Among kinds of approaches for dark matter (DM), collider experiments are advantageous in their high precision. The FASER (ForwArd Search ExpeRiment at the LHC) is equipment to probe long-lived particles created at the interaction point of the LHC at the distance of about 400m. Particles pass through the absorber between the FASER detector and the interaction point and have enough lifetime to reach the FASER detector should leave signatures there. Dark photon and axion-like particles are good candidates for such species, as well as DM.

The equipment is set at the front of the LHC beam direction. The position is really good at reducing the background particles and making use of already existing but not used space. Multiple layers of scintillators, emulsion for neutrino detection, silicon trackers, the decay volume for new particles with dipole magnets, and calorimeter at the endpoint consists of the facility. In combination with the works of these pieces, new long-lived particle signatures as rare-decay signatures of neutral pion decay can be searched. It is already working well with LHC Run 3 and neutrino properties are now being probed.

Furthermore, a new piece of the facility is decided to be installed to enhance the accessibility to axion-like particle signature in the channel of 2 photon decay. The installation does not disturb the current measurement and will be completed by the end of 2023.

The FASER experiments should become a key facility to probe new particles at m~O(1) GeV scale. In addition, our understanding of the Standard Model sector is also significantly improved with its measurements. The collaboration is now intensively working. The idea for physics with FASER is highly welcomed. Stay tuned and work hard!

Reported by Nagisa Hiroshima