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Frank Simon | MPI for Physics | Germany

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Teachers and Black Holes

Wednesday, March 24th, 2010
Sitting underneath an alpine panorama in the Lufthansa Lounge in Munich: A last touch of Bavaria before heading out to Asia.

Sitting underneath an alpine panorama in the Lufthansa Lounge in Munich: A last touch of Bavaria before heading out to Asia.

My travel spree continues, and while I’m waiting in the newly renovated Lufthansa Lounge at Munich for my flight to Beijing via Frankfurt, I have a few minutes to think back to my lecture at a teacher’s training event last Saturday. At a school in Zwiesel, a small town in some remote area of Bavaria, I was giving a lecture on black holes at hadron colliders, a topic I’ve been talking about frequently ever since I gave an extremely well attended lecture on this at the TU Munich in Summer 2008. Also this time, it was certainly something that kept the 100+ teachers awake and interested on a late Saturday afternoon.

I’m sure you’ve all followed the controversy on this topic, so I will not go into the details here. On the CERN website, answers to every conceivable scenario in connection to black hole creation can be found, proving beyond doubt that whatever we will create at LHC, it will be hopefully very exciting scientifically, but not dangerous for us and our planet. Actually just a few days before I gave my lecture, the Bundesverfassungsgericht, Germany’s highest court which judges on constitutional matters, came out with a press release about a decision on a complaint by a German citizen living in Switzerland, who saw her constitutional right to be save from bodily harm violated by the approaching start-up of the high energy run of LHC. For those of you that speak German, here is the link. It is a fantastic read. The court ruled that the complaint is not accepted, stating that the refusal to believe in well-established scientific laws is not sufficient to demand a stop to large scale science experiments. They clearly state that it is not enough to invent a disaster scenario tailored to a specific project, without providing a convincing chain of arguments that such a scenario could indeed take place. Otherwise, every large-scale project could be stopped by just inventing something crazy enough that would force the courts to end the projects. So, indeed, a very good ruling for science as a whole!

At the lecture, none of the teachers seemed worried by the experiments at the LHC, but they were certainly happy to be given arguments for discussions with their students. I hope I could also convey my excitement about the science ahead. While I personally think the creation of mini-black holes is extremely unlikely, it is certainly one of the most spectacular things that could come out of the LHC experiments: Finally, this would bring gravity into reach for particle physics experiments, and open a completely new world for us.

With that, I’m off to the Linear Collider Workshop in Beijing…

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Up in the Air

Tuesday, March 16th, 2010

Just barely 24 hours after getting off the plane from Chicago, I’m back again in the airport lounge in Munich, this time waiting for a short flight to Cologne/Bonn airport. I’ll spend the rest of the week attending the Spring Meeting of the German Physical Society in Bonn. At this annual event, essentially the whole German particle physics community gets together, so it is a great opportunity to catch up with colleagues. In addition, the breadth of the topics discussed there surpasses anything you can find in international conferences, which are usually way more specialized. So it is a great opportunity to find out about what is going on in fields a bit outside of what I normally do. There are some plenary talks in the morning covering a variety of subjects,  and a huge number of parallel sessions in the afternoon. The parallel talks are usually given by students, and each one of my students will be presenting their work at this conference. I’m not talking myself, a welcome change after the five talks I gave at the last meeting I attended, which will hopefully give me the opportunity to look around a bit and learn about things I’m not doing in my everyday life.

But attending the conference also means another few days away from home, again… At the moment, I’m really pushing the limit travel-wise. That reminds me of the final scene in the movie that gave the title to this post, which I saw on my way back over the Atlantic:

“Tonight, most people will be welcome home by jumping dogs and squealing kids. Their spouses will ask about their day, and tonight they’ll sleep. The stars will wheel forth from their daytime hiding places. And one of those lights, slightly brighter than the rest, will be my wingtip, passing over.”

Right now, this really fits the mood…

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CALICE in Texas

Saturday, March 13th, 2010
Sun glinting off the panorama windows of our meeting room.

Sun glinting off the panorama windows of our meeting room.

First stop on my spring travel binge: Check. The CALICE collaboration meeting at the University of Texas at Arlington. We just finished three days of presentations and intense discussions, and I guess I had more than my fare share: Since nobody else from my group wanted to travel to the meeting (to avoid getting into the same travel-crazy mode I’m currently in), I gave a total of five presentations on various topics that we cover in my group, from data analysis to hardware development and new ideas for a beam test we will have in the fall at CERN. A big plus of the location: While Europe is still deep in Winter (I was skiing last Sunday just 50 kilometers south of Munich!), spring is in full swing here: Sunshine and temperatures in the 60’s, certainly a nice change. Of course, while we could enjoy the sunshine on our way to the meeting, the blinds in the meeting room were always drawn, to allow us to see the presentations on the screen. So, even with spring sunshine outside, we are sitting in a darkened room, discussing results and plans for hours on end… But the meeting was definitely worth it: The plans for beam tests to study calorimetry at a multi-TeV Linear Collider are coming together, and our data analysis is getting more and more mature. New results, also from my group, are about to be released, hopefully in time for the Linear Collider Conference in Beijing, China, in less than two weeks.

