Abstract
FASER is a new experiment at CERN LHC located on the beam line-of-sight 480 m from the ATLAS collision point in the service tunnel TI12. A compact detector is designed to search for light and very weakly-interacting new particles which can be produced in LHC collisions. The additional FASER \(\nu\) emulsion sub-detector allows detecting neutrinos of all flavours produced at LHC. The detector started taking data in 2022. The first physics results from one year of data-taking are presented. A search for dark photons decaying to an electron–positron pair found no events, yielding new constraints. A search for muon–neutrino charged-current interactions in a tungsten target at the front of the FASER experiment found 153 neutrino candidates with a negligible background. The reconstructed muons charge and momentum distribution imply the observation for the first time of both neutrinos and antineutrinos from LHC with energy above 200 GeV.
