FUTURE COLLIDERS
break new ground. Electron collidersare akin to a precision instrument to dissect a specific particle.
Proton smashers can reach much higher energies but also produce an unholy mess. Protons are little bags of other particles: subatomic quarks and the gluons that stick them together. Each collision at the LHC produces millions of particles. It’s a huge job to tease out the telltale signature of a particular type, such as the Higgs.
Electrons and positrons, on the other hand, are fundamental, having no internal parts. As antimatter partners, they annihilate each other when they collide, creating a clean burst of pure energy. At the right collision speed, this pure energy is converted to Higgs bosons without the mess of extra particles produced by a proton collision.
With an electron collider, therefore, physicists can fine-tune the collision energy to produce just one kind of particle a bit like tuning a radio to a particular station. Set the dial at 250 gigaelectronvolts, and the ILC produces Higgs bosons in abundance, and not much else. Tune a bit higher, to 375 gigaelectronvolts, and the collision can produce Higgs particles along with a top quark. This would be a chance to see the Higgs get physical with nature’s heaviest known particle.
The main advantage a linear collider has over a circular one is that it’s much easier to accelerate electrons (or positrons) in a straight line than in a circle. Particles running in a circle shed lots of extra energy as gamma rays, which puts the brakes on.
After two decades of design work, the ILC is ready to be built, Taylor says. All that is needed is for the relevant parties to cough up the dough for construction – about US$10 billion (though some estimates go far higher).
The current agreement says the host country should pay half, but Japan is trying to renegotiate this with its partners in the US and Europe. The Japanese government is also being cautious in other respects, commissioning studies on how the massive project will affect life in the region. All this means we don’t have an ETA on the project yet.
Besides the ILC, another linear collider on the horizon is the Compact Linear Collider (CLIC). It would use a more advanced design to hit energies of three teraelectronvolts or even higher along a similar length to the ILC; but it’s only in a very early design stage.