[PPT] - Search for the electric dipole moment of the neutron at PSI Vira PowerPoint Presentation

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Search for the electric dipole moment of the neutron at PSI

Vira Bondar Paul Scherrer Institute

n behalf of the nEDM-Collaboration
Int. Workshop on Probing Fundamental

Symmetries and Interactions with UCN 11-15 April 2016, JGU Mainz

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nEDM Collaboration

nEDM Poland

JUC,Cracow
HNI,Cracow

Germany

PTB, Berlin
GUM, Mainz
IKC,Mainz

France

LPC, Caen
LPSC, Grenoble
CSNSM,Paris

Belgium

KUL, Leuven

USA

UKY, Lexington

UK

US,Brighton

Switzerland

PSI,Villigen
ETH,Zurich
FRAP, Fribourg

about 50 members from 7 countries and 14 institutions

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Motivation (remind)
Setup
Statistical sensitivity
Key systematic issues
Recent developments & applications
Summary and future plans

Overview

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Expectation from Big Bang: nB / ng ~ 10-18 Cosmological observations: nB / ng ~ 10-10

?

From Sakharov’s theses

Non zero EDM violates T and CP

RAL-Sussex-ILL:

dn < 3 x 10–26 e cm (90%CL)

C.A.Baker et al., PRL 97 (2006) 131801; J.M. Pendlebury et al., PRD 92 (2015) 092003

Searching for neutron electric dipole moment (nEDM)

Remind of the motivation

Baryon asymmetry of the Universe

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Storable neutrons (UCN)

E. Fermi & W.H. Zinn(1946),
Y. B. Zeldovich, Sov. Phys. JETP (1959)389

Magnetic ∼60 neV/T Gravity 102 neV/m

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Ultracold neutrons (UCN) for nEDM search

Strong

neV 350   Nb VF

V

Storage properties are material dependent

350 neV (↔ 8 m/s ↔ 3 mK)

N TE dn   2 ) (  

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Experimental setup

S. Afach et al. J. Appl. Phys. 116 (2014) 084510
S. Afach et al., EPJA(2015), A 51 (2015) 143

C.A. Baker et al., NIMA 736(2014) 184

Polarized UCN

Spin Analyzers & Detectors Precession Chamber (UCN & Hg) Passive Magnetic Shielding (4 layers) HV Electrode UCN Switch Vacuum Tank Cs magnetometers Mercury lamp Mercury lamp Mercury polarizing cell Magnetic field coils

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Experimental setup

S. Afach et al. J. Appl. Phys. 116 (2014) 084510
S. Afach et al., EPJA(2015), A 51 (2015) 143

C.A. Baker et al., NIMA 736(2014) 184

   

   

    B B μ 2 E E d 2 Δ

n n

 

B0=1μT

E=±1MV/m

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Statistical sensitivity

 Visibility of resonance T Time of free precession N Number of neutrons E Electric field strength

Sensitivity:

*Talk of B. Lauss **Talk of E. Wursten

RAL/Sx/ILL PSI 2015

best avg 10 8.3 18 000 14 300 130 130 240 240 0.6 0.453 2.3 3.0 best avg 11 11 14 800 10350 180 180 300 300 0.8 0.75 1.1 1.9 E-field (kV/cm) Neutrons * Tfree , s Tduty , s α ** ecm , 10

25 



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 Visibility of resonance T Time of free precession N Number of neutrons E Electric field strength

Sensitivity:

Statistical sensitivity

1.7×10-26 ecm RAL/Sx/ILL PSI 2015

best avg 10 8.3 18 000 14 300 130 130 240 240 0.6 0.453 2.3 3.0 best avg 11 11 14 800 10350 180 180 300 300 0.8 0.75 1.1 1.9 E-field (kV/cm) Neutrons * Tfree , s Tduty , s α ** ecm , 10

25 



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Systematics

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Systematic effects

   

   

    E E 2 B B μ 2 Δ d

n n

 

Main source: Magnetic field stability and homogeneity

    



    

11

Hz N T fn    11 2 1   fT B 400  

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Systematic effects

   

   

    E E 2 B B μ 2 Δ d

n n

 

Main source: Magnetic field stability and homogeneity

Control over magnetic field*:

