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Archive for November, 2007

Control Rooms

Thursday, November 29th, 2007

As control rooms go, I think the ATLAS control room has style. The visitors like it because there are lots of flat screens. The physicists like it because there are lots of flat screens.

atlas_control_room

The control room is set-up so that each sub-detector or sub-group has a desk. There are 15 stations. When the beam is running, there will be at least one person for each sub-detector on shift. 24 hours a day, 7 days a week. That will be the situation when we get into the swing of data taking. Right now, when we try to take cosmic data with multiple sub-detectors, there are usually 20 people at each station.

This picture was not taken on a day where we are trying to run a combined cosmic run. During those days, this room is packed. Standing room only, with people sitting on the floors, typing frantically on laptops. Mobs of people at each station. People yelling over the background noise in every language imaginable. The roaring cheers and clapping when everything is working. The massive sighs and moaning when everything isn’t working. If there is a heart to any experiment, it is the control room.

There is, however, one very strange aspect about the ATLAS control room that I have never really become comfortable with. It is way too clean. Where is the clutter? Where are all the random papers thrown on the desks? Where are remnants from last night’s 2am coffee run? A little dust even? The place is spotless. Always. It is not like it is usually a mess and then gets cleaned up for press tours. It is always clean. Not that I am complaining. I am all for less entropy in the workplace. But it is disconcerting all the same.

But as control rooms go, the LHC control room…. Now that’s style. Still too clean though.

lhc_control_room

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I started this on a friday, about 17:00 (5pm) when we’d been working all day underground again. We had endured one water cooling failure, network problems, and various configuration problems all day. It was a frustrating day so far, and it was hard to keep oneself motivated. Fortunately we have colleagues willing to set us up with a supply of coffee to help keep us going. We just contribute 50 Euro cents per cup (honor system) to pay for this supply.

To make it, one just takes the little aluminum coffee capsule (no advertising here for the brand), puts it in the coffee maker, fills the back with water if it is empty, puts a cute little plastic Euro-sized cup under the nozzle, presses one of two cup-size buttons, and in a few seconds…voila! you have coffee, hot and strong, with minimal mess.

Normally I object to these capsules because of the waste, but we don’t have a way to keep the coffee maker by a sink or anything, so these little capsules are the way to go. Its hard to keep the area clean anyways.

This keeps us going through our day. Now, not everyone drinks coffee, and some don’t even like the smell, so it is probably tough to sit downstairs near the maker. But I used to sneak sips from my mom’s cup at an early age, and we’d make a sort of cafe au lait after dinner with our leftover milk, so I guess it is natural that I am still drinking it.

The funny thing is, I don’t use it to stay up late like some folks. If I have a difficult project and I am falling behind, I usually get up early (have some coffee, of course) and get started with a fresh outlook.  I’m terrible at staying up late.

And soon, speaking of staying up late, I will probably do a shift. We are starting a two-week period taking data using cosmic-rays (mostly muons – a heavy electron, basically) to integrate and test our detector (all but three endcap disks have been lowered – its getting cozy in the cavern) and the various bits of software and hardware that we use to collect the data. The days will be managed by experts on the system, and the non-experts will take shifts…going from 17:00-1:00 (swing) and from 1:00-9:00 (graveyard). I volunteered early, with the hope that I could “reserve” swing shift. I won’t function properly for days if I do graveyard, its like jet-lag. Either way, I am glad I only have 2 km to drive home after shift to lovely downtown Versonnex.

Maybe it will be easy, and I can catch up on my blogging….I can only dream.

A la prochain…

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SNO vs. TileCal

Wednesday, November 21st, 2007

Last week I received the following comment from Chris and thought I might address it in more detail.

How does the work dynamic compare to your previous work on SNO? Is the TileCal working group your new “collaboration”? Do you feel lost in a sea of meetings? Does working with that many people mean there is enough organization such that it almost feels like *gasp* an industry job?

