CODEX-b

CODEX-b
Name	CODEX-b
Location	CERN, near LHCb
Type	Long-lived particle detector
Status	Proposed / under construction
Collaborator	CERN, University of Oxford, Imperial College London, etc.

CODEX-b CODEX-b is a proposed external detector to search for long-lived particles produced in proton–proton collisions at the Large Hadron Collider near the LHCb experiment interaction point. The proposal aims to complement searches performed by experiments such as ATLAS, CMS, and LHCb by instrumenting a shielded volume to detect displaced decays from neutral weakly interacting states predicted in models like the Minimal Supersymmetric Standard Model, Hidden Valley (particle physics), and theories invoking light dark sectors. The project brings together groups from institutions including University of Oxford, Imperial College London, CERN, University of Liverpool, and international collaborators from the United States Department of Energy and European research institutes.

Overview

CODEX-b was conceived in response to limitations of existing detectors such as ALICE, Belle II, Fermilab, and fixed-target facilities when searching for long-lived particles with macroscopic lifetimes. The concept proposes placing a ~10 m × 10 m × 10 m instrumented decay volume in a shielded cavern or service gallery adjacent to the LHCb detector at CERN's Point 8, instrumented with tracking, timing, and calorimetry to reconstruct displaced vertices from decays of neutral particles produced in proton–proton collisions at √s = 13–14 TeV. Motivations reference anomalies and theoretical frameworks developed in works related to Axion models, Dark photon, Sterile neutrino, Neutralino, and portal interactions used in studies by groups at Harvard University, Princeton University, SLAC National Accelerator Laboratory, Brookhaven National Laboratory, and DESY.

Detector Design and Subsystems

The baseline design includes a hermetic shielding matrix modeled after concepts used at Super-Kamiokande and MINOS with an interior instrumented by tracking planes and timing layers inspired by technologies from LHCb VELO, ATLAS Muon Spectrometer, and CMS Tracker. Tracking subsystem options consider scintillating-fiber modules developed by collaborations including STFC groups and silicon-strip technology used by CMS upgrade projects; timing layers draw on CUORE and LAPPD developments for sub-nanosecond resolution. Calorimetry and particle identification concepts borrow from NA62, KOTO, and T2K designs to distinguish leptonic and hadronic final states; a muon system concept references techniques from DØ and CDF legacy detectors. Shielding and background mitigation strategies use simulations validated against studies by GEANT4 teams and beamline analyses similar to those conducted for SHiP and FASER.

Physics Program and Sensitivity

The physics program targets displaced decays from predicted states in models developed at institutes such as MIT, Caltech, University of Chicago, and Columbia University, including dark photons, heavy neutral leptons, exotic Higgs decays, and supersymmetric long-lived particles like long-lived gluino or neutralino states. Sensitivity estimates compare CODEX-b to reach projections from FASER, MATHUSLA, SHiP, and dedicated experiments at DESY and CERN SPS, using benchmark processes calculated with tools from groups at CERN Theory Department, SLAC, IHEP, and IPPP. Projected exclusions and discovery contours are presented in parameter spaces used for portals like the vector portal, scalar portal, and neutrino portal, linking to theory results from Niels Bohr Institute, Perimeter Institute, Kavli Institute for Theoretical Physics, and collaborations that produced limits at LEP and Tevatron.

Construction, Commissioning, and Operation

Construction plans leverage civil engineering precedents from CERN projects such as LHC upgrade, service cavern refurbishments near Point 8, and lessons from installations at ISR and HERA. Commissioning strategies reference procedures used by ATLAS Collaboration and CMS Collaboration during Run 1 and Run 2, with beam background studies and alignment performed in cooperation with CERN Accelerator School experts and beam instrumentation teams from CERN Beams Department. Operation will coordinate with LHC run schedules, machine protection systems, and radiation monitoring practices established by CERN Radiation Protection and oversight by funding bodies including European Research Council and national agencies like UKRI and National Science Foundation.

Collaboration and Organization

The collaboration model mirrors governance structures from experiments such as LHCb Collaboration, ATLAS Collaboration, CMS Collaboration, Belle II Collaboration, and multinational projects like ITER and Square Kilometre Array. Management comprises steering committees, technical coordination, and physics working groups with institutional board representation from universities and laboratories including University of Manchester, University of Bristol, Oxford University, Imperial College, Lawrence Berkeley National Laboratory, TRIUMF, and continental partners from CNRS and INFN. Funding and memorandum of understanding negotiations involve agencies such as STFC, DOE, ERC, and national research councils.

Data Analysis and Results

Data analysis strategies adopt reconstruction algorithms and background rejection techniques pioneered by LHCb, ATLAS, and CMS analyses for displaced-vertex searches, with software frameworks interoperable with ROOT, GEANT4, and experiment-specific tools developed at CERN IT and university computing centers like GridPP and Open Science Grid. Early pathfinder studies and Monte Carlo results are benchmarked against limits from BaBar, Belle, NA62, and past searches at LEP and Tevatron, while prospective sensitivities are compared to global fits and combined limits produced by collaborations including Particle Data Group and theory consortia. Ongoing commissioning runs and analyses will feed into conference presentations at venues such as ICHEP, Moriond, EPS-HEP, and workshops hosted by CERN Theory.

Category:Particle physics detectors