Measurement of Spin-Polarized Observables inthe β+ decay of 37K

Benjamin Fenker

Texas A&M University Cyclotron Institute

June 18, 2014

Benjamin Fenker Measurement of Spin-Polarized Observables in the β+ decay of 37K

Outline

Brief physics goals

Outline of TRINAT’s double-MOT system

Overview of recent run

Benjamin Fenker Measurement of Spin-Polarized Observables in the β+ decay of 37K

Motivation: Fundamental Symmetries

Standard model weak interaction is strictlyVector − Axial-Vector (V −A)

Parity is conserved in strong and EM interactions but violated inweak ones?

SU(2)L ⊗U(1)Y?→ SU(2)R ⊗SU(2)L ⊗U(1)Y

Angular correlations in β-decay are sensitive to new physics

d5W

dEdΩedΩν∼ 1+aβν

pepν cos (θeν)

EeEν+b

me

Ee+

P

(

Aβpe

Eecos(θe)+Bν

pν

Eνcos(θν)

)

Parent

Unpolarized

e+

ν

θeν

Parent

Polarized

e+

ν

~Pθe

θν

AβSM=

−0.5702(6)

BνSM=

−0.7692(15)

Benjamin Fenker Measurement of Spin-Polarized Observables in the β+ decay of 37K

TRINAT’s x2-MOT system

Collection trap is coupled to ISAC beamline

To avoid backgrounds from untrapped atoms, transfer to second trapfor precision measurement

MCP

MCP

Push

beam 14"

Collection chamber Detection chamber

Ion

Neutralizer

beam

Electrostatichoops

Benjamin Fenker Measurement of Spin-Polarized Observables in the β+ decay of 37K

Overview

Magneto-Optical Trap (MOT) Provides a cold (∼ 1mK), localized (∼Ø1mm) source of atoms Shallow trap so products emerge unperturbed

Polarization AxisNuclear Detectors

Benjamin Fenker Measurement of Spin-Polarized Observables in the β+ decay of 37K

Overview

Magneto-Optical Trap (MOT) Optical Pumping Polarizes the Atoms

σ± lasers drive biased random walk towards Pnucl =±1

Polarization AxisNuclear Detectors

Benjamin Fenker Measurement of Spin-Polarized Observables in the β+ decay of 37K

Overview

Magneto-Optical Trap (MOT)

Optical Pumping Polarizes the Atoms Nuclear Detectors

β-telescopes measure position, energy along polarization axis

Polarization AxisNuclear Detectors

Benjamin Fenker Measurement of Spin-Polarized Observables in the β+ decay of 37K

Types of events

Silicon Strip Detector

BC408 Plastic Scintillator

eMCP rMCP

Nuclear polarization

~B

~E

Shakeoff e−

β+

Ar+ β+ incoincidencewith either MCP

ν is unobserved

Only able to bias one MCP at a time Development to bias both will reduce background and

systematicsBenjamin Fenker Measurement of Spin-Polarized Observables in the β+ decay of 37K

Types of events

Silicon Strip Detector

BC408 Plastic Scintillator

eMCP rMCP

Nuclear polarization

355 nm light

~B

~E

K+

Photoelectron e−

Monitor of trapposition, size,temperature

Ultra-cleanmeasure ofnuclearpolarization

Only able to bias one MCP at a time Development to bias both will reduce background and

systematicsBenjamin Fenker Measurement of Spin-Polarized Observables in the β+ decay of 37K

Photoionization signal

With time-of-flight and position cuts, this signal is very clean

Photoion Time-of-flight [ns]1100 1150 1200 1250 1300 1350 1400 1450 1500

Cou

nts/

200

ps

0

50

100

150

200

250

300

Time of flight

X-Position: X2-X1 [ns]-100 -50 0 50 100

Z-P

ositi

on: Z

2-Z

1 [n

s]

-200

-150

-100

-50

0

Position

Benjamin Fenker Measurement of Spin-Polarized Observables in the β+ decay of 37K

Optical Pumping

Stretched state has F = 2, MF = 2 or equivalently Iz =32 , Jz =

12

An atom in this state is dark to the laser light and is trapped

This state corresponds to total atomic and nuclear polarization

Ene

rgy

355 nm light

F = 1

F = 2

F = 1

F = 2S1/2

P1/2

P3/2

Angular Momentum Fz

Fz =−2 Fz =−1 Fz = 0 Fz = 1 Fz = 2

Benjamin Fenker Measurement of Spin-Polarized Observables in the β+ decay of 37K

Optical Pumping

Stretched state has F = 2, MF = 2 or equivalently Iz =32 , Jz =

12

An atom in this state is dark to the laser light and is trapped

This state corresponds to total atomic and nuclear polarization

Ene

rgy

355 nm light

F = 1

F = 2

F = 1

F = 2S1/2

P1/2

P3/2

Angular Momentum Fz

Fz =−2 Fz =−1 Fz = 0 Fz = 1 Fz = 2

Benjamin Fenker Measurement of Spin-Polarized Observables in the β+ decay of 37K

Polarized measurements must be done with MOT offWhen MOT is off, cloud expands; therefore alternate counting/trapping

