Wow, what a terrible trip to CERN I’ve been having. I’m here for the semi-annual CMS computing and offline software workshop week, but I took ill while here and have been confined to my room in the hostel for the past two days. That and my jet lag have totally put me off my game. I am definitely on the mend now and expect to be out and about today, and that will be a great relief. Thanks to all of our modern devices, I could keep up with what was going on in official meetings from my room, but I could have done that from my office in Lincoln too — the point of coming here is to see my friends and colleagues face to face and for us all to talk about what is really going on and what we should be doing about it. You don’t always learn that from the talks in the meetings; it’s all about the hallway conversations and the extended lunches (and those long periods of watching other people drink coffee that I’ve written about before).

But what I can see, even from inside, is the growing level of intensity as it becomes clear that the LHC restart is upon us. Seth of course mentioned earlier this week that particles were injected into the LHC over this past weekend, for the first time since last September. He didn’t mention that it wasn’t just protons injected, but also lead ions, and I think this was the first-ever injection of heavier nuclei into the LHC. With that done, fully circulating beam (making a complete circuit of the machine) could come as soon as next weekend, and that means that the detectors must be totally operational now. Even with only one proton beam (not colliding with another beam) there is a lot to learn, as we saw last year — you can see particles from the “beam halo” streaming through the detector, and also “beam splash” events. All indications are that we will have some kind of collisions, although probably at relatively low energies, before the Christmas shutdown. Then the pressure will be on the experiments (not the accelerator!) to quickly turn around and show that they can do something sensible even with the small number of collisions that we will probably get at first. Well, this is what we’ve spent twenty years preparing for — we must be ready.

It’s hard to believe that it’s really happening.  Let’s hope it seems as real after I finally get home, tomorrow night, and get some proper sleep.

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In a previous post, I mentioned that ATLAS will be collecting enormous amounts of data, approximately 6 Petabytes/year (i.e., 6,000,000 Gigabytes). How in the world are we going to handle it, and how do we make it available to all physicists on ATLAS? I spoke to one of my colleagues at Indiana University, Fred Luehring, who has major responsibilities for the US part of the Grid, to get some details.

First, let me mention some ATLAS jargon; if you wish, you can skip this paragraph for now, and come back to it when you run into strange acronyms.

The raw data that we collect is called ByteStream, basically, it is a stream of 1’s and 0’s, and is approximately 3-6 Megabytes/event. This gets “massaged” into Raw Data Objects (RDO); the only difference is that the data now has a “structure” that can be analyzed with software written in C++; it is now about 1 Megabyte/event. At this point, the ATLAS reconstruction software (written in C++) runs over these RDOs and produces tracks in the inner detector, electron and muon candidates, jets, etc., and outputs two other structured formats, ESD (Event Summary Data), AOD (Analysis Object Data), which contain different levels of detail; they are approximately 500 Kilobytes and 100 Kilobytes/event. As you can tell by the name, most physicists will run on AOD’s; there are other smaller formats, but I will skip them.

In a “normal” year, we expect to collect about 2 billion events. How do we handle all this data? To do this, physicists and computer scientists have been working on the Grid. It is basically a whole lot of computers spread all over the world that are networked with very fast connections; typical data transfer rates are 1-10 Gigabits/sec (in contrast, broadband connections to your home are about a thousand times slower).

You may ask why we need the Grid. Why can’t all the collaborating institutes just buy computers and send them to CERN, and let them set up a gigantic processing center? That is one approach. However, funding agencies don’t like this mode of operation. They would much rather keep the hardware in their respective countries, and build upon existing infrastructure at universities and laboratories, which includes people, hardware, buildings, etc. Another advantage of the Grid approach is the built-in redundancy; if one site goes down, jobs can be steered to others. Also, if a Grid site is appropriately configured, then if ATLAS is not using the computers, other scientists can use them (in an opportunistic manner); although, we keep the system pretty busy. In the US, each LHC experiment has its own grid sites, whereas in Europe, they tend to share them.

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First beam in the LHC since last year!

As reported by the BBC, last weekend particles were injected into the LHC for the first time in over a year.  This confirms what we’ve known all along — the scientists, engineers, and technicians working on the LHC are making steady progress toward restarting the machine — and it’s an excitingly concrete reminder of how close we are to taking data!

Last year’s big startup event was focused on circulating a beam around the entire ring, which hasn’t happened again yet.  This year’s really exciting milestone will be when beams are not only circulating in both directions, but actually colliding: that’s when we can start to do physics.

