One of the neat things about being at the CTEQ school last week (more on that in an upcoming post, by the way) was how the representatives from ATLAS and CMS, the two major detectors at the LHC, kept hinting that they’d be releasing some really interesting results at the European Physical Association’s HEP-2011 conference conference this week. Well, it looks like the cat is out of the bag: both detectors are already reporting an excess of events at \(2-3\sigma\) significance around \(\unit{120-150}{\giga\electronvolt}\) in the \(h\to WW \to ll\nu\nu\) decay channel.

What this means, in short, is that the number of times they detected two leptons (\(ll\)) and an amount of missing momentum that corresponds to two neutrinos (\(\nu\nu\)) exceeds the theoretical prediction when the total energy of the leptons and neutrinos is between roughly \(\unit{120}{\giga\electronvolt}\) and \(\unit{150}{\giga\electronvolt}\). This is the sort of thing we would expect to see if the Higgs boson has a mass somewhere in that range, around \(\unit{135}{\giga\electronvolt}\). Of course, it could be a fluke; that happens fairly often, because the way particles interact is essentially random …

Big news out of the CTEQ school tonight: we discovered that the various Twitter feeds which announce new arXiv papers only show you the title of the paper, not the author — not until you click on the link, anyway. So here’s a neat way to have fun at parties: someone who has a smartphone (or tablet) with a Twitter app brings up one of the aforementioned feeds, like HEPExperPapers, picks a paper title, and everyone tries to guess who the authors are, or at least which research group or institution is behind it. Anything with \(\sqrt{s} = \unit{7}{\tera\electronvolt}\) doesn’t count. Converting this into a drinking game is easy, you just drink every time you get it wrong. (i.e. every time) Or every time you get it right. (i.e. never) Or just have a beer in hand. I’m sure that’s within the error bars.

Oh, and for the record: one of the people behind this brilliant idea happens to be the chair of a major university’s physics department.

How many physicists does it take to go through a buffet line?

For some reason, this is one of the defining questions of my first day at the CTEQ summer school. (The answer, by the way, is “all of them.”) Nothing brings scientists together quite like coffee and donuts, except perhaps figuring out exactly where the end of the coffee-and-donut line is.

I won’t be posting daily updates or anything, but I figured this whole “sharing experiences” thing is just what normal people do with blogs, so why not try it? I arrived in Madison on Sunday, which shall henceforth be referred to as “yesterday,” and the first thing I noticed was how fancy the housing accommodations are. Granted, they’re probably putting us in the nicest building on campus, but seriously, no other college I’ve been to has anything like this: a 24-hour front desk, in-building dining, lounges on every floor, bathrooms with walled and curtained shower stalls, individual rooms with a mini-fridge and TV (equipped with expanded basic cable), daily housekeeping service… okay, to be fair the students never get most of that. But still, it’s remarkable how much the housing accommodations feel like a …

As I posted yesterday, I now have a paper (and an account) on arXiv. No, the point of this post is not to gloat (which wouldn’t make any sense because half the people I know already have their own papers out, and the other half are making productive contributions to society). Somehow, I always looked at the process of being “inducted” to arXiv as a big mystery, but it’s really not. I thought I’d explain how the process works.

For starters, there are two ways a person can be associated with arXiv: as a member, or as an author of a preprint. You get a “member account” by simply signing up using the “register” button on the login page. They will ask you for an institutional affiliation, which reflects the fact that the site is designed for academics, but technically anyone can sign up. Then again, there’s no reason to sign up for the site as a “random person”; the only thing your account allows you to do is submit papers, once you get approved as an author.

Becoming an author, on the other hand, doesn’t actually require any involvement on your part. When a …

This site hasn’t been very active recently, but I figured I could revitalize it a bit with a story of why I haven’t been making blog posts: for one thing, I’m preparing to spend a week and a half at the CTEQ summer school in Madison. I’m also involved in preparing a paper for publication (wooo getting published), which has involved a fair amount of proofreading and checking references.

There have been a couple of neat Mythbusters episodes recently which I would have loved to write about, including the one about surviving an underwater explosion. Unfortunately I don’t know enough about fluid dynamics and shockwave physics to say anything useful about it. (That may need to change) I’m also working on something about the older episode where they tested alternative solutions to a flat tire; there’s some interesting physics there, but the details haven’t been coming together as easily as I would have hoped.

And to top it off, I’ve been investing time in some other hobbies… which I should probably start writing about. So maybe that will provide some material to get this blog going again.

In the meantime, here …

When writing a computer program in a language that allows function definitions inside code blocks, it’s pretty common to create a function that references some variable in an enclosing scope. And sometimes you want to delete that variable without making it inaccessible to the function. In Mathematica, you can use Module to do this:

a = 4;
f[x_] = Module[{b=a}, If[x>0,x+b,0]];

Since I used a regular assignment = to define f[x_] rather than delayed assignment :=, this stores the value of a in a “local” variable named something like b$120938, so even after I run

Clear[a];

f[x] still adds four to \(x\), so, for example, f[1] would return 5.

In contrast, if I use Block, Mathematica won’t store the value of a.

a = 4;
f[x_] = Module[{b=a}, If[x>0,x+b,0]];
Clear[a];

After this code snippet f[1] would just return 1+b. (For some reason Mathematica doesn’t seem to recognize that b has a value of a inside the If statement… I’m not sure if this is intentional behavior.)

While catching up on some old Mythbusters episodes, I ran across an interesting myth about spinning bullets. Apparently when you shoot a bullet into the surface of a frozen lake, it bounces backward, bounces over the ice a little way, and keeps spinning even after it comes to rest.

This is a very curious result. At first, it kind of seems to make sense. A bullet comes out of the gun spinning at 80000 revolutions per minute, according to the show, which is pretty fast. So it makes sense that it has a sizable amount of angular momentum, which in turn means it’ll take quite a bit of torque to stop it. Colliding with the ice conceivably might not be able to exert enough torque to do that, so the bullet would keep spinning.

But if that were the case, the bullet should maintain its orientation — it’d keep pointing in the same direction that it came out of the gun, because angular momentum is a vector quantity and it won’t change in either magnitude or direction without an external torque. That clearly wasn’t the case; the bullets the Mythbusters shot skittered across the ice, spinning in …