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

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? 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 ~ 10 29 yr to  10 34 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) (experimentalist’s view)

4. 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? More Questions:

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): (1) (1)Baryon number violation (2) (2)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. Is (B  L) conserved? In our laboratory samples (B  L) = #protons + #neutrons  #electrons In our laboratory samples (B  L) = #protons + #neutrons  #electrons (B  L)  0 However, in the Universe most of the leptons exist as, yet undetected, 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: Non-conservation of (B  L) was discussed theoretically since 1978 by: Davidson, Marshak, Mohapatra, Wilczek, Chang, Ramond... 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) 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) “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. If (B  L) is violated at T above electroweak scale Violation of (B  L) implies nucleon instability modes: Rather than conventional p-decay modes: 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. Some  (B  L)  0 nucleon decay modes (PDG’04) (B  L)  0 modes Limit at 90% CLS/BExperiment’year >1.7  10 31 yr 152/153.7IMB’99 >2.1  10 31 yr 7/11.23Fréjus’91 >2.57  10 32 yr 5/7.5IMB’99 >7.9  10 31 yr 100/145IMB’99 >1.9  10 29 yr 686.8/656SNO’04 >7.2  10 31 yr 4/4.5Soudan-2’02 > 4.9  10 25 yr Borexino’03 e.g. for with a lifetime >1.7  10 31 yr Super-K would detect ~ 430 events/yr

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

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

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 ( ~ CH 2 )  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. Measurement idea: SIGNATURES OF NUCLEON DISAPPEARANCE IN LARGE UNDERGROUND DETECTORS. Edwin Kolbe and YK Phys.Rev.D67:076007, 2003 2 neutrons out of 6 in 12 C are is s ½ state Search for the sequence of events (  3 hits) correlated in space and time

18. De-excitation branching of J  =½ + 11 C* 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 12 C(n  ) 11 C*  n + 10 C*   + 10 C (3.35 MeV  )  10 B +  + (27 sec, Q EC = 3.65 MeV, 99%) one s ½ neutron dis. 11 C*  Br %Hits3-rd hit corr. time 1 n + 10 C gs (  + ) 3.0327.8 s 2 n +  + 10 C gs (  + ) 2.8327.8 s two s ½ neutrons dis. 10 C*  3 n + 9 C gs (  + ) 6.23182.5 ms 4 n + p + 8 B gs (  +,  ) 6.031.11 s 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 12 C: 7  10 29 yr current SNO limit is  > 1.9  10 29 yr For two n-disappearance from 12 C: 1.7  10 30 yr current Borexino limit is  > 4.9  10 25 yr

21. (3) Neutron  Antineutron Transitions

22. First considered and developed within the framework of Unification models by R. Mohapatra and R. Marshak, 1979 First considered and developed within the framework of Unification models by R. Mohapatra and R. Marshak, 1979 The oscillation of neutral matter into antimatter is well known to occur in 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. 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)": 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 was first suggested as a possible mechanism for explanation of BAU (Baryon Asymmetry of Universe ) by of BAU (Baryon Asymmetry of Universe ) by V. Kuzmin, 1970 Neutron  Antineutron Transition

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 n R 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. Bound n: J. Chung et al., (Soudan II) Phys. Rev. D 66 (2002) 032004 > 7.2  10 31 years  PDG 2004: Limits for both free reactor neutrons and neutrons bound inside nucleus Free n: M. Baldo-Ceolin et al.,  (ILL/Grenoble) Z. Phys C63 (1994) 409 with P = (t/  free ) 2 Uncertainty of R from nuclear models is ~ factor  2 models is ~ factor  2 Search with free neutrons is square more efficient than with bound neutrons

30. 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! Future n  nbar search limits with bound neutrons Future limits expected from SNO and Super-K

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

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

33. Future searches with free neutrons possible to increase sensitivity by more than  1,000 possible to increase sensitivity by more than  1,000  bound > 10 35 years;  free > 10 10 sec  bound > 10 35 years;  free > 10 10 sec compete with large Mt detectors if no background, one event can be a discovery if no background, one event can be a discovery use existing research reactor facilities? e.g. HFIR at ORNL? use existing research reactor facilities? e.g. HFIR at ORNL? Not available

34. New Scheme of N-Nbar Search Experiment at DUSEL  Dedicated small 3.4 MW power TRIGA research reactor with cold neutron moderator  v n ~ 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/cm 2 /s Courtesy of W. Whittemore (General Atomics) 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. ~ 1 ft

36. 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 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 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  10 14 n/cm 2 /s 2 MW PD spallation target can produce thermal flux ~ 2  10 14 n/cm 2 /s efficient reflector (e.g. D 2 O) and cryogenic D 2 moderator efficient reflector (e.g. D 2 O) and cryogenic D 2 moderator vertical 1000-m deep shaft under the target vertical 1000-m deep shaft under the target no interference with neutrino program no interference with neutrino program FNAL Proton Driver as a Source of Cold Neutrons?

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

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 (B  L) violating processes are important part of the baryon number violation search program n-nbar transitions might be most spectacular manifestation 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 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