Mercury co-magnetometer (volume averaged field) Cs magnetometer array (spatial field distribution)

*Talks of G. Bison and M. Kasprzak

    



    

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K. Green et al., Nucl. Instr. Methods
Phys. Res., Sect. A 404, 381 (1998)

Hg Hg n n Hg n

B B f f R    

Hz N T fn    11 2 1   fT B 400  

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Beauties of mercury co-magnetometer

Systematic effects

~1pT ~50pT

~50pT before correction ~ 1pT after correction

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Beauties of mercury co-magnetometer

Different density distribution for UCN & Hg
Geometric phase effect (vxE)
Non-adiabaticity for Hg atoms

but…

Crossing point analysis takes these effects into account

Nothing is perfect: …drawbacks

Systematic effects

~1pT ~50pT

~50pT before correction ~ 1pT after correction

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Systematic effects

1. Shift of center of gravity
2. Geometric phase effect:

interplay of motional magnetic field (vxE) and magnetic field gradients which translates into false EDM:

) / /( 10 418 . 4

27 ,

cm pT cm e z B d

z Hg false n 

    ) / /( 10 122 . 1

27

cm pT cm e z B d

z false Hg 

   

S. Afach et al. EPJD 69, 225 (2015)

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3. Hg atoms sample the field non-adiabatically,

whereas neutrons are adiabatic

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Measurements: apply a magnetic field gradient & measure R depending on gradient monitoring it with Cs-magnetometers

R-curves analysis

z

g B h R R

0 



Bup Bdown

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Corrections of R

Gravitational shift δGrav Transverse fields δT Earth rotation δEarth Mercury light shift δHg

due to different center

f mass for UCN & Hg

due to mercury non-adiabaticity (υUCN<< υHg )

199Hg & UCN

) 1 ( f f R

Hg Earth T Grav Hg n Hg n

           

Field maps

B h z B

Grav

    

        

  down up T T

B B B B , 10 ) 3 . 8 . ( , 10 ) 2 . . 1 ( 2

6 6 2



 

Earth Earth n Earth Hg n Hg 6

sin 5.3 10 f f γ δ λ γ f f



           

λ B0

6 6

10 ) 14 . 21 . ( 10 ) 18 . 34 . (

   

     

Hg Hg

  induced by the light beam that detects the Hg free- induction decay.

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Byproducts

S.Afach et al., PLB 745(2015)58

). 30 ( 8424562 . 3 ), 27 ( 8424583 . 3 , ) 5 ( 235 .    

 

R R cm h

+corrections +Search for axion-like particles

S. Afach et al., PLB 739 (2014) 128

Neutron to 199Hg magnetic ratio Bup Bdown

) 1 (

  

 

z

g B h R R ) 1 (

  

 

z

g B h R R

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New understandings…

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Gravitational depolarization

B0 up B0 down

→ →

Relative UCN dephasing in different energy bins -> change of frequency Gravitationally enhanced depolarization and associated frequency shift

?

S.Afach et al., PRD 92(2015)052008

Cs extracted gradient (pT/cm)

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Gravitational depolarization

Revised experimental upper limit

n the electric dipole moment of the neutron

B0 up B0 down

→ →

Relative UCN dephasing in different energy bins -> change of frequency Gravitationally enhanced depolarization and associated frequency shift

?

S.Afach et al., PRD 92(2015)052008

J. M. Pendlebury et al., PRD 92(2015) 092003

) % 90 ( 10 . 3

26

CL ecm dn



 

Height difference only With gravitational depolarizaiton Linear fit to data R'(ppm) Anticipated false EDM (10-26 ecm) Cs extracted gradient (pT/cm)

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How to probe gravitational depolarization?

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Spin-echo spectroscopy

A spin-echo method recovers energy dependent dephasing for T = 2t1 in a magnetic field with vertical gradient. gz Polarization

Estimation of UCN energy spectrum
Access to vertical gradient offset

S.Afach et al., PRL114(2015)162502

Impact on:

nEDM limit
Neutron lifetime

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For each field configuration measure UCNSE before and after nEDM run. Fit UCNSE with “standard spectrum” measured once. Extract gradient offset.

