Post on 03-Jun-2020
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