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  • The Large Hadron Collider is the largest and most powerful atom smasher in the world.

  • Built to hunt for new particles and probe the fundamental forces of nature, this massive

  • machine is a 27 kilometer underground loop filled with supercooled magnets and massive

  • detectors that whip particles at the highest speeds possible, to eventually collide into

  • each other.

  • And during one famous sprint in 2012, particles collided, and the Higgs Boson was officially

  • discovered.

  • "I would like to add my congratulations to everybody involved in this tremendous achievement."

  • The Higgs is a special particle.

  • Its presence confirmed the existence of an invisible quantum field that’s responsible

  • for giving particles their mass.

  • This field permeates the universe, leading some to suspect that the Higgs may play an

  • important role in the origin of everything.

  • But at this point, the Large Hadron Collider and the community that built it are at a crossroads.

  • Physicists haven't found the super symmetry particles they were hoping to see.

  • If they did, it would have solved some open mysteries we have about the Higgs and the

  • inner workings of the universe.

  • This has created a huge international debate over what to do next.

  • For many at CERN, the institution that runs the Large Hadron Collider, the next step in

  • the hunt for new physics is to build an even bigger machine.

  • People expected for 40 years before the Higgs was discovered that the Higgs could not be

  • a lonely elementary particle.

  • It would have to come along with a lot of other things in order to give a coherent,

  • rational explanation for the origin of its mass.

  • And the big surprise since July 4, 2012, when the Higgs was triumphantly discovered, is

  • that has not happened.

  • So that's really four decades of a certain paradigm for what's going on in physics associated

  • with the Higgs that has not worked out the way that theorists had imagined that it would.

  • And that's kind of fascinating.

  • I think the last time something of this degree of surprise happened in theoretical physics

  • was a little over 100 years ago.

  • What nature has in mind for what the Higgs is about is something different than what

  • theorists had in mind.

  • While theorists are very confused about it, the program for experimentalists is completely

  • clear.

  • When you run into a kind of elementary particle you've never seen before, youve never seen

  • anything like it in physics before you just put the damn thing under a microscope and

  • you study it to death.

  • It’s pretty remarkable that we need to build enormous machines that produce an incredible

  • amount of energy to probe the smallest things in the universe.

  • And the push towards higher collision energies to discover new particles is connected to

  • Albert Einstein’s famous equation, e=mc^2.

  • There’s an equivalence here between energy on one side and mass on the other side.

  • When we collide two particles, we gain access to the kinetic energy they carry.

  • And out of this kinetic energy, new particles can be made, according to Einstein's relation.

  • And of course, the higher the energy that we bring into this collision, the higher the

  • mass of a particle that is forming out of this energy can be.

  • To get more juice out of the machine, CERN shut the LHC down for performance upgrades.

  • Theyre working on cranking up the luminosity.

  • Luminosity is a measure for the quality of a collider.

  • And in some sense, it tells you how many collisions per second this collider can provide.

  • When two of the elementary particles have a head on collision, you can tell that happened

  • because the result of those collisions come out at larger angles relative to the beams.

  • But it's still an incredibly messy, kind of complicated environment and even when we produce

  • new elementary particles like the Higgs, they don't come out wearing a name tag saying I

  • am a Higgs, they decay in a blink of an eye.

  • It's the results of those decays that experimental colleagues have to sift through like they're

  • looking for a needle in a haystack in order to actually see the evidence.

  • This luminosity upgrade would ultimately produce more collisions and would make measurements

  • of particles like the Higgs even more accurate.

  • Once completed in 2026, itll produce an estimated 15 million Higgs per year, compared

  • to the 3 million in 2017.

  • It will be very beneficial to operate this infrastructure until about 2035 or 2040.

  • By then, we will have collected such a huge amount of data from the collisions that we

  • somehow saturate the knowledge that can be provided by this machine.

  • Operating it five years longer or 10 years longer will not give significantly more information,

  • which means for particle physicists that the useful time of life of this accelerator will

  • be reached.

  • These time scales seem way out in the future, but to put this in perspective: planning for

  • the Large Hadron Collider began back in the 1980s, construction was approved in 1994 and

  • the first runs didn’t start until 2008.

  • So to prepare for what comes next, teams are delivering conceptual designs for next generation

  • particle machines.

  • There are proposals for an International Linear Collider, which Japan just backed out on,

  • China has a circular collider project, and there’s one from CERN.

  • I'm in charge of the Future Circular Collider Study.

  • What were working on is really not an upgrade of the LHC machine.

  • It's really new machines to come after the LHC era, so from 2040 onwards.

  • Itll take international collaboration, billions of dollars, and scientists to invent

  • tools that don’t even exist yet.

  • First thing's first though, CERN wants a bigger tunnel.

