Limited funding and shortage of newly discovered particles force physicists to reduce their plans large accelerators : a a multi-billion dollar facility known as the International Linear Collider (ILC) in Japan.
On November 7, the International Committee for Future Accelerators (ICFA), which oversees the work of the ILC, approved the reduction of 500 to 250 gigaelectronvolts (GeV) from the planned energy of the machine and shortens its proposed tunnel of 33.5 km. as much as 13 kilometers. The reduced version should give up some of its planned research such as studies of the "superior" flavor of the quark, which is produced only at higher energies.
Instead, the collider would focus on studying the particle that feeds all the others - the Higgs boson, which was detected in 2012 by the Large Hadron Collider (LHC ) at CERN, particle physics in Europe. laboratory near Geneva, Switzerland.
The advanced particle physicists nevertheless remain optimistic. A 250 GeV machine still has "a compelling physics case," says Hugh Montgomery at the Thomas Jefferson National Accelerator Facility in Newport News, Virginia. He says it could be improved at higher energies in the future.
High energy physicists have been planning a future linear collider for 25 years, but it is unlikely that ILC will come into existence before at least 2030. They considered the linear collider as complementary to the LHC, allowing physicists to to scrutinize in detail any particle discovered at CERN.
Linear drawing
The circular LHC crushes the protons, which allows it to reach very high energies (13 teraelectronvolts). But, as composite particles (made of quarks), protons create disordered collisions with debris clouds.
In contrast, the ILC would have a collision between electrons and positrons after accelerating them into thousands of superconducting cavities joined end-to-end. Although producing lower energies, its collisions - between fundamental particles - would be cleaner and more accurate than those of a proton-proton machine.
The international physics community had hoped that Japan would pay much of the $ 10 billion needed to complete the original project, after researchers proposed to host the facility in October 2012, just after the discovery of Higgs. But the Japanese government, deterred by the enormous price of the project, according to Tatsuya Nakada, a physicist at the Swiss Federal Institute of Technology in Lausanne, Switzerland, has not yet made a funding offer .
This fact, coupled with the absence of any new particle discovery at the LHC beyond the Higgs, led the Association of High Energy Physicists of Japan to propose in 1945 to cap The energy of ILC at 250 GeV.
Aiming for higher energy, the association explained, was meaningless after data collected by the LHC in 2015 and 2016 showed that particles outside the standard model of physicists probably weigh no less than 1000 GeV and so would be out of reach. even reach for a large-scale version of the ILC. However, 250 GeV is high enough to produce a large number of Higgs bosons, which, according to the association, could produce indirect signs of new physics through measurements of their interactions with other known particles. .
Debate on the energy
This Higgs plant proposal was also approved by an international working group charged with formulating the ILC's scientific file, in a document uploaded to the pre-print server arXiv last month . ICFA then gave the green light to the collapsed collider at a meeting held in Ottawa, Canada this week
However, not all physicists are enthusiastic. John Ellis, a theoretician at King's College London and CERN, says that only a linear collider, when it runs at around 1000 GeV, will provide "a more complete picture of the Higgs". He acknowledges that the costs need to be reduced, but says that by limiting the ILC to 250 GeV, "you make significant scientific compromises".
A report uploaded to arXiv last week describes three possible configurations for the 250 GeV model (a technical design for the higher energy ILC was released in 2013). Each requires the halving of the length of the electron-positron superconducting accelerators, but two of the options retain additional space in the tunnel to allow for future upgrades.
Taking into account the anticipated savings from ongoing accelerator research, the report estimates that the collider's base cost could be reduced by 40 percent to about $ 5 billion by 2012. According to Lyn Evans, a physicist accelerators at CERN, which conducts research on the ILC, the workforce and detectors, would bring the total to about $ 7 billion.
Michael Peskin, a particle physics physicist at the SLAC National Accelerator Laboratory in Menlo Park, California, and a member of the ILC task force, does not doubt the value of a Higgs plant. He says that the theoretical studies of the Higgs boson and the weak nuclear force - one of the four known fundamental forces - have reinforced the experimental argumentation of the Higgs interaction force (the Higgs is required to give the carriers of the weak force finite mass). "The 250 GeV scene is actually more interesting scientifically than we thought," he says.
The decision of the Coalition now belongs to Japan. Evans describes the Japanese government's ongoing evaluation of the linear-collider project as "very long and very frustrating." But other countries will not engage until the host country makes its plans known, he says. "The rest of the world is waiting for the Japanese government to decide," he said.
This article is reproduced with permission and was published for the first time on November 9, 2017.
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