SND@LHC Upgrade for the High-Luminosity LHC: Physics Reach and Installation Scenarios

The SND@LHC experiment is currently taking data at the Large Hadron Collider (LHC), exploring the unique forward region at pseudorapidities from 7.2 to 8.4. Its physics programme covers neutrinos originating from heavy-flavour decays and feebly interacting particles produced in proton proton collisions. Building upon the successful operation of the present detector, this paper presents the physics reach of the approved SND@LHC upgrade for Run4 of the LHC, and compares it with an alternative installation scenario. Lowering the detector by approximately 40 cm and shifting it horizontally by about 30 cm, while keeping it off-axis, increases the total neutrino interaction rate by a factor of five. The paper describes the design of the upgraded detector and compare the physics performance in both installation scenarios.