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Do Neutrons Oscillate ?

Do Neutrons Oscillate ?

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Do Neutrons Oscillate ?

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  1. Do Neutrons Oscillate ? R. N. Mohapatra University of Maryland Beijing Colloqium, June, 2007 Theme Group 2

  2. Particle oscillations • Oscillations of quantum mechanical states is a familiar phenomenon in Nature. • In the domain of particle physics, electrically neutral particles such as Kaons and neutrinos have been observed to oscillate, teaching us a great deal about the fundamental forces and matter. • Neutron is another neutral particle- could it possibly be having any oscillation ? Theme Group 2

  3. What can neutrons Oscillate to ? • Conservation of electric charge allows: (i) Neutron to anti-neutron (requires violation of baryon number) (ii) Neutron to mirror neutron; (requires the existence of a mirror universe.) Both involve untested ideas and will reveal new physics. Here I discuss case (i) since there are reasons to suspect baryon number violation. Theme Group 2

  4. Why Baryon number non-conservation ? • Standard model has it. • Understanding the origin of matter in the universe requires it. • Most interesting new physics scenarios beyond the SM predict it. Theme Group 2

  5. Modes of interest • Two modes of interest are: • Proton decay • Neutron-anti-neutron oscillation Theme Group 2

  6. Phenomenology of N-N-bar Osc Theme Group 2

  7. Present expt situation in N-N-bar Osc. Range accessible to current reactor fluxes: Present limit:ILL experiment: Baldoceolin et al. (1994) New proposal by Y. Kamyshkov, M. Snowet al for an expt. DUSEL GOAL: Figure of merit ~ Theme Group 2

  8. De-gaussing of Earth B necessary • In free N-N-bar osc.,in the presence of Earth Mag. Field • Effect will be suppressed. • Needed de-gaussing to the level of Nano-Tesla. • Mu-metal shielding can do it. Known technology. Theme Group 2

  9. Oscillation inside Nuclei Theme Group 2

  10. Searches in Nucleon decay • Inside a nucleus e.g. Oxygen, • giving For This leads to nucleon lifetime Limits from Super-K, Soudan, IMB, SNO are of this order. Theme Group 2

  11. Comparision P-decay vs N-N-bar Theme Group 2

  12. Free vs Bound N-N-bar • Nuclear Physics uncertain: Uncertainty in R -need to do free neutron osc. Search. Theme Group 2

  13. A Proposal for N-Nbar search experiment at DUSEL  Dedicated small-power TRIGA research reactor with cold neutron moderator  vn ~ 1000 m/s  Vertical shaft ~1000 m deep with diameter ~ 6 m at DUSEL  Large vacuum tube, focusing reflector, Earth magnetic field compensation system  Detector (similar to ILL N-Nbar detector) at the bottom of the shaft (no new technologies) Kamyshkov,Snow et al. Theme Group 2

  14. Present collaboration: • Seeking collaborators: new site for expt. Theme Group 2

  15. Physics reason for N-N-bar • Different baryon non-conserving processes probe different physics: • Need both proton decay and N-N-bar for complete understanding of physics beyond SM Theme Group 2

  16. Modes and new physics scales P->e+ , P->K mediated by the operator: Obeys Present lower limit on Implies This probes very high scales close to GUT scale. Theme Group 2

  17. B-L=2 Processes • Neutron-anti-neutron oscillations : PROBES INTERMEDIATE SCALES; Leads to Or for M= Theme Group 2

  18. Power counting: model dependent • Depends on : (i) low energy symmetry (ii) TeV scale particle spectrum: • TeV scale SUSY: sparticles < TeV scale • Dominant P-decay operator Severely constrains SUSY GUTs : N-N-bar operator Allows N-N-bar to probe scales upto GeV. Much weaker suppressions also possible allowing probes till 10^11-10^12 GeV. Theme Group 2

  19. Key symmetry is B-L • Proton decay does not search for B-L breaking whereas Neutron anti-neutron oscillation does. • B-L connected to neutrino mass-N-N-bar can clarify the origin of nu mass. Theme Group 2

