by Ian Randall. Published: 18 March 2011

This issue, Matters chatted with ALICE’s current period coordinator, Jochen Klein, a PhD student from the University of Heidelberg who is writing a thesis on jet physics with ALICE.

Ian Randall

ALICE's Jochen Klein

Hello, Jochen. What do you do here at ALICE?

I joined the TRD project with my diploma thesis - which I started in 2007 - and since then I've been working on the commissioning of the TRD. I am frequently at CERN for hardware developments, and mainly the commissioning of the detector. Otherwise, I'm interested in jet physics and I'm working on jet reconstruction and analysis – so, the high pT part of heavy ion collisions.

For this month I took over the job of period coordinator. This means that I am taking care that everything runs smoothly, trying to coordinate the needs of the different detectors and making sure that everybody is aware of what is going on in ALICE.

How is that going so far?

I think so far it went quite well for us. After a period of installation of new detector modules, and many interventions in the technical stop, now we are back to a phase of data talking.

We tested all the detector read-out, the control systems, and so on during a period of technical runs to make sure that everything is working fine; tested calibrations; prepared trigger set-ups and things like that; and now we are ready and have just got the first collisions from the LHC in this year, although we have not yet reached the state of stable beams.

We are looking forward to getting stable beams for data taking quite soon - meaning in the next few days.

So, what is left to do?

At the moment we are mainly waiting for the LHC to deliver collisions, and we are ready to take them - which then would be used to test trigger scenarios which we would like to use for the intermediate energy run, which is one of the important steps in the next month. We will try to be prepared for that.

We have plans of what to do in that run, and that should be tested, of course, beforehand. We also had some changes in the detectors: like the Time Projection Chamber, which changed gas - we will have to run some tests and ensure that the calibration is fine, and that the data can be properly analysed.

It is a series of preparations which we want to have done, to understand the real physics program which will then follow. The most important issue for us is to be ready for the intermediate energy run, which is meant to be the reference for the heavy ion run taken last year.

What is happening with the LHC at present?

The LHC is performing a series of tests at the moment to understand the accelerator setup. They have a long schedule of things they have to check, and make sure are working properly, before they can put the nominal intensity of beams into the machine and operate it safely.

That’s always a concern - you must make sure that all the protection systems are in place to ensure that if something goes wrong, the machine is properly protected, and can handle those situations. This is what is taking time at the moment.

They are going up step by step in intensity, putting in more particles per bunch and seeing that that works fine and tuning in the machine parameters. When that is done - and they are now very close to that step - they will have one other major step, which is to inject not only single bunches of protons but trains of bunches - that means many bunches in one series from the injector chain, which will give a rise in intensity.

Now, the LHC is preparing to deliver a much higher luminosity than last year - so that is the next step. At the moment, from the experiment’s point of view, we are making sure that the LHC can run all the checks that are needed.

How did you get into physics in the first place?

I was interested in physics ever since my childhood and, well, at some point I just decided to study physics - and I continue to find it interesting. I think it is a very interesting subject: it is very general, one can understand how a lot of things work and it has the opportunity to have insights in many different aspects of things - especially in experimental physics, as here. There are also always technical aspects like detector developments - and that is quite a broad range of topics one can look into.

For how long have you been at CERN?

I came to CERN as a summer student in 2007, and I came back to do my diploma thesis later that year. Since then I've been here about half of my time; the other half I am at Heidelberg. So - I'm not permanently at CERN, but often; especially in periods in which we have commissioning of detectors ongoing.

Do you have any hobbies you pursue when you are not working?

I have, but recently I haven't had too much time for those. I like to play the guitar whenever I have some time. I also like to do some sports, like cycling, soccer and running.

What is the most exciting thing about working here at ALICE?

I would say that it is not one particular thing, but that there are so many things around which are going on, so many people from different backgrounds and contact with many topics – it’s not that you are limited to one view, or one aspect, of physics but you find people who are experts in many different fields. That is a very pleasant environment, in my opinion.

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