The ATLAS Book July 16, 2008
Posted by gordonwatts in ATLAS, life.1 comment so far
I learned about the ATLAS book at the Overview week. This is a coffee table book — looks stunning. There are sample chapters. Check it out. I think it will hit bookstores sometime near the end of the summer. I hope they will make it available at Amazon and similar places.
ATLAS Week July 15, 2008
Posted by gordonwatts in ATLAS, physics life.add a comment
Last week was the big once-a-year ATLAS Overview Week. ATLAS holds several collaboration meetings each year. The Overview week is a one week retreat — far enough from CERN that everyone can talk and discuss and isn’t constantly distracted by work. A retreat, of sorts. Many other collaborations do this – both CDF and D0, for example. I’m conflicted about the ATLAS version of these meetings.
First off, this one was better than the last. That isn’t to take anything away from the last one in Glasgow – which was well organized and had a lot of good talks and discussions. This one, in Bern, takes place about two months before we are expecting data, however. I think that gave it a totally different tone. There was much less star gazing — grand plans of the discoveries we would make when the LHC first turned on. That said… the week was organized to approximately follow the flow of the data, from the LHC, to the various sub-detectors, to the trigger, to basic object identification, and, finally, to physics.
The beginning of the week was fascinating. Almost all detector groups now have real data to play with in the form of cosmic rays. They have real problems. They are starting to measure actual numbers of dead channels. They are spending their time getting every channel and readout board working. Those talks had a good dose of realism. I particularly remember, in response to a question, the head of the trigger commenting that the first thing to do was get the most basic stupidest trigger working: a bunch crossing trigger. None of this fancy electron or muon identification. Just the most basic thing so that everyone else could start to see triggers – then everyone can work in parallel. Very cool.
As we got further and further away from the detector and cosmic ray data, the talks were not as compelling. This isn’t a criticism, it is just they don’t have real data to play with. The b-tagging work that I am participating in, for example, needs a collection of jets with tracks to make it real. That means that a trigger, a calorimeter, and a tracker have to work. That means the tracking software has to work, the jet reconstruction software has to work. While all of that has been testing in bits and some of it has been tested with Monte Carlo… well, nothing replaces real data. I can’t wait.
But those first few days where you could hear the panic of “data! We have to make this work now!” setting in definitely made the talks in this meeting well worth it. Which brings me to my main beef with this conference. I think this is one of the most expensive conferences I’ve ever attended – and it is an internal meeting. I understand why it was expensive – we are a large group and it is hard to find a cheap venue that will hold us and this is Switzerland, which is just expensive no matter how you look at it; doubly so for someone in the USA due to the exchange rate. The upshot is that many people who I think wanted to attend could not because their groups could not afford it. I noticed this with both European and US groups. This is too bad. More than one person explained that this was historical – Overview weeks were aimed to give an overview of the current status of the experiment – so just the big guys would attend.
I really like the idea that these meetings occur away from CERN. I hope that we in ATLAS can adapt them to become workshops which include postdocs and students – indeed, are more aimed at them then they are at old people like myself.
The other half of this meeting was that I had internet access between 8am and 6pm, and that was it. I found myself going out at night, always coming home a bit drunk, but up at 7am and sitting in the meeting room by 8 or 8:30 (except, ahem, for Friday). I got more done there than I have in a long time and I still managed to listen to most of the talks. Even got to bed at a more reasonable hour. Suddenly no Internet at home is starting to sound reasonable! Despite the horrible train ride home, I returned refreshed. That almost is never the case for me and a conference. I usually am more stressed out because I’ve fallen so far behind on work.
Internet In European Hotels July 7, 2008
Posted by gordonwatts in ATLAS, travel.add a comment
I’m at the ATLAS overview week conference in Bern this week. My hotel, which is excellent – big, comfortable, in the old section of town so really nice area… has no Internet. As a result, you may not see many posts from me this week…
Actually, I lied. I can pick up an Internet I can pay for if I stick my portable out the window. Not exactly comfortable… I guess I’ll have to take a mini-vacation during the evening…
US ATLAS Construction: Check! July 2, 2008
Posted by gordonwatts in ATLAS, USA, science.2 comments
This is a by-product of big science – and the resulting management and budget oversight. The last bit of the ALTAS detector was shipped over to CERN a long long time ago. For example, at UW, we spent almost three years running continuous production for the forward muon chambers (the picture is that of one of them being lifted into place). The last one left our lab more than 2 years ago (might even have been 3 now). In fact, an astro-physics experiment has chopped up the large granite block and taken over the space already.
