JRA2-FTE@LHC: Fixed Target Experiments at the LHC

The study of collisions of high-energy hadron beams with fixed targets, including polarised and nuclear targets, has the potential to significantly expand the range of fundamental physics phenomena accessible at hadron colliders. The high-energy proton and ion beams of the LHC allow for the most energetic fixed-target experiment ever performed. For 7 TeV proton (2.76 TeV per nucleon lead) beam, the center-of-mass energy is 115 GeV (72 GeV), in between the nominal RHIC and SPS energies. The fixed-target mode operated at high luminosity, on the order of the inverse femtobarn (nanobarn) in p-p (A-A) collisions, allows for an intensive study of rare processes, novel spin correlations, dynamics at high momentum fraction (x), QCD phase transition, nuclear phenomena. Most of these phenomena are not accessible otherwise. This Joint Research Activity (JRA) is motivated by physics questions related to quark and gluon distributions in the nucleon and nuclei at large-x, including charm content of the proton and its connection with astroparticle physics, quark and gluon Sivers effects and the proton spin, and novel hard probes of the quark-gluon plasma (QGP) close to the QCD phase transition. We plan to investigate and implement fixed-target experiments at the LHC with the ALICE and LHCb detectors and to shape convincing physics cases for these novel projects to pave the way for a Letter of Intent submission within these Collaborations. The most advanced proposals will be examined (gas target and crystal in ALICE and gas target in LHCb) and interactions between experiments will be enforced by the project. Due to the larger transverse size of the LHC beam at the injection with respect to the one at nominal energy, the storage cell must be openable to allow the passage of the proton bunches in any condition. In order to study the movement system and its interference, the beam induced charges, the wall coating and possible beam induced background, tests are foreseen at COSY. Different prototypes will be implemented directly into the vacuum chamber of the already existing polarised gas target. Measurements will be taken both with and without beam. Our aim is to develop new theoretical ideas, quantifying the phenomenological opportunities offered by the two facilities and, using realistic simulations accounting for experimental possibilities and limitations, to benchmark selected observables.