Weak Interaction Studies with Laser Trapped 6 He

Weak Interaction Studies with Laser Trapped 6 He P. Mueller 1, A. Leredde 1, T. P. Collaboration O’Connor 1, K. Bailey 1, A. Garcia 2, D. Zumwalt 2, R. Hong 2, Y. Bagdasarova 2, M. Sternberg 2, D. Storm 2, H. E. Svanson 2, X. Flechard 4, E. Liennard 4, O. Naviliat-Cuncic 3, A. Knecht 2, 5 1 Physics Division, Argonne National Laboratory 2 Center for Experimental Nuclear Physics and Astrophysics , University of Washington, Seattle 3 National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing 4 LPC Caen, France; 5 Paul Scherrer Institute, Switzerland

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Measure 6 He Lifetime 6 He decay curve 6 He half-life in ms ft-value Compare with ab-initio calculations of |MGT| to obtain g. A in nuclear medium A. Knecht et al. , PRL 108, 122502 (2012) A. Knecht et al. , PRC 86, 035506 (2012) 4

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Detector System Beta-detector (U Washington) • Multi-wire proportional chamber: X, Y • Scintillator: Tstart, E E-Field / HV suppl. (Argonne, U Washington) • Uniform electric field with optical access • Up to 2 k. V/cm, d. E/E < 0. 1% Beta det. - MWPC Scint. HV Electrodes Recoil-Ion detector (LPC Caen) • Multi-channel plate, delay line: X, Y, Tstop In-situ calibration via Ni mask to 10 mm • 100 mm position resolution • 100 ps timing resolution Digitial DAQ system (FATSER from LPC Caen) • 500 MHz FPGA based system for fast timing and beta energy MCP 6

MCP Imaging of Penning Ions 7

Q cut - event-by-event reconstruction of decay energy - assuming 1+, 2+, (3+) charge state - cut on +/- 3 x resolution w/o Q cut with Q cut 8

6 Li Charge state distribution – Trapped 6 He - state selective via fast (10 k. Hz) laser switching - charge distribution for exited states 2 s 3 S 1 & 2 p 3 P 2 - extraction independent of little-a Data Monte Carlo R. Hong et al. , Phys. Rev. A 96, 053411 (2017) - Significant discrepancy with recent theoretical calculation need improved theory with proper treatment of Li 3+ and 2 p 3 P 2 state 9

Decay Kinematics – beta-Energy Dependence Plot recoil ion TOF as function of MCP hit radius for increasing beta-energy slices 10

Full Analysis of June 2017 Data Y. Bagdaserova, 2019 UW Ph. D thesis 11

Full Analysis of June 2017 Data Y. Bagdaserova, 2019 UW Ph. D thesis 12

Full Analysis of June 2017 Data Statistical uncertainties only 13

Systematic Uncertainties 14

Full Analysis of June 2017 Data Y. Bagdaserova, 2019 UW Ph. D thesis 15

Systematic Issue: Timing Resolution Dependence 0. 3 ns 0. 1 ns • Timing resolution dependence 1. 6% in da/a per 100 ps • Data with photoions, betabackscattering, and sources insufficient to resolve issue 16

Systematic Issue: Unidentified Background • High statistics BG runs with un-trapped He-6 • Scaling to short TOF BG (also good agreement with MC/GEANT 4) • Unexplained BG at high (“unphysical”) TOF with trapped -> unknown contribution to BG after Q-cut 17

Conclusions (for now) • Demonstrated 6 He production, laser-trapping, and decay detection • Collected dataset with 1% statistical significance (4 days in June 2017) • Completed analysis (Y. Bagdaserova, Ph. D Thesis 2019) • Preliminary combined result a = -0. 3221 (38)stat (39)syst* (* systematic uncertainty not fully evaluated for low-field set) • Significant issues with systematic uncertainties unresolved • Detector system timing resolution • Unidentified background contribution • Trap position determination inconsistent, T 0 as fit parameter • … • Higher statistics possible (<= 0. 3%), but need to resolve systematic issues • … still sensitivity to CT limited -> rather move to He-6 b ? 18

- shake-up and shake-off probability in 6 He decay recoil induced contribution non-relativistic sudden approximation 1 S 0 and 3 S 1 atomic states in 6 He considered 7 -sigma discrepancy in recoil induced term vs. 1962 results 19

Results for 6 Li 1+, 2+ From ground state - From metastable state discrepancies with current theory - From ground- and metastable state - 3+ probability way off -> further calculations needed - proper treatment of 3+ - include 2 p 3 P 2 state 20

Background subtraction - background of un-trapped 6 He - flood chamber with 6 He for high statistics BG no Q cut with Q cut 21

Energy dependence – 6 Li 1+, 2+ - Select 1. 5 Me. V E-beta TH for unambiguous ID - event-by-event E-ion reconstruction Take ratio Equal efficiency, A 3 ~ 0 22

Results for 6 Li 1+, 2+ From ground state From metastable state 23

Weak Interaction Studies ß-Decay Rate J. D. Jackson, S. B. Treiman, H. W. Wyld, Nucl. Phys. 4 (1957) 206 da/a = 1% Standard Model Beyond Standard Model • Exotic couplings have not been excluded beyond the 5 -10% level • a = +1/3 for pure tensor GT • GT transition sensitive to CT & CT’ Johnson, Pleasonton, Carlson, Phys. Rev 1963 Right-handed • Only V-A terms • a. SM = -1/3 for GT • a. SM = +1 for Fermi from 6 He decay da/a = 0. 1% Left-handed F. Wauters et al. , ar. Xiv: 1306. 2608 24

Weak Interaction Studies: b-n Angular Correlations Atom Trap 0+ 6 He Qb=3. 510 Me. V t 1/2=0. 808 sec b 100% 6 Li 1+ Ion Trap 21 Na

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6 Li Charge state distribution – Ground State Recoil energy dependence 27