The Nab Experiment

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 gA and gV. • 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) Goals: Nab: δa/a = 0.1%, δb = 0.1% abBA: δA/A = 0.1%, δB/B=0.1% DNP Fall Meeting, Newport Beach, CA

3. Determination of Vud matrix element 0 . 9 8 0 Kaons +Unitarity [PDG 2010] 0 . 9 7 5 ft(0+→0+) [Hardy09] ft(0+→0+) [Liang09 – DD-ME2] PIBETA [Pocanic04] ft(0+→0+) [Liang09 – PKO1] Vud 0 . 9 7 0 τn [MAMBO II] τn [Serebrov05] λ [PDG 2010] 0 . 9 6 5 A [UCNA 2010] τn [PDG 2010] 0 . 9 6 0 - 1 . 2 9 0 - 1 . 2 8 0 - 1 . 2 7 0 - 1 . 2 6 0 λ= gA/gV courtesy S. Baessler A [PERKEO II, prel.] DNP Fall Meeting, Newport Beach, CA

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

5. Nab cos(θ) spectrometer Proton phase space (Dalitz plot) Probability (arb. units) 1.5 Ee = 1.25 700 keV cos θeν = 1 236 keV 1 0.75 75 keV pp2 [MeV2/c2] cos θeν = 0 0.5 cos θeν = -1 450 keV 0.25 0 0 0.2 0.4 0.6 0.8 courtesy S. Baessler DNP Fall Meeting, Newport Beach, CA Ee [MeV]

6. Proton TOF measurement 30 kV Segmented Si detector Adiabatic conversion TOF region (field rB∙B0) magnetic filter region (field B0) decay volume (field rB,DV∙B0) 0 kV Neutron beam 0 kV • Magnetic filter and longitudinalization of proton momentum 5 Si detector 4 3 B (on axis) z 2 Decay Magnetic Field volume 1 0 2 5 -1 0 1 3 4 z [m] Proton Trajectory courtesy S. Baessler DNP Fall Meeting, Newport Beach, CA

7. Detector response function Simulated counts [A.U.] Ee= 300 keV Ee = 500 keV Ee = 700 keV 0 0.002 0.004 0.006 1/tp2[µs-2] • TOF vs. pp assuming adiabatic proton spin transport • Edges confirm calibration • Slope of central part used to extract correlation ‘a’ courtesy S. Baessler DNP Fall Meeting, Newport Beach, CA

8. Fierz interference term ‘b’ ) s t i n u . b r a ( 5 10 d l b = +0.1 e i 4 10 SM Y 3 10 d l e i 2 Y 10 1 10 0 2 0 0 4 0 0 6 0 0 8 0 0 1 E ( k e V ) e , k i n 0 50 100 150 200 250 300 detected Ee [keV] • From the shape of the electron energy spectrum • Systematic uncertainties • Electron energy resolution • background Detector response to decay electron with Ee = 300 keV 2% of events in tail (deadlayer, external bremsstrahlung) Goal: Δb ~ 3×10-3 courtesy S. Baessler DNP Fall Meeting, Newport Beach, CA

9. Uncertainty Budget PLANNEDstatistical uncertainty budget: PLANNED systematic uncertainty budget: About 2×109 events can be detected in 6 weeks (Decay volume V = 246 cm3, decay density nd= 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

10. Nab Setup at the SNS • Fundamental Neutron Physics Beamline Si detectors Neutron beam Spectrometer magnet DNP Fall Meeting, Newport Beach, CA

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

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 . digitizer FPGA main FGPA readout hits fiber optics trigger bus lines rear I/O module DNP Fall Meeting, Newport Beach, CA

13. Nab Collaboration R. Alarcona, L.P. Alonzib, S. Baessler.b,c (Project Manager), S. Balascutaa, L. Barrón-Palos n, J.D. Bowmanc(Co-Spokesmen), M.A. Bychkovb, J. Byrned, J.R. Calarcoe, T.V. Ciancioloc, C. Crawfordf, E. Frležb, M.T. Gerickeg, F. Glückh, G.L. Greenec,i, R.K. Grzywaczi, V. Gudkovj, F.W. Hersmane, T. Itok, A. Kleink, M. Makelak, J. Martinl, S. McGovernb, S. Pageg, A. Palladinob, S.I. Penttiläc (On-site Manager), D. Počanićc (Co-Spokesmen), K.P. Rykaczewskic, A. Salas-Baccib, W.S. Wilburnk, A.Youngm 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 iDepartment 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 AlamosNationalLaboratory, 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 DNP Fall Meeting, Newport Beach, CA