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Archive for April, 2010

Higher Intensities

Friday, April 30th, 2010

Click for live LHC status.

The LHC is continuing studies to reach higher beam intensities.  There was a “technical stop” the past few days to turn on more of the machine protection system so that the they can safely operate at higher intensities.

A 3.5 TeV beam of protons can cause plenty of damage if there’s uncontrolled beam loss!


CERN Offices

Tuesday, April 27th, 2010

My office at CERN.

I’m curious to know what the best-looking office is at CERN. (If you know someone or if you think your office would be in the running for that let me know and I can post a picture!)

From what I’ve personally seen, most offices here aren’t all that different from mine.  A little cramped, but at least they have big windows.  The plant was my own doing – and it is still a little pathetic now due to a lack of watering over the holidays in December.

Looking at that picture now it just occurred to me you would notice we use mac laptops (mine is plugged into a monitor).  The use of macs among high energy physicists is pretty high – higher than the overall population – and I wonder how it became that way?



Feeling squeezed

Tuesday, April 27th, 2010

Here I am at CERN, after fairly smooth travels. (At least this time I didn’t show up with the flu.) The weather here is very nice for this time of the year, and the only evidence I can see for the eruption of Eyjafjallajokull (I love that name!) is somewhat lower attendance than usual for the semiannual CMS computing and software workshop. A number of people who had planned on flying here last week had their flights rescheduled far enough into the future such that it was not worthwhile for them to come.

While changing planes at Washington Dulles, I ran into a colleague (headed in the other direction, back to Chicago from CERN) who had some very good news to report. Over the weekend, LHC operators tried “squeezing” the beams for the first time, as Mike had alluded to last week. This is a focusing of the beams that, like the name says, squeezes them so that all the particles are closer together. A greater density of beam particles means that there is a greater chance that the particles in opposing bunches will actually collide. And that was in fact what happened — the observed collision rate went up, by about a factor of ten. It’s not every day that you gain a factor of ten! As a result, more collisions were recorded in a single day than had been recorded in the entire month beforehand.

The next steps include things like adding more protons to each bunch, and adding more bunches to each beam. We hope to get another four factors of ten in collision rate yet this year. The big question is how quickly they will come. But in any case, it is very encouraging to see such progress.


The Quark Gluon Plasma

Monday, April 26th, 2010

Much of the press coverage of the LHC has discussed the search for the Higgs, but ALICE was designed for something completely different.  We’re studying a hot, dense phase of nuclear matter called the Quark Gluon Plasma (QGP).

What we’re doing is mapping out the phase diagram of nuclear matter.  This is roughly what we know about the phase diagram of nuclear matter:

The x-axis, baryochemical potential, is the amount of energy needed to add a baryon (such as a proton or a neutron) to the system.  You can think of it as analogous to pressure in the phase diagram of water.   The y-axis is the temperature in MeV – one MeV is roughly 1160 megakelvin (MK) and 175 MeV is about 2,000,000MK.  That’s about 250,000 times hotter than the core of the sun.  At lower temperatures and lower baryochemical potentials (lower densities), we have a hadron gas.  (Neutrons and protons are hadrons.  The hadron gas is actually mostly made up of pions, a hadron with about 10% of the mass of the proton.)  At higher temperatures, we get the Quark Gluon Plasma.  Neutron stars are somewhere to the right, way off the chart.

We create a QGP in the lab by colliding two nuclei together at high energies.  The LHC will collide lead nuclei at a center of mass energy of 5.5 TeV per nucleon, which is over 27 times greater than the highest high energy nuclear collisions so far.  (Nucleons are the protons and neutrons in the nucleus.)  We expect our first data from lead-lead collisions this fall, if everything goes according to plan.  From studies of gold-gold collisions at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory on Long Island, we learned that a QGP is a liquid of quarks and gluons – and set record for the highest temperature reached in the laboratory in the process.  The fact that it acts like a fluid actually indicates the attraction between quarks and gluons isn’t negligible, as had been predicted – this is why it’s sometimes called a strongly-interacting QGP, or sQGP.  (At one point someone proposed a variation on this, the bound state QGP, but this name was thankfully abandoned.)  We’re actually not really sure what we’ll see at the LHC – will it still behave like a liquid?  Or will it behave like a gas?

