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Frank Simon | MPI for Physics | Germany

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Getting ready for Beam

Wednesday, September 1st, 2010
Tungsten absorber stack, 30 neat layers for the calorimeter. Our special setup will go all the way in the back.

Tungsten absorber stack, 30 neat layers for the calorimeter. Our special setup will go all the way in the back.

The excitement is growing: After I saw the first pieces for the absorber structure for our test beam in the fall during my last trip to CERN, photographic proof is now circulating that the mechanics are completely assembled: Several tons of Tungsten, all arranged in 30 vertical plates. Behind it all will go a special setup we are developing in Munich to make a first measurement of the time structure of the hadronic showers in this new calorimeter. This is one of the key open question for the hadron calorimeter at CLIC: Since many unwanted reactions will take place due to the extremely high energy of the collider, it is important to be able to determine exactly at which time a certain reaction took place. And for this it is important to know how long the detector itself takes to react to the passage of the particles.

Signs of life: First test pulses on the screen, with my student Lars pointig at it with some excitement.

Signs of life: First test pulses on the screen, with my student Lars pointig at it with some excitement.

To study this, we prepared 15 scintillator tiles that we read out with special oscilloscopes with a time resolution of better than 1 nanosecond. Now things are coming together: The scintillator tiles are wrapped in reflective foil, the support frame that will go into the calorimeter at CERN is prepared, and the lights are on on our data acquisition. Two of my PhD students are now very busy to write the code to control all this and read out the data. Just a few hours ago, we saw first signs of life: Test pulses recorded all the way through our electronics chain!

On Sunday, all of this will go to CERN, for a first integration test and some first exposure to muons from the accelerator. That is the first real stress test, and so far things are looking good. Exciting times ahead, and we are looking forward to successful data taking this fall…

Lights on: Oscilloscope modules that plug into our data acquisition PC - waiting for data!

Lights on: Oscilloscope modules that plug into our data acquisition PC - waiting for data!

A row of scintillator tiles for timing measurements - Where our data comes from.

A row of scintillator tiles for timing measurements - Where our data comes from.

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Hamburg or Munich?

Thursday, August 19th, 2010
Lighthouse near Munich... what's wrong with that picture?

Lighthouse near Munich... what's wrong with that picture?

Did I get on the wrong flight? Not really possible nowadays, I know… That’s why they don’t do the “destination check” announcement anymore. But, if this is Munich, what is a Lighthouse doing next to my place?

Apparently, a Hamburg Fishmarket will be here for the next couple of days… Lets see, it might be more what a Bavarian would expect a fishmarket to be like instead of authentic Hamburg style… That reminds me, this year I have not been to Hamburg as often as in previous years… It seems to be more of a Geneva year.

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Marine Life in Hamburg

Wednesday, July 7th, 2010

Since late Sunday night, I’m at DESY in Hamburg for a series of meetings, first on the CALICE Analog HCAL, then on plans for a new EU Project, and finally for the ILD workshop. Lots of things to discuss, ranging from test beam plans, financial matters, detector engineering to physics simulations and general physics issues at linear colliders. But topics connected to marine life are coming up surprisingly frequently. The most pressing one: Could Paul be right? I surely hope not, but we’ll know in a few hours. Meanwhile, will they be serving octopus at our meeting dinner tonight? I’ll go find out right now.

Baby seal on the beach in Hamburg right at the Strandperle bar. Searching for its mother, but maybe also a secret interest in calorimetry...

Baby seal on the beach in Hamburg right at the Strandperle bar. Searching for its mother, but maybe there is also a secret interest in calorimetry...

On Monday, we had our traditional CALICE outing, due to unstable weather we first went to a Bistro, and only later to the beach for beers. Same place as last year, but with a significantly reduced crowd, and no intentions of detector building. There we were greeted by a very unusual sight: A baby seal was lying on the beach, right at the bar. Apparently the poor guy had lost its mother, swam up all the way to Hamburg, and then crawled exhausted onto the beach. The baby was rescued and brought to a seal nursing station, and I hope it is on the way to growing big and strong to move back to the ocean in a while.

