1. CLAS12 activity at IPNO D2I: Design, realization and test of the Central Neutron Detector J. Bettane, J.L. Cercus, B. Genolini, G. Hull, M. Imre, A. Maroni, T. Nguyen Trung, J. Peyré, J. Pouthas

2.  Introduction: the CND for CLAS12  Design of the detector  Test on the prototypes  Detector status Summary - Outline Pag. 1

3. Introduction: from CLAS to CLAS12 Pag. 2 Continuous Electron Beam Accelerator Facility Hall B Hall A Hall C E max = 6 GeV E max = 12 GeV Jefferson Laboratory Newport News, USA CLAS12: Study of the proton and neutron structure via the deeply virtual Compton scattering

4. Introduction: The Issue Pag. 3  Limited space available  Strong magnetic field (~5T) Scintillator barrel and long light guide Neutron Detector to be added in the CLAS12 CD

5. Introduction: The proposed solution Pag. 4 Really challenging to collect the light on one side of the scintillator Use a “U turn” light guide to collect the light at the same side 24 elements of 6 scintillators each: 144 scintillator bars and 144 PMTs

6. Definition of the prototype Pag. 5 TEST !!! ShieldPMTWrapScintillatorGlueU-turn - 2.5 mm- R2083- Mylar Al- BC408- M-BOND 200- Triangular - 5 mm- 9954A- VM2000- EJ200- BC 600- Semicircular - R9779- Al foil - R10533

7. Light yield and time resolution study Pag. 6 Cosmic ray γγ We need to know the interaction point PMT BottomPMT Top POS-2 -1 0 1 2

8. Pag. 7 Magnetic field test @ LAL Average magnitude of the magnetic field at the location of the PMTs of the CND: B ~ 215 G

9. Pag. 8 Test on the prototype

10. Definition of the prototype Pag. 9 ShieldPMTWrapScintillatorGlueU-turn - 2.5 mm- R2083- Mylar Al- BC408- M-BOND 200- Triangular - 5 mm- 9954A- VM2000- EJ200- BC 600- Semicircular - R9779- Al foil - R10533 Better σt Same LY and σt, cheaper Better σt (worst LY), cheaper Good σt, cheaper “Play safe” - Optical grease - Silicone cookie - Optical glue Better mechanical properties

11. Electronic read-out 1 Pag. 10  High gain PMT to avoid the need of preamps  Active splitter from G0  Charge measurements: flash ADCs (provided by JLab) CAEN V1720 @ 250 MHz  Time measurements: 100 ps/ch TDCs (provided by JLab) Test @ position 0. TDC with 50 ps/ch, 75 ps/ch and 140 ps/ch provided same results

12. Electronic read-out 2 Pag. 11  Time measurements: CFD Best results with ENERTEC CFD G0 type Too much R&D and design needed – no pursued further 16 channels CAEN N843 Maybe usable after modification by CAEN – no pursued further 4 channels ORTEC 935 (ENERTEC equivalent) Too low density and too expensive 16 channels GAN ELEC FCC8 Results as good as with ENERTEC CFD Long term loan from Germany

13. Status of the detector construction Pag. 12  150 PMTs purchased from Hamamatsu. Calibration tests on- going  20 PMTs HV divider ready and other 130 on-going  All the scintillator purchased and delivered  μ–metal purchased and delivered (150 tubes Ø60x215 mm 3 )  Mild steel to be ordered  The light guide design will be finalized before spring 2013 and then the order will be place before summer

14. Pag. 13 Summary and future work  Final design established – and different element chosen Scintillator EJ200 + PMT R10533 + 1500 mm long light guide + Al foil wrapping + 1 mm thick μ- metal and 5 mm thick mild steel shielding + semicircular light guide at the “U turn” σ t (Dir) ~ 120 ps σ t (Ind) ~ 210 ps  The detector assembly will start in the fall 2013 Each block of 6 scintillators will be assembled and tested separately prior expedition to US  Expedition to US during summer 2014

15. The END!!!!