Who are you? Can you tell us something about yourself?

My name is Delia Hasch. I am currently working at the INFN (the Italian institute for nuclear physics) in Frascati close to Rome being involved in experiments which are carried out at DESY (Germany), at the European research centre CERN and at JLab (USA) by large international groups of physicists, engineers and technicians. This international atmosphere, in fact, is one of the great experiences when working in fundamental science.

I studied in Berlin, a fantastic town for young people with its own very special atmosphere, and chosed the subject of physics nearly by chance, I never regreted it ! Having the chance to work at different places all over the world I always considered as an important benefit for my personal experience and would absolutely recommend. 

You are leading an activity within the HP3 project – which are the scientifically exciting aspects of your research project?

Our 'Joint Research Activity' is called '3D-Mom', which contains a double meaning:

a) we want to describe the 3-dimensional structure of nucleons in 'momentum space' (short 'mom')

b) the functions which contain the above information are related to a kind of 'mother function' (again 'Mom') - the Wigner function' which provides the full, multidimensional information about nucleon structure.

What is so exciting about it?

Nucleons - the common name for protons and neutrons - form the overwhelming majority of all observed matter in the universe. We now understand that nucleons are not pointlike (electrons in contrast are), but composed of more basic constituents called 'quarks', which are bound together by the exchange of 'gluons'. In fact, quarks are glued or confined inside the nucleons - they have never been observed as free particles. Together with the electron and his heavier brothers and the elusive 'neutrinos', quarks represent, according to our current understanding, the 'ultimate constituents' of matter.
The theory describing the fundamental properties and the dynamics of these constituents is Quantum Chromodynamics (QCD). The description of the nucleon's multi-dimensional structure, goes directly to the heart of exploring and understanding the dynamics of matter within QCD.
Among the most intriguing aspects of QCD is the relation between its basic degrees of freedom, the quarks and gluons, and the observable physical states, i.e. hadrons such as the proton. The most prominent quantities that describe these relations are so-called 'parton distribution functions' (PDFs). The concept of PDFs is very powerful. These functions have been shown to be universal in the sense that the same distributions appear in completely different high energy physical processes. One can then calculate cross sections (counting rates) for various different scattering processes at various energies and compare with measurements. The successful prediction of the energy dependence of the parton distributions has been one of the great triumphs of QCD.
Standard PDFs, however, represent only one-dimensional projections of the distribution of quarks and gluons inside the nucleon. However, confinement induces transverse hadronic scales in the nucleon with accompanying quark orbital angular momentum and spin-orbit couplings which can be probed in experiments and give rise to a non-trivial 3-dimensional structure of nucleons. This complexity is exactly what we wish to study.

I just mentioned 'spin'. This property of a particle (we call it 'quantum number') enters, together with its mass, electric charge and a few other quantities, into the identity card of the particle itself. Something similar to the personal descriptions such as the name, surname, height, weight, colour of the eyes, etc. that enter into our identity cards.
The spin can be seen as an intrinsic angular momentum, although there is nothing which 'spins' in a classical way.
The spin of a particle was first postulated by Wolfgang Pauli as a pure mathematical construct at the time of the formulation of 'quantum mechanics' during the early 1900ies. At that time, it was not seen as something real, means something measurable. The formulation of spin ensured 'Pauli's exclusion principle'.
The 'real' discovery of the electron spin was made by the two young Dutch physicists G.E. Uhlenbeck and S.A. Goudsmit in 1925. They demonstrated that atomic spectra can be understood by the concept that the electron has a spin.
The spin of a particle plays a prominent role in all physics processes involving the particle. As an example, the spin of atomic electrons determines their distributions around nuclei and so has a great importance in all chemical processes, just as explained by our Dutch physicists. Similarly, the spin of the nucleons is essential to account for the structures of the nuclei. It is also of paramount importance in the NMR, the powerful technique for medical diagnoses.

In a very analogous sense, we are now studying a new type of PDFs, which provide 'tomographic pictures' of the nucleon. These transverse-momentum dependent (TMD) or unintegrated multi-dimensional parton distributions are nowadays widely recognized as an appropriate and necessary formalism for the understanding of hadron structure within the formalism of QCD and for the description of processes at high energy colliders. Spin observables play a central role in studying these new type of parton distributions.

In our project, the investigation of TMD distributions is joined with the research and development of new technologies for so-called 'RICH detectors'. Such a device allows for identification of the type of hadrons produced in a high energy reaction. As different types of hadrons are composed of different combinations of quarks - the elementary particles we wish to study as explained before - the 'name-tag' of a hadron allows for getting information about the type of quark we study in the reaction. This way we will be able to investigate TMD distributions for the various different quark types in the nucleon - a key information for finally extracting a 3-dimensional image of the nucleon.
RICH stands for Ring-Imaging CHerenkov. A Cherenkov detector contains a medium, a gas or a liquid for example, in which a charged particle emits light (photons) along his way, forming a cone around its track. The angle of emission of the photons is proportional to the velocity and mass of the particle. If we now already know the velocity of the particle, means we have measured it, the structure of the light cone tells us - via its relation to the mass - the type of the particle.
In a Ring-Imaging CHerenkov the produced light cone is projected on a photo-sensitive detector where it forms a ring, hence the name. Different types of hadrons produce rings with different diameters. This way we can know the particle type.
We joined the development of new materials for the production of the Cherenkov light and are studying different advanced devices for photo-detection at the frontier of photo-sensitive detector technologies for obtaining the full design for a large size RICH detector. This RICH detector will be built for the CLAS12 experiment at the JLab12 facility in the USA, which is currently under construction. One of the main physics objectives of the CLAS12 experiment will be the study of TMD distributions in a still unexplored kinematic region where transverse effects and spin-orbit correlations, described by the TMD distributions, are expected to be very relevant.

