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Neutron decay data are useful

Neutron decay data are useful. d ν e W u e −. u e − W d ν e. e − ν e W d u'. Many processes have the same Feynman diagram as neutron decay: Primordial element formation n + e + ↔ p + ν ' e σ ν ~ 1/ τ

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Neutron decay data are useful

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  1. Neutron decay data are useful d νe W u e− u e− W d νe e−νe W d u' Many processes have the same Feynman diagram as neutron decay: Primordial element formation n + e+↔ p + ν'eσν~ 1/τ (2H, 3He, 4He, 7Li) p + e−↔ n + νeσν~ 1/τ n ↔ p + e− + ν'eτ Solar cycle p + p ↔ 2H + e+ + νe p + p + e− ↔ 2H + νe etc. ~(gA/gV)5 Neutron star formation p + e− ↔ n + νe Pion decay π−↔ π0 + e− + ν'e Neutrino detectors ν'e + p ↔ e+ + n Neutrino forward scattering νe +n↔ e− + p etc. W and Z production u' + d ↔ W−  e− + ν'e etc. … precision data of weak interaction parameters today only from neutron decay Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  2. ILL-Millenium program calculated gains in neutron count rates Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  3. Start-ups 2001S-DH GmbH: Neutron optics, H. Häse 2006 CASCADE GmbH : large fast n-detectors, M. Klein, C. Schmidt Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  4. t … History of the universe: a succession of phase transitions TP NP AP FKP Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  5. Only few Standard Model parameters in n-decay n-decay rate:τ−1= const (|gV|2 + 3|gA|2)= constGF2 |Vud|2 (1+3|λ|2) Only 2 parameters needed: CKM matrix elementVud, (GF from muon decay) ratio of c.c. λ= gA/gV … but many n-decay observables: problem is overdetermined: many tests of Standard Model Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  6. Many derived quantities from n-decay Standard model: axial to vector coupling c.c. λ = gA/gV CKM- matrix element |Vud| unitarity test of CKM-matrix Δ = Vud2 + Vus2 + Vub2  1 = 0? weak magnetism μp−μn all ν- p, ... weak cross-sections σνp/Eν= 0.67·10−38cm2/GeV number of ν-families Nν= 2.5(6) baryonic matter in universe ρ/ρcrit = 3.3(7) % beyond Standard model: mass of right-handed boson m(WR) > 300 GeV/c2 (90% c.l.) left-right mixing angle 0.20 < ζ < 0.07 (90% c.l.) scalar weak interaction amplitudes gS tensor weak interaction amplitudes gT Fiertz interference amplitude b second class amplitudes neutrino helicity < 1? (semileptonic decays) T-viol. amplitudes ... and others Aim: measure all these parameters to the highest precision possible Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  7. History of neutron lifetime τ best measured with stored ultracold-neutrons ('UCN', Tn ~ 1mK) . · · . · · . . . · · . . . · .· .UCN N = Noexp(– t/τ) → decay rate: τ−1 = const × |Vud|2 (1 + 3λ2) short history: neutrons 'in-beam': 1960: τ = (101030) s 1982: τ = (92511) s stored UCN:1989: τ = (8883) s 2004:τ = (885.70.8) s R. Picker, Mo Abend Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  8. History: λ= gA/gV: • derived from β-asymmetry A: • λ=gA/gV = −1.19 ±0.02 1960 • = −1.25 ±0.02 1975 • = −1.261 ±0.004 1990 • = −1.2695±0.0039 2005 • = −1.2739±0.0015 2006 Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  9. Unitarity tests of upper row of CKM matrix |Vud|2 + |Vus|2 + |Vub|2 = 1 −ΔStandard Model: Δ = 0 ↑0.0000 i.e. test of cos2θC + sin2θC upper row, with: Vud= 0.9717±0.0013 n Vud= 0.9740±0.0005 Nuclei Vud= 0.9728±0.0030 π Vus= 0.21960±0.0023 K Vub= 0.0036±0.0009 B upper row, combined: Δ = 0.0040 ± 0.0012 first column, with Vcd, Vtd: Δ' = 0.0015±0.0054 if Δdue to right-handed currents: phase ζ = 0.0020 ± 0.0006 Aim: all entries in CKM matrix from particle decays Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  10. before nuclear corrections: after nuclear corrections: 1σ band→ Nuclear super-allowed 0+→0+β-transitions (plus corrections) with half life t, phase space factor f J.C. Hardy, I.S. Towner, PR C 71, 055501 (2005) (from > 100 measurements) Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  11. new neutron lifetime measurement reestablishes unitarity when using old Vus … Δ ≈ 0 ± 0.001 Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  12. New Vus value = by-product of ε'/ε-analysis: 2002↓↓2005 B.R. KL→πe ν, πμν reestablishes unitarity when using old τn: PDG 2006, all measurements: Δ = 0.0008 (5)ud (9)us Other strategy: assume unitarity to hold → strong-interaction physics Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  13. e− p+ B ~Tesla planned: PERC collect charged decay products from within a long piece of cold n-guide: n-guide = source of neutron decay products: "Proton-Electron Radiation Channel" PERC • bright: ~ 106 neutron-decays/sec/m of beam • clean: under well defined conditions: • spectral distortions ≤ 10−4, background/signal ≤ 10−4, … • versatile: vary width and divergence of emerging p+, e− beam • without change of spectral properties neutron puls in long piece of n-guide Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  14. ILL user 10m example for setup: example: B0=2T, B1=8T, B2=½T: count rates: 6104 s−1 for a continuous unpolarized n-beam; 1104 s−1 for a continuous beam polarized to 98%; 3103 s−1 for a pulsed unpolarized beam; 3102 s−1 for a pulsed beam polarized to 99.5%. beam time for ~10−4 statistical error: ½ h for continuous unpolarized, 3 h for continuous polarized, 10 h for pulsed unpolarized, 4 d for pulsed polarized Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  15. Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  16. θcr magnetic mirror limits beam divergence: n-guide magn. mirror→ to experiment = 'keyhole' B0 B1 B2 ~10m • example: • magnetic field: 2Tesla 8Tesla ½Tesla • gyration radius: 2mm ½mm 4mm • critical angle: 300 900 150 • beam width can be traded against beam divergence, with negligible spectral distortion Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  17. … of variable beam divergence: guide field B0 B1 high divergence low divergence n-decay products magnetic mirror field Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  18. cm Scale×10 cm B0=2T B1=8T B2=0.5T B0=2T B1=8T B2=0.5T ↑ n-guide ↑ n and γ e and p ↑ absorbers window frame ↑ n-guide ↑ n and γ e and p ↑ absorbers window frame neutron beamstop: • Charged neutron decay products can be guided anywhere (electro-)magnetically • Example: Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  19. B2 e− orifice energy sensitive detector EXAMPLES a) e−spectroscopy (from pol., unpol. n's): Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  20. b) magnetic p+, e−spectroscopy: MAGNETIC SPECTROMETER e− B2 B3 window- ↑ frame p+ γ-shielding ↑ ↑ position- sensitive detectors Fig. 6: Sketch of a magnetic spectrometer for neutron decay products installed at the end of the beam line. Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  21. p+ ↑orifice c) aSPECT retardation spectrometer: • ↑ aSPECT Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  22. d) Mott scattering: • MOTT SCATTERING APPARATUS e− ↑orifice test of: electron helicity He~ υe/c in hadron decay Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  23. B Transmission profile of the absorbing frame: n-guide orifice→ Error sources thin orifice: in 1st order no edge effect • thin orifice: no angular or spectral distortion of the p+, e− beam Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  24. 2mm 2nd order error sources of orifice: • 1. neutron beam not uniform over edge of orifice: • error 6·10−5 at Eβmaxfor 10% change of n-flux over 1cm width • 2.particles hit inner face of orifice: • solution: oblique edge angle >θ2 • 3.non-perfect absorption near edges: • error 4·10−3 × 0.1 "active edge" • N.B.: electron scattering effects can be calculated reliably to better than 10% Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

  25. b) effect of mag. mirror field B1 on p+, e−: a) CRITICAL ANGLE b) COUNT RATE 1 80 0.8 60 0.6 0 0 N c 40 N/ 0.4 20 0.2 0 0 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 B0/B1 B0/B1 c) ASYMMETRY d) EFFICIENCY 1 1.2 1 0.8 0.8 0.6 0 2 A A 0.6 A/ N 0.4 0.4 0.2 0.2 0 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 B0/B1 B0/B1 Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM

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