# Presentation: 524833

## N-Nbar Oscillation Search With Cold Neutrons @DUSEL

- Phenomenology/previous experiment
- Improved limit of 1000 in transition rate possible with cold neutrons
- Also at this workshop:
- A3: _R&D plans, cost schedule_ (Y. Kamyshkov/Tennessee)
- B1: Low level counting: _backgrounds from TRIGA_ (J. Hill/CSUDH)
- B2: Other Uses: _vertical facility_ (Y Kamyshkov/Tennessee)
- B3: Instrumentation:_nnbar technologies_ (G. Greene/Tennesee-ORNL)
- B4: Theory: _nnbar oscillations_ (R. Mohapathra/Maryland)
- B5: Facilities: _nnbar facility requirements_ (Lee Petersen/CNA)
- B5: Facilities: _reactor facility at DUSEL_ (Y. Kamyshkov/Tennessee)
- B6: Management: _TRIGA licensing and ownership_ (Y. Kamyshkov)
- B7: nnbar education and outreach plans (S. Pfiffnet/Tennessee)

- M. Snow
- Indiana University/IUCF
- DUSEL workshop

## http://inpa.lbl.gov/blnv/blnv.htm 

- http://inpa.lbl.gov/blnv/blnv.htm

- Scientific Reach: Discussed in Recent LBL Workshop

## Neutron-Antineutron transition probability: quasifree condition

- Contributions to V:
- <Vmatter>~100 neV, proportional to density
- <Vmag>=B, ~60 neV/Tesla; B~10nT-> Vmag~10-15 eV
- <Vmatter> , <Vmag> both  >>

- Figure of merit=                 N=#neutrons, T=“quasifree” observation time

## N-Nbar search at ILL (Heidelberg-ILL-Padova-Pavia)

- No GeV background
- No candidates observed.
- Measured limit for
- a year of running:

- Baldo-Ceolin M. et al., Z. Phys. C63,409 (1994).

## Scheme of N-Nbar search experiment at DUSEL

- ·  ~3 MW TRIGA research reactor with vertical hole and cold neutron moderator ® vn ~ 1000 m/s
- ·  Vertical shaft ~1000 m deep with diameter ~ 4-5 m  at DUSEL
- ·  Large vacuum tube, focusing
-     reflector, magnetic shielding
- ·  Detector (similar to ILL N-Nbar
-    detector) at the bottom of shaft
- Letter of intent to DUSEL submitted

## Sources of x1000 Improvement on ILL Experiment 

- with Cold Neutrons

- -increased phase space acceptance of neutrons from source (use new supermirror technology, some R&D, see G. Greene talk B3): x~60
- -increase running time: x~3
- -increase neutron free-flight time time: x~100
- -decreased source brightness :x~1/20
- Must maintain quasifree condition: magnetic shielding R&D (see G. Greene talk B3)
- For horizontal experiment: greater source brightness ~counteracted by (dispersive) gravitational defocusing of Maxwellian neutron spectrum

## Annular core TRIGA reactor (General Atomics) 

- Annular core TRIGA reactor (General Atomics)
- for N-Nbar search experiment

- annular core TRIGA reactor 3.4 MW
- with convective cooling, vertical channel,
- and large cold LD2 moderator (T*n *~ 35K).

- Courtesy of W. Whittemore
- (General Atomics)

- ~ 1 ft

- •  GA built ~ 70 TRIGA reactors 0.01 ̧14 MW (th)
- •  19 TRIGA reactors presently operating in US
-     (last commissioned in 1992)
- •  25 TRIGA reactors operating abroad
-     (last commissioned in 2005)
- •  some have annular core and vertical channel

**Well-established technology**

- See Y Kamyshkov talk B6

## “Supermirrors”: critical mcritical  

- 1

- 

- c

- Reflectivity

- 

- c

- m

- ~ 1000 layers

*Commercial Supermirror Neutron Mirrors are Available With m *≈* 3 - 4. *
*Phase space acceptance for straight guide ****m**2**, more with focusing reflector*

- “Items of commerce”

- Multilayer mirror

- _Engineering R&D issues @DUSEL:_
- (1) Mechanical support of large vertical neutron reflector in tube
- (2) Assembly of reflector into tube

## Bt<<ћ ILL achieved |B|<10 nT over 1m diameter, 80 m beam,one layer 1mm shield in SS vacuum tank,  1% reduction in oscillation efficiency (Bitter et al, NIM A309, 521 (1991).

