# Presentation: 467010

##  Ultra-Cold Neutrons: From neV to TeV 

- What are UCN? (how cold?)
- How to produce UCN?
** ****Conventional reactor sources **
** ****New “superthermal” sources**
- Experiments with UCN
** ****Neutron beta-decay ****(********n****, n decay asymmetry)**
** ****Neutron Electric Dipole Moment**

**Fermilab**
**7/13/06**

## Slide 2

## The Caltech UCN group

**Nick Hutzler**
**Gary Cheng**
**Jenny Hsiao**
**Riccardo Schmid**
**Kevin Hickerson**
**Junhua Yuan**
**Brad Plaster **
**Bob Carr**
**BF**

## Ultra-Cold Neutrons (UCN) (Fermi/Zeldovich)

- What are UCN ?
- Very slow neutrons
** ****(v < 8 m/s  **’****** > 500 Å )**
- that cannot penetrate into
- 	  certain materials
- 		 Neutrons can be
-      trapped in bottles
- 		  or by magnetic
-        field

## Material Bottles 

**Recall (for short-range potential):**
**  ****At low energies (*****kr*****0****<<1; eg s-wave) elastic **
**  ****scattering determined solely by scattering **
**  ****length ****a**

**For *****k***** **’**0**
******elas********a****2**

**Neutron “repulsion” comes from coherent scattering from nuclei in solids.**

**Material Bottles **

## Fermi Pseudo-potential

**The coherent nuclear potential can lead to repulsive pseudopotential (Fermi potential) for a > 0**

**Attractive potential can also lead to neutron absorption **
**but often *****L*****mfp**** >> ********n **** (~10****-5**** probability per bounce) **

**For E****UCN**** < V****F****, UCN are trapped**

**E****UCN**

**Fermi Pseudo-potential**

## Typical Fermi Potentials

| Material | VF (neV) |
| --- | --- |
| Al | 54 |
| 58Ni | 350 |
| Ti | - 48 |
| Graphite | 180 |
| Stainless Steel | 188 |
| Diamond-like Carbon | 282 |

**neutron velocity**
**v****n ****~ 8 m/s**

## Magnetic Bottles 

**   ****produces a potential**
** ****Thus can produce a 3D potential well **
**at a  field minimum ****(traps one spin state)**

**Magnetic Bottles **
**also possible**

**Ioffe Trap**

**For v****n****<8 m/s need B<6T**

## UCN Properties

**g**

**3m**

**UCN**

## How to make UCN?

**Conventional Approach:**
- Start with neutrons from nuclear
- reactor core
- Use collisions with nuclei to slow down neutrons

**Some of neutron’s energy lost**
**to nuclear recoil in each collision **

**Gives a Maxwell-Boltzmann Distribution**

## But...

- Only small fraction of neutron distribution is UCN

## Can we make more?

- Can improve some via gravity and moving turbines
- Record density at
- Institut Laue-Langevin
- (ILL) reactor in
- Grenoble

**(1971)**

**Best vacuum on earth**
**~10****4**** atoms/cm****3**

**Can we make more?**

## Higher Density UCN Sources

- Use non-equilibrium system
-      (aka Superthermal)
-   **Superfluid ****4****He **
**	****	****	****(T<1K)**

**Very few 11K phonons if T<1K**
** ******** ****minimal upscattering **

**11K (9Å**** ****) incident n**
**produces phonon &**
**becomes UCN**

**NIST ********n**** Experiment**

**(neutron)**

** ****Solid deuterium (SD****2****)** Gollub & Boning(83)
- Small absorption probability
- Faster UCN production
- Small Upscattering if T < 6K

**UCN**

**Phonon**

**Cold Neutron**

## LANSCE

**LANSCE**

**(Los Alamos Neutron Science CEnter)**

## Schematic of prototype SD2 source

- Liquid N2

- Be reflector

**Solid D****2**

- 77 K polyethylene

**Tungsten Target**

**58****Ni coated stainless guide**

**UCN Detector**

- Flapper valve

- LHe

**Caltech, LANL, NCState, VaTech, Princeton, Russia, France, Japan**
**Collaboration**

## First UCN detection

**Total flight path ~ 2 m**

**50 ml SD****2**

**0 ml SD****2**

**Proton pulse at t = 0**

## New World Record UCN Density 

**Measurements of Ultra Cold Neutron Lifetimes in Solid Deuterium [PRL 89,272501 (2002)] **
**Demonstration of a solid deuterium source of ultra-cold neutrons [Phys. Lett. B 593, 55 (2004)]**

