This fortnight, ALICE Matters spoke with Anders Knospe, a STAR graduate from the United States who is working full time at ALICE, as a post doc from the University of Texas at Austin.
Anders KnospeALICE's Anders Knospe
How long have you been at ALICE?
Two months, now: since May 2011.
What do you do here?
I’m kind of juggling several different projects. I spent most of this morning and afternoon working on the VHMPID - the Very High Momentum Particle Identification system - we have a test beam going on right now; testing various configurations.
I’m also working on the High Level Trigger, developing and testing a new clustering algorithm for the calorimeter and then trying to get started on an actual analysis – that’d be resonances in jets.
So, that’s three different things at once?
Yeah. Trying to get them all in - haven’t made a lot of progress on the resonances yet; need to move forward on that.
What is a clustering algorithm?
The calorimeter lets us measure the energy of photons or electrically charged particles. It’s made up of a grid of what we call towers – which are a kind of sandwich of lead and scintillator, which emit light when particles pass through it.
When an electron hits the calorimeter, it produces photons, which produce more electrons and positrons - and we get this big burst of particles. The calorimeter lets us measure that shower of particles.
The shower has a certain size, which is larger than the dimensions of one of our square cells, so we measure the energy in each cell and we need to group those energies together, so we can reconstruct the energy of the entire shower. The clustering algorithm lets us group these separate measurements of energy back into one measurement.
What about the other things you are doing?
Yeah, so – we have the VHMPID: this is a proposed detector for ALICE, which would use Cherenkov radiation to identify particles at very high momentums. We have the High Momentum Particle Identification system right now; this would be at a higher momentum than that. We are testing the prototype right now.
How does that work?
When a charged particle passes through matter at higher than the speed of light within that matter, it produces a cone of radiation, which is Cherenkov radiation. The trick then is measuring that.
At the moment we are using a wire chamber to detect the location of the photons – I mean the photons get to the photocathode – and when they strike this they emit electrons, which we can then detect. So, we kind of see the ring, where the cone of photons hits our detector.
How are the tests going?
As far as I can tell, they’re going okay. Again, we’re not using the final, proposed, set-up, but we’ve seen rings in a liquid radiator, and a gas radiator.
Where are you undertaking these tests?
It’s in a test facility attached to the Proton Synchrotron. Our beam hits a target and produces a beam of pions, which gets directed into our experimental area. I think we get about three bursts of pions every minute or something like that.
Can you tell us a little more about what you are doing concerning resonances?
I’m by no means an expert on this – it’s not what my PhD was on – but the goal of the heavy ion stuff is to measure the properties of the quark gluon plasma. There’s one particular aspect called chiral symmetry restoration – one way to see whether this is happening or not is to measure the yields of resonances produced in the quark gluon plasma itself.
The issue with this is that there’s a background of resonances that are produced (in that case of hadrons) with jets – we need to distinguish between those two, I’m going to be doing the Phi-meson, in and out of jets.
My most immediate task is to get a signal out of lead-lead. This is what I’ll be working on over the next few months, and hopefully getting some result out for Strangeness in Quark Matter.
So, what was your PhD on?
I did heavy flavour – charm and bottom quarks. I was on the STAR collaboration for that, at RHIC.
So, how did you come from STAR to be here at ALICE?
My PhD advisor is the head of ALICE USA, and my current boss was a postdoc in the Yale group – although, before I joined - and then my PhD advisor apparently gave me a good recommendation to her.
Do you like it here?
Yes. I’m kind of adjusting to not speaking the language, but otherwise I’m enjoying it.
Is that a big difficulty, do you think?
Not too bad. You know, at CERN, most people speak English; but for dealing with people outside of the lab, it would be useful to be able to speak a little French.
I did study German, but I guess that was the wrong language for these purposes. Whenever I meet someone who doesn’t speak English, I always ask them if they speak German, but it never works…
How did you get into particle physics?
Particles have always been something I’ve found interesting. Before working in heavy ions, I did a summer on a neutrino project. So, it’s not like I went into grad school saying “I want to study heavy ion physics”, but it is an interesting topic – we use a lot of regular particle physics tools, but then you’ve got this more nuclear physics angle – it’s kind of a hybrid between the two.
So, why physics in the first place?
I guess I just like knowing how things work. Physics is kind of learning how things work, on a very basic level.
What do you like to do in your spare time?
Spare time? I think I remember that…
When I was at Yale... I was going to New York a lot, and enjoying the theatre scene there, but for the last year and a half it’s just been work, work, work....
What’s your favourite thing about CERN?
There are a lot of people around to help me out when I have problems, so that’s cool. On STAR we did a lot more stuff over the phone, but here, as I’m at the centre of the experiment, I find that useful. It’s easy to approach people.