What we’re doing is kind of like colliding two ice cubes together to study the phase diagram of water.  If you had two ice cubes in outer space (where it’s really cold) and you got them moving really fast and slammed them into each other, the ice would melt for a very short time and then as the system expanded, it’d freeze again and you’d end up with little flakes of ice scattering all over the place.  On the surface of the Earth, nuclei are essentially frozen nuclear matter.  We have to figure out the properties of melted nuclear matter by looking at the frozen shrapnel.  We have the luxury of having better ways to study water than by smashing ice cubes together, but we don’t have any other way of studying nuclear matter.

Everyone learns that water has three phases, solid, liquid and gas.  This is a pretty good approximation, but it is a simplification.  There are 15 different phases of ice (that we know about).  Analogously, the diagram above is definitely an approximation.  There’s probably a lot of structure in there – a lot of extra phases – we don’t know about.  In the era of the LHC, we’ll be able to move over about two orders of magnitude in temperature along this phase diagram because both the LHC and RHIC are actively taking data.  There have also been a lot of improvements in detector technology and data analysis techniques in the last couple decades, so we’ll be able to do better measurements than ever before.  We’re in the golden age of the field.

ps –  I haven’t forgotten about the questions from my first post on Facebook but I just haven’t gotten to them all.  I did post replies to the comments posted on the blog in the comments section.


“If they could teach Koko the gorilla sign language, surely I could teach you rudimentary physics.”
-Sheldon to Penny (last Monday night’s episode)

Sure, they routinely throw up things like the Schrodinger equation and make references to things like quantum mechanics… and whether or not I may laugh periodically… I really dislike The Big Bang Theory (BBT from here on out).

Don’t get me wrong, I know people who love it – my parents for example. When I tell them I went to trivia night, they say things like “Oooh! that’s just like on the BBT”. They ask which of my friends is like Leonard or Sheldon and ask me if the equations they randomly throw up on the screen are actually physics equations. Of course my parents think I’m pretty smart, and they have met some of my physicist friends.

It’s not the science of BBT that I have problems with. It’s how the only physicists in the show are nerdy, socially awkward, and intolerant. Granted Sheldon (the stereotype of stereotypes) is kind of the jerk of the group, but he likens someone who for all intent and purposes is reasonably intelligent to a gorilla… but Penny can’t be smart, she’s pretty and blonde, and likes shoes. >Sigh<

Screen shot from the BBT

“Newton was a smart cookie… ooh is that where Fig Newtons come from?” – Penny

Granted the goal is to be funny, but I hate how the show only has socially incompetent and extraordinarily nerdy guys. And how they make physics completely inaccessible to anyone who doesn’t wear glasses. Sheldon starts teaching Penny physics with a history lesson starting 3000 years ago and chastises her for not taking notes. Instead he could tell her to looking around and see nature. Physics is the study of how nature works. (But that’s not Sheldon’s character… he wants physics to be inaccessible).

I have 20/20 vision, enjoy shoes, hair cuts, showering daily, monkey pants, Glee, and books that don’t have an equation in the text… so do lots of my (physics) friends.  I think lots of people are pushed away from physics at an early age because of shows like this. And it’s self fulfilling: only a certain type is portrayed therefore only that certain type feels welcome… so only a certain type becomes physicists.

Of course, at the end of the day, the BBT is a comedy show. But that doesn’t mean that the writers can’t do something positive for physics… like maybe have a woman physicist on the show who isn’t a sociopath, or a guy who has interests outside of physics.

Granted it’s not just this show in particular. One of my childhood favorites – Saved by the Bell – always has the science teacher as a nerdy, white guy in a lab coat who was really really weird (this was also true of the math teacher… whereas the history/English/art teachers were always women… way to break down barriers Saved by the Bell…). I guess that wasn’t enough of a deterrent for me, but I also had a really cool science teacher in 4th grade. She told me that the world needed little girls like me to go into science. I remember the conversation to this day – I think at the time, I wanted to be an astronaut :).

