From: Hannah Pell

Neutrinos are ubiquitous and notorious. At this moment billions are going through you. Sometimes referred to as the “spirit of a particle”, neutrinos are virtually massless, making them extremely difficult to detect experimentally (“neutrino”, which means “small neutral” in Italian, was first used by Enrico Fermi in the early 1930s). Neutrinos were first confirmed in 1956 (thanks to a nearby nuclear reactor) and have since been detected from various sources including the sun and cosmic rays, but not yet in a particle collider. Their vanity has since been the source of much intrigue (and, of course, research funding) within particle physics.

What else is it that makes you so curious? Neutrinos come in three variants – electron neutrino, muon neutrino and tau neutrino – and can switch between them through the oscillation process. Neutrino oscillations were only confirmed experimentally on the Super-K detector in Japan in the last decade (the physicists Takaaki Kajita and Arthur B. McDonald shared the 2015 Nobel Prize in Physics for this). This discovery marked an important direction in the search for physics beyond the Standard Model, since the long-standing theory does not explain neutrino vibrations and describes them as completely massless particles. Something is not quite right.

Enter: FIBER. The ForwArd Search Experiment (FASER) was originally proposed in 2018 and is CERN’s newest experiment to detect neutrinos, possibly up to 1,300 electron neutrinos, 20,000 muon neutrinos and 20 tau neutrinos. FASER and its corresponding sub-detector FASERν were built in an unused service tunnel about 500 meters from an interaction point of the Atlas experiment. They were developed to investigate the interactions of high-energy neutrinos (probably between 600 GeV and 1 TeV).

Illustration of the FASER experiment. Photo credit: FASER / CERN.

“These neutrinos will have the highest energies of artificial neutrinos to date, and their detection and investigation at the LHC will be a milestone in particle physics that will enable researchers to carry out highly complementary measurements in neutrino physics,” said Jamie Boyd, co-spokesman for FASER, said in December 2019.

The physicists are confident that FASER will capture new light particles that have previously escaped detection and could possibly help explain dark matter. These particles are long-lived and migrate far beyond an interaction point before they break down further into particles, which FASER recognizes based on their position and size. Surprisingly, FASER is relatively small – only 25 cm wide, 25 cm high and 5 meters long – but weighs an astonishing 1.2 tons. The Super-K neutrino detector weighs a comparatively whopping 50,000 tons!

The LHC is currently in a further shutdown phase for maintenance and upgrades. However, FASER is expected to be fully online and collecting data by the next LHC Run 3 from 2021 to 2023. The FASER collaboration consists of 70 members from 19 institutions and 8 countries.

“We are very pleased that this project is being implemented so quickly and smoothly,” said Boyd. “Of course this would not have been possible without the professional help of the many CERN teams involved!”

Map with the location of FASER. Photo credit: CERN / FASER.
The FIBERĪ½ The collaboration released the first pilot detector results to arXiv on May 13, 2021, including Observation of the first neutrino interaction candidates.


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