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Posts Tagged ‘student life’

Particles of the Day

Tuesday, November 20th, 2012
My copy of the 2012 PDG booklet

My copy of the 2012 PDG booklet

Last week, I got my copy of the 2012 Particle Data Group Review of Particle Physics booklet — which, along with its heavy, 1000-page full-length counterpart, we simply call “the PDG.” My very first copy, during my first months at CERN in the summer of 2003, is a vivid memory for me. Here was a book with almost everything you want to know, about every particle ever discovered! It was like the book of dinosaurs I had when I was a kid, and I read it in exactly the same way: flipping to a random page and reading a few facts about, say, the charged kaon.

My new copy of the PDG has inspired me to adapt this fun for non-experts. So each day, I’ll feature a new particle on Twitter; I’m @sethzenz, and the hashtag will be #ParticleOfTheDay. Since starting last week, I’ve featured the B0s meson, the pion, the kaon, the electron, and the Higgs.

How long can I keep this up? That is, how many particles are there? Well, that depends on how you count. The Standard Model has 3 charged leptons, 3 neutrinos, 6 quarks, the photon, and the W, Z, and Higgs bosons. But then there’s all the antiparticles. Dark matter candidates. The graviton. I could even argue for taking 8 days covering all the gluon colors! (Don’t worry, I won’t.) But most of all, there’s all the composite particles — those that are made from a combination of quarks. There are a very large number of those, and there will always be more to find too, because you can always add more energy to the same combination of quarks.

The point isn’t to be systematic. I might go back and be more specific. I might repeat. What I really want to do is find a particle each day that’s in the news or I can say something interesting about.

Flipping at random through a book of particles turns out not to be the best way to learn particle physics; ultimately, I needed to learn the principles by which those particles are organized. But it is an interesting way to tell the story of particle physics: its history and how it’s done today. After all, the particles do come out of accelerators in a random jumble; it’s our job to organize them.

Have an idea for the Particle of the Day, and what to say about it? Let me know!

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Zombies at CERN!

Tuesday, October 30th, 2012

Some friends of colleagues of mine made a zombie movie here at CERN. It looks pretty neat, and will be available for free soon online, so here’s the trailer:

Now, then. There are some things I should probably clarify:

1. This film has not been authorized or endorsed by CERN.

2. The Higgs boson obviously cannot turn people into zombies. Never mind the biology, it’s enough to know that the Higgs decays instantaneously into more ordinary particles, and never leaves the detector. If any LHC collisions could make zombies, the earth would already be filled with zombies created when ultra high-energy cosmic rays hit the atmosphere.

3. Zombies do not really exist, and they will not eat your brains. Really. I promise.

4. The LHC cannot be operated when anyone is in one its tunnels or experimental caverns. The safety systems that prevent this are quite a bit more sophisticated than the trailer seems to imply.

5. The tunnels in the film aren’t the LHC tunnels — which are continuously being used for science rather than cinematography — but they do appear to be real steam tunnels from some of the buildings here at CERN. Rather interesting and spooky, but maybe not as polished and high-tech as you were expecting.

In conclusion: it’s always fun to see zombies in cool places, especially in your own back yard. I look forward to the movie coming out. For more information, you can look at decayfilm.com, facebook.com/decayfilm, or twitter.com/decayfilm

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More Multitasking

Friday, April 13th, 2012

I fell out of practice at multitasking at the end of grad school. For the final six months, almost all of my work went into finalizing how to present my analysis results. There were two versions of the presentation: the paper and my thesis, but the general direction of work was all the same. The previous tasks I had worked on, geared toward keeping ATLAS running, were all long since “done,” at least as far as I was concerned.

Starting a postdoc means a sudden change of gears, with more multitasking than ever before. I’ve started many new projects from scratch at the same time, and because I’m new to CMS, every one of those tasks involves tools and procedures that I don’t know. It’s easy to lose track of some of those tasks at any given time, or simply to want to focus on one thing until I understand it, but the job doesn’t work that way. Being succesful as a postdoc will mean significant contributions to the running and understanding of the detector and significant contributions to keeping my group’s analysis running and starting a new analysis (sub)channel of my own. None can be dropped, and most of the things I’m doing have deadlines in the next few months.

