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

Search for the electric dipole moment of the neutron at PSI Vira Bondar Paul Scherrer Institute on behalf of the nEDM-Collaboration Int. Workshop on Probing Fundamental Symmetries and Interactions with UCN 1 11-15 April 2016, JGU Mainz

nEDM Collaboration about 50 members from 7 countries and 14 institutions Belgium USA KUL, Leuven UKY, Lexington France • LPC, Caen UK • LPSC, Grenoble • CSNSM,Paris US,Brighton nEDM Germany • PTB, Berlin Switzerland • GUM, Mainz • PSI,Villigen Poland • IKC,Mainz • ETH,Zurich • FRAP, Fribourg • JUC,Cracow • HNI,Cracow 2

Overview  Motivation (remind)  Setup  Statistical sensitivity  Key systematic issues  Recent developments & applications  Summary and future plans 3

Remind of the motivation Searching for neutron electric Non zero EDM From Sakharov’s theses dipole moment (nEDM) violates T and CP RAL-Sussex-ILL : Baryon asymmetry of the Universe Expectation from Big Bang: d n < 3 x 10 – 26 e cm (90%CL) n B / n g ~ 10 -18 ? Cosmological observations: C.A.Baker et al., PRL 97 (2006) 131801; n B / n g ~ 10 -10 J.M. Pendlebury et al., PRD 92 (2015) 092003 4

Ultracold neutrons (UCN) for nEDM search    Storable neutrons ( d n )  2 TE N (UCN) Gravity Strong 102 neV/m 350 neV (↔ 8 m/s ↔ 3 mK) V  Nb  V F 350 neV Storage properties are material dependent Magnetic ∼ 60 neV/T E. Fermi & W.H. Zinn(1946), 5 Y. B. Zeldovich, Sov. Phys. JETP ( 1959) 389

Experimental setup Passive Magnetic Precession Chamber Shielding (4 layers) (UCN & Hg) Cs magnetometers HV Electrode Vacuum Tank Mercury Mercury lamp polarizing cell Magnetic field Mercury lamp coils UCN Switch Polarized UCN Spin Analyzers & Detectors S. Afach et al. J. Appl. Phys. 116 (2014) 084510 S. Afach et al., EPJA(2015), A 51 (2015) 143 6 C.A. Baker et al., NIMA 736(2014) 184

Experimental setup          Δ μ  2 d E E 2 B B     n n B 0 =1 μ T E= ± 1MV/m S. Afach et al. J. Appl. Phys. 116 (2014) 084510 S. Afach et al., EPJA(2015), A 51 (2015) 143 7 C.A. Baker et al., NIMA 736(2014) 184

Statistical sensitivity RAL/Sx/ILL PSI 2015 Sensitivity: best avg best avg E-field (kV/cm) 10 8.3 11 11  Visibility of resonance Neutrons * 18 000 14 300 14 800 10350 T Time of free precession T free , s 130 130 180 180 N Number of neutrons T duty , s 240 240 300 300 E Electric field strength α ** 0.6 0.453 0.8 0.75   25 10 , ecm 2.3 3.0 1.1 1.9 *Talk of B. Lauss 8 **Talk of E. Wursten

Statistical sensitivity RAL/Sx/ILL PSI 2015 Sensitivity: best avg best avg E-field (kV/cm) 10 8.3 11 11  Visibility of resonance Neutrons * 18 000 14 300 14 800 10350 T Time of free precession T free , s 130 130 180 180 N Number of neutrons T duty , s 240 240 300 300 E Electric field strength α ** 0.6 0.453 0.8 0.75   25 10 , ecm 2.3 3.0 1.1 1.9 1.7 × 10 -26 e cm 9

Systematics 10

Systematic effects Main source: Magnetic field stability and homogeneity   1        Δ μ      2 B B f n 11 Hz    2 T N   d n    n 2 E E        B 400 fT    11

Systematic effects Main source: Magnetic field stability and homogeneity   1        Δ μ      2 B B f n 11 Hz    2 T N   d n    n 2 E E        B 400 fT    Control over magnetic field*: Mercury co-magnetometer Cs magnetometer array (volume averaged field) (spatial field distribution) K. Green et al. , Nucl. Instr. Methods Phys. Res., Sect. A 404 , 381 (1998)  f B   n n n R  f B Hg Hg Hg 12 *Talks of G. Bison and M. Kasprzak

Systematic effects Beauties of mercury co-magnetometer ~50pT before correction ~ 1pT after correction ~50pT ~1pT

