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Archive for August, 2009

Sziget

Monday, August 24th, 2009

My earliest memory that has something to do with politics is the Fall of the Berlin Wall in 1989. I was five at the time, and I remember that my parents sat in front of the television stating over and over that this was a day of international importance. And that my future would be so much different from theirs at my age. My dad traveled to Berlin not to long after that and brought us a piece of the Wall in a plastic box. It was pink on one side. Maybe, we all should throw a German party this year at November 17, to celebrate twenty years after the Fall.

Het Oostblok (The Eastern Bloc), as the countries behind the Wall are still referred to, still give me a feeling of far-awayness. I expected the Danube to be very grand, cold and dirty. I expected Budapest to be very crowded, grey and harsh. A city in Hungary is probably very hot in summer and extremely cold in winter. Arriving to Budapest I found out that the city is indeed grey, but almost empty, and spacious because of the Danube, which is (luckily) broad, cold and brownish. The city is beautiful in a faded glory kind of way.

Just north of town one of the Danube’s Szigets (Islands) in turned into a festival arena once a year. We spend a week surrounded by (Balkan) music, beer and people from all over Europe. The nice thing about a festival is that you have the change to go and listen to music you usually would not hear. The concert of The Prodigy was by far the most forceful. One of my friends mistook my face of wild panic for crude pleasure, just before I ran for coverage. It made me think about that time when my father mistook my expression of utmost incomprehension for surprise when we were listening to his African drum beats and he told me that this was improvised. I had not guessed differently. Seen from a large dustbin, the Prodigy concert was good, by the way.

Back at the Nikhef, I have to say I enjoyed the combination of Eastern Europe obscurity and music. I will defenetely be back.

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So as Frank already posted we had a nice dinner as an early finale to the Lepton Photon conference. Good food, conversation and an almost constant flow of wine made for an enjoyable evening. As did the impeccable organization of our Hamburg hosts. The conference has been expertly run and everything has been planned and thought out down to the finest of details.

Post conference dinner where abstract lighting is crucial to mask reality.

post conference dinner where abstract lighting is crucial to mask reality.

I have been lucky enough to use this week to get back into work after my holidays and although I’ve been at all of the conference talks and absorbed some interesting and useful physics I don’t really feel like it’s been hard work at all. Of course I’ve had the privilege of meeting current (Ingrid and Frank), and some recently retired (Robert and Tony) Quantum Diaries members.

It’s funny to ‘know’ someone by sight without ever having met and to have something in common prior to having spoken a word. We’ll have to see how many future Quantum Diaries conference photos we can make!

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The Morning After

Friday, August 21st, 2009
The conference attendees heading into the sunset on a Mississippi steam boat (well, a fake one obvously, it is Hamburg after all).

The conference attendees heading into the sunset on a Mississippi steam boat (well, a fake one obvously, it is Hamburg after all).

The Big Bang at Lepton-Photon did happen after all… Although not in the form of truly spectacular results, but in the form of the conference dinner. For most conferences, the dinner is an important event: For the attendees, it is a perfect opportunity to hang out together, chat about projects, or just to have fun. And for the organizers, the dinner is a way of adding a little extra note to the conference… And it was really well done this time!

We headed out to a former warehouse in the Hamburg harbor by ship, a fake Mississippi steam boat (well, the wheel at the back actually did work, and was the thing driving the boat), and then got a fantastic dinner. There was no shortage of wine either, which, at least at my table, meant a really fun evening.

And: We also managed to take a QD bloggers group picture: Ingrid, Paul and myself!

Paul, Ingrid and yours truly, after a healthy dose of wine...

Paul, Ingrid and yours truly, after a healthy dose of wine...

Getting up early in the morning (the session starts at 8:30, which is really brutal), was painful, but I dragged myself out of bed for the first talk on top physics… Another topic I like, also because of the lectures I’m giving. And the talks was really worth it. And of course life always looks better after a shower and coffee.

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I am currently very busy preparing to give a talk at a very prestigious and exciting conference later this year. I can’t say much until after the event but it is a very important step in my career, so I won’t have much blogging time. However, I can pop little snippets on here and there. It was my birthday recently and my boyfriend bought me a dvd boxset of Jonathan Creek. I haven’t had much chance to watch it (for reasons mentioned) but I watched it when I was younger and it was nice to be reminded of what I like about it.

