Experimental Limit on d (e cm)

Nuclear and Particle Physics Very Low Energy Neutrons with

“Fundamental Neutron Physics”

Geoff Greene

University of Tennessee

&

Oak Ridge National Laboratory

Sept, 2009

Fundamental Neutron Physics Beamline

Drift Tube Linac

• System includes 210 drift tubes, transverse focusing via PM quads, 24 dipole correctors, and associated beam diagnostics

Coupled-Cavity Linac

• System consists of 48 accelerating segments, 48 quadrupoles, 32 steering magnets and diagnostics

Bridge Coupler 44 final machining

Installation Complete August 2004

Target, Reflectors, and Moderators

Be reflector Cryogenic

H₂ moderators

Ambient H 0 moderator

Mercury target Proton Beam

~1 GeV

Mercury

Mercury

Mercury Mercury

At ~1.4 GeV, each incident proton liberates ~60 neutrons

Typical neutron energy 10’s – 100 MeV

Target-Moderator System

4A - Magnetism Reflectometer Commission 2006 4B - Liquids Reflectometer Commission 2006

5 - Cold Neutron Chopper

Spectrometer Commission 2007 13 - Fundamental

Physics Beamline Commission 2007

11A - Powder Diffractometer Commission 2007

12 - Single Crystal Diffractometer Commission 2009

7 - Engineering Diffractometer IDT CFI Funded Commission 2008

6 - SANS

Commission 2007

14B - Hybrid Spectrometer Commission 2011

15 – Spin Echo

9 – VISION

Beamline 13 Has Been Allocated for Nuclear Physics

The NIST Cold Neutron research Center

Solid State Physicist’s view of the Neutron

Solid State Physicist’s view of the Neutron

The neutron is a point-like particle whose interaction with a point-like nuclei is described by a single well know

parameter; b_coh, the coherent (s-wave) scattering length

u d

d

A Nuclear Physicist’s view of a Neutron

A “Sea” of Gluons, “Strange”

Quarks, Anti-Quarks,….

Continuous creation and annihilation of particles and

anti-particles (π’s,ρ’s,ω’s,..) Lot’s of stuff in here that we Wish we know how to calculate

“Virtual Particles” of many different types.

Why Neutron Nuclear Physics?

The neutron exhibits much of the phenomenology of nuclei physics without the complexity of nuclear structure

“The neutron is complicated enough to be interesting, but simple enough to be understood.”

Why the SNS for Nuclear and Particle Physics?

The SNS has:

• The world’s highest peak flux of cold neutrons

• A time averaged flux that is competitive with the most intense continuous neutron sources in the world

• A well defined pulse structure

Neutrons Can Address Important Issues

• Why is there matter?

The neutron electric dipole moment, the origin of Baryon asymmetry, the nature of T and CP violation, …

• What Happened during the first 3 minutes of the Big Bang The neutron lifetime, The origin of the light elements, Big Bang Nucleosynthesis, the baryon density of the Universe,…

• Why is the Universe Left-Handed?

Parity violation in neutron decay, Left-right symmetry and spontaneous symmetry breaking,…

• What is the nature of the weak interaction between quarks?

Nucleon nucleon weak interactions, Parity violation between nucleons,

A Classical Electric Dipole Moment Violates T Non-Invariance

 ^

_J ^  ^

_J ^

EDM limits: the first 50 years

Experimental Limit on d (e cm)

1960 1970 1980 1990



Left-Right

10^-32 10^-20 10^-22 10^-24

10^-30

Multi

Higgs SUSY



Electro- magnetic

neutron:

electron:

2000 10^-20

10^-30

Baryon Asymmetry

The nEDM Experiment at the FNPB

Important Processes with the same Feynman Diagram as Neutron Decay

Ioffe-Type Magnetic Trap

0 0.5

1 1.5

-1.5 0 1.5

r (cm)

0 0.5 1 1.5

-30 -20 -10 0 10 20 30

Magnet form

Racetrack coil

Cupronickel tube

Acrylic lightguide

TPB-coated acrylic tube Solenoid

Neutron shielding Collimator

Beam stop Trapping region

The Magnetic Neutron Bottle

Recent Results From

The Harvard/NIST/LANL/HMI Neutron Lifetime Expt.

