This week, ALICE Matters met with David Silvermyr - a staff scientist from Oak Ridge National Laboratory, one of the largest National Labs in the United States. David, who hails from Sweden, works here at CERN on the ALICE ElectroMagnetic Calorimeter (EMCal).
David Silvermyr, and his colleague Fan Zhang, in one of the laboratories where electronics for the DCal upgrade are being developed.
Hello, David. So, how long have you worked at CERN?
I was a summer student here in 1997 - I guess many of the people you meet at CERN were summer students at some point - and then I started in ALICE in 2007. In the years between, I was a graduate student at Lund, in Sweden - that's where I from - and then I graduated in 2002. In those ten years that I was not at CERN, I was mainly working at the PHENIX experiment, in Brookhaven, outside of New York.
At first, after I graduated from Lund, I was a post-doc at Los Alamos, in New Mexico; and since 2003 I've been at Oak Ridge National Lab in Tennessee. I've been stationed here at CERN in periods for a total of about 3 years, and I guess I will stay here until later this year.
Do you enjoy it here?
Yeah, sure. Since I am European, it's also quite nice to be back in Europe. I like CERN, it has a great environment. I mean, for instance when I was a summer student I met so many people; more than 100 students from different countries - it was probably the most international summer I've ever enjoyed. It’s a great experience.
Could you tell us more about the summer student programme?
So, you have about 8-10 weeks - and for about six weeks or so of that you have lectures in the morning - and certainly when I was there they were really excellent - and then in the afternoon you work on some projects. For mine, I was working on the OPAL experiment, at LEP, in those days. I worked with a CERN fellow from the UK - his name was Hawkings - looking at something called secondary vertex reconstructions of B (beauty) hadrons, for studying CP violation. It really was a very educational and fun project.
Now, in ALICE, I work with the EMCal - and so I'm one of the subsystem run coordinators. In July I will be the Period Run Coordinator. This week I am on call for the EMCal, and also for radiation protection. You know after we have beam in the machine, and people want to go down into the experiment, a radiation protection person has to go down first and make sure (measure) that it's safe.
A funny thing to me is that when you do go down, when the beam is off, the radiation that you measure is mostly actually lower than what you see at the surface. The reason for that is that the counts that you see are mostly caused by cosmic background; but when you are down below you are shielded by some matter - so the environment where you are most “safe” is inside the magnet - that's where we have the least counts, with less radiation than you have on the surface!
I think, however, in other places - like ATLAS and CMS - where the luminosity is higher and there are more collisions, there will soon be elevated radiation levels - and we do have some places in ALICE with somewhat elevated levels already too, so you wouldn't want to spend too much time there!
So, what work do you do with the EMCal in ALICE?
So, we work with the read out electronics - what's called the front-end (FEE) cards. The work on the electronics involves several collaborating institutions (ORNL, CERN, Wuhan, Grenoble and Jyvaskyla); for instance, Fan Zhang (of Wuhan, seen in the photo above) is currently working on firmware for several important readout components.
We've just completed the installation of the EMCal in January, in the long shutdown - and we now have a total of 10 supermodules (there were four before January). One number to perhaps note is that, in total, the EMCal weighs about 100 tons - we might not have the most channels in ALICE, but we can boast to being among the heaviest!
For that we have about 370 FEE cards installed, and some other auxiliary equipment on top of that. For example, in order to check that everything is working, we have a LED pulser system - where we can send a signal to all of the detector elements, and see if they actually receive that signal - like a kind of heart rate monitor to see that things are alive. This is something that we do once a second during data taking. So, along with all the physics events we also send these calibration events in order to make sure that everything is ok.
How did you get involved in ALICE in the first place?
Well, I think it was via Terry Awes (also from ORNL) who had been involved in the discussions with ALICE and folks in the US for some years - to do with the EMCal upgrade to the project. One of the main purposes of the calorimeter is to have a trigger for hard processes - things like jet physics. I was working in the same group as Terry in PHENIX, and we were thinking about what to do next and working on ALICE seemed like an interesting thing to do.
We had our first beam tests at Fermilab in 2005 - that was my first involvement in ALICE; then I moved here in 2007 when we installed the support structure for the EMCal - we were setting up and testing for quite some time before we installed the detector itself. We didn't actually become an official project and start construction until 2008, we partly installed in 2009 and finished in 2011 - so I think we came quite late - but finished quite quickly!
Of course, most of the particles produced in the collisions are measured very well by the TPC and others - everything that leaves a charged track - but an additional part that the calorimeter gives is that you can also measure some of the neutral particles, like photons and neutrons, and triggering on high energy particles and jets and so on.
The plan now is to put some extra calorimeter modules around the PHOS calorimeter - the DCal project - this is what we are working on at the moment, and that will be installed in 2013, in the long shutdown.
The DCal will give us, with the EMCal, some back-to-back jet acceptance. It will be nice to have some extra calorimeter acceptance on the other side.
So, as you work both for ALICE and Oak Ridge - which of the two countries do you prefer out of Europe and the US?
I think there are many good things that I like about each of them. I don't really speak French, so that's one problem here. I used to like learning languages, but now it’s not a priority - at CERN you can survive just by speaking English. Another great thing about being at CERN is that it's much easier to cycle into work than in the US!
Tennessee, on the other hand, has some nice things - the most visited national park in the US, the Great Smoky Mountains National Park, is near Oak Ridge - so they have mountains, kind of like the Jura; the people are very nice; there's even an amusement park run by Dolly Parton nearby, called Dollywood - an example of the humour over there.
Do you miss Sweden?
Sure - I mean, I tend to go to Sweden two to three times a year. I don't miss the Swedish weather - but I do miss living closer to my family. Of course, there are certain things that one always misses - a special kind of food, speaking one's own language - you miss what you grew up with. On the other hand, being in a place like this is very nice - you meet a lot of people; it's a very international atmosphere.
What is your favourite thing about working here at CERN?
Well, I'm spending a lot of time at Point 2. I kind of like the atmosphere there, I have to say. It's a very nice collaboration - and a very interesting time to be here at CERN.
When you are not doing physics - how do you like to spend your free time?
I used to play a lot of football - and I do some skiing - but the most regular exercise I do is table tennis. There's a table tennis club here at CERN. I played quite a bit when I was younger and I've also played a bit in Tennessee - there are a lot of technical people (programmers etc) playing it there, too - I suppose it's a bit of a nerdy sport?
Here at CERN, we play together with people at the Meyrin forum - there are even some Swiss champions there. The CERN people play on Friday evenings. We've had a CERN tournament for 3 years now. I have participated twice, and won once.
What are your plans for the future?
Well, I don't know. For the next few years, there's certainly lots of interesting physics to do here and also in the US - but on the longer term, there's a future facility that's starting in Lund - they haven't started construction yet, but at some point they will need manpower, and that's something I would be interested in, I think.