SELDOM has successfully delivered on its ambitious objectives, developing novel experimental techniques to measure the electric (EDM) and magnetic dipole moments (MDM) of strange and charm baryons at the Large Hadron Collider (LHC). The project has significantly advanced the experimental frontiers of baryon dipole moment studies and has led to the emergence of new research directions at CERN.
Overview of Work Performed and Achievements
1. Event Reconstruction and Trigger Development
The project developed and validated dedicated reconstruction and trigger algorithms for long-lived Λ baryons, enabling their detection even when decaying downstream of the LHCb magnet. These techniques were successfully applied to both simulated datasets and Run 2 LHCb data, confirming the feasibility of EDM/MDM measurements for strange baryons. New trigger lines were deployed in LHCb Run 3 for charm and beauty decays involving long-lived baryons. Additionally, reconstruction strategies were also optimised for Λc+ and Ξc+ decays, including in fixed-target configurations using the LHCb SMOG system.
2. Data Analysis and Physics Results
The project completed the first measurement of the EDM and MDM of Λ and anti-Λ baryons, a major milestone in precision baryon physics. Furthermore, the SELDOM team carried out amplitude analyses and polarisation measurements for Λc+ and Ξc+ baryons in proton–proton collisions, establishing new methodologies for spin-dependent observables. An analysis of Λc+ polarisation in proton–neon fixed-target data has also been performed. The improved formalism for multi-body helicity amplitudes developed in the project is now being adopted in other LHCb analyses and hadron spectroscopy studies.
3. Fixed-Target Setup and Experimental Implementation
SELDOM significantly contributed to the experimental developments for measuring charm baryon dipole moments via spin precession in bent crystals. This culminated in the design, construction, and installation of the TWOCRYST experiment at LHC-IR3. The system uses bent crystals to deflect protons from the beam halo to a tungsten target, where charm baryons are produced and channeled through a second crystal. A pixel tracking detector inside Roman Pots monitors these events. Data taking is currently ongoing and will continue through 2025. This is the first operational test of such a method at a collider environment.
Final Period – Overview of Results, Exploitation and Dissemination
SELDOM achieved the following results:
- Successful start of data taking with the TWOCRYST setup at the LHC, validating the beam halo steering and bent crystal alignment and channeling of protons at TeV energies.
- Development of a supporting international collaboration and submission to CERN of the Letter of Intent for the ALADDIN experiment, a dedicated setup at CERN for charm baryon EDM/MDM measurements. The proposal received positive feedback from the LHCC.
- Consolidation of new research directions at LHCb, including long-lived particle searches and spin-related observables in baryonic decays.
- Refinement of crystal engineering techniques, including anodic bonding for high-uniformity crystal fabrication.
Exploitation and Dissemination
Exploitation:
The experimental and analytical methods developed through SELDOM are already being integrated into the LHCb Run 3 programme and proposed future experiments (ALADDIN). The work on crystal channeling and beam halo deflection has applications beyond EDM searches, including beam diagnostics and advanced steering techniques for high-energy colliders.
Dissemination:
- Peer-reviewed publications in major journals, including Physical Review D, Physical Review Letters, and EPJ C.
- Presentations at leading international conferences (ICHEP, EPS-HEP, CHARM), CERN workshops, and Physics Beyond Colliders forums.
- Supervision of a wide array of student research projects: several PhD theses and Master's theses, and joint PhD programmes with the University of Valencia (Spain) and Paris-Saclay (France).
- Inclusion of results in strategic documents such as the CERN Physics Beyond Colliders report and the European Strategy Update for Particle Physics.
