The SMOG2 project

"A proposal for an upgraded version of the existing gas injection system for the LHCb experiment (SMOG) is presented. The core idea of the project, called SMOG2, is the use of a storage cell for the injected gas to be installed upstream of the VELO detector. The main advantage of the proposed system is to increase by up to two orders of magnitude the effective target areal density, thus resulting in a significant increase of the luminosity for fixed-target collisions. Other important advantages are the possibility to inject additional gas species, including H$_2$ and D$_2$, a better defined interaction region, displaced with respect to the nominal interaction point, and thus possibly compatible with running in parallel to the collider mode (resulting in a further huge increase in luminosity). A technical design of the target system is presented together with a description of the installation procedure. Impedance properties and Electron Cloud effects have been studied for the proposed system, and the possible beam instabilities estimated. The geometry of the system has been integrated into the GEANT4 model of the LHCb detector in order to validate the target design with reliable simulation studies, and to ensure that the near-beam material budget has negligible effects in terms of beam-induced background. The loss in reconstruction efficiency with respect to SMOG for selected physics channels, due to the displaced interaction region with respect to the nominal interaction point, is found to be of the order 10%, thus largely over-compensated by the expected increase in luminosity. The installation of the system is proposed for the LHC Long Shutdown 2. This will open new physics frontiers at LHCb already from the LHC Run-3."