Neutron Detector: INFN plans

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

2. LEAD FIBERS d=1mm x 12.15 cm 9.6 cm z 60 cm y beam Option discarded Detector Simulations A Spaghetti Calorimeter option has been extensively studied by the INFN group with Monte Carlo simulations in order to determine: Neutron detection efficiency TOF resolution(for n- separation in the momentum range of interest) 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 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: Too efficient for  Energy loss localized in few fibers  limitation for signal read-out

3. 1 event @ L=1033cm-2s-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 0 0,2 0,4 0,5 0,6 0,7 0,8  We can handle it Background Simulations_1 Simulation of the background were done with gemc • Results: • The background consists of photons • The overall rate is 2 GHz at luminosity of 1035 • The maximum rate on a single paddle is 22 MHz (1.5 for Edep>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 - 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 All event rate • First estimate of hadronic background based onclasDISevent generator(pythia) • Background events that could mimic a DVCS event are defined as: • Q2>1 GeV2 • W>2 GeV • one energetic photon (Eg>1 GeV) in forward direction • one photon in the central detector • MM(eg) < 1.1 GeV • Estimated rate at full luminosity (1035 cm-2 s-1) • ~ 5 Hz (with one photon in CD) eg 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 • 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. Fermilab estruded scintillator SiPM SiPM Spread of these quantities is a measurement of the timing resolution Timing Tests Cosmic ray PMT1 PMT2 X1 PMT3 PMT4 X3 PMT5 PMT6 X5 t1=t0+x/v+c1 t2=t0+(L-x)/v+c2 (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

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