Florian Piegsa – nnbar at ESS – June 13 th Florian Piegsa ETH Zürich – Institute for Particle Physics Magnetometry – nnbar at ESS

Florian Piegsa – nnbar at ESS – June 13 th

3 Neutron EDM – Situation & Perspective ► ►A neutron EDM violates CP, if CPT is conserved: ‘Classic Picture’ Baker et al., PRL 97, (2006) d n < 2.9 × e cm ► ►Current limit: ► ►Several experiments are aiming for sensitivities of about 5 × e cm (e.g. PSI, SNS-EDM, TUM) using ultracold neutrons. Important with respect to the apparent Baryon Asymmetry in the Universe.

Florian Piegsa – nnbar at ESS – June 13 th ►Determine the neutron Larmor frequency with Ramsey’s technique applied to neutrons (usually with storable ultracold neutrons: E kin < 200 neV) : ►Stabilization and monitoring of the magnetic field is of paramount importance – on the ~ 10 fT level (Earth’s magnetic field ~ 50 µT) ! Measurement Principle of the nEDM for B 0 = const. B0B0 E n

Florian Piegsa – nnbar at ESS – June 13 th A new nEDM Beam Experiment ►Main systematic in nEDM beam experiment caused by v×E effect: angle between E- and B 0 -field UCN Beam for: ► ►Separate the two effects by directly measuring the frequency shift as a function of the velocity:

Florian Piegsa – nnbar at ESS – June 13 th A new nEDM Beam Experiment ► ►Side view: ► ►Sectional drawing: Piegsa, PRC 88, (2013)

Florian Piegsa – nnbar at ESS – June 13 th mapprox. 50 m A new nEDM Beam Experiment Mu-metal shield will be a huge investment – one should make further use of it, e.g. in a novel nEDM beam experiment. ► ►nEDM-Beam Experiment: ► ►nnbar-Experiment: tapered Mu-metal shield

Florian Piegsa – nnbar at ESS – June 13 th A new nEDM Beam Experiment * Dress et al., PRD 15 (1977) 9 (100 kV/cm) Baumann et al., PRD 37 (1988) 3107 (60 kV/cm) ► ►Statistical sensitivity: N = 2 × / cm 2 s × 1/15 × 1/3 × 1/100 × 2 × (2 × 20 cm 2 ) ~ 3.5 × 10 8 / s PF1B capt. Flux (ILL) Polarization Beam cross sections Divergence losses monochrom. particle flux (6-10 Å) ‘Pancake target’ (factor ~ 3) α = 0.75, T = 0.1 s, E ~ 100 kV/cm *

Florian Piegsa – nnbar at ESS – June 13 th A new nEDM Beam Experiment * Dress et al., PRD 15 (1977) 9 (100 kV/cm) Baumann et al., PRD 37 (1988) 3107 (60 kV/cm) ► ►Statistical sensitivity: N = 2 × / cm 2 s × 1/15 × 1/3 × 1/100 × 2 × (2 × 20 cm 2 ) ~ 3.5 × 10 8 / s PF1B capt. fluxPolarization Beam cross sections Divergence losses monochrom. particle flux (6-10 Å) Pancake target (factor ~ 3) α = 0.75, T = 0.1 s, E ~ 100 kV/cm * A measurement of the neutron EDM with a beam at the ESS is complementary and can deliver a competitive result.

Florian Piegsa – nnbar at ESS – June 13 th Back to magnetometry…

Florian Piegsa – nnbar at ESS – June 13 th ►‘Non-free neutron’ (in a magnetic field): nnbar-Oscillation H.V. Klapdor-Kleingrothaus, ‘Non-accelerator particle physics’

Florian Piegsa – nnbar at ESS – June 13 th ►‘Non-free neutron’ (in a magnetic field): with: and nnbar-Oscillation Flight time ‘Mixing strength’ H.V. Klapdor-Kleingrothaus, ‘Non-accelerator particle physics’

Florian Piegsa – nnbar at ESS – June 13 th nnbar-Oscillation ‘quasi-free condition’: ►‘Non-free neutron’ (in a magnetic field): with: and H.V. Klapdor-Kleingrothaus, ‘Non-accelerator particle physics’

Florian Piegsa – nnbar at ESS – June 13 th ► ►‘Non-free neutron’ (in a magnetic field): ► ►Quasi-Free Propagation Efficiency: nnbar-Oscillation ‘quasi-free condition’:

Florian Piegsa – nnbar at ESS – June 13 th How was the field measured in the ILL-experiment ?