A project like ATLAS evolves. There is no real beginning. And it will be hard to identify an end. People will be working on it long after it has ceased to take data, for example.
But that isn’t true for the bureaucracy. Budgets and oversight demand a definite start and a definite end. And that just happened for the construction phase for the ATLAS project in the USA. The budget was tied off. No more money for construction. All wrapped up.
I originally wasn’t going to write anything about this. From the point of view of science and public interest in how ATLAS is doing this is, basically, a non-event. What do you care as long as ATLAS sees collisions and produces physics? You don’t care so much about the meat grinder aspect, just that the sausage tastes good, right?
It was the fairly continuous stream of emails that came after the announcement that changed my mind. It has slowed to a trickle now, but there is still about one a day congratulating everyone involved. From the point of view of the managers and people working in the funding agencies this is really a very big deal. BTW — most of the people managing this both inside and outside the funding agencies are scientists or ex-scientists themselves. At any rate — many of these folks labor outside the public eye, but they have done a great job keeping ATLAS going in the USA. After all, without funding, there is no way I or anyone else could participate in the physics! Howard Gordon, at Brookhaven, is mostly singled out for keeping the project on track, though many other names are mentioned.
As one of the congratulatory messages said: “On to operations!”… which happens to be what the physics phase of the funding will be called. 
Weird to see how the bureaucracy in a project like this maps to the real life.
UPDATE: Fixed Howard Gordon’s affiliation.
Curious About ATLAS Reconstruction? June 24, 2008
Posted by gordonwatts in ATLAS, computers.3 comments
This dataflow diagram showed up the other day (warning: VERY LARGE JPEG) in an ATLAS e-news article. It shows how we go from raw data in ATLAS to fully reconstructed objects. It is part of an article describing our reconstruction software performance.
On the left side of the diagram signals digitally recorded enter. We also have information about where in space those signal occurred, and, of course, in what detector (calorimeter, muon system, tracking, etc.). As the data moves from the left to the right it is slowly assembled into objects like charged particle tracks, muon candidates, electron candidate, etc. One thing to keep in mind is we never know with 100% certainty what we are looking at. We might be 99% sure we are looking at an electron, for example, but never 100%. Heck — when we start we dont even know if those signals that appear in the detector are real: they could be noise! These uncertainties must be tracked along with the objects as they move from the left to the right. It takes of order 15 seconds to get from one side of that diagram to the other on a modern processor (we write data to tape at about 200 Hz).
I don’t know what the oldest bit of software is in ATLAS. We, of course, have all the software in a cvs repository. But this is the product of over 10 years of work (this is just the software, remember, not the hardware which has been going on even longer).
Lets hope that it works! 
Agile programmers we are not!
Angles and Demons – ATLAS June 5, 2008
Posted by gordonwatts in ATLAS, CERN, photography, physics life.2 comments
Apparently the ATLAS detector will make an appearance in the film based on Dan Brown’s book Angels and Demons (at least, if the detector scenes aren’t left on the cutting room floor).
Quote from the article:
Anyone at ATLAS who has read the novel is sure to have their own opinions on the author’s particular “creative” take on the laws of physics and his representation of CERN. But, like it or not, CERN plays an important part in the story – as the location from which antimatter is stolen by a secret society intent on creating a bomb to destroy the Vatican.
Right. ’nuff said about the book.
What I thought was very cool was instead of trying to film a scene in the detector – it is almost impossible now as the detector hall is so crowded – they will instead do a 3D model of it and use that. How cool is that? Too bad we can’t do that to all the various bits of equipment that we install and then save them. Sort of the way we currently take digital photographs.
Stammers, who is doing the 3D work for the movie, described the process as follows:
We use these [images] with our own in-house software – an image-based modelling tool – to pinpoint certain areas within each image that are also in other images,” he explains. “From that we can extrapolate a 3D model which is scale accurate, and the photographs can then be used as textures to apply to that model.
