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Zachary Marshall | USLHC | USA

Read Bio

Us Too!

Tuesday, March 16th, 2010

Hi there!

ATLAS just put out its first paper, much like CMS did a few weeks ago. Ours is called Charged-particle multiplicities in pp interactions at sqrt(s)=900 GeV measured with the ATLAS detector at the LHC. It’s a light 19-page read with an extra page of acknowledgements, 3 pages of references, and a 17 page authors list at the end!! (Look for your favorite bloggers hidden in there somewhere!)


Here’s a very quick run down of what on earth that title means. First, the LHC collides protons, so these were proton-proton collisions (pp interactions). Each of the incoming protons had 450 GeV of energy (about half of the current energy of the Tevatron, and about 1/3 of the highest energy we’ve reached at the LHC). Instead of writing “450 GeV each”, we write down one of the Mandelstam variables describing the collision. It’s a better measure because it includes both particles’ energies in a “natural” way. For example, if you had a car accident, it matters whether you were going 30 and the other car was stopped, or you were both going 30 and collided head on, or you both were going 30 in the same direction and bumped each other. Each of those would have a different “Mandelstam s”.

We use a detector called the “tracker” in ATLAS to measure charged particles bending in a magnetic field. By just counting how many we see coming out of a collision we can say some interesting things about what physics we see. We can count the number in terms of momentum, or in terms of numbers per event (roughly equivalent to “how fast are the cars going on each road,” and “how many cars are there on each road”).

In my opinion, the hardest part of the measurement is putting good errors on everything. We have to be very quantitative – we can’t just say “it’s probably right.” And each piece has to be quantified. The easiest analogy I know of is polling. When someone takes a poll, they usually say, for example, 45% “+/- 3%”. That 3% is the “error” on the poll – though it’s usually only statistical, or telling you something about how many people they sampled. If they wanted to add systematic errors, they would have to include other effects that can be very hard to quantify like: how did the sample they polled differ from the general population? How likely are certain populations to answer the phone or respond to a survey? How likely are people to give honest answers on a survey? Those can vary from hard to almost impossible to quantify, but we have to be honest about how they might affect our results before we can publish with any confidence!



Pi Day and Technical Difficulties

Sunday, March 14th, 2010

Happy Pi Day everybody!

The LHC has been running quite happily over the last few days, even ramping up the energy to 1.18 TeV – that’s 1200 times the mass of a proton, and 20% more energy than the Tevatron. ATLAS has been running and collecting data the whole time, even for the few exiting periods when there have been two beams in the machine.

At the beginning of this week we’ll have a short “technical stop.” There are a few things that the LHC guys want to try to fix. There are rules that say we may not run the machine while there are people working on it, so we’ll stop the machine for a few days. In fact, they want to open up a few areas that may be “activated” (read: a very, very, very little bit of radiation could be there). So we’ll stop, and the work on those areas will only start after about a day of waiting (when the areas have “cooled down” enough).


Because of the radiation, all the experiments have very complicated documents describing what we’ll do when the beam turns off at the end of each year. There are rules about which pieces of the detector you can work on right away, which bits you have to wait a day to work on, which bits you have to wait a week for, and so on. And all the different areas have to be marked off carefully so that no one wanders into the wrong spot!! Actually, the rules make it really safe – if you hang out in your basement a lot, you will likely get more radiation than any of the people working on the LHC.

So don’t worry too much if you don’t hear exciting news about collisions this week – we’re still working hard, and the machine will be back soon (could even be by Wednesday)! And in the meantime, enjoy some pie!!!!

Update: You can read about the weekend’s fun here



The Beam is Back – with Sound!

Saturday, March 6th, 2010

It keeps going and coming back, but (at least for me) it hasn’t lost the thrill. I’m sure in a few months this will be boring, but right now: the beam is back in the LHC!!!

Beam coming back into the LHC

Mike wrote about this page a few days ago. I’m in the control room again, and there are about 15 pretty tired physicists here with me (it’s 5:30am on Sunday morning, and we’ve been here for at least 6 or 7 hours by now). But you can see everyone start to perk up when the beam comes back.

The most entertaining part of the return is the return of the sound effects. When the LHC main control room says they are ‘ready’, an alarm goes off in here that sounds like we’re on the bridge of the Enterprise and we’re under attack. I keep expecting read lights to start flashing and for someone to tell us to stumble to our left!

