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Technical University of Munich

The PanEDM Experiment at ILL

The neutron electric dipole moment (nEDM) is a flagship probe for CP and T symmetry violation beyond the Standard Model.
At our chair, we participate in the PanEDM collaboration at the Institute Laue-Langevin (ILL) in Grenoble.
The goal of PanEDM is to achieve a sensitivity of better than 10-27 e·cm, exploring new territory in fundamental physics.

Our approach combines ultra-cold neutron storage, Ramsey’s method of separated oscillatory fields, and an advanced magnetic environment. Magnetometry, shielding, and systematics control are central to reach the required precision.

Scientific Motivation

A nonzero nEDM would would be a manifestation of new physics beyond the standard model of particle physics as it would be a time-reversal (T) violation and thus CP violation via the CPT theorem, offering insight into one of the deepest puzzles in physics — the dominance of matter over antimatter. Given the absence of new physics signals at high-energy colliders, precision experiments like the nEDM search provide a complementary route.

However, achieving the target sensitivity demands rigorous suppression and characterization of spurious magnetic effects.
Small field drifts, gradients, motional magnetic fields (E × v effects), and geometric phase shifts must be monitored and mitigated.
Hence, our expertise in optically pumped magnetometers, shielding, and sensor arrays is essential.

Methods & Experimental Setup

PanEDM magnetic shields and central components. 1: UCN cells, 2: vacuum
chamber, 3: high-voltage insertion, 4: cylindrical shield and field coils (not shown) for B0 and B1, 5: three-layer inner magnetic shield (Insert), 6: outer magnetic and RF shield (MSR), 7: MSR door.
  • We apply Ramsey’s method of separated oscillatory fields to ultra-cold neutrons (UCN) stored in a double-chamber geometry. A shift in precession frequency under a reversed electric field is the signature of an EDM.
  • The magnetically shielded environment is crucial: the experiment uses a large multi-layer magnetic shield with active compensation coils (≈ 180 channels) to suppress external fluctuations and gradient contributions.
  • Inside the shielding, a homogeneous magnetic field is generated. Co-magnetometers (e.g. vapor-based or atomic magnetometers) are placed above and below the neutron storage chambers to monitor any field drifts or perturbations.
  • In addition, optical atomic magnetometers (e.g. cesium vapor cells) are used in array configurations inserted in access tubes to measure multipole perturbations and magnetic gradients while the experiment is running.
  • All sensor data is analyzed externally. The design avoids electrical cabling inside the sensitive region to reduce magnetic interference.

Results & Ongoing Goals

  • The PanEDM setup aims for a statistical sensitivity of σ₍d,stat₎ < 5 × 10⁻28 e·cm (3σ) with ~200 days of measurement time.
  • The systematic error budget target is σ(d,sys₎ < 2 × 10⁻28 e·cm, which necessitates stringent control over all magnetic and motional effects.
  • Current efforts focus on finalizing the field environment, and with this, building the completed magnetometer array, characterizing drift and gradient stability
  • In addition, the neutron guides and storage chambers will be characterized, and the interface will be completed so that initial tests of UCNs from the SuperSUN source can take place in the panEDM apparatus.

Contact

For collaboration, thesis opportunities, or further inquiries, please contact:

Foto von Peter Fierlinger

Prof. Dr.sc.nat. Peter Fierlinger

Publications and finished Theses

  • Wurm, D. et al., “The PanEDM neutron electric dipole moment experiment at the ILL,” EPJ Web Conf. 219, 02006 (2019)
  • Chupp, T. E., Fierlinger, P., Ramsey-Musolf, M. J. & Singh, J. T., “Electric dipole moments of atoms, molecules, nuclei, and particles,” Rev. Mod. Phys. 91, 015001 (2019)
  • Altarev, I. et al., “A magnetically shielded room with ultra low residual field and gradient,” Rev. Sci. Instrum. 85, 075106 (2014)
  • Altarev, I. et al., “A large-scale magnetic shield with 10⁶ damping at millihertz frequencies,” Journal of Applied Physics 117, 183903 (2015)

Involved Persons and Former Members

Currently Involved persons: Luca Kaess, 

Former members: Dr. David Wurm, …

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