raise crucial questions that guide large parts of the future particle physics program. Indeed, this discovery changes everything. It calls for a three-pronged research program at high energy accelerators: first, to determine the properties of the Higgs boson as accurately as possible, second, to make precise measurements of the heavy particles $W$, $Z$, and the top quark, which can carry the imprint of the Higgs field; and, third, to search for new particles predicted by models of the Higgs boson and electroweak symmetry breaking. These questions also drive experiments in other frontiers. The expectation of TeV scale particles directly motivates the search for WIMP Dark Matter and flavor changing rare decays.

For at least the next fifteen years, the experiments at the Large Hadron Collider at CERN will drive the Energy Frontier program forward. The Higgs boson discovery at the LHC now becomes a precision study of the properties of this particle. The high-luminosity LHC will measure Higgs boson couplings at the few-percent level and provide the first measurement of the Higgs self-coupling. The steps of the LHC to 300 fb$^{-1}$ and then to 3000 fb$^{-1} will explore deeply for new particles produced through either the strong or the electroweak interactions. They will probe for new dynamics of $W$, $Z$, and Higgs at TeV energies and study rare decays using a sample of billions of top quarks. The LHC experiments have already proven their ability to work as global collaborations. US contributions to the leadership, detector and accelerator components, technology, and physics insight have played indispensable roles.

There is compelling scientific motivation for continuing this program with lepton colliders. Experiments at these accelerators can reach sub-percent precision in the Higgs boson properties in a unique, model-independent way, enabling discovery of percent-level deviations predicted in theoretical models. They can improve the precision of our knowledge of the $W$, $Z$, and top properties by an order of magnitude, allowing the discovery of predicted new physics effects. They search for new particles with unequivocal discovery or exclusion, complementing new particle searches at the LHC. A global effort has now completed the technical design of the International Linear Collider (ILC) accelerator and detectors that will provide these capabilities. The Japanese high energy physics community has named this facility as its first priority.

The Snowmass study considered many other options for high-energy colliders that might be realized over a longer term. These included higher energy linear colliders, circular e+e- colliders, muon colliders, and photon colliders and all merit continued study. The Snowmass study called out in particular the potential of a 100 TeV hadron collider. While higher energy per se is always an advantage, this threshold seems to reach benchmarks suggested by questions about dark matter and naturalness. Our conclusions call for renewed accelerator R&D and physics studies for such a machine over the next decade.

In all of the projects listed above, US leadership in developing experimental and accelerator technology is playing a critical role. These US initiatives are essential to meet the world-wide scientific goals in particle physics.