Gradiometry: Spectrometry:

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Spin-echo application

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Improvements:

Double chamber setup
New mu-metal shield
Better UCN statistics
Improved magnetometry

Towards n2EDM

Expected new limit:

~ factor of 10 better

Optimistic time scale:

~ mid-end 2018

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Summary and outlook

 Improved performance of UCN source  Optimization of magnetic field conditions  Improved control over systematic effects  Gravity revised  Spin-echo spectrometry New methods & understandings

we are taking data with so far best sensitivity

End of 2016: we expect

statistical sensitivity of n2EDM 2018 onwards

Sensitivity Stat Syst Tot RAL/Sx/ILL(2015) 1.53 0.99 1.82 PSI(2015) 1.65 0.36 1.69

σ~1x10-26ecm nEDM data

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“Be realistic: plan for a miracle!”

Osho

Thank you!

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Backup

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The Ramsey’s technique

Sensitivity

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Stabilization and monitoring of the magnetic field on the ~ 10 fT level is essential!

Measurement Principle of the nEDM

for B0 = const.

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Measurement Extraction Result

Spin-echo: analysis strategy

UCN energy spectrum Gradient offsets

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Systematics

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UCN Spin-Echo

       

n cm 1 1

( , ) cos 2 1 2 d ,

z

B α α T E πγ h E T p E z t t E



                  

The rate of transverse depolarization in an applied field gradient is dependent of the UCN energy spectrum.

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Average magnetic field

(volume and cycle)

σB ~ 400 fT
τ > 100 s without HV
s/n ~ 500 without HV

Mercury co-magnetometer

¼ wave plate linear polarizer Hg lamps PM polarization cell HgO source B0 ≈ 1μT τ = 140s

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16 CsM array High precision field mapping

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Error budget

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Average magnetic field

(volume and cycle)

σB ~ 400 fT
τ > 100 s without HV
s/n ~ 500 without HV

Mercury co-magnetometer

¼ wave plate linear polarizer Hg lamps PM polarization cell HgO source B0 ≈ 1μT τ = 140s

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Hg laser readout

Sensitivity improvement from ~400fT → <100fT

( M. Fertl, PhD-Thesis 2013 )

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nEDM Collaboration at PSI

PTB, Physikalisch Technische Bundesanstalt, Berlin, Germany
US, University of Sussex, Brighton, United Kingdom
LPC, Laboratoire de Physique Corpusculaire, Caen, France
JUC, Jagellonian University, Cracow, Poland
HNI, Henryk Niedwodniczanski Institute of Nuclear Physics PAN, Cracow, Poland
FRAP, Université de Fribourg, Fribourg, Switzerland
LPSC, Laboratoire de Physique Subatomique et de Cosmologie, Grenoble, France
UKY, University of Kentucky, Lexington, USA
KUL, Katholieke Universiteit, Leuven, Belgium
GUM, Institut für Physik, Gutenberg Universität, Mainz, Germany
IKC, Institut für Kernchemie, Gutenberg Universität, Mainz, Germany
CSNSM, Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, Paris, France
PSI, Paul-Scherrer-Institut, Villigen, Switzerland
ETHZ, Eidgenössische Technische Hochschule Zürich, Switzerland

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ALPS limits

A: V.V. Voronin et al., JETP Lett. 90 (2009) 5; B: T. Jenke et al., PRL112 (2014) 151105; C: A.P. Serebrov et al., PLB 680 (2009) 423; D: A.P. Serebrov et al., JETP Lett. 91 (2010) 6; E: A.K. Petukhov et al., PRL 105 (2010) 170401; F: K. Tullney et al., PRL 111 (2013) 100801; G: M. Bulatowicz et al., PRL 111 (2013) 102001; H: this work; I: Proposal for same measurement with copper electrode

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s s H B d E s s        

C-even P-even T-even C-even P-odd T-odd Non zero EDM violates T and CP

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New methods & understandings

Summary and outlook

Bright future  Improved performance of UCN source  Optimization of magnetic field conditions  Improved control over systematic effects  Gravity revised  Spin-echo spectrometry

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Thank you!

Sensitivity Stat Syst Tot

RAL/Sx/ILL(2015) 1.53 0.99 1.82 PSI(2015) 1.65 0.36 1.69 we are taking data with so far best sensitivity

nEDM data

n2EDM 2018 onwards