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V ud from Neutron Beta Decay Presence & Prospects Bastian Mrkisch Physics Department Technical University of Munich PERKEO III Current and Future Status of the First-Row CKM Unitarity, Amherst, 16.5.2019 V ud from Neutron Decay

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Vud from Neutron Beta Decay – Presence & Prospects

Bastian Märkisch Physics Department Technical University of Munich

Current and Future Status of the First-Row CKM Unitarity, Amherst, 16.5.2019

PERKEO III

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Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Vud from Neutron Decay

from D. Pocanic arXiv:1704.00192v1

Marciano, Sirlin PRL 96 (2006) [Update Czarnecki, Marciano, Sirlin, PRL (2018)]

Requires only two experimental inputs: neutron lifetime τ nucleon axial coupling: λ = gA/gV

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Neutron Lifetime Review recent major results wall storage, magnetic storage, beam Outlook Axial Coupling Recent result by PERKEO III Outlook: Nab, PERC, ESS Next instrument PERC at FRM / MLZ: Status

3 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Outline

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4 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Neutron Classification

Cold neutrons

Moderated in thermal bath (e.g. liquid D2) E ~ 3 meV, T ~ 40 K, v ~ 800 m/s, l~ 0.5nm High flux densities: 2·1010 s-1 cm-2 Density ~105 cm-³ Decay rate of 10 6s-1 per metre

Ultracold neutrons (UCN)

E < 300 neV, T ~ 1 mK, v < 7 m/s, l > 60nm Reflect from surfaces under any incident angle : storable Moderate densities: 30 cm-3

Fermi potential ~ 100 neV Gravity ΔE=mn g Δh ~ 100 neV / meter Magnetic field ΔE= μn B ~ 60 neV / Tesla

Vn

Vn < Vcrit Vn > Vcrit

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Tony [CC BY 2.0]

Boston Custom House

Neutron Lifetime

Warning: Speaker not involved in UCN

  • experiments. Not a review, but some

personal remarks.

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Storage experiments with UCN “counting the survivors”

 0 (extrapolation)

) t ( N ) t ( N ln t

  • t

1 τ 1

2 1 1 2

 

m

... τ 1 τ 1 τ 1 τ 1 τ 1

vacuum leak wall β

    

m

 0 (experiment)

eff wall

v μ τ 1  

β

τ 1 τ 1 

m

N(t1) N(t2) “UCN bottle”

relative measurements absolute measurements

n

τ v n β

τ dt d

 

  

l

e N N n

nβ

“counting the dead”

e,p N0 l

In-beam experiments with cold neutrons

6 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Measurements of the neutron lifetime τn

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7 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Wall Storage: Spectral Dependency of Losses

Major systematic correction: losses at walls (upscattering, absorbtion): Loss probability per bounce p ~10-4. Spectral dependence! Extrapolate to infinite volume and zero „effective collision rate“. Cool walls. (But still Eth,wall >> Eneutron)

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8 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Wall Storage: Spectral Dependency of Losses

Major systematic correction: losses at walls (upscattering, absorbtion): Loss probability per bounce p ~10-4. Spectral dependence! Extrapolate to infinite volume and zero „effective collision rate“. Cool walls. (But still Eth,wall >> Eneutron)

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9 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Largest Measured Storage Time vs. Lifetime

Gravitrap, Serebrov et al. 2005 Requires smallest extrapolation.

  • D. Dubbers & M. G. Schmidt,
  • Rev. Mod. Phys, 2011
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10 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Gravitrap

Gravitrap: LHe cooling Gravitrap II: running at ILL. no LHe cooling yet Many systematic analyses, extensive MC with good agreement

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11 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

UCNτ : Magnetic Storage

Multipole setup

Eliminates wall losses

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12 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

UCNτ : Result

Taken from A. Saunders talk at CKM2018

877.7 ± 0.7 (stat) +0.4/–0.2 (sys)

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13 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

UCNτ : Result

Only correction, for residual gas interactions, is smaller than statistical and systematic uncertainties: no extrapolation! All major systematics appear to scale with statistics Data on tape for 0.4 s total uncertainty, acquisition continues 877.7 ± 0.7 (stat) +0.4/–0.2 (sys) “does not require corrections larger than the quoted uncertainties.” Pattie et al., Science 360, 627 (2018)

Taken from A. Saunders talk at CKM2018

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14 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Status Neutron Lifetime

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15 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

No Dark Side to Neutron Decay

Using our averages of neutron decay data, including all measurements. Assuming V-A, neutron lifetime can be inferred from nuclear Ft, Unaffected by common rad. corrections.

