The Science Program at the Los Alamos Ultra-cold Neutron Source Alexander Saunders Los Alamos National Lab 3 rd PSI Workshop Sep LA-UR

Outline The Ultra-cold neutron source at LANSCE – LANSCE and its capabilities – The UCN source in Experimental Area B – Improvements possible for the source Projects using the UCN source – UCNA, UCNB, SNS nEDM cell

LANSCE LINAC provides unique, highly-flexible beam delivery to multiple facilities 7 months per 24/7 with ~1200 user visits Lujan Center  Materials science and condensed matter research  Bio-science  Nuclear physics  BES National User Facility WNR  Nuclear physics  Semiconductor irradiation Proton Radiography  HE science, dynamic materials science, hydrodynamics Isotope Production Facility  Nuclear medicine  Research isotope production Ultracold Neutrons Facility  Fundamental nuclear physics The Los Alamos Neutron Science Center 800 MeV protons, up to 1 mA at 120 Hz and 12% DF

The heart of LANSCE is a very flexible 800-MeV proton linear accelerator (LINAC)-- one of the most powerful in the world! LINAC provides uniquely time-structured pulsed beams of varying power levels “simultaneously” to five different experimental areas

UCN Experiment Hall at LANSCE (Area B) Dedicated experiment hall 25 x 25 m Beam line shared with proton radiography 1 hr to switch beams UCN dedicated beam ~100 hours/wk (Nights and weekends!)

Top view of experiment hall UCNA UCN  Protons in LHe Supply UCN Source

UCN Source Experimental Hall UCN Source Polarizer magnet and spin flipper UCNA Spectrometer “Prepolarizer” and safety foil

UCN Source Experiment Hall

UCN Source Layout 6 m horizontal guide here W at ~100 C Be and C at 300 K CH2 at K Al and Be walls to minimize heating Coated with 58Ni Flapper valve to isolate UCN from D2 and minimize radiative heating Shield plug starts here

Layout of Test Port Area UCN from source (7 m of steel guides) Shield Wall Monitor Det. Gate Valve 6 T Pre-Polarizer Magnet Zr Window Switcher Test Port To Polarizer and UCNA 25 polarized UCN/cm3 52 UCN/cm3

The Bottom Line Source and Test Port are available and running now Parameters: – LANSCE runs 7 months/year – Proton beam is shared with PRAD available ~100 hrs/wk while accelerator is on – UCN source is shared with UCNA Test port beam can be on 10 minutes per hour while UCNA runs – ~25 UCN/cc at Test Port (after PPM), 52 at shield wall, up to 180 neV (at 5 kW incident proton power) – UCNs at Test Port are polarized to be high-field seekers – Backgrounds outside of beam gate are largely natural Beam gate is 0.2 s per 5 s Allocation by UCNA Executive Committee for now – But we hope for a PAC process soon

Future Improvements??? Beam pattern: spread out pulses – x ~2 – Funded! Testing in progress Replace cryogenic insert; improve pre-moderator and d2 cooling – x ~4 – Funded! Design work starts Oct – Sharapov et al. Arxiv ; Sharapov et al. Arxiv Improved proton beam tune – x ~2 – Requires 0.2 M$ for new diagnostics Lower loss, higher potential guides – x ~3 – Requires 0.3 M$ and six months to replace Duty factor: kick beam to pRad – x ~2 – Requires 3 M$ for kicker and shield wall

Projects using the LANL UCN Source UCNA UCNB Nab UCN    See Clayton’s talk up next UCNb SNS nEDM  Fillipone Monday Programmatic Materials Research Source and Guide Development

User Experiment location in LANSCE Area B

Neutron Lifetime Experiment on Test Port

Angular correlations in polarized neutron decay (Jackson et al ‘57) Neutron  decay and V ud See Greene, Monday, and Maerkisch, Tuesday for reasons to measure g A UCNA provides method of measuring with independent systematics from cold neutron experiments

Principle of the A-coefficient Measurement B field Detector 1Detector 2 Polarized neutronDecay electron (End point energy = 782 keV) n e  dW=[1+  PAcos  ]d  (E) Systematics: Polarization Backgrounds Backscatter

Spectrometer and Detectors

Results from 2010 Data Run

Current UCNA Status and Plans data run: 57.4 million events Analysis underway now Expected uncertainties:  A/A < 0.4% (stat.),  A/A < 0.6% (tot.) 2013: Engineering run to reduce remaining largest sources of uncertainty – Statistics (Source improvements) – Angle effect (Tagged timing source) – Polarization (Shutter)

