A Next Generation Neutron-Antineutron Oscillation Experiment at Fermilab A. R. Young NCState University For the NNbar. X Collaboration
Outline • • • Motivation Previous free neutron measurement at ILL NNbar. X baseline and critical technologies R & D (as time permits) Conclusion
Importance of Observation of Baryon 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! 3
Neutron-Antineutron Transformations ΔB=2 Neutron-antineutron transformation is natural in L-R symmetric models at scales where neutrino masses are also explained (Mohapatra & Marshak); Observable together with Te. V-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) http: //www. mpi-hd. mpg. de/BLV 2013/ Z. Berezhiani (BLV-2013) 4
BSM: examples of (B-L) violating models with observable Supersymmetric Seesaw for m B L , L R Non-SUSY model Left-Right symmetric GUT nn nn SUSY GUT PDK Plank scale Dutta-Mimura-Mohapatra (2005) Goity, Sher (1994) Mohapatra & Marshak (1980) Observable effects at LHC Berezhiani; Babu et al. (2013) Berezhiani Bento (2005) Post-Sphaleron Baryogenesis Babu, Mohapatra, et al. (2013) Low QG models LHC nn Experimental motivation! large increase of sensitivity: factor of 1, 000 is possible compared to existing limit Dvali & Gabadadze (1999) Shrock & Nussinov (2002) 5
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 τnn = h/α Contributions to V: <Vmatter>~100 ne. V, proportional to density <Vmag>= B, ~60 ne. V/Tesla; B~10 n. T-> Vmag~10 -15 e. V <Vmatter> , <Vmag> both >> Figure of merit= N=#neutrons, T=“quasifree” observation time In nuclei, n, n splittings (V) large huge suppression factor R
x ROx = 5× 1022 s-1 Free Neutron and Bound Neutrons NNbar Search Limits Comparison Large improvement with free-neutron experiments is possible Factor of 1, 000 sensitivity increase Recent S-K (2011) limit based on 24 candidates and 24. 1 bkgr. Post-Sphaleron Baryogenesis Babu et al 50 kt intranuclear search exp. limits: Super-K, Soudan-2 Frejus, SNO Free neutron search limit (ILL - 1994) Ultimate goal of new n-nbar search with free neutrons 8
ILL Layout • Free neutron n-nbar search experiment in 1989 - 1991 at ILL: measured PNNBar < 1. 606 x 10 -18 sensitivity: Nn∙t 2 = 1. 5 x 109 s 2/s (90% CL) 9
ILL Detector Configuration • Effective run time = 2. 4 x 107 s, Nevents = 6. 8 x 107. • n-nbar detection efficiency (∆Ω/4 = 0. 94): 52% ± 2%. • No background & no candidate events after analysis. 10
NNbar. X at Project X NNbar. X: • CW 1 Ge. V proton beam • 1 MW spallation target Beamline and cold source optimized for NNbar. X Caveat: Spallation target likely shared by other users
Conceptual Horizontal Baseline Configuration with elliptical focusing reflector (method proposed by us in 1995) D ~ 4 m Typical initial baseline parameters: Cold source configuration C Luminous source area, dia 30 cm Annihilation target, dia 200 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 n. T MC Simulated sensitivity Nt 2: 150 “ILL units” x years Sensitivity and parameters are subject of optimization by Monte. Carlo including overall cost N-nbar effect can be suppressed by weak magnetic field. 12
Project X (see Bob Tschirhart’s talk) 13
Key technologies • Spallation driven cold source (1 MW at Project X) SNS PSI Two 1 MW spallation sources already in operation with adequate performance! • Focusing neutron optics (already in use) • High m neutron guides (m=7 now available) Most of the gain from high m guides, large effective area source, and longer flight time
Optimal Neutron Production Energy Spectrum of Primary Neutrons ~ 1. 3 Ge. V Yield is ~ 24 neutrons per Ge. V proton ~ 1. 5 1017 n/s/MW N. Mokhov, MARS simulations, FNAL, 2011 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
(UT group) A LD 2 Pb Configuration (B) F. Gallmeier/SNS with LH 2 D 2 O B 1 MW P 1 Ge. V Configuration (A) G. Muhrer/LANL C Fe D 2 O ~ 1 m 2 @ 1 m Pb LD 2 Preliminary B H 2 O Initial UT model (C) L. Castellanos/UT C A Energy spectrum of neutron currents in different models 16 Special thanks to Michael Wohlmuther and Tibor Reiss for details concerning SINQ!
