FASER Experiment

FASER (ForwArd Search ExpeRiment) is planned to be one of the eight particle physics experiments in 2022 at the Large Hadron Collider at CERN. It is designed to both search for new light and weakly coupled elementary particles, and to study the interactions of high-energy neutrinos.

The experiment is installed in the service tunnel TI12, which is 480 m downstream from the interaction point used by the ATLAS experiment. This tunnel was formerly used to inject the beam from the SPS into the LEP accelerator. In this location, the FASER experiment is placed into an intense and highly collimated beam of both neutrinos as well as possible new particles. Additionally, it is shielded from ATLAS by about 100 meters of rock and concrete, providing a low background environment. The FASER experiment was approved in 2019 and will start taking data during Run 3 of the LHC, starting in 2022.

New physics searches

The primary goal of the FASER experiment is to search for new light and weakly interacting particles, that have not been discovered yet, such as dark photons, axion-like particles and sterile neutrinos. If these particles are sufficiently light, they can be produced in rare decays of hadrons. Such particles will therefore be dominantly produced in the forward direction along the collision axis, forming a highly collimated beam, and can inherit a large fraction of the LHC proton beam energy. Additionally, due to their small couplings to the standard model particles and large boosts, these particles are long-lived and can easily travel hundreds of meters without interacting before they decay to standard model particles. These decays lead to a spectacular signal, the appearance of highly energetic particles, which FASER aims to detect.

Neutrino physics

The LHC is the highest energy particle collider built so far, and therefore also the source of the most energetic neutrinos created in a controlled laboratory environment. Collisions at the LHC lead to a large flux of high-energy neutrinos of all flavours, which are highly collimated around the beam collision axis and stream through the FASER location. The dedicated sub-detector FASERν (FASERnu) is designed to detect these neutrinos. It will record and study thousands of neutrino interactions, which allows to measure neutrino cross sections at TeV energies where they are currently unconstrained.

FASERnu will be capable of exploring the following physics domains:

# Interactions of all neutrino flavors and anti-neutrinos and measurement of the cross-section at TeV energy scales.
# With the ability to detect ~10000 neutrinos during its run period, FASERnu will be able to see the highest number of nucleus-tau neutrino and nucleus-electron neutrino interactions and will open ample opportunities for neutrino studies.
# The collaboration will carry out very precise measurements of the rate of muon neutrino interactions at an energy scale never explored before.
In 2021, the FASER collaboration announced the observation of the first neutrino interaction candidates at the LHC.

Detector

Located at the front end of FASER is the FASERν neutrino detector. It consists of many layers of emulsion films interleaved with tungsten plates as target material for neutrino interactions. Behind FASERν and at the entrance to the main detector is a charged particle veto consisting of plastic scintillators. This is followed by a 1.5 meter long empty decay volume and a 2 meter long spectrometer, which are placed in a 0.55 T magnetic field. The spectrometer consists of three tracking stations, composed of layers of precision silicon strip detectors, to detect charged particles produced in the decay of long-lived particles. Located at the end is an electromagnetic calorimeter.

References

External links

Official FASER websiteFASER experiment
record on INSPIRE-HEP

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CERN experiments
Particle experiments
Large Hadron Collider