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It is almost 40 minutes past midnight.  I just came back from my last CMS DAQ (Data Acquisition) trainee shift.  Strangely, I still have a lot of energy, so the first thing that comes to mind, after eating something (shifts make me hungrier than usual), is to keep doing something productive.  However, I need to get up early in the morning (well, it is effectively the morning already) to cover my first solo shift at 7 am, so I know I need to get some rest.  The problem is not the amount of rest needed, however, it is just that I am not used to waking up that early!

It won’t be easy to fall asleep though.  It seems that sometimes I get these bursts of energy out of air, particularly during the night.  Maybe that is why I do not drink coffee like every other physicist I know (besides it makes your teeth yellow).  Then, I think I should write while the energy “euphoria” lasts.  Write in a more natural way, that is; in a more spontaneous way.  Maybe it will be fun to read this entry again when the sun is up… I’ve been thinking about doing that for a while….

DAQ shifts are fun: you have the “control” of all the CMS detectors; everything passes trough DAQ’s hands. I liked them at the Tevatron and like them now at the LHC.  Besides, it is nice to be at P5 (point 5) where the CMS detector is located (in Cessy, France).  There, in the control room, I feel at home.  I like the excitement, and I can only imagine it being multiplied by 100 times, once first collisions come.

Then I think about neutrinos.  Those sneaky neutrinos that have been making me think a lot during the weekend.  Those sneaky neutrinos that we, at CMS, cannot detect directly but simply infer their presence by the imbalance of transverse energy in the detector.  I’ve been thinking about them because of this recent and excellent article about relic neutrinos, and how much closer to us they seem to come from compared to the relic photons. Those sneaky and skinny (their mass is really tiny) relic neutrinos, almost as old as the Universe.  I am sure they have great stories to tell about the past. They are like the grandpas of the Universe. If we could only get them to like us, to interact with us somehow.  But no, trillions of them pass through my body without me even noticing.  Maybe they keep the secret of the origins, the answer to the question that drove most of us into this, apparently, endless quest.

Edgar Carrera (Boston University)

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This weekend the weather has been playing tricks on me in New York. I intended to go camping upstate with some friends, but after a valiant attempt on Friday evening/Saturday morning, we decided to take our soggy sleeping bags and head back to Long Island. It literally rained all day, night and the next morning – which being from Colorado – I’ll never get used to. I decided to share this with you on a Sunday afternoon sitting in my apartment looking out my window at this:

A room with a view

The gods must be conspiring against me to make sure I get work done this weekend .  So I thought I’d update everyone as to the status of the LHC. My email’s been a buzz with information. So far all the repairs have been completed and the entire ring is back at the operating temperature of 1.9 K. The schedule is still on to start circulating beams in mid November with low energy collisions soon to follow. Although we probably won’t be at the full energy this year, any collisions would be an amazing milestone.

There’s also a new LHC First physics Physics Website that you will probably want to check out. It will have the most up-to-date information. Happy reading on a beautiful Sunday!

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It’s two in the morning here in Geneva and I just got home.  While walking back, I had some ideas about how to understand the impact on track jets from tracking lower-energy particles, and how to better understand the efficiency of finding those track jets as a function of what part of the detector they hit.  So time to fire up the Internet and get back to work!  — Seth

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Americans are becoming poorer!

Most graduate students I know are paid enough to live fine in France. I do occasionally, however, hear about a grad student who isn’t being paid nearly enough and is digging into savings just to get by.

That is why it is important to know how much it will cost for you to live somewhere before you agree to move there. If a professor (or boss) isn’t offering you enough compensation to move you should make them aware of this and negotiate a higher pay.

For reference to potential future students moving to France to work or do research at CERN, here are some costs to think about. Continue Reading »

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In preparation for the upcoming first LHC collisions, ATLAS has started operating 24 hours a day, 7 days a week.  I have been on shift 7am to 3pm for the last 3 days.  The control room is full of activity as everyone is making sure we are ready (hopefully in about a month) for beam and then proton collisions in the LHC.
What we are doing now is recording data on muons created in cosmic-ray collisions in the atmosphere.  In the picture you can see a screenshot of a web page where you can go to see displays of the last 100 events collected by the ATLAS detector.
You can also see what’s happening in the ATLAS control room right now on the web cam (or the other one).

