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Journées GDR Nucléon - Instrumentation April 8-9, 2008 – Saclay

Neutron detection with the KLOE Pb-scintillanting fiber calorimeter. A. Ferrari Fondazione CNAO (Milano) & LNF for the KLONE Group. M.Anelli, G.Battistoni, S.Bertolucci, C.Bini, P.Branchini, C.Curceanu, G.De Zorzi, A.Di Domenico, B.Di Micco, A.F., S.Fiore, P.Gauzzi,

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Journées GDR Nucléon - Instrumentation April 8-9, 2008 – Saclay

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  1. Neutron detection with the KLOE Pb-scintillanting fiber calorimeter A. Ferrari Fondazione CNAO (Milano) & LNF for the KLONE Group M.Anelli, G.Battistoni, S.Bertolucci, C.Bini, P.Branchini, C.Curceanu, G.De Zorzi, A.Di Domenico, B.Di Micco, A.F., S.Fiore, P.Gauzzi, S.Giovannella,F.Happacher, M.Iliescu, M.Martini, S.Miscetti, F.Nguyen, A.Passeri, A.Prokofiev, P.Sala, B.Sciascia, F.Sirghi Journées GDR Nucléon - Instrumentation April 8-9, 2008 – Saclay

  2. Lead 1.2 mm 1.0 mm 1.35 mm The KLOE calorimeter Pb - scintillating fiber sampling calorimeter of the KLOE experiment at DANE (LNF): Active material: • 1.0 mmdiameter scintillating fiber • (Kuraray SCSF-81, Pol.Hi.Tech 0046), lPeak~ 460 nm • Core: polystyrene, r=1.050 g/cm3, n=1.6 High sampling structure: • 200 layers of 0.5 mm grooved lead foils (95% Pb and 5% Bi). • Glue: Bicron BC-600ML, 72% epoxy resin, 28% hardener. • Lead:Fiber:Glue volume ratio = 42:48:10 Calorimeter thickness = 23 cm Total scintillator thickness ~ 10 cm Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  3. Operated from 1999 to 2006 good performance and high efficiency for electron and photon detection good capability of π//e separation Energy resolution: (KSKL; KSπ+π─ KL2π04) Time resolution: E/E=5.7%/E(GeV) t=54 ps/E(GeV)147 ps (see KLOE Collaboration, NIM A482 (2002),364) The KLOE calorimeter Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  4. Detection of neutrons of few to few hundreds of MeV is traditionally performed with organic scintillators via elastic scattering reactions (n,p) on H atoms p  efficiency scales with thickness  ~1%/cm • Preliminary estimate with KLOE data:   40%for low energy neutrons (Ekin≤ 20 MeV) confirmed by KLOE MC (expected:  10%) • n are important for the DAFNE-2 program @ LNF : - Measurement of the neutron e.m. form factors in the time-like region (DANTE) - Search for deeply bounded kaonic nuclei (AMADEUS) Why neutrons at KLOE ? • Use of high-Z materials enhances the neutron efficiency  seeNIMA 297 (1990) 250, NIM A 338 (1994) 534 • a Monte Carlo study has been performed with the FLUKA code • experimental tests have been carried out with the neutron beam of the The Svedberg Laboratory of Uppsala (October 2006 and June 2007) Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  5. LEAD base module GLUE FIBERS replicas 200 layers The FLUKA simulation - part (I) The Pb-SciFi structure • Using the FLUKA tool LATTICE the fiber structure of the whole calorimeter module has been designed. • In the base module the calorimeter is simulated in detail, both under the geometrical point of view and with respect to the used materials • All the compounds have been carefully simulated. - for the fibers, an average density between cladding and core has been used : ρ = 1.044 g/cm3 - glue: 72% epoxy resin C2H4O, r=1.14 g/cm3, + 28% hardener, r=0.95 g/cm3 hardenercomposition Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  6. Typical reactions on lead:n Pb x n +y+ Pbn Pbx n +y+p + residual nucleus n Pb x n +y+ 2p + residual nucleus Neutron interactions in the calorimeter Simulated neutron beam: Ekin = 180 MeV Each primary neutron has a high probability to have elastic/inelastic scattering in Pb In average, secondaries generated in inelastic interactions are 5.4per primary neutron,counting only neutrons above 19.6 MeV. In addition,secondaries created in interactions of low energy neutrons (below 19.6 MeV) are - in average –97.7particles per primary neutron. Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  7. X(cm) n4 n3 n p n2 n1 Z(cm) A typical inelastic process primary vertex En = 175.7 MeV En (p) = 126 MeV The enhancement of the efficiency appears to be due to the huge inelastic production of neutrons on the lead planes. These secondary neutrons:- are produced isotropically; - are produced with a non negligible fraction of e.m. energy and of protons, which can be detected in the nearby fibers; - have a lower energy and then a larger probability to do new interactions in the calorimeter with neutron/proton/γ production. Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  8. ( 2 cm) 5.31 m KLOE calorimeter module EKIN (MeV) The measurement of the neutron efficiency @ TSL Neutron beam • A quasi-monoenergetic neutron beam is produced in the reaction 7Li(p,n)7Be. • Proton beam energy from 180 MeV to ~ 20 MeV • Neutron energy spectrum peaked at max energy (at 180 MeV fp = 42% of neutrons in the peak) • Tail down to termal neutrons Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  9. (3) (2) (1) Experimental setup ( 1 )Old prototype of the KLOE calorimeter 60 cm long, 3 x 5 cells (4.2 x 4.2 cm2), read out at both ends by Hamamatsu/Burle PMTs ( 2 )Beam position monitor array of 7 scintillating counters, 1 cm thick. ( 3 )Reference counter NE110, 10×20 cm2, 5 cm thick A rotating frame allows for: - vertical positions (data taking with n beam) - horizontal positions (calibration with cosmic rays) Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  10. Trigger No beam extraction signal available Scintillator trigger: Side 1 – Side 2 overlap coincidence Calorimeter trigger: analog sum of the signals of the first 12 cells (4 planes out of 5)  A•B overlap coincidence Trigger signal phase locked with the RF signal (45 - 54 ns) DAQ Simplified version of the KLOE experiment DAQ system (VME standard) Max DAQ rate : 1.7 kHz - Typical run: 106 events For each configuration/energy: scans with different trigger thresholds Three data-sets: Epeak = 180 MeV -- October 2006 - two weeks Epeak = 46.5 MeV --June 2007 Epeak = 21.8 MeV -- “ Y X Z n Trigger & DAQ last plane not integrated in the acquisition system 4 days Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  11. RTRIGGER En = 180 MeV e = RNEUTRON× fLIVE× a flive Method of measurement Global efficiency measurement integrated on the full energy spectrum RNEUTRON: from beam monitor via neutron flux intensity measured by TSL. fLIVE : fraction of DAQ live time a : acceptance (assuming the beam fully contained in the calorimeter surface: a≈ 1 RTRIGGER must be corrected for a sizeable beam halo Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  12. Absolute flux of neutrons measured after the collimator 2 monitors of beam intensity (see A.Prokofiev et al., PoS (FNDA2006) 016): Ionization Chamber Monitor (7 cm ): online monitor, not position sensitive Thin-Film Breakdown Counter (1 cm ): offline monitor; used to calibrate the ICM by measuring the neutron flux at the collimator exit Rate(n) = Rate(ICM)  K  πr2 / fp r = collimator radius (1 cm) K = calibration factor (TFBC to ICM) fp = fraction of neutrons in the peak  accuracy: 10% at higher peak energy (180 MeV) 20% at lower peak energy (20 – 50 MeV) Neutron rate Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  13. Trigger threshold calibration in MeV eq.el.en.: Scintillator calibration ADC counts Events  6 counts/mV ADC counts Thr. (mV)  source to set the energy scale in MeV: 90Sr ─ endpoint = 0.56 MeV 90Y ─ endpoint = 2.28 MeV 25 keV/ADC count Events ADC counts Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  14. Check of the method and of the beam monitor accuracy (%) - scint. En Scintillator efficiency Agrees with the “thumb rule” (1%/cm) at thresholds above 2.5 MeV el.eq.en. • Agrees with previous measurements in the same energy range after rescaling for the thickness En = 180 MeV (%)/ cm of scintillator Low energy data have large errors due to a worse accuracy of the beam monitors and a big uncertainty in the beam halo evaluation Correction factor for beam halo  0.9  0.1 Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  15. Trigger threshold calibration QtrigA 15mV thr 75mV thr MeV eq. el. en. Calorimeter calibration • From data sets taken at different thresholds, the distributions of the discriminated signals of A , B have been fit with a Fermi-Dirac function to evaluate:  cutoff in trigger energy  width of the used energy in MeV • Same exercise with the sum of the cluster energies side A and B Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  16. (ex.)Fermi-Dirac fits for the sum of the cluster energy side B MeV eq. el. en. Thr. (mV) Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  17. n Energy spectrum from TOF Energy spectrum can be reconstructed from TOF • Rephasing is needed, since the trigger is phase locked with the RF (45 ns period) • From TOF   spectrum of the neutrons • Assuming the neutron mass  kinetic energy spectrum Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  18. Li target 5.5° n Proton beam At the Li-target