Abstract
The present document discusses plans for a compact, next-generation
multi-purpose detector at the LHC as a follow-up to the present ALICE
experiment. The aim is to build a nearly massless barrel detector consisting of
truly cylindrical layers based on curved wafer-scale ultra-thin silicon sensors
with MAPS technology, featuring an unprecedented low material budget of 0.05%
X$_0$ per layer, with the innermost layers possibly positioned inside the beam
pipe. In addition to superior tracking and vertexing capabilities over a wide
momentum range down to a few tens of MeV/$c$, the detector will provide
particle identification via time-of-flight determination with about 20~ps
resolution. In addition, electron and photon identification will be performed
in a separate shower detector. The proposed detector is conceived for studies
of pp, pA and AA collisions at luminosities a factor of 20 to 50 times higher
than possible with the upgraded ALICE detector, enabling a rich physics program
ranging from measurements with electromagnetic probes at ultra-low transverse
momenta to precision physics in the charm and beauty sector.