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Simulations of signal and background for an Nnbar Experiment with Free Neutrons

Simulations of signal and background for an Nnbar Experiment with Free Neutrons. A. R. Young, D. G. Phillips II, and R. W. Pattie, Jr. North Carolina State University Triangle Universities Nuclear Laboratory on behalf of the NNBarX Collaboration. Overview.

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Simulations of signal and background for an Nnbar Experiment with Free Neutrons

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  1. Simulations of signal and background for an Nnbar Experiment with Free Neutrons • A. R. Young, D. G. Phillips II, and R. W. Pattie, Jr. • North Carolina State University • Triangle Universities Nuclear Laboratory • on behalf of the NNBarX Collaboration

  2. Overview • Detector Strategy Review and General Detector Specifications • Antineutron Annhilation Events • A Proto-Detector for Neutron-Antineutron Oscillations • MC Acceptance Results • Background Analysis and Challenges 4/26/13 A. R. Young et al., 2013 Intensity Frontier Workshop

  3. ILL Layout • Free neutron n-nbar search experiment in 1989 - 1991 at ILL [1]: measured PNNBar < 1.606 x 10-18 sensitivity: Nn∙t2 = 1.5 x 109 s2/s (90% CL) 4/26/13 A. R. Young et al., 2013 Intensity Frontier Workshop

  4. ILL Detector Configuration • Effective run time = 2.4x107 s, Nevents = 6.8x107 • n-nbar detection efficiency (∆Ω/4π = 0.94): 52% ± 2% • No background & no candidate events after analysis. Ethresh> ~800 MeV, at least 1 charged particle track, at least 2 tracks which reconstruct as emerging from target 5 m 4/26/13 A. R. Young et al., 2013 Intensity Frontier Workshop

  5. ILL Detector Configuration ILL Target [2,3]: 130 μm thick. ILL Scintillator Counters [4,5]: ILL Vertex Detector [6]: 10 LST planes operated at 4.6 kV Vertex = ±4 cm; ILL Calorimeter: 12 LST planes interleaved w/Pb & Al plates. ILL Cosmic-Ray Veto (CRV) Cosmic-Ray Veto 6.0x104 electronics chnls. 4/26/13 A. R. Young et al., 2013 Intensity Frontier Workshop

  6. ILL Experiment: Backgrounds • Backgrounds which scale with source strength or CN current • γ’s & fast n’s from reactor: • γ’s from n capture in propagation region and target (not shieldable contribution due to abs. on target of incident beam) Eliminated w/ bent 58Ni guides in shielding crypt before propagation region • Capture on beamline surfaces: • Complete containment of n-beam in propagation region (2% losses) • 8 rings of 10B-enr. glass in drift vessel (absorb vertically falling n’s), 6LiF beam dump • Residual beamline and target captures→”stochastic” background • Drives trigger criterion: 400 MeV threshold, one charged track, two total tracks (timing signal) 4/26/13 A. R. Young et al., 2013 Intensity Frontier Workshop

  7. ILL Experiment: Backgrounds • Backgrounds which are independent of source or CN-beam time structure: • cosmic-rays • activation • Veto layer • Timing layers (veto “inward-going”) • Trigger and track reconstruction: must reconstruct to target and have at least one other calorimeter track 4/26/13 A. R. Young et al., 2013 Intensity Frontier Workshop

  8. NNBar at ESS • Adapt detector to pulsed cold neutron source driven by 5 MW spallation target with very large increase in flux due to concentrating optics • Goal: 0 background events, ε > .5 for annihilation events • Background Challenges: • High energy n/p backgrounds present during proton beam • Larger CN fluxes and optics will increase capture gamma rates • Fast n’s (0-10 MeV) present due to beta-delayed n’s • Larger detector volume will increase cosmic and capture gamma rates • Must be sufficient for longer running periods (1y for ILL→3y+) 4/26/13 A. R. Young et al., 2013 Intensity Frontier Workshop

  9. Overall Simulation StrategyFirst Steps • Scale successful ILL geometry to larger beam and target size required for next generation experiment • Develop generalized geometry with modern degree of granularity using GEANT framework (perhaps overkill here to begin with) • Evaluate state-of-the art for the annihilation vertex (exploring impact of GENIE-based simulation of decay modes and pion-fields interaction in nucleus) • Implement geometry-specific analysis of backgrounds (begun with NNbarX experiment) – using appropriate analysis tools, typically MCNP-X/MCNP-6 in addition to GEANT4 4/26/13 A. R. Young et al., 2013 Intensity Frontier Workshop

