Science

The 3-sigma bump reported by Fermilab on Wednesday has garnered a lot of attention. Understandable, since it might be a precious sign of particle physics beyond the Standard Model — but it’s also just a 3-sigma bump, and usually those go away.

Via Matt Strassler and Lisa Randall, here’s a set of plots that helps indicate exactly how hard this game really is. The plots can all be found on this web page at CERN. In comments Matt and Peter note that they were made by Tommaso Tabarelli de Fatis, as explained on Tommaso Dorigo’s blog. Here is the original plot from the CDF paper:

We’re looking at the number of events that produce a W boson and two jets, as a function of the energy of the jets. The bottom plot is all the data, while at the top they’ve subtracted off most of the Standard Model background, leaving only the predicted red curve from WW/WZ events. You see the extra little bump around 150 GeV, that’s what’s getting everyone so excited. It’s unlikely that the data are a good fit to the prediction; the “KS (Kolmogorov-Smirnov) probability” is given as 5×10^-5, which means that it’s not bloody likely.

But, just for giggles, let’s imagine that the energy of the jets wasn’t measured very accurately. Obviously the experimenter worked hard to get it right, and I would trust their judgment over my own any day, but you never know. Jets are complicated things with many particles in them, you can imagine being off by a bit.

So here is the same plot, just scaling the jet energy by two percent: …

Science is HardRead More »

The Tevatron accelerator at Fermilab is shutting down soon, for some unavoidable reasons (the LHC is taking over) and some frustrating ones (we’re out of money). But there may be life in the old beast yet; a couple of intriguing anomalies have particle theorists raising their eyebrows in charmingly understated excitement.

Two different anomalies are getting attention right now. One, which has been around for a while but doesn’t seem to be going away, is a forward-backward asymmetry in top quark production. Unlike the LHC, which just smashes protons together, the Tevatron has a proton beam and an antiproton beam. Intriguingly, when collisions produce a top-antitop pair, they seem to be preferentially produced in the direction of the protons rather than the antiprotons. If you want a popular-level account, here’s Ron Cowen at Science News, while Jester gives you the technical details at Résonaances. I’ll just show you a pretty picture; the horizontal axis is “forward” cross section, while the vertical axis is the “backward” cross section, both in units of the Standard Model expectation. The center of the plot is where we should be, and as you can see we are just a bit off.

A completely different anomaly seems to have just cropped up, this time in collisions that produce a W boson as well as two “jets” (particle-physics speak for “bunches of particles typically associated with the production of strongly-interacting stuff). Once again we have explanations in the MSM and on the blogs: Dennis Overbye at the NYT, and Flip Tanedo at US LHC Blogs. What happens here is that you just measure how many events you see as a function of how much energy is in the jets. Then you look for a “bump,” which as John has taught us is often a signature of a new particle that has been produced and then quickly decayed. Do you see the bump?

…

Anomalies at FermilabRead More »

Over on the Facebooks, Matt Strassler points to a BBC story about the role of quantum mechanics in explaining our sense of smell. There aren’t any equations in the article, and I haven’t read the research papers, but the idea seems to be that electrons move from one part of a protein to another part via quantum tunneling. The potential that allows this to happen is only set up if you have the right chemical involved, which is how the protein purportedly “smells” the existence of this chemical. The resulting mechanism is just absurdly sensitive — apparently fruit flies can smell the difference between hydrogen and deuterium (chemically identical, but tiny differences in atomic energy levels from having an extra neutron in the nucleus).

It’s still a controversial theory, but apparently not crackpotty. The question of how important quantum mechanics (as opposed to just its classical limit) is for biological processes was brought up in our earlier post on quantum photosynthesis. Which reminds me in turn of this worthwhile talk by Seth Lloyd, on the basic topic of “quantum life” and photosynthesis in particular. In between learning about how quantum phenomena might remain relevant in the hot, warm environment of a plant, you can enjoy Lloyd’s principled stance not to use PowerPoint under any circumstances.