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Heavy Lifting

Thursday, July 1st, 2010

Busy times, that’s why I’ve been really slow on the blog lately. Right now, there is a brief downtime, while I’m waiting for a flight from Geneva to Munich, and it’s not worth starting real work, boarding is (hopefully) just 20 Minutes away. I spent the whole day today at CERN, in various meetings. The main purpose for this rather short trip (I arrived here last night) was a meeting to discuss plans for a beam test this fall. We will have two weeks of beam time at the PS (Proton Synchrotron) at CERN for a first test of a hadron calorimeter using Tungsten absorbers. The CALICE HCAL physics prototype I’ve been writing about repeatedly uses steel, so this will be new and exciting. But why use tungsten at all?

A Tungsten plate for our test beam in the fall: Heavy lifting!

A Tungsten plate for our test beam in the fall: Heavy lifting!

This study is motivated by plans for a Linear Collider based on the CLIC technology developed at CERN (I briefly wrote about this a while ago): This machine is aiming for an energy of 3 TeV, quite a bit higher than the ILC. This requires a “deeper” calorimeter, meaning more absorber material to contain the energy of the particles. This is where Tungsten comes in: It is one of the densest materials you can get. The mix we are using has a density of almost 18 g/ccm, that is more than 2 times the density of steel (a bit less than 8 g/ccm). That way, we can built a “thinner” detector, which is crucial to be able to fit everything inside a magnet. At CLIC, the time structure of particle showers is a big issue, and I’m planning a measurement of some aspects of this topic with a special setup to go along with our new Tungsten calorimeter. This calorimeter will use the same active layers, our highly granular scintillator planes, that were also used in previous tests. A team from my group will then add some additional specialized equipment behind the whole setup. Today, we discussed the plans for these measurements, and I also had the opportunity of looking at some of the first Tungsten plates that arrived at CERN. I can hold them up in one hand, but once you grab a plate, you are shocked at the unexpected weight: It is truly heavy lifting!

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Hunting Background

Sunday, May 30th, 2010

Now that I am almost back home from my short trip to KEK, sitting on LH715 back to Munich I finally have a few minutes to look back at what has been going on. The primary goal of my trip was to participate in an experiment to study background at BELLE. Here is what this is about:

Two photon QED process, producing low-energy electrons and positrons that will hit our detector.

Two photon QED process, producing low-energy electrons and positrons that will hit our detector.

When we make measurements in physics, we are always interested in a signal. Background is what makes our life harder: Things that do not belong into the signal category, but still show up in your measurement. In the case of the new silicon pixel detector we are developing for BELLE-II, background are hits that we see in the detector, which come from particles that do not belong to an interesting physics event. Actually, most of the hits will be in that category.

Now, this is not really a problem as long as you can associate the right hits to particle tracks of interest, which works since we have detectors that see much less background than ours will, which then will help us decide which hits are good and which ones aren’t. However, this scheme works only as long as there is not too much of the background. And that is of course the key issue here: How much background do have to expect? After all, the accelerator for the BELLE-II experiment has not yet been built, so we can not measure it. We have to extrapolate from what we know from the present KEK-B collider, where the BELLE experiment operates. This is a complicated business: The new collider will have a factor 40 higher luminosity (interaction rates), so we have to extrapolate quite a bit. There are several types of background, for example beam-gas interactions (particles coming from collisions of beam particles with gas atoms in the beam pipe, due to the non-perfect vacuum), synchrotron radiation and Touschek Background (coming from electrons which stray of their nominal path in the collider due to intra-beam scattering). Those two strongly depend on the accelerator parameters, such as the beam currents, focusing, and so on. Usually these types of background are the dominant contributions. And by clever designs of the machine and its operational parameters, they can be reduced to tolerable levels. And most importantly: They don’t usually scale with the luminosity of the machine.

Members from the Munich team, including my grad student Andreas, looking at first events of our background run in the BELLE control room.

Members from the Munich team, including my grad student Andreas, looking at first events of our background run in the BELLE control room.