There are lots of programs out there to try to combat this stereotype (as an undergrad, I was involved in Expanding your Horizons and Girl scout Badge day both of which were targeted on getting girls interested in science), but social “norms” are entrenched in everything that we see and do. The only real way to promote change is to talk to normal guys, girls and minorities face to face and tell them that science is for everyone – not just the socially awkward.

And that’s why I dislike the Big Bang Theory 🙂

– Regina


Lost in Transition

Sunday, April 25th, 2010

No, this is not a story about being stuck at an airport during the flight chaos last week. I was always expecting that one of the quantum diarists would report on this, but so far nobody reported. I hope that everybody is where he/she wants to be and not stuck at some far away airport.
But the topic is of course the volcano in Iceland and its consequences:
We organized the ATLAS Upgrade Week 2010 at DESY for last week. More than 170 people registered and were supposed to arrive last Monday. In the week before the meeting I was rather busy with the preparation but also other work. When they close the Hamburg airport on Thursday evening I did not even think that this could affect our meeting.
But the longer the airports were closed, the more I started to doubt that people come to Hamburg. During last weekend it was decided that the meeting will start anyway and that people should join via EVO (meetings where people can dial in via computer or a phone bridge). Originally we had planned only very few EVO meetings but now we had to adjust. Luckily DESY is a large national lab and we have the facilities for this kind of meeting. On Monday morning I contacted our IT group and told them, that we have to rearrange due to the changed situation. And within no time, we had arranged the meeting rooms and the colleague at IT booked EVO meetings for the whole week. I implemented the links in the agenda and we were ready to start.

Almost 100 people had to cancel as they could not reach Hamburg. Others arrived one or two days later. So we thought that we should reward some people for the most strenuous journeys with a little award. One person needed 18 hours per train from Udine. Another person flew in from Israel and had long delays during the trip. But the first place was won by a group from Liverpool. They actually took the train through London, Paris, Strasbourg, Karlsruhe to Hamburg. 20 hours with 5 changes is not really the best connection between Liverpool and Hamburg. I hope they enjoy the German wine and remember Hamburg as a sunny nice place.
In the end all participants were happy that we still could discuss important issues and I think the “DESY volcano meeting” will be remembered for a long time.

Group picture of the participants of the ATLAS Upgrade Week 2010 at DESY in Hamburg (Barbara Warmbein, DESY). It will probably be remembered as DESY volcano meeting.

Group picture of the participants of the ATLAS Upgrade Week 2010 at DESY in Hamburg (Barbara Warmbein, DESY). It will probably be remembered as DESY volcano meeting.


Hubble Turns 20

Saturday, April 24th, 2010
Google Celebrates Hubble

Google Celebrates Hubble

As Google helped proclaim with their banner we have another landmark day in physics with the Hubble Telescope turning 20 years old!

I know this isn’t exactly related to particle physics, but I find it simply amazing that an experiment that was “doomed” from the beginning with problems and failures has turned out to be such a overwhelming success and has lasted 20 years. Hubble’s scientific contributions are numerous and outstanding (see more about them here) including being able to distinguish elements present in the atmospheres of planets orbiting other stars. That is to say something scientists weren’t even sure existed 30 years ago (Exo-planets) we now know their chemical makeup (and it is the same stuff we have here on earth)!!!

hubble-telescopeBut Hubble has done more than just raised our scientific knowledge of the world. With its amazing images and profound ability to see deep into space Hubble has raised our collective conscience about the universe we live in and the science that brings us to it. We’ve all seen the awe-inspiring images of stars being born, giant clouds that stretch 100’s of light-years, and we have marveled at the science that created such beauty.

With the last repairs (that are to be the last servicing Hubble will receive) the space telescope is ready to run another 5 years and continue to bring us some of the most deep reaching and astounding images ever seen by humans.

So while I celebrate and congratulate the world of astronomy for inspiring a generation of would-be scientists to pursue the deep truths of the world, I would also set out a challenge to myself and my colleagues around the world. Let us find our Hubble, and raise the worlds awareness of the beauty and description of particle physics. Let us bring outstanding images that “tell the whole story” and set a new generation of people down the path of science and enlightenment.