  10. NNBar Proto-Detector Simulation: a Work in Progress Geant simulations by D. G. Phillips, II • All sims use Geant 4.9.6 (with every known library installed). • GENIE nnbarevent generator (5e4 events available). • In this preliminary study, randomly selected 5e3 nnbar events. • Generated 5e4 background events (n & psingles). • Detector geometry consists of target, straw tube tracker • & Minerva-style polystyrene/Pb calorimeter. • Target is 100 um, 2 m diameter 12C disk. • Vacuum tube is 2 cm thick Al. 6/13/14 A. R. Young, D. G. Phillips II, R. W. Pattie Jr.

  11. NNBarX Annih. Event Simulation Branching Fractions Baseline: Annih. event generator based on IMB expt. code (K. Ganezer, B. Hartfiel, CSUDH) Annihilation Point Inv. mass of mesons leaving nucleus X-sections rescaled for 12C SK (16O) NNBAR 0.5 1 1.5 GeV 2 4 6 r (fermi) 4/26/13 A. R. Young et al., 2013 Intensity Frontier Workshop

  12. GENIE: NNBar Final State Primaries Preliminary Final state list prepared by R. W. Pattie GENIE-2.0.0: intranculear propagation based on INTRANUKE C.Andreopoulos et al., The GENIE Neutrino Monte Carlo Generator, Nucl.Instrum.Meth.A614:87-104,2010. 6/13/14 A. R. Young, D. G. Phillips II, R. W. Pattie Jr.

  13. NNBar Proto-Detector Simulation 2 Legend 3 1 π+ π- ϒ 1 Annihilation Mode Event n + 12C ->11C + 3π0 ( 45, 268, 320 MeV ) + π+ ( 81 MeV ) + π- ( 207 MeV ) 4 0 3 3 5 7 2 2 1 6 6/13/14 A. R. Young, D. G. Phillips II, R. W. Pattie Jr.

  14. NNBar Proto-Calorimeter Geometry Calorimeter MINERvA-style Extruded Scintillator 20 layers of 4 cm thick Scint +0.2 cm thick Pb. MINERvA images credit: E. Ramberg (FNAL) 6/13/14 A. R. Young, D. G. Phillips II, R. W. Pattie Jr.

  15. NNBar Proto-Tracker Geometry • 5 mm kapton straws • Fill gas: 70% Ar, 30% CO2. • 50XY planes (0.5 m thick). Tracker (4 cm diam in fig.) ρ = 0.023 g/cm3 1.3 e6 straws ATLAS TRT Assembly at Indiana University 6/13/14 A. R. Young, D. G. Phillips II, R. W. Pattie Jr.

  16. Event Reconstruction n + 12C ->11C + 3π0π+π- 2 3 1 4 0 2.5 m 15 m 2.5 m 5 7 6 6/13/14 6/13/14 A. R. Young, D. G. Phillips II, R. W. Pattie Jr.

  17. NNBar Final State Primaries (Signal) 6/13/14 A. R. Young, D. G. Phillips II, R. W. Pattie Jr.

  18. Energy Threshold Acceptance (Signal) ILL Trig. Thresh. 6/13/14 A. R. Young, D. G. Phillips II, R. W. Pattie Jr.

  19. Tower Hit Acceptance (Signal) ~ILL 6/13/14 A. R. Young, D. G. Phillips II, R. W. Pattie Jr.

  20. Timing Window Acceptance (Signal) ILL 6/13/14 A. R. Young, D. G. Phillips II, R. W. Pattie Jr.

  21. MC Acceptance Summary Conclusion: the proto-detector could in principle provide improved detection efficiency relative to the ILL experiment for n-nbar events using modern technology Challenges: how to minimize cost and meet background rejection goals 6/13/14 A. R. Young, D. G. Phillips II, R. W. Pattie Jr.

  22. Missing Events 6/13/14 A. R. Young, D. G. Phillips II, R. W. Pattie Jr.

  23. Background Simulations: A Prospectus Simulation which addresses problem of a false positive is challenging: must suppress rate after cuts to < 10-8 Hz! ILL experiment provides a baseline from which we can scale… ESS: CN flux on target ×100 CN “lost” in transit ×3000 also new potential sources of bkg Specific challenge: beam-generated backgrounds very closely tied to geometry of source, CN beam and shielding geometry! 6/13/14 A. R. Young, D. G. Phillips II, R. W. Pattie Jr.

