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The main objective of the PrimeNet network is to coordinate activities and to exchange information from different experiments with overlapping interests in meson physics, in particular the h-h' meson system, at different European research infrastructures and at university theory centers. Mesons are produced in very different processes at the different European laboratories. At DAPHNE (INFN Frascati) they are produced by means of e⁺ e^- collisions while at the MAMI (UMainz) and ELSA (UBonn) electron accelerators, the mesons are created in photon-nucleon reactions. At the ion cooler storage ring COSY (FZJ), they are produced in hadronic interaction via proton-nucleon and deuteron-deuteron collisions. Coordinated efforts making use of all of these complementary processes and different detector techniques will lead to a deeper understanding of the underlying physics. PrimeNet will coordinate these different activities in order to reach the best results achievable.

From previous experience in the FP6 EtaMesonNet network it has become increasingly clear that the physics involved in the decay and production of the h meson must be investigated with different experimental techniques and analyzing procedures to give reliable and consistent results. This has turned out to be the only way to really understand the crucial systematical errors from the different measurements. Another important outcome is that the interaction between theory and the experimental groups allows for data to be looked at an early stage with respect to e.g. theoretical consistency. Different theoretical issues may also directly affect the experimental program.

The EtaMesonNet primarily covered the experimental and theoretical activities of h physics. PrimeNet will extend this program to h' physics, to selected rare processes in h physics and to processes involving other light mesons. The h' physics is now accessible due to a substantial upgrade of the infrastructures, both with respect to higher energies and more advanced detector systems. This includes the Crystal Ball detector at MAMI-C (upgrade from 800 to 1500 MeV), KLOE2 at DAPHNE2 (higher luminosity), WASA at COSY (4p detector) and Crystal Barrel/TAPS at ELSA (improved detector performance and higher luminosity). These upgrades will enable a viable experimental program on new precision studies of meson physics and thus provide a new experimental base for advances in our understanding of low-energy QCD.

A second objective of PrimeNet is to strive for joint and well-targeted goals in the theoretical approach towards a better understanding of phenomena in low-energy QCD. Several European theory groups are engaged in problems relevant to the experimental scientific program. A collaboration among these theory groups, based on the input from experimentalists, is vital to guide the future experimental efforts on the most relevant physics problems.

The h-h' system offers an excellent opportunity to study symmetries and their violation in low-energy QCD. The simultaneous treatment of both the h and the h' imposes tighter constraints on theoretical approaches than just the h. The present plan to move into the h' sector is therefore highly motivated. There are many examples of the richness of the η-η'system to study symmetries and symmetry-breaking patterns in QCD. One example are the hadronic isospin-violating decays h,h' ® 3p, which primarily occur due to the light quark mass difference. In fact, a comparison of the decay widths with predictions of Chiral Perturbation Theory (CPHT) combined with a dispersion theoretical framework is currently considered to be the most precise extraction of the quark mass difference m_u − m_d. There are inconsistencies between theory and experiments here that will be addressed within PimeNet and an urgent experimental goal for all facilities in the network is to improve the precision measurements of the decay widths and Dalitz plots for h,h' ® 3p. One may also gain insight into the gluonic degrees of freedom in low-energy QCD via improved experimental information on the h-h' mixing.

The quark mass difference also enters in the isospin-breaking corrections for processes like the semileptonic decays of charged and neutral kaons that have been measured by KLOE. They constitute a powerful independent crosscheck on the value of the light quark mass difference. Results from CPHT  are in rather poor agreement with the experimental value, however, and more precise experimental measurements on relevant decays for both the kaon and the h (h'), as well as further theoretical work are needed. This is an effort that can be coordinated within PrimeNet.

Most of the data necessary for the investigations mentioned above also provide important and new information on the interaction of h and h' mesons with nucleons and nuclei. A thorough theoretical analysis of those will provide insights into the nature and dynamics of selected resonances, such as the S₁₁(1535) in the h channel, as well as into the existence of possible new states of matter like h-mesic nuclei heavily discussed in recent years. The necessary tools for the former, like coupled-channel analyses, will be developed and improved by various institutions in the network.

The establishment of the PrimeNet constitutes a new channel for communication and coordination between physicists involved in the experimental programs at COSY, DAPHNE, ELSA and MAMI, as well as between theorists at different universities. The tasks are listed below and the role of the partners are given in Table 1.

Task 1: A coordination of the experimental programs at these facilities. In particular, experimental projects will be planned and optimized by utilizing the variety of capabilities of the facilities including their detector systems.

Task 2: Evaluation of experimental techniques as well as the tools for data analysis and simulations. Assessment of the experimental uncertainties in all experimental data from the detectors Crystal Ball (MAMI), Crystal Barrel (ELSA), KLOE2 (DAPHNE2) and WASA (COSY).

Task 3: Establishment of a common database for all experimental results.

There will be a close interaction between the PrimeNet experimentalists and theoreticians in the theory tasks below.

Task 4: Development of theoretical models establishing the links between different data and their relationship to basic concepts of hadron physics. Extraction of information from the data concerning properties of resonances, chiral dynamics and the nature of some resonances as well as different light mesons. A coordination of the theoretical model developments.

Task 5: Establishing the interaction of the h and h’ with nucleons and nuclei and the possibility to have h bound states in nuclei. The interaction between other light mesons and nucleons should also be considered.

Task 6: Extension of the techniques of chiral perturbation theory and chiral Lagrangians from a thorough investigation of the h decay modes.

Task 7: Two main workshops involving all participants in the network.

Table 1 - Tasks engaging the different partners together with task leaders.

The nature of the networking activity is such that the deliverables sometimes cannot be strictly scheduled in specific time frames. For example, proposals for experiments are submitted on a regular basis but their content most often depend on the outcome of a previous experiment. Publishing is a continuous process. The tasks within the PrimeNet networking activity are continuous activities during the contract period. The only task with clearly specified deliverables in time is the organization of two workshops, taking place during the second and third year, respectively. The establishment of the database will also take place at a fixed date and will be continuously updated afterwards.

The European research infrastructures COSY, DAPHNE, ELSA and MAMI provide unique opportunities for studies of meson physics in the low-energy QCD regime, involving rare decays, nucleon resonances and mesonic degrees of freedom in nucleon-nucleon collisions. An intensified collaboration and the exchange of people and ideas between these facilities will lead to a better and more efficient utilization of the infrastructures. This will create a coherent and vigorous working scheme to solve the most relevant problems in this subfield of hadron physics. This will be done in close collaboration with the European theorists that are active in the field and will lead to a better planning for future projects, adding to the European research potential. Therefore, the proposed network will bring around an increased distribution of knowledge, of particular value for young researchers.

The participants in PrimeNet will benefit greatly from this network by becoming a coherent body of physicists focused on common goals in Meson Physics in Low-Energy QCD. The synergy effects from this network will be significant. Many of the institutions in PrimeNet have an active interest in the future hadron facility FAIR in Darmstadt. PrimeNet will therefore provide added value to this future European facility.