The Time Scale for the Big Bang (1)

Time Since Big Bang

<10^-43s

~10^-43s

~10^-35s

~10^-35s - 10^-33s

T (K)

 (g/cm^-3)

Quantum era Universe consists of “soup” of leptons & quarks Grand Unification Era

Gravity separates from other Grand Unified Forces End of Grand Unification

Strong Force breaks symmetry w/

ElectroWeak Force.

Inflationary epoch Universe inflates by a factor of 10³⁰ or more (“observable

10³²K

10²⁷K

The Time Scale for the Big Bang (2)

Time Since Big Bang

~10^-12s

~10^-6s

0.01s

1 s

T (K)

 (g/cm^-3)

Particle Era Electromagnetic force and Weak Force break symmetry.

Quark Hadron transition.

Protons and neutrons (plus antiprotons and anti neutrons) are formed from quarks - at this time the

“matter’ particles have an excess of ~one in a billion over “antimatter” particles.

The Universe is expanding rapidly, scale is doubling every 0.02s. As Universe expands it cools,

T ~ 1/R. Although the temperature is too low for Protons and neutrons to be created from the thermal energy of the early universe reactions such as:

_e+ n p⁺+ e^-

And vice-versa, maintain an equal number of

protons and neutrons. As the temperature decreases proton/neutron balance shifts in favor of less

massive protons.

Weakly interacting neutrinos “decouple”

from the rest of the Universe 10¹³K

10¹¹K 10¹⁵K

4 x 10⁹

10¹⁰K 4 x 10⁵

The Time Scale for the Big Bang (2)

Time Since Big Bang

~10^-12s

~10^-6s

0.01s

T (K)

 (g/cm^-3)

Particle Era Electromagnetic force and Weak Force break symmetry.

Quark Hadron transition.

Protons and neutrons (plus antiprotons and anti neutrons) are formed from quarks - at this time the

“matter’ particles have an excess of ~one in a billion over “antimatter” particles.

The Universe is expanding rapidly, scale is doubling every 0.02s. As Universe expands it cools,

T ~ 1/R. Although the temperature is too low for Protons and neutrons to be created from the thermal energy of the early universe reactions such as:

_e+ n p⁺+ e^-

And vice-versa, maintain an equal number of

protons and neutrons. As the temperature decreases proton/neutron balance shifts in favor of less

massive protons.

10¹³K

10¹¹K 10¹⁵K

4 x 10⁹

At about this temperature, only familiar “nuclear physics”

particles are present, only well understood processes are relevant, and the density is well below nuclear densities.

The Time Scale for the Big Bang (3)

Time Since Big Bang

15s

3 min

3 1/2 min

5 x 10⁵ yr

T (K)

 (g/cm^-3)

Temperature is below threshold for creation of electron/positron pairs e⁺/e^- annihilate: e⁺ + e^-  +  The Universe is “reheated” about 35% by annihilation.

Era of Nucleosynthesis

Nuclei can begin to hold together, e.g.

p + n d + 

At this time the baryons are divided into about 87% protons 13% neutrons.

Era of Galaxy Formation 10⁹K

10⁸K

10⁹ yr

3 x 10⁹K

4000K

4 x 10⁴

Era of Recombination nuclei &

electrons “recombine to form atoms Universe becomes transparent

End of Nuclear Reactions Neutrons have

been “used-up” forming ⁴He Universe is now 80% H nuclei (p⁺) & 20% He nuclei

400

p 2 He

He He

p He

He D

n He

T D

p T

D D

n He

D D

He D

p

d n

p

e p

n

4 3

3

3

4 3 3























































Some of the reactions in Big Bang Nucleosynthesis

The Cosmic He/H Ratio Depends upon three quantities:

1) The Cooling rate of the Universe

Given by the heat capacity of the Universe

Determined mainly by the number of “light particles”

(m ≤ 1 MeV )

Includes photons, electrons (positrons), neutrinos (x3) 2) The Rate at which Neutrons are decaying

The neutron lifetime

3) The rate at which nuclear interactions occur

Determined by the the logarithm of the density of nucleons (baryons)

) 28 . 10 (

018 .

0 N

012 .

0 log

023 .

0 228

. 0

Y_p  





Cosmic H

elium A

bundance

Numb

er of Ne

utrino Fla vors Neutro

n Life

time in M inutes

The Parameters of Big Bang Nucleosynthesis

Cosmic Bary

on De nsity





log





Cosmic

Baryo

n Density

Neutro n Life

time in M inu Cosm

ic Heliu

m Abun dance

We can “invert” this line of reasoning. If we measure the Helium Abundance, the Neutron Lifetime, and if we know the Number of “light” Neutrinos is 3, We can determine the

density of “ordinary” matter in the universe.