Jonathan Creek is a magician’s technical advisor and assistant. He befriends a pushy journalist and they go solving mysterious murder cases and other crimes together. It sounds a little cheesy, but in reality, the mysteries they solve are always baffling, and they are always resolved through careful, logical reasoning. For example, *WARNING, A SPOILER MAY FOLLOW*, an old building developed a terrifying myth because a handful of men had mysteriously died there of heart failure, by the window, after taking their shoes off getting ready for bed. Witnesses for each death who were standing outside claimed to have seen them come to the window, see something horrifying and drop dead. Through careful, logical and methodical investigation, and avoiding completely the trap of “it must be a supernatural, haunted thing”, Mr Creek discovers what caused their deaths was a set of small electrified pins hidden in the floorboards in holes disguised as woodworm (he first noticed the woodworm was not on the skirting boards but appeared only on the floor) *SPOILER OVER*.

So why am I telling you about Jonathan Creek? After watching a few episodes again, I realised something. If Jonathan Creek had tried to be a physicist he would have been brilliant at it. Investigating something strange by considering the possible logical explanations, searching for little clues, things which look unusual, even if you can’t explain the significance of them right away… can lead you quite nicely to a discovery. This goes not only for general physics analysis problem solving but for computer program debugging too! 🙂

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Ode to the AC

Thursday, August 20th, 2009

I’ve never fully appreciated air conditioning until I spent a summer in Europe. Summer of 2004 – August – Rome. I understood the true feeling behind the phrase “I’m mellllllllting”.  Although it’s not quite as hot as that, France has it’s moments. My car doesn’t have an AC, the buses don’t have it, the building I work in doesn’t have it, and my apartment doesn’t have it and it’s 97 deg F. So I decided to give my brain a rest, and went browsing through one of my favorite web comics. I remember one particular that I’d like to share:

xkcd... it tells us about life

xkcd... it tells us about life

This hits close to home since as a HEP (High Energy Physics) grad student, I do most of my work at the computer.  While waiting for code to compile, and in between reading papers and sword fighting. I’ve come up with my own way to pass the time: rewriting Shakespeare. I’ll share.

Inspired by Hamlet:

To fit, or not to fit: that is the question:
Whether ’tis nobler in the mind to suffer
The slings and arrows of outrageous divergences,
Or to take arms against a sea of parameters,
And by opposing converge them? To analyze: to plot;
No more; and by a plot to say we end
The heart-ache and the thousand natural shocks
That work is heir to, ’tis a consummation
Devoutly to be wish’d. To analyze, to plot;
To plot: perchance to present: ay, there’s the rub;
For in that analysis of plots what presentation may come

(you can guess what I was doing when inspiration struck)

Inspired by Macbeth:

To-morrow, and to-morrow, and to-morrow,
Creeps by and so we wait from day to day,
Until the first byte of recorded data;
And all our software rels. have lighted grads
The way to endless updates. Out, out, broken splice!
Work’s but a hiding particle, a deviation
That appears to be within acceptances
And then is understood no more. It is a tale
Told by a student, desperate to graduate
Signifying discovery.

Dorky, yes. Sad, maybe – but I’m a physicist in training so cut some slack. Now back to work.

-Regina

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Waiting for the Big Bang

Thursday, August 20th, 2009

Now we are well into the Lepton Photon conference, mentioned several times already here… And it is a quite interesting conference, giving a very broad overview over what is going on in Particle Physics, Astroparticle Physics and other related fields. However, for such a big meeting, there is surprisingly little heated debate. I have the feeling that that, and also the wide range of topics being discussed here, is a symptom of the current state of high energy physics: We are all waiting for the “Big Bang”: Exciting, maybe even totally unexpected, new results!

Of course, there are new results that are discussed here at the conference: New limits on the Higgs, and improved measurements on all sorts of processes from the Tevatron, new results from Ultra-high energy cosmic rays (a topic I got quite interested in because of a lecture I’m giving at TU Munich)… But those latter ones are at least partially a disappointment: The correlation of ultra-high energy particles from outer space, single protons or iron nuclei with the kinetic energy of a well-pitched base ball, with known potential astrophysical sources such as active galaxies, got a lot weaker with more data… So, no “particle astronomy” yet, but of course that might well be the fault of the catalogs of active galaxies that are used, which are far from complete… All in all a lot of interesting stuff to listen to and to discuss about, but nothing fundamentally new that totally blows you away.

