Sad Passing… July 6, 2007
Posted by gordonwatts in physics.add a comment
Not of a person, but of an experiment. HERA has finished. Its last beam was on June 30th. Many many people worked on the experiments (H1 and ZEUS) at this accelerator — I know many of them. When something like this happens it is like a hole opens up in your life. Our experiments now run for so long…
It Comes Down To A Fan July 4, 2007
Posted by gordonwatts in computers, physics.add a comment
Recently one of the readout crates in D0 started having odd problems. The hardware my group is responsible for started crashing. These were Linux kernel panics: the OS on the board had given up the ghost and was checking out for lunch — instead of taking data for the D0 experiment.
These problems are very hard to track down. And this one was starting to look really tough. All of us were thinking about what software bug had been recently introduced or perhaps the other hardware in the crate had started feeding us bad data and we weren’t protected against it?? The error was happening in the Linux kernel too - which makes debugging rather difficult.
Then Dan, who was in charge of the whole crate, noticed that one of the cooling fans had died. He fixed it, and there have been no crashes since. The problem was that most of us haven’t had to deal with the hardware in so long that it didn’t really occur to us that this could be a hardware problem — less that it could be a cooling problem! The basic problem, is, that the hardware has been too reliable. 
This reminds me of a set of computers we purchased to run a farm in this same system. The fans on the CPU’s were all cheap, and started to fail. It took us a while to figure it out: the machines started randomly crashing.
It isn’t all software! How many of us are still working hard on hardware? Probably not enough!
The Single Top PRL Is "Worth Reading" June 30, 2007
Posted by gordonwatts in physics.add a comment
My Dad just pointed out to me that D0’s single top PRL has been marked by PRL as “worth reading.” I wasn’t aware of this designation — but it is generally meant to get readers who are in other sub-fields of physics to read the paper because it is both well written and important. That is cool!
I am also impressed that my Dad still gets the printed version!
N.B. Some of the above links point into the PRL archives. These may require you or your associated university to have a subscription. Sorry!
Together We Stand June 20, 2007
Posted by gordonwatts in physics.4 comments
Listening to a Higgs talk yesterday talking about prospects for a Standard Model Higgs search in 4 fb-1 and 8 fb-1 of data (2008 and 2009 results) one realizes that neither experiment can really do the job alone. Together, the two experiments can do a lot and cover a rather broad mass range. But apart neither of us are going to be able to do all that much. The Higgs is just too hard to find!
Combining results is difficult. It is difficult because of errors. When DZERO says that it has a 20% error due to Jet Energy Scale, is that really the same error that CDF reports as its Jet Energy Scale? In all likelihood, the answer is no. To do the combination properly is key to get these sorts of thing right and clear. This will require quite a bit of collaboration between the two experiments. Together, we have a chance of ruling out large stretches of the low mass range of the Standard Model Higgs: exactly the area the LHC has the most difficulty with.
I can’t wait.
Luminosity Profile June 19, 2007
Posted by gordonwatts in physics.5 comments
Yesterday, Dmitri, one of our co-spokes person, showed this plot. I like this plot because it really made me rethink what is going on with our experiments luminosity. I like plots that jar me out of some preconceived notion I have.
Our experiment lives and dies by the amount of data it gets. Until recently the Tevatron accelerator was breaking high luminosity records. These high luminosities are tough to handle for the experiments: so much data arrives in such a short time that we often have to throw some of it on the floor just to keep up! Not good. We tend to focus most of our conversation on these issues.
The plot, however, shows that the bulk of the data we collect is otherwise. That plot is the luminosity profile for Run IIb. IIb is since we installed our inner layer of silicon — last summer. The x axis of that plot is the luminosity. The bulk of the events we have recorded were taking close to 50E30 — a fairly low luminosity (we get stressed out at about 200 or above). So it isn’t incorrect that our systems are still optimized for those lower luminosities: that is where we get most of our data!
That being said, however, there is a general rule of thumb in particle physics. New and interesting results and physics only occurs when you double your data. Most results coming out of the experiment are about 1 fb-1 of data. The next round of results will be between 2 and 3. After that we will need more than 4 to make real progress. In order to do that in a timely fashion (i.e. before the LHC starts up), the Tevatron will have to deliver more and more luminosity. One main way to do that is move the average of that plot to the right! And then we will need to re-optimize our system to deal with the higher luminosities!