At the calorimeter Ekin(MeV) Y(cm) Shielding (concrete and steel) 7Li Target Calorimeter Z(cm) The simulation of the beam line • The beam line has been simulated starting from the neutrons out of the Litium target Gaussian angular distribution (Journal of Nuclear Science and Technology, supplement 2(2002), 112-115) At the entrance of the beam monitor Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  19. Neutron fluence X(cm) F (E) beam Z(cm) Ekin (MeV) dN/dΩ (n sr-1 per prim) cos(θ) Neutron yield inside the calorimeter Energy distribution 1° plane 4° plane Isotropic angular distributions from inelastic scattering Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  20. Proton fluence X(cm) Protons are mainly concentrated along the direction of the primary beam beam Z(cm) Energy distribution F (E) dN/dΩ (prot sr-1 per prim) cos(θ) Ekin (MeV) Proton yield inside the calorimeter Angular distribution Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  21. A key point: the high sampling frequency proton lateral profile neutron lateral profile The energy deposits of the ionizing particles (protons and excited nuclei) are distributed mainly in the nearby fibers:the high sampling frequency is crucial in optimizing the calorimeter Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  22. E(tot)(ril) = Σ En(ril)+ Σ Ep(ril) + ΣEem(ril) + ΣEresnuc(ril) E(ril)/E(tot)(ril) Particle contribution to the signal Protons Neutrons E.m. energy Others Ekin (GeV) Particle contribution to the energy response Particle contribution to the energy released in the fibers: To evaluate the particle contribution to the energy response, we have to take into account: - the contribution of the highly ionizing particles: protons and excited nuclei; - the contribution of the e.m. energy The neutron contribution is not to take into account in general, because the neutrons transfer energy to the nuclei of the fibers basically as invisible energy. For this reasons, we evaluate the Monte Carlo efficiency without taking into account the neutron energy deposits Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  23. Data reconstructed clusters with a single fired cell show a ratio lateral/central fired cellshigherthen in MC • TOF distributions of data have been fit with: - a linear parametrization for the background; - the MC shape for the signal for each single calorimeter plane and for each trigger threshold The halo fraction has been measured for each trigger threshold Background subtraction: the beam halo evaluation • Lateral cells show also a flatter time distribution compared with MC Background due to low energy neutrons forming a halo around the beam core Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  24. collected charge (MeV eq.el.en.) Data MC (corr. for the halo contr.) Data composition Total Signal Halo Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  25. Very high efficiency at low threshold Agreement between high and low energy measurements Correct. factor for beam halo at low energies:  0.80.1 Calorimeter efficiency: results Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  26. Data - Low thresh. (%) En (MeV) Preliminary Data/MC comparison MC • No cut in released energy • No simulation of the trigger threshold  Upper limit on  Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  27. The first measurement of the detection efficiency for neutrons of 20 - 180 MeV of a high sampling Pb-sci.fi. calorimeter has been performed at the The Svedberg Laboratory in Uppsala The cross-check measurement of the n efficiency of a NE110 scintillator agrees with published results in the same energy range. The calorimeter efficiency, integrated over the whole neutron energy spectrum, ranges between 32-50 % at the lowest trigger threshold. Full simulation with FLUKA is in progress. Further test foreseen for spring 2008 at TSL Conclusions Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  28. Spares Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  29. Calorimeter details cladding TR= 21 TR= 21 36 core 1 mm diameter scintillating fiber (Kuraray SCSF-81, Pol.Hi.Tech 0046), emitting in the blue-green region, lPeak<460nm. 0.5 mm lead grooved layers (95% Pb and 5% Bi). Glue: Bicron BC-600ML, 72% epoxy resin, 28% hardener. Core: polystyrene, r=1.050 g/cm3, n=1.6 Cladding: PMMA, n=1.49 Only 3% of produced photons are trapped in the fiber. But: small transit time spread due to uni-modal propagation at 21, small attenuation (l=4-5m), optical contact with glue (nGLUEnCORE) remove cladding light 1.2 mm 1.0 mm 1.35 mm Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  30. 