Amorphous Carbon-coated Storage Cell Tests for the Polarized Gas Target at LHCb

The LHC beams cannot be polarized. Hence, the implementation of a dense polarized gas target at the LHCb experiment at CERN, to be operated simultaneously with beam-beam collisions, will enable fixed target interactions to explore a new energy range of spin physics measurements. Unfortunately, typical surface coatings like water, Teflon or aluminium, normally used to avoid polarization losses, are forbidden due to vacuum and beam policies. Using the former ANKE atomic beam source at Forschungszentrum Jülich to provide a polarized atomic hydrogen beam, we investigated the properties of a storage cell coated with amorphous car- bon. A notable recombination rate, lying between 93 and 100%, and a preservation of polarization during recombination exceeding 74% was observed. We were able to generate H 2 molecules with a nuclear polarization of P∼0.59. Remarkably, no water layer accumulated on the cooled storage cell surface, even over extended periods. Furthermore, we examined the influence of Lyman- radiation on the recombination rate on carbon, addressing a prominent question in the field of astrophysics. A similar talk was given at "1 𝑠𝑡 Workshop on Polarized Beam and Target - Physics and Appli- cations (PBT2024)" from 26.-28.02.2024 in Huizhou, China, by T. El-Kordy and is based on a corresponding paper [1].