Dear Jon, Dear Colleagues,
Here are the long-promised questions from the Energy Frontier
conveners to the other Frontiers. Thank you for your patience.
Best wishes,
Michael Peskin and Chip Brock
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Questions from the Energy Frontier group to other Frontiers:
EF-IF: It is especially interesting in studies of rare processes for a discovery of a new physics effect beyond the Standard Model to point to a mass scale that would be the basis for a future accelerator search for new particles. What are the most important rare processes that have the potential to point to a specific mass scale, and how specific can their information be?
EF-IF: Describe the increase in sensitivity to new particles in loops as a function of time for the g-2, mu-e conversion, tau -> ell gamma, and EDM experiments. There should be separate estimates for SUSY models, in which the flavor-changing effects come from loops, and from models in which the flavor-change comes from a tree-level effective operator. This will facilitate plotting this evolution along with the evolution in sensitivity predicted for direct searches for new particles at the LHC.
EF-IF: Describe the increase in sensitivity to new particles in loops as a function of time coming from improved measurements of b->s gamma, B and Bs -> mu mu, and related observables. There should be separate estimates for SUSY models, in which the flavor-changing effects come from loops, and from models in which the flavor-change comes from a tree-level effective operator. This will facilitate plotting this evolution along with the evolution in sensitivity predicted for direct searches for new particles at the LHC.
EF-IF: What is the impact of higher precision measurements processes that determine the CKM angles, such as sin 2beta, sin 2 beta_s, and V_{ub}. Is it realistic that tensions between these parameters can be sufficiently strong to signal the presence of new physics?
EF-IF: What is the impact of measurements of direct CP violation in charm decay on the search for new physics? In what processes is the Standard Model prediction sufficiently well understood, including perturbative and nonperturbative effects, to allow a strong conclusion of a deviation from the Standard Model?
EF-IF: Improvements in the muon g-2 meausurement need to be accompanied with improvements in the Standard Model prediction for the term involving the hadronic vacuum polarization. What are the prospects for improvement of the current estimate? To reach the parts per billion level in the error, the contribution from light-by-light scattering must also be improved with input from low-energy data. How can this be done?
EF-IF: The best current limits on the electron EDM come from experiments using polar molecules such as YbF in which atomic physics effects enhance the influence of an electron EDM. How can we check or calibrate the atomic physics calculations that go into the interpretation of these experiments?
EF-IF: With a grand unification scale at 10^16 GeV as predicted by SUSY-GUTs, the lifetime of the proton to K nu is naively expected to be below 10^33 yr. What are we testing as we push the limits to 10^35 yr ? What are the crucial parameters of GUTs that allow the proton lifetime to be longer? Is the sensitivity to these parameters quartic, as for m_GUT, or, more optimistically, quadratic ? Is the expectation for the proton lifetime increased if superpartner masses are heavier than expected, and what is the relation between these quantities?
EF-IF: Imagine that one measures the CP violating phase in the neutrino sector to be 85 degrees (for example). What does this imply for the hypothesis that the matter-anti-matter asymmetry is due to leptogenesis? What is the next measurement that one should make to clarify this relation?
EF-InstF: High luminosity running at a hadron collider will depend on efficient triggering in a difficult environment. Isolation requirements will likely be compromised, and, as a result, triggering on leptons may need to depend heavily on tracking. What are the most promising enabling technologies for electron/photon/tau triggers in this environment, considering luminosities up to 10^{35} cm^{-2}s^{-1}? What are likely R&D paths to realizing these technologies?
EF-InstF: In the context of proposals of large tunnels that could host both pp and e+e- colliders, it is interesting to ask whether it is possible to design 4 pi detectors that can be used both for pp and e+e- experiments (perhaps with some interchangable inner tracking layers). Is there an optimal design of such a multi-purpose detector? What are the most important compromises required?
EF-InstF: In a hadron collider environment, the ability to recognized displaced vertices and to trigger on them at level 1 would be a transformative technology. Can this be realized?
EF-InstF: In some studies for ILC and CLIC, the sophistication of particle flow calorimetry approaches the ability to resolve single hadrons. At what point does the evolution of particle flow calorimetry give a qualitative, rather than just a quantitative, boost to experimental capabilities? Can we realistically reach this point?
EF-Computing: To what extent is high-energy physics still generating the world's largest randomly-accessed databases? Can we claim to be a world leader in data science? Along what dimensions?
EF-Computing: Our ability to collaborate globally and to use global resources is limited by rates of transfer of large data sets. What are the limits, and how are these expected to evolve?
EF-Computing: Proposed very high statistics experiments at the Z resonance require large rates -- many kHz -- at which data is written to storage. What are the limits?
EF-CF: If dark matter has no SM interactions stronger than gravitational, are there any prospects for discovering its particle nature?
EF-CF: If the dark matter particle is detected through non-collider experiments, what can we learn about its properties? (e.g., can we learn its spin?) Would we be able to learn whether it interacts with SM matter only through the "Higgs portal"?
EF-CF: Suppose there is a 10 GeV WIMP or a 100 GeV WIMP with direct detection cross section just below current limits. This is the best case for understanding the particle nature of the dark matter. What is the full set of measurements that we are likely to make on such a particle from Cosmic Frontier probes alone?
EF-CF: If there is more than one type of dark matter particle, how can we discover this in Cosmic Frontier experiments? Can we measure the dark matter fraction from different sources?
EF-CF: In indirect detection of dark matter, it is notoriously difficult to rule out all hypotheses that a signal is of astrophysical origin. But perhaps other knowledge from particle physics can help. Would it be helpful, for example, to know the mass of a dark matter candidate? What accuracy is needed? Can direct detection provide sufficient accuracy?
EF-CF: For a long time, there have been indications that the number of light degrees of freedom required in cosmology is greater than 3. However, recent measurements from the CMB and other sources have given more precise information on this question. What are the prospects for establishing that this number of degrees of freedom is indeed greater than 3, or, alternatively, for providing an upper bound well below 4?
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Michael E. Peskin [log in to unmask]
HEP Theory Group, MS 81 -------
SLAC National Accelerator Lab. phone: 1-(650)-926-3250
2575 Sand Hill Road fax: 1-(650)-926-2525
Menlo Park, CA 94025 USA www.slac.stanford.edu/~mpeskin/
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