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Mike Anderson | USLHC | USA

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Ex-Particle Physicist Investigating Crash

Tuesday, September 21st, 2010

There is an interesting article about Gregg Berman, who received a PhD in particle physics from Princeton about 20 years ago, who is heading the investigation into the stock-market free fall on May 6:

In investigating the crash, Mr. Berman says he finds himself in a position similar to his physics work 20 years ago, when he was collecting huge amounts of data and comparing the competing views of many laboratories on a question dividing particle physics — whether the neutrino, one of the least known and most common elementary particles, actually had mass.

Particle physicists sometimes show up in surprising places.

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Collisions Recorded

Sunday, September 19th, 2010

This essentially shows the amount of proton collisions created by the Large Hadron Collider as a function of time.

I have my own personal “analysis” code set up so that every Friday I run on the newest data available.  Then, by the afternoon or Monday morning I have new plots to look at and show colleagues.

I do this on Friday because that’s when a list of “good” data-taking periods is published.  That is, there is a group of people that decide when the detector was fully operational, working as expected, and recording useful data.  They then publish a list of this “good data”, and everyone else uses that list so that they run on useful data.  An example of “not useful” data (for physics) would be if one or more parts of the detector were off, or not working properly.

The plot I show here is the amount of proton-collision data available.  It grows more than linearly because the intensity of the  beams is being increased as well.  Someday, in the distant future, the LHC will be able to deliver an amount of collisions in one work-week equivalent to everything we’ve recorded since turning on in May this year.  Someday.

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Month-long Vacations in France

Friday, August 20th, 2010

Workers in France are guaranteed at least 5 weeks paid vacation time each year.[1,2] Many people take that time off in the month of August.  I don’t know how August became the vacation month, but that’s the way it is.  Hours for many stores become even more limited or simply close – for the month!

Even in my hometown of Madison, WI there is a French bakery owned by a french family and they close up shop for most of August.

The disappearing of French workers also happens at CERN – professors, scientists, etc, many of them are gone.  That leaves the rest of us with the chance to either get ahead in our work, or relax and take it easy as well.

(Oh, and did I mention that the French also have a 35-hour work week?[3])

Don’t worry though, the LHC is still on and they’re trying to reach higher beam luminosities.  At the moment they’re working on some cryo problems:

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Right now: Trying to collide 25×25 bunches

Thursday, July 29th, 2010

As we speak there are 25 bunches of protons in both proton beams in the LHC.  See all those steps in the graph (red and blue lines)?  Each little step is one bunch being added, and each “big” step is 4 bunches being added.  So if you count the steps yourself you should get a total bunch count of 25 in each beam.  The red and blue lines correspond to the left-hand y-axis showing “Intensity”.

The energy of the proton beams is in black and goes with the right-hand y-axis, “Energy (GeV)”.  As I write this the protons are around 500-some GeV and being ramped up to 3500 GeV which should take about half an hour.

Once both beams are at 3500 GeV and they declare stable beams, it’s time to record some data with the most bunches in the LHC to date!

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That’s what I like to see

Sunday, July 18th, 2010

Stable proton beams colliding at some of the highest luminosities reached by the LHC so far!

Right now the luminosity is at 1030/cm2s.  Up until now, the luminosity collected these past few months has been at a luminosity around, at most, 1029/cm2s.

This is significant because this basically means that in about a day we can collect the same amount of data that we have collected over the past few months.  That’s why it’s so useful to do studies on increasing the luminosity rather than continuing to run at lower luminosities.

There’s a short term downside though: doing studies to increase luminosity makes it hard to get clean, stable beams for data taking.  It’s kind of like deciding whether you should buy a computer now, or wait a few months until prices come down and hardware is better.

The LHC has a balanced program of stable running and also doing studies to increase luminosity.  From the looks of it, it’s going well.

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On the border

Sunday, June 27th, 2010

The LHC ring crosses the France/Switzerland border in something like 6 places.  Unfortunately, since Switzerland isn’t in the EU, one needs to have both Euros and Swiss Francs when working and living near CERN.  The main site is just barely in Switzerland, while several other CERN sites are in France.  For example, our detector, CMS, is about 8 miles into France.