The Cosmic Helium Abundance “Y_P” vs the Baryon Density

Density of “Normal Matter”

(protons & neutrons)

The “Preposterous Universe”

~3% “Ordinary” Matter

~30% “Dark” Matter

~67% “Dark Energy”

Phenomenology of Neutron Beta Decay

n

p e



pe

pp

p



n

p e



pe

pp

p



Momentum Must Be Conserved!

Phenomenology of Neutron Beta Decay

n

p e



pe

pp

p



n

p e



pe

pp

p



V-A says that neutrinos are purely “Left-Handed” with

1 p  

 



Momentum Must Be Conserved!

Conservation of linear and angular momentum implies that there are strong correlations between the initial neutron spin and decay particle momenta.

Correlations in Neutron Decay

Parity violation implies a rich phenomenology in neutron decay.

V-A implies that All experimental Quantities can be related to the axial and vector coupling constants g_A and g_V.



     



 

  

   

 B E

A E E

b m E

a E 1

) E ( 1 F

dW ⁿ

e e n

e e e

e e n

p p

p p



 



 



 







V A

2

V A

g 3 g 1

g 1 g

a b  0

2

V A

V A 2

V A

g 3 g 1

g g g

g 2 A



 



 



 







 







 ₂

V A

V A 2

V A

g 1 g

g g g

g 2 B



 







 







 







2

2

3 g )

g

( 

) g 3 g

/(

1 _A² _V²

n  



Leptonic Weak Interaction

Semi-Leptonic Weak Interaction

“Pure” Hadronic Weak Interaction

ν_e e

e ν_e

d d u

u d u

e^- ν_e

d d u

u d u u

d u

u d d

Leptonic Weak Interaction

Semi-Leptonic Weak Interaction

“Pure” Hadronic Weak Interaction

ν_e e

e ν_e

d d u

u d u

e^- ν_e

u d u

u d d

Yukawa Potential

e^mr

The Weak Interaction between Nucleons is

“Overwhelmed” by the Strong Interaction

N N

N N

N N

N N

W^±,Z⁰

>>

N N

N N

PC

PNC

W^±,Z⁰

π,ρ,ω

π,ρ,ω

Parity Violation provides a “Tag” for the Weak Interaction

The Weak Interaction Mediated by a Meson is Observable

HADRONIC Weak Interaction

n p

d



Linear Polarization



Medium with

circular birefringence

PNC Capture Gamma asymmetry

Weak Nuclear PNC Spin Rotation p (or d)

d (or t)

n γ

Liquid He (or H₂)

The n+p^→d+ ^γ completed data collection at LANSCE in 2006.

Polarizor, Field Coils, Spin Flipper, & Detector Liquid H₂ Target

H Safety System

30 cm

30 cm

The NPDGamma Experiment at SNS

Supermirror polarizer CsI Detector Array

Liquid H₂Target H₂Vent Line

Magnetic Shielding H₂Manifold Enclosure

There are several proposed experiments

FNPB Beamline Characterization and Commissioning Approved UCN Beam (SNS, ORNL, LANL, IUCF, NCSU,…)

Determination of τ_n Lifetime Using Magnetically Trapped UCN Conditional Approval (Harvard, NIST, NC State)

Measurement of “a” & “b” Correlations in Neutron Beta Decay Deferred (U of Va., ORNL, LANL, Indiana, UNH,…)

Measurement of “a,b,B,A” Correlations in Neutron Beta Decay Deferred (LANL, Indiana, Michigan, NIST, ORNL, UNH,…)

Measurement of “A+B” Correlation in Neutron Beta Decay Deferred (Michigan, Indiana, NIST, ORNL, UNH,…)

Measurement of Parity Violation in n-p Capture Conditional Approval (LANL, Indiana, Manitoba, NIST, Berkeley, ORNL,…)

Measurement of Parity Violation in n-d Capture Further study (LANL, Indiana, Manitoba, NIST, Berkeley, ORNL,…)

Precise Measurement of Neutron Spin Rotation in H₂ and He Conditional Approval (Indiana, Washington, NIST, NC State, Indiana, ORNL,…)

New Search for an Electric Dipole Moment Approved UCN Beam (LANL, Caltech, Berkeley, ORNL, NC State, …)

END OF PRESENTATION