**Previous record for bottled UCN =  41 UCN/cm****3**** (at ILL)**** **

## Physics with higher density UCN Sources

- Macroscopic Quantum States
- Neutron decay (lifetime & correlations)
- Solid Deuterium Source
- Neutron Electric Dipole Moment (EDM)
- Superfluid He Source
**Also possible:**
**	****Characterize structure of large (~ 500****Å**** ****) systems**
**(Polymers, Biological molecules)**

## Macroscopic Quantum States in a Gravity Field

**1-d Schr****ö****dinger potential problem**

**neutron in ground state**
**“****bounces” ~ 15 ********m high**

## Height Selects Vertical Velocity

**UCN @ ILL**

**Neutron Energy Levels in Gravity**

## May allow improved tests of Gravity at short distances

**May allow improved tests of Gravity at short distances**
**(need more UCN!)**

**Nesvizhevsky, et al, Nature 2002**

## Neutron Beta Decay

## Precision neutron decay measurements

**Neutron lifetime essential in Big-Bang **
**       ****Nucleosynthesis Calculations**
**Can provide most precise measurement of V****ud**
**< 0.3% measurements can be sensitive to new physics ****(from loops in electroweak field theory)**

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**b**

**s**

**d**

**V**

**V**

**V**

**V**

**V**

**V**

**V**

**V**

**V**

**b**

**s**

**d**

**tb**

**ts**

**td**

**cb**

**cs**

**cd**

**ub**

**us**

**ud**

**w**

**w**

**w**

**Weak eigenstates**

**Mass eigenstates**

**Single complex phase**
**is possible **
**(gives “CP” Violation**
**-more later) **

**a.k.a. Radiative Corrections**

**Particle Data Group**

**Primordial He Abundance**

## Neutron Lifetime versus Year

**Phys. Lett. B 605, 72 (2005)**
**(878.5 ± 0.7 ± 0.3) seconds**

**Neutron Lifetime versus Year**

**Data points used by Particle Data Group (PDG) 2004 for averaging**

** **

## Big-Bang Nucleosynthesis Constraints

**Big-Bang Nucleosynthesis Constraints**

**WMAP**

** ****New neutron lifetime**

**New Lifetime **
**Experiment using our **
**Solid Deuterium Source**
**is under development**

## Neutron Decay in the Standard Model

**G****A****  = Axial vector weak coupling constant**
**G****V****  = Vector weak coupling constant**

**G****A****/G****V ****from parity violating decay asymmetry in n decay **

**G****F****  = Fermi Constant (known from ******** decay)**
**V****ud**** = up-down quark weak coupling (more later)**

**f   = phase space integral**
******R****  = Electroweak radiative correction**
**	****   ****Note: Z****0**** Boson (M=91 GeV) gives 2% correction!**

## Sensitivity to New Physics?

**	****(from ******** vs. ********-decay)**

**Sensitivity to New Physics?**

**Kurylov&Ramsey-Musolf**
**Phys. Rev. Lett. 88, 071804 (2002)**

**Supersymmetric particles produce loop corrections**

## UCNA

**UCNA**

## Asymmetry measurement with UCN

**All previous measurements of G****A****/G****V**** used cold neutrons from a reactor**
**Gives continuous, large, background from reactor and polarizer (magnetized solid)**
**Gives > 1% systematic error due to neutron polarization (95-98%)**
**New experiment uses pulsed UCN source**
**Neutron decays counted with the source “off”**
**Can produce high neutron polarization (~99.9%) using 6T magnetic field**

## Experiment Layout

**Superconducting Spectrometer **

**Electron Detectors**

**UCN Guides**

- Neutron Polarizing Magnets

**UCN Source**

## UCNA experiment

- Liquid N2

- Be reflector

- Solid D2

- 77 K poly

- Tungsten Target

- LHe

**UCNA experiment**

**Experiment commissioning underway**
**Initial goal is 0.2% measurement of A-correlation**
**           ****(present measurement ~ 1%)**

**UCNA**

## Most Recent Collaborator

**Most Recent Collaborator**

## Neutron Electric Dipole Moment (EDM)

**Why Look for EDMs?**
**Existence of EDM implies violation of Time Reversal Invariance **

**+**

**-**

** ****Time Reversal Violation seen in K****0****–K****0**** system**
** ****May also be seen in early Universe **
**	****- Matter-Antimatter asymmetry**
**but the Standard Model effect is too small !**