  • D. Dubbers, H. Saul, B. Märkisch,
  • T. Soldner and H. Abele
  • Phys. Lett. B 791, 6-10 (2019)

Original analysis:

  • A. Czarnecki, W.J. Marciano, A. Sirlin,

Neutron lifetime and axial coupling connection, Phys. Rev. Lett. 120 (2018)

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16 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

PENeLOPE

Precision Experiment on Neutron Lifetime Operating with Proton Extraction

  • Lossless magneto-gravitational

storage of UCN

  • Determination of neutron lifetime

via neutron and proton counting Precision goal: 0.1 seconds Status: preparation of full magnet system test. Requires MLZ / FRM UCN source for full reach.

proton detector absorber movement mechanism

  • uter pressure

vessel helium vessel storage walls (electropolished) 2.5 m

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Decay Correlations

  • O. Naviliat-Cuncic and M. Gonzalez-Alonso, Ann.
  • Phys. 525, 8–9, 600–619 (2013)
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18 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Correlations in Neutron Decay

Determination of 𝜇 = 𝑕𝐵/𝑕𝑊 from neutron decay via angular correlation coefficients: (typically) beta asymmetry A, or electron-neutrino correlation a

Electron pe σe Proton pp Neutrino pν Neutron Spin J

A B

C

  • O. Naviliat-Cuncic and M. Gonzalez-Alonso, Ann. Phys. 525,

8–9, 600–619 (2013) Dubbers and Schmidt, Rev. Mod. Phys (2012)

Typically, specialised instruments / set-up required for different observables.

𝐵 = −2 𝜇2 + 𝜇 1 − 3𝜇²

𝑏 = 1 − 𝜇² 1 − 3𝜇²

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19 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Current Neutron Correlation Experiments

PERKEO III A, B, C, b ILL aCORN a NIST

… and PERC

aSpect a ILL Nab a,b SNS UCNA / UCNB A, B, b Los Alamos PERC A, B, C, b MLZ / FRM

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20 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Correlation Coefficients

 

 

 

3 2 2 2 2 F ud e e e 5 e e

d 1 1 3 d d d 2 2 p E E E E G V

 l      

n e e e e n e e e e

1 p p p p p p E E E E E E a A B D m E b

     

                        

Jackson, Treiman, Wyld,

  • Nucl. Phys. 4, 1957

But: experiments do not actually measure these correlations Energy cuts, angular constraints, coincidences PERKEO: experimental asymmetry Aexp, UCNA: superratio (A) aSpect: integral proton kinetic spectrum aCorn: wishbone Nab: proton TOF, electron spectrum

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21 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Correlation Coefficients

aCorn aSpect (prelim) UCNA UCNA PERKEO III New results

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Experimental asymmetry, polarisation P

PERKEO: Measuring Beta Asymmetry

  cos 1 ) , ( A c v E W  

Electron angular distribution: Magnetic field to as quantisation axis

V A

g g  l

Within Standard Model: Integration over hemispheres: 2 × 2π detection

Polarised Neutrons Electron

Detector 1 Detector 2

2 1 cos  

A P N N N N A

c v 2 1 exp

   

   

22 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

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PERKEO III

Spectrometer originally built by Heidelberg University, Now run by TUM, TU Wien, Heidelberg, ILL Installed at ILL, Grenoble, 3 times, next run summer 2019

beer-bench as reference

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Detector 1 Detector 2 Beamstop electrons Active volume (~2m) B = 150 mT (homogeneous) B = 90 mT Total length: 8 m ~50.000 decays / sec in the continuous beam

Beam preparation

Mechanical disc chopper Adiabatic Fast Passage Spin Flipper Supermirror Polarizer Velocity Selector

Pulsed COLD Neutron Beam

Duty cycle: ~7%

Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Spectrometer PERKEO III

24

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25 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

PERKEO III: Pulsed Neutron Beam

Related Uncertainties: Time dependence ΔA/A=0.8×10-4 Chopper disc uniformity ΔA/A=0.7×10-4

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Installation at PF1B, ILL, Grenoble

Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

One of two trucks Plastic scintillator Experimental Zone PF1b Running time: 140 days (55 set-up / 25 pol. / 60 decay) 96% of data acquired in analysis 6 ∙ 108 neutron decay events

26

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1 of 4 datasets shown 6·108 events in analysis

Statistical Uncertainty ΔA/A=14×10-4

27 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Asymmetry Extraction

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28 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Energy-Dependent Analysis

(Courtesy Heiko Saul)

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29 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Detector Model

Non-linearity of scintillation light prod. Non-uniformity of detector Non-linearity of electronics (Courtesy H. Saul)

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PERKEO III Detector Calibration Fit

Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Related Uncertainties Sources: ΔA/A=1×10-4 Statistics: ΔA/A=0.1×10-4 Non-linearity: ΔA/A=4×10-4 Stability: ΔA/A=3.7×10-4

137Cs 113Sn 207Bi 139Ce

114 full calibration sets measured (4 sources) Simultaneous Fit: Χ2/NDF = 1.0 – 1.3 Free parameters: Non-linearity, gain, photo-electrons, norms

