Measuring the Neutron Electric Dipole Moment - A Tiny Number with Big Implications

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1 Measuring the Neutron Electric Dipole Moment - A Tiny Number with Big Implications Imperial/RAL Kyoto University nd, 2005

2 The Universe passed through a period of the very high energy density early in the Big Bang Matter was produced via reactions like γ+γ p+p This should have produced equal quantities of matter and anti-matter.

3 It didn t.

4 Kyoto Seminar

5 Diffuse γ-ray flux expected from annihilation d 0 = 20 Mpc d 0 = 1000 Mpc See Cohen, De Rujula, Glashow; astro-ph/

6 Sakharov Conditions: (A.D. Sakharov, JETP Lett. 5, 24-27, 1967) To produce a matter anti-matter asymmetry requires: Baryon number violation Conserved at tree level in the Standard Model More complex SM processes lead to B violation C violation

7 Sakharov Conditions: (A.D. Sakharov, JETP Lett. 5, 24-27, 1967) To produce a matter anti-matter asymmetry requires: Baryon number violation Conserved at tree level in the Standard Model More complex SM processes lead to B violation C and CP violation

8 CP violation in weak decays K 0 L 2π

9 CP violation in weak decays BELLE and BaBar CPLear (amongst others)

10 Sakharov Conditions: (A.D. Sakharov, JETP Lett. 5, 24-27, 1967) To produce a matter anti-matter asymmetry requires: Baryon number violation Conserved at tree level in the Standard Model More complex SM processes lead to B violation C and CP violation

11 Sakharov Conditions: (A.D. Sakharov, JETP Lett. 5, 24-27, 1967) To produce a matter anti-matter asymmetry requires: Baryon number violation Conserved at tree level in the Standard Model More complex SM processes lead to B violation C and CP violation

12 Sakharov Conditions: (A.D. Sakharov, JETP Lett. 5, 24-27, 1967) To produce a matter anti-matter asymmetry requires: Baryon number violation Conserved at tree level in the Standard Model More complex SM processes lead to B violation C and CP violation Departure from thermal equilibrium

13 Sakharov Conditions: (A.D. Sakharov, JETP Lett. 5, 24-27, 1967) To produce a matter anti-matter asymmetry requires: Baryon number violation Conserved at tree level in the Standard Model More complex SM processes lead to B violation C and CP violation Departure from thermal equilibrium Phase transitions

14 Sakharov Conditions: (A.D. Sakharov, JETP Lett. 5, 24-27, 1967) To produce a matter anti-matter asymmetry requires: Baryon number violation Conserved at tree level in the Standard Model More complex SM processes lead to B violation C and CP violation Departure from thermal equilibrium Phase transitions Expansion of the Universe

15 So are we done now? No (you don t get out of this talk that easy) The CP violation in the Standard Model is too small by many orders of magnitude to explain the observed matter-anti-matter asymmetry (also called the baryon asymmetry) of the Universe (hep-ph/ ) There must be CPV in laws of physics we don t know yet! We have to keep looking

16 Neutron Electric Dipole Moment

17 Neutron Electric Dipole Moment

18 Neutron Electric Dipole Moment _ +

19 Neutron Electric Dipole Moment _ + s

20 Neutron Electric Dipole Moment _ + s Would lead to a non-zero value for d n, either parallel or anti-parallel to s d n would be: P odd T odd CP odd!

21 Particle EDMs are a particularly promising laboratory for CP violation The Standard Model contribution is very small Contributions from new physics tend not to be

22 neutron Range of d (e cm) in various models Standard Model electron

23 Multi Higgs Left-Right Electromagnetic SUSY φ 1 φ α/π neutron Range of d (e cm) in various models Standard Model electron

24 Basic Idea of the Measurement B µ B

25 Basic Idea of the Measurement B E µ B d n??

26 Basic Idea of the Measurement B E µ B d n?? Look for a shift in the Larmor frequency of 2 E d n as E is flipped relative to B

27 The Ramsey Separated Oscillator Method Spin up neutron... Apply π/2 spin flip pulse... Free precession... N.F. Ramsey, Phys.Rev (1949) 4. Second π/2 spin flip pulse.