INCO_mine Ah, SNO! How I miss it! I had no idea what emptiness or the phrase ‘as far as the eye could see’ really meant until I had spent a winter in Sudbury, Ontario. When looking out over the landscape I was always simultaneously awed by the vastness of space and depressed by the physical scarring of the landscape from more than a century of mining. This picture perhaps shows a little of this. In the background is the head-shaft for shaft number 7. The Creighton mine, which is where SNO was located, has 11 shafts in total but only one, shaft number 9 is still used for passenger, equipment and ore transport. The only trees that can survive in the soil near the mines are these skinny white birch as seen in the picture’s foreground. But my advisor, Gene Beier used to tell me that 20 years ago there were zero trees. So life has been making a comeback in the area.

In the high energy physics world, the SNO collaboration was minuscule. Our author list of roughly 150 people could fit on a single page. That is compared to the ATLAS author list which last time I checked was 11 pages of names and 7 pages of institutions. But there are many similarities in terms of work dynamic between these two experiments.

Although ATLAS has an order of magnitude more people than SNO, TileCal is about the same size. In terms of experimental complexities, TileCal is also comparable with SNO. TileCal has roughly 12,000 electronics channels whereas SNO had 10,000 channels. But the major difference between SNO and TileCal, or SNO and ATLAS is that SNO was designed with one major goal in mind: measurement of the solar neutrino flux. And although SNO published other results such as a search for antineutrinos, the measurement of the solar neutrino flux was its main measurement. For the most part, everyone in the collaboration was focused on that goal.

In the TileCal community, people are largely interested in the calibration and studies of ‘jets’ (collimated showers of energetic particles which deposit energy in the Liquid Argon and Tile calorimeters). But there is a huge range of physics measurements to focus on such as measurements of the Top quark mass, discovery of the Higgs particle, or searches for new physics such as SUSY. Within a single physics group, there are members from every sub-detector, each bringing to the discussion expertise from his/her sub-system. In that sense I think it is easier to ‘get lost’ within ATLAS compared to SNO. Because the people working with you on TileCal might have totally different physics interests. There are so many different things to work on it is hard to decide what to work on.

Considering how many different institutions, sub-detectors, and physics groups there are, ATLAS is surprisingly unorganized (though not necessarily disorganized) and yet still functional. ATLAS can never be organized like an industrial company because there is no real power of ‘purse or sword’ within the administrative hierarchy. For example, most institutions are individually funded. So if institution A is unhappy with someone at institution B, institution A can appeal to the ATLAS administration but that administrative body has no power to remove anyone at institution B. Therefore to get what they want and need, the institutions, sub-detectors, physics groups have to negotiate with each other, trading the only resources they have: their people’s time, electronics/construction facilities, expertise, etc. And the elected ATLAS hierarchy has the very difficult task of trying to channel all of these independent networks in one general direction.

It is a thankless task, which is why I am glad that as a post-doc I am near the bottom of the chain where I have the luxury of being able to focus on the detector and the physics.

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Dimensions of String Theory

Wednesday, November 21st, 2007

Just as a follow up to my post on the string theory & RHIC workshop Columbia, the cover article of this week’s Science News is about the “duality” between gravity and gauge theories which has turned out to be one of the hottest topics for RHIC physics. The idea is that theorists can use gravity models to do things with strongly-coupled systems of quarks and gluons that they thought would require heroicially complicated quantum field theory calculations. One particular calculation from 2001 found that there is a lower bound on the viscosity of a strongly interacting system, and RHIC physicists have been putting enormous efforts into proving or disproving the bound in a real physical system. That this could be the first application of string theory in the real world has made both experimentalists and theorists excited, and given a lot of focus to the LHC heavy ion program (of which I am a part — an embattled part, but a part nonetheless!)

In any case, this is a nice human-readable article summarizing the state of the field, with only a factual errors that I noticed on first glance. Have a look!

