Record-breaking collisions (Large Hadron Collider producing more mesons than expected)

Initial results from high-energy proton collisions at the Large Hadron Collider offer first glimpse of physics at new energy frontier.

In December, the Large Hadron Collider, the world’s largest particle accelerator, shattered the world record for highest energy particle collisions.

This week, team led by researchers from MIT, CERN and the KFKI Research Institute for Particle and Nuclear Physics in Budapest, Hungary, completed work on the first scientific paper analyzing the results of those collisions. Its findings show that the collisions produced an unexpectedly high number of particles called mesons — a factor that will have to be taken into account when physicists start looking for more rarer particles and for the theorized Higgs boson.

“This is the very first step in a long road to performing extremely sensitive analyses that can detect particles produced only in one in a billion collisions,” says Gunther Roland, MIT associate professor of physics and an author of the new paper.

Roland and MIT professors Wit Busza and Boleslaw Wyslouch, who are members of the CMS (compact muon solenoid) collaboration, were among the study leaders. The CMS collaboration runs one of four detectors at the collider.

The Large Hadron Collider (LHC), located underground near Geneva, Switzerland, started its latest run in late November. On Dec. 8, the proton beams around the 17-mile ring collided at a peak energy of 2.36 tera electron volts (TeV), breaking the previous record of 1.96 TeV achieved at the Fermi National Accelerator Lab. Because of Einstein’s equation, E=mc2, which correlates mass and energy, higher energy levels should produce heavier particles — possibly including some never seen before.

In the new paper, submitted to the Journal of High Energy Physics by CMS, the physicists analyzed the number of particles produced in the aftermath of the high-energy collisions. When protons collide, their energy is predominantly transformed into particles called mesons — specifically, two types of mesons known as pions and kaons.

To their surprise, the researchers that the number of those particles increased faster with collision energy than was predicted by their models, which were based on results of lower-energy collisions.

Taking the new findings into account, the team is now tuning its predictions of how many of those mesons will be found during even higher energy collisions. When those high-energy experiments are conducted, it will be critical to know how many such particles to expect so they can be distinguished from more rare particles.

“If we’re looking for rare particles later on, these mesons will be in the background,” says Roland. “These results show us that our expectations were not completely wrong, but we have to modify things a bit.”

Using the Large Hadron Collider, physicists hope to eventually detect the Higgs boson, a particle that is theorized to give all other particles their mass, as well as evidence for other physical phenomena such as supersymmetry, extra dimensions of space and the creation of a new form of matter called quark-gluon plasma (QGP). The new data provide an important reference point when CMS will look for signatures of QGP creation in collisions of lead ions at the LHC later this year.

The CMS team, which includes more than 2,000 scientists around the world, has 45 members (including faculty, students and research scientists) from the MIT Laboratory for Nuclear Science’s Particle Physics Collaboration and heavy-ion research groups.

The Large Hadron Collider is capable of creating collisions up to 14 TeV, but scientists are gradually easing the machine up to that level to try to avoid safety issues that have arisen in the past. In September 2008, the collider had to be shut down for several months after a connector joining two of the collider’s magnets failed, causing an explosion and leakage of the liquid helium that cools the magnets.

During the collider’s next run in March, researchers hope to create collisions of 7 TeV, says Roland. The success of the latest effort “makes us extremely optimistic about the detector,” he says. “It performed beautifully during the run.”

“This does not prove Quantum Mechanics wrong.”

But if the predictions are wrong, then how can you say that?

In fact, it is the “fantastic accuracy” of the predictions that has been cited by physicists as proof that the theory is right.

I think that what you’re trying to say is that they did their math wrong, and that the theory itself is not the problem. But how do you know? I think that the physicists like to use lofty language to describe the success of the theory because of the need to convince doubters, but in reality, it does not measure up to the claims.

The crown achievement of quantum mechanics, for example, is Feynman’s calculation of the charge of an electron. He calculated it to... I forget... something like the 32nd decimal point? But what is often not mentioned is that no one has ever measured the charge to that level of accuracy, so no one really knows that the prediction is correct. They only know that it he made a very precise PREDICTION. And sometimes, physicists use inexact verbiage and claim that he made an “accurate” prediction instead of a “precise” one.

In fact, there has been very little comparison of the predicted probabilities to the actual probabilities.

I think that what you’re trying to say is that they did their math wrong, and that the theory itself is not the problem.

That's not it. QM provides the pots and pans and the kitchen to cook up a theory, but you have to bring the different ingredients for each type of interaction. The Dirac equation describes the behavior of electrons, and Dirac bragged that it "explains all of chemistry and most of physics". Of course the equation only has meaning in terms of the matrices, operators, and other apparatus of QM.

Today's particle physics depends on the "Standard Model" largely developed in the 1950's through the 1970's. Frankly most of it is beyond my ken, but it also is formulated in the context of QM. It is this "Standard Model" which might be the more worthy focus of your scorn.

To add my own 2 cents. My immediate thought was that this increase in meson production, were it to be amplified as they go to higher energies, could constitute an impenetrable fog which brings all their high hopes and expectations to naught.