But then there are other backgrounds which come from reactions of the colliding particles. Those are irreducible since they scale with luminosity, just as the signal we are interested in. And something that is totally irrelevant in the present BELLE detector might become a show stopper, or a serious headache in BELLE-II, once the luminosity (and the rate of these backgrounds) has increased by a factor of 40. The biggie here might be two photon QED background, which produces low energy electrons at high rate. In principle this can be calculated, but it is complicated. Predictions varying by a factor of 10 exist for BELLE-II. The high end of the predictions are a problem, while the low end are no concern whatsoever. So our goal is to measure the amount of QED background in BELLE, to figure out which of the predictions is right. The tough thing is that the QED background is swamped by beam gas and other things, so we have to work hard to tease it out.

Accelerator experts in the KEK-B control room, working their magic.

Accelerator experts in the KEK-B control room, working their magic.

What we did on Friday, in one monster effort lasting from 8 am in the morning to 1 am Saturday morning, was to vary the luminosity in BELLE in different ways which might affect the QED background and other backgrounds in a different fashion, allowing us to extract the contributions of the different things, or at least give us an upper limit. This required a lot from the machine operators, who had to operate the collider outside of its usual parameter range. And the experts really delivered in a way that still amazes me. They really understand their collider in all detail. For us, it was an exiting study, and one of the last chances to participate in the running of the BELLE experiment before it will be shut down and dismantled in the summer to make space for BELLE-II. Of course it was also a very tough day: at some point after 8 pm, without any breaks, all that kept me going was hot espresso out of a can… The wonders of Japanese vending machines!

Staying focused after 14 hours of work: Fast offline data analysis, fueld by espresse in a can.

Staying focused after 14 hours of work: Fast offline data analysis, fueled by espresso in a can.

Now, the analysis is just starting, we got some hints already during data taking that the worst-case scenario very likely is not the right one, and I put in a few hours on the laptop on the plane. But hard numbers will be hard work, and will take quite a while… As usual in high energy physics!

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Equipment Failure

Wednesday, May 26th, 2010

Sometimes travel can be a curse. After barely 9 days at home in Munich, I’m again back in Asia, Japan this time. And getting here proved to be more annoying than usual, due to technical problems with the aircraft, something that would be called equipment failure in industry terms, I guess. So instead of getting on board, settling in and taking off, by the time we were already supposed to be in Russian airspace we were still sitting at the gate, with technicians all over the plane trying to fix a broken fuel computer. In the end, they gave up and we had to wait for another aircraft. Probably a smart choice, I can imagine better things than running out of kerosene 36 000 feet above eastern Sibera. But annoying none the less: Adding 3 hours at the gate to a flight that already takes more then 11 hours is not something you usually wish for. In the end, things turned out not so bad due to favorable winds, so only 2 hours later than expected I made it finally to my hotel close to KEK in Tsukuba, Japan, a bit more than 21 hours after leaving my office in Munich.

So, what is going on here at KEK? Most importantly, I’m here for a special run of the KEKB accelerator and the BELLE experiment, where we want to learn more about the background (meaning unwanted particles not related to interesting physics) we have to expect for the new pixel detector we are constructing for the BELLE-II experiment. The current word is that we’ll be on tomorrow, with 16 hours scheduled for us. Depending how things go, we might get a bit more time, even. Since this study requires extremely close collaboration with the accelerator operators, we’ll have a preparatory meeting with them in a bit more than an hour, to make plans for tomorrow.

In addition to the experiment, I’m also here to give a seminar at KEK this afternoon, about Particle Flow and Imaging Calorimeters, the jet reconstruction and detector technologies we are developing for a future Linear Collider. So, for once, this trip really covers my two main areas of research, all withing the space of a few hours.

It’s going to be a few intense days, and I hope I’ll have some interesting impressions from our experiment to talk about soon.

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CALICE at the Wall

Thursday, May 13th, 2010
A small subset of CALICE on the Great Wall of China at Badaling.

A small subset of CALICE on the Great Wall of China at Badaling.