This plot was done by Boris Tuchming for some of his muon studies. If you want to see it in context, check out D0’s talk at the P5 meeting.
Update: See comments for more details of the makeup of this sample.
Rumor News June 18, 2007
Posted by gordonwatts in physics.3 comments
A fairly decent article on the rumor appeared. It is written by Wired (but I could only find it on ABC news). I was alerted to this by T’s comments in my previous post. It actually tries to address what a statistical fluctuation means, and finishes up with the following paragraph:
Whatever the final outcome, the weeks of rumors and response say more about the sociology of science than about science itself. The hard physics will come only when (and if) data is released, and the business of testing, interpreting and re-analyzing begins.
Hear! Hear! Worth a read.
Bye Bye Table June 6, 2007
Posted by gordonwatts in physics, university.1 comment so far
This is a picture of a a very very large and very very flat granite table in the basement of the UW physics building. It is about to be split into bits and carted out and thrown in the trash.
It was used as the construction platform for UW’s ATLAS forward muon chamber construction. In order to correctly reconstruct muons this granite table had to be ultra flat — the specs say to 0.000125 at 71 degrees F (measured May 17, 1999). For almost three years a glue robot traveled its surface putting together the muon chambers. That task finished more than a year ago, and the physics building needs the space back for some astrophysics experiments.
That granite table doesn’t fit through any doors. In fact, we had to knock out part of the wall of the room and the hallway in order to move it in (I wish I had some pictures from then). Sadly, since no one else is interested in it, we will be splitting it into bits instead of the wall. The week of June 11th a group will use a diamond saw to cit it into bits. Sadly, because of dust and mess, the whole section will be sealed off: it isn’t likely I’ll be able to get in to see the work in progress.
More recent pictures of the table, if you are interested, can be found here.
Enough Already! June 5, 2007
Posted by gordonwatts in blog, physics.22 comments
Just stop! The latest batch of rumors of a bump in a D0 analysis has gotten way out of hand. My original plan was not to say anything: I can’t participate in rumor mongering here: I’m a member of D0. So I have little to gain, and a lot to lose!
So, before I get to what pissed me off. If you want to read the rumors head over to Tommaso’s blog (here and here). He even left me a comment recently:
On a totally different matter, Godon: please leak something about the new evidence for weird bbbar production found by D0. Is it true it is a 5-sigma effect ? Is it at 180 GeV ? How about its width ?
Let us know!
I will now tell all. It is definitely true that there are people in D0 working on such an analysis. The people working on the analysis are some of D0’s best. And the review board for this analysis (a hot analysis long before any of these rumors started) has a number of very good people. The point is: D0 isn’t going to release anything officially until they are sure it is right. It is the same with every analysis we release. So, till then — rumor away (I’m keeping score) – but they are rumors.
So, when that analysis makes it out this blog will not be the place to see it first. I am not directly involved in it — or even in reviewing it (except as a collaboration member). The official D0 results page will have all the info you need. I’ll certainly put a pointer to it since there seems to be so much interest in it. When will it come out? Some of the speculation on release doesn’t seem unreasonable, but remember that the criteria here isn’t a conference deadline, but, rather, getting it right. I’ve seen a number of analyzers work very hard to make a conference deadline only to have their review board force them to spend an extra several weeks doing cross checks (and those analyses had no rumors associated with them).
Just remember, ladies and germs: Rumors are rumors, science is science.
So, two things set me off to writing this post. First, Tommaso did it in a minor way:
Will science magazines be willing to wait ? Hmmm. I bet there already are a few investigations ongoing (but I swear I personally have not been contacted by the press yet).
Dude! If you get called by the press to comment on this rumor – you will be making second hand comments on rumors! You have almost no position of authority to talk about this (at least last time you were a member of the collaboration releasing the result — and more importantly, it was public already). A minor misquote by a reporter and you’ll have all of DZERO yelling at the CDF spokes people about your behavior. The previous New Scientist article has already gotten quite a few people upset! Tread carefully here (just some friendly advice, eh…?).
But the thing that really got me angry was the Slate article.
The current rumor, which comes in time for the summer conference circuit, may be different. It claims an experiment at the Tevatron has found a peak twice as high as the previous rumors’ bumps. And unlike the other rumors, this one includes details: the new particle’s mass, for instance, which fits within theoretical bounds on the standard model Higgs. Some versions include a decay chain, which describes what the new particle turned into as the experiment progressed, and which may be consistent with the standard model’s predictions.