New Shutter

Angular correlations in polarized neutron decay (Jackson et al ‘57) Neutron  decay and V ud In Standard Model:

Analyze relation of ε S and ε T to other measurements (including LHC signals) within BSM extensions b = f b (ε S,T* g S,T ) B 1 = f B (ε S,T* g S,T ) Measure these quantities with UCNs Calculate these hadronic matrix elements in QCD  s and  t are non-(V-A) contributions to the effective Hamiltonian Motivation for b and B measurement: BSM Physics (scalar and tensor) g T ~ g S ~

Principle of the antineutrino asymmetry B-coefficient Measurement B field Detector 1Detector 2 Polarized neutron Decay electron (Electron end point energy = 782 keV; Max proton energy < 800 eV) n e  Decay proton p 3 body decay: detect beta and proton in coincidence, reconstruct momentum Count N  p = N ±± = aligned and anti-aligned with  n Statistical sensitivity One month to reach 0.1% at 10 Hz decay rate

Challenge: detecting protons and electrons in coincidence

Detector requirements Detect protons – Thin dead layer to minimize energy loss – Bias detector and entire DAQ to -30 kV: accelerate protons through dead layer – Low noise requires cooling to LN2 temperature Detect electrons – Minimize missed backscattering using thin dead layer – Identify missed backscatters using fast timing (10 ns) Detect coincidences – 1 T field guides decay particles to detectors – Pixelated (4 mm Larmor radius in 1 T B field) – Detect hits in adjacent pixels – Electrons arrive in nanoseconds, protons in microseconds

Large Area Silicon detectors

Status: now taking beam at LANL UCN source 7 pixels instrumented and connected to DAQ Detectors biased in full field DAQ and detector development Electrons from beta decay counted at ~0.1 Hz/pixel (sufficient for ~1 month 0.1% measurement) First individual proton-electron coincidences detected Electron Proton

UCNB Status and Plans System capable of detecting beta decay electrons and protons in 7 pixels Operating at full field and 30 kV bias Beam is on! Detecting electrons and coincident protons Tuning DAQ and noise reduction continues Coming Soon: – Instrument all pixels on two detector stacks – Study timing, energy, angle effects from dedicated sources – Statistics for 0.1% measurement – Study of requirements for 0.01%

SNS nEDM Storage Cell Need to establish long storage time for SNS nEDM production/storage/measurement cell 2000 s wall loss time requirement ~1800 s measured dPS+dTPB cell, 3 L

Conclusions LANSCE UCN Source is in production – Supplying beam to eight projects including UCNA, SNS nEDM, UCN , UCNB – Design of further improvements now beginning UCNA has completed ~0.6% measurement, now engaged in engineering run UCNB now getting first results See next talk for UCN  status!

UCNA Collaboration California Institute of Technology: R. Carr, B. W. Filippone, K. P. Hickerson, M. P. Mendenhall, A. Perez-Galvan, R. Picker, S. Slutsky; Idaho State University: R. Rios, E. Tatar; Indiana University: C. Cude, A. T. Holley, D. Salvat, C.-Y. Liu; Institut Laue- Langevin: P. Geltenbort; Los Alamos National Laboratory\: M. Blantnik, T. J. Bowles, L. J. Broussard, S. Currie, S. Clayton, G. Hogan, T. M. Ito, M. Makela, C. L. Morris, J. Ramsey, A. Saunders (co-spokesperson), S. Seestrom, S. Sjue, E. Sharapov, W. Sondheim, T. Womack; Michigan State University: C. Wrede; North Carolina State University/TUNL: E. B. Dees, R. W. Pattie Jr., S. D. Moore, D. G. Phillips II, B. M. VornDick, A. R. Young (co-spokesperson), B. A. Zeck; Shanghai Jiao Tong University: J. L. Liu; Texas A&M University: D. Melconian; University of Kentucky: S. Hasan, B. Plaster; University of Washington: Y. Bagdasarova, A. Garcia, R. Hong, A. Knecht; University of Winnipeg: J. W. Martin; Virginia Polytechnic Institute and State University: D. B. Berguno, X. Ding, M. L. Pitt, R. B. Vogelaar UCNB Collaboration Los Alamos National Lab: L. Broussard, M. Makela (Principal Investigator), P. McGaughey, J. Mirabal, C. L. Morris, J. Ramsey, A. Saunders, S. Sjue, Z. Wang, W. S. Wilburn, T. Womack; North Carolina State University: B. vornDick, A. R. Young, B. Zeck; University of Kentucky: S. Hasan, B. Plaster