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Michael Schmidt 1954-2007

Tuesday, November 20th, 2007

This has been percolating around the community the last few days, but some sad news just came in via the ATLAS Secretariat:

Dear Colleagues,

We are saddened by the passing of Prof. Michael P. Schmidt, 53 years old, from Yale University who worked on the ATLAS TRT since 2003. He brought the Yale group into ATLAS with Colin Gay who is now at U British Columbia. The Yale group took on successfully a very critical item with the design, layout and prototyping of the TRT Read Out Drivers. Michael authored and co-authored numerous papers in physics and his advice was sought for many critical national committees. He was a Fellow of the American Physical Society and was honoured by his colleagues at a reception at Yale on Oct. 18, 2007. He is survived by his children Daniel and Julia, and by his parents.

We send our sympathy to all his family and friends.

Michael Tuts and Howard Gordon, U.S. ATLAS
Michael Zeller, Yale University
Fido Dittus, ATLAS TRT Project Leader
Peter Jenni, ATLAS Collaboration Spokesperson

A memorial page can be found online.

I took Michael Schmidt’s first-year course as a somewhat-unprepared Yale sophomore. Of course, the first few months were pretty tough for me, as I had not yet gotten used to the physicist’s way of seeing the world. Luckily for me, he was always straightforward and clear — and generous with his time to go over exams etc. But most important, he conveyed to me a real sense of the physicist’s lifestyle, e.g. when he explained why he was missing various lectures, to jet off to conferences or labs — which I found very exciting. Thus, my interaction with him was a non-trivial part of my eventual decision to become a physicist. So while I never interacted with him much after that, his too-early passing has a particular poignancy for me.

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Back from the dead

Saturday, November 17th, 2007

Oops, sorry about the hiatus. In some sense blogging is somewhere between a luxury and a requirement, so I guess the lack of blogs is a sign that I’m busy doing what I should be doing, which is a good thing since I don’t get paid or get grant money for blogging.

Nonetheless, there’s been some interesting things going on. Our beautiful tracker is going to move to its final resting place – the CMS cavern! It will be tough to get it installed before the holidays but we don’t want to wait until afterwards, so (at least according to the latest info – this is of course subject to change) in it will go. Just to give you a feel for what this device is, it is the largest Silicon tracking device ever built, with over 200 square meters of silicon wafers , think of a backyard swimming pool or tennis court covered in 0.5 mm thick silicon wafers. Currently this object resides in a clean room at CERN where we tested the bejeezus out of it over the first six months of 2007, but we closed up shop in the beginning of July to get it ready for transport (which took 2 months) However, things at the experiment went a bit slower than expected, so the last few months it has ben waiting for things over there to be ready. This is not the kind of device you want to bring ahead of time and then look to stash it someplace – way too fragile for that. We sort of knew this would happen, and it is a little bit too bad we wrapped up early, but as far as schedule goes it is far better to be early than late. Just to put a scale on things, here’s a picture of an older Silicon device from the LEP era compared with ours:

Opal vs. CMS Silicon

 

Alan and Marcello are holding the Opal Silicon detector, and the aluminum cylinder behind them with the spaghetti (actually cables) on the end is the same detector for CMS.

 

First the detector has to make the drive – roughly 15 km at around 5 km/hour (that’s 10 miles at 3 mph for you metriphobes), a 3 hour trip starting at 10:00 PM. The truck is a super-special truck with the ability to measure accelerations in real time, not to mention a highly advanced suspension system. All roads along the way will be closed to all traffic except the tracker (the French are good at this, they do it for bike races all the time). We insured for at least 2 Million Swiss Francs ($1.6 Million) but there was talk of upping that a bit, so it may be more.

Still, that doesn’t take the cake for transport this year. In my book, that honor goes to the Katrin experiment which my good friend Joe Fromaggio is on. He gave a seminar the other day and showed us how they got their behemoth spectrometer through a little town in Germany on its way home:

Thumbnail of Katrin

This is not an LHC experiment, it is an experiment to measure the mass of the neutrino, but it is still one of those big questions we don’t have the answer for yet.