3) Who are the participants to your project?

Altogether, more than 50 scientists from 25 Institutions from 8 European Countries participate in the multi-task '3D-Mom' Joint-Research Activity. Our activity practically joins the entire research community (of both experimentalists and theorists) working on TMDs in Europe with the efforts for developing new detectors for the investigation of TMDs. Many of the scientists in our activity are among the leading experts in the field worldwide. Their cooperation and complementarities ensures the success of the project.
The participating experimentalists carry out their research at the three major international collaborations active in the study of the 3-dimensional structure of the nucleon: COMPASS at CERN (Switzerland and France), HERMES at DESY (Germany), and CLAS at JLab (USA). Our project promotes and stimulates cooperation between experimentalists working on competing experiments and between experimentalists and theorists. The complementarities of the different expertises and their correlations are very clear: the experimental groups provide observables sensitive to TMD distributions, which are analysed in the appropriate theoretical framework developed by the theorets of the project. Information from different experiments and different physics reactions, obtained with different analysis techniques are combined into a global knowledge about the multi-dimensional nucleon structure.
The joined expertise in the field of studying TMDs, yielded the proposal of a RICH detector for the CLAS12 experiment at the near-future JLab12 facility, a crucial tool for future investigations of TMD distributions in a yet unexplored kinematic region.

4) What do you want to achieve with this activity?

The exploration of the multi-dimensional structure of hadrons is a central focus and driving science case in the planning and building of future particle accelerators in Europe (FAIR), USA (JLab12, EIC at JLab or RHIC) and Japan (J-PARC). The centre of gravity for those studies was so far in Europe with pioneering experiments at DESY (HERMES) and CERN (COMPASS). With the shutdown of HERA (DESY) in 2007, the COMPASS experiment is the only remaining facility for dedicated studies of TMDs in Europe. The engagement of European groups in experiments at JLab and in design studies for future facilities is therefore crucial for attracting and training young scientists and ensuring future development of the field in Europe. With its participation in a major detector upgrade for CLAS12 at JLab12 and the preparation for data analysis and interpretation, our project will help to maintain the leading role of European physicists in worldwide projects of hadron physics.

Our activity effectively connects the entire research community working on TMDs in Europe and promotes a further development of this community. It strengthens the mutual interaction of experimentalists and theory experts in the field thereby directly identifying key measurements at the participating research infrastructures, providing their interpretation, including setting the stage for new experiments and the need of advanced instrumentation.

The innovative technologies for particle identification which are applied and further developed within this activity will have impact on instrumentation in future nuclear and particle physics experiments. The peculiarity of this project is the combination of novel aerogel radiators with advanced photo-detection techniques for application to the large size CLAS12 RICH detector. The developed solutions will be exemplary for building RICH detectors of the next generation that require large surfaces and photo-detectors operating under extreme conditions and having affordable costs.

5) In which way your activity could be of benefit for the society?

The understanding of matter, of 'what we are made of' and 'where we are going to' is certainly a focus of human curiosity. Our research contributes to our basic understanding of nature and thus to our self-perception and cultural life. It is a knowledge which, to my personal view, has an intrinsic, incommensurable value and is in close connection with philosophy.
Basic science has always yielded a vast technological return, a 'spin-off' how we call it. It will eventually produce benefits, which, however, cannot be foreseen right from the beginning. Just as an example, the technologies for accelerating paticles which we use for our basic research have nowadays a broad application in medical diagnostic and therapy, starting from the widely used nuclear magnetic resonance (NMR) and positron emission tomography, till the very recent center for hadron acceleration facilities for cancer therapy.

6) Why do you think a young person should choose to study science and is there any reason for which should they do so in Europe?
First of all for curiosity. To my view, you should study science when you feel you wish to 'understand'. If you fear mathematics - which is a beautiful art - you could of course also study, for example, philosophy. But science provides a particularly deep view at nature which naturally yields more questions than answers. It is a real adventure. Whatever you will do later on, a study of science usually provides you special skills in understanding and efficiently attracting and solving problems of various different types. Among physicists, we often realize that we think differently from other people - tell it also crazy if you wish ;-). Looking at my study mates and friends, at my own, I realize that scientists work extremely creative and efficiently in the many different fields of our community life.
Why Europe?
European Universities have a long standing tradition in teaching science and are often closely connected with research institutes which provide a direct scientific training of students. In many european countries, the access to Universities is still (quasi) free, a great benefit of our societies, which we need to defend.
Apart from this, if you are curious for different cultural approaches, you should go abroad, possibly out of continent and explore. Nothing can teach you better than own experience.

7) Would you like to add anything?

To my view, the only one golden rule to fully respect: treat others as you would like others to treat yourself. This applies also to nature and our whole world. Nothing really important to add.


The HadronPhysics3 project is supported by the European Union
under the 7th Framework Capacities Programme in the area of Research Infrastructures (RI).