  20. Plan for the rest of the talk 1. Why B-L symmetry ? 2. Two classes of local B-L models 3. Proton Decay, and N-N-bar Oscillations as tests of these models. Theme Group 2

  21. Why B-L Symmetry ? • Standard model has global B-L symmetry. • Immediate questions therefore are: • What is the nature of this symmetry ? Is it a global or local symmetry ? • Is it broken or exact ? If broken, what is the breaking scale and what new physics is associated with it ? Theme Group 2

  22. Any Hint of B-L symmetry beyond SM? • Neutrino Mass points towards a B-L symmetry beyond the standard model. • As does SUSY dark matter. • One popular way to understand the origin of matter also involves B-L breaking. Theme Group 2

  23. Neutrino mass and -standard model • Starting point: add RH neutrino to SM for nu mass: Theme Group 2

  24. Seesaw paradigm for neutrino masses Add right handed neutrinos to the standard model and give them a large Majorana mass: Minkowski (77); Gell-Mann, Ramond, Slansky; Yanagida; Glashow; RNM, Senjanovic (79) Theme Group 2

  25. Seesaw scale and B-L symmetry • Seesaw formula applied to atmospheric neutrino data tells us that • Simple way to understand this inequality is to have a new symmetry that protects M_R. B-L is the appropriate symmetry since Majorana mass of RH neutrino breaks B-L by 2 units. Theme Group 2

  26. Another reason to suspect a B-L sym. • Common belief: SUSY at TeV scale for various reasons: (i) Gauge hierarchy (ii) EWSB: origin of W, Z mass (iii) Dark matter: requires R-parity exact. Note that ifB-L is a good symmetry beyond MSSM and breaksby two units (as in the RH neutrino mass), R-parity is exact in MSSM, dark matter is stable: otherwise not !! (RNM,86; Font, Ibanez, Quevedo, 89; Martin,92) Theme Group 2

  27. Origin of matter and B-L • If matter-anti-matter symmetry originated from early universe above the TeV scale, then, it must break B-L. If it did not, Sphalerons would erase it !! • Proof: Suppose generated in the early Universe is such that it has B- L=0; Then = ; But B+L is violated by sphalerons which are in equilibrium down to the electroweak phase transition temp and will therefore wipe out B+L and hence all baryon asymmetry. Theme Group 2

  28. B-L: Local or Global ? • SM or MSSM: • But • So B-L is not a local symmetry. • Add the RH neutrino: • (B-L) becomes a gauge-able symmetry. • We will consider B-L to be a local symmetry. Theme Group 2

  29. New electroweak symmetry with B-L • Gauge group: • Fermion assignment • Higgs fields: Theme Group 2

  30. Symmetry breaking Theme Group 2

  31. Electric Charge Formula • New Improved Formula for electric charge Standard model: Y has no physical meaning. The formula In LR models: Theme Group 2

  32. Parity Violation leads to B-L violation • Electric charge formula of LR models imply: • Connects the origin of parity violation to B-L violation. Understanding B-L violation will elucidate the origin of parity violation. implies: or Majorana neutrinos or neutron-anti-N oscill. (RNM, Marshak,80) Theme Group 2

  33. Minimal Models with B-L and N-N-bar • Need to unify quarks and leptons to transmit the B-L=2 information to generate N-N-bar oscillations. • Two simple models with local B-L: (A): SO(10) : the minimal GUT theory with B-L (Georgi; Fritzsch and Minkowski (75)) (B) Partial Unif. Th. In both cases, fermions fit into the basic representation: • (Pati, Salam,73) Theme Group 2

  34. B-L scale in SO(10) Grand unification Note that SUSY at TEV SCALE + no new physics till GeV implies that coupling constants unify: This suggests that perhaps local B-L is part of a grand unifying symmetry and it breaks at GUT scale. Related physics is GUT physics. Theme Group 2