This sounds a lot like the PhotoSynth project out of Microsoft Research. I’ve been waiting for someone to make this sort of thing available to someone like me to play around with (read: basically free except for CPU time). While I’m sure I’d never do as high quality job as someone paid for the movies, imagine what you could do with all the detector bits, some of the collision halls, etc.? Now, that would be cool. And then if you could make decent 3D viewing software – what a great outreach project (well, I think it would be cool – no telling what others would think, of course).
The Real Monte Carlo Story April 14, 2008
Posted by gordonwatts in ATLAS, physics.add a comment
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.
ATLAS Week April 12, 2008
Posted by gordonwatts in ATLAS, LHC, physics.add a comment
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…
HEP in the Cloud March 20, 2008
Posted by gordonwatts in ATLAS, computers.10 comments
Amazon has done a lot of work to make GRID computing services accessible to anyone that wants it. Actually, it surprised me that Google or Microsoft didn’t do it first — to run their search engines and other similar things they must have farm computing down to a tee.
In HEP we spend a huge amount of money and cost and time with the GRID. A discussion in a bar some time back generated the question: what would it cost to move HEP into the cloud?
Databases
Yesterday I mentioned databases for storing event data. Amazon has SimpleDB (see this posting to get an idea of how it works). On the surface it looks rather poorly suited to do what we would want to do with our highly structured data. But, ignoring that and some of the overhead it will charge – for the 100 GB of data that Rich had in his database it would cost about 150 bucks a month to store it. Querying is dirt cheap — 14 cents per hour of CPU time used. I have no idea what the performance would be on a database like this, but even if it were x10 slower I doubt it would matter much.
ATLAS’ equivalent database to Rich’s project is thought to be 14 TB/year. That works out to be $21,500/month.
Event Data
Amazon has a simple storage service as well (Amazon S3). Because the data is just a binary blob the cost of storage is much cheaper: 15 cents per GB per month. However, trying to figure out what size ATLAS will actually use if it stored everything in the cloud, and ignored the actual design, is difficult. Making some rough estimates from an old version of the computing model, I’m going to guess about 10 PB per year (that is petabyte!). That is about 1.6 million bucks per month. But we aren’t done with this yet, however – it costs money to move the data in and out. First, just to load the data it will cost about 1 million.
Then we have to use the data – lets say each year we cycle through all the data once — so all 10 PB. That will run about 2.5 million per year (not per month!). But if we use Amazon’s EC2 compute cloud, moving data to it and back is free. In that case, only final datasets will probably be moved. That would be much cheaper.
Computing
This is even harder for me to calculate. This matches up with Amazon’s EC2. One cool thing is data between these computers and S3 is free. Otherwise, for a 32 bit single processor machine that has enough memory to run ATLAS software it looks like it costs about 10 cents per hour of use. Now, in ATLAS an estimate in 2005 was it would take about 3000 kSI2k to reconstruct the average event. So, for an Amazon machine (that is about 1.9 kSI2k) that would take about 26 minutes. So, about 5 cents per event to reconstruct the event. If we expect 2,000,000,000 events per year, then that will cost us $100 million dollars to reconstruct. If someone is familiar with SpecINT2000 and how it works, perhaps they can verify I did this math “ok”. And I’ve not included analysis time which is probably x2 more.
So, there you have it. A lot of money would go into running this in the cloud. Of course, we could never walk up to someone like Amazon and dump this on them. In almost all cases we will do better on our own as we can optimize what we are doing for our uses. Further, the cash that gets spent on this is from all over, and in all different colors. Many nations, for example, buy GRID installations for all scientists in their country. ATLAS just piggybacks on these purchases and uses a portion of them. Still, interesting to see what the cost would be – about 120 million before you even start to analyze the data to produce a physics result!
WARNING: this is very much a back-of-the-envelope calculation!!
National Geographic LHC Article and Pictures March 13, 2008
Posted by gordonwatts in ATLAS, LHC, photography.1 comment so far
Thirsting for some stunning pictures of the LHC? Check out this article in the National Geographic magazine. Make sure to look at the photo-gallery that comes along with the article. Some of the pictures — like the ALICE and CMS detector pictures are really stunning (ATLAS too, of course, but we’ve seen that one already).
BTW — the ATLAS detector is no longer all that photogenic on a grand scale – the cavern is now so full of bits of the detector it is quite difficult to get an idea of how big it is – all your site lines are blocked!
The picture is one of mine of ATLAS. The ones from ATLAS are much better!