Wafles in the shape of Texas... Things are different here!

Wafles in the shape of Texas... Things are different here!

This is my second time in Texas, and it certainly is true: Things are bigger, or at least a bit different, in Texas. There is no escaping that: Waffles in the shape of Texas for breakfast in the morning, to just point out one thing.

Now the meeting is behind behind me, but I still have a day to spend here. The reason is flight prices: when flying intercontinental from Europe, usually the only way to get a halfway decent ticket price is to stay the night from Saturday to Sunday, and spending it on the airplane does not count. Right now this is annoying, since it stretches my trip by a day, in a period I’m barely home anyway, but it also gives me the opportunity to see a little bit of what is outside the meeting room. We already got some local flavor at the collaboration dinner at Billy Bob’s Texas two nights ago, and tonight a few of us are planning to go to a rodeo in the historic Fort Worth Stockyards. I’ve never been to one before, I’m sure it will be fun!

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Travel Madness – Reloaded

Monday, March 8th, 2010

As usual with a sequel, things have to be a bit more crazy, and a bit more spectacular than the original. The travel period I’ve just started is certainly fits that bill, compared to the previous (rather short one) I’ve written about at some point… As usual in these days, I’m sitting in the Munich Lufthansa Lounge in the early hours, waiting for boarding. Once I get on the plane, I’m off to something that is almost a world tour: two meetings, two conferences, one lecture to give, three continents (America, Asia, Europe), 4 countries, and all that before Easter. At least I could arrange it so that I stop at home for a night from time to time… I guess otherwise my wife would consider changing the locks ;-).

Well, today I’m heading to the CALICE collaboration meeting in Arlington, TX, USA, via Frankfurt. The transatlantic is a long flight, more than 11 hours, but there is more than enough to do: A couple of talks to prepare for the meeting, and maybe, just maybe, getting started on the lecture I have to give at a seminar for teachers later in the month. My laptop is fully charged, spare battery in the bag… I guess I’m good to go.

I hope I’ll find the time to post a bit about what is going on as I make my way from meeting to meeting…

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Light from Plastic

Saturday, March 6th, 2010

After a shamefully long absence from the blogosphere, I’m finally back with a post about my work on calorimeters for the Linear Collider. I’ve already written about this a bit, for example here and here, and more details about the CALICE analog hadron calorimeter I’m mostly focusing on here and on my webpage. The key theme is always granularity, to get a detailed 3D picture of the particle showers to be able to use Particle Flow to get the best possible resolution.

So far, so good, but how do we measure the particle showers? We use so-called sampling calorimeters, which consist of layers of passive and active material. The passive material is usually dense stuff, in our case steel plates, where the incoming particles interact and form particle showers. After a passive layer follows an active layer that essentially measures how many particles have been created in the passive layer in front. By doing this layer after layer until the complete shower is absorbed, you get the total number of created particles, which then tells you the energy of the incoming particle if you know how the showering works in the absorber. Of course it is not quite that simple once you look deeper into this, but to understand the principle its certainly good enough…

Blue light emitted by a piece of plastic scintillator.

Blue light emitted by a piece of plastic scintillator.

But: how do we get a signal out of the active layers? After all, in the end we want some information that can be processed by a computer… In the hadron calorimeter, we use plastic scintillators, which emits light if a charged particle flies through it. The granularity of the detector then comes from building the active layers out of small scintillator tiles, in our case typically 3 cm by 3 cm, 5 mm thick. The light created in the tiles is detected with tiny silicon-based light detectors, so-called silicon photomultipliers, SiPMs, which we put on each little piece of scintillator. Those guys are capable of detecting individual photons in the visible spectral range, and transforming the light into an electrical signal… exactly what we need!  But again, it is not quite that simple: The scintillator emits blue light (as you can see nicely illustrated in the picture on the right), but the first generation of SiPM that we use in our calorimeter that went into various test beams, most recently last May at Fermilab, are best at detecting green light. That is why a wavelength-shifiting fiber, a plastic fiber that absorbs blue light and then emits green light, is embedded in each scintillator tile. This fiber collects the light, changes it to green and leads it to the SiPM. That works quite well, with the added benefit that the response of the scintillator tile is quite uniform over the full surface, meaning that the signal you get out in the end for a particle that goes through the scintillator is the same no matter where it went through the tile. The downside is that it is mechanically quite complicated to put the fiber into each tile, in particular once we think about a full-scale experiment, which would use about 8 million of such tiles!