  24. Reminder: unique capability to test for false positive with free neutron expt! Dedicated runs possible with free neutron expt to explore false positive: Oscillation phenomenon “switched off” when magnetic field at mG level (backgrounds not affected)! Second graphite target placed after first to explore event reconstruction to second target (all annihilation products removed from beam) G. Greene 6/13/14 A. R. Young, D. G. Phillips II, R. W. Pattie Jr.

  25. Sources of Background • Stochastic gamma backgrounds • Capture in beam-tube (distributed,shieldable) ~1012/s • Capture on target (not shieldable) ~1010/s • CN scatter from target into detector • High energy n,p (~20 n/p at source) • Beta-delayed n • Cosmic rays Not important for ILL experiment 6/13/14 A. R. Young, D. G. Phillips II, R. W. Pattie Jr.

  26. Gamma Backgrounds • Design experiment so gamma backgrounds dominated by capture on 10B (beam baffles) or 12C (target) – highly geometry dependent! • Simulation task: • Assess passive (shielding) strategy to reduce beamline backgrounds • Assess active detector event reconstruction for improved suppression factors 6/13/14 A. R. Young, D. G. Phillips II, R. W. Pattie Jr.

  27. Beamline Gamma Backgrounds • 10B beam baffles preferred because no fast n branch and resultant gamma (10B + n →7Li + α + γ(0.48 MeV), 94% of time) possible to shield (increase number from 8 used on ILL expt) • Explore recessed detector geometry to further limit fluxes from beamline (may be necessary for ESS experiment) – no line of sight to beam-dump, limited line of sight from near beamline baffles • Currently using MCNP-X/MCNP6 for beamline shielding studies • Must integrate with Geant4 detector simulations 10B glass rings 6LiF beam dump shielding detector

  28. Stepped Tube Background Intensity Matthew Frost: UTK • Simulation Performed for 1e5 neutrons crossing Target Plane, 1b Deuterium Moderator Source. • Large section of tube is 4 meter radius. • Normalized to source statistics ,source intensity, and bin size (0.6 meters) • Note the Step at 190 m has a ~100x higher interaction • 10% Statistics or better in each bin.

  29. Tapered Tube Background Intensity • Simulation Performed for 1e5 neutrons crossing Target Plane, 1b Deuterium ESS Moderator. • Large section is 4 meter radius and tapers to 2 meters over 30 meters along beam. • Normalized to source statistics ,source intensity, and bin size (0.6 meters) • Intensity is identical after target position (200 meters) as in the stepped geometry. • Taper begins at 170 m • 10% Statistics or better in each bin.

  30. Target Gammas • Ensure contaminants (H, N) at adequately low levels – H < 0.1% • Relatively straightforward event generator for 12C (dominated by emission of one 4.95 MeV gamma) – see next slide • Simulation task: evaluate suppression based on absence of pion-like tracks which point to target • Tied closely to trigger logic • Signal proportional to time window  factor of 5 improvement possible w/ modern dets (still need at least factor of 20) • Particle-ID in calorimeter and position resolution for pointing-to-target are good candidates for making up needed suppression (how to implement “tracklike cuts” at trigger level – perhaps duplicate previous cut using factor of 100 more detector subvolumes, and perhaps an adjacent volume summing ) Interesting problem on “to-do” list! 6/13/14 A. R. Young, D. G. Phillips II, R. W. Pattie Jr.

  31. Target γ Event Generator Prepared by B. M. Vorndick Capture gammas from n+12C and n+10Be May be advantages to Be target (thanks to P. Bently) (Essentially 100% prob. for ~5 MeV in gammas)

  32. High Energy n,p Backgrounds • Serious consideration for experiments at a CW spallation source • 5 μs cut around primary proton beam pulse adequate to complete suppress H.E. primaries at ESS! (CN mean transit time a few ms, ESS pbeam pulse every 71 ms) • ESS Shielding strategy important: P. Bentley’s talk (Performed studies of CW fast n backgrounds using MCNP) High energy products from 1 GeV proton beam incident on W target (at 90 degrees) – MARS calculation by S. Striganov 6/13/14 A. R. Young, D. G. Phillips II, R. W. Pattie Jr.

  33. Input for Simulations: High Energy n Detection Efficiency • First attempts to model high energy neutron detection efficiency for gas detectors with Geant4 problematic (note: part of both nnbar signal and backgrounds) • Collaboration has undertaken a campaign to assess absolute detection efficiency for plastic scintillator and gas detectors at WNR facility 6/13/14 A. R. Young, D. G. Phillips II, R. W. Pattie Jr.

