Yuri Kamyshkov University of Tennessee kamyshkov @utk

1. SLAC Experimental Seminar, Tuesday, May 17, 2005 Searches for Baryon Number Violation Yuri Kamyshkov University of Tennessee kamyshkov @utk.edu

2. Plan (1) Introduction: (BL)=0 vs (BL)0 (2) Search for neutron disappearance in KamLAND (3) Future prospects in nnbar search

3. What can we learn from ~30 years of proton decay search? (experimentalist’s view) • no nucleon decay is observed • exp. sensitivity is close to the limits set by background • original SU(5) is ruled out (Georgi and Glashow, 1974) • several other GUT and SUSY-extended models are ruled-out • theoretical predictions for certain decay modes were “improved” from initial ~ 1029 yr to 1034 yr • gauge couplings in GUT do not unify without SUSY • even with SUSY addition the unification is not perfect (S. Raby, PDG 2004) • conspiracy of GUT and SUSY models (both not experimentally proven)

4. More Questions: • is nucleon instability search motivated purely by GUT and SUSY? • do we still believe in Great Desert ? • are low-energy scale QG models testable with nucleon decay? • how can we motivate young experimentalists to search for a proton decay? • are we diligently exploring alternative ideas and experimental options?

5. What is telling us that baryon number is not conserved? Observed and yet unexplained Baryon Asymmetry of the Universe (BAU) Three ingredients needed for BAU explanation ( A. Sakharov, 1967): Baryon number violation C and CP symmetry violation (3) Departure from thermal equilibrium BAU does not tell us how baryon number is violated. Violation/decay modes are predictions of theoretical models. What modes are relevant for BAU explanation?

6. Two types of baryon instability

7. • In our laboratory samples (BL) = #protons + #neutrons  #electrons (BL)0 Is (BL) conserved? • However, in the Universe most of the leptons exist as, yet undetected, relic neutrino and antineutrino radiation (similar to CMBR) and conservation of (BL) on the scale of the whole Universe is still an open question • Non-conservation of (BL) was discussed theoretically since 1978 by: Davidson, Marshak, Mohapatra, Wilczek, Chang, Ramond ...

8. Important Theoretical Discoveries • Anomalous nonperturbative effects in the Standard Model lead to nonconservation of lepton and baryon number (’t Hooft, 1976) B and L nonconservation in SM is too small to be experimentally observable at low temperatures, but can be large above TeV scale. • “On anomalous electroweak baryon-number non-conservation in the early universe” (Kuzmin, Rubakov, Shaposhnikov, 1985) Rate of SM nonperturbative (B+L)-violating electroweak processes at T > TeV (sphaleron mechanism) exceeds the Universe expansion rate. If B = L is set in the Universe at some very high temperatures (e.g. at GUT scale) due to some (BL) violating interaction all quarks and leptons along with BAU will be wiped out by (B+L)-violating electroweak processes. For the explanation of BAU (BL) violation is required.

9. Violation of (BL) implies nucleon instability modes: Rather than conventional p-decay modes: If (BL) is violated at T above electroweak scale If conventional (BL)-conserving proton decay would be discovered e.g. by Super-K, it does not help us to understand BAU. “The proton decay is not a prediction of the baryogenesis” Yanagida @ 2002

11. 2003, M. Shiozawa 28th International Cosmic Ray Conference Spectacular work of Super-K, Soudan-2, IMB3, Kamiokande, Fréjus All modes (BL)=0

12. e.g. for with a lifetime >1.71031 yr Super-K would detect ~ 430 events/yr Some (BL)0 nucleon decay modes (PDG’04)

13. • would be an interesting alternative (BL) = +2 B, L0 searches in particle decays (PDG’2004) • All these above limits are for (BL)=0 modes • Note, that nucleon decay e.g. p e+is (BL) = 2

14. (2) Searches for Baryon non-conservation in KamLAND 1 kt ~ CH2 KamLAND schematic