Luckily, silicon technology is advancing at incredible speed, so by now you can buy SiPMs that are optimized to detect blue light off the shelf. The fiber is no longer necessary, which has a number of advantages: Most notably an easy (and thus cheap) manufacturing of the scintillator tiles and a faster signal, since we get rid of the detour of absorption and reemission of the light in the fiber (this will be important for some beam tests I’m planning at CERN in the fall, more about this at some later time…). But one question immediately comes up: What about the uniformity? After all, the fiber is collecting the light, leading it to the SiPM. What happens if we throw it out, and stick a SiPM directly to a piece of plastic?

My grad student Christian and I studied this, with a small experimental setup developed exactly for this purpose.  It scans a small radioactive source over a scintillator tile, and measures the response (meaning the number of photons we detect with the SiPM), depending on the position of the source. The figure below shows a picture:

Test setup to study scintillator tiles with SiPM readout in detail: Scanning a radioactive source across the surface.

Test setup to study scintillator tiles with SiPM readout in detail: Scanning a radioactive source across the surface.

A first try was to just stick a SiPM directly to a piece of plastic, which gave rather disheartening results: A large signal close to where the photon sensor sits, and a much lower signal elsewhere. Not exactly what we want to use in our calorimeters:

Naive fiberless coupling of a SiPM: Just stick it to the side of a scintillator tile. The result: Not at all uniform...

Naive fiberless coupling of a SiPM: Just stick it to the side of a scintillator tile. The result: Not at all uniform...

However, just by looking at the figure of the response, you can already come up with a possible solution: Reduce the amount of plastic close to the SiPM, and you’ll reduce the huge spike. After quite a few iterations, we came up with a shape for the plastic tile that works extremely well. It also now includes a SiPM that is embedded into the tile, which is important or a realistic calorimeter since then the individual cells can be placed edge on edge, without any gaps between them. We get a large signal, and beautiful uniformity, at least as good as with the fiber, with something that is quite a bit easier to produce:

Making it work: A special "dimple" at the spot where the SiPM is attached solves the uniformity problem. The SiPM we use is also shown in the left part of the picture.

Making it work: A special "dimple" at the spot where the SiPM is attached solves the uniformity problem. A zoomed photograph of the SiPM we use is also shown in the left part of the picture.

A few weeks ago, we submitted a paper on the results which you can already find on the ArXiv. Meanwhile, we have also found uses for our studies outside the Linear Collider project, which I’ll post about soon, hopefully… But for today I’ve written more than enough!

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Heat to kill the pain

Sunday, February 7th, 2010
A sliver of sunlight on the next mountain, amindst clouds and snowfall.

A sliver of sunlight on the next mountain, amidst clouds and snowfall.

I’ve been a bit slow with blogging lately… And the reason is not a lack of things that are going on, far from that. Things got even more busy because of a long-planned week of skiing, and all the things I had to finish before then. Now, teaching is over for this semester, and since yesterday around noon, we are in a small mountain village in south western Austria.

Over the last few days there has been quite a bit of fresh snow, good for the slopes, but bad for visibility, especially since the clouds this morning were right at the altitude of the ski resort. After lunch, we saw a first sliver of sunlight, and the day ended with sunshine. The snow was great to ski on, but of course in the middle of a cloud I went into a little depression a bit to fast without seeing it, and jolted my back. But the sauna in our hotel hopefully helped to loosen the muscles again… Nothing like baking for a while to kill the pain of a long day of skiing.

I hope that over the next few days I’ll also have the time to write a bit about things that have been going on lately: A submitted paper, meeting in Paris, maybe more…. But no promises, skiing comes first!

The tool to soothe sore muscles: The sauna in our hotel in the ski resort.

The tool to soothe sore muscles: The sauna in our hotel in the ski resort.

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No better time…

Tuesday, January 26th, 2010

As the popular saying goes, there truly is no better time to close the barn door than after the horse has escaped… OK, it does not quite fit here, as you will see, but still I was reminded of that saying when I just passed security in Munich Airport’s Terminal 2. Just the very Terminal that was evacuated less than a week ago following a security scare that luckily turned out to be a false alarm (as they usually do). In that particular case, a laptop apparently triggered an explosives detector, but the owner of the computer disappeared, with the laptop in question, while the results from a wipedown were being evaluated. Following that, with quite a delay however, the complete terminal was evacuated. It turned out that everything was perfectly harmless, and the traveler in question probably just did not understand the security screeners’ instructions to wait for the test results… As far as I heard, there is video footage showing him wandering around the duty free shops, and then leaving the terminal with all others once the evacuation was started. Apparently he later passed security without any problems. There has been an intense debate about what all went wrong… Such as loosing track of the guy in the first place. I assume the security screeners here in Munich had to endure quite a dressing down. As a consequence, they are now extra thorough, and keeping a very close eye on laptops in particular. There is also a much increased police presence after security, to prevent anyone from leaving the area unnoticed. Luckily, my way through security was still quite fast and without trouble… I hope things stay that way, with all the new measures being discussed at present.

