neutron electric dipole moment; active magnetic field compensation
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The search for electric dipole moments (EDM) of fundamental systems presents a very promising route for finding new physics beyond the Standard Model (SM) of particle physics. A permanent electric dipole moment violates parity and time reversal symmetries and, invoking the CPT theorem, also CP symmetry. New sources of CP violation are expected to be found in order to understand the observed large baryon asymmetry of our universe (BAU) and because most extensions of the SM allow for new CP violating phases. Various non-observations of finite EDM, of the neutron as well as of nuclei, e.g. with the Hg-199 atom, and the electron, e.g. via the Tl-205 atom, so far present the most stringent constraints on new physics models of CP violation involving particles of the first generation. Many efforts world wide are underway to search for EDM in various systems like atoms, molecules, muons, light nuclei and neutrons.In this proposal we ask for a substantial support of the ETH group in the new neutron EDM (nEDM, d_n) search at PSI. The ETH group will play an important role, both in the data analysis of the ongoing experiment and in the design and construction of the new apparatus.During 2012/13, i.e. essentially the period covered by the present request, we expect to improve the sensitivity of the nEDM search by more than a factor of 5 to set a limit of d_n < 5E-27 ecm (95% C.L.) in case no EDM will be found or to establish a finite value with at least 5 sigma significance in case d_n > 1.3E-26 ecm. The present best limit is d_n < 2.9E-26 ecm (90% C.L.). The ETH group contributes to the operation of the nEDM experiment at PSI and plans on playing an important role in the data analysis and systematic studies.During the same period, i.e. until 2014, we plan to finish the design and begin construction for the subsequent n2EDM phase which aims at another order of magnitude improvement in sensitivity with a new apparatus. The collaboration aims at starting significant n2EDM construction in summer 2012. The magnetic environment will be crucial for the experiment and the ETH group is contributing to two installations which will help to gain control over the magnetic fields: An active compensation coil system and a passive multi-layer mu-metal shield. For the required mu-metal shielding a R'Equip proposal to the Swiss National Science Foundation is in preparation from ETH together with PSI.With the proposal presented here, we ask for support of two postdocs and two doctoral students to realize the final R&D effort for the magnetic environment of the n2EDM experimental setup. One postdoc will be in charge of the ETH contribution to the active magnetic compensation system and one postdoc for the passive magnetic shield including the inner field coil system. The PhD students will be assigned to the postdocs and work towards resolving the related open R&D issues. At the same time they will be heavily involved in the ongoing nEDM data analysis and study magnetic field fluctuation related systematic issues. As the experiment will last longer than can be covered by the present request, we foresee applying later for a continuation of this SNF project.