1. Julien Bettane, Giulia Hull, Silvia Niccolai, Daria Sokhan 31/1/2012 Status and commissioning plan for the Central Neutron Detector

2. Concept of the detector Neighboring bars connected by semi- circular light guide One of the two bars acts as light guide for the other one Light comes out from the upstream side of the detector, goes through 1.5m-long light guides to reach PMTs placed out of the high-magnetic field region Position of the PMTs of the CND ~ 215 G CND: barrel of scintillators - 3 radial layers, 48 bars per layer coupled two by two with a “u-turn” light guide

3. Test bench in Orsay Two scintillators coupled to two PMTs via two 1.5m-long light guides, “u-turn” guide on the other side; two scintillators on top and bottom and two PMTs for trigger and hit position

4. Light guide PMT D PMT N Scintillator xxxxx A factor of ~2 of light loss due to the « u-turn » Hit position PMT D PMT N TRG  D)  [105, 136] ps  N)  [194, 262] ps Mesurements with cosmic rays Two scintillators coupled to two PMTs via two 1.5m-long light guides, “u-turn” guide on the other side; two scintillators on top and bottom and two PMTs for trigger and hit position Test bench in Orsay

5. PMT-N PMT-D Tests completed to chose: shape of the « u-turn » (semi-circular) scintillator (ELJEN) PMTs (R9779) wrapping (aluminum foil) magnetic shielding for the PMTs Two scintillators coupled to two PMTs via two 1.5m-long light guides, “u-turn” guide on the other side; two scintillators on top and bottom and two PMTs for trigger and hit position Test bench in Orsay

6. B    ~ -71° Angle B/PM ~ 110° Mesurements done at the LAL in Orsay (summer 2011) ~ 215 G Choosen solution: µ-metal and 5mm of mild steel Tests completed to chose: shape of the « u-turn » (semi-circular) scintillator (ELJEN) PMTs (R9779) wrapping (aluminum foil) magnetic shielding for the PMTs Two scintillators coupled to two PMTs via two 1.5m-long light guides, “u-turn” guide on the other side; two scintillators on top and bottom and two PMTs for trigger and hit position Test bench in Orsay

7. Three-layers prototype Six scintillators, wrapped Three « u-turn » light guides Six 1.5m-long bent light guides Six R9779 PMTs, with shielding Construction completed at the end of December 2011

8. Three-layers prototype Early January: tests with top-bottom trigger → reproduced performances of the one-layer setup Ongoing measurements without top-bottom trigger (three-layers coincidence)

10. CND plan What’s next for CND in 2012: This month: end of current prototype tests and JLab review (February 21) Rest of the year 2012: Optimization of electronics and DAQ chain Purchase of the rest of PMTs and scintillators Prototypes for mechanics (tests of deformations with magnet mock-up) 2013-2014: purchase of the rest of components (light guides, discriminators) checks and tests (see next slide) construction of the 24 2x3 detector segments shipping tests at JLab installation and commissioning

11. Commissioning plan: 1) in Orsay All of the component of the CND (scintillators, light guides, PMTs and magnetic shieldings) will be checked individually in Orsay by the technicians and engineers of the Detectors Group of IPN and the IPN scientists involved in CLAS12 Check of the quality of the scintillator by looking for cracks or impurities. Calibration of PMTs with a light source to measure the gain as a function of applied HV. Coupling PMT with scintillator and light guide with proper wrapping and check for light leaks by looking at signal from cosmic rays with oscilloscope. Verify the functioning of voltage divider, splitter, discriminator for each channel: signal from scintillator (cosmic rays), check output with oscilloscope. SHIPPING TO JLAB: 24 boxes each containing a 2x3 segment of the detector (same as our current prototype)

12. Commissioning plan: 2) at JLab This work will be carried out by the technicians and engineers of the Detectors Group of IPN and the IPN scientists involved in CLAS12 Tentative plan: test of functioning of each ADC and TDC channel using one detector segment in cosmic rays (need test room for this) Installation in the CD by inserting one 2x3 segment at a time Check quality of PMT signals in the magnetic field of the solenoid (cosmics)

13. Calibration procedures Without beam: TDC calibration with pulser run ADC pedestal run With cosmic rays: Time resolution measurements With beam: Noise studies at various beam currents Ordinary data taking for calibration purposes (energy loss, effective velocity, etc.) With 11 GeV beam and proton target: Measurement of neutron-detection efficiency by analyzing the ep→en  + channel

14. PMT-N PMT-D 0.2 GeV/c 0.4 GeV/c CND simulations (GEMC), digitized, were used to determine:  efficiency  PID (neutrons/photons separation)  momentum and angular resolution  definition of reconstruction algorithms  background studies Measured values of  (TOF) and light loss due to the “u-turn” are implemented in the simulation Software status: simulations Efficiency ~ 8-9% For a thrshold of 3 MeV, TOF<8 ns and p n = 0.2 - 1 GeV/c

15. Software status: simulations β Misidentification n/  for p n <1 GeV/c Error bars on β represent 3 σ  p/p ~ 4-10%  ~ 2-4° In the hypothesis of Equal rates of n and 

16. Software status: reconstruction Reconstruction software for cosmic tests – done. Input: ROOT tree with ADC and TDC values from each PMT. Output: ROOT file with energy deposited, time of hit, z co-ordinate of hit (along length of paddle), and paddle in which hit took place. Histograms for overall monitoring and trees for individual event data. Cosmic ray test is self-triggered : PMT output from each pair of coupled paddles is time-averaged with a Mean Timer (MT). Output of the three MTs in a segment (one for each layer) is passed to a coincidence unit. If a time coincidence is observed, it sends a common start signal to all TDCs and opens up a gate for ADCs. Reconstruction procedure: First choose struck paddle in each layer based on lowest TDC value for the coupled pair. Based on TDC values, reconstruct hit position and discard event if outside the paddle length. Discard events where no coincidence in hit position between the three layers, allowing for trajectories at an angle. Calculate time of hit on basis of TDC values and hit position. Calculate energy deposited on basis of hit position and ADC values. Determine energy loss through optical coupling of lightguides, etc, by calibrating to known energy peak of cosmic ray (~ 2 MeV / cm). Reconstruction for neutrons with external trigger – in progress. ROOT software based on reconstruction of GEMC-simulated TCD and ADC values. For neutrons / photons: multiple hits in a single paddle for each triggered event possible. Reconstruction software (in ROOT) for GEMC simulation of CND - done