Unstable Muon Particle Having Mean Lifetime Of Just 2.2μs
If you would like to probe(study) the boundary of fundamental physics, you’ve got to collide particles at very high energies: with enough energy that you simply can create the unstable particles and states that don’t exist in our everyday, low-energy Universe. As you obey the Universe conservation laws and have enough free energy at your disposal, you’ll create any massive particle (and/or its antiparticle) from that energy via Einstein’s equation.
E = mc².
Traditionally, there are two strategies to try this.
Collide electrons occupation one direction with positrons occupation the other direction, tuning your beams to whatever energy corresponds to the mass of particles you would like to supply .
Collide protons in one direction with either other protons or anti-protons within the other, reaching higher energies but creating a way messier, less controllable signal to extract.
One Nobelist, Carlo Rubbia had involved in physics just to create something entirely novel: a muon collider. It’s ambitious and presently impractical, but it just could be the longer term of high-energy physics .
Above, you’ll see the particles and antiparticles of the quality Model, which have now all been discovered. The massive Hadron Collider (LHC) at CERN discovered the Higgs Boson, the long-sought-after last holdout, earlier this decade. While there’s still much science left to be done at the LHC — it’s only taken 2% of all the info it’ll acquire by the top of the 2030s — particle physicists are already looking ahead to subsequent generation of future colliders.
All of the plans put forth involve scaled-up version of existing technologies that are utilized in past and/or current accelerators. We all know the way to accelerate electrons, positrons, and protons during a line . We all know the way to bend them into a circle, and maximize both the energy of the collisions and therefore the number of particles colliding per second. Larger, more energetic versions of existing technologies are the only approach.
Of course, there are both benefits and disadvantages to every method we could use. You’ll build a linear collider, but the energy you’ll reach goes to be limited by how powerfully you’ll impart energy to those particles per-unit-distance also as how long you build your accelerator. The disadvantage is that, without endless injection of circulating particles, linear colliders have lower collision rates and take longer amounts of your time to gather an equivalent amount of knowledge .
The other main sort of collider is that the style currently used at CERN: circular colliders. Rather than only getting one continuous shot to accelerate your particles before giving them the chance to collide, you speed them up while bending them during a circle, adding more and more particles to every clockwise and counter-clockwise beam with every revolution. You found out your detectors at designated collision points, and measure what comes out.
This is the well-liked method, as your tunnel is long enough and your magnets are strong enough, for both electron/positron and proton/proton colliders. Compared to linear colliders, with a circular collider, you get
1. Greater numbers of particles inside the beam at anybody time,
2. Second and third and thousandth chances for particles that missed each other on the prior undergo
3. And far greater collision rates overall, particularly for lower-energy heavy particles just like the Z-boson.
In general, electron/positron colliders are better for precision studies of known particles, while proton/proton colliders are better for probing the energy frontier.
In fact, if you compare the LHC — which collides protons with protons — with the previous collider within the same tunnel (LEP, which collided electrons with positrons), you’d find something that surprises most people: the particles inside LEP went much, much faster than those inside the LHC!
Everything during this Universe is restricted by the speed of sunshine during a vacuum: 299,792,458 m/s. It’s impossible to accelerate any massive particle there to speed, much less past it. At the LHC, particles get accelerated up to extremely high energies of seven TeV per particle. Considering that a proton’s energy is merely 938 MeV (or 0.000938 TeV), it’s easy to ascertain how it reaches a speed of 299,792,455 m/s.
But the electrons and positrons at LEP went even faster: 299,792,457.9964 m/s. Yet despite these enormous speeds, they only reached energies of ~110 GeV, or 1.6% the energies achieved at the LHC.
Let’s understand how colliding particles create new ones First, the energy available for creating new particles — the “E” in E = mc2 — comes from the center-of-mass energy of the 2 colliding particles. During a proton-proton collision, it’s the interior structures that collide: quarks and gluons. The energy of every proton is split up among many constituent particles, and these particles zip around inside the proton also . When two of them collide, the energy available for creating new particles might still be large (up to 2 or 3 TeV), but isn’t the full-on 14 TeV.
But the electron-positron idea may be a lot cleaner: they’re not composite particles, and that they don’t have internal structure or energy divided among constituents. Accelerate an electron and positron to an equivalent speed in opposite directions, and 100% of that energy goes into creating new particles. But it won’t be anywhere near 14 TeV.
Even though electrons and positrons go much faster than protons do, the entire amount of energy a particle possesses is decided by its speed and also its original mass. The electrons and positrons are much closer to the speed of sunshine , it takes nearly 2,000 of them to form up the maximum amount mass as a proton. they need a greater speed but a way lower mass , and hence, a lower energy overall.
There’s an honest physics reasons why, even with an equivalent radius ring and therefore the same strong magnetic fields to bend them into a circle, electrons won’t reach an equivalent energy as protons: synchrotron radiation. Once you accelerate a charged particle with a magnetic flux , it gives off radiation, which suggests it carries energy away.
This is where the large idea of using muons comes in. Muons (and anti-muons) are the cousins of electrons (and positrons), being:
1. Fundamental (and not composite) particles,
2. Being 206 times as massive as an electron (with a way smaller charge-to-mass ratio and far less synchrotron radiation)
3. And also, unlike electrons or positrons, being fundamentally unstable.
That last difference is that the present dealbreaker: muon particle have a mean lifetime of just 2.2 microseconds before decaying away.
If we could accelerate a muon particle up to an equivalent 6.5 TeV in energy that LHC protons achieved during their prior data-taking run, that unstable muon particle would live for 135,000 microseconds rather than 2.2 microseconds: enough time to circle the LHC some 1,500 times before decaying away. If you’ll collide a muon/anti-muon pair at those speeds, you’d have 100% of that energy — all 13 TeV of it — available for particle creation.
Humanity can always prefer to build a much bigger ring or invest in producing stronger-field magnets; those are easy ways to travel to higher energies in high-energy physics . But there’s no cure for synchrotron(a cyclotron in which magnetic field strength increases with the energy of particle in order to remain orbital radius constant) radiation with electrons and positrons; you’d need to use heavier particles instead. There’s no cure for energy being distributed among multiple constituent particles inside a proton; you’d need to use fundamental particles instead.
The muon particle is that the one particle that would solve both of those issues. The sole drawback is that they’re unstable, and difficult to stay alive for an extended time. However, they’re easy to make: smash a proton beam into a bit of acrylic and you’ll produce pions( a meson having mass approximately 270 times than that of an electron), which can decay into both muons and anti-muons. Accelerate those muons to high energy and collimate them into beams, and you’ll put them during a circular collider.
The MICE collaboration — which stands for Muon Ionization Cooling Experiment — continues to push this technology to new heights, and should make a muon collider a true possibility for the longer term . The goal is to reveal whatever secrets nature may need waiting future for us, and these are secrets we cannot predict.
As Carlo Rubbia himself said, these fundamental choices are coming from nature, not from individuals. Theorists can do what they like, but nature is that the one deciding within the end.