Precise neutrino and neutron spectroscopy using trapped radioactive ions August 8, 2009

1. Nicholas Scielzo Lawrence Fellow Physics Division, Physical Sciences Precise neutrino and neutron spectroscopy using trapped radioactive ions August 8, 2009 Lawrence Livermore National Laboratory, P. O. Box 808, Livermore, CA 94551 This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 LLNL-PRES-408002

2. Spectroscopy of “invisible” and difficult-to-detect particles Combine ion-trapping techniques with modern detector technology to perform b-decay and b-delayed neutron decay measurements with unprecedented precision • Entire decay kinematics reconstructed to determine energy/momenta of: • Neutrinos in beta decay • Neutrons in beta-delayed neutron emission • Ion traps • Efficiently collect any isotope nearly at rest, suspended only by electromagnetic fields • Recoil nucleus momentum available for study • <1mm3 volume b n Neutrino escapes detection! b n n Neutron emission

3. Scientific goals Scientific goals Improved decay spectroscopy can address many interesting questions: Nuclear beta-decay correlations Beta-delayed neutron emission Existence of new particles influences the correlation between momenta of emitted beta and neutrino particles • Measurements of beta-delayed neutron emission branching ratios and energies are needed to better understand: • the distribution of stable nuclei produced by the rapid-neutron capture process (r process) when the exotic nuclei produced decayed back to stability • the evolution of nuclear structure in neutron-rich nuclei • fission reactor performance Are there massive particles that have never been observed? 8.6 km SN1987A supernova: r-process site ion trap for beta-decay Large Hadron Collider at CERN Table-top device sensitive to physics at TeV energies! 86 cm

4. d b n W u Nuclear b decay Coupling constants: CS, CV, CA, CT Compare experimental values to SM predictions Put limits on terms “forbidden” by SM

5. The b-n angular correlation Neutrino too difficult to detect – correlation must be inferred from nuclear recoil Example Recoil Energy Spectrum (21Na) b Neutrino escapes detection! n Nuclear recoil a > 0 leads to larger average recoil energy Direct detection – acceleration of daughters Energy shift in subsequent particle emission Sensitive to detector thresholds and resolution Correlation easily perturbed by scattering

6. 18 MeV Qb=16.003 MeV 8Li t1/2=0.84 s 2+ 15 12 b- 9 6 100% 2+ 3 0+ 0 8Be a+a 8Li b decay • In most beta decays there are 5 degrees of freedom: • 3 × 3 - 4 = 5 • Of course, 8Li (and 8B) decays are not like most beta decays – the excitation energy of the 8Be daughter is broad, leading to another degree of freedom – the beta-decay Q value. • Even still, we can overconstrain the system – by measuring 7 degrees of freedom! • b energy, Jb, fb • a energy sum  the Q value • a energy difference  recoil energy, Jr,fr conservation of energy/momentum energy/momentum of beta, neutrino, nucleus

7. Beta-neutrino correlation in 8Li Beta-neutrino correlation measurement takes advantage of 1 mm3 trapped ion sample and position and energy resolution of double-sided silicon strip detectors to precisely reconstruct momentum vectors of all emitted particles (including neutrino!) 8Li  8Be* + b- + n a + a Plastic scintillator DSSD Neutrino momentum/energy can be determined from b- and recoiling 8Be momentum/energy b- momentum/energy measured from DSSD and plastic scintillator detector 8Be momentum/energy determined from a particle break-up… with no recoil, a particles would have same energy and would be back-to-back. With recoil, energy difference can be up to 730 keV and the angle can deviate by as much as ±70 n a 8Li+ b a Low mass of 8Li and Q ≈ 13 MeV lead to large recoil energies of 12 keV which makes the correlation easier to measure. Other b-n correlation measurements have had to deal with recoil energies of only 0.2-1.4 keV.

8. Beta-delayed neutron emission Novel approach: determine neutron energies and branching ratios by detecting beta particles and recoil ions that emerge from ion trap Provide reliable data for: r-process nucleosynthesis, nuclear structure, nuclear reactor performance, modeling of environments where fission fragments are produced 95Rb  95Sr* + b- + n 94Sr* + n Example Q = 4.9 MeV t1/2 = 0.378 sec Pn ≈ 9% MCP ion detector n 94Sr Plastic scintillator 95Rb+ • 1-mm3 trapped-ion sample and 1-ns timing resolution of detectors determines neutron momentum/energy to ~1% from time-of-flight of recoiling daughter ion • intrinsic efficiency for MCP detectors can be ~100% • many fission fragments available from the newly-developed CARIBU facility (an intense source of fission-fragment beams) at ANL b n Plastic scintillator