Take What You Need April 22, 2009
Posted by gordonwatts in ATLAS, CERNVM, computers.add a comment
I don’t know where this idea came from, but it was brilliant – CERNVM. It solves two big problems, all at once. And in such a elegant way.
Here is the basic problem: you want to build and run ATLAS (or CMS, ALICE, LHCb, etc.) software on your local university machine or laptop. This is painful for two reasons. The first reason is that it is not likely you are running the proper kind of Linux. Scientific Linux was designed to run science and particle physics code, not run email or have a nice gui (i.e. it isn’t a Mac, or Windows, or ubuntu). There are ways around this, of course – start up a virtual machine and install scientific linux on it, etc. But then you hit the second problem: you have to install the ATLAS software. I’m not sure about the other experiments, but for ATLAS this is a 6 gig affair. And, each time a new version of the release comes out you have to install it all over again. In a virtual machine this can be painful (take hours of your time).
This is where CERNVM comes in. The first realization was that when you compile, build, and test-run, you need only about 10% of that 6 gigs of software. Of course, everyone needs a different 10%, but in general, it is only a small fraction of the release that is needed. So why download everything? The second realization was: automatically install each release or file only when it was needed – and automatically add each release. This second bit means that I, as an end user, never have to install another ATLAS release. Ever! How sweet is that!?!? I can just use it. As soon as a new release is out, and CERN publishes it, then I can access it!
CERNVM is a virtual machine. For folks that have been around CERN a while, they will know that CERNVM refers to the venerable IBM system that CERN used to have as one of its mainframes. According to Predrag Buncic, so I believe is the lead on the modern CERNVM project, that choice of names was on purpose. See Predrag’s talk slides from CHEP for some more details.
CERNVM accomplishes its magic with a FUSE file system. This brilliant open source project creates a virtual file system. Whenever you try to access a file in it, FUSE hands the request off to some user-written code. In CERNVM’s case, this code looks for the file up on a master server at CERN, and then downloads it locally. Once it has been cached locally, the file is accessible like any other file. So, CERN can publish a whole ATLAS release on their master servers, and then when I try to setup that release, CERNVM will automatically bring down exactly the files that I need to get my work done. Better yet, if I’ve already got the files locally, then I can hope on an airplane and everything will still work! Not to shabby!
The virtual machine part of this gets around the wrong OS type – it is based on Scientific Linux. Thus, the two main problems with running local build code are solved! Very nice, eh!?
That Is A Lot Of Work! January 6, 2009
Posted by gordonwatts in ATLAS.6 comments
The thing I spent half my sabbatical on is finally public. It started as an ATLAS wide exercise to make sure our computing environment could handle physics analysis. What better way than to actually do a “dry” run of physics analysis. It grew from there. So much work was invested in it (years, by some peoples account) that it seemed crazy not to make the results public. That took a year: I and my colleagues stopped doing real analysis work for this note over a year ago.
Well, today it was put out on arXiv: Expected Performance of the ATLAS Experiment – Detector, Trigger, and Physics. It is 1852 pages long, so I can’t exactly see everyone rushing to print this out for bedtime reading. No fears; I won’t be disappointed. But it is the PDF to download if you want to know what ATLAS thinks it will be able to do. We even do our best to simulate initial data conditions (misalignment, small data sets). It has chapters on all the big physics topics (Higgs, Top, Exotics, Standard Model, B, etc.) and performance expectations too (electron, muon, tau, b-tagging, etc.).
2009. Ready or not January 2, 2009
Posted by gordonwatts in ATLAS, CERN, D0, Fermilab, LHC, politics, science.4 comments
We’ve made it through the first day of 2009. I have mixed feelings about this coming year.
- Federal Science Funding Levels. The economy is crashing down around our ears. Business responds quickly (layoffs
) – government is a bit slower. If things followed their natural course of action that would mean science funding, along with everything else, will take yet another hit. However, the incoming Obama administration seems to be committed to spending the USA’s way out of this recession, so in the end funding might not change very much. I am hopeful that hard sciences funding will remain at least stable. - Federal Science Funding Directions. Climate change is what the Obama administration is focused on. There is a good chance that if you are researching something connected with climate change you may have access to increased funding opportunities. I would expect a funding profile similar to NIH’s funding during its years of increase. I would like to think that funding will spill over into the physical sciences – it should because there are connections between the physical sciences and clean air technologies. All of this is applied scientific research. I hope that the pure research funding gets an increase as well, as an investment in this countries future (particle physics is pure research, of course). I’m feeling neutral here.