28 Kyoto Seminar

29 λ>> interatomic spacing; neutrons see Fermi potential V F Critical velocity for reflection: ½mv c2 = V F Ultracold neutrons (UCN): v 6 m/s: total internal reflection possible. n

30 λ>> interatomic spacing; neutrons see Fermi potential V F Critical velocity for reflection: ½mv c2 = V F Ultracold neutrons (UCN): v 6 m/s: total internal reflection possible. n v c depends on orientation of neutron spin, so can polarise by transmission.

31 λ>> interatomic spacing; neutrons see Fermi potential V F Critical velocity for reflection: ½mv c2 = V F Ultracold neutrons (UCN): v 6 m/s: total internal reflection possible. n v c depends on orientation of neutron spin, so can polarise by transmission. n s B s n

32 Prepare neutrons in polarisation state 1, execute Ramsey cycle and measure the number left in states 1 and 2, repeat with B and E fields parallel ( ) and anti-parallel ( ), then: ( N N N 2αETN N dn = ) h Where α = the product of the neutron polarisation and the analyzing power, E is the applied field strength, T is the storage time, and N is the number of neutrons detected The resulting statistical sensitivity is: σ ( d ) n = 2 α h ET N Must add any systematics to this to determine the sensitivity of the experiment.

33 The Institute Laue-Langevin

34 Neutron Turbine Vertical guide Reactor Core Liquid D 2 moderator

35 Neutron Energy Annoyances Cold neutrons have: E mev v 100 m/s λ 1-10 Å T 10 K Ultra-cold neutrons have: E 1 10 nev v 0-15 m/s λ 1000 Å T real small (normally not thermal)

36 Four-layer mu-metal shield Quartz insulating cylinder High voltage lead Coil for 10 mg magnetic field Main storage cell Hg u.v. lamp Vacuum wall Upper electrode PMT to detect Hg u.v. light Current Room- Temperature nedm Experiment RF coil to flip spins Magnet UCN polarising foil S N Mercury prepolarising cell Hg u.v. lamp UCN guide changeover Ultracold neutrons (UCN) UCN detector

38 Four-layer mu-metal shield Quartz insulating cylinder High voltage lead Coil for 10 mg magnetic field Main storage cell Hg u.v. lamp Vacuum wall Upper electrode PMT to detect Hg u.v. light Current Room- Temperature nedm Experiment RF coil to flip spins Magnet UCN polarising foil S N Mercury prepolarising cell Hg u.v. lamp UCN guide changeover Ultracold neutrons (UCN) UCN detector

39 Top view: PMT Hg Co-magnetometer T' Digitised voltage (bits) ADC reading no.

40 Kyoto Seminar

41 1999 Results (PG Harris et al, PRL 82, 904 (1999)) d n = (1.9 ± 5.4) e cm d n e cm (90% c.l.)

42 If neutron were the size of the earth... +e -e x... current EDM limit would correspond to charge separation of x 10 µ.

43 Multi Higgs Left-Right Electromagnetic SUSY φ 1 φ α/π neutron Range of d (e cm) in various models Standard Model electron

44 Experimental Limit on d (e cm) neutron: Cited ~250 times already Multi Higgs Left-Right Electromagnetic SUSY φ 1 φ α/π neutron Range of d (e cm) in various models Standard Model electron

45 Recall: σ Published Data ( dn ) = 2 α ET Current Room-Temp h N Cryogenic Experiment E T N

46 Recall: σ Published Data ( dn ) = 2 α ET Current Room-Temp h N Cryogenic Experiment 0.5 E T N 4.5 kv/cm 130 s 13000

47 Recall: σ Published Data ( dn ) = 2 α ET Current Room-Temp h N Cryogenic Experiment New polarisers E on Si wafers T N 4.5 kv/cm 130 s 13000

48 Recall: σ Published Data ( dn ) = 2 α ET Current Room-Temp h N Cryogenic Experiment E 4.5 kv/cm 12 kv/cm Shorter, wider T bottle130 s 4 He buffer gas Better cleaning N methods 13000

49 Recall: σ Published Data ( dn ) = 2 α ET Current Room-Temp h N Cryogenic Experiment E 4.5 kv/cm 12 kv/cm T N 130 s s

50 Recall: σ Published Data ( dn Larger volume bottle 0.5 Better neutron guides Loss of 50% from source E 4.5 kv/cm ) = 2 α ET Current Room-Temp kv/cm h N Cryogenic Experiment T N 130 s s 14000

