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Marcello Barisonzi (promotion date: 31 May 2006)

Top mass measurements in the electro weak channel at the ATLAS experiment

Promotion date: 31 May 2006

Marcello Barisonzi

First of all I would like to say that my thesis is a bit out of the scope of the University of Twente. The Elementary Particles Physics group of professor Bob van Eijk is mainly operating in Amsterdam, and not in Twente.

The ATLAS experiment in Geneva, Switzerland, is part of CERN, a huge laboratory on particle physics. In 2007 they will finish to build a large proton accelerator (LHC) in a underground tunnel with a 27 km circumference. ATLAS is one of the four particle detectors that will be installed at LHC. It is 40 meters long and 20 meters high: 7000 tonnes of instrumentation.

The idea of the experiment is to let protons collide to measure the properties of the particles you create. One of these particles is the Top quark.

There are 6 quarks in nature.

What is your thesis about?

First of all I would like to say that my thesis is a bit out of the scope of the University of Twente. The Elementary Particles Physics group of professor Bob van Eijk is mainly operating in Amsterdam, and not in Twente.

The ATLAS experiment in Geneva, Switzerland, is part of CERN, a huge laboratory on particle physics. In 2007 they will finish to build a large proton accelerator (LHC) in a underground tunnel with a 27 km circumference. ATLAS is one of the four particle detectors that will be installed at LHC. It is 40 meters long and 20 meters high: 7000 tonnes of instrumentation. The idea of the experiment is to let protons collide to measure the properties of the particles you create. One of these particles is the Top quark.

There are 6 quarks in nature.

And you are dealing with the quarks in the proton?

Yes. As I said, there are six quarks, with strange names: Up and Down, Charm and Strange and Top and Bottom. The proton is made up of 2 Up and 1 Down and the neutron of 1 Up and 2 Down. The Up is heavier and the Down is lighter. By making the quarks inside the proton collide you are creating other ones. Strange was found in the 1950’s, Charm around 1971, Bottom in the 1980’s and Top was found in 1995. We think that there aren’t any more. We want to measurements and establish why Top is so much heavier than the other quarks.

What did you actually do?

My thesis was divided into two projects. The first two years I did work on a very fast electronic board to read out the Muon spectrometer (100.000 events in one second!) at Nikhef, in collaboration with the university of Nijmegen. I was programming the boards, so this had little to do with actual physics. The board was tested in CERN in a small experimental setup and we found out it worked quite well. The second two years I worked on the simulation software of the detector. I generated a about half a million of simulated data and made an analyses of the mass.

But if you make a simulation you must be pretty sure of what is going on in real life.

The part simulating the collision is written by theorists doing the physical modelling. That makes the theoretical part critical. The detector simulation is easier in a sense, because we have already been studying the interaction between particle and matter for 50 years.

Are they going to use your software?

I hope so.

What are you going to do next?

At the moment I have a job as a software developer at ASML near Eindhoven.
In experimental physics there is a lot of scientific software to be written and I like that.
Later I will see if I want to go back at physics or not.

You are from Italy. How did you get here?

For my Master thesis I built part of the ATLAS detector using an infrared measurement system that was developed at NIKHEF. So I already knew the place and after my Master Diploma I heard that a position was available there via the University of Twente. I liked NIKHEF, I liked the city so I went.

What did you like best about your research of the past four years?

The international atmosphere of a physics institute, the international collaborations, the monthly meetings in Geneva. And the independence. You make your own decisions and take your own risks. On the other hand a bit more supervision would have been welcome. Gaining scientific independence is of course a goal, but sometimes I was a bit in the deep. When you start you are not a real scientist yet.

Are you confident that you are a scientist now?

I am not so sure. In writing this thesis I have had my share of science for a while. But I may go back to physics sooner or later.