- Federal Science. Obama’s science team is just a BLAST of fresh air when compared to the current administration’s. After all, his DOE nominee is a Nobel prize winning experimental physicist. Even if the science advisor isn’t elevated to a cabinet position (PDF), there will be someone in the room that knows a great deal about science, research, and how it is done. Even if there are cuts to science funding, I’m very hopeful there will be intelligent cuts rather that unscientifically motivated cuts. I’m very hopeful in this respect.
- State Universities. The economy in states is depressing. Some states, like my own (Washington) that rely on sales tax are being hit hard and very fast. State universities can’t escape that, obviously, and my university is no exception. Unfortunately, this usually translates to reduced raises, inability to counter offers from outside, reduced support for research, etc. In our own department I wouldn’t be surprised if some people left for other universities that, for whatever reason, were able to make good offers in this awful climate. There is, in fact, already evidence this is happening. The only consolation is most universities are in the same boat, and so most of them are having similar problems. I know less about private universities, but I do know the endowments of many of them are also having difficulty. I’m very downbeat about this: it will be a rough two years at least, I think.
- My Science. When it comes to the Tevatron and the LHC… Well, I see no reason that the Tevatron shouldn’t continue to break records in luminosity (they just broke one earlier this week). And the experiments will continue to be flooded with data. While it is possible for one experiment or the other to have a catastrophic failure, I doubt that will happen. And they should continue to produce papers and science at a furious rate. I also am looking forward to real LHC collision data this year. While I hope it will be at the full 14 TeV, I suspect it is more likely to be at 2 TeV, just a hair above the Tevatron’s luminosity. We’ll hopefully know what the machine scientists think about that sometime in February. I’m really hopeful about this.
- New Years Resolutions. Well, I made only one. That way I have a hope of keeping it: make bread more often.
I think there is a chance that I will keep this one. Especially now that I’ve said it publically.
Of course, this should also be a fun year, as noted by the Beacon News:
Frustrated with their failed attempt to destroy the world in 2008, the scientists at Fermilab and their counterparts at Switzerland’s CERN physics lab resolve to perfect their new device, the Large Planet-Sucking Black-Hole-o-Tron.
Here is to another great year of data collection and science at the Tevatron and first collision data at the LHC!
How Times Change August 26, 2008
Posted by gordonwatts in ATLAS, computers.add a comment
I was looking at some predictions for the size of the Trigger Processing farm for ATLAS. This farm is basically racks and racks of computers that will decide, in real time, if the data should be kept or discarded as it rolls off the ATLAS detector.
Back in 2003 (see powerpoint slides, page 23, for example) we were predicting that the computer industry would be making 8 GHz processors by now. Of course, due to power and heat problems, we are now sitting around 3 GHz, but with many cores.
Ahhh.. the good old days! 
Will it really take ATLAS 3 years to see 5 sigma Higgs? August 20, 2008
Posted by gordonwatts in ATLAS, CERN, D0, Fermilab.15 comments
Probably (for ATLAS new predictions on this should be released in a few months). But in the context of the Tevatron and the LHC Higgs search that isn’t really what is important.
The ATLAS prediction that it might take 3 years to reach the 5 sigma level for a low mass Higgs discovery got a lot of airplay. It got me to thinking. Lets say the two accelerators are in close competition for the Higgs. The Tevatron can really only speak to the 3 sigma level. It isn’t ever going to get to the 5 sigma level. Further, at the Tevatron the CDF and DZERO experiments will have to combine their results to even reach this 3 sigma level. So, I find it highly unlikely that the LHC will sit back and let the Tevatron get away with this. I certainly wouldn’t (and I’m on a LHC experiment). So what to do? Obvious – beat the Tevatron at its own game: combine results from CMS and ATLAS and the 3 sigma level will be obtained much more quickly. At that point the LHC has stolen the thunder from the Tevatron and CMS and ATLAS can now race each other to individual discoveries of the Higgs at the 5 sigma level.
I don’t expect the experiments to combine for the 5 sigma discovery (I could well be wrong, of course – I know of no plans to not do this or to do this!). There are many forces at play that are driving each experiment to make the first paper submission of a 5 sigma signal. This may, indeed, be what gives the Tevatron space to slip in with a 3 sigma evidence paper. And in the grand scheme of things – the Tevatron goes out with a 3 sigma evidence and the LHC with a 5 sigma discovery – that doesn’t seem like a bad “split”. But who has ever heard of the free market working like that!?