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ATLAS Spam Filter

Thursday, November 15th, 2007

I’m beginning to think that the phrase ‘combined TileCal/Level-one trigger tests’ is synonymous with the phrase ‘TileCal is experiencing cooling failures’. The TileCal cooling system is designed to keep the electronics at an acceptable operating temperature. If the cooling fails, then the power to the system must be shut down to prevent damage to the electronics. It is not that TileCal experiences cooling failures often, but it seem we always experience cooling failures when doing combined tests with the level-one. And no cooling means no power which means no combined testing for you today. Seriously, you can set your clock by it. The first time it happens, you’re frustrated. The second time you’re laughing. The third time you’re suspicious. The fourth time, you’re convinced you are the butt of some cosmic joke.

I am exaggerating of course. Usually we recover from the failure rather quickly and are able to continue the tests. But the correlation is uncanny….

The level-one trigger is like ATLAS’ spam filter. The beam will collide inside ATLAS approximately 40 million times per second. We can’t possibly store all of that data to disk, nor would we want to. Most of those 40 million per second events aren’t very interesting. Rather I should say, they aren’t AS interesting. They are ‘old physics’, physics we have studied before. We are interested in ‘new physics’, physics we have never seen before. Here is an example:

MC Susy Event

This is a simulation of what a supersymmetry (SUSY) event might look like in the detector. (Much more complicated then the cosmic data we are taking now.) SUSY, like other theories of new physics, predicts certain types of events that will be produced at the LHC. Typically these events involve lots of particles, with lots of energy, flying everywhere as seen in the picture. The goal of the level-one trigger is to sift through those 40 million events per second, find the interesting one like SUSY and ditch the not-so-interesting ones. And it has to cut the event rate down by a factor of 500, meaning for every event that the level-one accepts, it has rejected 500 events. There are additional layers to the trigger. Once an event passes the level-one, it must also pass the ‘high level triggers’ before being written to disk. The final rate of events being stored for analysis is approximately 100-200 events per second. Imagine that. For every email in your inbox, there are 200,000 deleted as spam.

The Tile Calorimeter as well as the electromagnetic calorimeter (called the Liquid Argon Calorimeter) plays a critical role in the level-one trigger decision. In this picture, TileCal is the orange sections (the upper and lower row of orange) and the liquid argon is the gray sections (plus the two orange sections in the center on the left and right). The level-one makes a decision based on the amount of energy deposited in small regions of the calorimeters. SUSY events are predicted to have very large energy deposits. The purpose of combined tests between TileCal and the level-one is to calibrate the electronics’ signal in voltage and convert that to the amount of energy deposited in the calorimeter. If the electronics aren’t working properly or the calibration is incorrect, the trigger might delete as spam the very events that you are interested in studying. The calibration is a long process and will take many months but it is crucial to get right. Because once the events are rejected, we can’t get them back. There will be more tests on Monday. The cooling gods allowing of course.

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Snow!

Wednesday, November 14th, 2007

Or if you are from the Madison, Wisconsin area, “The White Stuff”, of which there was plenty there. But this morning, in Versonnex, France, we woke up to a soggy couple of inches. While it is soggy down here, it means the mountains could have high quality white stuff – which they do – several Swiss resorts open this weekend.  Time to wax the skis…

I spent the weekend getting away from it all up in Zurich. It was a fun trip, even though there was rain, and a very cold Monday. This is not a cheap city, and with the recent fluctuations in the exchange rates, so I am glad we had advance purchase tickets. The highlight of the trip was a solo acoustic concert by John Hiatt on our last night there. For those of you not familiar with him, you might remember a song done by Bonnie Raitt:  “Thing Called Love”, he wrote that and performed it on his break though album “Bring the Family”, but she got the hit.  His music probably is not to everyones’ taste, but I have enjoyed it since my uncle introduced me to “Slow Turning” in 1989.

As for work, we have really had a struggle lately with our infrastructure.  It has been frustrating, we plan some tests, and are thwarted.  This is supposed to be all over by friday.  So, in the meantime, I am looking at ways to test the 108 cables I installed recently.  It requires me to think a little differently than I have done, with each of  our crates receiving information from 5 other crates.  I’ve set them up to send “fake” data from one to crate the other to test the cards themselves, but all 18 share information (you should see the rat’s nest of cables).  Some of the tools are already in place – I want to make things more random to test lots of bits.   I’m making progress, even though nothing has been written yet,  sometimes its just a though exercise worked out while walking to lunch.