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Recently, I came across a BBC article about juggling.  Apparently, it can increase the white matter of your brain by as much as 5%.  I have not done much juggling in my life, so I really hope that the juggling I am doing now as a postdoctoral researcher counts! Let me explain…

The position title Postdoctoral Researcher is given to someone who has completed his doctoral degree but who is not quite ready to be hired as Professor or Researcher at some university.  It is the transition from being a Ph.D. student, who was told almost always what to do, to this mature scientist who can take decisions by his own and can lead a particular project of research.  I became a “postdoc” not too long ago, after a rather quick period of doctoral training, which made it a very tough enterprise.  Like any other Ph.D. student, I sometimes felt really exhausted with my academic work and its intensity, so I have to admit that I was a little scared about becoming a postdoc.

In fact, the life of a young postdoc does not become any easier, on the contrary, you are being demanded a lot more than when you were a student.  Basically, you have to juggle with many activities that range from aiding graduate students with their physics analysis (something really new that requires a different mind set) to working on your own physics analysis.  In between, you are expected to complete little service projects in a fraction of the time you spent in a similar project as a student.  To summarize, stress does not decrease.

Life is now much better though. It is maybe that I found that learning how to lead and how to abandon that advisor-dependency is much more enriching and fulfilling.  I still have a long way to go, but so far, I have been having quite some fun with this new postdoc life.

Edgar Carrera (Boston University)

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The first paper from the CMS collaboration has been posted to arXiv.  (It has also been submitted for review at a real-life journal!) It discusses how aligning part of the detector using a few hundred million cosmic rays was successfully done.

The text of the paper itself is 20-some pages.  And the author list?  Almost the same size.  It includes people from 160 institutions around the world (48 of those are in the US).

There’s even a special footnote to mark those that have deceased – and there are several in a list this long.

Alignment of the machine is an important early step to having a detector we can use to make physics discoveries.  Congratulations to everyone.

PS: Does anyone know how many of the authors are graduate students?  If I made a completely naïve assumption that the whole author list contains the same fraction of grad students as just my institution, then that would be a fraction of 8/32 for a total of about 600 graduate students in the CMS collaboration.

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There’s a great story on NPR’s Morning Edition about UC Berkeley’s “Nobel Laureate” parking spots. From the article:

Winning a Nobel Prize is difficult enough. But on the campus of the University of California, Berkeley, there is something that might be even more difficult to get: a parking space on the central campus.

That’s why Berkeley has made it a practice to offer its Nobel laureates an extra-special perk: a free lifetime permit to park in the highly coveted spaces near the central campus. The spots would normally cost about $1,500 a year.

Five of the ‘NL’ spots are by the Berkeley Physics department and the article mentions ‘06 physics laureate and Cal cosmologist George Smoot. I spent a summer in Berkeley in 2006 and dug up the following photo from the time:

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Ciao!  I just returned to CERN from a few days in Milan.  It was a very productive trip (unfortunately that meant I didn’t see much of Milan).  I met with two people from Milan and one who came from the US, and we basically sat in a conference room for 3 days working together.
This was a very effective way for us to work because we were able to discuss our long term plans (for the ATLAS MissingET software), and to design and even write some software.  We ended by coming up with a plan to carry out the rest of the work.
This trip highlights the positive and negative aspects of the international character of particle physics.  It is positive because it brings together the best people from around the world, but it is also negative because it sometimes requires people to travel halfway around the world just to talk together for a few days.
It also reminded me that even in the modern interconnected world where everyone is a phone call or email away, there are certain advantages to meeting in person.  One of the big advantages is that it is hard for someone you are talking to to be too distracted by other things.  A meeting like this forces a focus that is really useful.

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Sigh…
I was reading the New York Times today (ok so I’m a couple of days behind because I was reading it from October 12th) and I came across this article:

The Collider, the Particle and a Theory About Fate

To save you some time, the article references an arXiv paper posted in 2007 about backward causation and time travel. (for those who don’t know arXiv is not a publication, articles are posted, and not necessarily reviewed – although it has to be approved). They argue that any collider searching for the Higgs is destined to fail because god/nature/or whatever doesn’t like little Higgsies. They then point to the failure of the SSC, and the recent failures at CERN as proof.

Instead of trying to refute this, because I think it’s silly, I’d like to discuss correlation. I’ve been watching a lot of baseball recently because the play-offs are going on (poor Rockies just got defeated by the Phillies in a nail biter on the 9th). Anyway, baseball is littered with uncorrelated statistics. Batter X hits a 0.280 on Thursdays against right handed pitchers as opposed to Fridays when he bats 0.320. Does the day that the batter is at bat really change how well he hits? Maybe he’s working for the weekend, but it could be a coincidence or other factors that we’re not taking into account which are correlated and this result is just part of the picture.