Systematic effects Nothing is perfect: Beauties of mercury but… …drawbacks co-magnetometer • Different density distribution for UCN & Hg • Geometric phase effect (vxE) ~50pT before correction • Non-adiabaticity for Hg atoms ~ 1pT after correction ~50pT Crossing point analysis takes ~1pT these effects into account 14

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:  B    false 27 z d 1 . 122 10 e cm /( pT / cm )  Hg z  B    false , Hg 27 z d 4 . 418 10 e cm /( pT / cm )  n z S. Afach et al. EPJD 69, 225 (2015) 15

3. Hg atoms sample the field non-adiabatically, whereas neutrons are adiabatic 16

R-curves analysis Measurements: apply a magnetic field gradient & measure R depending on gradient monitoring it with Cs-magnetometers B up B down h  0  R R g z B 0 17

Corrections of R  f           R ( 1 ) n n  Grav T Earth Hg f Hg Hg Gravitational shift δ Grav Transverse fields δ T due to mercury non-adiabaticity due to different center ( υ UCN << υ Hg ) of mass for UCN & Hg Field maps   B h     6 2 ( 1 . 0 0 . 2 ) 10 , B   B    up T   Grav z B   T  2 B  6 ( 0 . 8 0 . 3 ) 10 , B 0 199 Hg & UCN 0 down Earth rotation δ Earth Mercury light shift δ Hg   γ f f       induced by the light beam B 0 6   ( 0 . 34 0 . 18 ) 10   δ n  Earth Earth  sin λ   Hg Earth γ f f that detects the Hg free-   Hg n Hg       λ 6 ( 0 . 21 0 . 14 ) 10 induction decay.    6 Hg 5.3 10 18

Byproducts Neutron to 199 Hg magnetic ratio S. Afach et al., PLB 739 (2014) 128 B up B down h     h 0 . 235 ( 5 ) cm ,    R R ( 1 g ) 0 z B   R 3 . 8424583 ( 27 ), 0 +Search for axion-like particles h   0    R R ( 1 g )   0 z R 3 . 8424562 ( 30 ). B 0 0 S.Afach et al., PLB 745 (2015)58 +corrections 19

New understandings… 20

Gravitational depolarization ? Gravitationally enhanced depolarization → and associated frequency shift → S.Afach et al., PRD 92(2015)052008 B0 up B0 down Cs extracted gradient (pT/cm) Relative UCN dephasing in different energy bins -> change of frequency 21

Gravitational depolarization ? Gravitationally enhanced depolarization Revised experimental upper limit → and associated frequency shift on the electric dipole moment of the neutron → S.Afach et al., PRD 92(2015)052008 J. M. Pendlebury et al., PRD 92(2015) 092003 B0 up B0 down Height difference only Anticipated false EDM (10 -26 ecm) With gravitational depolarizaiton Linear fit to data Cs extracted gradient (pT/cm) R'(ppm)   Relative UCN dephasing in different  26 d n 3 . 0 10 ecm ( 90 % CL ) energy bins -> change of frequency 22

How to probe gravitational depolarization? 23

Spin-echo spectroscopy Polarization A spin-echo method recovers energy dependent dephasing for T = 2t 1 in a magnetic field with vertical gradient . g z Impact on:  nEDM limit  Neutron lifetime • Estimation of UCN energy spectrum • Access to vertical gradient offset 24 S.Afach et al., PRL114(2015)162502

Spin-echo application Gradiometry: For each field configuration measure UCNSE before and after nEDM run. Fit UCNSE with “standard spectrum” measured once. Extract gradient offset. Spectrometry: 25

Towards n2EDM Improvements: • Double chamber setup • New mu-metal shield • Better UCN statistics • Improved magnetometry Expected new limit: ~ factor of 10 better Optimistic time scale: ~ mid-end 2018 26

Summary and outlook  Improved performance of UCN source  Optimization of magnetic field conditions  Improved control over systematic effects nEDM data  Gravity revised we are taking data  Spin-echo spectrometry with so far best sensitivity New methods Sensitivity Stat Syst Tot & understandings RAL/Sx/ILL(2015) 1.53 0.99 1.82 End of 2016: PSI(2015) 1.65 0.36 1.69 we expect statistical sensitivity of σ ~1x10 -26 ecm n2EDM 2018 onwards 27

“Be realistic: plan for a miracle!” Osho Thank you! 28

Backup 29

The Ramsey’s technique Sensitivity 30

Measurement Principle of the nEDM for B 0 = const. Stabilization and monitoring of the magnetic field on the ~ 10 fT level is essential! 31

Spin-echo: analysis strategy Measurement Extraction UCN energy spectrum Gradient offsets Result 32

Systematics 33