- Cartoon

## Quantum Picture – Discrete Symmetries

- Non-Relativistic Hamiltonian

- C-even
- P-even
- T-even

- C-even
- P-odd
- T-odd

- 

- 

## Sakharov Criteria
Baryon Number Violation
Departure from Thermal Equilibrium 
CP & C violation

Standard Model CP violation is insufficient
Must search for new sources of CP
B-factories, Neutrinos, EDMs

- Baryon Number Violation
- Departure from Thermal Equilibrium
- CP & C violation
**Standard Model CP violation is insufficient**
- Must search for new sources of CP
- B-factories, Neutrinos, EDMs

**Possible Mechanisms for Matter/Antimatter Asymmetry in the Universe**

## Standard Model EDMs are due to observed CP violation in the K0/B0-system but...
e- and quark EDM’s are zero at first order
Need at least two “loops” to get EDM’s
Thus EDM’s are VERY small in standard model

- e- and quark EDM’s are zero at first order
- Need at least two “loops” to get EDM’s
- Thus EDM’s are VERY small in standard model

**Origin of EDMs**

**Neutron EDM in Standard model is**
**~ 10****-32**** e-cm (****=10****-19**** e-fm****)**

**Electron EDM in Standard Model is**
**< 10****-40**** e-cm**

## Physics Beyond the Standard Model

- New physics (e.g. SuperSymmety = SUSY) has additional CP violating phases in added couplings
- New phases: (CP) should be ~ 1 (why not?)
- Contributions to EDMs depends on masses of new particles
- 	In Minimal Supersymmetric Standard Model
-         dn ~ 10-25 (e-cm)x (200 GeV)2/M2SUSY

**Note: exp. limit: d****n**** < 0.3 x 10****-25**** e-cm**

## Possible impacts of non-zero EDMs

**Must be new Physics **
**Sharply constrains models **
**    ****beyond the Standard Model **
-     (especially with LHC data)
**May account for matter-**
**   ****antimatter asymmetry of **
**   ****the universe **

## Experimental EDMs

**Present best limits come from atomic systems and the free neutron**
**Electron EDM - ****205****Tl **
**Quark ColorEDM - ****199****Hg **
**Quark EDM - free neutron **
**Future best limits (x10 – 1000) may come from **
**Molecules**** ****(PbO, YbF = e****-****)**
**Liquids**** ****(****129****Xe = nuclear)**
**Solid State systems**** ****(Gadolinium-Gallium-Garnet = e****-****)**
**Storage Rings**** ****(Muons, Deuteron)**** **
**Radioactive Atoms**** ****(****225****Ra, ****223****Rn)**
**New Technologies for Free Neutrons**** **
**Switzerland = PSI**
**France = ILL**
**US = Spallation Neutron Source = SNS**

## n-EDM vs Time

## Simplified Measurement of EDM

- B-field

- E-field

- 1. Inject polarized particle

- 2. Rotate spin by /2

- 3. Flip E-field direction

- 4. Measure frequency shift

- Must know B very well

## ILL-Grenoble neutron EDM Experiment

- Trapped Ultra-Cold
- Neutrons (UCN) with
- NUCN = 0.5 UCN/cc
- |E| = 5  kV/cm
- 100 sec storage time
-        ******d ****= 3 x 10****-26**** e-cm**

- Harris et al. Phys. Rev. Lett. 82, 904 (1999)

## Careful magnetometry is essential ! 

- 199Hg Magnetometer

##  New EDM Experiment

**Superfluid He UCN converter **
**with high E-field **

**>2 orders-of-magnitude **
**improvement possible**

**(ASU/Berkeley/Caltech/Duke/Harvard/Indiana/Kentucky/LANL/**
**MIT/NIST/NCSU/ORNL/HMI/SFU/Tennessee/UIUC/Yale)**

**(AMO/HEP/NP/Low Temp expertise)**

## New Technique for n-EDM

- B-field

- E-field

- Inject polarized neutron
-           & polarized 3He

- 2. Rotate both spins by 90o

- 4. Flip E-field direction

- 3. Measure n+3He capture
- 	vs. time
- 	(note: >>)

**3****He functions as “co-magnetometer”**

## EDM Sensitivity

|  | EDM @ ILL | EDM @ SNS |
| --- | --- | --- |
| NUCN | 1.3 x 104 | 2 x 106 |
| |E| | 10 kV/cm | 50 kV/cm |
| Tm | 130 s | 500 s |
| m  (cycles/day) | 270 | 50 |
| d (e-cm)/day | 3 x 10-25 | 3 x 10-27 |
| SNR (signal noise ratio) | 1 | 1 |