Live LHC Beam Plans

Friday, April 23rd, 2010

Click for live LHC Beam Plans.

The LHC team have thankfully created a live status page to show all beam plans for the near future.  This is helpful to many of us who want to have some idea of what to expect when we’re on shift “babysitting” our detectors.

You can see at present the main goal is to “complete squeeze to 2m.”  This is referring to a measurement (sometimes just called “beta”) that is related of the width of the LHC beam.  (It does not mean the beam is 2 meters wide!)  Basically, the smaller that number, the narrow the proton beams are at their collision point.  This also results in more proton collisions, and more data for the detectors.

I believe the original LHC design was to achieve a squeeze to 0.5 m, so they are well on their way.



ALICE’s second paper!

Tuesday, April 20th, 2010

ALICE’s second paper has been submitted!  If you’ve been following carefully, you’ll have heard that it’ll take at least a couple of years to get enough statistics to see the Higgs (if it’s there) – but we don’t have to wait that long for other results.  This paper presents a measurement of the number of charged particles produced in proton-proton collisions at center of mass energies of 0.9 TeV and 2.36 TeV.  (CMS actually published their paper on the same subject first.)  Proton-proton collisions are actually pretty complicated and we still don’t understand everything about them.  Protons are made up of quarks and gluons, so when we slam them together we get a combination of quark-quark, quark-gluon, and gluon-gluon interactions.  We can describe the products of these interactions pretty well when both particles hit each other hard, but not if they barely interact.  They can also interact multiple times.  So proton-proton collisions are really difficult to model.  Theorists have come up with models that try to describe proton-proton collisions, but these models still need improvement.  Counting the number of particles produced in a collision is a relatively straight forward measurement.  (Not to say it’s easy – there’s still a lot of work that has to be done for this, but there’s even more work needed for other measurements.)  And this measurement gives us data we can compare to models.   The models seem to be underestimating the number of particles produced – only by a few percent, but they’re still not quite right.

ALICE and CMS’s measurements also agree.  This is very important.  These measurements are very complicated and many things can go wrong.  Since two experiments did the same measurement with very different detectors, different methods, different code, different people, etc. and still agree, this gives us greater confidence in the measurement.  This is one of the reasons for having multiple collaborations doing the same measurement.

You won’t read about these results in the newspapers because there have been no dramatic paradigm shifts in our understanding of proton-proton collisions, but these are very important basic measurements that improve our understanding incrementally and they have to be done before we can hope to discover new physics.

Update April 21 – the third ALICE paper, on the 7 TeV data, was submitted today!


Computing and Volcanos

Monday, April 19th, 2010

The past few weeks have been really busy. Of course the flood of data and the prospects of an analysis are driving the work, so it’s a welcome change. I’ll also be heading over to CERN in about a week to go on shift. I’ll be there for about a month, and am excited to get back to where the action is. This is however, if planet earth doesn’t have other plans for me. I have to say, I’ve had flights get cancelled before, but I can honestly say, never because of a volcano eruption.

Geneva's on top :).. notice Reykjavík isn't cancelled

My sympathies are with the people who are stranded, I know I’ve received about 10 emails saying people had to phone into meetings because they couldn’t get back to CERN. I’ll have to keep everyone update on my status… it looks like most airports should be open on Tuesday (my flight leaves Sunday).

Until then, analyses await… and with those analyses come one word: Grid.
The Grid is the mechanism by which we do large scale computing. Instead of running an analysis on a local computer (which has limited capabilities), I send a “job” to a set of computers which copies the conditions of my work area, and breaks the large job into a bunch of smaller ones so it can run over the data set faster. I say this in confidence… I’ve now sent 3000 jobs to the grid. I <3 analyzing 🙂 I usually send my jobs to BNL (Brookhaven National Lab) and I’ve never had  a problem… but now I’m getting  the following message:

WARNING : Your job might be delayed since BNL is busy. There are 10398 jobs already queued by other users while 292 jobs are running. Please consider replicating the input dataset to a free site or avoiding the –site/–cloud option so that the brokerage will find a free site

I guess lots of people are running over data. Although it’s annoying to have to wait, it makes me happy to think about all the activity that’s been happening.