A report discussing the opportunities for physics discoveries with a future 100 TeV hadron circular collider was presented earlier this summer during the 2016 FCC Week.
A future hadron-hadron collider machine will be able to cover previously unexplored territory at energies never before reached in a laboratory environment. Standard Model calculations will enable precise predictions for known particles and forces in the new frontiers. The comparison of observations against predictions will allow for the structure of the Standard Model to be tested at unprecedented energies and with unparalleled precision.
If observations and predictions agree within estimated uncertainties this would provide a stunning confirmation of the present Standard Model for particle physics, that however leaves a number of questions unanswered including those on the nature of dark matter, the masses of neutrino and the observed matter/antimatter asymmetry. If on the other hand, observations do not agree with theoretical predictions this would mark the need to rethink the physics that might lie beyond the Standard Model while we might observe the rise of new phenomena. In that sense, a 100 TeV collider will push to a more fundamental understanding of the laws of nature and our understanding of how the Universe evolved after the Big Bang.
One of the most fascinating questions is related to the phase transition between unbroken and broken electroweak symmetry that took place during the Big Bang and is responsible for the baryonic asymmetry that we observe in today’s Universe. In the SM, a Higgs boson heavier than 60 GeV is too weak to generate the required asymmetry between matter and antimatter. This means that a 125 GeV Higgs boson like the one discovered at the LHC must also come with other interactions beyond the SM and additional sources of CP violation that are responsible for the observed matter/antimatter asymmetry.
The scale of these phenomena should be within few TeV; not too far from the electroweak breaking scale. Models have been proposed for these new phenomena, but their direct manifestation could escape detection at the LHC, if the masses are too large. The FCC could give a conclusive answer to the question whether the baryon asymmetry was generated at the electroweak phase transition. Likewise it is expected that a collider at 100 TeV could provide conclusive answers to the question of whether the Higgs sector is made of a single Higgs or whether there are other Higgs bosons at the TeV scale, and whether physics at the electroweak scale is responsible for dark matter.
A hadron collider at 100 TeV could allow for precise measurements of the Higgs self-interaction process, whose structure is deeply related to the origin and mass of the Higgs particle itself. Extending the study of the Higgs and its interactions with other particles of the SM to energies well above the TeV scale could provide a way to analyse in detail the mechanism underlying the breaking of the electroweak symmetry. At a more fundamental level the proposal of a 100 TeV proton-proton collider stems from the bold leap into the completely uncharted new territory that it offers, probing energy scales, where fundamental new physical principles might be at play.
The observation of Standard Model processes has an interest per se. Billions of Higgs bosons and trillions of top quarks will be produced, creating new opportunities for the study of rare decays and flavour physics within the SM which tremendously benefit from higher collision energies. The huge rates available at 100 TeV allow to push to new limits the exploration of rare phenomena (e.g. rare decays of top quarks or Higgs boson) the precision in the determination of SM parameters and the test of possible deviations from Standard Model predictions.
Standard Model processes provide a necessary reference to benchmark the performance of the detectors of future experiments both for studying SM processes with higher precision but are also key in searches for new physics. It should be noted however that one should rethink any statements about the precision of theoretical calculations in the time-window for a post-LHC facility.
The leap in energy to 100 TeV gives a huge increase in the reach for new physics that could lie beyond the Standard Model. A seven-fold increase of the centre-of-mass energies relative to the LHC with a luminosity comparable to that of the LHC increases the mass reach for new particles significantly. The possible observables that will be accessible are extensively discussed in the FCC-hh physics report.
The 100 TeV pp collider will significantly extending the energy reach allowing to hunt for new fundamental particles roughly an order of magnitude heavier than what we can possibly produce with the LHC. It may also be the case that particles currently produced at the LHC in small numbers will be produced with up to a thousand times higher rate, giving us a new window into the mechanisms at play in the evolution of our Universe and provide experimental evidence for some of the theoretical developments that try to explain the deficiencies of the Standard Model.
Finally, the FCC-hh collider is also foreseen to be used a heavy-ion collider opening the path to a heavy-ion physics programme at the FCC. The highest energy reach will offer an opportunity to push the exploration of the collective structure of matter at the most extreme density and temperature conditions to new frontiers through the study of heavy-ion collisions.
Though one has to wait for the results of the current run of the LHC, there are reasons to believe that a new description beyond the Standard Model may be required at energies up to 100 TeV and a number of different scenarios are included in the report offering a solid basis for discussing the physics possibilities and opportunities that FCC-hh could open to the international scientific community.
The findings of this report will serve as a reference for future studies and to stimulate new ideas on how to best exploit the immense potential of a future circular collider like the one studied under the FCC-hh scenario. In addition the report will serve as a baseline for the different communities (accelerator design, detector design) involved in the FCC study toward the preparation of a conceptual design report for 2019.
The first Future Circular Collider (FCC) physics workshop will take place at CERN on January 16 through 20, 2017 preceding the 2017 FCC Week that will take place in Berlin from 29 May to 02 June 2016.
The physics workshop focuses on the broad physics opportunities offered by the FCC study. All sessions will be plenary, with an emphasis on the complementarity of the different components of the programme (ee, hh and eh). Original ideas and contributions on alternative experimental approaches in the global context of the FCC – also including physics with beam dumps and the injector complex, and physics in the forward region – are strongly encouraged. Please register at the workshop website.