So I’m having to remember and improve my multitasking skills, quickly. Step one is bringing this post to a close, and asking you to wish me luck, and getting back to work!

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Look Mom No Nabla’s!

Monday, August 8th, 2011

From time to time I find myself looking back at my class notes from my undergraduate studies, just to brush up on a topic or two (usually when I am taking the graduate class on the subject matter). And I’ve begun to notice a trend while comparing my undergraduate and graduate notes. I’ve gotten lazier.

That is, the notation I use to describe mathematics has gotten simpler. I think the reason for this is because there has been simply more material to write down, and less time for me to do it. I’ve seen professors at least double (sometimes triple) my age move faster with a white board marker then I can move on a treadmill. I have a tough time keeping up. So to keep up with them (aside from nagging them to slow down) I’ve started adopting a shorthand notation.

But unlike the late Dr. Feynman, I’ve not come up with my own short hand notation [1]. Instead I’ve just tried to incorporate what’s known as four-vector notation.

Four Vectors

Four vector notation is the notation of choice for quantum field theory. It allows a great simplification in how much you have to write (once you know the rules).

Let’s start with a simple example. Four vector notation allows me to describe a point in space-time (with respect to some reference frame), take the point:

(ct, x, y, z)

I can write this as:

Well that’s not astonishing in the least bit, I could have just as well labeled the point P.

Let’s take a second example. I can combine a scalar and a vector together in four-vector notation. For instance, if I wanted to describe a particle’s energy and it’s momentum (again, with respect to some reference frame) I could use a four-vector:

We can even go a bit more abstract and use four-vectors as mathematical operators:

Here we have a partial derivative with respect to time and the “del” operator (sometimes referred to as a nabla).

Now suppose I wanted to multiply two four-vectors, how would I do this? The product of two arbitrary four-vectors goes like this:

Notice how A and B have either a super-script or a sub-script in the above equations. In one case we have a contra-variant four-vector (super-script); and in the other we have a co-variant four-vector (sub-script).  However, their components are always labeled with super-scripts.  Notice how the product of four-vectors A & B is described by a “dot-product like” operation in which their respective components are multiplied together; but the last three are assigned a minus sign.

In fact I can only ever take the product of a contra-variant with a co-variant (nothing else); but the order in which one comes first doesn’t matter, their product is left invariant. I should also point out the name of the game is “summation over repeated index.” This means if I toss a third four-vector into the mix, if it has a different index (sub- or super-script) it’s ignored:

Notice how A & B have index μ and C has index ν. The μ is the “repeated” index, and the four-vector product acts between A & B. I realize this isn’t a true summation because there is a minus sign involved, but that’s just what the process is referred as.

Maxwell’s Equations – The Lazy Way

Now let’s dive into a serious example to really show the power of four-vector notation. And let’s go outside the realm of quantum field theory, instead let’s take Maxwell’s Equations:

With these four equations-and appropriate boundary conditions-I can describe all phenomenon in classical electrodynamics (I chosen to work in Heaviside-Lorentz units as opposed to the standard SI system, this causes the pesky μ’s & ε‘s to drop out. Remember I’m lazy!!).

These are four coupled first order differential equations that relate two vector fields (electric & magnetic). But from the theory of classical electrodynamics I can write these two vector fields as originating from a scalar and a vector potential (note, I did not say potential energy, which is very different from potential):

With this I can actually express Maxwell’s four first order equations as two second order equations:

Of course this is an awful mess when you look at it. Why on earth would anyone want to do this!? There are so many more terms and derivatives all over the place.

But, in physics there is something known as the “Lorentz Condition,” sometimes also called the Lorentz Gauge [2], which says:

(When I put this into Heaviside-Lorentz units the με again drop away).