Yeah, I thought about that too. But then you can learn a lot from even a null experiment. How you explain it to the taxpayer is another question.

I don’t know how you separate QM from the Standard Model, though. Obviously, the thing that went wrong here was their calculation of the probabilities. That methodology is provided by QM. If you constantly find something else to blame for the failure of the predictions besides QM, then of course you’ll never find fault with QM.

If you constantly find something else to blame for the failure of the predictions besides QM, then of course you’ll never find fault with QM.

You've got the wrong idea. When I search for "meson production", dozens of paper abstracts pop up, a sampling of the many hundreds written in recent years. Here's one from 1982:

Differential cross section for cumulative π--meson production in high-energy deuteron-proton interactions

Abstract. Presents a model of cumulative pi --meson production in the interaction of relativistic deuterons with protons. The interaction of three nucleons is calculated by taking two- and three-particle forces into account. The differential cross section calculated for pi --meson production shows good agreement with the experimental data.

It's a complicated business! When discrepancies with experimental data are found, nobody thinks "Uh oh, Quantum Mechanics is wrong!"

Yes, I know. But I think skepticism is healthy, and there isn’t any here. There is a herd mentality with QM. Of course, it is not just QM. Relativity is another theory that has been “proven” correct. But there is a conflict between relativity and QM. They can’t both be right. It’s sort of like the question of what happens if an unstoppable force meets an immovable object? I suspect that in reality, they are both not quite right. Quantum mechanics is the one that I think may be off the most. The idea of probability playing such a huge role in all this doesn’t make any sense to me. The fact that the mathematics works out doesn’t save it in my mind, especially when you see stories like this one, reporting that the physicists’ calculations of the probabilities told them one thing, but the experiment is telling them something different.

The defects in relativity can’t be very big. But I would not even discount the possibility that there are problems with it. When you hear physicists say that it’s the most extensively tested theory of all time, they are just talking about certain aspects of it, especially the Lorentz transformation. Other aspects, like time dilation, have only been tested in a superficial way, and the simultaneity conclusions have not been tested at all, except to the extent you can say that they are a necessary result of the time dilation conclusions.

The recent dark energy and dark matter observations ought to be a clue that there is something not quite right with the theory of relativity. Maybe you need to observe these things on a universal scale to see that the theory deviates from reality. When you are measuring things on the scale of a laboratory, there is not much difference between x and dx. But if you are measuring on the scale of the universe, you better have the derivative correct, or it will noticeably affect the conclusion.

A lot of what went into Einstein’s theory was his conviction that it had to be right because of the beauty of the rotational and lateral invariances resulting from the Lorentz transformation. Other aspects of the theory, like the twin paradox, which results from the time dilation conclusions, aren’t so beautiful. He traded one kind of beauty for another. But I think he could have come up with a theory that did away with the twin paradox, while making only a minor change to the Lorentz transformation. Obviously, that would have done away with the lateral invariance, and possibly the rotational invariance. But maybe not in a significant enough way to be noticeable in experiment.

Quantum mechanics is the one that I think may be off the most. The idea of probability playing such a huge role in all this doesn’t make any sense to me.

Quantum uncertainty provides the very key to our understanding of atomic structure and the periodic table, which by the way, has to be considered the "crown jewel" of quantum theory, IMO. The uncertainty relation is what defines the ground state of each atomic element, and the basis for all the common material properties that we accept as natural and obvious.

Consider the Hydrogen atom. Why doesn't the single electron just collapse into the nucleus? We can see that uncertainty provides the answer. As it is confined to a smaller and smaller volume, decreasing the uncertainty in position and increasing the ( negative ) binding energy, the uncertainty in velocity grows, giving it a greater ( positve )kinetic energy. At some point the growth in kinetic energy balances the binding energy, and this defines the "ground state", which is a purely quantum concept.

Of course we don't have to be content with a conceptual explanation. All the features of atomic and molecular spectra, binding, reactions, and crystal structure, are beautifully predicted to an astounding degree of exactitude. Further than that, many new predictions are made, and have been exploited to found, among other things, our silicon based society.

What more could one ask? As a theory, it far surpasses any sort of historical expectation. But it doesn't make sense to you! You've got lots of company to be sure. Feynman advised that we should just make our peace with it, and not try to make it conform to our own prejudices. I have found that by thinking in terms of phenomena, and the way they are uniquely accounted for by QM, this is easy to do.

Here's a snapshot I took of my desk lamp. I might give it the title, MY QUANTUM WORLD AND WELCOME TO IT

I’ll grant to you that it holds together as a THEORY. But does it actually describe reality? If the equations predict x number of mesons, and you actually get many times that, then maybe there is a reason.

I personally think there could be other explanations for the fact that electrons don’t crash into the nucleus. For example, we know that the genesis of quantum mechanics was Planck’s discovery that there is a graininess at the finest level. But that graininess does not necessarily have to take the form of uncertainty. It could be that the quantum field is a physical field that simply is disconnected at the finest level. If you tie beads to the weave of a fishnet, for example, no more than one between each two knots, they will never touch, providing of course that you keep the net tight.

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