40 ns Beam time structure 2.4 ms 4.2 ms  5 ns FWHM 41 ns Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  31. TSL beam experts measured a sizeable beam halo at low peak energy (21.8 and 46.5 MeV): TFBC scan of the area near the collimator  integrated flux over the ICM area  5% of the “core” flux (with large uncertainty)  halo shape also measured Confirmed by our background counters Our calorimeter is larger than the projection of ICM area By integrating over the calorimeter we obtain an estimate of the halo contribution to the trigger rate of (20  10)% Only 10% on the reference scintillator due to the smaller area Beam halo Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  32. Neutron spectrum from ToF - 1 a) b) c) For the 3 cells of first calorimeter plane: • Correct raw spectra (a) for T0 (b) and convert into ns (c) • TDC spectra of single cell show a 41 ns time structure (from phase locking). • Has to be corrected for wrong clock association (d). • At 5 m from target, rephasing needed for n kinetic energies less than 50 MeV. d) n Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  33. Neutron spectrum from ToF - 2 e) f) EKIN (MeV) • From ToF spectrum obtain velocity spectrum (e). • Assuming neutron mass determine kinetic energy spectrum (f). Compare with the input theoretical n spectrum. The “per cell” exercise has to be repeated for the whole calorimeter after the cluster procedure definition. Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  34. Clustering For each side: group adjacent cells in “side cluster”. For event with at least a “side cluster” on each side, compute “event cluster” information. Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  35. Side A: x and z coordinates Weighed energy average on cell: Z 0 0 X Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  36. Side A: time and energy Weighed energy average on cell: Sum of cell energies: Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  37. Cluster: coordinates Y 0 n Z X 0 Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  38. Cluster: time and energy Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  39. Signal development time - 1 Time difference between a cluster in one of the first four plans (trigger) and one in the fifth plane. As a reference, KLOE expected time resolution for 5-20 MeV photons is 0.8-0.3 ns. n ns Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  40. Signal development time - 2 Difference between the cluster time (computed as energy weighed average) and the time of the cell making up the cluster itself. As a reference, KLOE expected time resolution for 5-20 MeV photons is 0.8-0.3 ns. ns ns Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  41. The readout simulation Fluka gives energy deposits in the fiber. The light is propagated ‘by hand’ at the end of the fiber taking into account the attenuation. The energy read-out has been simulated by including: • the generation of photoelectrons • the constant fraction distribution • the discriminator threshold. • No trigger simulation is included at the moment. The simulation of the Birks effect The energy deposits are computed in Fluka taking into account the Birks effect, that is the saturation of the light output of a scintillating materialwhen the energy release is high, due to the quenching interactions between the excited molecules along the path of incident particles: In literature and in GEANT: dL/dx = k dE/dx / [ 1 + c1 dE/dx + c2 (dE/dx)2] c1 = 0.013 c2 = 9.6×10-6 Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  42. Simulation of the energy read-out fiber (active material) The light is propagated by hand at the end of the fiber using the parametrization: energy deposit given by FLUKA Ea,b(fib) = E(dep) ·[0.35 e-x(a,b)/50 + (1- 0.35) e–x(a,b)/430 ] Kuraray Attenuation Ea,b(fib) = E(dep) ·[0.35 e-x(a,b)/50 + (1- 0.35) e–x(a,b)/330 ] Politech ta,b(fib) = t(dep) + X(a,b) /17.09 The number of photoelectrons generated by the light collected by each fiber is evaluated: t(a,b)(p.e.) = t(a,b)(fib)+ tscin+ 1ns(smearing) na,b(pe-fib) =E(fib)(MeV)(a,b) · 25 na,b(pe-cell) = ∑ t(pe)<300ns generated according to a Poisson distribution the constant fraction distribution is simulated (15% fr., 10 ns t.w.) to obtain the time Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

  43. The efficiency correction for the halo Journées GDR Nucléon - Instrumentation April 8-9, 2008 - Saclay

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