Which simplifies the above two equations rather nicely:

Now this is truly enticing, these equations are almost identical! Suppose I made a set of four-vectors:

Notice how the last two are mathematical operators, one is a co-variant and the other is a contra-variant. They are just begging to be multiplied, so let’s do just that:

This is actually a new mathematical operator known as the d’Alembertian Operator, its usually represented by a square, but I don’t know the LaTeX command to make that. =(

But, with this set of four-vectors and the two equations above I can write mankind’s sum knowledge of all electromagnetic theory in one line:

Let’s pause on this for a moment.  I think this is really an astonishing miracle that physicists over the years have figured out how to write so much information about the natural world in such a small space (one line)!  Some of you might remember the Standard Model Lagrangian, which is conveniently written on a coffee mug should you forget.  That coffee mug contains A LOT of information, but it definitely cannot  fit on one line, at least with my handwriting (maybe someone someday will come up with some ingenious notation of their own?!).

But, just like that four vector notation has allowed physicists to simplify Maxwell’s Equations (all four of them) in a single concise statement. Talk about saving space on your final exam’s equation sheet! So hopefully you’ve come to appreciate the power of four-vector notation.

Until Next Time,

-Brian

 

References

[1] Richard Feynman routinely used his own notation for trigonometric functions, logarithms and other common functions in mathematics, he did this because it was simpler & faster for him to write in such a fashion. For more details and other great stories, see Feynman’s own “Surely You’re Joking Mr. Feynman,” W. W. Norton & Company, Inc. 1985.

[2] See for instance D. J. Griffiths, “Introduction to Electrodynamics,” 2nd ed., Prentice-Hall, Inc., 1989.

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My Crazy Semester: Thesis Writing

Monday, February 28th, 2011

Oops, I seem to have done things in the wrong order. The good news is that I have a job lined up for when I graduate. The… challenging… news is that I still have a few things to finish here in Berkeley: little things, like finalizing my analysis and writing my thesis! This has made for a rather busy semester, to say the least.

From the perspective of readers here, though, I’m not going anywhere fast. I will be switching universities, and (gasp!) switching experiments, but in neither case am I going far enough that I fall outside the subject of this blog. I didn’t mean “far enough” too literally, but the distances are about 2500 miles and 5.3 miles respectively.

This gives me lots to write about, so let me start with my thesis. It’s not that much fun. It has two parts: background stuff I have to look up, and describing my analysis in more detail. But it is, I have to admit, probably all wortwhile. The former part is all stuff that’s relevant to my work and I ought to be able to describe off the top of my head — and in fact, I usually can, but not with all the numbers and equations and details just right. The latter part is a good chance to really document what I did in my analysis, which is information that might not be public elsewhere. Maybe someone, someday, will want to look up what I did. Maybe I’ll look it up myself out of nostalgia. Once I get my thesis written at last, though, one thing I’m sure of: I won’t look at it again for a while. I’m already ready to move on!

While I’m working on that, here are some goodies from my thesis. The output of a helpful script I wrote:

Seth-Zenzs-MacBook-Pro:~ sethzenz$ python scripts/thesistimeleft.py

You have 75 days left to file your thesis!!!

It recalculates every day. I could make it send me automatic emails, if I really want to make myself nervous.

And here’s a bit of my (first draft) introduction, which tries to explain how my work fits into the overall context of the LHC program:

The Large Hadron Collider (LHC) was built to produce new particles and rare interactions at a high rate, but its first and foremost byproduct is sprays of low-energy hadrons. At its full design capacity, the LHC will cross proton bunches 31.6 million times per second at each interaction point, with an average of about 20 proton-proton collisions per crossing. Most of these collisions will be “soft” interactions, with relatively little energy exchanged and the outgoing hadrons having relatively little momentum perpendicular to the beam axis. These interactions are described in principle by Quantum Chromodynamics (QCD), the quantum field theory of the strong interactions. In practice, however, they are the most difficult to understand, because the theory becomes non-perturbative at low energies. Predictions can only be made via approximations and phenomenological models. This difficulty with low-energy strong interactions appears even in interactions that are initially well-described by perturbation theory. Outgoing high-energy quarks and gluons quickly “clothe” their strong color charge by evolving into jets of lower-energy hadrons, a process that again requires approximation and modelling.

