Yuri Kamyshkov/ University of Tennessee email: kamyshkov@utk

1. DUSEL Theory Workshop, OSU April 4, 2008 Experimental Status of NNbar Search and plans for DUSEL Yuri Kamyshkov/ University of Tennessee email: kamyshkov@utk.edu

2. Existing NNbar limits Sensitivity for free neutron search (observation probability) Sensitivity for bound neutron search (in nucleon decay expts) known from nuclear theory

3. Previous free neutron N-Nbar search experiment At ILL/Grenoble reactor in 89-91 by Heidelberg-ILL-Padova-Pavia Collaboration M. Baldo-Ceolin M. et al., Z. Phys., C63 (1994) 409 No background! No candidates observed. Measured limit for a year of running: = reference unit of sensitivity

4. Previous bound neutronN-Nbar search experiments *Preliminary S-K result Observed improvement weaker than SQRT is due to irreducible background of atmospheric neutrinos

5. Free Neutron and Intranuclear NNbar Limits Comparison Important to know theoretical uncertainty e.g. intranuclear nn pions with presumably large uncertainty is not accounted intranuclear search experiments Free neutron search limit

6. Nuclear reactor as a source of neutrons 1.5 km vacuum flight tube Anti-neutron detector NNbar unique for DUSEL Yates Ross #5; 5137 Shaft #5 might not be usable

7. 3.4 MW annular core research TRIGA reactor with Liquid D2 cold neutron moderator TRIGA = Training Research Isotopes from General Atomics

8. Neutron shaft Schematic of annihilation detector Detector Hall Door Access Tunnel Control Room & Electronics Neutron Dump

9. Why Vertical and TRIGA are needed ? and not Horizontal and existing high-power reactors? • First, one needs RESEARCH not POWER reactor since • by design virtue neutron fluxes are higher in former • Second, most important reason: vertical gravity produces • devastating effect on the cold horizontal neutron beam •  vertical layout doesn’t suffer from this effect, thus • 3.5 MW TRIGA is more efficient that largest 100 MW • research reactor HFIR at ORNL • There are no research reactors with the cold beam available; • they are all occupied by “fundamental” material research

10. DUSEL NNbar Baseline Features Vertical flight path 1 km Shaft diameter 15-20 ft Vacuum chamber with 105 Pa Active + passive magnetic shield 1 nT Annular core TRIGA reactor 3.4 MW LD2 cryogenic cold moderator; neutron temperature 35K Running time 3-5 years Robust detection signature nA  several pions 1.8 GeV Annihilation properties are well modeled LEAR physics Active magnetic shielding allows effect ON/OFF Sensitivity increase more than 1000 Expected background at max sensitivity <0.01 event with no background one event can be a discovery!

11. NNbar DUSEL Sensitivity Reach Most exciting for experiment is a possibility of increasing sensitivity by large factor  1,000 (or nucl  1035 years) Conservative DUSEL baseline configuration based on established technologies Possible improvement by on-going developments

12. Other factors that could enhance the sensitivity (a) Larger shaft length (b) Larger reactor power (c) New reflector quality (developments at KEK/Japan)(d) New “colder” moderator thermalizing neutrons to lower temperatures Thermalization of n to the temperatures lower that 35K is a challenge for CM theory; non-sufficient R&D efforts

13. Development of neutron reflectors H. Shimizu, KEK/Japan Economically possible in future

14. Can NNbar create a background for other DUSEL experiments? Neutrinos ? For reactor located at the distance 2 km from the DUSEL main campus reactor antineutrino flux is not larger (e.g. by scaling from KamLAND) than solar neutrino flux • Might be still essential for CC • antineutrino detection experiments • at DUSEL (e.g. geo-neutrinos)

15. Thermal neutrons? can be easily shielded down to the environmental level. The environmental thermal neutron level is not precisely known at Homestake mine  ongoing R&D to measure it and then we will have to make sure that TRIGA reactor will not increase this level. Attenuation of thermal neutron flux by concrete shield

16. NNbar Collaboration North Carolina State University: A.I. Hawari, B.W. Wehring, A. Young Indiana University: W.M. Snow, C. M. Lavelle University of Tennessee: W. Bugg, H.L. Dodds, Y. Efremenko, G. Greene, Y. Kamyshkov, S. Pfiffner California State University at Dominguez Hills: K. Ganezer, J. Hill Oak Ridge National Laboratory: G. Flanagan, J.O. Johnson, K. Williams Los Alamos National Laboratory: T. Haines, A. Saunders National Institute of Standards and Technology: Pieter Mumm CNA Consulting Engineers: L. Petersen International Collaborators: KEK, PNPI, Dubna, ILL, Swiss Neutronics • The group has experience and expertise in • large projects construction (L3 /LEP Hadron Calorimeter, KamLAND) • participation in large underground experiments (UT, CSUDH) • large scale underground construction (CNA Engineering: MINOS,S1) • reactor licensing, commissioning, operations (NCSU and ORNL) • cold neutron sources and cold neutron experiments (IU, NCSU, UT) • neutron technologies like supermirrors and mag. shield (IU, UT) • neutron transport simulations (NCSU, ORNL, UT) • intranuclear NNbar transition search (CSUDH) • particle detector design, construction, simulations, cost estimate, etc.

18. Preliminary Project Development Plan construction feasibility 2009 2015 2011 2013 conceptual design decision like CD0 is needed prelim design board approve construction

19. Vertical experiments at DUSEL are non-traditional “other uses”. Unique feature of DUSEL among other underground labs.  Homestake PAC received in 2005 following “vertical” LOIs: #7 Search for neutron to antineutron transitions (Yu. Kamyshkov/UT) #23 Study of diurnal Earth rotation (W. Roggenthen / SDSMT) #33 Physics of cloud formation (J. Helsdon / SDSMT)  New Vertical LOIs (2007): # Cold atom interferometry for detection of gravitational waves (M. Kasevich / Stanford U) # Search for transitions to mirror matter (n  n) Mirror matter is an alternative explanation of the dark matter (A. Serebrov / PNPI)