Particle Physics

New experiment to look for dark matter

Print edition : March 29, 2019

A computer drawing shows the FASER instrument in a tunnel at CERN’s LHC in Geneva, Switzerland. Photo: FASER/CERN

On March 5, the research board of the European Organisation for Nuclear Research (CERN) approved the Forward Search Experiment (FASER), giving a green light to the assembly, installation and use of an instrument that will look for new fundamental particles at the Large Hadron Collider (LHC) in Geneva. FASER will complement CERN’s ongoing physics programme, extending its discovery potential to detect some long-sought-after particles that are associated with dark matter.

The five-year FASER project is funded by grants of $1 million each from the Heising-Simons Foundation and the Simons Foundation, with additional support from CERN.

FASER’s focus is to find light, extremely light and weakly interacting particles that have so far eluded scientists, even in the high-energy experiments conducted at the CERN-operated LHC, the largest particle accelerator in the world. The four main LHC detectors are not suited for such particles that might be produced parallel to the beam line. They may travel hundreds of metres without interacting with any material before transforming into known and detectable particles such as electrons and positrons. FASER will be placed at a specific point along the 26.7-km loop of the LHC and will be precisely aligned with the collision axis of the six-storey-sized ATLAS instrument, about 480 m away. As proton beams pass through the interaction point at the ATLAS instrument, new particles created will go through concrete in the LHC tunnel and then into FASER, which will track and measure the progress of their decay. FASER will collect data any time ATLAS, which was used to discover the Higgs boson, operates.

“Seven years ago, scientists discovered the Higgs boson at the LHC, completing one chapter in our search for the fundamental building blocks of the universe, but now we are looking for new particles,” said FASER co-leader Jonathan Feng at the University of California at Irvine (UCI). “The dark matter problem shows that we don’t know what most of the universe is made of, so we’re sure new particles are out there.”

The FASER team will have 30-40 members, including researchers from CERN, and 16 other collaborating institutes from the United States, Europe, China and Japan. The strength is relatively small compared to other groups conducting experiments at the LHC. The FASER instrument is also compact, measuring about 1 m in diameter and 5m long.

“One of the advantages of our design is that we’ve been able to borrow many of the components of FASER—silicon detectors, calorimeters and electronics—from the ATLAS and LHCb collaborations,” said Jamie Boyd, CERN research scientist and co-spokesperson for the project. “That’s allowing us to assemble an instrument that costs almost hundreds of times less than the largest experiments at the LHC.” Another advantage is FASER’s rapid construction schedule.

The FASER detector is being built and installed during the collider’s current hiatus and will collect data from 2021 to 2023. The LHC will be shut down again from 2024 to 2026. During that time, the team hopes to instal the larger FASER 2 detector, which will be capable of unveiling an even wider array of mysterious, hidden particles.