A new simultaneous spin analyser (USSA) for the PSI nEDM experiment Challenges of the world-wide experimental search for the EDM of the neutron Ascona 2014 A new simultaneous spin analyser (USSA) for the PSI nEDM experiment V. Hélaine*, T. Lefort, G. Ban, D. Goupillière, Y. Lemière, G. Quéméner on behalf on the PSI nEDM collaboration * Shared PhD between PSI and LPC Challenges of the world-wide experimental search for the EDM of the neutron, Ascona 2014 Lefort Thomas – Laboratoire de Physique Corpusculaire - Caen

The reasons for the spin analysis Neutron EDM extraction requires neutron frequency measurement Neutron frequency extracted from the central Ramsey fringe fit Higher fit sensitivity where the slope is the largest: 4 working points N↑ and N↓ need to be analysed and counted in order to get : Challenges of the world-wide experimental search for the EDM of the neutron, Ascona 2014 Lefort Thomas – Interactions fondamentales – LPC Caen

The experimental set-up: OILL spectrometer I would like to thank you all for your interest and all these colleagues for their excellent work! Thank you very much. Challenges of the world-wide experimental search for the EDM of the neutron, Ascona 2014 Lefort Thomas – Interactions fondamentales – LPC Caen

The sequential spin analyser Spin analysis performed by transmission: - Magnetised iron layer: V = VF(Fe) ± µ.Bfoil - spin down component able to cross, spin up reflected ASF use to flip the spin up component Spin analysis is sequential: one spin is counted while the other one is stored above the foil I would like to thank you all for your interest and all these colleagues for their excellent work! Thank you very much. Main drawbacks UCN losses and depolarisations during storage above the foil Challenges of the world-wide experimental search for the EDM of the neutron, Ascona 2014 Lefort Thomas – Interactions fondamentales – LPC Caen

The simultaneous spin analyser: principle* SCOPE Analyse both spin states at the same time in order to reduce the UCN losses and depolarisations MEANS Double the sequential analyser system  two arms Each arm analyse one spin component RESULTS Storage time is reduced: N and α are increased I would like to thank you all for your interest and all these colleagues for their excellent work! Thank you very much. Room for improvements: - UCN reflections on the magnetised foil - slits in the switch [* I.S. Altarev et al, PLB 102 (1981) p 13] Challenges of the world-wide experimental search for the EDM of the neutron, Ascona 2014 Lefort Thomas – Interactions fondamentales – LPC Caen

The simultaneous spin analyser: design For each spin states, two sets of UCN ½ are directly going into their dedicated arm (directly counted) ½ are going in the wrong arm and need to travel back Directly counted UCN:  specular reflection on the walls  separation piece between both arms Reflected UCN: get back UCN gone in the “wrong” arm  define the upper part of the spin analyser I would like to thank you all for your interest and all these colleagues for their excellent work! Thank you very much. Challenges of the world-wide experimental search for the EDM of the neutron, Ascona 2014 Lefort Thomas – Interactions fondamentales – LPC Caen

The simultaneous spin analyser: design* U-shaped Simultaneous Spin Analyser (USSA)  design based on GEANT4-UCN simulations Directly counted UCN:  low roughness (glass walls)  separation piece between both arms (30 °) Reflected UCN:  define the USSA upper part geometry (45 °) Make sure that spin analysis is symmetric  Identical spin analysers (yoke, magnets, foils, ASF) I would like to thank you all for your interest and all these colleagues for their excellent work! Thank you very much. As compact (and light) as possible: L ~1 m, M ~150 kg (Vacuum chamber not drawn) (*Mechanical design performed by D. Goupilliere) Challenges of the world-wide experimental search for the EDM of the neutron, Ascona 2014 Lefort Thomas – Interactions fondamentales – LPC Caen

The simultaneous spin analyser: glass walls USSA walls (15 assembled plates): made of float glass (roughness ~nm; non-magnetic) NiMo (85/15) coating: non-magnetic, VFermi = 220 neV I would like to thank you all for your interest and all these colleagues for their excellent work! Thank you very much. (Coating performs @ PSI sputtering facility) Assembled plates are not vacuum tight: surrounding vacuum chamber is used Challenges of the world-wide experimental search for the EDM of the neutron, Ascona 2014 Lefort Thomas – Interactions fondamentales – LPC Caen