After a few weeks break from QuantumDiaries, I’m back again, and again on travel: The CALOR2010 conference in Beijing, China. At this conference, all aspects of calorimetry in high energy physics are discussed in great detail. I already got a few useful ideas for new things to try out, so certainly a worthwhile event. In addition, this time my trip is “family neutral”, since my wife is with me to visit a mutual friend and to do some sightseeing. The consequence: No complaints from home, no minus points for being away so much this time :-).

While I’m spending long days in the auditorium listening to talks and participating in discussions, it is not all work here in Beijing: Yesterday afternoon we had the opportunity to visit the Great Wall at Badaling. We even took a group photo of a small subset of the CALICE collaboration (with a clear bias towards hadron calorimetry). Not such a big showing as for our beach event, but way more work: Some of us had quite a climb up the wall behind them at that point (others took the easy way by cable car).

The Wall is by far not the only thing to discover in Beijing, even given the very limited amount of free time. Every dinner is a new adventure, and one night we got to witness noodle making to make an Italian cry. Erika (front center in the Wall picture) certainly was deeply impressed…

A noodle making demonstration in a fancy restaurant in the center of Beijing. Even Italians were impressed...

A noodle making demonstration in a fancy restaurant in the center of Beijing. Even Italians were impressed...

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Matter in the Universe and a Mechanical Masterpiece

Saturday, April 3rd, 2010
The mechanical model of the Belle-II pixel vertex detector, PXD: A bit larger than a soda can. The silicon part (the black modules in the center) would fit in a Red Bull can.

The mechanical model of the Belle-II pixel vertex detector, PXD: A bit larger than a soda can. The silicon part (the black modules in the center) would fit in a Red Bull can.

Another meeting, this time the Belle-II Collaboration meeting at KEK, near Tokyo in Japan. Right now I’m on the way back, just as in my very first post to this blog, on LH 715 bound for Munich from Tokyo’s Narita Airport.

For three days, we were discussion the open issues, and the solutions, for the new detector that is scheduled to start taking data in 2014, with an impressive increase in data rate over the present Belle experiment. Just as the Belle experiment, Belle-II will explore, among other things, a phenomenon called CP violation. At first sight, this seems horrifyingly abstract and complicated (the way the data analysis is performed certainly is), but the subject of study as at the very heart of our existence: CP violation is the mechanism that leads to unequal behavior of matter and antimatter, and is necessary to explain why the universe today is only made out of matter. If matter would not have been preferred over antimatter in the early phases of the universe, it would now be completely empty, just filled with light. So, understanding CP violation is a key goal of particle physics.

Belle-II members crowding around the model of the PXD.

Belle-II members crowding around the model of the PXD.

And here is where Belle-II comes in: The amount of CP-violation that we have observed so far with the existing experiments is by far not enough to explain the amount of matter in the universe today. So we know that there have to be more sources of CP violation than those we have studied so far. These could show up at higher mass scales which we can not study today, but might be able to get at with the LHC. Precision measurements at Belle-II will provide another way. By comparing extremely precise measurements to theoretical expectations, we might be able to detect inconsistencies, which could point to new effects, potentially well beyond what LHC can observe directly.

Precision measurements also need precision instruments. And one such piece is the new pixel vertex detector for Belle-II, which I’ve written about before. The design of this device is constantly progressing, and at this meeting, we had a real highlight: A first mechanical mock-up, full size, with real (however, inactive and unprocessed) silicon modules. And if you look very close, you can see that some of these silicon modules have been thinned down to a thickness of 50 microns, just a bit more than a human hair, with just a small rim of thicker silicon to provide stability. This is done to reduce the interference of our measurement device on the particles we want to study. Part of the mechanical support, which will later provide the precision mounting and the high power cooling, has been fabricated with rapid prototyping, a 3D printing technique. Now still out of plastic, the final product will be made from copper or stainless steel. The nice device certainly drew a lot of attention, and gave everyone a sense of how tine such a masterpiece is: Years of work by many people in a lot of institutes all over Europe, and substantial amounts of funding go into a device that is not much larger than a soda can. But it will be a digital camera, with 8 million pixels, able to take 50 000 pictures a second, providing extremely detailed pictures of the particle interactions going on in Belle-II. And with the first mechanical prototype, a true masterpiece from our engineer, this project starts feeling even more real.