  34. WNR Tests - Layout LANL WNR-15R Beamline Predicted n-flux 20m from target 250 MHz 8-chnl 12-bit fADC 4/26/13 A. R. Young et al., 2013 Intensity Frontier Workshop

  35. WNR Tests - Fission Foil Fission Chamber TOF Spectra Blue = MCNPX Red/Black = Fission Foil Data (Agreement good) 4/26/13 A. R. Young et al., 2013 Intensity Frontier Workshop

  36. Efficiency results

  37. Agreement with Monte Carlo (Geant Libraries): current status 1. Generic Hadron – No neutron scattering 2. HPLE+IBC - This uses the High precision Low Energy libraries for E_n<20 MeV and a Ion binary Cascade model above 20 MeV 3. HPLE+IBC + SHEN - Shen scattering cross section libraries added 4. HPLE+IBC +SHEN+TRIPATHI - Tripathi and tripathi light cross sections are added. 4/26/13 A. R. Young et al., 2013 Intensity Frontier Workshop

  38. Beta-delayed neutrons and cosmic-rays 6/13/14 A. R. Young, D. G. Phillips II, R. W. Pattie Jr. 38

  39. Conclusions • Appropriate event generators are available for annihilation signal and some background processes • Starting points for discussion seem to be that somewhat improved efficiency and shorter trigger time-windows can probably achieved with modern detector • A detailed treatment of the background simulations requires careful integration of experimental geometry into detector model, and also involves many interesting avenues of investigation – plenty of opportunities for involvement! 4/26/13 A. R. Young et al., 2013 Intensity Frontier Workshop

  40. NNbarX Working Group Experimentalist Group K. Ganezer, B. Hartfiel, J. Hill California State University, Dominguez Hills S. Brice, N. Mokhov, E. Ramberg, A. Soha, S. Striganov, R. Tschirhart Fermi National Accelerator Laboratory D. Baxter, C-Y. Liu, C. Johnson, M. Snow, Z. Tang, R. Van Kooten Indiana University, Bloomington A. Roy Inter University Accelerator Centre, New Delhi, India W. Korsch University of Kentucky, Lexington M. Mocko, G. Muhrer, A. Saunders, Z. Wang Los Alamos National Laboratory H. Shimizu Nagoya University, Japan P. Mumm National Institute of Standards A. Hawari, R. W. Pattie Jr., D. G. Phillips II, B. Wehring, A. R. Young North Carolina State University, Raleigh T. W. Burgess, J. A. Crabtree, V. B. Graves, P. Ferguson, F. Gallmeier Oak Ridge National Laboratory, Spallation Neutron Source S. Banerjee, S. Bhattacharya, S. Chattopadhyay Saha Institute of Nuclear Physics, Kolkata, India D. Lousteau Scientific Investigation and Development, Knoxville, TN A. Serebrov St. Petersburg Nuclear Physics Institute, Russia M. Bergevin University of California, Davis‎ L. Castellanos, C. Coppola, T. Gabriel, G. Greene, T. Handler, L. Heilbronn, Y. Kamyshkov, A. Ruggles, S. Spanier, L. Townsend, U. Al-Binni University of Tennessee, Knoxville P. Das, A. Ray, A.K. Sikdar Variable Energy Cyclotron Centre, Kolkata, India Theory Support Group K. Babu Oklahoma State University, Stillwater Z. Berezhiani INFN, Gran Sasso National Laboratory and L’Aquila University, Italy Mu-Chun Chen University of California, Irvine R. Cowsik Washington University, St. Louis A. Dolgov University of Ferrara and INFN, Ferrara, Italy G. Dvali New York University, New York A. Gal Hebrew University, Jerusalem, Israel B. Kerbikov Institute for Theoretical and Experimental Physics, Moscow, Russia B. Kopeliovich Universidad Técnica Federico Santa María, Chile V. Kopeliovich Institute for Nuclear Research, Troitsk, Russia R. Mohapatra University of Maryland, College Park L. Okun Institute for Theoretical and Experimental Physics, Moscow, Russia C. Quigg Fermi National Accelerator Laboratory U. Sarkar Physical Research Laboratory, Ahmedabad, India R. Shrock SUNY, Stony Brook A. Vainshtein University of Minnesota, Minneapolis 4/26/13 A. R. Young et al., 2013 Intensity Frontier Workshop

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