The JRA 3D-Mom will join the proposed R&D for innovative instrumentation of key experiments at the future JLab12 facility with the expertise and highly collaborative work of European scientists working in the field of TMDs.
The joint research activities of the participants pursue three main objectives involving both experimentalists and theoreticians:
• design studies, test measurements and prototype construction for the CLAS12 RICH detector;
• basic studies of fundamental field theoretical properties of TMDs within the framework of QCD and model calculations of TMDs;
• measurement of spin-dependent and -independent azimuthal modulations at various facilities and the global
analysis of all available data for the extraction of TMDs.

 Description of work and role of partners

In order to ensure a highly efficient collaboration among participants, four experimental and four theoretical teams have been formed (as shown in the following list) which join their research efforts for the envisaged tasks.
Exp1 - Ferrara, Frascati, Genova-Exp
Exp2 - Bari, Glasgow, Roma
Exp3 - Torino-Exp, Trieste
Exp4 - Freiburg, Saclay
Th1 - Amsterdam, Dublin, Groningen, London, Sofia
Th2 - Desy, Regensburg, Tuebingen
Th3 - Bilbao, Cagliari, Torino-Th, ECT*-Trento
Th4 - Alessandria, Como, Genova-Th, Pavia, Perugia

Task 1. CLAS12 RICH detector (Exp-1, Exp-2)
JLab will increase its beam energy from currently 6 GeV to 12 GeV by 2013. The current design for the upgraded CLAS detector, called CLAS12, does not allow for pion, kaon and proton separation over the full momentum range of 1 GeV to 10 GeV which is crucial for using SIDIS measurements as a powerful tool for flavour separation in the extraction of parton distribution and fragmentation functions. The CLAS12 particle identification capabilities could be significantly enhanced by replacing the existing low threshold Cherenkov detector with a RICH detector without any impact on the baseline design of CLAS12. The design and construction of this detector is lead and to a large extent carried by European groups and will maintain the leading role European groups are playing in SIDIS studies with CLAS12.

  • Innovative new technologies both for the radiator material and photo-detection will be applied for the RICH in order to cope with the geometrical restrictions for integration in the CLAS12 spectrometer and with the operation in the high intensity electron beam and in presence of magnetic fields. This requires intensive R&D before final design of the RICH detector under stringent time constraints.
  • Radiator: test measurements of newly available aerogel radiators with variable refraction index; comparative studies of superposition of aerogel layers with increasing refraction index and monolithic aerogel tiles with refractive index variable in steps or with a gradient; development of the final radiator design.
  • Photo-detector: study of the reply of SiPMs to the Cherenkov light produced in the chosen aerogel type; test measurements for comparative studies of the characteristics of SiPM; final design for the photo detection regarding an optimized performance to cost ratio; development of a fast readout system.
  • Construction of a RICH prototype of final design and test measurements of the RICH performance.
  • Technical Design Report.


Task 2. Study of fundamental properties of TMDs (Th-1, Th-2, Th-3, Th-4)Studying the properties of TMDs and modeling them is indispensable for an interpretation of the observables
and an extraction of information about the hadron structure in terms of spin degrees of freedom in combination with the role of orbital motion of partons. The fundamental working ground for global data analysis needs to be provided, especially when combining data from different processes and measured at different scales, and new observables and experiments need to be suggested for making progress in the field.
The experimental extraction of the TMDs for the neutron will require a more refined theoretical study of the nuclear effects in the He-3 target. Moreover, improved TMD models will be essential to reduce the freedom in TMD parameterizations and establish a connection with Generalized Parton Distributions (GPDs). TMDs and GPDs will be studied in a unified framework as limiting cases of Wigner distributions which provide a genuine multi-dimensional (in momentum and impact parameter space) image of hadrons.

  • Study of the universality (process dependence) of TMDs.
  • Study of factorization for observables in hadron-hadron scattering.
  • Model and lattice calculations of TMDs and guidance for their parameterization.
  • Study of the nuclear effects in the extraction of neutron TMDs.
  • Model calculations of the Wigner functions and relation between TMDs and GPDs.
  • Task 3. Global analysis of TMDs and preparation for new experiments (Exp-1, Exp-3, Exp-4, Th-1, Th-2, Th-3, Th-4):

An advanced stage of data analysis for various different TMD observables has been reached at the involved experiments from CERN, DESY, JLab, KEK and RHIC that needs to be disseminated among the groups and pooled for access by the whole community. First milestone results on TMDs were obtained from combined fits to SIDIS and electron-positron annihilation data. These results were then used to predict new measurements and to also describe observables in hadron-hadron scattering. The project aims at setting a new standard in TMD global fits by including their evolution properties and a more advanced treatment of uncertainties. In parallel, new Monte Carlo tools based on TMDs will be developed and employed to tune existing parameterizations of TMDs. There is very valuable expertise within the teams from global NLO fits for polarized Parton Distribution Functions (PDFs) where data from inclusive DIS, SIDIS and hadron-hadron scattering were combined. At variance with standard PDF studies, the inclusion of hadron-hadron scattering data requires further investigations of TMD factorization in such processes.
The scientists joined in this project provide expertise of great importance for the preparation of the science case for a dedicated electron-ion (EIC) or electron-nucleon (ENC) collider which is under active consideration by the hadron physics community. They will participate in the design studies for the various different options of such a new facility.

  • Finalization of analysis of SIDIS data from HERMES and from CLAS with 6 GeV electron beam and publication of all TMD related observables; data preservation for future reanalysis.
  • Analysis of existing and near future SIDIS data taken at COMPASS with longitudinally and transversely polarized targets; dissemination of the results; preparation for Drell-Yan measurements at COMPASS with a pion beam.
  • Pooling of analysis techniques for TMD observables and release and maintenance of an analysis data base.
  • Development of a dedicated Monte Carlo event generator based on TMDs.
  • Global analysis of existing and near future world data for the extractions of TMDs.
  • Development of a framework for the inclusion of hadron-hadron scattering data in global TMD fits.
  • Study of di-hadron fragmentation functions as probes of TMD PDF.
  • Release and maintenance of a public data base for TMDs.
  • Feasibility studies, simulations and predictions for TMD measurements at EIC/ENC; contributions to the reports on the science case of an EIC/ENC; contributions to design studies for the different options at FAIR, JLab or RHIC.

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