Every once in a while, the beam gets steered off course and is “dumped” out of the machine (actually, a kinda cool process where it’s “painted” across a block of graphite down a side tunnel so the energy can be safely absorbed). If they intended to dump the beam, then all’s quiet here. If something went wrong, a loud FLUSH (toilet flush) plays in the control room. Right now I’m watching the pixel detector, and I’m also responsible for checking (when there is a toilet flush) if there might have been damage to ATLAS after the beam was dumped.

Now back to listening for the toilet flush!!


Grad School Musings on a Slow Night

Friday, March 5th, 2010

Hi there blog-readers,

I’m on shift tonight watching part of ATLAS, but the beam is having some teething troubles right now. Nothing to worry about, but we won’t be running for the next 11 hours or so. So instead, I thought I’d pile on the talk about graduate school with my own addition. I hope you’ll forgive me if this is long – shifts are eight hours…

I admit it’s not new news, but this is my reply to a New York Times op-ed piece by Mark Taylor of Columbia University. He really put a hit on graduate and general higher education and “specialization.” Read it all at the NYT online.

First, I believe we are leaving out medical school, law school, business school, pharmacy school, trade schools, teaching certificate programs, and many other kinds of “higher education,” instead focusing on academic PhDs. I’ll try to restrict myself similarly.

Two claims in the first paragraph I find to be worth examining closely:

-) “There is no market” for graduate students. Our obvious example is that the professors at any large university are all PhD’s. One doesn’t get a PhD in art history so that one may become a plumber. If we want to argue that there are too many graduate students in fields that are too small to support the students, then we need to better educate students about their job prospects prior to graduate school. Graduate school isn’t a default position – there should be a reason that you want that degree.

Graduate school has another stated purpose: at the end of it, you should know a single subject better than any other person on earth (okay, as close as possible, we can’t all be geniuses!!). If you learn how to write the perfect comma over four years, then you’ve set your self up for a career as a professor – or as a typographer, publisher, editor, printer (yep, they’re still around), graphic artist…

-) “All at a rapidly rising cost (sometimes well over $100k in student loans).” Personally, I don’t know anyone in academic graduate school who is paying for his or her education (remember, we left out medical school, law school, business school, etc). The point of those teaching positions is so that graduate students can support themselves. I make a very comfortable living – and I’m living in Geneva! Still, graduate school is an investment, just like buying a house. You pay for it over the years, and at the end you have something of value. If you play your cards right, you can easily make money on the deal – if that is what you are after. And if you don’t care so much about money, you can live very comfortably.

Finally, I’ll try to go through his proposal point-by-point (my paraphrasing in parentheses).

(1 – Restructure the curriculum to avoid departmental specialization) This seems to be a misunderstanding of what “specialization” means in the modern world. I am a student in high energy particle physics, and my thesis will be on hadronic jet shapes using the calorimetry of the ATLAS detector at the LHC (sounds specialized). That means that I am a combination of student, physicist, mathematician, computer scientist, electrical engineer, author, editor, presenter, graphic artist, webmaster, teacher, manager, and politician – and that’s on a slow day. I don’t want to learn how to be a better computer scientist from someone like me. I want to learn how to be a better computer scientist from someone who knows a lot about computer science! At some point I may “raise” my own graduate students – and at that point, I will be able to teach them about those areas that I know best. And I hope I have the wit to send them to the appropriate place or person to be trained in the other specialties they will need to know in order to better do their job!

I claim that to really specialize, one also needs to know things about all the other fields that in any way overlap with ones own. Richard Feynman wasn’t a great physicist just because he knew a lot of physics. He knew enough about physics to be able to look at a problem a chemist was having and propose a solution.

(2 – “Abolish permanent departments” in favor of “problem-focused programs”) Essentially, this is a repeat of claim #1. I don’t want a “water” teacher. I want a political science teacher to teach me about the aspects of political science pertaining to water distribution across nations. I want a geophysicist or atmospheric chemist or oceanographer teaching me about where the drinkable water will be 100 years from now. I want a chemical engineer or chemist teaching me about new desalinization techniques.

If we are talking about a major in “water”, then I think that’s a good idea. In fact, most universities already support “create your own major” programs for students interested in an interdisciplinary major (which, incidentally, does not mean it is more or less specialized than any other major). Many PhDs are interdisciplinary in some sense. In fact, I know of one person with two PhDs in water-related fields (water distribution, and… don’t remember). I don’t want a department of “time.” If someone wants to study the philosophy of time, they should join the philosophy department. And that person would be nuts to not talk to a physicist about relativity at least once during their graduate career.

