V ud from Neutron Beta Decay Presence & Prospects Bastian - PowerPoint PPT Presentation

V ud from Neutron Beta Decay – Presence & Prospects Bastian Märkisch 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 Marciano, Sirlin PRL 96 (2006) [Update Czarnecki, Marciano, Sirlin, PRL (2018)] Requires only two experimental inputs: from D. Pocanic arXiv:1704.00192v1 neutron lifetime τ nucleon axial coupling: λ = g A /g V Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019 2

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

Neutron Classification V n < V crit Cold neutrons Moderated in thermal bath (e.g. liquid D 2 ) V n E ~ 3 meV, T ~ 40 K, v ~ 800 m/s, l ~ 0.5nm High flux densities: 2·10 10 s -1 cm -2 Density ~10 5 cm - ³ V n > V crit Decay rate of 10 6 s -1 per metre Fermi potential ~ 100 neV Ultracold neutrons (UCN) Gravity ~ 100 neV / meter E < 300 neV, T ~ 1 mK, v < 7 m/s, l > 60nm ΔE= m n g Δh Reflect from surfaces under any Magnetic field ~ 60 neV / Tesla incident angle : storable ΔE= μ n B Moderate densities: 30 cm -3 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019 4

Neutron Lifetime Warning: Speaker not involved in UCN Boston Custom House experiments. Not a review, but some Tony [CC BY 2.0] personal remarks.

Measurements of the neutron lifetime τ n Storage experiments with UCN In-beam experiments with cold neutrons “counting the survivors” “counting the dead” “UCN bottle ” 1 1 N ( t )   1 ln n β τ t - t N ( t ) e,p m 2 1 2 l 1 1 1 1 1      ... τ τ τ τ τ β m wall leak vacuum N(t 2 ) N(t 1 )  0 (experiment) 1   μ v  0 (extrapolation) eff τ wall l N 0  d N N     τ v 1  0 n e n 1 β τ dt τ τ n β m absolute measurements relative measurements Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019 6

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 E th,wall >> E neutron ) Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019 7

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 E th,wall >> E neutron ) Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019 8

Largest Measured Storage Time vs. Lifetime Gravitrap, Serebrov et al. 2005 Requires smallest extrapolation. D. Dubbers & M. G. Schmidt, Rev. Mod. Phys, 2011 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019 9

Gravitrap Gravitrap: LHe cooling Gravitrap II: running at ILL. no LHe cooling yet Many systematic analyses, extensive MC with good agreement Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019 10

UCN τ : Magnetic Storage Eliminates wall losses Multipole setup Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019 11

UCN τ : Result 877.7 ± 0.7 (stat) +0.4/ – 0.2 (sys) Taken from A. Saunders talk at CKM2018 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019 12

UCN τ : Result Only correction, for residual gas 877.7 ± 0.7 (stat) +0.4/ – 0.2 (sys) interactions, is smaller than “does not require corrections larger statistical and systematic than the quoted uncertainties .” uncertainties: no extrapolation! All major systematics appear to Pattie et al., Science 360, 627 (2018) scale with statistics Data on tape for 0.4 s total uncertainty, acquisition continues Taken from A. Saunders talk at CKM2018 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019 13

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

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. Original analysis: A. Czarnecki, W.J. Marciano, A. Sirlin, D. Dubbers, H. Saul, B. Märkisch, Neutron lifetime and axial coupling T. Soldner and H. Abele connection, Phys. Rev. Lett. 120 (2018) Phys. Lett. B 791, 6-10 (2019) Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019 15

PENeLOPE P recision E xperiment on Ne utron L ifetime O perating with P roton E xtraction absorber movement • Lossless magneto-gravitational mechanism storage of UCN • Determination of neutron lifetime via neutron and proton counting proton detector Precision goal: 0.1 seconds 2.5 m Status: preparation of full magnet outer pressure system test. vessel Requires MLZ / FRM UCN source for full reach. helium vessel storage walls (electropolished) Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019 16

Decay Correlations O. Naviliat-Cuncic and M. Gonzalez-Alonso, Ann. Phys. 525, 8 – 9, 600 – 619 (2013)

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 𝐵 = −2 𝜇 2 + 𝜇 𝑏 = 1 − 𝜇² 1 − 3𝜇² 1 − 3𝜇² A Neutron Spin J  Electron p e σ e B Neutrino p ν C Proton p p 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. Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019 18

Current Neutron Correlation Experiments PERKEO III a Spect A, B, C, b a ILL ILL aCORN a NIST Nab a,b SNS UCNA / UCNB A, B, b … and PERC Los Alamos PERC A, B, C, b MLZ / FRM Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019 19

Correlation Coefficients    3 d 1    2  l 2  2 2 G V 1 3 p E E E     F ud e e 0 e  5 d E d d 2 2  e e        p p m p p p p            n  e e  e e  1 a b A B D       E E E E E E E     e e n e e Jackson, Treiman, Wyld, Nucl. Phys. 4, 1957 But: experiments do not actually measure these correlations Energy cuts, angular constraints, coincidences PERKEO: experimental asymmetry A exp, UCNA: superratio (A) aSpect: integral proton kinetic spectrum aCorn: wishbone Nab: proton TOF, electron spectrum Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019 20

Correlation Coefficients New results UCNA PERKEO III aCorn aSpect (prelim) UCNA Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019 21

PERKEO: Measuring Beta Asymmetry Electron angular distribution: v Detector 1     W ( , E ) 1 A cos c Within Standard Model: g l  A g  Electron V Magnetic field to as quantisation axis Polarised Neutrons Integration over hemispheres:   1 cos 2 2 × 2π detection Experimental asymmetry, polarisation P    N N   v A 1 P A Detector 2   exp  2 c N N Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019 22

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

Spectrometer PERKEO III Detector 1 Total length: 8 m ~50.000 decays / sec in the continuous beam electrons Detector 2 Pulsed COLD Neutron B = 90 mT B = 150 mT Beam (homogeneous) Active volume Beam preparation (~2m) Beamstop Duty cycle: ~7% Mechanical Velocity Supermirror Adiabatic Fast disc chopper Selector Polarizer Passage Spin Flipper Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019 24

PERKEO III: Pulsed Neutron Beam Related Uncertainties: Time dependence Δ A/A=0.8×10 -4 Chopper disc uniformity Δ A/A=0.7×10 -4 Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019 25

Installation at PF1B, ILL, Grenoble Running time: 140 days (55 set-up / 25 pol. / 60 decay) 96% of data acquired in analysis 6 ∙ 10 8 neutron decay events One of two trucks Experimental Zone PF1b Plastic scintillator Bastian Märkisch (TUM) | Vud from Neutron Decay - Status and Prospects | 16.5.2019 26