on behalf of NNbar Collaboration

1. Yuri Kamyshkov University of Tennessee May 5, 2006 SUNY Stony Brook on behalf of NNbar Collaboration Search for neutron  antineutron transitions at DUSEL N-Nbar proto-collaboration

2. Motivation  The origin of matter-antimatter asymmetry in the Universe (BAU) remains an unresolved problem • 1967 A. Sakharov: 3 BAU conditions, including baryon number violation. The mechanism of B violation was undefined • 1976 ’t Hooft: B and L are violated in SM; 1985 Kuzmin, Rubakov, Shaposhnikov: large effect in Early Universe (sphalerons) at the temperature scale >EW erasing (B+L). Need (BL) violation above EW scale to explain BAU! • Proton decay modes conserving (BL) e.g. p e++ 0 can not generate BAU  PDK at GUT scale is not the mechanism of baryogenesis • Leptogenesis: very high-temperature ~ 1012 GeV heavy-Majorana transition with L=2 and  (BL)0, then converted to baryon asymmetry by sphalerons at EW energy scale. Beautiful idea but untestable directly • Neutron  antineutron transition with B=2 and  (BL)0 is possible testable mechanism of BAU

3. |B|=2 ; |(BL)|=2 •There are no laws of nature that would forbid the N  Nbartransitions 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 • N  Nbar was first suggested as a possible mechanism for explanation of Baryon Asymmetry of Universe by V. Kuzmin, 1970 • N  Nbarworks within GUT + SUSY. First considered and developed within the framework of L-R symmetric Unification models by R. Mohapatra and R. Marshak, 1979 … • Several recent theory papers beyond SM related to N  Nbar: K. Babu and R. Mohapatra, PLB 518 (2001) 269 S. Nussinov and R. Shrock, PRL 88 (2002) 171601 G. Dvali and G. Gabadadze, PLB 460 (1999) 47 H.Davoudiasl, et.al, PRL 93 (2004) 201301 B. Dutta, Y. Mimura, R. Mohapatra, PRL 96 (2006) 061801

5. Supersymmetric Seesaw for  BL , LR New n-nbar experiment ILL/Grenoble experiment limit (1994) New n-nbar experiment Low QG models nn LHC Dvali & Gabadadze (1999) Non-SUSY models Plank scale Left-Right symmetric GUT SUSY GUT PDK nn nn Dutta-Mimura-Mohapatra (2005) Mohapatra & Marshak (1980)

6. 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 ! R is “nuclear suppression factor” Uncertainty of R from nuclear models is ~ factor of 2

7. Previous n-nbar search experiment with free neutrons At ILL/Grenoble reactor in 89-91 by Heidelberg-ILL-Padova-Pavia Collaboration M.Baldo-Ceolin M. et al., Z. Phys., C63 (1994) 409

8. 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  

9. How one can improve on such state-of-the-art experiment and achieve 3-4 orders of magnitude higher sensitivity? • Two major improvements: • Focusing of neutrons: use of larger solid angle • Vertical layout: compensating Earth gravity • (even with weaker neutron source)

10. N-Nbar search experiment idea with vertical layout at DUSEL  Dedicated small-power research reactor with cold neutron moderator  Vn 1000 m/s  Vertical shaft 1000 m deep with diameter 5 m  Large vacuum tube 105 Pa, focusing reflector; Earth magnetic field compensation system ~ nT  Detector (similar to ILL N-Nbar detector) at the bottom of the shaft (no new technologies)  No background: one event discovery! 105 Pa The possibility of a large increase in sensitivity of the experimental search for n anti-n transition is a central motivation of our LOI Not to scale

11. Neutron source needed: small power 3.4 MW TRIGA reactor TRIGA Reactor picture courtesy of General Atomics

12. Annular core TRIGA reactor (GA) for N-Nbar search experiment • GA built ~ 70 TRIGA reactors 0.0114 MW (th) • 19 TRIGA reactors are presently operating in US (last commissioned in 1992) • 25 TRIGA reactors operating abroad (last commissioned in 2005) • some have annular core and vertical channel • most steady, some can be pulsed up to 22 GW • safe ~ 20% EU uranium-zirconium hydride fuel ~ 1 ft Economic solution for n-nbar: annular core TRIGA reactor 3.4 MW with convective cooling, vertical channel, and large cold LD2 moderator (Tn ~ 35K). Unperturbed thermal flux in the vertical channel ~ 21013 n/cm2/s Cold neutrons Courtesy of W. Whittemore (General Atomics)

13. 2.2K Maxwellian J.M. Carpenter et al., 2005 New ANL development enhancing n-nbar search sensitivity Very Cold Neutron Source with Tn ~ 2.2K (IPNS/ANL R&D project by J.M. Carpenter et al., 2005)

14. Soudan-II limit  ILL/Grenoble limit = 1 unit of sensitivity DUSEL

15. TRIGA Very Cold Vertical Beam, 3 years TRIGA Cold Vertical Beam, 3 years Cold Beam

16. • further experiments with free neutrons will allow high-sensitivitytesting (L. Okun et al, 1984) (S. Lamoreaux et al, 1991) • wide class of SUSY-based models will be removed (K. Babu and R. Mohapatra, 2001) Possible impact of NNbar search at DUSEL If discovered: • nnbar will establish a new force of nature and a new phenomenon leading to the physics at the energy scale of > 105 GeV • will provide an essential contribution to the understanding of BAU • might be the first detected manifestation of extra dimensions and low QG scale • new symmetry principles can be experimentally established: (BL)0 If NOT discovered: • within the reach of improved experimental sensitivity will set a new limit on the stability of matter exceeding sensitivity of X-large nucleon decay experiments

17. Possible N-Nbar location at DUSEL/Henderson ? L~ 670m Ø ~ 10’ > 2026

18. Possible N-Nbar location at DUSEL/Henderson dia 6’  dia 20’ L ~ 580 m Avail.  2014

19. What is required for NNbar experiment at DUSEL? • Vertical shaft > 0.5 km deep, with dia  5 m to be instrumented • Construction access from the top and the bottom of the shaft • Location far frommain underground labs • Reactor s are background for geo-neutrino studies... • Ownership of the reactor ? • Heat removal from 3.5 MW TRIGA reactor Cryogen equipment for cold moderator • Many other things (to be discussed later)

20. Timeline of NNbar project development at Henderson/DUSEL  2007 Letter of Interest to DUSEL. Site non-specific/specific R&D  2008 Development of experiment proposal for NSF/DOE  2009 Proposal approval with funding agencies. CD0 2010 decision on vertical shaft enlargement 2010-2014 TDR, reactor license, more R&D, reviews …  ~ 2 years of construction  ~ 3 years of running

22. In the Supersymmetric Seesaw model describing the neutrino masses, leading N-Nbar operator was shown to have very weak power dependence on the seesaw scale i.e. 1/M2seesaw rather than 1/M5seesaw as in naive dimensional arguments. That makes N-Nbar observable within the reach of present experimental techniques. That also opens up the window for leptogenesis.

23. Proton decay is strongly suppressed in this model, but n-nbar should occur since nR has no gauge charges

24. 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! If not seen, n-nbar should restrict a wide class of SUSY models.

25. 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.

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