I’m sure those who are versed with pastafarians are familiar with the argument that the decreasing pirate population is causing increased global temperature. Sure, the number of pirates has decreased over the past 150 years, while the global temperature has increased (seen below), but does the presence of pirates inherently cause a decrease in the global temperature. I think I’m going to go with probably not. There are clearly other factors to take into account.

Pirate number vs. golbal temperature

Anyway, why do I bring this up? People like to find correlation between things. Our inherent nature as humans forces us to like to try to understand relationships between events. That’s why I want to be a scientist when I grow up. That being said just because as one thing is happening, another happens too, doesn’t mean that they have anything to do with each other. To say that there is evidence to show that god/nature/or anything else is spiting scientists for searching for the Higgs is not only destructive, but unprovable and not science. Fermilab is currently running just fine and searching for the Higgs (a couple people in Stony Brook’s D0 group are doing just that, in fact.) But it also takes away from what the engineers and scientists are doing to make machines like this work. The LHC is a brand new machine pushing the limits of engineering. Of course it’s expensive and things don’t work as we expect. (we have no examples to base our expectations on). And as for the SSC, I think that’s more an example of how scientists need to better explain to Congress why science funding shouldn’t be cut than someone out to stop us from finding the Higgs.

But I guess that’s what I get for reading essays in the NY Times. I should stick to the food section

Until next time,

-Regina

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Now time for another installment of “symmetry in physics.” For those of you tuning in late (or who have forgotten what we’ve been discussing), we started out in part 1 with a very general discussion of the symmetries of spacetime and how this constrains the form of our theories. Next, in part 2 we looked at discrete symmetries and how they relate the notion of antimatter to charge and parity conjugation. We’ll be using some of the jargon of part 2, so make sure you brush up and remember what “CP” means. Now we’d like to address another mystery of the Standard Model: why is there so much repetition?

Family Symmetry

Let’s review the matter content of the Standard Model:

The top two rows are quarks, the bottom two are leptons (charged leptons and neutrinos). Each row has a different electric charge. The top row has charge +2/3, the 2nd row has charge -1/3, the third row has charge -1, and the last has charge 0. As discussed in part 2, there are also the corresponding anti-particles with opposite charges [note 1]. Just about all of the matter that you’re used to is made up of only the first column. All atoms and everything they’re made of are more-or-less completely composed of up and down quarks and electrons (the neutrinos haven’t done much since early in the universe).

The replication of the structure of the first column is known as family symmetry. For each particle in the first column, there are two other particles with nearly the same properties. In fact, they would have exactly the same properties, except that they are sensitive to the Higgs field in different ways so that the copies end up having heavier masses. Technically the Higgs discriminates between different generations and breaks this symmetry, but we are still left with the question: why are there two other families of matter?

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Here at CMS, we are in the midst of something that, I guess for lack of a better name, has been dubbed the “October exercise.” For the past week and the week to come, we have been trying to get as many people as possible to use the distributed computing system just as they would if they were doing a real analysis with real data. A new set of simulations have been released, and people are trying to work them through the system and their data analyses as quickly as possible, to demonstrate the turnaround time and the scale at which we will be hammering the computing clusters that are distributed around the world.

Halfway through, I would have to consider this at least something of a success. I don’t have anything resembling an accurate count of how many people have gotten involved, but it seems that we are seeing lots of people who had been just been doing their data-analysis work on local computing clusters now trying to use the grid for the first time. Tens of individual exercises have been designed by the dozen-ish CMS physics groups, each with multiple steps involving processing, writing and transferring data. As someone who has been working on the distributed computing for some years now, it is encouraging to see so many new people try out the system, and be successful more often than not.

On the other hand, it’s not as if everything has gone perfectly. A number of new tools and rules were developed just in advance of the exercise, and running these things out of the box at scale has been a bit bumpy. We were certainly aware of the weaknesses in the system, but now they are on full display. One thing that has proved particularly challenging is the “staging out” of outputs made by users in their processing jobs. In CMS computing, different datasets get distributed to different computing sites, and physicists who want to run on those datasets send their jobs to those sites. But everyone has a “home” site, and the output of the jobs has to be returned to the home site. This means that the data must be transferred from a somewhat random site X to the user’s site Y, and not every site Y can handle the volume of transfers that might be coming in. We’re keeping an eye on this and thinking about how we can improve it in the future.

After a week of this, I’d have to say that it’s somewhat exhausting to try to keep up with all that’s going on. And we don’t even have data yet — how exhausted will I be then? But on the flip side, I’m glad that we’re learning all of these lessons now, rather than a month or two from now.

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