Ask Ethan: Can Free Quarks Exist Outside Of A Bound-State Particle?
“In our low-energy, modern-day Universe, we only find quarks and antiquarks in bound, hadronic states: baryons, anti-baryons and mesons. But that’s only because the quarks that conventionally exist are long-lived, at low densities, and at low enough energies and temperatures. If we change any one of those three, the existence of free quarks is not only possible, but mandatory.
If the conditions for forming a bound state aren’t met, then confinement is impossible. The four ways we know how to get there are to create a top quark, to look to the early stages of the hot Big Bang, to collide heavy ions together at relativistic speeds, or to look inside the densest objects (like neutron stars or the hypothetical strange quark stars) to find the quark-gluon plasma inside. It’s not an easy feat to accomplish, but if you want to create matter in the most extreme states we know of, you have to go to extreme ends to get there.”
Have you ever wondered, if protons and neutrons are made of quarks, whether it’s possible to have a quark (or antiquark) exist outside of a bound-state system? There are lots of ways that we’ve tried to separate quarks out from their bound states that fail. Split a proton apart and it will split, but into other bound states. Take a meson and pull the quark and antiquark apart, and a new antiquark/quark pair will snap into existence to give you two new mesons instead. Even if you create a quark/antiquark pair in a collider that move in opposite directions, they hadronize and only produce the baryons and mesons we can detect: bound states.
But that’s not the end of the tricks up our (and the Universe’s) sleeve. We can create free quarks after all. If you’re curious, you can now find out how.
Does Particle Physics Have A Future On Earth?
“Will it be successful? Regardless of what we find, that answer is unequivocally yes. In experimental physics, success does not equate to finding something, as some might erroneously believe. Instead, success means knowing something, post-experiment, that you did not know before you did the experiment. To push beyond the presently known frontiers, we’d ideally want both a lepton and a proton collider, at the highest energies and collision rates we can achieve.
There is no doubt that new technologies and spinoffs will come from whichever collider or colliders come next, but that’s not why we do it. We are after the deepest secrets of nature, the ones that will remain elusive even after the Large Hadron Collider finishes. We have the technical capabilities, the personnel, and the expertise to build it right at our fingertips. All we need is the political and financial will, as a civilization, to seek the ultimate truths about nature.”
With the discovery of the Higgs boson and nothing else at the LHC, many physicists are legitimately entertaining what’s been called the “nightmare scenario,” where no new particles exist beyond the Standard Model that can be discovered by terrestrial colliders. But it isn’t a foregone conclusion that there aren’t such particles, and there are two generic types of plan for how we might find any new particles that do exist beyond the LHC’s reach. If the experimental particle physics community comes together to develop a single, coherent proposal for their future, we could probe the frontiers of nature as never before.
Does particle physics have a future on Earth? It should, and here’s what I would recommend they choose if they have the political and financial will to do so.
Why Physics Needs, And Deserves, A Post-LHC Collider
“If what we observe and measure is identical to what the Standard Model predicts, then we haven’t found anything new. So far, that’s what the LHC has revealed: particles that behave in perfect accord with the Standard Model.
But there might be new particles out there. There might be new physics, new forces, new interactions, new couplings, or any slew of exotic scenarios. Some of them are scenarios we haven’t even yet envisioned, but the dream of particle physics is that new data will lead the way. As we peel back the veil of our cosmic ignorance; as we probe the energy frontiers; as we produce more and more events, we start obtaining data like we’ve never had before.”
There are some big differences between theorists and experimentalists. Theorists look at the big picture, come up with their preferred hypotheses and ideas, and work to create a consistent, predictive framework that provide possible signatures of what might extend our knowledge of the Universe. But experimentalists have, as their main goal, to gather more data and probe what is currently unknown. Both work hard to extend our knowledge of the Universe, but experimental results are useful and interesting in their own right, regardless of what truths they do or do not reveal. To some, the LHC’s results, discovering a Standard Model Higgs, and nothing else new, have led to a nightmare scenario.
But the real nightmare would be if we didn’t ask the Universe the next set of questions that a future collider experiment could answer. Learn what could come next today!
For The Last Time: The LHC Will Not Make An Earth-Swallowing Black Hole
“To prevent decay, new, unknown physics — for which no evidence exists — must be invoked.
Even if the newly created black hole were stable, it could not devour the Earth. The maximum rate it could consume matter is 1.1 × 10-25 grams-per-second.
It would take 3 trillion years to grow to a mass of 1 kg.”
Well, it was only a matter of time before someone trotted out the long-debunked claim that the LHC could possibly create an Earth-destroying black hole. I, like most of you, just didn’t expect that person to be the esteemed astronomer Sir Martin Rees!
Well, you’ll be happy to know that not only is his claim untrue, but it’s very easy to demonstrate why. You don’t have to point to cosmic rays (which are more energetic and have struck Earth for billions of years) or rely on anything we haven’t already directly observed. In fact, we can even imagine exotic scenarios that could result in the creation of a black hole, and even then, the Earth is entirely safe.