Super-mirrors material for large elliptical focusing reflector Group of H. Shimizu (Nagoya University) Commercial products of Swiss Neutronics Progress in neutron super-mirrors v 30 m/s v 50 m/s (H. Shimizu, 2012) 17
NNBar. X Detector Strategy • Scale successful ILL geometry to larger beam and target size required for NNbar. X • Identify promising technologies for tracker and calorimeter, signal is ~5 π’s from common vtx. (w/~200 Me. V K. E. each), similar requirements to stopped kaon experiments (see E 949) • Evaluate candidate geometries with target performance specifications • Annhilation events, ε > 0. 5 • Improved vertex reconstruction (± 1 cm) 4/26/13 18 A. R. Young et al. , 2013 Intensity Frontier Workshop
Detector simulation: GEANT 4 Scintillator/Pb plate Calorimeter 4/26/13 A. R. Young et al. , 2013 Intensity Frontier Workshop 19
NNBar. X Annih. Event Simulation Branching Fractions 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 12 C SK (16 O) NNBARX 2 4 6 r (fermi) 4/26/13 20 A. R. Young et al. , 2013 Intensity Frontier Workshop 0. 5 1 1. 5 Ge. V
Fast Backgrounds • Beam for Project X: quasi-CW 1 Ge. V Quasi-continuous production of fast n’s, protons and γ’s. • Cold neutron beam has mean velocity of roughly 600 m/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 4/26/13 A. R. Young et al. , 2013 Intensity Frontier Workshop 1 Ge. V p’s, lead target, 90 deg, per p S. Striganov (FNAL) 21
Fermilab PAC recommendation sets for horizontal option a “minimal sensitivity goal” of ~ 30 or free = 5 108 s 22
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…
NNBar. X Tracker Candidates IU group of R. Van Kooten • Straw tube array in barrel and end-cap configuration (ala ATLAS). Image credit: S. Schaepe (ATLAS) • ATLAS TRT – hit precision: ~130 μm, ε ~ 94%, [18]. • Straw tube fill gas options need to be identified and tested. Straw Tube Schematic Other Options • MWPCs • TPC(s) • liquid scintillator 4/26/13 24 TRT Assembly at Indiana University A. R. Young et al. , 2013 Intensity Frontier Workshop
WNR Tests - Layout LANL WNR-15 R Beamline Predicted n-flux 20 m from target Interested in these energies, very similar to those we will encounter at Project X 4/26/13 25 A. R. Young et al. , 2013 Intensity Frontier Workshop
Results and Plans Complete: LANL proportional tube efficiency measurement 26 Nov. 2013: straw tube measurements ε < 10 -5 for E > 100 Me. V
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Colder moderator R&D at Indiana University / CEEM Fit to the Spectrum 13 Me. V, CH 4, 6 K Super-m acceptance tech. development Cold moderator tech. development Dave Baxter, Chen-Yu Liu / Indiana U. 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!
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. Mc. Gaughey, 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 30 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
WNR Tests - Gas Tubes & Prep 4/26/13 34 A. R. Young et al. , 2013 Intensity Frontier Workshop
R&D Program: WNR Tests Goal: evaluate response of specific gas and plastic scintillators to fast neutrons (few Me. V < En < 800 Me. V) 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 4/26/13 A. R. Young et al. , 2013 Intensity Frontier Workshop 35
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