We all, well, I for one definitely, are longing for the first results from LHC, and hopefully for a few surprises! That would make for a some very hot meetings next year…

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Voodoo Lounge

Thursday, August 20th, 2009

Last week I was working together with “my” summer students Jeanette and Silvia at the DESY test beam. We looked into the electronic noise of the “old” ZEUS strip telescope.

The ZEUS MVD strip telescope at DESY test beam

The ZEUS MVD strip telescope at DESY test beam

This is a relative old telescope build something like 10 years ago to characterize the ZEUS MVD silicon strip modules (MVD stands for Micro Vertex Detector and was an upgrade silicon strip detector of the ZEUS tracking system). Since then many different groups used the telescope as a tool to define the tracks of the test beam particles at the DESY test beam. But as you can imagine, the system is getting old after 10 years of operation. And recently the performance is not as it used to be. Mainly the electronic noise increased quite a bit. Electronic noise is a random signal characteristic of all electronic circuits and a constant offset underlying the real signal. Therefore the signal to noise ratio is a crucial performance parameter of our detectors. If the noise increases too much, the signal disappears in this carpet of noise and we have a hard time to track the particles. There are of course books on how to design and set up the readout system to reduce the noise to a minimum, but somehow noise is  most of the time  tricky. This I experienced many times before.

When Jeanette, Silvia and I were investigating the noise of the telescope last week we checked if the grounding was done according to the book (no loops, connections from on ground to all component etc.). Everything seemed to be ok, but somehow we still had a high noise level. So we started to change the system, just to see what happens. Whenever we expected the system to improve, it got worse and vise versa. In the end we found a configuration with really good noise behavior, but we absolutely did not understand why it improved.

So this was a really nice demonstration for the summer students, that an exact science like physics can also be something not at all exact, but rather like voodoo…

Silvia and Jeanette taking data

Silvia and Jeanette taking data

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Life as a shifter…..

Thursday, August 20th, 2009

Life as a shifter…..

As part of the contribution with CMS, every University should do a number shifts when the experiment is taking data. For those no familiar with this, you might be wondering, how it is possible that we are taking data if the LHC haven’t started yet? Well, we are being bombarded by millions of cosmic rays every day, and those are the source that we use to understand our detectors and  find problems with the hardware and software. I have being taking some shifts for offline Data Quality Monitoring (DQM) for the tracker system and online shifts for the pixel detector.

For DQM shifts, you should go over the data that have been taken and check some specific plots in order to see the performance and/or errors generated during that particular run. It is cool to go over the different plots and see the efficiency  of each component of the tracker system (silicon strip tracker and the pixel detector).  It is important to see and try to understand the different errors that were generated during the run and report them (if they haven’t been reported before) to the shift leader. The shift leader is the person that usually saves you when you have no idea of what to do. Thanks to all of them!

Pixel online is super nice, but carries a lot more responsibility! Basically, you are baby-sitting a several million dollars detector and believe me, you don’t want to screw things up for not being aware of what you are doing…..During the shift, you should keep track of the temperature, humidity, voltages and currents of the detector (in this case the pixel detector)….Other important issue are the Front End Drivers (FEDs). These are electronic cards used for the detector control and readout. Personally, I believe that the FEDs are one of  the most complicated and important devices in the experiment and if something goes wrong with them, you better pay attention to it!

In general you never know how your shift is going to be. It could be smooth and you almost don’t have to do much during 8 hours, or it could be really busy and stressful, but in the end fun (sometimes). Usually, I get shifts where weird things happen (I think that the detector is a live and it doesn’t like me)…….

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Another brick in the wall!

Wednesday, August 19th, 2009

I thought I’d give you a sense of what it takes to put together a detector like ATLAS, e.g., how much time, how many people, etc. For an overview of the ATLAS detector, please look at the ATLAS webpage and Monica’s post. Since ATLAS is huge, I will focus on just one sub-system, the Barrel Transition Radiation Tracker (TRT), which was built in the US. Its main purpose is to provide hits so that we can map the trajectory of charged particles and improve the measurement of their momentum (see Seth’s post on tracking). It can also discriminate between electrons and pions.

Figure 1: End view of the barrel TRT

Figure 1: End view of the barrel TRT

You can see the barrel TRT in Fig. 1 (this is an end view where you can see the electronics and cables); more information is ATLAS website. This detector is divided into 96 modules and extends from about 50 cm to 108 cm in radius, contains about 52,000 individual wires (about 2 m long) each of which is strung inside a specially built plastic straw. As the name suggests, the barrel TRT is in the central part of ATLAS. Two other parts of the inner detector, the Pixel and the Silicon tracker, reside inside the barrel TRT 1 (that unit was being inserted into the assembly at the time this picture was taken – you can see it at the other end of the barrel).