In less than 200 words, you, too, can learn why the LHC will not make an Earth-swallowing black hole. Sorry, all you armchair supervillains out there.
Has The Large Hadron Collider Accidentally Thrown Away The Evidence For New Physics?
“It’s eminently possible that the LHC created new particles, saw evidence of new interactions, and observed and recorded all the signs of new physics. And it’s also possible, due to our ignorance of what we were looking for, we’ve thrown it all away, and will continue to do so. The nightmare scenario — of no new physics beyond the Standard Model — appears to be coming true. But the real nightmare is the very real possibility that the new physics is there, we’ve built the perfect machine to find it, we’ve found it, and we’ll never realize it because of the decisions and assumptions we’ve made. The real nightmare is that we’ve fooled ourselves into believing the Standard Model is right, because we only looked at one-millionth of the data that’s out there.”
Ten years. Over 200 Petabytes of data. That’s how long it’s been and how much data has been collected since the Large Hadron Collider first turned on. During its data-taking runs, the LHC collided bunches of protons at the incredible speed of 299,792,455 m/s: just 3 m/s slower than the speed of light. Bunches smashed together roughly every 25 nanoseconds inside each detector, and we’ve written that data down as fast as our electronics and the limits of physics will allow.
But even at that, it means that 99.9999% of the collision data needed to be discarded. We’ve only collected data from 1-in-a-million collisions, and that’s a big potential problem. We haven’t seen any evidence for physics beyond the Standard Model there, and one can’t help but wonder if maybe there’s an alternative to the nightmare scenario.
Perhaps new physics is out there, right at our fingertips, and we’ve simply missed it because of what we’ve thrown away. Perhaps the “nightmare” is one we brought upon ourselves.
Five Years After The Higgs, What Else Has The LHC Found?
“There is every reason to be optimistic, since the LHC will produce tons of b-mesons and b-baryons, as well as more Higgs bosons than every other particle source combined. Sure, the biggest breakthrough we could hope for would be the detection of a brand new particle, and evidence for one of the great theoretical breakthroughs that have dominated particle physics in recent decades: supersymmetry, extra dimensions, technicolor, or grand unification. But even in the absence of that, there is plenty to learn, at a fundamental level, about how the Universe works. There are plenty of indicators that nature plays by rules we have not yet fully discovered, and that’s more than enough motivation to keep looking. We already have the machine, and the data will be on its way in unprecedented amounts very soon. Whatever new hints are hiding at the TeV scale will soon be within reach.”
There are lots of calls out there for the LHC to be the last great particle physics collider out there, as fears that there’s nothing new to discover at the energies we can create grip the community. After all, the great hope was that they would find new, unexpected particles at CERN, and that would guide the way forward in the field with experimental evidence. Well, we didn’t get as lucky as we could have, but there are plenty of reasons to be optimistic: there appears to be new physics in the b-quark sector; we’re entering the era of precision Higgs measurements; and the total amount of data we’ve obtained at the LHC is just 1/50th of the total amount we’ll wind up with after Runs III, IV and V are complete. Just because the greatest victory we could have imagined didn’t come true doesn’t mean there isn’t an incredible amount left to learn from this remarkable machine.
Come see, five years on, what we have and haven’t found. The future of particle physics is bright even without made-up evidence for our favored hypotheses!
Nuclear Physics Might Hold The Key To Cracking Open The Standard Model
“Interestingly, this could also lead to a renewed interest in the search for glueballs, which would be the first ever direct evidence of a bound state of gluons in nature! If the exotic QCD predictions of tetraquarks and pentaquarks are borne out in our Universe, it stands to reason that glueballs should be there as well. Perhaps the existence of these composite particles will be verified at the LHC as well, with incredible implications for how our Universe works either way.”
Nuclear physics has, for decades now, been regarded less as a window into fundamental physics and more of a derived science. As we’ve discovered that nuclei, baryons, and mesons are all composite particles made out of quarks, antiquarks, and gluons, though, we’ve realized that there are other possible combinations that nature allows, that should exist. In recent years, we’ve discovered tetraquark and pentaquark states of quarks and antiquarks, and yet there should be even more. QCD, our theory of the strong interactions, predicts that a set of exotic states of bound gluons – known as a glueball – should exist. Finding them, or proving that they don’t exist, might be a way to crack open the Standard Model in an entirely new way.
Nuclear physics might, after all these years, hold the key to going beyond the current limitations of physics.
the central part of the UA1 detector which was used to discover the W- and Z-bosons
The Synchro-Cyclotron; CERN’s first accelerator
sculpture: “Wandering the immeasurable”
“Wandering the immeasurable” and the Globe of Science and Innovation
The bottle of champagne which was opened when the Higgs boson was discovered
a brief insight into my great tour to CERN!