Wow. I’m a member of D0, I’ve read the note, and I still learned some new things from this article! But then it goes on to say:
So, if the rumor is true and the standard model Higgs has been found at the Tevatron, the LHC is in big trouble: Immediately, its “guaranteed” success—the final particle of the standard model, not to mention a couple of Nobel Prizes for European scientists—is gone.
….
The irony is that things look just as bleak for the LHC if the rumor is false, and the Europeans end up finding the standard model Higgs themselves.
WTF!???!? There are so many busted things about this. First off, simple discovery of a SM Higgs is not, at least to me, an obvious Nobel. Definitely worth something like that for effort! Isn’t a Nobel prize supposed to be for something that really changes people’s understanding of the world? A standard model Higgs won’t do that — it will confirm it. Perhaps a shared Nobel with Higgs himself? I suppose. Now, a non standard model Higgs. That is definitely worth a Nobel. No question there in my mind. So they give Nobel’s for guaranteed successes? 
His second paragraph, of course, contradicts everything he says in his first paragraph — if the LHC did find the Higgs and get a bunch of Nobel prizes then hey — that would be pretty bleak. Riiight.
The point he is making, I think, is that he doesn’t think there is much chance of the LHC seeing anything beyond the Higgs:
Physicists have developed such a complete description of elementary particles that, once the final piece of the theory is in place, the chances that the LHC will find anything the standard model doesn’t predict are almost negligible.
In short. The LHC just isn’t worth it once the SM Higgs is found. Just shut it down! Spend the money on something else.
He is right in the sense that it is certainly possible we will see a Standard Model Higgs at the LHC and nothing more. From the point of view of moral and the future of particle accelerator based physics that will be awful. From the point of science it will be very interesting. The reason? Because what we know about the Standard Model suggests that something must be happening around the 1 TeV scale. If there is nothing — then there must be a mechanism to “fix” the Standard Model.
What does that mean? Well, if nature does the simplest thing then we would expect the LHC to see something beyond the Standard Model.
Finally, even if the Tevatron does find a Higgs there is no way we will make enough of them to know if it is a SM Higgs or something more interesting. No matter how you look at it, the LHC will be scientifically interesting.
Turns out the Slate author has a web site of his own, and a blog entry where he has a few more details about the rumors. I’m not familiar with him, sounds like he is an ex theorist from Harvard from the blog entry.
The New Yorker on the LHC May 12, 2007
Posted by gordonwatts in physics, physics life.3 comments
The New Yorker has a nice (long - duh!) bit on the LHC. It includes this classic line near the start:
The place was so crowded that it took me five minutes to pay for a cup of coffee, proving the elemental truth that man can build a superconducting collider but not a functional cafeteria.
The spend a bit too much time addressing how the LHC might (or might not) destroy the earth as we know it, but at least bring it to a slightly humorous conclusion.
There is also this quote from Arkani-Hamed (a theorist at Harvard), which I do not think I need to comment on.
It’s a general fact about physics that the people you tend to remember are the theorists,” he went on. “At least in the mythology, experiment plays a less central role. And there’s a natural reason for that, because the ultimate goal isn’t to observe things about nature; the ultimate goal is to understand and explain things about nature. So, for that reason, it’s a chicken-and-egg problem. But definitely you want to be the chicken.”
(the previous paragraph is worth reading too). All-in-all, a good read.
This is Particle Physics? May 2, 2007
Posted by gordonwatts in physics, physics life, science.6 comments
The Wikipedia entry for particle physics does a passable job:
Particle physics is a branch of physics that studies the elementary constituents of matter and radiation, and the interactions between them. It is also called “high energy physics“, because many elementary particles do not occur under normal circumstances in nature, but can be created and detected during energetic collisions of other particles, as is done in particle accelerators.
They talk about finding physics beyond the standard model and the LHC… Nice. But then they have that picture (that I’ve reproduced here). This is the picture of a gold-gold collision at the STAR detector on RHIC (Relativistic Heavy Ion Collider). RHIC is definitely doing physics, though I think it is a stretch to call it particle physics. A gold atom is very complex — many different parton interactions. In particle physics we study mostly two partons interacting. Very different. Indeed, RHIC is often called a nuclear physics experiment for that reason: the whole atom interacts, not just a couple of quarks inside the atom.
I wonder how that picture ended up in Wikipedia?