  • On a map, you can imagine you have a circle, which is the LHC, and then you would put a

  • new circle that is roughly four times larger.

  • The whole existing CERN accelerator complex, including the LHC, would serve as a pre-accelerator

  • for this future 100 km machine.

  • Like the gearbox in a car, if you want to drive very fast you must have several gears.

  • You start in a small gear at low velocity, and once you accelerate, you go to the second

  • gear, third gear, fourth gear, fifth gear.

  • This thing is very similar.

  • We would start with small accelerators at low energy, and then we go larger, larger,

  • larger, and to higher energy, higher energy, higher energy.

  • The CERN study presents a path forward to achieve these energy gear shifts.

  • There’s a new lepton collider, which collides electrons and positrons, a more advanced hadron

  • collider, which collides protons and protons and then heavy ions and then a third option,

  • an electron-proton collider.

  • The big difference between an electron and the proton, which are the two particles that

  • we have for these colliders, is essentially that the electron and its anti-particle positron

  • are point-like particles that to our present knowledge have no substructure.

  • When we say the electron looks point-like and the proton does not, it actually means

  • if you bounce things off the electron you see that the way photons bounce off of it,

  • you'll see that the electron has no substructure of any sort.

  • Who knows, if we're probing things with microscopes that are a million times stronger than anything

  • we've seen in some alien civilization that's a million times stronger than the LHC, maybe

  • we would see some substructure to the electron too.

  • Or, if you believe string theorists, if we look at ridiculously short distances, everything

  • is made out of some little loop of string.

  • In what sense are things elementary or composite?

  • But that's a story for another day.

  • The Higgs is kind of point like, the Higgs is sort of point liken and that's just not

  • good enough to sort of really settle this theoretically dramatic question.

  • We can try to measure all the known particles like the Higgs particle, the W, and the set

  • particle in the top quark with the best precision possible.

  • And for this, you will build this lepton collider, because the lepton collider could produce

  • exactly these particles in a very clean environment, in huge numbers.

  • The electrons are super clean for collisions, but we cannot reach extremely high energies.

  • The protons are a bit more dirty in the collision, but we can accelerate them to far, far higher

  • energies.

  • Unlike the electron, a proton is not an elementary particle.

  • The proton is kind of a big messy object that's made up out of these smaller constituents

  • known as quarks that are held together inside the proton by the imaginatively named gluons.

  • When we smash protons into each other at incredibly high energies, one set is going this way at

  • .9999999 the speed of light, the others are going the other way the same number of 9s

  • times the speed of light, and when they smash into each other, mostly they go splat.

  • And the debris of the collisions goes into the direction of the beams that were coming

  • in.

  • The next generation Hadron Collider would smash protons together like the LHC, except

  • it'd reach energies of 100 trillion electron volts.

  • The Hadron Collider would provide much higher collision energies that would allow direct

  • creation of, today not known particles.

  • This boosted machine could be used as a tool to search for theoretical particles like WIMPS,

  • which are connected to dark matter.

  • It’s one of the most abundant and mysterious forms of matter in the universe, and we haven't

  • detected it directly yet.

  • We might be able to, and answer other big questions, by upping the power and tweaking

  • the detector's precision.

  • A factor of 100 in precision is what we need to decisively settle the question of whether

  • the Higgs looks more point-like than anything we've seen before as far as its probes interact

  • with other particles, factor of 10 higher in energy will let us produce billions of

  • Higgs.

  • 100 TV is what we need to settle this question of the simplest model of weakly interacting

  • particles.

  • The natural sequence is clearly to start with a lepton collider, which is also a machine

  • that is today technically ready for construction.

  • And in parallel to the operation and physics analysis of this machine, you can use the

  • time to develop the very high field superconducting magnets that you need for the successor machine.

  • The magnets that we have presently operating in the LHC tunnel can only reach eight or

  • nine Tesla, which is the magnetic field strength.

  • So we want to double this to 16 or even higher.

  • Magnets, is in this case the really big challenge for such a project.

  • All these things need to be addressed from the very beginning in small setups because

  • you do not want to build 15 meter long heavy magnets every time to test something new.

  • While this project is an incredible scientific endeavor, the price tag is very steep.

  • These future colliders could cost over $25 billion dollars and would need investment

  • from the international community to even get off the ground.

  • For this decision process, there are several aspects, of course.

  • There's a scientific political one, there is an economical one.

  • There is of course also a physics community process.

  • And this is exactly what started out as a bottom-up opinion making process, which is

  • taking place in Europe in the coming year.

  • While the discussions continue, some have even questioned whether an investment like

  • this is even the right course forward for the particle physics community.

  • There are questions over whether the science case is as strong, if investing in this project

  • is worth the cost compared to other global issues, and how we can be so sure a machine