- Bt<<ћ ILL achieved |B|<10 nT over 1m diameter, 80 m beam,one layer 1mm shield in SS vacuum tank,  1% reduction in oscillation efficiency (Bitter et al, NIM A309, 521 (1991).

- Quasifree Condition: B Shielding

- _Engineering R&D _
- _issues @DUSEL:_
- (1) Mechanical support of
- large vertical magnetic shield
- (2) Assembly of shield
- (3) Magnetic environment
- of shaft

## Voptt<<ћ: 

***Control Room & Electronics***

***Detector Hall***

***Neutron Dump***

***Neutron shaft***

***Access Tunnel***

***Door***

- See L. Petersen CNA Engineering, B5

- Voptt<<ћ:
- Need vacuum to eliminate
- neutron-antineutron optical
- potential difference.
- P<10-5 Pa is good enough,
- much less stringent than LIGO

- Quasifree Condition: Vacuum

- _Engineering R&D _
- _issues @DUSEL:_
- Mechanics of vertical tube
- (2) Assembly of vertical tube
- (3) Straight shaft #5?

## The conceptual 

- The conceptual
- scheme of
- antineutron detector

## New Experiment at Existing Research Reactor?

- •  need cold neutron source at high flux reactor, close access of
- neutron focusing reflector to cold source, free flight path of >~300m

- •  No luck so far (requests to all >20 MW research reactors
- with cold neutron sources)

- Cutaway view HFIR reactor at ORNL

## Education/Outreach (S. Pfiffnet/B7)

- “teach the process” to students: just how does one do such a large-scale engineering study?
- Engineering and physics workshop at/near DUSEL
- Public seminars/lectures associated with project meetings (energy resources, nuclear technology)
- Undergraduate/graduate research (ex: neutron optics simulations, antineutron detector backgrounds,...)
- College coursework enhancement in Systems Design (UT, NCSU)
- DUSEL-related lesson plans for local high school teachers

## Conclusions

- Sensitivity of cold neutron experiment for n-nbar transition rate
- can be improved by factor of ~1000. Combination of improvements in neutron optics technology, longer observation time (from vertical arrangement @DUSEL), and larger-scale experiment
- Clearly serious engineering and other issues remain to be addressed before any vertical experiment can be seriously proposed. Work on these issues is in progress, see next talk by YK.
- A* *R&D effort would be needed to provide the information required to prepare a reliable cost estimate

- “What strikes me most is where you found space for all this”
- M. Bulgakov, The Master and Margarita

## NNbar Summary 

- New physics beyond the SM can be discovered by  NNbar search at DUSEL
- Expected improvement in N-Nbar transition probability is a factor of ~1,000

## Proto-collaboration for R&D Studies

- Ayman Hawari, Bernard Wehring, Albert Young, _NC State _
- Alexandre Kozlov
- Anatoli Serebrov, _PNPI_
- Kenneth Ganezer, Brandon Hartfiel, Jimm Hill, _CSUDH _
- David Baxter, Chris Lavelle, Chen-Yu Liu, W. M. Snow, _Indiana_
- George Flanagan, Jeffrey Johnson, Gary Mays, _ORNL_
- H Lee Dodds, Yuri Efremenko, Geoff Greene, Susan Pfiffner, Y. Kamyshkov, _Tennessee_
- JeeSeung Jang
- Pieter Mumm, _NIST_
- Y. Pokotilovskiy, _Dubna _
- Rabindra N Mohapatra, _Maryland _
- Takeyasu Ito,_ LANL_
- William Bugg, _SLAC_
- H. Shimizu, _KEK_

## (Specific) Scientific Motivation for nnbar search: Neutrino mass-NNbar connection

**Majorana neutrino -> implies ********(B-L)=2;**
**In quark-lepton unified theories B and L get connected, ********L=2 implies ********B =2  via B-L symmetry **
**-> N-N-bar oscillation.**
**There are reasons to think that there  may be quark lepton unification at high energies.**
**N-N-bar oscillation can be new window to Q-L unification as well as B-L symmetry. **
**(see R. Mohapathra talk B4)**
- Baryon and Lepton Number Violations Workshop
- Sept. 20-22, 2007, LBL http://inpa.lbl.gov/blnv/blnv.htm

## Sensitivity of vertical experiment

- For 3 years operation
- improvement in
- limit on
- transition rate
- is ~1000
- horizontal
- experiment could
- be comparable
- (shorter length
- compensated by
- higher neutron flux)