Florian Piegsa – nnbar at ESS – June 13 th (1) Using Fluxgates Transverse fields: Strongly surpressed by Mu-metal screen In addition, transverse fields are com- pensated by two surrounding coil-pairs T. Bitter et al., NIM A 309 (1991) 521

Florian Piegsa – nnbar at ESS – June 13 th (1) Using Fluxgates Field recording/mapping system: Uniaxial fluxgate (usually long. direction) Regular automized checks of the field, using a transport system (2 times per day & one scan took about 15 min) But probe is not in center of flight tube Fluxgate ‘zeroed’ in internal double zero field chamber T. Bitter et al., NIM A 309 (1991) 521

Florian Piegsa – nnbar at ESS – June 13 th (1) Using Fluxgates Axial/Longitudunal field compensation: 80 m solenoid wound on vacuum chamber Active feedback system, with a fixed uniaxial magnetometer at half the length of the shield Field is monitored with a 2 nd fluxgate Mu-metal smoothens out winding irreg- ularities T. Bitter et al., NIM A 309 (1991) 521

Florian Piegsa – nnbar at ESS – June 13 th (1) Using Fluxgates - Result Compare Talk by Prof. Dubbers

Florian Piegsa – nnbar at ESS – June 13 th U. Schmidt et al., NIM A 320 (1992) 569 (2) Neutron Zero Field Spin Echo S-shape bender Auxiliary coil Current sheet SF Analyzer & Detector L ~ 70 m Spin Echo-condition: φ z = (1.8 ± 1.1)° B z = (3.4 ± 2.0) nT Other field directions similar.

Florian Piegsa – nnbar at ESS – June 13 th Great technique – measure field which neutrons really see. ZFSE in good agreement with fluxgate measurements. However, one averages over neutron flight path. Question: Was it scanned over the neutron beam cross section ? Could one use a Position Sensitive Detector ? (2) Neutron Zero Field Spin Echo compare: Neutron Spin Phase Imaging: Piegsa et al., PRL 102 (2009) BzBz Neutron Zero Field SE [nT] Fluxgate scan [nT] 5 mm

Florian Piegsa – nnbar at ESS – June 13 th Fluxgate Mapping in the nEDM-Experiment at PSI Thanks to Jochen Krempel (ETHZ) for information and discussion.

Florian Piegsa – nnbar at ESS – June 13 th nEDM Apparatus at PSI Vacuum tank Ø ~ 1 m UCN precession chamber 4 layer Mu-metal shielding 6 surrounding field compensating coils

Florian Piegsa – nnbar at ESS – June 13 th Magnetic Field Mapping in Vacuum Tank Automated field mapping using a 3-axis precision fluxgate Robot-arm made from non-magnetic materials (PEEK, POM, Ceramics), with: z = ±200 mm, r = -10…+400 mm Perform regular offset-calibration runs to compensate for drifts Maps with inclinometer (magnetic) to determine/adjust robot arm alignment z

Florian Piegsa – nnbar at ESS – June 13 th Fluxgate Commercial 3D fluxgate sensor Reduced range: ± 2μT (larger pre-amplification, less cable noise) Powered by a stable voltage source: ± 15V Thin coax cables – to avoid that power supply-currents cause signal DAQ: 16 bit, 1 MHz ADC (4 separate ch.) / average over 1 ms per datapoint

Florian Piegsa – nnbar at ESS – June 13 th Fluxgate (Allan standard deviation) Performed ASD-measurement in a 4 layer Mu-metal test shield over night In fluxgate maps: integrate over 0.5 sec – better than 30 pT ASD [pT RMS ] Integration time [s]

Florian Piegsa – nnbar at ESS – June 13 th Example Maps at ‘Zero Field’ [nT] Vector field representation (one map takes about 3 hours) Transversal fields (cut in z-plane)

Florian Piegsa – nnbar at ESS – June 13 th Fluxgate Offset Calibration/Drift Perform offset calibration before and after each map Problem might arise due to non- orthogonality of 3 probes in fluxgate Accuracy on the order of 4 nT level probably feasible