We’re not very good at defining what “consciousness” is, although we think we know it when we see it. One promising avenue of attack on the problem is to consider how consciousness may have developed over the course of the evolution of life. There’s a great blog post about this by Malcolm MacIver over on our sibling blog Science Not Fiction. He is thinking about an obviously-important event in the history of life — the moment when aquatic organisms first flapped up onto land and starting breathing air, if we may greatly simplify a complicated process — and asking about its consequences for consciousness.

The idea is one of those deceptively simple ones that makes you wonder why you didn’t think of it all along. The point is: attenuation lengths. In water, you just can’t see very far; your vision becomes blurry after a matter of meters. Consequently, you don’t have much time — maybe seconds — to react to the world around you, whether what you see is prey, a danger, or a potential love interest. So the evolutionary pressure is to “make up your mind” extremely quickly, essentially right away.

Now imagine you crawl up into the air. Suddenly, you can see for kilometers! Now a different mode of action becomes useful: thinking about hypothetical alternatives. Under water, too much Hamlet-like equivocation would have made you someone’s dinner before long; now, you can ask yourself whether it would be better to duck under a rock, scurry up a tree, or finally take a stand against that big bully.

The ability to contemplate competing alternatives before making a decision is a crucial part of what we call consciousness. It’s related to another idea I believe I first got from Steven Pinker’s The Language Instinct, although I don’t remember the precise passage: the claim that what really separates the conscious from the non-conscious is the ability to use grammar. In particular, the subjunctive mood, in which we talk about hypothetical futures. (“If I were to go and bring you back some tasty fish, would you let me live?”) Lots of animals can communicate using something like “language,” but the ability to make agreements based on contrary-to-fact scenarios is what separates the shouters from the negotiators. And of course, the ability to contemplate hypothetical scenarios is an important prior step to being able to communicate about them.

Be sure to read the comments, where man good questions are asked (“What about octopuses?” “Aren’t there senses other than vision?”) and also answered. Malcolm also provocatively tries to imagine what it would mean if we vastly improved our sensory capabilities, which of course technology is doing for us all the time. What’s next after consciousness?

Ah, the life of an experimental physicist. Long hours of mind-bending labor, all in service of those few precious moments in which you glimpse one of Nature’s true secrets for the very first time. Followed by the moment when your bosses tell you it was all just a trick.

Not that you didn’t see it coming. As we know, the LIGO experiment and its friend the Virgo experiment are hot on the trail of gravitational waves. They haven’t found any yet, but given the current sensitivity, that’s not too much of a surprise. Advanced LIGO is moving forward, and when that is up and running the situation is expected to change.

But who knows? We could be surprised. It’s certainly necessary to comb through the data looking for signals, even if they’re not expected at this level of sensitivity.

Of course, there is something of a bias at work: scientists are human beings, and they want to find a signal, no matter how sincerely they may rhapsodize about the satisfaction of a solid null result. (Do the words “life on a meteorite” mean anything to you?) So, to keep themselves honest and make sure the data-analysis pipeline is working correctly, the LIGO collaboration does something sneaky: they inject false signals into the data. This is done by a select committee of higher-ups; the people actually analyzing the data don’t know whether a purported signal they identify is real, or fake. It’s their job to analyze things carefully and carry the whole process through, right up to the point where you have written a paper about your results. Only then is the truth revealed.

Yesterday kicked off the LIGO-Virgo collaboration meeting here in sunny Southern California. I had been hearing rumors that LIGO had found something, although everyone knew perfectly well that it might be fake — that doesn’t prevent the excitement from building up. Papers were ready to be submitted, and the supposed event even had a colorful name — “Big Dog.” (The source was located in Canis Major, if you must know.)

Steinn Sigurðsson broke the news, and there’s a great detailed post by Amber Stuver, a member of the collaboration. And the answer is: it was fake. Just a drill, folks, nothing to see here. That’s science for you.

When the real thing comes along, they’ll be ready. Can’t wait.