Vending machines do not take more than once kind of currency.  Also, border guards don’t take kindly to bringing wine or meat across the border.

As for the American dollars, I only happened to have those because I recently traded euros to someone who was moving to France permanently, while I was going back to the US within a week or so.

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Millions of Simulations

Thursday, June 17th, 2010

Proton-Proton collision simulation "jobs" for the CMS detector running on the grid.

To compare with the data we record from our detector (CMS), we need to run a few simulations…well more like billions of simulations.

Each “job” in the plot above is actually a program running on a computer at a university.  Each program typically simulates a few hundred, or a few thousand, proton-proton collisions.  Each individual “collision simulation” calculates what a certain kind of collision would look like in our 12,500-ton detector.

And I don’t mean they just make pretty pictures.  A single simulation really consists of: some particles within each proton interact with some probability, they produce other particles with some probability, those particles decay to other particles with some probability, and so on…  Eventually, stable particles are made and the passage of those particles through the detector are also simulated.

As you can imagine, this requires a lot of random numbers.  One mistake that happens sometimes is that different jobs have the same initial ‘seed’ for the random numbers, and this results in duplication of simulations.  Not only is that a waste of CPU-cycles, but it also means a fuller range of collision possibilities doesn’t get simulated.

My job at times is to herd thousands of simulation jobs at a time to various places and monitor them, make sure they don’t crash, and finish in a timely fashion to return the needed data.

By the way, when I wrote the job monitoring script that makes plots like the one above (written in Python and using matplotlib), I tried using their school colors when I could, but sometimes that resulted in colors that were too similar or confusing.

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Room for promotion?

Saturday, June 12th, 2010

Yesterday about a dozen or so people from our university research group were asked to sit down in a room here at CERN and talk with a professor who is the DOE reviewer for our main grant.

This fall our 3-year grant is up for review, and he’ll help decide our fate, basically.

Our group had about 9 graduate students there and he asked questions to figure out what problems we were experiencing either within our group, within particle physics, or living in Europe.

Towards the end he also asked us about what we all wanted to do after we graduate.  He then led us through a somewhat sad “back of the envelope” calculation:

“Lets say the average professor’s tenure at a university is 30
years, roughly.  That typical professor has about 2 graduate students
at any time, and the average time for completion is 6 years.
So, the typical professor produces a total of about 10 PhD’s.
Well, they only need 1 to replicate themselves, and 1 more to
replicate positions available at national labs.  And that’s it, that’s
all there is room for in academia, typically, 2 out of 10.”

It’s an over-simplified example, but I think not too far off the mark.  About 1,000-some physics PhD’s are awarded in the US every year(AIP), but the number of vacant positions at universities each year is only a fraction of that(AIP Chart).

Update June 13:  I began searching for the names of my advisor’s former students and happened upon an on-topic article from the American Physical Society, Sean Mattingly, PhD High-Energy Particle Physics, Dedicated Client Support, Bank of America.  Sean is quoted as saying “I think every student should be thinking about a job outside physics.”  And that “in grad school we all think that we’re on the academic path, but you’re not – there’s a lot of competition for the few jobs available and most of you are going to have to leave the field.”

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Wrapping up another owl shift

Saturday, June 5th, 2010

It’s 5:45am, and my shift doesn’t end for another hour at 7am.

We were so close to getting to record some more collision data during this shift, only for the beam to be dumped due to some problems.  I’ll have to ask experts to see what a “1/3 resonance” means.

Hopefully they’ll have more luck during the morning and afternoon shift so that by the time I’m on shift again at 11pm I’ll get to watch more data being taken in person.

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On Trigger Shift

Friday, June 4th, 2010

I’m currently in the CMS control room doing Trigger shift.  The ‘Trigger’ is what selects interesting events to record.  Unfortunately, there is nothing interesting being recorded at the moment because, as you can see on the LHC status page, currently access is required to work on the “Quench Protection System” in a specific sector.

So, I’ll keep watching the trigger recording cosmic ray muons, making sure things stay looking ok.

In the meantime I can keep working on a paper we’d like to have a draft of by Monday.

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