15. KamLAND Collaboration • Tohoku University:K.Eguchi, S.Enomoto, K.Furuno, J.Goldman, H.Hanada, H.Ikeda, K.Ikeda, K.Inoue, K.Ishihara, W.Itoh, T.Iwamoto, T.Kwaguchi, T.Kawashima, H.Kinoshita, Y.Kishimoto, M.Koga, Y.Koseki, T.Maeda, T.Mitsui, M.Motoki, K.Nakajima, M.Nakajima, T.Nakajima, H.Ogawa, K.Owada, T.Sakabe, I.Shimizu, J.Shirai, F.Suekane, A.Suzuki, K.Tada, O.Tajima, T.Takayama, K.Tamae, H.Watanabe • University of Alabama:J.Busenitz, Z.Djurcic, K.McKinny, D.-M.Mei, A.Piepke, E.Yakushev • LBNL/UC Berkeley:B.E.Berger, Y.D.Chan, M.P.Decowski, D.A.Dwyer, S.J.Freedman, Y.Fu, B.K.Fujikawa, K.M.Heeger, K.T.Lesko, K.-B.Luk, H.Murayama, D.R.Nygren, C.E.Okada, A.W.P.Poon, H.M.Steiner, L.A.Winslow • California Institute of Technology:G.A.Horton-Smith, R.D.McKeown, J.Ritter, B.Tipton, P.Vogel • Drexel University:C.E.Lane, T.Miletic • University of Hawaii:P.W.Gorham, G.Guillian, J.G.Learned, J.Maricic, S.Matsuno, S.Pakvasa • Louisiana State University:S.Dazeley, S.Hatakeyama, M.Murakami, R.C.Svoboda • University of New Mexico:B.D.Dieterle, M.DiMauro • Stanford University:J.Detwieler, G.Gratta, K.Ishii, N.Tolich, Y.Uchida • University of Tennessee:M.Batygov, W.Bugg, H.Cohn, Y.Efremenko, Y.Kamyshkov, A.Kozlov, Y.Nakamura • TUNL/NCSU:L.De Braeckeleer, C.R.Gould, H.J.Karwowski, D.M.Markoff, J.A.Messimore, K.Nakamura, R.M.Rohm, W.Tornow, A.R.Young • IHEP, Beijing:Y.-F.Wang

16. Unique features of KamLAND detector:  Large mass: 1,000 ton of Liquid Scintillator ( ~ CH2)  Low detection threshold: < 1 MeV  Good energy resolution:  Position reconstruction accuracy in x,y,z: ~ 15 cm  Low background: 2700 mwe; buffer shield; veto-shield; Rn shield; LS purification for U, Th < 1016 g/g These features allow observation of a sequence of nuclear de-excitation states produces by a disappearance of nucleon.

17. SIGNATURES OF NUCLEON DISAPPEARANCE IN LARGE UNDERGROUND DETECTORS. Edwin Kolbe and YK Phys.Rev.D67:076007, 2003 Measurement idea: Search for the sequence of events (3 hits) correlated in space and time 2 neutrons out of 6 in 12C are is s½ state

18. De-excitation branching of J=½+11C* state vs excitation energy in statistical code SMOKER: J.J. Cowan, F.-K. Thielemann, J.W. Truran, Phys. Rep. 208 (1991) 267; further code developments by E. Kolbe n-hole excitation

19. Neutron Disappearance Modes in KamLAND 12C(n)11C* n+10C* +10C (3.35 MeV ) 10B ++(27 sec, QEC = 3.65 MeV, 99%) Modes favorable for detection in KamLAND (Br calculated in SMOKER) 30%

20. Expected 90% CL sensitivity (analysis is in progress) small accidental background For one n-disappearance from 12C: 71029 yr current SNO limit is  > 1.91029 yr For two n-disappearance from 12C: 1.71030 yr current Borexino limit is  > 4.91025 yr

21. (3) Neutron Antineutron Transitions

22. • The oscillation of neutral matter into antimatter is well known to occur in and particle transitions due to the non-conservation of strangeness and beauty quantum numbers by electro-weak interactions. • There are no laws of nature that would forbid the transitions except the conservation of "baryon charge (number)": M. Gell-Mann and A. Pais, Phys. Rev. 97 (1955) 1387 L. Okun, Weak Interaction of Elementary Particles, Moscow, 1963 • was first suggested as a possible mechanism for explanation of BAU (Baryon Asymmetry of Universe ) by V. Kuzmin, 1970 Neutron Antineutron Transition • First considered and developed within the framework of Unification models by R. Mohapatra and R. Marshak, 1979

23. For wide class of L-R and super-symmetric models predicted n-nbar upper limit is within a reach of new n-nbar search experiments!

24. Quarks and leptons belong to different branes separated by an extra-dimension ; proton decay is strongly suppressed, n-nbar is NOT since quarks and anti-quarks belong to the same brane.

