A Next Generation Neutron-Antineutron Oscillation Experiment at Fermilab A.R.Young NCState University For the NNbarX Collaboration

Outline Motivation Previous free neutron measurement at ILL NNbarX baseline and critical technologies R & D (as time permits) Conclusion

3  Violation of Baryon number is one of the “pillars” needed for modern Cosmology and Particle Physics: - required for explanation of BAU (Sakharov); - present within SM, although at non-observable level (‘t Hooft); → Sphaleron excitation - motivated by BSM models (Georgi & Glashow, Pati &Salam,...)  Proton decay  B = 1 and  B = 2 are complementary many models exist in which proton decay is forbidden, but allowed at current limits! Importance of Observation of Baryon Violation

4  Neutron-antineutron transformation is natural in L-R symmetric models at scales where neutrino masses are also explained (Mohapatra & Marshak); Observable together with TeV-scale color-sextet scalars at LHC in a new scheme of Post-Sphaleron Baryogenesis (Babu, Mohapatra).  Interesting theoretical discussions on G. Dvali and G. Gabadadze (1999) R. Schrock and S. Nussinov (2002) K. Babu and R. Mohapatra et al. (> 2001) J. Arnold et al. (2012) G. Durieux et al. (BLV-2013) Z. Berezhiani (BLV-2013) Neutron-Antineutron Transformations ΔB=2

LHC nn Low QG models Dvali & Gabadadze (1999) nn Supersymmetric Seesaw for m B  L, L  R Mohapatra & Marshak (1980) Dutta-Mimura-Mohapatra (2005) Non-SUSY model Left-Right symmetric GUT SUSY GUT PDK Plank scale 5 Experimental motivation! large increase of sensitivity: factor of  1,000 is possible compared to existing limit Post-Sphaleron Baryogenesis Babu, Mohapatra, et al.(2013) Goity, Sher (1994) Berezhiani Bento (2005) Observable effects at LHC Berezhiani; Babu et al. (2013) Shrock & Nussinov (2002) BSM: examples of (B-L) violating models with observable

Experimental NN-bar Searches Nucleon decay (bound N oscillates to N-bar and annihilates on other nucleons) Free N-Nbar oscillations in beams of cold neutrons Given huge number of atoms available in large scale underground nucleon decay experiments, seems likely to provide best limits…how can free neutron be competitive?

Neutron-Antineutron transition probability: quasifree condition Contributions to V: ~100 neV, proportional to density =  B, ~60 neV/Tesla; B~10nT-> Vmag~ eV, both >>  Figure of merit= N=#neutrons, T=“quasifree” observation time τ nn = h/α In nuclei, n,n splittings (V) large  huge suppression factor R

intranuclear search exp. limits: Super-K, Soudan-2 Frejus, SNO Free neutron search limit (ILL ) Factor of 1,000 sensitivity increase 8 Recent S-K (2011) limit based on 24 candidates and 24.1 bkgr. Post-Sphaleron Baryogenesis Babu et al x R Ox = 5×10 22 s kt

9 ILL Layout Free neutron n-nbar search experiment in at ILL: measured P NNBar < x sensitivity: N n ∙t 2 = 1.5 x 10 9 s 2 /s (90% CL)

10 ILL Detector Configuration Effective run time = 2.4x10 7 s, N events = 6.8x10 7. n-nbar detection efficiency (∆Ω/4 = 0.94): 52% ± 2%. No background & no candidate events after analysis.

NNbarX at Project X NNbarX: CW 1 GeV proton beam 1 MW spallation target Beamline and cold source optimized for NNbarX Caveat: Spallation target likely shared by other users

D ~ 4 m Conceptual Horizontal Baseline Configuration with elliptical focusing reflector (method proposed by us in 1995) Typical initial baseline parameters: Cold source configuration C Luminous source area, dia 30 cm Annihilation target, dia200 cm Reflector starts at 2 m Reflector ends at 50 m Reflector semi-minor axis 2.4 m Distance to target 200 m Super-mirror m=7 Vacuum < 10  5 Pa Residual magnetic field< 1 nT MC Simulated sensitivity Nt 2 : 150 “ILL units” x years Sensitivity and parameters are subject of optimization by Monte- Carlo including overall cost 12 N-nbar effect can be suppressed by weak magnetic field.