51 Recall: σ Published Data ( dn ) = 2 α ET Current Room-Temp h N Cryogenic Experiment E 4.5 kv/cm 12 kv/cm T N 130 s s 14000

52 Overall factor of ~3 improvement Published Data Current Room-Temp Cryogenic Experiment E 4.5 kv/cm 12 kv/cm T N 130 s s 14000

53 1999 Results (PG Harris et al, PRL 82, 904 (1999)) limit set here EDM (10-25 e.cm) Stat. limit now 1.54 x e.cm d n = (1.9 ± 5.4) e cm d n e cm (90% c.l.)

54 EDM (10-25 e.cm) New nedm data χ 2 /ν = 1.13; CL = 0.7%! Smells fishy... Kyoto Seminar What s going on here?

55 Conspiracy Theory Two effects: B Br r z and, from Special Relativity, extra motion-induced field B = r r 1 v E 2 γ c

56 B net Geometric Phase B r B net B v... so particle sees additional rotating field B v Frequency shift E Looks like an EDM B v B net B r B net

57 Field Gradient Effect Verified in data: Measured EDM depends upon applied magnetic field gradient, with exactly predicted dependence Mercury magnetometer now provides our largest systematic! More precise field measurements will allow us to compensate this effect to ~4x10-27 e.cm Magnetic Field Down Magnetic Field Up False EDM (1E-25 e.cm) db/dz (nt/m) -20 db/dz (nt/m)

58 Statistical Dipole & quadrupole shifts Enhanced GP dipole shifts 1.54E-26 e.cm 6E-27 e.cm (E x v)/c 2 from translation 1E-27 e.cm (E x v)/c 2 from rotation 1E-27 e.cm Light shift: direct B fluctuations E forces distortion of bottle Tangential leakage currents AC B fields from HV ripple Light shift: GP effects Error Budget for Total Data Set 4E-27 e.cm 8E-28 e.cm 7E-28 e.cm 4E-28 e.cm 1E-28 e.cm <1E-28 e.cm included

59 d n = (-0.31 ± 1.54 ± 1.00) x e.cm My colleagues announced new results at SUSY05 (preliminary) New (preliminary) limit: d n < 3.1 x e.cm (90% CL) Preprint expected soon

60 How will we do better?

61 Do we want to do better? Existing limits are already a challenge for theorists for instance, the strong interaction CP phase θ s must be Many other models are also challenged, for instance the natural scale for nedm caused by CP violation in SUSY models is to e cm. We have therefore already learned something significant about SUSY if SUSY exists, there is some structure to the theory to suppress CP violation.

62 Do we want to do better? If we can push our sensitivity to ~ e cm, then either: We will observe an nedm SUSY is not a property of nature (see below) CP violation is an approximate symmetry of nature CP violation has an off-diagonal structure, or there are large cancellations, or some as-of-yet unknown other mechanism strongly suppresses EDMs If SUSY does not exist, we still must explain the baryon asymmetry so investigations sensitive to new sources of CP violation are critical.

63 Cryogenic nedm Collaboration University of Sussex - K. Green, M.G.D. van der Grinten, P.G.Harris, J.M.Pendlebury, D.B.Shiers, K.Zuber RAL - S.N.Balashov, M.A.H.Tucker, D.L.Wark University of Oxford - H.Kraus, S. Henry Kure University H. Yoshiki Visiting Scientists P. Iaydjiev and S. Ivanov.

64 How will we do better? Need a new source of UCN. 11 K; 2π/k = 8.9 Å Landau-Feynman dispersion curve for 4 He excitations To use this we need. Dispersion curve for free neutrons Golub and Pendlebury, Phys. Lett. A53 133(1975)

65 How will we do better? Need a new source of UCN. 11 K; 2π/k = 8.9 Å Landau-Feynman dispersion curve for 4 He excitations To use this we need. Dispersion curve for free neutrons Golub and Pendlebury, Phys. Lett. A53 133(1975)