(3 – “Increase collaboration among institutes.”) This is already done in many other countries. I see no reason that state universities in the US should not do the same. I see many reasons why private universities in the US should under no circumstances attempt to spread themselves out like that (Ok – Harvard, you guys get math. Yale gets classics. Stanford – you get Physical Education. Everybody okay with that?)

(4 – “Transform the traditional dissertation”) Let me just change this point for him a bit: “Reformat” the traditional dissertation. In the modern era, there is no reason that a dissertation should be published as a paper book. Publish all theses electronically, in a publicly accessible catalog. Rather than simply citing a text, one could electronically link the texts. Links could be included to permanent web addresses. Humanities departments should try to catch up with the sciences (and I mean sciences broadly, to include most research fields) in their use of electronic formats. That’s not a “transformation” of the dissertation any more than binding was a “transformation” of the Iliad – it’s the same story. It’s just easier to carry around.

(5 – “Expand the range of professional options for graduate students”) Graduate students are trained in a huge expanse of fields. See my point above. That I might not be employed next year in a job that uses the exact same combination of skills I have now developed is no surprise. Would anyone suggest the skill set developed during high school is identical to the one used by a carpenter? Or that an undergraduate economics major uses the same skills an economist? Or that a journalism major uses the same skills as a journalist? And yet, that is a part of their training. On the job training is just as important for academia as for any other job – it’s just different. To be an academic, one must learn how to advise students, interact with a department, balance a budget…

I find it deeply unnerving that he suggests that all a PhD is “trained for” is to become a professor. Of my current advisor’s six previous students and three most recent former post-docs, zero are professors. All of them left academia. Two of my closest non-physicist friends are preparing themselves for a career in industry – which they will begin after receiving their PhDs.

If a graduate degree in religion is only sufficient preparation for a professorship, so be it. But then it should be made clear to the entering graduate students that they are preparing for a life as an academic. One does not enter the seminary and complain that the only career path open to him is the priesthood!

(6 – “Impose mandatory retirement and abolish tenure”) Mandatory retirement is a bad idea in any field. Some people need to retire when they are 55. Some people should keep working until they are 75. Some people should keep working until they die. I’ve met – and taken classes from – all of those in academia. Abolishing tenure is something that I am not fundamentally opposed to, and I know that puts me in the minority. Suggesting that every professor should come up for job renewal every seven years is pretty excessive, though. Having “performance evaluations” regularly is not a bad idea – and already takes place in many universities, irrespective of the possibility of firing someone.

Academia is not quite like blue collar work, nor is it like most corporations. In blue collar work – for the most part – once a worker gets old enough, they cease to be as productive as a young guy. Not, mind you, a new guy – the new guy still has to learn the job. The alternative is to move into “management” – essentially, into the corporate side of the work. In a corporation – for the most part – one moves up the ladder, and by the end of a career one might be near the top. In academia, quite frequently the best professors have no interest in “moving up the ladder” to become deans or presidents of universities. In this sense, academia is most like construction work – one begins as a graduate student, doing the grunt work, writing as much as possible. Eventually, one becomes a full professor, managing graduate students and undergraduates of ones own.

Knowledge is a funny thing. It’s not always well-transferred by a book, article, or talk. Sometimes the only way to keep the knowledge around is by keeping the person around. Over a lifetime as a professor, one develops a certain set of skills – one “specializes” in being a professor, which requires understanding many different fields. Universities hire professors to teach and do research. Perhaps it’s entirely appropriate that in their final years, even those professors who can no longer contribute to the knowledge in what used to be their field can continue to teach students what they know better than anyone else. They could even try to teach the young guys how to be a better professor.


The Olympics at CERN

Sunday, February 28th, 2010

Hi sports fans!

