Beta decay experiments with separated fragmented beams Oscar - PowerPoint PPT Presentation

Beta decay experiments with separated fragmented beams Oscar Naviliat-Cuncic National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy Michigan State University

Scope and Outline • Discuss recent measurements and future plans for experiments in beta decay using separated fragmented beams. 1. Spectrum shape measurement in 6 He and 20 F decays 2. Correlation measurements with polarized beams 3. Summary Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 2 National Science Foundation

Context • The specificity of rare isotopes beams produced by fragmentation (NSCL/FRIB) are often considered in terms of their exoticity or their production yields. • We consider here separated fragmented beams to explore their potential to eliminate some instrumental effects for the measurement of beta spectrum shapes. Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 3 National Science Foundation

Measurement of the spectrum shape in 6 He decay

Constraints on Tensor Couplings ONC and M. Gonzalez-Alonso, Ann. Phys. (Berlin) 525 (2013) 600 • During the past 20 years, experiments with traps have had no impact in improving constraints on tensor couplings in nuclear beta decay. • Assuming LH n , the most precise parameter to search for contributions of tensor couplings is the Fierz term (or the contribution of the Fierz term to other correlation coefficients). • At the light of LHC results, the precision requirement for new experiments corresponds to D b < 10 -3 Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 5 National Science Foundation

Sensitivity to Fierz term in 6 He decay For 10 8 collected events D b (‰) a.u. Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 6 National Science Foundation

Weak Magnetism • Any attempt to reach D b < 0.01 from the measurement of the shape of the beta spectrum, will first see the contribution of the Weak Magnetism form factor, which is signed by an additional linear term in the beta spectrum. • For 6 He decay, the contribution of the Weak Magnetism form factor to the linear term is estimated to produce a slope +0.66 %/MeV (1) (has never been measured). • A first step toward a measurement of the spectrum shape in 6 He consists to tests CVC. (1) F. Calaprice and B.R. Holstein, NPA 273 (1976) 301 Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 7 National Science Foundation

General principle Choose your Range of b particles Favorite isotope Single detector • Well localized (and clean) source • 4 p solid angle and 100% detection efficiency • Detection of b particles without backscattering, out-scattering, or energy loss in dead-layers. How close can we get to such conditions with separated implanted ions produced by fragmentation? Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 8 National Science Foundation

NSCL Coupled Cyclotron Facility Primary beam: 18 O 150 MeV/A Extraction: 1.2 × 10 5 6 He/s Production target (Be) Wedge • D p/p = 1% (Al) • D x × D y = 1.5 × 2 mm 2 • No traces of 8 Li or 9 Li contamination Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 9 National Science Foundation

Beam purity and profile Beam energy at implantation detector Vary degrader thickness by rotation (operating the detector at lower gain) CsI-run040-segs:0 Pile-up Range distribution in Al degrader • No traces of 8 Li or 9 Li. • Tail is due to induced reactions in the detector Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 10 National Science Foundation

Setup • Implant 6 He ions in detectors. 6 He • The range of 3.5 MeV electrons in CsI is 6 mm. • Requires 40-50 MeV/A ions CsI(Na) or Al degrader NaI(Tl) • CsI(Na) (2" × 2" × 5") 6 He • NaI(Tl) ( Ø 3" × 3") • 46 MeV/nucleon after degrader • 2 small CsI(Na) and NaI(Tl) detectors ( Ø 1" × 1") g detectors for background identification Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 11 National Science Foundation

Measuring sequence Decay spectrum NaI-run182-segs:0,1-Ew:500-2500 Implantation NaI 2.5 s 10-15 s Decay (3/4 of background level due to ambient background) Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 12 National Science Foundation

Theoretical corrections Z a 2 (Sirlin’87) Z 2 a 3 (could be neglected) Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 13 National Science Foundation

MC simulations Calculate spectrum of the energy absorbed in the detector. including the effect of escaping bremsstrahlung radiation. • G4 EM packages Standard CsI(Na) Livermore Generated Penelope Absorbed X. Huyan • EGSnrc Imp-0 Imp-1 The differences in the comparison between codes/ packages/ implementations have been observed to be < 5×10 -4 /MeV. Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 14 National Science Foundation