Now I’m waiting for my flight to Paris, which is up to now still listed as “on time”… Lets see how this develops, it has been snowing quite heavily in Munich earlier today, and quite a few flights are delayed or canceled. Hopefully I’m off soon, to attend the ILD meeting in Paris, where we’ll discuss plans to move towards a complete detector design for the International Linear Collider, to be fully worked out over the next two years.

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Skiing… Finally!

Sunday, January 10th, 2010
Officially, it has been Winter for quite a while. And while large parts of Europe are suffering from massive snow falls, there has been very little snow in the Alps in western Austria, the region that is easily within reach for a day trip from Munich. Since the new year, it has been quite cold here though, excellent conditions for artificial snow making. So, even with only a rather pitiful natural snow cover (there is way more snow in Hamburg than in Munich at the moment, totally unbelievable!), skiing is now possible. Especially in the bigger resorts with serious infrastructure for snow making… The artificial lakes that are used as water reservoir for the snow makers are as empty as I’ve ever seen them, though.
Ready for skiing.

Ready for skiing.

Well, a friend and I took advantage of a holiday in southern Germany on Wednesday to head to the “Skiwelt Wilder Kaiser”, the biggest interconnected ski area in Austria, 90 minutes drive from our place. We set out early in the morning at 7, brutal for a holiday, in somewhat uncertain weather conditions. It was a great day, though, no sunshine but good visibility and decent snow conditions, a good (but very late) start into the skiing season. The resort even allows you to track your ski day through the area online, using the lift ticket that is logged at every lift base station. Even with two longer breaks (no point pushing the limit on the first day of the season), we accumulated more than 8 vertical kilometers… After a break of more than 9 months, it is nice to be skiing again!
I hope that the ski addicts among you will also have quite a few enjoyable days on the slopes this season!
Our path through the ski area, with a total of 8340 vertical meters covered during the day.

Our path through the ski area, with a total of 8340 vertical meters covered during the day.

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Volcanic Activity West of Munich

Saturday, January 9th, 2010
Flaming onion volcano, a challenge for experimentalists and a nice way to greet the new year.

Flaming onion volcano, a challenge for experimentalists and a nice way to greet the new year.

A big celebration on New Year’s eve is a tradition for most of you, I guess, and I am no exception here. For the last couple of years, I’ve been getting together with friends from university, most of them physicists. As usual, we had a scary amount of food, in all sorts of different varieties. On my suggestion, we also included Teppanyaki in our repertoire this year. And, not surprisingly, the “flaming onion volcano” was an irresistible challenge for the experimentalists among us… As usual, we did not do fireworks for the new year, no point in spending money on things that blow up if you can spend it on food and drink, but we greeted the new year in style, by discovering volcanic activity in the West of Munich.

Happy New Year to all of you!

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Deceleration

Thursday, December 24th, 2009

The last lecture and the last meetings for this year are done, and I’ve just returned the second iteration of the proofs for my STAR spin physics paper to the journal.

Snow next to teh Autobahn on the way to Frankfurt.

Snow next to the Autobahn on the way to Frankfurt.

Now Christmas is here, and it is time to “decelerate”. The year has been a wild ride: New Projects starting, significant progress in others, two diploma theses finished successfully in my group, another one started and now five PhD students in various stages of their research projects… After one year of getting started in 2008, this year my new group has picked up speed and is now buzzing more than ever with life and energy. For myself, it has been, among other things, a year of travel: More than 70 000 miles in airplanes, 20 multi-day trips, six of them intercontinental, and quite a few new places and impressions.

I am sure next year will be just as exciting, for me as well as for particle physics as a whole. Serious physics running will begin at the LHC, and answers to the question of where to go with the next big projects might start to emerge.

Before this happens though, now is the time to shift back a gear or two, and take a week to relax with friends and family, which is exactly what my wife and I will be doing. Despite the weather chaos that closed airports all throughout Europe, we were quite lucky not to hit any serious traffic or very bad road conditions on the way from Munich to the Frankfurt area, where we are both from. For quite a while, the Autobahn was leading us through a winter landscape, complete with falling snow and covered trees…

Now I’m ready for Christmas. Happy Holidays to all of you!

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