Of course, being an American here at CERN, we have to find some way to keep up with American sports! Tonight was the US vs. Canada Olympic Hockey final, and I went to the nearest pub to take in the action. That was an incredible game, for anyone who missed it, and we watched in a crowd of Canadians and Americans (with a Swede and a few others in the mix):

A crowd of Canadians and Americans focused on a great hockey match

A crowd of Canadians and Americans focused on a great hockey match

It seems there are British Pubs no matter where in the world one goes. So we headed down to our regular pub in Geneva to enjoy the game. The last few weeks we’ve had to compete for viewing space with the Carling Cup and a few Champions’ League matches (that’s European football for the baffled Americans…), but we’ve been able to find enough space. And watching the US beat the Swiss team twice in 10 days was quite a treat! In fact, one of the best Swiss teams is the Geneva-Servette Hockey Club, and they (and the league, I assume) took three weeks off to let some of their players head for the Games (Servette is the neighborhood of Geneva just west of the main train station, where I happen to live).

Next week baseball’s spring training games will start, which can be even harder to find on the television over here. I’m lucky that the Cubs have a long history of playing many day games, which are night games over here (the Superbowl started at 2am over here…). But we find a way to watch when the big games come around – frequently via internet, or even via videochat with a friend who’s willing to point there computer at the television!

During the summer, I play on one of the CERN softball teams, called the “Quarks,” in the Geneva Softball League. It serves as a little trip back to American every Sunday. The games are hosted, very kindly, at the US Marine Corps House just north of Geneva, and the league includes a team of Marines (jocks vs nerds anyone?), a team of Cubans (Buena Vista Softball Club), and two CERN teams (the Quarks and the Leptons). Our team is usually about half homesick Americans wanting to swing a bat, and half Europeans wondering why the bat isn’t flat and there are four bases instead of two. But we have a lot of fun, and we even occasionally win a game.

The 2009 Quarks Softball Team!

The 2009 Quarks Softball Team!

But I’m a Cubs fan, so I know it’s not all about winning….



It’s Just Like Work!

Saturday, February 27th, 2010

It’s Like Work

Several bloggers have talked about the LHC Computing Grid already. We use a lot of computing resources as physicists. The WLCG homepage actually has some nice information about the Grid, including cool pictures of what’s online now:

Screen shot 2010-02-27 at 5.44.11 PM

There’s a wonderful thing that comes along with using all these computing resources. Frequently, I’ll set up some task and set it off to run on a few hundred computers somewhere. It feels like I’m working hard – even if the computers are doing all of the heavy lifting!! It also lets you justify a long coffee break: “I’m working right now! The Grid is whirring away because of me!!”

I’ve spent a lot of my time working on improving the ATLAS software (usually trying to make it faster). Most computers these days use around 80 Watts of electricity – about as much as a bright light bulb (or one of those lightbulbs you might find in a dimming lamp). That means, if we leave them on and running year-round, we spend about $100 for the electricity for each computer we have. The Grids that ATLAS uses (there are three, actually) have about 30,000 computers on them, which means that we spend about $3M a year for the electricity to run the computers on the Grid.

Of course, you have to cool all those machines, and most of the buildings that they live in are not the most elegant, modern, energy-efficient buildings that you might construct today. So you can guess that we spend about the same amount on air conditioning – another $3M (that is actually pretty close to right, based on CERN’s experience).

Recently, ATLAS changed the operating system that we run our applications on – like an upgrade from Windows XP to Vista, or Mac OS X 10.5 (Leopard) to 10.6 (Snow Leopard). The operating system we use is called “Scientific Linux,” and we moved from Scientific Linux 4 to Scientific Linux 5. Because of a few of the fancy new tricks that came along with that change, our software suddenly runs 20% faster.

So an operating system upgrade just saved us $1.2M a year!!

Actually, that’s not quite true. The electricity for computers on the Grid is pretty cheap compared to some of the other parts of the budget. So rather than turning off the computers, we run them more, and we can process more data in the same amount of time. Still, it’s a nice thought! And little calculations like this make me think they should give me a bonus when ever I make our software a little bit faster…

Richard asked about LHC@home after my last post. You can read all about it at their website. That’s a neat project, and we’ve talked about different ways to use it to our advantage. There are a few problems, though, that are perhaps interesting to mention (note: I’m a mere blogger – this is just one fellow’s opinion).

LHC@Home Screensaver

LHC@Home Screensaver

One problem is that the software we use is pretty big. A typical installation is around 7 GB, and runs natively on linux machines. On top of that, the data files are typically a few more GB. There aren’t a whole lot of people who are willing to blow 15GB of their hard drive space on a nice screen saver, so we have to think carefully about whether there is a slimmed down version that we can send out and run on Windows or Apple computers (to reach a broader audience).

