Life as a Physicist

Ok, this wasn’t April 1st, rather April 4th. What is worse is CMS saw him first. Darn!

That picture is of the ATLAS detector and Peter Higgs, the fellow whose last name is attached to the Higgs particle - the particle that all of us are after.

See? ATLAS saw him!

Coincidentally an email conversation broke out on a D0 mailing list around the time of this picture discussing the origins of the Higgs mechanism. It was sparked by this yahoo news article. The title is “‘God particle’ expected to be found soon.” Hmmm. Expected to be found? Not sure we are that sure… At any rate.

The email conversation was interesting because because it pointed out that in science often more than one person has the same idea at the same time. Discovery is partly having all the bits in place to build the discovery on. Once all the bits are in place then several people can make the leap.

I’m not familiar with this bit of history, besides Peter Higgs, there was also Robert Brout, Francois Englert, and Tom Kibble in Europe. There are two in America too - Gerald Guralnik and C.R. Hagen. I note that on the Englert page what we normally call the Higgs mechanism is called the Brout-Englert-Higgs mechanism. On the Kibble page it notes that he is credited with the co-discovery of the Higgs with Guralnik and Hagen, the beauty of wikipedia! [they are all basically right, I believe]. Oh — hey — and the UR home page has something up about Hagen as well.

I went to the University of Rochester for my graduate work and my quantum mechanics class was taught by Hagen. At the time I didn’t fully appreciate the work he had done.

There is an essay by Dennis Overbye in the NYTimes today that is a much better discussion of the black hole flap that occurred a week ago, generated by a real article by Dennis. My favorite (laugh) quote:

Besides, the random nature of quantum physics means that there is always a minuscule, but nonzero, chance of anything occurring, including that the new collider could spit out man-eating dragons.

And my favorite serious quote:

“As in all explorations of uncharted domains, there may be a risk,” Dr. Rees wrote, “but there is a hidden cost of saying no.”

Definitely worth a read - much more so that the actual article itself, I think.

A few posts ago I poked fun at the idea that we’d be running 10 TeV Monte Carlo in ATLAS. Not Even Wrong linked to it. So, now I have to eat my words.

We will all be running the Monte Carlo.

Here is the deal. In an experiment like ATLAS we have a huge software base. Think of it like your favorite operating system - Windows, Mac OS, or Linux. Every now and then a new version is created. It is a huge undertaking each time. Lots of source code, lots of updates, lots of new functionality, lots of old things break, etc.

It is the same thing for us in particle physics. The software code to run these experiments, simulate Monte Carlo, reconstruct the data, and analyze the physics is in constant flux. Hopefully improving. Every now and then (say every 6 months or a year or so) all the recent changes are gathered up and released. Once the release is shown to work we let it loose on all of our computer farms with the express task of generating Monte Carlo for us.

This means we regenerate most of our Monte Carlo about once or twice a year. In ATLAS we are working on the version of the code we expect to run when data taking finally arrives (how exciting is that - when data arrives!!). If all goes well in a few months or so it will be in good enough shape to start producing Monte Carlo. And guess what. Whatever the LHC will initially turn on at - that is the energy we will produce the Monte Carlo.

So the whole experiment will be producing Monte Carlo at this energy, not just someone in a back room in secret. Oh well.

I couldn’t have said it better. Though perhaps I’d use a little less sarcasm. It is too bad that Obama and Clinton will talk not at any point discuss science. I guess it makes sense — the hot topic in the USA is faith - perhaps I should be glad that science isn’t the hot topic? I’m having trouble convincing myself.

ATLAS has just finished one of its large collaboration meeting. One of the nice things about these meetings is we get to hear a fairly detailed report on the machine status - something I don’t always hear except in rumors. In this case it was filling in some of the blanks that were in the recent press release explaining that the start up of the LHC would be at the reduced energy of 10 TeV instead of 14 TeV.

The problem is some of the dipole magnets. They have to be trained to run at full field. Full field for most magnets is 8 Tesla, which is about 133333 times stronger than the earth’s magnetic field. They have to be that strong in order to bend the very high energy 7 TeV beams of protons (magnets are to charged particles like protons what lenses are to light). The power requirements are stupendous (scientific term). In fact, they would probably melt if they were made out of regular copper wire. Instead they make them out a special wire that is superconducting when it is very cold. About -270 degrees Celsius.

