Category: particle physics

Has The Large Hadron Collider Accidentally Thr…

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.

Ask Ethan: Does The Measurement Of The Muon&rs…

Ask Ethan: Does The Measurement Of The Muon’s Magnetic Moment Break The Standard Model?

“[There’s a notable] difference between theory and experiment [for the muon’s magnetic moment]. Is the fact that the [uncertainties are large] more meaningful than the >3 sigma significance calculation? The Mercury precession must have a very small sigma, but is cited as a big proof of relativity. What is a good measure of significance for new physics results?”

Whenever theoretical predictions and experimental results disagree, that’s surely a sign of something interesting. If we’re extremely lucky, it might be a sign of new fundamental physics, which could mean new laws of nature, new particles, new fields, or new interactions. Any of these would be revolutionary, and certainly it’s the great hope of anyone who works on these projects: to peel back the curtain of reality and find the next layer inside. But there are two other possibilities, far more conservative and mundane, that must be ruled out first. One is an error, either on the theoretical or experimental side, that has simply been overlooked. The other is even more subtle, though: an effect from a known physical cause that’s at the heart of this discrepancy, which we haven’t thought we needed to include until now.

The muon’s anomalous magnetic moment might be a harbinger of new physics. But it might also be a subtle effect of gravity that’s appearing for the first time. Come look at the evidence and see for yourself!

This Is Why Physicists Think String Theory Mig…

This Is Why Physicists Think String Theory Might Be Our ‘Theory Of Everything’

“String theory offers a path to quantum gravity, which few alternatives can truly match. If we make the judicious choices of “the math works out this way,” we can get both General Relativity and the Standard Model out of it. It’s the only idea, to date, that gives us this, and that’s why it’s so hotly pursued. No matter whether you tout string theory’s successes or failure, or how you feel about its lack of verifiable predictions, it will no doubt remain one of the most active areas of theoretical physics research. At its core, string theory stands out as the leading idea of a great many physicists’ dreams of an ultimate theory.”

You don’t have to be a fan of string theory to understand why it’s such a promising area of scientific research. One of the holy grails of physics is for a quantum theory of gravitation: that describes gravity on the same footing as the other three forces, in very strong fields and at very tiny distances. Surprisingly, by looking at analogies between gravity and field theories, replacing particles with strings might be the answer.

It’s an incredibly difficult concept to understand why this would be the case without a slew of advanced mathematics, but in 2015, the world’s leading string theorist, Ed Witten, tried. That is to say, he wrote a piece for other physicists entitled, “What every physicist should know about string theory.” 

But what if you want to understand it and you’re not a physicist? Then you should read this.

Five Years After The Higgs, What Else Has The …

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!

Can a black hole erase your past? If a physicist knew exactly…

Can a black hole erase your past?

If a physicist knew exactly how the universe started out, then they would be able to calculate its future for all of space and time. In this universe there is only one future which is uniquely determined by the past. The physical laws of our universe just don’t allow for more than one possible future. But a UC Berkeley mathematician has found some types of black hole where where this law completely breaks down. These claims have been made before but physicists said that a catastrophic event, such as a horrible death, would prevent observers from entering a region of spacetime where their future was not uniquely determined.

Peter Hintz, from UC Berkeley, uses mathematical calculations to show that for some specific types of black hole in a universe is expanding at an accelerating rate, it is possible to survive the passage from a deterministic universe with only one possible future, into a non-deterministic black hole.

If you did manage to travel into one of these benign singularities, then your past would be completely obliterated but it would open you to an infinite number of possible futures.

Ask Ethan: What’s So ‘Anti’ …

Ask Ethan: What’s So ‘Anti’ About Antimatter?

“On a fundamental level, what is the difference between matter and its counterpart antimatter? Is there some sort of intrinsic property that causes a particle to be matter or antimatter? Is there some intrinsic property (like spin) that distinguishes quarks and antiquarks? What what puts the ‘anti’ in anti matter?”

