The first aim of this JRA is to contribute to the R&D of a series of new detectors to be installed at 1/the COMPASS and 2/the CLAS12 facilities. Consequently, the objectives of this JRA are:

  • study of two new recoil detectors and an upgraded calorimeter for COMPASS (“project 1”)
  • study of a new cylindrical tracker, a recoil neutron detector and a forward calorimeter/tagger for CLAS12 (“project 2”).

The second aim of this JRA consists of:

  • development of new methods and techniques for the analysis and interpretation of all available and upcoming data on hard exclusive reaction ("project 3").

Description of work and role of partners


The study of exclusive reactions like DVCS and DVMP is one major part of the COMPASS-II program in order to investigate nucleon structure through GPDs. In order to exploit the 200 GeV high energy polarized muon beam from the CERN SPS, a series of extensions of the existing COMPASS spectrometer are required: a time-of-flight based recoil proton detector (RPD) surrounding a long 2.5 m hydrogen target to ensure the exclusivity of the reactions, an extension of the calorimetry with ECAL0, and a recoil proton detector (RPD-Pol) coupled with a transversely polarised target for a future extension of this program.


1. Development for silicon-based multi-pixel photon detectors for RPD and ECAL0: It is necessary to detect the recoil hadrons in order to ensure the exclusivity of the DVCS and DVMP processes. This is done by installing a recoil detector, based on the time-of-flight technique. Here, it is envisaged to do the time measurement with silicon-based multi-pixel photon detectors. Also, for photon detection, the new ECAL0 will be equipped with such detectors. They are very compact and cost-effective photo-detectors developed for experimental physics research as well as for medical imaging applications. Two classes of modules are of interest for our applications.
The relevant characteristics for time-of-flight are time resolution, rate capabilities and photon conversion efficiency while for calorimetry they are high density of pixels, single pixel recovery time, stability and linearity of the gain. The Hamamatsu S10362-33 MPPC module with an area of 3 × 3 mm2 and a density of 400 pixels per mm2 corresponds to the first class and the newly developed Zecotek MAPD-3A model with an area of 3 × 3 mm2 and a density of 15000 pixels per mm2 to the second class.

  1. We propose to compare the timing resolution obtained with MPPC to the one obtained with traditional photomultiplier tubes coupled with long light guides foreseen for the Recoil Proton Detector (RPD) (already designed in the previous HardEx proposal). The MPPC solution has the advantage to make less amount of material in the RPD acceptance. We project also to design a prototype for a new pre-amplifier and front-end electronics compatible with the COMPASS readout.
  2. We propose to study the gain of MAPD and its stability in temperature as well as the single pixel recovery time (about 100 microseconds) coupled with the instant rate on the photodetector in the COMPASS environment.
  3. Development of the front-end electronics for the MAPD compatible with the COMPASS readout will also be performed. A characterizing method to test the MAPD detectors, on a large scale, for the 2500 modules needed for ECAL0, will be developed.

2. TIGER module for a trigger using the GANDALF boards: Recently we developed an intelligent 1GS/s sampling ADC, dubbed GANDALF, with an effective resolution of 10 Bit (also presented in HardEx). This module will be used for the digitization of signals from the photomultipliers of the recoil detector in the COMPASS-II experiment. GANDALF is built around the VITA-41 VME64x/VXS switched serial standard. The calculated signal amplitude from the recoil detector, the integral and the time stamp of each hit are transmitted on Multi-Gigabit serial transmission lanes of the VXS backplane to the switch module, dubbed TIGER module (Trigger Implementation for GANDALF Electronics Readout). This will allow us to form a fast trigger on the TIGER Module based on geometrical considerations of the recoil particle, its energy loss in the two recoil detector rings and correlations in the time stamps of the signals. The TIGER module, which we propose to develop within the GPDex project, will be a versatile tool and will find applications far beyond its presently foreseen application in the COMPASS experiment. The heart of the module will be a Virtex-7 FPGA chip with LVDS inputs. All data handling, calculations and extraction of data correlations will be done on this single chip.
The chip will be supported by a fast graphical processing unit (GPU) for all parallel data processing.

3. Commissioning of the COMPASS-II RPD around the liquid hydrogen target: Optic characteristics determination and calibration of all the 48 scintillators must be performed. A reliable simulation of the extended apparatus including the new recoil detector based on a detailed study of the data has to be performed.

4. R&D for a new detector RPD-Pol integrated with a transversely polarised target: Until now the highly polarised targets of large size (1.2 m long in the case of the polarised target presently used in COMPASS) were realized using a large superconducting magnet placed around the target and preventing the installation of a recoil proton detector. New developments in cryogenics and superconducting magnet technology at the Bochum and Bonn universities aim at the realization of thin superconducting coils placed inside the polarisation refrigerator of long targets which enable a continuously operated spin orientation in a chosen direction. The main risk for this challenging project is that the timelines for development could be exceeded, so an alternative back-up solution should be developed. We propose to study a more conventional solution, based on a modification of the device in order to insert a detector between the refrigerator system for the target and the refrigerator system for the polarizing magnet. We consider two types of detection: one with scintillator bars of reasonable thickness and another one with layers of scintillating fibres wound helically in two different directions around the target.
Simulations have to be carried out and a prototype has to be built to determine the achievable timing resolution and the purity of proton selection in the COMPASS environment.

5. DVCS and DVMP analysis: Many data have already been produced during several years or are still produced in 2010 at COMPASS for vector meson production on a transversely polarized target but without recoil detection to assure the exclusivity. The DVCS process is the golden channel to reach GPDs. A first experimental test has been realized in 2009 while a first complete data taking with the COMPASS-II RPD and the liquid hydrogen target should start after spring 2013. We propose to analyse all these data in a coordinate effort between all the teams involved in this framework.
Project 2: CLAS12 Central Detector and Forward Tagger (CNRS/IN2P3 IPNO, CEA-IRFU, INFN-LNF, INFN-GE, UGlasgow, UEDIN)
JLab will increase its beam energy from currently 6 GeV to 12 GeV by 2013. This requires an upgrade of the CLAS detector, called CLAS12, consisting of a forward spectrometer and a Central Detector. The European groups have a leading involvement in some of the key components necessary to accomplish the GPD program: Central Tracker (CT), Central Neutron Detector (CND) and Forward Tagger (FT). The first two were already started in the previous HardEx proposal while the FT project is new. Significant R&D has to be developed for these three sub-projects, all in close collaboration between the European groups.

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