New measurements in fixed-target collisions at LHCb
November 12, 2022
Owing to the injection of noble gases into the LHC accelerator beam-pipe at CERN, LHCb is
developing a full-scale fixed-target experiment studying collisions of protons and lead ions on
gas atoms at the as of today’s highest energy ever reached in a fixed-target experiment. Such a
scale, intermediate between the past experiments and the LHC ones, is mostly unexplored and
the accessible physics prospects, addressing different fields of interest among which nucleon
characterization and astrophysics, are unique at the LHC. The gas injection system, SMOG, has
recently been upgraded in view of the LHC Run3. The gas will be confined in a 20-cm-long
cell, SMOG2, installed in August 2020 40 cm upstream of the LHCb nominal interaction point.
Leveraging on the precise definition of the beam-gas luminous region, the gas areal density seen by
the beam will be increased by two orders of magnitude for the same gas flow as in Run2 and many
gas species, notably non-noble ones such as hydrogen and oxygen, will be injected. Moreover,
the separation between the beam-beam and beam-gas interaction regions opens the possibility to
operate LHCb at the same time as a fixed-target and a collider experiment. In this document, two
examples of the LHCb physics reach in its fixed-target configuration are presented, describing
recent published results obtained from the analysis of Run2 data and the prospects for Run3.
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