13 Project X (see Bob Tschirhart’s talk)

Key technologies Spallation driven cold source (1 MW at Project X) Focusing neutron optics (already in use) High m neutron guides (m=7 now available) SNS PSI Two 1 MW spallation sources already in operation with adequate performance! Most of the gain from high m guides, large effective area source, and longer flight time

N. Mokhov, MARS simulations, FNAL, 2011 ~ 1.3 GeV Yield is ~ 24 neutrons per GeV proton ~ 1.5  n/s/MW For target made of fissionable materials (e.g. Th, DU) neutron yield can be factor ~ 2 higher (geometry dependent) Spectrum of primary fast n from spallation target and from fission (Courtesy of Gary Russel). Potential source of the “fast ” background for n-nbar that was non-existent in the previous ILL experiment

D2OD2O LD 2 Pb Initial UT model (C) L. Castellanos/UT C A B C Preliminary Energy spectrum of neutron currents in different models Configuration (A) G. Muhrer/LANL A Configuration (B) F. Gallmeier/SNS with LH 2 B Pb D2OD2O LD 2 1 MW P 1 GeV ~ 1m 1m 16 H2OH2O Fe Special thanks to Michael Wohlmuther and Tibor Reiss for details concerning SINQ! (UT group)

Progress in neutron super-mirrors v   50 m/s Commercial products of Swiss Neutronics v   30 m/s (H. Shimizu, 2012) Super-mirrors material for large elliptical focusing reflector 17 Group of H. Shimizu (Nagoya University)

18 NNBarX Detector Strategy 4/26/13A. R. Young et al., 2013 Intensity Frontier Workshop Scale successful ILL geometry to larger beam and target size required for NNbarX Identify promising technologies for tracker and calorimeter, signal is ~5 π’s from common vtx. (w/~200 MeV K.E. each), similar requirements to stopped kaon experiments (see E949) Evaluate candidate geometries with target performance specifications Annhilation events, ε > 0.5 Improved vertex reconstruction (± 1 cm)

19 Detector simulation: GEANT4 4/26/13A. R. Young et al., 2013 Intensity Frontier Workshop Scintillator/Pb plate Calorimeter

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

21 Fast Backgrounds 4/26/13A. R. Young et al., 2013 Intensity Frontier Workshop Beam for Project X: quasi-CW 1 GeV Cold neutron beam has mean velocity of roughly 600 m/s 1 GeV p’s, lead target, 90 deg, per p S. Striganov (FNAL) Quasi-continuous production of fast n’s, protons and γ’s. Two scenarios: 1.Beam on always max. sensitivity (statistics) max. fast backgrounds 2.Modulated beam – e.g 1 ms on, 1 ms off sensitivity x 0.5 No fast backgrounds

22 Fermilab PAC recommendation sets for horizontal option a “minimal sensitivity goal” of ~ 30 or  free = 5  10 8 s

Research and Development Detector R&D – Fast neutron sensitivity and background rejection – Minimize cost (leverage existing resources at Fermilab) Cold source R&D – Moderator configuration (e.g. re-entrant geometries) – Reflectors – Cold moderator choices (lower n temperature) Vertical Geometry – Roughly another factor of 100 in sensitivity possible…

24 NNBarX Tracker Candidates 4/26/13A. R. Young et al., 2013 Intensity Frontier Workshop Straw tube array in barrel and end-cap configuration (ala ATLAS). ATLAS TRT – hit precision: ~130 μm, ε ~ 94%, [18]. Straw tube fill gas options need to be identified and tested. Other Options Straw Tube Schematic TRT Assembly at Indiana University Image credit: S. Schaepe (ATLAS) MWPCs TPC(s) liquid scintillator IU group of R. Van Kooten

25 WNR Tests - Layout 4/26/13A. R. Young et al., 2013 Intensity Frontier Workshop LANL WNR-15R Beamline Predicted n-flux 20m from target Interested in these energies, very similar to those we will encounter at Project X

26 Results and Plans Complete: LANL proportional tube efficiency measurement Nov. 2013: straw tube measurements ε 100 MeV

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Fit to the Spectrum 13 MeV, CH4, 6K Dave Baxter, Chen-Yu Liu / Indiana U. Colder moderator R&D at Indiana University / CEEM Cold moderator tech. development Cold moderator tech. development Super-m acceptance tech. development Super-m acceptance tech. development 28

Conclusions A very large increase in sensitivity to neutron-antineutron oscillations is possible using cold neutron beams Project X at Fermilab provides an ideal opportunity to develop an optimized cold source and beamline, with a factor of 450 improvement over current free neutron limits in 3 years of running for a horizontal geometry possible R&D continues toward improvements to the horizontal geometry and exploration of a vertical geometry with additional, very large enhancements in sensitivity possible!

30 Collaboration 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, P. McGaughey, G. Muhrer, A. Saunders, S. Sjue, Z. Wang Los Alamos National Laboratory H. Shimizu Nagoya University, Japan P. Mumm National Institute of Standards E. Dees, 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

Challenge: Quasi-free condition satisfied very briefly for bound neutrons Compare: However…

Incremental progress expected by scaling to larger mass due to backgrounds

34 WNR Tests - Gas Tubes & Prep 4/26/13A. R. Young et al., 2013 Intensity Frontier Workshop

35 R&D Program: WNR Tests 4/26/13A. R. Young et al., 2013 Intensity Frontier Workshop Goal: evaluate response of specific gas and plastic scintillators to fast neutrons (few MeV < E n < 800 MeV) Technique: use known absolute n spectrum for pulsed beam at LANSCE WNR facility to measure efficiency (and timing) vs. energy Detectors: Atlas straw tubes (delayed till fall) fission foil detector carbon fiber gas proportional counters plastic scintillator