## Spallation Neutron Source (SNS) @ Oak Ridge National Lab

**1 GeV proton beam **
**1.4 MW on spallation target**

**Fundamental Physics **
**Beamline**

## EDM Experiment at SNS 

- Isolated
- floor

- He
- Liquifier

## New n-EDM Sensitivity

- 2000

- 2010

- EDM @ SNS

**d****n**** < ****1x10****-28**** e-cm**

## Future Outlook

**Improvements in UCN densities > 10****2**** possible in next generation sources**
**First superthermal UCN source experiments are underway**
**Substantial promise for future high precision neutron experiments**

## The End

## Additional Slides...

## Hadronic (strongly interacting particles) EDMs are from 
 QCD (a special parameter in Quantum Chromodynamics – QCD) 
or from the quarks themselves

-  QCD (a special parameter in Quantum Chromodynamics – QCD)
- or from the quarks themselves

**Origin of Hadronic EDMs **

##  EDM from QCD 

- This is the Strong CP problem in QCD
- Small QCD does not provide any new symmetry for LQCD
- Popular solution is “axions” (Peccei-Quinn symmetry) – new term in LQCD
- No Axions observed yet
- Extra dimensions might suppress QCD
-                   (Harnik et al arXiv:hep-ph/0411132)
- Remains an unsolved theoretical “problem”

## Hadronic EDM from Quarks

- Quark EDM contributes via

- q

- q

- 

- q

- q

- g

- Quark EDM

- Quark
- ChromoEDM e.g.

## Atomic EDMs 

**Atomic EDMs **

- Schiff Theorem
- Neutral atomic system of point particles in Electric field readjusts itself to give zero E field at all charges

**-Q**

**+Q**

- With E-field

**E**

## Determination of Vud

**Determination of V****ud**

**New ********n**** !!**

**UCNA**

## EDM Measurements

| particle | Present Limit (90% CL)
(e-cm) | Laboratory | Possible Sensitivity
(e-cm) | Standard Model
(e–cm) |
| --- | --- | --- | --- | --- |
| e-  (Tl)
e-  (PbO) 
e-  (YbF)
e-  (GGG) | 1.6 x 10-27 | Berkeley
Yale
Sussex LANL/Indiana | 
10-29
10-29
10-30 | 
<10-40 |
|  
  | 9.3 x 10-19 | CERN
BNL | 
<10-24 | <10-36 |
| n 
n
n
n  | 6.3 x 10-26 | ILL
ILL
PSI
SNS | 1.5 x 10-26
~ 2 x 10-28
~ 7 x 10-28
< 1 x 10-28 | 
~10-32
 |
| 199Hg
129Xe
225Ra
223Rn
   d | 1.9 x 10-27 | Seattle
Princeton
Argonne
TRIUMF
COSY/JPARC? | 5 x 10-28 
10-31
10-28
1 x 10-28
<10-27 | ~10-33
~10-34
 |

## Status of new EDM experiment

- Estimated cost ~ 18 M$
- Approved with highest priority for SNS fundamental physics beamline
- Recent R&D indicates no “showstoppers”
- DOE recently (12/05) granted first stage funding approval (Critical Design 0). Funding from NSF also being sought

## Status of Electroweak Baryogenesis

- Appeared to be “ruled out” several years ago
- First order phase transition doesn’t work for MHiggs > 120 GeV
- MSSM parameters ineffective (CP<<1)
- Recent work has revived EW baryogenesis
- First order phase transition still viable
-    (with new gauge degrees of freedom)
- Resonance in MSSM during phase transition

- Lee, Cirigliano, and Ramsey-Musolf: arXiv:hep-ph/0412354

- Note: Leptogenesis is also  possible

## How to measure an EDM?

- Classical Picture:
-  If the spin is not aligned with B there will be a precession
-            due to the torque
-  Precession frequency      given by

- Recall magnetic moment in B field:

## Cabibbo-Kobayashi-Maskawa 

**(CKM) Matrix**

**Unitarity,                                                 , (or lack thereof) of CKM matrix tests existence of possible new physics **
**(eg. Supersymmetry – “beyond the Standard Model”)**

**u,c,t quarks couple weakly to superposition of other quarks**

**eg. |V****ud****|****2**** + |V****us****|****2**** + |V****ub****|****2**** = 1**