Neutron-Antineutron Oscillation Search with Cold Neutron-Antineutron Oscillation Search with Cold NeutronsNeutrons

ILL beam experimentImproved experiment with horizontal beam:(1) Reactor source, (2) pulsed sourceVertical experiment: DUSEL proposal

M. SnowM. SnowIndiana University/CEEMIndiana University/CEEMNANO WorkshopNANO Workshop

Thanks for slides and calculations to: Yuri Kamyshkov, Geoff Greene, Hiro Shimizu

Neutron-Antineutron transition probability

For H =E +V αα E −V

⎛⎝⎜

⎞⎠⎟ P n→ n t( ) =

α 2

α 2 +V2 ×sin2 α 2 +V2

ht

⎡

⎣⎢⎢

⎤

⎦⎥⎥

where V is the potential difference for neutron and anti-neutron.

Present limit on α ≤10−23eV

For α 2 +V2

ht

⎡

⎣⎢⎢

⎤

⎦⎥⎥<<1 ("quasifree condition") Pn→ n =

αh×t⎛

⎝⎜⎞⎠⎟

2

=tτnn

⎛

⎝⎜⎞

⎠⎟

2

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

Figure of merit= N=#neutrons, T=“quasifree” observation timeNT 2

Neutron Cooling: MeV to neV

10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 10010-6

10-5

10-4

10-3

10-2

10-1

100

101

102

103

W(En)

En [eV]

T30K T293K

UCN Very cold Cold ThermEpitherm

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

with L ~ 90 m and t =0.11 sec

measured Pnn <1.6 ×10−18

τ > 8.6 ×107 sec

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

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

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). For new experiment need |B|<~1 nT

Quasifree Condition: B Shielding and Vacuum

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

If nnbar candidate signal seen, easy to “turn it off” by increasing B

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

The conceptual scheme of antineutron detectorThe conceptual scheme of antineutron detector

pionsAn 5⟩⟨→+ (1.8 )GeV Annihilation targ :et ~100 thick Carbon film

annihilation 4 Kb n C capture 4 mb

Better Cold Neutron Experiment (Horizontal beam)Better Cold Neutron Experiment (Horizontal beam)• • need cold neutrons from high flux source, access of neutron need cold neutrons from high flux source, access of neutron focusing reflector to cold source, free flight path of ~200-300mfocusing reflector to cold source, free flight path of ~200-300m

Improvement on ILL experiment by factor of ~1000 in transitionImprovement on ILL experiment by factor of ~1000 in transitionprobability is possible (but expensive) with existing n optics probability is possible (but expensive) with existing n optics technology and sourcestechnology and sources

L = 300 m

D ~ 2-3 m

concept of neutron supermirrors: Swiss Neutronics

neutron reflection at grazing incidence (< ≈2°)neutron reflection at grazing incidence (< ≈2°)

refractive index n < 1

total external reflection e.g. Ni c = 0.1 °/Å

@ smooth surfaces@ smooth surfaces @ multilayer@ multilayer @ supermirror@ supermirror

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.40.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

λ = 5 Å

reflectivity

[°]0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0d

λ = 5 Å

reflectivity

[°]0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0d

2>d

1

λ = 5 Å

reflectivity

[°]0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

λ = 5 Å

reflectivity

[°]

d3>d2>d1

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.40.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

λ = 5 Å

reflectivity

[°]

λ sin2d=

Supermirror Neutron Optics: Elliptical Focusing GuidesSupermirror Neutron Optics: Elliptical Focusing Guides

Muhlbauer et. al., Physica B 385, 1247 (2006).

Under development for neutron scattering spectrometers

Can be used to increase fraction of neutrons delivered from cold source(cold source at one focus, nbar detector at other focus)

“Supermirrors”: critical mcritical

1

c

Ref

lect

ivity

cm

~ 1000 layers

Commercial Supermirror Neutron Mirrors are Available With m ≈ 3 - 4.

Phase space acceptance for straight guide m2, more with focusing reflector

“Items of commerce”

Multilayer mirror

H.

Shi

miz

u, K

EK

/Jap

anSupermirror Neutron Optics: Higher m and reflectivitySupermirror Neutron Optics: Higher m and reflectivity

m=10!

From H. Shimizu

Prototype supermirrors with m~6 produced

Useful neutron flux scales roughly as m2

Image Courtesy; H. Shimizu

New Experiment at Existing Research Reactor?New Experiment at Existing Research Reactor?

• • Requests to all >20 Requests to all >20 MW research reactors MW research reactors

with cold neutron with cold neutron sourcessources

Cutaway view HFIR reactor at ORNL

• • need close access to need close access to cold source to fully cold source to fully illuminate elliptical illuminate elliptical

reflectorreflector

• • Can a reactor be Can a reactor be found? Not yet…found? Not yet…

Advantages of a Next-Generation Pulsed Neutron Advantages of a Next-Generation Pulsed Neutron Source (ESS) for Source (ESS) for

A Neutron-Antineutron Oscillation ExperimentA Neutron-Antineutron Oscillation Experiment

Possibility to use active neutron optics to partially correct forgravitational defocusing

Possibility to optimize the target/moderator system with this experiment in mind, and take advantage of a “colder” cold source if moderator research is successful.