The simultaneous spin analyser: spin analysis Analysing foils: 400 nm of sputtered Fe on 25 µm Al - field within the foil: 2 T Magnetisation system: 40 magnets + soft iron yoke - Magnetising field at the foil location : 80 -120 mT - mounted outside the vacuum chamber I would like to thank you all for your interest and all these colleagues for their excellent work! Thank you very much. (Iron layer sputtered @ PSI) Challenges of the world-wide experimental search for the EDM of the neutron, Ascona 2014 Lefort Thomas – Interactions fondamentales – LPC Caen

The simultaneous spin analyser: spin analysis Adiabatic spin flipper (ASF): - axial RF field: coils wounded around each arm (BRF~ 0.2 mT, fres~ 20 kHz) - transverse static field gradient: stray field of the mag. syst.* + 2 coils (dBtrans/dz~ 0.15 mT/cm) Adiabaticity parameter k ~ 20 at the ASF location (Vn = 8 m/s) Transverse field gradient define the ASF location: We want to have the adiabatic SF as close as possible -> compact system The field gradient has to rather low in order to increase the adiabaticity parameter. During USSA operation: 1 SF ON, 1 SF OFF - RF shielding is required to avoid crosstalk between arms - 1 mm thick copper tube surrounding the RF coils [* S.V. Grigoriev et al, NIM A 384 (1997) p 451] Challenges of the world-wide experimental search for the EDM of the neutron, Ascona 2014 Lefort Thomas – Interactions fondamentales – LPC Caen

The simultaneous spin analyser: UCN detectors Two multi-channels detectors (NANOSC): based on 6Li doped glass fast scintillators ( ~70 ns) n + 6Li  3H (2.73 MeV) +  (2.05 MeV) Channel composition - stack of scintillators: 6Li depleted + 6Li enriched  edge events are suppressed - molecular sticking between scinti.: optical coupling I would like to thank you all for your interest and all these colleagues for their excellent work! Thank you very much. Main characteristics - able to count up to 106 counts/s - same efficiency as 3He gas detector - first one is in operation since 2010 Light pipe Couple to the FASTER acquisition syst. (http://www.faster.in2p3.fr) PMT Challenges of the world-wide experimental search for the EDM of the neutron, Ascona 2014 Lefort Thomas – Interactions fondamentales – LPC Caen

USSA: first characterization @ ILL & PSI First tests have been performed at ILL (04/2013)* Further characterization performed at PSI (08/2013): WEST-2 beam line NANOSC: same detection efficiency εA = εB ± 2 % UCN detection within USSA (no polarisation, no spin analysis) Transmission (no foil): 80.8 ± 0.6 % Asymmetry between arms w/o foils: 0.43 ± 0.07 % Asymmetry between arms with foils : 0.40 ± 0.11 % Spin analysis ASF efficiencies: fA = 97.0 ± 1.2 % ; fB = 97.1 ± 0.9 % Analysing power: PA = 91.0 ± 3.4 % ; PB = 89.7 ± 2.7 % Crosstalk between arms: ΔN/N = 0.15 ± 0.62 % I would like to thank you all for your interest and all these colleagues for their excellent work! Thank you very much. Symmetric UCN detection and spin analysis *(thanks to Peter, Thomas and participating collaborators ) Challenges of the world-wide experimental search for the EDM of the neutron, Ascona 2014 Lefort Thomas – Interactions fondamentales – LPC Caen

USSA: tests below the spectrometer USSA has been tested during nEDM run and compared to sequential analyser I would like to thank you all for your interest and all these colleagues for their excellent work! Thank you very much. Sensitivity (dn) improvement: 18.2 ± 6.1 % Further improvement using 58NiMo ? Challenges of the world-wide experimental search for the EDM of the neutron, Ascona 2014 Lefort Thomas – Interactions fondamentales – LPC Caen

USSA: first characterization @ PSI First beam polarisation P is measured: (P1 removed) (P1 removed) (P2 removed) (P1 removed) (P removed) Beam polarisation: P=70.6 ± 1.2 % Then USSA characterization with P and SF1: fA = 97.0 ± 1.2 % fB = 97.1 ± 0.9 % (PB removed) (PA removed) I would like to thank you all for your interest and all these colleagues for their excellent work! Thank you very much. PA = 91.0 ± 3.4 % PB = 89.7 ± 2.7 % (PB removed) (PA removed) Cross-talk measurement: - PA removed: NB counted with SFA ON or OFF Challenges of the world-wide experimental search for the EDM of the neutron, Ascona 2014 Lefort Thomas – Interactions fondamentales – LPC Caen