  35. Does seesaw favor GUT scale B-L breaking ? • Atmospheric mass measured by Super-K can be related to B-L scale using the seesaw formula: assuming GUT relation for the 3rd generation that This gives for the seesaw scale IN THIS CASE, SEESAW SCALE IS GUT SCALE and B-L PHYSICS IS GUT PHYSICS: Theme Group 2

  36. LOWER B-L SCALE POSSIBLE ? However, Experiments do not tell us the value of . if is suppressed by some symmetries (e.g. family sym.), seesaw scale could be lower. In case of lower B-L scale, possible unification theory is the Model. Minimal B-L scale in this case is: Could also be at the TeV scale. Theme Group 2

  37. So two key questions are: • What is the physics associated with B-L symmetry in this case ? • What is the scale of B-L symmetry ? Theme Group 2

  38. Message of this talk: P-decay, N-N-bar osc. probe the scale of local B-L sym. P-decay if it is GUT scale and N-N-bar if it is intermediate!! HOW SO ? Theme Group 2

  39. Digression on GUTs and Proton decay SU(5) as a Warm-up example: Theme Group 2

  40. Nucleon Decay in Generic SUSY GUTs • Gauge Boson exchange: Theme Group 2

  41. SUSY changes GUT scale dependence • Sakai, Yanagida, Weinberg (1982) • Murayama, Pierce; Bajc, Perez, Senjanovic (02); Perez,Dorsner,Rodrigo(06) Theme Group 2

  42. Predictions for proton decay in SO(10)-16 • B-L could be broken either by {16}-H or {126}-H. • SU(5) type problem avoided due to cancellation between diagrams. • Proton decay in {16} models: highly model dependent: in one class of models (Babu, Pati and Wilczek (2000)) Theme Group 2

  43. Predictions for proton decay in SO(10)-126 • Minimal SO(10) model with 10+126 which predict neutrino mixings: • 4 parameter model: predicts • (Goh, R.N. M, Nasri, Ng (2004)) Decay model highly suppressed . So again proton decay modes like these are highly model dependent. Theme Group 2

  44. Truly “model independent” prediction • Gauge exchange mode P-> e+ , which is predicted in minimal GUT models to be around 10^36 years. • “The true holy grail of grand unification” • N-N-BAR IN SO(10) HIGHLY SUPPRESSED. Theme Group 2

  45. Now to N-N-BAR OSCILLATION • Can observable N-N-bar emerge in realistic seesaw models with sub-GUT B-L scale ? • Second question is: since high dim N-N-bar operators go out of equilibrium only around the electroweak scale, are they not going to erase any preexisting baryon asymmetry- • So can one understand the origin of matter if N-N-bar is visible in expts. ? • The answers to both questions -“YES”. Theme Group 2

  46. Testing Sub-GUT B-L with N-N-bar • Recall with SM spectrum in the TeV range, NN operator is O • Feynman diagram for N-N-bar Feynman noSUSY • RNM and Marshak,80 • Tiny n-n-bar for M >100 TeV. Can n-n-bar test higher B-L scales ? Theme Group 2

  47. Things change with SUSY and new particles A. Dominant operator with SUSY: B.SUSY + diquark Higgs field , at TeV scale C.If the TeV scale has fields, effective op. is /M Note weaker Seesaw suppression Supression Still weaker ! Weakest Suppression Theme Group 2

  48. A G(224) theory for case B and N-N-bar Theme Group 2

  49. Estimate of N-N-bar in Minimal 224 model: • New Feynman diagram for N-N-bar osc. Observable N-N-bar osc (Dutta, Mimura, RNM; PRL (2006) Theme Group 2

  50. Other examples-Babu,RNM,Nasri-PRL (2007) • 3x2 seesaw model with the third RH neutrino in the TeV scale and decoupled from the neutrino sector: • Plus a pair of color triplets: X and X-bar with couplings: + Impose R-parity symmetry as in MSSM. This simple extension provides a remarkably natural model for dark matter, neutrinos and baryogenesis andhas testable predictions !! Theme Group 2