A close look: Mechanical silicon dummies, including a few thinned down to a thickness of 50 microns.

A close look: Mechanical silicon dummies, including a few thinned down to a thickness of 50 microns.

With this last stop, my world tour is coming to an end, for now.

… “In preparation for our landing, please switch off all electronic devices, adjust the backrest of your seat to its full upright position and stow away your tray tables” … Finally!

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Changing Gears

Tuesday, March 30th, 2010

A light earthquake (magnitude 4.6), which woke me up a bit after 6 am local this morning, helped to again focus my sense of location: I’m in Japan, at KEK. Already last night, as I was gliding into Narita Airport for an unusually smooth approach with a view of Mt Fuji in the dusk, I was slowly beginning to change gears, physics wise. From high energy colliders at the Terascale I’m switching to low energy, extremely high rate experiments for the next few days: Precision measurements at Super Flavor Factories.

Combining results from different experiments, at different energies and with different particles, has been a very successful strategy in particle physics. Measurements at high energy hadron colliders, the measurements at LEP and the precision study of the flavor sector at the B factories have given us the understanding of the Standard Model that we currently have. And we have every reason to expect that this strategy will also be the best path to fully understand the physics beyond the Standard Model. So while we are all watching the LHC with big excitement and anticipation, it is important to think ahead and work towards a next generation of high energy lepton colliders as well as towards new experiments in flavor physics with unprecedented luminosity. So here I am, at KEK at the Belle-II collaboration meeting. Over the next three days, we’ll discuss the physics of this new experiment, and focus on the technological challenges to be overcome in the next few years to prepare for a start of data taking in 2014. Again, some intense days are ahead of me!

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LCWS: A Quick Look Back

Tuesday, March 30th, 2010
Me in front of the Bird's Nest, the stadium from the 2008 Olympics, last night. Thanks to Daniela for the picture!

Me in front of the Bird's Nest, the stadium of the 2008 Olympics, last night. Thanks to Daniela for the picture!

Time flies. LHC is taking data at 7 TeV… And I missed this, while sitting on a plane! I’m now well and truly out of sync with wherever in space-time I’m now located. I guess this is Tsukuba, Japan and it is a bit before midnight local time. But no matter when and where, it is an exciting time for particle physics. Just as Barry Barish, the director of the ILC Global Design Effort has said last night at the conference dinner of the Linear Collider Workshop (LCWS) in Beijing: The workshop will be remembered by most people not only for the things that were discussed there, but for being the workshop on the eve of the LHC physics startup.

As usual, there was very little time to go and explore the city, and I spend most of the days (which were quite sunny and clear due to some winds in Beijing) in darkened, windowless conference rooms. Still, in the evenings there were some opportunities to explore some Beijing landmarks, and the variety of Chinese cuisine. And: I have already seen parts of Beijing on a previous visit, and I’ll be back again in just a few weeks.

At the workshop, there were a number of new results reported from detector development, in-depth discussions on physics, and controversial arguments about the new baseline parameters of the accelerator. And, also as usual, I had my share to report at the meeting, too. While the technology development is moving forward, there is also a sense of hesitation of where to go: Particle physics is about to go through a revolutionary period, with discoveries by the LHC maybe (hopefully!) just around the corner. And these discoveries will shape the future of the field. They will decide what the right energy for a precision machine like the ILC is. So right now, while we are busy preparing detailed detector designs to be ready to go once the direction is clear, I am also wondering what that direction will be. The key factor here is the necessary energy. New (for example supersymmetric) particles at low mass could be explored with the already well established superconducting acceleration technology of the ILC, while in the case of higher mass scales for new physics we will need the CLIC technology which is still in its development phase. If LHC is going to perform as well as the initial success suggests, then we might know in just a few years. By that time, we will have a good answer how to provide the precision necessary to nail the details of the physics that the LHC is hopefully about to discover!

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