As a member of DZERO I want to push as hard as possible to nail a low mass Higgs. As a member of ATLAS, I want the experiment to scramble as fast as possible to get the Higgs – evidence and discovery. After all, that is one of the LHC’s main points.
Play it safe, or… August 17, 2008
Posted by gordonwatts in ATLAS, CERN, D0, Fermilab.add a comment
There was an unspoken theme at the DZERO workshop this week. Stick with the Tevatron for a huge, but iffy, payoff. Or switch to the LHC now because it is a “sure” bet (as sure as anything gets in research).
This is all about the Standard Model Higgs search at the two accelerators. If such a Higgs does exist the LHC is bound to discover it. The LHC has some “difficulty” at low mass Higgs (below about 125 or so). Difficulty for the LHC means it could take up to 3 years for a single experiment to declare a 5 sigma discovery, the gold standard of “discovery”.
At the Tevatron the Higgs analysis is all about difficulty. Each new Higgs result you hear or read about is a tour-de-force of new techniques and new methods of extracting every last bit of signal out of the experiments. As a graduate student I never remember techniques this sophisticated. And the LHC pre-trial analyses are not as sophisticated either (on the other hand, they don’t need to be).
Global fits to the Standard Model currently predict the Higgs to be low mass – between 114 GeV and 120 or 125 GeV. The Tevatron is currently x2 away from being sensitive to this mass range. By doubling our dataset to 6 fb-1 of data and making a number of improvements to our analyses, we expect that we should be there. These improvements are not easy – it will require a lot of work and a lot of people. Nor are they assured. At best, if the Higgs is there, and we aren’t unlucky, we should be able to see it at the 3 sigma level. But never the 5 sigma discovery level. That will have to be left to the LHC in any case.
So is it worth sticking with the Tevatron? Well… the payoff would be huge to see something at the 3 sigma level. So it is like a lottery with high stakes. The chance of winning is not all that sure, but the jackpot is big!
Me? Well, I’m working on both the LHC and the Tevatron (as are many US physicists). I have a student working on the Higgs search at Fermilab, for example. I’m deeply involved in a number of topics at the LHC as well.
What will happen? Hard to tell. Things to watch? Well, that is easy. There are only two things that really matter here – the performance of the Tevatron and the performance of the LHC. Each physicist who is on both collaborations is performing some complex calculus to optimize their time on the two experiments depending on the chances of success.
I wish us all luck.
Where To Watch For LHC Startup News August 11, 2008
Posted by gordonwatts in ATLAS, LHC.7 comments
A few posts back some folks were wondering where to watch for LHC news as the startup nears. The “LHC First Beam” website seems like a pretty good place to start. For example, recently posted:
After a period of optimization, one bunch was kicked up from the transfer line into the LHC beam pipe and steered about 3 kilometres around the LHC itself on the first attempt. On Saturday, the test was repeated several times to optimize the transfer before the operations group handed the machine back for hardware commissioning to resume on Sunday.
Hey! There has been beam in the LHC!! The website contains a “count-down” clock too. 28 days…
Now I have a stupid question for the folks putting this website together: Why isn’t there a RSS feed!?!?! So old-skool!
Are We Asking This Question? August 8, 2008
Posted by gordonwatts in ATLAS, physics life, press.16 comments
There is a book review in the NYTimes right now by Overbye titled “Inside Story of the Telescope That Nearly Wasn’t Built” – about the Hubble.
The space agency wanted to make sure its long-awaited and astronomically expensive telescope — soon to be launched into orbit above the turbulent fog of the atmosphere — made an appropriately cosmic splash. The advice from those of us in the press peanut gallery was always the same and simple: pictures — cosmic postcards like the live pictures of other planets being transmitted from the Viking and Voyager spacecraft — early and often.
This is PR 101 — everyone, including us scientists, is easily captured by pictures. Especially stunning ones. Sure — they may not be the best way to convey accurate scientific measurements – but they are very easy to relate to. Are we doing the right thing for the start of the LHC? Do we know what pictures – science pictures – we are going to be pushing to the public?
ATLAS has a whole outreach group (as does CMS, I’m sure). We have the ATLAS Book. We have a movie. But what cool picture are we going to give the press when the science starts? Another picture of our detector – like the one attached to this blog posting? Surely we can do better. Our event displays – most are tuned for us to look at as scientists, not for the press or the public. Do we have anything?