Every particle that exists has an antiparticle counterpart, with some particles behaving as their own antiparticles. Every time a particle collides with its antiparticle, it can annihilate away into pure energy; every time two particles collide with enough free energy, they can create particle/antiparticle pairs. But the key is that there are a whole slew of quantum numbers that must be conserved, and conserving energy is just the start of the story. Not every particle is matter; not every antiparticle is antimatter. Only fermions can have that designation. In fact, every fermion is a matter particle, and every anti-fermion is an antimatter particle, while the bosons, regardless of their other properties, are neither matter nor antimatter. Why is that? Because there are only two quantum numbers that are relevant to the question of whether you’re matter or not: baryon number and lepton number.

How do these come together to put the “matter” in normal matter, and the “anti” in antimatter? Find out on this edition of Ask Ethan!

How does a quark that lives as short a time sp…

How does a quark that lives as short a time span as the Top, interact with a Higgs Boson? Also – if a particle is made that is larger than a Top Quark, is it a quark, a boson or something different? To me it seems the T is more a boson than a quark….

The class a particle belongs to is defined by its spin (quark’s spin ½, boson’s spin 0,1,2…) and electrical charge, because these are the numbers that define the symmetry properties of a particle, not their mass. So I guess if a more massive particle turned out, what it is would depend on its spin and charge. 

I don’t know enough about the Higgs boson to answer your first question, but maybe this could help you?

The top quark does not seem to exist long enou…

The top quark does not seem to exist long enough to feel the weak interaction. Because of its enormous mass, the top quark is extremely short-lived with a predicted lifetime of only 5×10−25 s. As a result, top quarks do not have time before they decay to form hadrons as other quarks do. How does the T interact weakly?

As far as i know, the classical Standard Model theory tells you that the top quark interacts only by means of the strong interaction, and is mainly produced via strong interaction (source). The top quark does not interact weakly with other quarks, but it decays through the weak force. All the quarks in the nucleus interact by means of the strong nuclear force, actually. There might however be a higher order contribution given by a weak interaction (higher order = not really physically relevant). Also, the lifetimes of particles are defined in a system at rest with respect to the frame of reference. But in an accelerator, such as the LHC, all the velocities are relativistic, so the lifetimes are dilated (source), and the lifetime of the top quark from the point of view of a stationary observer is longer  than 

10(−25) s. I guess that’s how one could detect higher order weak interactions in top quarks, but only in relativistic situations  (example).

Also i’m sorry for answering after decades from getting this message.

How Neutrinos Could Solve The Three Greatest O…

How Neutrinos Could Solve The Three Greatest Open Questions In Physics

“Perhaps ironically, the greatest advance in particle physics — a great leap forward beyond the Standard Model — might not come from our greatest experiments and detectors at high-energies, but from a humble, patient look for an ultra-rare decay. We’ve constrained neutrinoless double beta decay to have a lifetime of more than 2 × 1025 years, but the next decade or two of experiments should measure this decay if it exists. So far, neutrinos are the only hint of particle physics beyond the Standard Model. If neutrinoless double beta decay turns out to be real, it might be the future of fundamental physics. It could solve the biggest cosmic questions plaguing humanity today. Our only choice is to look. If nature is kind to us, the future won’t be supersymmetry, extra dimensions, or string theory. We just might have a neutrino revolution on our hands.”

When we look at the Standard Model of particle physics, there’s a big problem that leaps out at us right away: it works well. It works so practically perfectly well that it leaves us very little room for solving some of the problems we have in the Universe: problems like dark matter, dark energy, and the origin of matter. The only hint we have that the Standard Model isn’t fully correct comes from our observations of neutrinos: they have very tiny masses, and they oscillate from one flavor into another. Furthermore, they only come in one chirality: neutrinos are always left-handed and anti-neutrinos are always right-handed. This could be explained if neutrinos weren’t normal (Dirac) fermions like the other Standard Model particles, but were their own antiparticles, and behaved as Majorana fermions. If this scenario is true, it could not only solve the dark matter, dark energy, and matter/antimatter asymmetry problems all at once, but there’s an experimental signature we can look for.

That experiment is running right now! While the LHC is all the rage as far as looking for new physics goes, neutrinoless double beta decay just might bring about the future of fundamental physics.

The LHCb experiment investigates the slight differences…

The LHCb experiment investigates the slight differences between properties of matter and antimatter by studying a type of particle containing the “beauty quark” (or “b quark”). The LHCb Experiment at CERN will shed light on why we live in a universe that appears to be composed almost entirely of matter, but no antimatter.