Pho

toio

n ev

ents

1

10

210

310

MOT Collects, CoolsOptical PumpingQuench B

Photoion events and duty cycle

s]µTime since MOT-OFF [0 500 1000 1500 2000 2500 3000 3500 4000

rMC

P D

elay

line

ano

de p

ositi

on [n

s]

-110

-100

-90

-80

-70

-60

0

200

400

600

800

1000

1200

~ 0.9 mmσ

Benjamin Fenker Measurement of Spin-Polarized Observables in the β+ decay of 37K

This great signal allows clean measurement of polarizationOnline analysis gives P & 0.990, but that is not even the full data set

Benjamin Fenker Measurement of Spin-Polarized Observables in the β+ decay of 37K

β+ energy spectrum

Coincidence with silicondetector will reduce 511background

Have enough β-electroncoincidences for < 0.5%measurement

BC 408 Plastic Scintillator

silicon strip detector

β+

300 µm thick 40×40 mm2

Entries 7760313

Underflow 0

Overflow 0

Integral 7.759e+06

QDC Channel

0 500 1000 1500 2000 2500

Co

un

ts

1

10

210

310

410

510

610 Entries 7760313

Underflow 0

Overflow 0

Integral 7.759e+06

QDC_LowerPMT

Benjamin Fenker Measurement of Spin-Polarized Observables in the β+ decay of 37K

Recoil Ar+ time-of-flight spectrum

Recoiling Ar ion is swept to rMCP and detected in coincidence with βTime-of-flight spectrum can be used to measure

Beta-neutrino correlation when 37K is unpolarized

Rslow when 37K is polarized

TOF_recoilsEntries 21792Mean 904.6RMS 369

Recoil TOF [ns]0 500 1000 1500 2000

Cou

nts

0

20

40

60

80

100

120

140

TOF_recoilsEntries 21792Mean 904.6RMS 369

TOF w.r.t. scintillator (Run 423)

Benjamin Fenker Measurement of Spin-Polarized Observables in the β+ decay of 37K

Shake-off electron spectroscopy (S1446)

X-Position [channel]30 40 50 60 70 80 90 100 110 120 130

Z-P

ositi

on [c

hann

el]

-40

-30

-20

-10

0

10

20

30

40

50

60

position-Shake off e

Electrons deflected1cm by field of 2G

Position spectrumin perpendiculardirection → energyspectrum

Benjamin Fenker Measurement of Spin-Polarized Observables in the β+ decay of 37K

Conclusions

TRINAT’s x2 MOT system provides an ideal source of β-decayingatoms for studying fundamental symmetries of the weakinteraction

Highly spin-polarized with clean measurement of polarization Multiple physics observables all measured simultaneously

β-asymmetry with respect to polarization axis (Aβ) β-ν correlation (aβν) with recoil time-of-flight spectrum Rslow is a sensitive probe of right-handed currents Shakeoff electron energy spectrum down to a few eV

Stay tuned, lots of analyses under way!

Benjamin Fenker Measurement of Spin-Polarized Observables in the β+ decay of 37K

Acknowledgments

Collaboration members: Melissa Anholm (TRIUMF),Daniel Ashery (Tel Aviv), Spencer Behling (TAMU), John Behr(TRIUMF), Iuliana Cohen (Tel Aviv), Alexandre Gorelov(TRIUMF), Gerald Gwinner (U of Manitoba), Michael Mehlman(TAMU), Dan Melconian (TAMU), Praveen Shidling (TAMU)

Thanks to the targets group for developing the HpTiC target Consistently 2× 108 37K/s! 5-10 thousand atoms in the trap

Thanks to Konstantin Olchanski and the DAQ group

Benjamin Fenker Measurement of Spin-Polarized Observables in the β+ decay of 37K

Benjamin Fenker Measurement of Spin-Polarized Observables in the β+ decay of 37K

Benjamin Fenker Measurement of Spin-Polarized Observables in the β+ decay of 37K