Vincenzo Cirigliano

Jens Erler

Krishna S. Kumar

Michael J. Ramsey-Musolf

Program Coordinator:
Inge Dolan
(206) 685-4286


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Low Energy Precision Electroweak Physics in the LHC Era

September 22 - December 5, 2008

The purpose of this workshop is to review the status of and explore future directions in the searches for physics beyond the Standard Model that are complementary to direct signatures of new physics to be probed at the Large Hadron Collider (LHC). Our aim is to comprehensively span the full range of accessible energy scales for such searches, from table experiments to accelerator-based measurements. In the process, the workshop will address the interplay of nuclear physics with both atomic and high-energy physics.

One important thrust will be those precision electroweak measurements and related theoretical issues that are directly correlated to potential new physics signatures in the LHC data. The complementarity between precision observables (both at the energy frontier and at lower energies) and discovery searches enters through the diagnostic power of the network of precision data as opposed to a single measurement. Breakthrough discoveries at the LHC can be better understood and subsequently the parameter spaces of the favored new physics models constrained.

Another important focus will be to explore opportunities for measurements sensitive to new physics signatures that cannot be accessed by high energy colliders. While the overriding theme of the workshop is to explore the experimental and theoretical issues relevant to precision electroweak measurements, we would address wherever appropriate those atomic, hadronic, nuclear physics and experimental issues that are relevant to making further progress on indirect searches for multi-TeV scale physics.

We have broken down this broad thrust along seven categories:

  1. Precision Electroweak Measurements at the LHC: The LHC data should allow greatly improved measurements of the W boson and top quark masses. In addition, the forward-backward asymmetries for e and final states will provide an independent, precise determination of the weak mixing angle, which may conceivably be competitive with the current world average. We anticipate the discussion at our workshop to focus on the theoretical and experimental issues in performing these measurements (reliable input parton distribution functions (PDFs) will be vital) and interpreting the results (one needs to control the hadronic vacuum polarization contribution below the percent level).

  2. Parity Violating Electron Scattering: The precision determination of semi-leptonic and purely-leptonic low energy weak neutral current coupling constants will continue to play an important role in constraining models of new TeV scale physics. Parity-violating electron scattering (PVES) has emerged as a precision tool to measure these coupling constants, from which precision measurements of the weak mixing angle can be extracted. We anticipate the discussion to focus mostly on future PVES measurements with the 12 GeV upgrade of JLab and their impact not only in testing the standard electroweak theory (and constraining its extensions) but also in addressing long-standing issues in nucleon structure via precision deep-inelastic scattering studies.

  3. Muon Physics: High precision muon physics offers rich opportunities to detect new physics in the LHC era through: (i) the search for SM forbidden observables, such as e , 3e, e conversion in nuclei, which probe the flavor structure of new physics at the TeV scale and the muon electric dipole moment, which probes the CP properties of new physics; (ii) the search for deviations from the SM expectation in the precision measurement of SM-allowed observables, such as the Michel parameters and the muon anomalous magnetic moment. In both classes (i) and (ii) there are several ongoing experimental programs. The workshop will offer the opportunity to summarize current results, analyze their implications and motivate additional experimental efforts.

  4. Semileptonic Weak Decays: Thanks to recent experimental and theoretical progress, semileptonic weak decays involving light quarks (u,d,s) are beginning to probe the virtual contribution of (sub-)TeV scale particles appearing in SM extensions (that are also accessible at the LHC). We anticipate the discussion of beta decays to focus on: (i) Testing the quark-lepton universality of the weak interactions at the 10-3 level through improved determination of the CKM quark-mixing matrix elements Vud and Vus. While experimental issues are rapidly being settled, several open issues remain to be settled on the theoretical side. (ii) High sensitivity searches of non V-A couplings and T-violation through T-odd correlations in beta decays of polarized neutrons and nuclei.

  5. CP Violation and EDM searches: The search for new CP-violating physics has important implications for cosmology, including the presently unexplained baryon asymmetry of the universe. Searches for permanent electric dipole moments (EDMs) of leptons, hadrons, and atoms provide powerful probes of new CP violating phases and strongly complement the new particle searches that will occur at the LHC. There exist a variety of deep theoretical issues involving the interpretation of EDM searches and their connection with cosmology. Discussion at the workshop will include obtaining reliable computations of EDMs for many-body systems, delineating the complementary information from various EDM and collider searches, and pursuing robust baryogenesis computations, for which EDMs provide crucial phenomenological input.

  6. Neutrino Scattering: We plan to have a review of ongoing and planned measurements of the MSN matrix in the neutrino sector, with the dual aim of: a) addressing the possibility of a parasitic, competitive measurement of the weak mixing angle in anti-neutrino electron scattering; b) address the impact of complementary measurements of the nucleon axial form factor via detailed measurements of neutrino-nucleon scattering (that are necessary to understand neutrino oscillation backgrounds).

  7. Atomic Parity Violation (APV): The semi-leptonic weak neutral current couplings are accessible not only in PVES but also in APV experiments. The electroweak and new physics entering APV is conveniently summarized in the weak charges of heavy elements. Currently, cesium has the most precisely known weak charge, obtained from a single isotope APV measurement. The workshop will host discussions on future directions, which include: (i) much-improved single isotope APV in atoms or ions, where the hardest issue is the atomic theory in complex many electron systems. (ii) The possibility to address ratios of the weak charges of isotopes in which the atomic physics largely drops out.