The beauty about superconducting wire is that it doesn’t dissipate any energy of the current it is carrying. You know how an overloaded plug socket gets warm? That is because some of the current is converted into heat instead of being used to run your computer - a waste. When dealing with the currents in these magnets - well, it would be so hot that it would melt the magnet.

These magnets have a tendency to quench. Which is a problem. Lets say you have a bundle of wires all at -270 degrees carrying a huge amount of current. Lets say a flaw in one part of one wire causes it suddenly to loose its superconducting property. As a result the current flowing through that bit of wire starts to generate heat. That heat, of course, warms up all the wire around it, which causes it to “go normal” as well. This process rapidly cascades until the whole magnet ceases to be superconducting. This is called a quench. If not handled correctly this can be disastrous - you could melt the whole thing (and these things are expensive!). Part of the magnet design is quench protection.

Now, here is the cool thing. To get to their full field strength you have to train the magnets. This is particularly true when you are pushing the envelope of what the technology can do. You do this by slowly increasing the current in the magnet until it quenches. Once it has, you cool it down again and try again. And repeat.

This process is what will prevent the LHC from being ready to run at 14 TeV this year. The retraining of some magnets is taking too long (all the magnets were trained to full strength before they were installed - so some have become “untrained”). So their plans are to retain these magnets that are not properly trained over the first shutdown in the winter of 2008-2009.

And that, right there, tells us how long we will be running at the reduced energy of 10 TeV. If we are very lucky we will see beam in August and that will be our first run. So, probably a few months. Now, if I’m allowed to put on my old-guy hat, I’m going to guess that we won’t really get collisions until later than that and then the data coming out of our detector won’t make much sense until just around the shutdown. So it could well be this initial 10 TeV run gets almost no useful physics out - but is exactly what we need to get our brand spanking new detector into shape for the first real 14 TeV run.

BTW, I should say that the LHC has not told the experiments at what energy it will actually run yet. People think it will probably be 10 TeV, but the official word has not come from the machine division yet. Next week that should happen.

There were several other things of general note at the meeting (actually, there was a lot, but…). One thing is if you watched Peter Jenni’s talk - he gave out a few links you can go for status info. One has the current cooling status of the accelerator. I don’t think it is meant for everyone to look at, so I won’t post the link. But if you are member of ATLAS you can just look at Peter’s talk on the agenda server. The graphic is cool! I want to make it the background on my computer!

The other thing that, as a member of ATLAS, really makes this time exciting is the detection of cosmic rays. More and more detectors are getting turned on - and the first thing that is done with them is to look for cosmic rays. A few months ago people talked about the first cosmic ray having been seen. Now everyone in ATLAS is showing these things. Maybe this thing will work after all…

BaBar closed down the other day. Well, the long running PEP-II collider shut down, and BaBar depended on it for its collisions. The shutdown came a bit earlier than planed due to the science budget cuts.

BaBar has had a long career. If you are curious about its legacy just check out the 528 or so published papers that can be found on SPIRES. It will be missed!

I’m here at CERN and everyone has been talking about the funding mess over in the UK. I was forwarded this BBC article. Reading, besides shaking my head at the mess, I was very impressed at the level of reporting. I don’t think any of the major newspapers or news programs in the USA do nearly as good a job. For example:

When news of likely cuts to certain programmes was announced earlier this year, the STFC process was branded as short-sighted and unsustainable by some.

This is because there is a perception that high-profile projects have been saved, while lower profile areas of basic research, which feed into and support these very same applied programmes, have been axed.

Ok. Ignore the spelling (not that I would be one to complain!). Very clear description of what the main point of friction is. In other places they assume the reader knows a bit about the science being discussed - which results in an article that is fairly high level rather than getting bogged down in defining every word that is used.

If you want to know more, here is another article. By a science reporter with my same last name, no less!

Wow. The way the French medical system operates is totally the opposite of what I’m used to! Paula’s Mom was in the hospital for over two weeks. In the USA I’ve always got the impression that a hospital tries to shoo you out the door as fast as it can. Sometimes it seems like they do it before you are comfortable. The French system is the opposite. In the end it seemed like they were holding her there just so they could give her several shots a day (which are now being delivered by a nurse who comes to the house twice a day for 6 euros each visit).