30

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31 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Asymmetry: Four datasets

fit range

Two chopper frequencies, two detectors Fit to energy- dependence

  • f experimental

asymmetry Aexp(Ee) Only one free parameter: λ

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32 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Magnetic Mirror Effect

Flux through cross section of gyration is adiabatic invariant B0×r0

2 = B1×r1 2

Critical angle for reflection

1

arcsin B B

c 

 Magnetic field curvature leads so significant rate change on single detector:

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33 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Mirror Effect

Most of the effect cancels by averaging detectors. Calculate correction from measurements of the magnetic field and neutron pulse. Correction: ΔA/A = 46.1(4.5) × 10-4

3 3.5 4.0 4.5 5.0 (ms)

upstream downstream average

Time-dependence of asymmetry

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34 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

PERKEO III Result

Blinded by separate analysis: electrons, polarisation, magnetic mirror

  • B. Märkisch, H. Mest, H. Saul,
  • X. Wang, H. Abele, D. Dubbers,
  • M. Klopf, A. Petoukhov, C. Roick,
  • T. Soldner, D. Werder

arXiv:1812.04666, Phys. Rev. Lett., accepted

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35 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Axial Coupling: Status

electron-neutrino correlation a UCNA (newer results mostly include older data) PERKEO II (newer A results include older data) Scale: 2.4 PERKEO I PERKEO III Results from beta asymmetry A, unless where noted otherwise

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36 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Axial Coupling: Status

PERKEO III (arXiv:1812.04666): λ = −1.27641(56), Δλ

λ = 4.4 × 10 −4

UCNA and PERKEO III: blinded analysis. All new results consistent – but disagree with older measurements. Newer measurements of A have much smaller corrections. New average (PDG2016+UCNA+PERKEO III): λ = −1.2756 10 ; S = 2.15 Only UCNA + PERKEO II/III: λ = −1.2762 5

(ILL PPNS conference)

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37 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Comparision to Superallowed Decays

Neutron: vector part of neutron Ft

Using updated world averages

  • D. Dubbers, H. Saul,
  • B. Märkisch, T. Soldner and H. Abele
  • Phys. Lett. B 791, 6-10 (2019)

λ = −1.2𝑡756 10 ; S = 2.15

Data from J.C. Hardy, I.S. Towner,

  • Phys. Rev. C 91 (2015) 025501.

𝜐 = 879.7 8 ; S = 1.9

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38 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Vud from Neutron Decay

Using our result of the beta asymmetry A and the average neutron lifetime 879.7(8)s, and the new common rad. corrections Seng et al., Phys. Rev. Lett. 121 (2018) and arXiv:1812.03352v2: Or using Czarnecki, Marciano, Sirlin PRL 120 (2018): In agreement with the value from superallowed decays. See J. Hardy‘s talk on all-neutron values. Superallowed: Vud = 0.97395(23)

Seng et al. 1812.03352v2

Superallowed: Vud = 0.97417(21))

Hardy, Towner, PRC (2015)

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39 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Axial Coupling: Prospects

comissioning Δ λ λ = 3 × 10 −4 construction Δ λ λ = 1 × 10 −4 proposed statistics: 0.3 × 10 −4

Strong efforts to improve: Goal 𝑃(10 −4) and below. New beamlines and sources: FRM, Garching; SNS, Oak Ridge; ESS, Lund;

Nab PERC ESS

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The next generation: PERC (Proton Electron Radiation Channel) at MLZ / FRM

Goal: Order of magnitude improvement. New observables.

Priority Programme of the German Research Foundation

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Proton Electron Radiation Channel (PERC)

Cryostat

Active volume in a 8 m long neutron-guide, B0 = 1.5 T: phase space density and statistics Magnetic Filter, B1 = 6T: phase space, systematics (solid angle, backscatter suppression) Source for specialised spectrometers Aims to improve results by an order of magnitude. New Observables. (A, B, C, b, weak magnetism)

12 2

1

  B B

  • Nucl. Instr. Meth. A 596 (2008) 238 and

arXiv:0709.4440

B0 B1 B2

Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Magnetic Filter B1

41

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42 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Future Prospects: Cold Beamline for Particle Physics at ESS

x Chopper Selector Reactor t ESS: Peak brightness = 30 × ILL Chopper x Instrument

Time

European Spallation Source under construction. Design goal is same time average neutron flux as ILL. Statistics gain factor for a PERC-like system: x 15 !

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43 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019

Summary and Outlook

Particle Physics with Cold and Ultra-Cold Neutrons

Newer measurements on beta asymmetry consistent, small corrections, Some experiments blinded PERKEO III (arXiv:1812.04666, PRL accepted): λ = −1.27641(56),

Δλ λ = 4.4 × 10 −4

Magnetic storage of neutrons eliminates leading systematics of material wall storage

  • experiments. UCNτ result from blinded analysis.

Vud results agree with superallowed decays. Prospects for neutron experiments to improve by an order of magnitude.

PERKEO III at ILL