The world’s largest and most powerful particle accelerator is getting a new experiment. In March 2021, the CERN Research Board approved the ninth experiment at the Large Hadron Collider: SND@LHC, or Scattering and Neutrino Detector at the LHC. Designed to detect and study neutrinos, particles similar to the electron but with no electric charge and very low mass, the experiment will complement and extend the physics reach of the other LHC experiments.
SND@LHC is especially complementary to FASERν, a neutrino subdetector of the FASER experiment, which has just recently been installed in the LHC tunnel. Neutrinos have been detected from many sources, but they remain the most enigmatic fundamental particles in the universe. FASERν and SND@LHC will make measurements of neutrinos produced at a particle collider for the first time, and could thus open a new frontier in neutrino physics.
SND@LHC is a compact apparatus consisting of a neutrino target followed downstream by a device to detect muons, the heavier cousins of electrons, produced when the neutrinos interact with the target. The target is made from tungsten plates interleaved with emulsion films and electronic tracking devices. The emulsion films reveal the tracks of the particles produced in the neutrino interactions, while the electronic tracking devices provide time stamps for these tracks. Together with the muon detector, the tracking devices also measure the energy of the neutrinos.
Like FASERν, SND@LHC will be able to detect neutrinos of all types – electron neutrinos, muon neutrinos and tau neutrinos. Unlike FASERν, which is located on one side of the ATLAS detector and along the LHC’s beamline (the line travelled by particle beams in the collider), SND@LHC will be positioned slightly off the beamline, on the opposite side of ATLAS. This location will allow SND@LHC to detect neutrinos produced at small angles with respect to the beamline, but larger than those covered by FASERν.
“The angular range that SND@LHC will cover is currently unexplored,” says SND@LHC spokesperson Giovanni De Lellis. “And because a large fraction of the neutrinos produced in this range come from the decays of particles made of heavy quarks, these neutrinos can be used to study heavy-quark particle production in an angular range that the other LHC experiments can’t access.”
SND@LHC will be installed in an unused tunnel that links the LHC to the Super Proton Synchrotron over the course of 2021, and it is expected to begin taking data when the LHC starts up again in 2022.