ALADDIN: A New Experiment to Probe the Dipole Moments of Charm Baryons at the LHC
ALADDIN (An LHC Apparatus for Direct Dipole moment INvestigation) is a proposed fixed-target experiment at CERN’s Large Hadron Collider (LHC) that aims to open a new frontier in the search for physics beyond the Standard Model. The experiment is designed to measure the electric (EDM) and magnetic dipole moments (MDM) of charm baryons, such as the Λc+, with unprecedented precision.
Understanding the EDM and MDM of fundamental particles is key to exploring the limits of the Standard Model. Charm baryons are an especially attractive probe because of their high quark mass differences, which makes them sensitive to new physics at high energy scales.
However, the ultrashort lifetime of charm baryons (~10⁻¹³ s) makes conventional magnetic precession techniques impractical. ALADDIN proposes a novel solution: using the intense electromagnetic fields inside bent silicon crystals to induce a measurable spin precession as the particle is deflected.
The ALADDIN Experimental Concept
In the proposed setup, a first bent crystal extracts stray protons from the LHC beam halo and steers them onto a fixed target installed directly inside the LHC vacuum, where charm baryons are produced. A second, significantly longer, bent crystal then induces spin precession in the resulting baryons. A downstream detector reconstructs their decay products, enabling the extraction of spin-related observables. A particularly elegant aspect of the concept is its use of halo particles—protons that would otherwise be absorbed by the LHC collimation system. ALADDIN therefore extends the physics reach of the LHC without interfering with standard high-luminosity operation, making use of particles that would otherwise be lost.
The ALADDIN Detector
The ALADDIN detector is designed to reconstruct the decay products of charm baryons with high precision and to extract spin-related observables from their angular distributions.
It consists of two main subsystems:
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A magnetic spectrometer, composed of multiple tracking stations placed upstream and downstream of a dipole magnet, provides precise momentum reconstruction of charged particles emerging from charm baryon decays. The tracking technology is based on silicon pixel detectors derived from the VELOpix system developed for LHCb, and later implemented in the TWOCRYST experiment. The detector modules are housed in movable Roman Pots, allowing 2D detectors to be inserted into the LHC vacuum in close proximity to the circulating beam.
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A Ring-Imaging Cherenkov (RICH) detector provides charged hadron identification, enabling the experiment to distinguish between pions, kaons, and protons across a broad momentum range. This capability is essential for the exclusive reconstruction of key decay channels, such as Λc+ → p K- π+. The charged particles enter the gaseous radiator medium (Neon or Nitrogen) through a thin exit window integrated into the top of the LHC beam pipe.
The entire detector system is located downstream of the bent crystals and will be engineered to operate in the high-radiation environment of the LHC. Its design leverages proven technologies from LHCb and TWOCRYST, ensuring robust tracking, efficient particle identification, and reliable operation under realistic beam conditions.
The ALADDIN Collaboration
The ALADDIN proto-collaboration brings together over 70 scientists from 24 institutes across 8 countries. ALADDIN is coordinated within the Physics Beyond Colliders (PBC) framework, and benefits from strong synergy with the TWOCRYST experiment, and technologies developed in the CERN community.