While the USA seems to error on the side of sending people home a little to early, the French system seems to error - way error — on the other side. Crazy. And thank goodness the insurance back in Canada is willing to pay for it all!

There is a joke going around ATLAS right now. There are various people who are obsessed by their physics studies. Each time something new about the detector is found they want to re-run their analysis. Nothing wrong with that - except that if it requires re-simulating the Monte Carlo that can take real resources (minutes per event just to reconstruct the event - we need millions of events in order to do one out of 1000’s of analyses).

Well, a big one was dropped the other day. Actually, we’ve all heard rumors this was coming, but now it is official, so I can joke about it. This is a big one because it changes everything - the production cross sections, average energy will find in our calorimeter, and other things. So, if you want to know how you are going to discover the Higgs at 10 TeV - well, better restart your simulation.

Of course what really matters is how long the accelerator remains at that energy. I don’t know details (perhaps I’ll learn them at ATLAS week next week) but the release claims that the magnets just need some re-training. If that is the case, that is no big deal and we will be at 10 TeV for less time that it will take the detectors to get themselves in shape to take physics-quality data.

At any rate. I’m sure, in some private cluster, somewhere, some 10 TeV data is being simulated as I type this!

I really didn’t want to say something about this article. Actually, at first I wondered if it was just an excuse to show a truly awesome picture I wasn’t going to write anything. But then it started showing up on tech blogs, it rose to near the top of the New York Time’s most emailed articles. And non-physics friends of mine started asking what I thought about it. And then I saw some of the comments left on the article at the Herald Tribune’s version of the article (read them - it is worth it). I agree with Peter Woit: “it’s unclear why the story deserves any attention” However, I can hold out only so long.

Here is what I think: this article has the legs for reasons similar to why ID and Creationists are able to push the “evolution is only a theory” so effectively.

If you don’t have time to read the article: Wagner (ex physics researcher, lives in Hawaii) and Sancho (author, researcher on time theory (!?), lives somewhere in Spain) are suing Fermilab, the Department of Energy, and CERN to prevent the LHC from being turned on. Their’s is a doomsday worry: a small black hole or something similar will be created in the center of one of the detectors and will quickly expand to eat up the whole universe. Including us. I actually think that I’ve seen Wagner. One day, when I was a graduate student at Fermilab, I remember seeing a collection of people protesting outside the Batavia gate. I didn’t stop, but some friends did. It was someone from Hawaii who was worried we were going to end the universe. I don’t remember the name, but I suspect it was Wagner.

Now, in the evolution and creationism debate we scientist types call evolution a theory. In science it doesn’t get much more iron clad than that - pretty much the top of the heap. Note that we very carefully do not call it a fact. The reason is that science is always looking to improve the answers. We may have a model that fits all of our observations - but that isn’t to say that we’ve not missed something thus will need to extend the model or theory at a later time to account for new observations. Scientists are very careful about declaring the limits of their knowledge, and are very reluctant to go out on a limb and make a statement for which they do not have supporting evidence. That is part of the reason why we don’t call evolution a fact.

Now, lets go back to the article. There are lots of papers talking about mini-black holes and their possible production at the LHC. So far no one has seen any evidence of a black hole generated at any of the operating accelerators. But can you get any scientist to declare: “Absolutely, under no circumstances, ever will there be a black hold like this produced.”? I doubt it. If you asked a particle physicsts if they were worried about it - I don’t know of any that would be. Most would love to be at CERN, in fact, when the LHC starts up. I’d love to be there, but I may be teaching instead.

There is another aspect in this - risk evaluation. For example, it is much more dangerous to drive in your car than fly in an airplane. That is the raw science (statistics, whatever) of it. Yet we fear flying. When it comes to something like this how do you evaluate the risk? There is no way a non-scientist can do it themselves. The more science literacy there is the better people will understand the language that scientists use, but… And there is no way you would want to limit scientific endeavors and research to the list of topics that the non-scientist can easily understand! Ahhh… outreach!

Obligatory joke: fear not; us particle physicists will be first to pay if we’re wrong.

But you have to admit — that is one amazing picture of CMS! These large detectors are stunning. I think someone should gather up the copyrights for some of these pictures and make a lulu.com book or something like that.