Possibility to upgrade reflector with other developments in neutron optics (higher m higher reflectivity supermirrors, …)

At a pulsed neutron source like ESS, neutrons of a given speed reach the mirror at a known time. We can therefore imagine an array of mirrors tiling an ellipse and phased to the source to condition the beam

Piezodrivers

This tilting can be used to counteract the defocusing of the beamfrom gravity, thereby reducing the beam/detector size and thereforereduce the cost of the experiment.

Nt2 distribution vs vertical Y in the target plane

m=4; | xtarget | < 1 m.

Radius of beam is smaller by~factor of 2->cost of experiment is smaller (scales generically as the area)

Supermirror Neutron Optics: Future PossibilitiesSupermirror Neutron Optics: Future Possibilities

“In the future one may consider varying the shape of the guides actively by means of piezo actuators. If used at pulsed sources, beam size and therefore the divergence for each wavelength during a neutron pulse can be optimized. This corresponds to a kind of active phase space transformation that will allow the circumvention of Liouville’s theorem. The combination of fast mechanical actuators with supermirror technology may become useful for active phase space transformation.”

P.Boni, NIM A586, 1 (2008).

One could design the experiment to be able to take advantageof such advances in active neutron optics technology throughmodification of the reflector

1 m

100 m

3.4 MW Annular Core TRIGA reactor 3E+13 n/cm2/s thermal flux

Deuteriummoderator

Focusing ReflectorL~150 mVacuum

TubeL~1000mD~3-4m

AnnihilationTarget D~2 m

Beam dump

Detector

Neutrontrajectory

Approximatescales

MagneticShield

· ~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 proposed US DUSEL facility

· 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

Scheme of Vertical N-Nbar experiment

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

annular core TRIGA reactor 3.4 MWwith convective cooling, vertical channel, and large cold LD2 moderator (Tn ~ 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

Cold NeutronSource

Example

Made in PNPI, Russia

Liquid hydrogen at 20K

Inserted vertically into research reactor

Delivered to new Australianresearch reactor, 18 MW power

3.4 MW annular coreresearch TRIGA reactor with Liquid D2 cold neutron moderator

TRIGA =TrainingResearchIsotopesfrom General Atomics

Vertical flight path 1-1.5 km

Shaft diameter 15-20 ftFocusing mirror reflector 4c

Vacuum chamber with 105 Pa

Active + passive magnetic shield 1 nT

Annular core TRIGA reactor 3.4 MWLD2 cryogenic cold moderator; neutron temperature 35K

Running time 3-5 years

Robust detection signature nC several pions 1.8 GeV

Annihilation properties are well understood LEAR physics

Active magnetic shielding allows effect ON/OFF

Free-n sensitivity increases more than 1000

Expected background at max sensitivity 0.01 event

Talks posted at http://hepd5s.phys.utk.edu/nnbar/April/

1km Vertical Space Working Group1km Vertical Space Working Group

NNbar: search for neutron to antineutron transitions (Yuri Kamyshkov/UT)Study of diurnal Earth rotation (Bill Roggenthen/SDSMT)Physics of cloud formation (John Helsdon/SDSMT)Search for transitions to mirror matter (n n) (Anatoli Serebrov / PNPI)Cold atom interferometry for detection of gravitational waves (Mark Kasevich / Stanford U)

Experiment Length Dia Pressure Mag. shield

Purpose

NNbar 1.5 km 4-5 m <10 Pa ~ 1 nT

Mirror neutrons 1.5 km 4-5 m <10 Pa ~ 1 nT n disappearance

Atom interferometry 1-4 km 0.3 m < .1 Pa ~ 1 nT grav. wave detection

Cloud Form Physics 0.5-1 km 3-5 m 0.2 atm N/A atm. physics facility

Diurnal rotation 0.1-1 km 1m <10 Pa N/A E&O

Sources of x1000 Improvement on ILL Experiment Sources of x1000 Improvement on ILL Experiment with Cold Neutronswith Cold Neutrons

-increased phase space acceptance of neutrons from source (using m=3 supermirrors): x~60

-increase running time: x~3

-increase neutron free-flight time (t2): x~100 (vertical), ~4-10 (horizontal)

-source brightness :x~1/20 (vertical 3.4 MW TRIGA)X~1/2 (horizontal, 20-60MW research reactor)

For horizontal experiment: greater source brightness ~counteracted by (dispersive) gravitational defocusing of Maxwellian neutron spectrum

Sources of x1000 Improvement on ILL Experiment Sources of x1000 Improvement on ILL Experiment with Cold Neutrons from CW Sourcewith Cold Neutrons from CW Source

-increased phase space acceptance of neutrons from source (using m=3 supermirrors): x~60

-increase running time: x~3

-increase neutron free-flight time (t2): x~4-10 (horizontal)

-source brightness :x~1/2 (horizontal, 20-60MW research reactor)

For CW horizontal experiment: greater source brightness ~counteracted by (dispersive) gravitational defocusing of Maxwellian neutron spectrum