To set the scale, the barrel TRT occupies about the half the volume of the inner detector in the barrel, which ends at a radius of about 1 m. The calorimeters, solenoid magnet and cryostat come after and go out to about 5 m in radius, and the muon system goes out to about 10 m in radius. The barrel TRT probably represents a few percent of the total cost of building the ATLAS detector, and is arguably the most sophisticated of a class of detectors called “drift chambers”; one of its selling points was that it was a low-cost way of tracking charged particles. It also has fewer electronic channels to read out (each wire is read out at both ends); in comparison, the Pixel and the Silicon tracker detectors have about 80 million electronic channels to read out.

I spoke with my colleague at Indiana University, Harold Ogren, who was one of the lead physicists on this project, as well as being the manager of the construction effort in the US. Harold and one of his colleagues originally built a similar straw tube device for an experiment that ran at the Stanford Linear Accelerator in the 1980’s. When the Superconducting Super Collider was proposed in the US, a straw tube tracker design was accepted for one of the two main experiments; when it was cancelled in 1993, he and his colleagues moved onto ATLAS, where they joined forces with the groups already working on a straw tube design.

They started building a prototype for ATLAS around 1994. Some of the groups who were on SSC joined this effort, and they had a working chamber by about 1999 that was then put in a test beam at CERN. Actual construction of the 96 modules began after the successful beam test, and it took them another 3 years to finish; each of the 52,000 wires had to be individually strung. The construction effort involved about 6-7 physicists and about 40 technicians, engineers, graduate students from Indiana, Duke and Hampton Universities and the University of Pennsylvania The electronics to read out the detector was also designed by them.

Since it was a modular design, they could ship individual modules to CERN as they were being completed, where they were put through extensive tests, e.g., each wire was scanned along every inch of its length with X-rays to check for uniformity of performance. A few wires were bad and had to be disconnected; since the bad wires are randomly distributed they don’t affect performance. These tests took another 2-3 years. All in all, the detector was ready sometime around 2006. The picture you saw above was when it was being readied to be installed in ATLAS.

Fig 2: Cosmic shower in the TRT

Fig 2: Cosmic shower in the TRT

The barrel TRT has been running successfully and collecting cosmic ray data. In Fig 2, most likely a cosmic shower hit the TRT, the kind described in Regina’s post. You are looking at an end view of the hit wires. Each blue dot represents a single wire being hit; we can locate the position of a track within a straw with an accuracy of 0.15 mm (human hair has a thickness of about 0.1 mm). You can see curved tracks; they are curving because the magnetic field was on. You will also see that one sector, at about 8 o’clock, was (temporarily) turned off. Isolated hits are due to electronic noise; operating parameters are set so that these wires register the presence of nearby charged particles with a very high efficiency, but this also leads to 1-2% of the wires “firing” randomly; our reconstruction algorithms can easily ignore them. The tracks that you see here are then matched to hits in the Pixel and Silicon Tracker detectors to get a complete trajectory.

Now for real data!

— Vivek Jain, Indiana University



1 There is also the endcap TRT, which is on the two ends of the ATLAS detector, but that was built by other groups; it uses the same design as the one in the barrel.

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Using Facebook for Physics

Wednesday, August 19th, 2009

Often in my day-to-day work I encounter some little problem in software or mathematics that I figure somebody ought to know the answer to.  In my years as a graduate student, I’ve learned that the quickest way to solve these problems, if a cursory search of the internet and a few standard references doesn’t help, is to actually go around the office and ask the people I know who work around me.  Sometimes they don’t happen to know either — but I can’t shake the nagging feeling that somebody I know knows how to solve the problem.  My solution to this, on a few recent occasions, has been to turn to Facebook.

Thus last Thursday afternoon, my Facebook status was:

Seth Zenz needs a statistician. Or anyone else who knows how to find the error on a correlation coefficient.

Within a couple hours, two of my friends, one a physicist and one a friend from college, had replied with the correct answer, which turned out to be explained on Wikipedia — which pointed, in turn, back to the original statistics paper from 1921 that answered the question.   So Facebook is good for more than just keeping up with my friends; it also expands the size of “the office” I can go around to ask questions in!

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