Background CsI-run145-segs:0,1,2-Ew:0500-7000 CsI-run145-segs:0,1,2-Tw:0300-0400 CsI-run145-segs:0,1,2-Tw:1100-1200 CsI-run145-segs:0,1,2 Time (s×100) Analysis in progress Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 15 National Science Foundation

Instrumental effects Comparison of detector properties Property NaI(Tl) CsI(Na) Effect Signal decay time 230 ns 630 ns Pile-up Average Z 32 54 Bremsstrahlung Composition Na, I Cs, I Induced reactions Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 16 National Science Foundation

Measurement of the spectrum shape in 20 F decay

Spectrum shape in 20 F decay • The measurement of the WM form factor in 20F provides the most sensitive test of the strong form of CVC. • Measure the beta spectrum shape in coincidence with the subsequent g ray. (P. Voytas et al.) CsI(Na) array Implantation detector Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 18 National Science Foundation

Correlation measurements with polarized beams

Context N. Severijns and O.Naviliat-Cuncic, Annu.Rev.Nucl.Part.Sci. 61 (2011) 23 • Measurements of the longitudinal polarization of beta particles from pure F and pure GT transitions provide the most stringent constraints on tensor couplings. • Relative measurements with polarized nuclei offer enhanced sensitivity to the mass scale of RHC. • Potential candidates: 21 N and 37 K Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 20 National Science Foundation

37 K production Courtesy: Chandana Sumithrarachchi (adapted) 40 Ca, 140 MeV/A B ρ 3,4 = 2.50310 Tm (50 pnA max) B ρ 1,2 = 2.65770Tm 957 mg/cm 2 Wedge 957 mg/cm 2 • Production rate 1.3 × 10 5 pps/pnA • dp/p = 0.5% Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 21 National Science Foundation

37 K thermalization Courtesy: Chandana Sumithrarachchi (adapted) ANL gas catcher (He) Ion Extraction system To low energy area 37 K Alkali ion-source Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 22 National Science Foundation

Transport efficiencies and rates BECOLA Out of gas Transport to RFQ Transport Extracted catcher (pps) RFQ transmission BECOLA (pps) 4 × 10 4 2 × 10 3 Demonstrated 0.72 0.80 0.1 2.6 × 10 4 10 5 Projected 0.70 0.75 0.5 Polarization in BECOLA by collinear optical pumping Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 23 National Science Foundation

Double arm positron polarimeter (Side view) (Top view) q Time resolved spectroscopy of Ps decay J b nucelar spin beta polarimeter Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 24 National Science Foundation

Polarimetry improvements Projected improvements relative to LLN/ ETH/ PSI Ps polarimeter Parameter Factor Analyzing power 1.7 Depolarization in matter 2.0 g detection efficiency 4.0 Nuclear polarization 2.0 Total (sensitivity) 13 Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 25 National Science Foundation

Summary 1 • Hadronic contributions (WM) should manifest on the way to a precision measurement of b . This provides a sensitive test to any experimental technique. • We have explored the use of implanted ions from fragmentation reactions at NSCL and have performed a high statistics measurement of the 6 He beta energy spectrum. • The first shot [10 8 net events in 2 days] indicates that beam induced activation is ~3 times smaller than ambient background. • Data analysis is under way Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 26 National Science Foundation

Summary 2 • We are building a positron polarimeter with a factor of ~10 improved sensitivity. • The polarimeter will be installed at the low energy beam line BECOLA and will enable measurements of beta longitudinal polarizations from polarized nuclei. • The first phase will consist of “energy integrated measurements” of beta longitudinal polarizations. • … Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 27 National Science Foundation

Differential longitudinal polarization Never measured in nuclear decays R L0 ( E ) in 21 Na decay J= 0.4 0.8 q J b 1.0 nucelar spin beta polarimeter For muon decay see R. Prieels et al. 1408.1472 Michigan State University ACFI-FRIB Workshop, Oct. 23-25, 2014 28 National Science Foundation