Beta decay experiments with separated fragmented beams

Transcription

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

2 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 ACFI-FRIB Workshop, Oct ,

3 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. ACFI-FRIB Workshop, Oct ,

4 Measurement of the spectrum shape in 6 He decay

5 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 LHn, 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 Db < 10-3 ACFI-FRIB Workshop, Oct ,

6 Sensitivity to Fierz term in 6 He decay a.u. For 10 8 collected events Db ( ) ACFI-FRIB Workshop, Oct ,

7 Weak Magnetism Any attempt to reach Db < 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 %/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 ACFI-FRIB Workshop, Oct ,

8 General principle Choose your Favorite isotope Range of b particles Single detector Well localized (and clean) source 4p 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? ACFI-FRIB Workshop, Oct ,

9 NSCL Coupled Cyclotron Facility Primary beam: 18 O 150 MeV/A Production target (Be) Extraction: He/s Wedge (Al) Dp/p = 1% Dx Dy = mm 2 No traces of 8 Li or 9 Li contamination ACFI-FRIB Workshop, Oct ,

10 Beam purity and profile Beam energy at implantation detector (operating the detector at lower gain) Vary degrader thickness by rotation 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 ACFI-FRIB Workshop, Oct ,

11 Setup 6 He Al degrader CsI(Na) or NaI(Tl) Implant 6 He ions in detectors. The range of 3.5 MeV electrons in CsI is 6 mm. Requires MeV/A ions CsI(Na) (2" 2" 5") NaI(Tl) (Ø3" 3") 2 small CsI(Na) and NaI(Tl) detectors (Ø1" 1") 6 He 46 MeV/nucleon after degrader g detectors for background identification ACFI-FRIB Workshop, Oct ,

12 Measuring sequence Decay spectrum NaI-run182-segs:0,1-Ew: Implantation 2.5 s NaI s Decay (3/4 of background level due to ambient background) ACFI-FRIB Workshop, Oct ,

13 Theoretical corrections Za 2 (Sirlin 87) Z 2 a 3 (could be neglected) ACFI-FRIB Workshop, Oct ,

14 MC simulations Calculate spectrum of the energy absorbed in the detector. including the effect of escaping bremsstrahlung radiation. G4 EM packages Standard Livermore Penelope CsI(Na) Generated Absorbed EGSnrc X. Huyan Imp-0 Imp-1 The differences in the comparison between codes/ packages/ implementations have been observed to be < /MeV. ACFI-FRIB Workshop, Oct ,

15 Background CsI-run145-segs:0,1,2-Ew: CsI-run145-segs:0,1,2-Tw: CsI-run145-segs:0,1,2-Tw: CsI-run145-segs:0,1,2 Time (s 100) Analysis in progress ACFI-FRIB Workshop, Oct ,

16 Instrumental effects Comparison of detector properties Property NaI(Tl) CsI(Na) Effect Signal decay time 230 ns 630 ns Pile-up Average Z Bremsstrahlung Composition Na, I Cs, I Induced reactions ACFI-FRIB Workshop, Oct ,

17 Measurement of the spectrum shape in 20 F decay

18 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 ACFI-FRIB Workshop, Oct ,

19 Correlation measurements with polarized beams

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

21 37 K production Courtesy: Chandana Sumithrarachchi (adapted) 40 Ca, 140 MeV/A (50 pna max) Bρ 3,4 = Tm Bρ 1,2 = Tm 957 mg/cm 2 Wedge 957 mg/cm 2 Production rate pps/pna dp/p = 0.5% ACFI-FRIB Workshop, Oct ,

22 37 K thermalization ANL gas catcher (He) Courtesy: Chandana Sumithrarachchi (adapted) Ion Extraction system 37 K To low energy area Alkali ion-source ACFI-FRIB Workshop, Oct ,

23 Transport efficiencies and rates BECOLA Out of gas catcher (pps) Transport to RFQ RFQ transmission Transport BECOLA Extracted (pps) Demonstrated Projected Polarization in BECOLA by collinear optical pumping ACFI-FRIB Workshop, Oct ,

24 Double arm positron polarimeter (Side view) (Top view) J q b Time resolved spectroscopy of Ps decay nucelar spin beta polarimeter ACFI-FRIB Workshop, Oct ,

25 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 ACFI-FRIB Workshop, Oct ,

26 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 ACFI-FRIB Workshop, Oct ,

27 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. ACFI-FRIB Workshop, Oct ,

28 Differential longitudinal polarization Never measured in nuclear decays R L0 (E) in 21 Na decay J q J= b 1.0 nucelar spin beta polarimeter For muon decay see R. Prieels et al ACFI-FRIB Workshop, Oct ,

29 People V. Bader 1, D. Bazin 1, S. Beceiro-Novo 1, M. Bowry 1, W. Buhro 1, A. Gade 1, M. Hughes 1, X. Huyan 1, S. Liddick 1, K. Minamisono 1, O. Naviliat-Cuncic 1, S. Noji 1, S. Paulauskas 1, A. Simon 1, P. Voytas 2, D. Weisshaar 1 1 NSCL/, MI, USA 2 Wittenberg University, OH, USA ACFI-FRIB Workshop, Oct ,