Beta decay experiments with separated fragmented beams · catcher (pps) Transport to RFQ RFQ transmission Transport BECOLA Extracted (pps) Demonstrated 4×104 0.72 0.80 0.1 2×103

Beta decay experiments with

separated fragmented beams

Oscar Naviliat-CuncicNational Superconducting Cyclotron Laboratory

and Department of Physics and Astronomy

Michigan State University

ACFI-FRIB Workshop, Oct. 23-25, 2014 2Michigan State University

National Science Foundation

Scope and Outline

• Discuss recent measurements and future plans for

experiments in beta decay using separated fragmented

beams.

1. Spectrum shape measurement in 6He and 20F decays

2. Correlation measurements with polarized beams

3. Summary



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.

Measurement of the spectrum

shape in 6He decay



Constraints on Tensor Couplings

• 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

ONC and M. Gonzalez-Alonso, Ann. Phys. (Berlin) 525 (2013) 600



Sensitivity to Fierz term in 6He decay

Db (‰)

For 108 collected events

a.u

.



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 6He 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 6He consists to tests CVC.

(1) F. Calaprice and B.R. Holstein, NPA 273 (1976) 301



General principle

Range of b particlesChoose your

Favorite isotope

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?



NSCL Coupled Cyclotron Facility

• Dp/p = 1%

• Dx×Dy = 1.5×2 mm2

• No traces of 8Li or 9Li

contamination

Production target

(Be)

Primary beam: 18O

150 MeV/A

Wedge

(Al)

Extraction:

1.2×105 6He/s



Pile-up

Beam purity and profile

Vary degrader thickness by rotation

Range distribution in Al degrader

Beam energy at implantation detector (operating the detector at lower gain)

• No traces of 8Li or 9Li.

• Tail is due to induced reactions in the

detector

CsI-run040-segs:0



Setup

CsI(Na) or

NaI(Tl) Al degrader

6He

6He

• 46 MeV/nucleon

after degrader

• CsI(Na) (2"×2"×5")

• NaI(Tl) (Ø3"×3")

• 2 small CsI(Na) and

NaI(Tl) detectors

(Ø1"×1")

g detectors for background identification

• Implant 6He ions in detectors.

• The range of 3.5 MeV electrons in CsI is

6 mm.

• Requires 40-50 MeV/A ions



Measuring sequence

Decay spectrum

Implantation

2.5 s

10-15 s

(3/4 of background level due to ambient

background)

Decay

NaI

NaI-run182-segs:0,1-Ew:500-2500



Theoretical corrections

Za2

(Sirlin’87)

Z 2a3

(could be neglected)



MC simulations

Calculate spectrum of the energy absorbed in the detector.

including the effect of escaping bremsstrahlung radiation.

X. Huyan

Generated

Absorbed

Standard

Livermore

Penelope

• G4 EM packages

• EGSnrc

The differences in the comparison between codes/ packages/

implementations have been observed to be < 5×10-4 /MeV.

Imp-0

Imp-1

CsI(Na)



Background

CsI-run145-segs:0,1,2-Ew:0500-7000

Time (s×100)

CsI-run145-segs:0,1,2-Tw:0300-0400

CsI-run145-segs:0,1,2-Tw:1100-1200

CsI-run145-segs:0,1,2

Analysis in progress



Instrumental effects

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

Comparison of detector properties

Measurement of the spectrum

shape in 20F decay



Spectrum shape in 20F 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.)

Implantation

detector

CsI(Na) array

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: 21N and 37K



37K production

Bρ 3,4= 2.50310 Tm

Bρ 1,2= 2.65770Tm

957 mg/cm2

Wedge 957 mg/cm2

Courtesy: Chandana Sumithrarachchi

(adapted)

• Production rate 1.3×105 pps/pnA

• dp/p = 0.5%

40Ca, 140 MeV/A

(50 pnA max)



37K thermalization

Courtesy: Chandana Sumithrarachchi

(adapted)

Alkali ion-source

ANL gas catcher (He)

To low energy

area

Ion Extraction system

37K



Transport efficiencies and rates

Out of gas

catcher (pps)

Transport to

RFQ

RFQ

transmission

Transport

BECOLA

Extracted

(pps)

Demonstrated 4×104 0.72 0.80 0.1 2×103

Projected 105 0.70 0.75 0.5 2.6×104

BECOLA

Polarization in BECOLA by collinear optical pumping



Double arm positron polarimeter

(Side view) (Top view)

Time resolved spectroscopy of Ps decayJ

beta polarimeter

b

nucelar spin

q



Polarimetry improvements

Parameter Factor

Analyzing power 1.7

Depolarization in matter 2.0

g detection efficiency 4.0

Nuclear polarization 2.0

Total (sensitivity) 13

Projected improvements relative to LLN/

ETH/ PSI Ps polarimeter



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 6He beta energy spectrum.

• The first shot [108 net events in 2 days] indicates that beam

induced activation is ~3 times smaller than ambient

background.

• Data analysis is under way



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.

• …



Differential longitudinal polarization

RL0(E) in 21Na decay

J=0.4

0.8

1.0

J

beta polarimeter

b

nucelar spin

q

Never measured in nuclear decays

For muon decay see R. Prieels et al. 1408.1472



People

V. Bader1, D. Bazin1, S. Beceiro-Novo1, M. Bowry1, W. Buhro1, A.

Gade1, M. Hughes1, X. Huyan1, S. Liddick1, K. Minamisono1, O.

Naviliat-Cuncic1, S. Noji1, S. Paulauskas1, A. Simon1, P. Voytas2, D.

Weisshaar1

1 NSCL/Michigan State University, MI, USA2 Wittenberg University, OH, USA

Documents

Beta decay experiments with separated fragmented beams · catcher (pps) Transport to RFQ RFQ transmission Transport BECOLA Extracted (pps) Demonstrated 4×104 0.72 0.80 0.1 2×103