The LHC’s general-purpose experiments, ATLAS and CMS, are equipped with multi-stage trigger systems that select against these common processes, for example by identifying leptons and missing energy produced in electroweak interactions. However, low-energy QCD still has a significant impact on the physics program in several areas. With so many collisions in each crossing, the most interesting collisions will have many low-energy collisions whose signals in the detector overlap with the objects of interest. In order for their effects to be subtracted, these features of these pileup collisions must be known quantitatively. The evolution of high-energy hadronic jets must also be well-understood. This is partially to account for their contribution as pileup events, but their energy must also be calibrated so they can be studied in their own right. Although even very high-energy jets are relatively common at the LHC, they can also serve as signatures of the decay of new particles.

The quantitative investigation of low-energy QCD is thus a foundational element of the LHC program, which will inform the studies and discoveries of the coming years. Initial low-energy QCD measurements have divided the problem between low-energy events and the study of higher-energy jet properties. In the former case, inclusive charged particle distributions are produced from events identified using a “minimum bias” trigger. In the latter case, higher-energy jets are triggered and studied using the calorimeter system built for the purpose.

This work focuses on the additional information to be gained in the case that the two issues are not-so easily factorized, by studying the emergence of low-energy jets from soft interactions. Particles are identified using the methods of the lowest-energy measurements, but grouped together into jets according to the algorithms used to study jets at higher energies. Low-momentum jets and their properties are measured using the ATLAS Inner Detector, the component of the ATLAS experiment that tracks charged particles, in events identified using the ATLAS Minimum Bias Trigger Scintilators.

That’s very unlikely to be final, but in any case that gives you a picture of the sort of thing I’m working on.

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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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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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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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Scoring Points!

Sunday, May 30th, 2010

In our collaboration (CMS), every institution involved is required to do a certain number of shifts watching the detector, making sure it runs smoothly while recording data.  The number of required shifts depends on the number of members in the institution’s group, and it’s up to each group to split up the work among their members as they wish.

For example, this means that if a professor doesn’t want to do shifts, their scientists, post-docs, or students must do them.

One complicating factor is that not every shift is worth the same.  The least popular shifts, or the ones “harder” to do – like overnight shifts – are worth more than others.

Here’s how many points each shift is worth in our collaboration:

  • Weekday morning shift (7am-3pm) is 0.75 points
  • Weekday afternoon shift (3pm-11pm) is 0.75 points, and
  • Weekday overnight shift (11pm-7am) is 1.5 points.
  • Weekend shifts add extra +0.5 points to above.

And since we are asked to do 24-points worth of shifts in a year, what kind of shift is most attractive to me, an unmarried, childless, young graduate student?

The weekend-overnight shifts, of course!  At 2-points each they’re pretty attractive.

Sometimes you have to take the shifts you can get, however, so I’ll be do weekday overnight shifts starting tomorrow.

Control room for the CMS detector.

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After a short stay in the US, I have returned back to CERN.

I flew on a Boeing 767 for about 9 hours.  That was not a comfortable flight.  An Airbus A330 has much more leg room.  Also, on the Airbus, each seat has it’s own personal screen to select from a couple dozen movies and shows to watch, whenever you want.

The science of a nicer airline flight isn't so complicated.

Airplanes could be more comfortable, but there are things you can do yourself to make trips better.  The best thing I ever did to make all my flights more comfortable was to buy noise-canceling headphones.

I was skeptical of noise-canceling headphones at first.  I didn’t have any friends that owned a pair, and most stores don’t have them out in the open for you to test.  I did research on them, all the way from the basic physics of noise-canceling headphones, to actual reviews of headphones.

Basically, noise-canceling headphones reduce low frequencies the most.  That means engine noise, low rumbles, wind, etc are reduced considerably, but you’ll still be able to hear a baby cry, cat meow, or a phone ring.  (I hope you never have to sit next to a cat on a flight.  I love cats, but I’ve found they’re not so pleasant on airplanes.)

I’ve been using noise-canceling headphones for two years now on all my flights, and I can’t recommend them enough for people that fly a lot.

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