Enough of my ideas. What should we have ready when science starts to roll out? At the Tevatron we write these plain-English-summaries. They aren’t totally plain, unfortunately. But perhaps we should get someone from the PR office to work with every analysis that is published to work on something like that?
Other ideas?
Working Together, Apart, on a Paper August 4, 2008
Posted by gordonwatts in ATLAS, computers, physics life.4 comments
A bunch of us are trying to finish up a paper and get it past internal referees in ATLAS. Time scales are extremely short. In order to make sure we beat a deadline we have had to respond to comments from the referees on extremely short timescales (like a day or two). I am located in Marseille, and my student is located at CERN, in Geneva. It really isn’t possible for either one of us to answer the questions and update the paper on our own.
We’ve hardly used email for this process. Two tools we’ve used rather intensely: IM and cvs and LaTeX. IM is exactly what it sounds like – instant messaging. I’m using Pidgin and I think my student, who is on a Mac, is using AOL’s IM client. cvs is a source control system. We have all of the papers’ files hosted by the central cvs system, along with a local copy on each of our machines. When we want to update a file, we edit it, and once we are satisfied, we up load it to the central cvs system, and then the other person downloads the updated file. TeX is a typesetting tool designed for the sciences. It is quite old and while many people swear by it, I don’t think so much of it in today’s modern world of WYSIWYG editors. The central system keeps track of all the changes we make. Finally, we posted the questions from the referees on a twiki. A twiki is basically the same software that is used by Wikipedia – it allows you to edit a web page on the web. As we moved along the document we would update the response to the referees. Occasionally the issue was too complex for IM and we’d resort to Skype.
This worked very well. There were a few places it could have been better. For example, when working on the wording there would often be fights… errr, discussions… between me and my student over wording. So we’d end up putting the paragraph in IM and sending it back and forth. It would have been very cool if I could have just typed something in my editor and he could have seen the update in context where he was working. The other thing that would have been nice was if we didn’t have to worry about which file we were modifying. Because of the way cvs works, if two people modify the same file at the same time, there is a chance that it won’t be able to resolve the conflicting edits. The result is it is often simpler to just communicate which file is being edited and the other person stays out. I have to say that I don’t care much for the editing experience on the twiki. There is a WSIWIG web editor, but it just feels very awkward. It would be cool if I could suck the page into Word, modify it, and then spit it back out again.
The other thing that would have been nice is if Pidgin didn’t keep crashing. And also it would have been nice if we could have sent files or pictures back and forth. For whatever reason this did not work with my students AOL client.
Other novel ways to solve this set of problems?
Basic Physics in ATLAS July 17, 2008
Posted by gordonwatts in ATLAS, physics.4 comments
There are times when I worry that things I have taught in introductory physics – like electricity and magnetism – aren’t really used in particle physics (At UW these are called Physics 121, 122, and 123).
The biggest example is momentum conservation. We use this all the time. In fact, one of the primary ways we will discover a new beyond-the-standard-model particle is via momentum conservation. A common line of reasoning is that we’ve not been able to detect this particle up to now because it doesn’t interact with our matter and our detectors as we expect it to. This is where basic physics comes to the rescue. We know the initial momentum of the collision in our detector. If this new particle were to fly off into the distance and not interact with our detector, then when we summed up the momentum of all of the outgoing particles… well, there would be some missing momentum! Score! Of course, it isn’t quite that simple, things like neutrinos will mimic exactly that signal, but there are ways around it.
The second place basic physics often comes into play is in detector construction and operation. For example, ATLAS has two large and very powerful magnetic fields. The first is the inner tracking field, and the second is the outer toroid field. Magnetic fields interact – think of bringing together two North pole magnets. So these two fields were carefully designed not to interact.
Except, one has to pump current through the outer toroid field to the inner solenoid magnet. As anyone who has taken a basic E&M course will tell you, a current generates a magnetic field. This means the cables that carry the current have to be able to withstand the force of the magnetic field interaction! At these field strengths and the 1000’s of amps of current flowing – that is a lot.
Of course, the engineers knew about this, and designed the cable housing to withstand this. Trickier than it sounds since all of this is superconducting. Still, it was nice to hear the reported successful test of this.
In the picture the 8 large tubes that surround the ATLAS detector generate the toroid field – they are 8 really giant superconducting magnets.