66 Entire Cryostat and pumps provided by Hajime Yoshiki from Kure

67 Next Generation Experiment

ULTRA silicon detectors Coated with a thin layer of 6 LiF Observe

be further improved by lowering 0 noise 0 100 200 300 400 500 600

68 Detectors that will work in 0.5K Development funded by PPARC Blue Skies Detector Fund LHe ORTEC ULTRA silicon detectors Coated with a thin layer of 6 LiF Observe n+ 6 Li α+t They work, although the efficiency could be further improved by lowering 0 noise See C.A.Baker et al., NIM A (2002) Counts/sec Channel F 7%

69 Must demonstrate that the production A velocity-selected beam of cold neutrons passes through LHe, the UCN are bottled and detected mechanism really works 1.19±0.18 UCN cm -3 s -1 expected, 0.91± 0.13 observed See C.A.Baker et al., Phys.Lett. A (2002)

Polariser aligned Polariser anti-aligned UCN

70 Show that polarisation is retained Inferred polarisation during downscattering No Fe polariser Polariser aligned Polariser anti-aligned UCN polarisation is (0.93 ± 0.10) of the polarisation of the incoming beam

71 Kyoto Seminar

72 SCV Ramsey Cell

73 All New Magnetometry System SQUID Magnetometers Developed at Oxford for CRESST Sensitivity sufficient to monitor field Measure field coupling a loop rather than volume average, therefore need quite a few

74 All New Magnetometry System SQUID Magnetometers Developed at Oxford for CRESST Sensitivity sufficient to monitor field Measure field coupling a loop rather than volume average, therefore need quite a few Neutron Magnetometers

75 Ramsey Cell and SF Vessel

76 Kyoto Seminar

77 Recall: σ Published Data ( dn ) = 2 α ET Current Room-Temp h N Cryogenic Experiment E 4.5 kv/cm 12 kv/cm 40 kv/cm T N 130 s s s

78 Kyoto Seminar

79 Kyoto Seminar

80 The Competition A group at KEK/Osaka is building an experiment to be used at JPARC A group at PSI based around the group from PNPI are proceeding with an experiment. A very large American collaboration is proposing an experiment at the SNS their proposal lists 36 names, requests $11M, with a target date for first data of There is a German group at the new reactor in Munich. There are also experiments to measure the eedm, atomic EDMs, and even the muon EDM. Competition is good, but uncomfortable when you are the target of it! However any observation would need to be confirmed extended, so many experiments are needed.

81 Conclusions Strong evidence exists from astrophysical measurements that CP violation exists in some asof-yet undiscovered properties of fundamental interactions. Particle EDMs offer a sensitive probe of such new physics (at very modest cost) the final nedm limit from the existing experiment extends the sensitivity by another factor of 2. We have not yet reached any fundamental limits to increased sensitivity. The Japanese have made a very significant contribution to our new cryogenic experiment, and are welcome to help exploit it. Other EDM experiments are just as important.

82 Kyoto Seminar

83 Experimental Limit on d (e cm) neutron: Multi Higgs Left-Right Electromagnetic SUSY φ 1 φ α/π neutron Range of d (e cm) in various models Standard Model electron

84 Kyoto Seminar

85 Experimental Limit on d (e cm) neutron: Multi Higgs Left-Right Electromagnetic SUSY φ 1 φ α/π neutron Range of d (e cm) in various models Standard Model electron

86 Experimental Limit on d (e cm) neutron: electron: Multi Higgs Left-Right Electromagnetic SUSY φ 1 φ α/π neutron Range of d (e cm) in various models Standard Model electron

87 199 Hg Electric Dipole Moment Optically pumped 199 Hg atoms precess in B, E fields, modulating absorption signal hep-ex/ Dual cells remove effect of drifts in B Result: d( 199 Hg) < 2.1 x e cm Provides good limit on CPv effects in nuclear forces, inc. θ QCD If from valence neutron, corresponds to d n <2x10-25 ecm, because of electrostatic shielding.

88 Experimental Limit on d (e cm) neutron: electron: 199 Hg atomic EDM Relative value of neutron, electron, atomic (and µ and τ) EDM is modeldependent, must pursue all Multi Higgs Left-Right Electromagnetic SUSY φ 1 φ α/π neutron Range of d (e cm) in various models Standard Model electron

The cryogenic neutron EDM experiment at ILL

The cryogenic neutron EDM experiment at ILL and the result of the room temperature experiment James Karamath University of Sussex In this talk (n)edm motivation & principles Room-temperature nedm experiment