A la prochain…

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Meetings, meetings, meetings

Saturday, November 10th, 2007

Yet another big ‘week’ has passed us by. A few weeks ago it was ‘ATLAS week’, a week of meetings about the detector’s status. This week was ‘Trigger and Physics week’, another week of meetings about all the physics studies being done in preparation for the beam turn-on.

Some friends and I were discussing the volume of meetings within ATLAS. And I thought I might support this discussion with some statistics. This is the 13 year summary of the number of ATLAS meetings registered on our main scheduling website:

atlas_meetings

Really? Really guys? Did we really have 4531 meetings in the past year? I would have guessed like 1000 per year.

Actually what is shown here is the number of ‘events’ in the past year. For example, Trigger and Physics week which was five full days of meetings is listed as one event in this figure (which makes this figure all that more depressing). Say there are approximately 250 working days at CERN, this would be approximately 18 meetings per day. It baffles me that we actually have that much to talk about!

And since I just couldn’t resist I decided to look at the number of CMS events in the past few years.

cms_meetings

947 to ATLAS’ 4531. Hmm.

I think there are two possible explanations here. CMS uses a different scheduling/conference website. This is entirely possible. They might want to avoid having random ATLAS bloggers comb through their meeting statistics. Or. CMS is just more verbally efficient. They say in one word what ATLAS says in four.

It would be interesting to see the monthly statistics but the website doesn’t generate those. This is probably for the greater good of the experiment. People can really get into plotting all the various statistics. And knowing ATLAS, we would probably have to schedule a meeting to discuss the results.

If you were to ask me (and I feel represent the population well for this question), ‘Do you spend too much time in meetings?’ I would say, yes. But if the next question was, ‘Which meetings do you think ATLAS could afford to get rid of?’. I would say, none.

Take Trigger and Physics week. Of the talks that I attended, the information presented was useful and relevant. Meaning that for the most part it was information that I needed to know. Information that I need for the continuation of my own work. I can not point to a single talk that was not worth having. Nor are there many talks that are redundant. Certainly there is some overlap, where one talk might be using as input some work presented elsewhere. But I didn’t feel like I was being told the same thing twice. So maybe 4500 meetings per year is the reality of doing physics in an experiment with 2000 people.

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Cable Trays

Sunday, November 4th, 2007

I spent the last couple of weeks trying to arrange a cable tray under our RCT racks. It goes for a few meters – maybe 8 – and we are going to lay excess cable in it. I thought this would be easier, but there is a bit of overhead in the whole operation. First I had to get the approval of one of the people who is in charge of the fibers that sit below it. I didn’t want to be in their way. Which is important, since they belong to the Hadronic Calorimeter, which supplies the RCT with slightly over half of its signals. Then I had to ask the technical people who are in charge of installing these things if it was all right. They said sure, we can do this, no problem. However, then it sat for a bit, so I pestered and finally got referred to someone who could do “small jobs” like this to do it. So now it is in. I am happy. Small things like this just make life easier, and now I can install 108 cables on monday, which is a good time to do it.

There is a lot of other equipment around, so I really don’t want to just go ahead and install the cable tray, and then have to rip it out again.  I already had some of the cables in, only to have to pull them out again.   We had wanted the cables to go another way, but there just isn’t space for  it.

The rest of my week I learned how to send a message from one program to another.  This was kind of fun – I like to learn new computing tricks.  I did however run into a bug with another program that stalled me for a bit, but there turned out to be a work around.  What it did is save us from ourselves – forgetting to click a button on one web browser while we ran another program.  Now the test program is all self contained – much better.

On the other side of life – it got quite cool the last week. It probably could have snowed in the mountains, but we aren’t getting much rain at all.  Its a little worrisome.  We really want to ski this winter!

A la prochain…

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