1. Tracker Neutron Detector: INFN plans CLAS12 Central Detector Meeting - Saclay 2-3 December 2009 Patrizia Rossi for the INFN groups: Genova, Laboratori Nazionali di Frascati, Roma Tor Vergata  Simulations  Timing Tests

2. LEAD FIBERS d=1mm Detector Simulations A Spaghetti Calorimeter option has been extensively studied by the INFN group with Monte Carlo simulations in order to determine: 1)Neutron detection efficiency 2)TOF resolution (for n-  separation in the momentum range of interest) 3)Angular resolution ( for the definition of the neutron direction) Simulation done with FLUKA (KLOE) Parallelepiped shape (12.15 x 60 x 9.6) cm Beam  to the longer side, and to fibers 20 cells (5 x 4), each 2.43 x 2.4 cm (x,z) each cell contains 360 fibers beam 60 cm y z x 9.6 cm 12.15 cm Compared to Scintillator Barrel : Neutron Efficiency: spaghetti calorimeter ~30-40% more efficient Angular resolution: the two options give comparable results TOF resolution: the two options give comparable results But spaghetti calorimeter: 1)Too efficient for  2)Energy loss localized in few fibers  limitation for signal read-out Option discarded

3. Background Simulations_1 ELECTROMAGNETIC BACKGROUND We want to understand: the actual rates seen by the CND, their energy distribution etc. the probability of such background to be reconstructed as a “good neutron” event 1 event @ L=10 33 cm -2 s -1 Results: The background consists of photons The overall rate is  2 GHz at luminosity of 10 35 The maximum rate on a single paddle is 22 MHz (1.5 for E dep >100KeV) This background can be reconstructed as a neutron: - using a 5 MeV energy threshold the resulting rate is few KHz - the  of this “fake”neutrons is <0.1-0.2 Simulation of the background were done with gemc We can handle it 0 0,2 0,4 0,5 0,6 0,7 0,8  - the actual contamination depends on the hadronic rate in the forward part of CLAS12 (@ 1 KHz the rate of fake events is 0.4 Hz)

4. Background Simulations_2 PHYSICS BACKGROUND First estimate of hadronic background based on clasDIS event generator (pythia) Background events that could mimic a DVCS event are defined as:  Q 2 >1 GeV 2  W>2 GeV  one energetic photon (E  >1 GeV) in forward direction  one photon in the central detector  MM (e  ) < 1.1 GeV Estimated rate at full luminosity (10 35 cm -2 s -1 ) ~ 5 Hz (with one photon in CD) All event rate e  missing mass We need to finalize nDVCS event generator to estimate neutron rates

5. Timing Tests  TOF resolution required to separate  from n for neutron momentums up 1 GeV/c ~100-120 ps  Constraints on photodetectors: - Light collection in high magnetic field - Limited space for signal read-out No space for light guides due to the presence of the CTOF light guides Timing tests wil be performed in 2010 by the INFN groups using different setup

6. Timing Tests Scintillator typeReadout BC-408PMT H2431-50 BC-408SiPM 1x1 mm 2 / 3x3 mm 2 /matrix 12x12 Fermilab estruded scintillators +1 WLS SiPM 1x1 mm 2 / 3x3 mm 2 /matrix 12x12 Fermilab estruded scintillators > 1 WLS SiPM 1x1 mm 2 / 3x3 mm 2 /matrix 12x12  BC-408: =380 cm ; decay constant=2.1 ns  PMT H2431-50: rise time = 0.7 ns; transit time spread = 0.37 ns  Acquisition: Full electronic chain  discriminator+TDC Electronics, redout, scintillators in Genova

7. Estruded scintillator + WLS

8. Redout

9. Timing Tests PMT1PMT2 PMT3PMT4 PMT6PMT5 Cosmic ray X1 X3 X5 (t1-t2)=(2x1-L)/v+c1-c2 (t1+t2)=2*t01+L/v+c1+c2 (t3-t4)=(2x3-L)/v+c3-c4 (t3+t4)=2*t03+L/v+c3+c4 (t5-t6)=(2x5-L)/v+c5-c6 (t5+t6)=2*t05+L/v+c5+c6 taking into account that: (x1+x5)=2*x3 or (t01+t05)=2*t03 (t1-t2)+(t5-t6)-2(t3-t4)=costant(t1+t2)+(t5+t6)-2(t3+t4)=costante t1=t0+x/v+c1 t2=t0+(L-x)/v+c2 Spread of these quantities is a measurement of the timing resolution SiPM Fermilab estruded scintillator

10. Conclusions  INFN groups of Genova, Laboratori di Frascati, Roma Tor Vergata are involved in the development of the central neutron detector  Simulations have been done to determine its characteristics (neutron detection efficiency, angular resolution, timing resolution..) as well as the e.m. and physics background  Timing tests are planned for 2010 using different scintillators and redout systems