1. The Nab Experiment 2012-10-26 Christopher Crawford DNP Fall Meeting, Newport Beach, CA University of Kentucky

2. Correlations in Neutron Decay Parity violation implies a rich phenomenology in neutron decay. V-A implies that all experimental quantities can be related to the axial and vector coupling constants g A and g V. Neutron beta decay measurements give: Test of CKM unitarity Test of CVC / search for SCC Test of tensor or scalar couplings Jackson et al., PR 106, 517 (1957) 2012-10-26DNP Fall Meeting, Newport Beach, CA2 Goals: Nab: δa/a = 0.1%, δb = 0.1% abBA: δA/A = 0.1%, δB/B=0.1%

3. Determination of V ud matrix element 2012-10-26DNP Fall Meeting, Newport Beach, CA3 -1.290-1.280-1.270-1.260 λ = g A /g V 0.960 0.965 0.970 0.975 0.980 V ud τ n [Serebrov05] τ n [MAMBO II] τ n [PDG 2010] ft(0 + →0 + ) [Hardy09] ft(0 + →0 + ) [Liang09 – PKO1] ft(0 + →0 + ) [Liang09 – DD-ME2] PIBETA [Pocanic04] λ [PDG 2010] A [UCNA 2010] A [PERKEO II, prel.] Kaons +Unitarity [PDG 2010] courtesy S. Baessler

4. Present limits (n decay data) SM: (0,0) Future limits, assuming a = -0.1059(1), A = -0.11860(3), B = 0.987(1), τ n = 882.2(8) s Sensitivity to scalar/tensor couplings G. Konrad, S.B. et al., ArXiv:1007.3027; courtesy S. Baessler Left-handed currentsRight-handed currents 2012-10-26DNP Fall Meeting, Newport Beach, CA4

5. E e [MeV] p p 2 [MeV 2 /c 2 ] cos θ eν = 1 Proton phase space (Dalitz plot)Probability (arb. units) 0 0.25 0.5 0.75 1 1.25 1.5 00.20.40.60.8 cos θ eν = 0 cos θ eν = -1 E e = 75 keV 236 keV 450 keV 700 keV Nab cos(θ) spectrometer courtesy S. Baessler 2012-10-26DNP Fall Meeting, Newport Beach, CA5

6. Segmented Si detector decay volume (field r B,DV ∙B 0 ) 0 kV 30 kV magnetic filter region (field B 0 ) Neutron beam TOF region (field r B ∙B 0 ) Proton Trajectory Magnetic Field Adiabatic conversion Proton TOF measurement Magnetic filter and longitudinalization of proton momentum courtesy S. Baessler 2012-10-26DNP Fall Meeting, Newport Beach, CA6

7. Detector response function TOF vs. p p assuming adiabatic proton spin transport Edges confirm calibration Slope of central part used to extract correlation ‘a’ courtesy S. Baessler 2012-10-26DNP Fall Meeting, Newport Beach, CA7

8. Systematic uncertainties – Electron energy resolution – background Goal: Δb ~ 3×10 -3 2% of events in tail (deadlayer, external bremsstrahlung) Y i e l d 1 10 1 2 3 4 5 detected E e [keV] 050100150200250300 Detector response to decay electron with E e = 300 keV Fierz interference term ‘b’ From the shape of the electron energy spectrum courtesy S. Baessler 2012-10-26DNP Fall Meeting, Newport Beach, CA8