Another problem is that our data is still “sensitive.” In order to make full use of our friends’ computers, we would want to give them full access to our data. But we want to be the first to publish results with that data! So it is a bit nervous-making to just send the data to whoever asks for it. More likely, there would be someone out there who would try to use the data, but wouldn’t really understand it, and so would end up misidentifying something interesting. Then we’d have to spend our time trying to fix the things they’d done wrong. There was an interesting discussion about that at a conference I attended a few years ago. Someone asked that all LHC data be made publicly available. Of course, we raised this objection then (that they wouldn’t understand what we were giving them). And then a person asked a very nice question: “The data from the previous experiment at CERN (called LEP) is publicly available. Has anyone looked at it?” No one outside the experiments had. So one more reason to not try to make our data public.

One more problem is dealing with “conditions.” What we get out of the detector depends on the state that the detector is in at the time – which pieces are on or off, what temperature those pieces are, what voltage is being used, and so on. All that information (called “conditions”) is put in a big database at CERN. When ever we want to use the data, we have to read some of that information, and so we have to access the database. If more than a few thousand people tried to connect at the same point, it would bring down the database, and no one would be able to use it! We have duplicates set up around the world now to ease that problem. On top of that, we now have caching servers set up near those. When you ask one of those servers for information, it checks whether it has it around, and only if it doesn’t will it go back to the original database. That way we make the most frequently used conditions available all over. But I am not sure that we have the infrastructure to allow that many new people to request conditions information! And it would be risky to launch a program that might bring our work to a halt, just as the LHC is getting up and running!!

Of course, Moore’s Law continues to hold, and computers continue to get cheaper. So by 2020 this might all be easy, and everyone might be running our software as a screen saver. But for now, it’s quite a challenge!



Late Edition

Tuesday, February 23rd, 2010

Hi there blog enthusiasts!

I thought it would be appropriate to write my first post sitting here in the ATLAS control room. I’m manning the very same desk that Seth blogged about over a year ago as we prep ATLAS for the restart of the LHC in the next week or so. It’s late Saturday night (Sunday morning? Which one is it at 4am?), and so it seems like a good time for an existential crisis.

How did I get here?

I was always a math and science kid. One of my friends read The Physics of Star Trek in 6th or 7th grade, explained it to me, and eventually loaned me his copy. That was enough for me. I was ready to find E.T. My parents are both English professors, and they had no idea where they went wrong. My Mom was a product of New Math, and my Dad gave up on physics as soon as electricity and magnetism came around (“Field Lines???”).

I had two great physics teachers in High School (for the real physics nerds: I went to the same High School as Michael Peskin and Jack Steinberger). Those two convinced me that physics was as interesting as I hoped and that it was something I could actually do for a living. One bit of advice that I took to heart: “Take math until you really don’t understand it any more. Then stop.”

At the end of High School, I decided to go to Berkeley (Go Bears!!) and major in math and physics. My first physics professor was a young Russian, one of the smartest and hardest working guys I’ve ever met. I spent the rest of college working for him on an experiment at SLAC. I had a great time in the physics department there, and settled on the idea of graduate school around my Sophomore year. The only questions were where, and doing what.

Until my Junior year, I thought I might be a theorist (much like Flip). Then two things happened in one year: I stopped understanding math, and I took a full-year lab course that was some of the most fun I’d had at Cal. The course was repeating famous physics experiments: working on a C02 laser, measuring Rutherford Scattering, measuring the flux of cosmic rays, making Joshephson junctions… I loved every minute of it. And there were a lot of minutes to love!

So I tried to see what the experimental physicists I respected most were doing. Many of them were heading towards the LHC (I also thought about IceCube, but the thought of spending a few winters at the south pole was hard to stomach). I applied to graduate school knowing I wanted to work on the LHC, and even knowing which professors I wanted to work for. Physics professors pick their projects, so heading to Caltech was the last major decision I’ve made on my own. Since then, I’ve worked on the ATLAS simulation software (full details to come) and pixel detector, and I’m heading back into the world of “jets” (like these, but using the calorimeter).

And now, here I am in the control room on a Saturday night. It does make one wonder. Either I really love what I’m doing, or I have made some horrible choices along the way. But since these shifts are all volunteer work, the choice is obvious, right?!?

Even though none of the green lights have turned red yet, I’ll stop here for the time being. More about science, and less about me, soon!