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

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 500 Å ) that cannot penetrate into certain materials Neutrons can be trapped in bottles or by magnetic field

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

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 MaterialV F (neV) Al54 58 Ni350 Ti- 48 Graphite180 Stainless Steel188 Diamond-like Carbon 282 neutron velocity v n ~ 8 m/s

B-field and neutron magnet moment 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 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 UCN Source Proton Linac (½ mile long) (Los Alamos Neutron Science CEnter)

Schematic of prototype SD 2 source Liquid N 2 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, (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 (~ 500Å ) systems (Polymers, Biological molecules)

Macroscopic Quantum States in a Gravity Field 1-d Schrödinger potential problem neutron in ground state “bounces” ~ 15  m high V z mgz

Height Selects Vertical Velocity ILL Neutron Energy Levels in Gravity

Classical expectation May allow improved tests of Gravity at short distances (need more UCN!) Nesvizhevsky, et al, Nature 2002

Neutron Beta Decay or in quark picture… u d d u d u e e-e- n p W-W-

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)                                b s d VVV VVV VVV b s d tbtstd cbcscd ubusud 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

Serebrov et al., 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 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!

V ud in Standard Model (from  vs.  -decay) Sensitivity to New Physics? Kurylov&Ramsey-Musolf Phys. Rev. Lett. 88, (2002) W-W- e-e- G F V ud --  W-W- e-e- GFGF d u e e --  W-W- e-e- e  ~ ~ 00 ~ d W-W- e-e- e d ~ u ~ 00 ~u Supersymmetric particles produce loop corrections

Asymmetry Measurement with UCN e-e- n  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

Liquid N 2 Be reflector Solid D 2 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

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 – D iscrete Symmetries -+- B -++ J +-- E -+- d -+-  TPC 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 Possible Mechanisms for Matter/Antimatter Asymmetry in the Universe

Standard Model EDMs are due to observed CP violation in the K 0 /B 0 -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 Origin of EDMs Neutron EDM in Standard model is ~ e-cm ( = e-fm ) Electron EDM in Standard Model is < e-cm

Physics Beyond the Standard Model New physics (e.g. SuperSymmety = SUSY) has additional CP violating phases in added couplings (why not?) –New phases: (  CP ) should be ~ 1 (why not?) Contributions to EDMs depends on masses of new particles –In Minimal Supersymmetric Standard Model d n ~ (e-cm)x (200 GeV) 2 /M 2 SUSY Note: exp. limit: d n < 0.3 x 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 Pospelov, et al, 2004 A/A/ M SUSY =750GeV // e- 199 Hg n Chang, et al, hep-ph/

Experimental EDMs Present best limits come from atomic systems and the free neutron –Electron EDM Tl –Quark ColorEDM 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 N UCN = 0.5 UCN/cc |E| = 5 kV/cm 100 sec storage time  d = 3 x e-cm Harris et al. Phys. Rev. Lett. 82, 904 (1999)

Careful magnetometry is essential ! 199 Hg 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 1.Inject polarized neutron & polarized 3 He 2. Rotate both spins by 90 o 4. Flip E-field direction 3. Measure n+ 3 He capture vs. time (note:   >>   ) 3 He functions as “co-magnetometer”

EDM Sensitivity ILL SNS N UCN 1.3 x x 10 6 |E| 10 kV/cm50 kV/cm TmTm 130 s500 s m (cycles/day)  d (e-cm)/day 3 x x SNR (signal noise ratio) 11

Spallation Neutron Source 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 SNS d n < 1x 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 Origin of Hadronic EDMs

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

Hadronic EDM from Quarks Quark EDM contributes via qq  qq g Quark EDM Quark ChromoEDM e.g.

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 V ud New  n !! UCNA

EDM Measurements particlePresent Limit (90% CL) (e-cm) LaboratoryPossible Sensitivity (e-cm) Standard Model (e–cm) e - (Tl) e - (PbO) e - (YbF) e - (GGG) 1.6 x Berkeley Yale Sussex LANL/Indiana <  9.3 x CERN BNL< < nnnnnnnn 6.3 x ILL PSI SNS 1.5 x ~ 2 x ~ 7 x < 1 x ~ Hg 129 Xe 225 Ra 223 Rn d 1.9 x Seattle Princeton Argonne TRIUMF COSY/JPARC? 5 x x < ~ ~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 M Higgs > 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/  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                                b s d VVV VVV VVV b s d tbtstd cbcscd ubusud w w w Weak eigenstates Mass eigenstates Single complex phase is possible (gives CP Violation -more later)