9. PLANNED systematic uncertainty budget: About 2×10 9 events can be detected in 6 weeks (Decay volume V = 246 cm 3, decay density n d = 20 cm -3, 12.7 % of decay protons go to upper detector, 80% duty factor) → (Δa/a) stat < 1×10 -3 can be reached Compare to Δa/a = 5 % of existing experimental results lower E e cutoffnone 100 keV 300 keV upper t p cutoffnone 40 μs ΔaΔa 2.4/√N2.5/√N 2.6/√N Δ a (E cal, l variable) 2.5/√N2.6/√N2.7/√N Δ a (E cal, l variable, inner 70% of data) 4.1/√N Experimental parameter Systematic uncertainty Δa/a Magnetic field... curvature at pinch5·10 -4 … ratio r B = B TOF /B 0 2.5·10 -4 … ratio r B,DV = B DV /B 0 3·10 -4 Length of the TOF region(*) Electrical potential inhomogeneity: … in decay volume / filter region5·10 -4 … in TOF region1·10 -4 Neutron Beam: … position4·10 -4 … profile (including edge effect)2.5·10 -4 … Doppler effectsmall Unwanted beam polarizationcan be made small Adiabaticity of proton motion1·10 -4 Detector effects: … Electron energy calibration(*) … Electron energy resolution5·10 -4 … Proton trigger efficiency2.5·10 -4 Residual gassmall Backgroundsmall Accidental coincidencessmall Sum1·10 -3 Uncertainty Budget PLANNED statistical uncertainty budget:

10. Spectrometer magnet Si detectors Neutron beam Nab Setup at the SNS Fundamental Neutron Physics Beamline 2012-10-26DNP Fall Meeting, Newport Beach, CA10

11. 6” ion-implanted silicon detectors 2 mm thick, 127 pixels 70-100 nm dead layer 2012-10-26DNP Fall Meeting, Newport Beach, CA11 front back fiducial volume background dark noise pedestal proton, 32 keV 0.5 mm Dead-layer thickness measured at NCSU

12. DAQ – Digital Signal Processing Readout waveform (energy, time) – offline pulse shape analysis Form e-p coincidences – 50 – 750 keV prompt electron – 30 keV proton 12 – 40 μs TOF Energy and Timing Resolution – 2 keV electron (energy sum) – 10 ns proton TOF resolution Resolve backscattered events HV Optical Isolation – 30 kV potential between detectors Event / Data rate – 5000/s electrons; 600/s protons – Accidentals <1% in 40 us window – 256 channels, 100 MHz, 12 bit ADC – 11 MB/s data rate -> 12 TB Trigger levels – 1) DIGITIZER threshold, 2) FPGA readout, 3) CPU storage – Energy sum trigger, adjacent pixels – Read out 7 nearest neighbor pixels in each detector. 2012-10-26DNP Fall Meeting, Newport Beach, CA12 main FGPA hits trigger bus lines digitizer FPGA fiber optics readout rear I/O module

13. R. Alarcon a, L.P. Alonzi b, S. Baessler. b,c (Project Manager), S. Balascuta a, L. Barrón-Palos n, J.D. Bowman c (Co-Spokesmen), M.A. Bychkov b, J. Byrne d, J.R. Calarco e, T.V. Cianciolo c, C. Crawford f, E. Frlež b, M.T. Gericke g, F. Glück h, G.L. Greene c,i, R.K. Grzywacz i, V. Gudkov j, F.W. Hersman e, T. Ito k, A. Klein k, M. Makela k, J. Martin l, S. McGovern b, S. Page g, A. Palladino b, S.I. Penttilä c (On-site Manager), D. Počanić c (Co-Spokesmen), K.P. Rykaczewski c, A. Salas-Bacci b, W.S. Wilburn k, A.Young m a Department of Physics, Arizona State University, Tempe, AZ 85287-1504 b Department of Physics, University of Virginia, Charlottesville, VA 22904-4714 c Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 d Department of Physics and Astronomy, University of Sussex, Brighton BN19RH, UK e Department of Physics, University of New Hampshire, Durham, NH 03824 f Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506 g Department of Physics, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada h IEKP, Universität Karlsruhe (TH), Kaiserstraße 12, 76131 Karlsruhe, Germany i Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996 j Department of Physics and Astronomy, University of South Carolina, Columbia, SC 29208 k Los Alamos National Laboratory, Los Alamos, NM 87545 l Department of Physics, University of Winnipeg, Winnipeg, Manitoba R3B2E9, Canada m Department of Physics, North Carolina State University, Raleigh, NC 27695-8202 n Universidad Nacional Autónoma de México, México, D.F. 04510, México Nab Collaboration 2012-10-26DNP Fall Meeting, Newport Beach, CA13