Florian Piegsa – nnbar at ESS – June 13 th Conclusions Mu-metal shielding could be also used for a new nEDM beam experiment – keep in mind ! nnbar: Both fluxgate (3D) & ZFSE measurements of the magn. field are important – make scans over whole beam cross section !? Other atomic magnetometers ? We use: Cs (3D), Hg, 3 He – however, at 1 μT not at zero field. Romalis:SERF (spin exchange relaxation-free magnetometer) Potassium, high densities, heated, low fields ~nT, uniaxial(?) J.C. Allred et al., PRL 89 (2002) D. Sheng et al., PRL 110 (2013)

Florian Piegsa – nnbar at ESS – June 13 th Thank you for your attention. Zürich

Florian Piegsa – nnbar at ESS – June 13 th

Florian Piegsa – nnbar at ESS – June 13 th

Florian Piegsa – nnbar at ESS – June 13 th The Ramsey method Count rate Detector Spin analyzer Count rate Ramsey signal (central part) z y x B0B0 Measure (pseudo-) magnetic fields using neutrons:

Florian Piegsa – nnbar at ESS – June 13 th The Ramsey method “Two beam method” Suppression of common noise / global drifts (magnetic field, HF-phase, temperature etc.) z y x B0B0

Florian Piegsa – nnbar at ESS – June 13 th Magnetic & pseudmagnetic fields Piegsa et al., NIM A 605 (2009) 5 Piegsa & Pignol, PRL 108 (2012) magn. materials exotic interactions nEDM incoh. scattering lengths relativistic v x E magn. fields van den Brandt et al., NIM A 611 (2009) 231 Piegsa et al., PRL 102 (2009)

Florian Piegsa – nnbar at ESS – June 13 th Ramsey setup at BOA (December 2013) Patrick’s Spinflipper B 0 -Field Spin- Analyser 2 x 3 He-Detectors Pi/2 RF- Spinflipper Beam aperture Guide fields White polarized neutron beam Two well collimated beams à 18 (h) x 2.5 (w) mm 2 Magnetic field B 0 of about 170 µT Field stability ~ nT (actively stabilized) 2.2 m 3D magnetic field cage

Florian Piegsa – nnbar at ESS – June 13 th Typical Ramsey scans at B 0 = -168 µT at fixed RF freq. of 5 kHz -170 µT -168 µT (working field) -166 µT “Classic Ramsey” (Frequency scan) with a white neutron beam Alternatively: Ramsey phase-scan Phase shift ≈ 17° / µT

Florian Piegsa – nnbar at ESS – June 13 th Allan standard deviation plot Precision of better than 1 nT achievable in about 15 hours of data taking ! So far no systematic limitation – purely statistical ! 30 nT in 1 min 1 nT ~ 0.014° Neutron kin. energy ~ 5 meV Magnetic field energy = µ n B ~ 6 x meV

Florian Piegsa – nnbar at ESS – June 13 th

Florian Piegsa – nnbar at ESS – June 13 th

Florian Piegsa – nnbar at ESS – June 13 th Hg-atoms are polarised using circular polarised UV light (254 nm). They are then filled in the same precession volume as the UCN (‘co-magnetometer’). The magnetic field is measured by a free induction decay of the Hg nuclear spins (8 1µT) using a UV reading light – absorption of the light depends on the orientation of the spin and causes a modulation of the light intensity detected with a photo- multiplier. 50 pT 199 Hg co-Magnetometer

Florian Piegsa – nnbar at ESS – June 13 th Cs Magnetometer (HV-compatible)

Florian Piegsa – nnbar at ESS – June 13 th

Philipp Schmidt-Wellenburg Les Houches,GRANIT 2014, nEDM Ramsey- Messung am PSI Befüllen UCN Quelle (PSI)nEDM Experiment UCN: v < 6 m/s E kin < 200 neV Magnetfeld- abschirmung Präzessions- kammer Polarisierte UCN ω HF UCN Ventil

Philipp Schmidt-Wellenburg Les Houches,GRANIT 2014, nEDM Ramsey- Messung am PSI Spin Präzession ~ 100 sec EntleerenSpin Analyse & Detektion ω HF Analysator Folie Detektor