25. Proton decay is strongly suppressed in this model, but n-nbar is not since nR has no gauge charges

26. Effective D = 7 operators can generate n-nbar transitions

27. nnbar transition probability -mixing amplitude

28. nnbar transition probability (for given )

29. PDG 2004: Limits for both free reactor neutrons and neutrons bound inside nucleus Bound n: J. Chung et al., (Soudan II) Phys. Rev. D 66 (2002) 032004 > 7.21031 years Free n: M. Baldo-Ceolin et al.,  (ILL/Grenoble) Z. PhysC63 (1994) 409 with P = (t/free)2 Search with free neutrons is square more efficient than with bound neutrons Uncertainty of R from nuclear models is ~ factor 2

30. Future nnbar search limits with bound neutrons Future limits expected from SNO and Super-K Since sensitivity of SNO, Super-K, and future large underground detectors will be limited by atmospheric neutrino background (as demonstrated by Soudan-2 experiment), it will be possible to set a new limit, but difficult to make a discovery!

31. Free neutron experiment Best reactor measurement at ILL/Grenoble reactor in 89-91 by Heidelberg-ILL-Padova-Pavia Collaboration

32. No background! No candidates observed. Measured limit for a year of running: = 1 unit of sensitivity Detector of Heidelberg -ILL-Padova-Pavia Experiment @ILL 1991 (size typical for HEP experiment)  

33. compete with large Mt detectors Not available Future searches with free neutrons • if no background, one event can be a discovery • possible to increase sensitivity by more than  1,000 bound > 1035 years; free > 1010 sec • use existing research reactor facilities? e.g. HFIR at ORNL?

34. New Scheme of N-Nbar Search Experiment at DUSEL  Dedicated small 3.4 MW power TRIGA research reactor with cold neutron moderator  vn ~ 1000 m/s  Vertical shaft ~1000 m deep with diameter ~ 6 m  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!)  Inverse scheme with reactor at the bottom and detector on the top of the mine shaft is also feasible  Possible sites ? WIPP, Soudan, Homestake, Sudbury

35. Annular core TRIGA reactor for N-Nbar search experiment Annular core TRIGA reactor 3.4 MW with convective cooling, vertical channel, and large cold moderator. Unperturbed thermal flux in the vertical channel 3E+13 n/cm2/s ~ 1 ft Example: UT Austin research TRIGA reactor. It is a 1.2-MW core. The last university reactor installed in the country (about 1991). It costs about $3.5 M plus fuel; the cost of the fuel depends on whether you get it from DOE or not. Courtesy of W. Whittemore (General Atomics)

36. FNAL Proton Driver as a Source of Cold Neutrons? • A 2 MW 8-GeV Proton Driver could be designed to be a very efficient source of cold neutrons with average flux equivalent to that of the ~ 20 MW research reactor • e.g. at SNS ~ 22 neutrons are produced per 1 GeV proton in Hg target • 2 MW PD spallation target can produce thermal flux ~ 21014 n/cm2/s • efficient reflector (e.g. D2O) and cryogenic D2 moderator • vertical 1000-m deep shaft under the target • no interference with neutrino program

37. (An example) SNS Target-Moderator System Reflector Target Moderators Proton Beam

38. Soudan-2 limit  ILL/Grenoble limit = 1 unit of sensitivity

39. Science impact of n-nbar search

40. Conclusions • (BL) violating processes are important part of the baryon number violation search program • n-nbar transitions might be most spectacular manifestation of (BL) violation due to large possible increase of sensitivity and no background • new possibilities for the large next step in baryon number violation search can be in connection with DUSEL and FNAL PD

42. Suppression of nnbar in intranuclear transitions

43. How CPT violation works in nnbar transitions? Following Yu.Abov, F.Djeparov, and L.Okun, Pisma ZhETF 39 (1984) 493 • Transitions for free neutrons V=0 are suppressed when • Suppression when m >  • In intranuclear transitions where V~10 MeV small provides no additional suppression. Intranuclear transitions are not sensitive to m !

44. m vs  in nnbar search (if 0) Experimental limits on mass difference Uncertainty of intranuclear suppression If nnbar transition will be observed this will be a new limit of CPT m test

45. TRIGA Cold Vertical Beam, 3 years Cold Beam

46. Future p-decay sensitivity J. Wilkes, 25 Feb '05 at Neutrino Telescopes