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Schleching 2008 4.1 Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM Many processes have the same Feynman diagram as neutron decay: Primordial.

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Presentation on theme: "Schleching 2008 4.1 Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM Many processes have the same Feynman diagram as neutron decay: Primordial."— Presentation transcript:

1 Schleching Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM Many processes have the same Feynman diagram as neutron decay: Primordial element formation n + e + ↔ p + ν' e σ ν ~ 1/τ ( 2 H, 3 He, 4 He, 7 Li) p + e − ↔ n + ν e σ ν ~ 1/τ n ↔ p + e − + ν' e τ Solar cycle p + p ↔ 2 H + e + + ν e p + p + e − ↔ 2 H + ν e etc. ~ (g A /g V ) 5 Neutron star formation p + e − ↔ n + ν e Pion decay π − ↔ π 0 + e − + ν' e Neutrino detectors ν' e + p ↔ e + + n Neutrino forward scattering ν e + 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 Neutron decay data are useful u e − W d ν e e − ν e W d u' d ν e W u e −

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

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

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

5 Schleching Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM n-decay rate: τ −1 = const (|g V | 2 + 3|g A | 2 ) = const G F 2 |V ud | 2 (1+3|λ| 2 ) Only 2 parameters needed: CKM matrix element V ud, (G F from muon decay)ratio of c.c. λ = g A /g V Only few Standard Model parameters in n-decay … but many n-decay observables: problem is overdetermined: many tests of Standard Model

6 Schleching Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM Standard model: axial to vector coupling c.c.λ = g A /g V CKM- matrix element |V ud | unitarity test of CKM-matrix Δ = V ud 2 + V us 2 + V ub 2  1 = 0 ? weak magnetismμ p − μ n all ν - p,... weak cross-sectionsσ νp /E ν = 0.67·10 −38 cm 2 /GeV number of ν-families N ν = 2.5(6) baryonic matter in universeρ/ρ crit = 3.3(7) % beyond Standard model: mass of right-handed boson m(W R ) > 300 GeV/c 2 (90% c.l.) left-right mixing angle  0.20 < ζ < 0.07 (90% c.l.) scalar weak interaction amplitudes g S tensor weak interaction amplitudes g T 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 Many derived quantities from n-decay

7 Schleching Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM. · ·. · ·... · ·... ·. ·. UCN best measured with stored ultracold-neutrons ('UCN', T n ~ 1mK) 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 N = N o exp(– t/τ) → decay rate: τ −1 = const × |V ud | 2 (1 + 3λ 2 ) History of neutron lifetime τ R. Picker, Mo Abend

8 Schleching Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM History: λ = g A /g V : derived from β-asymmetry A: λ =g A /g V = −1.19 ± = −1.25 ± = −1.261 ± = −1.2695± = −1.2739±

9 Schleching Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM upper row, combined: Δ = ± first column, with V cd, V td : Δ' = ± Unitarity tests of upper row of CKM matrix upper row, with: V ud = ± n V ud = ± Nuclei V ud = ± π V us = ± K V ub = ± B if Δ due to right-handed currents: phase ζ = ± |V ud | 2 + |V us | 2 + |V ub | 2 = 1 − Δ Standard Model: Δ = 0 ↑ i.e. test of cos 2 θ C + sin 2 θ C Aim: all entries in CKM matrix from particle decays

10 Schleching Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM 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, (2005) before nuclear corrections: after nuclear corrections: 1σ band→ (from > 100 measurements)

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

12 Schleching Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM = by-product of ε'/ε-analysis: 2002↓ ↓2005 B.R. K L → π e ν, π μ ν reestablishes unitarity when using old τ n : PDG 2006, all measurements:Δ = (5) ud (9) us Other strategy: assume unitarity to hold → strong-interaction physics New V us value

13 Schleching Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM planned: PERC bright:~ 10 6 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 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 neutron puls in long piece of n-guide B ~Tesla e−p+e−p+

14 Schleching Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM example for setup: example: B 0 =2T, B 1 =8T, B 2 =½T: count rates: 6  10 4 s −1 for a continuous unpolarized n-beam; 1  10 4 s −1 for a continuous beam polarized to 98%; 3  10 3 s −1 for a pulsed unpolarized beam; 3  10 2 s −1 for a pulsed beam polarized to 99.5%. beam time for ~10 −4 statistical error: ½ hfor continuous unpolarized, 3 hfor continuous polarized, 10 hfor pulsed unpolarized, 4 dfor pulsed polarized 10m ILL user

15 Schleching Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM Error budget of PERC (not all measurements sensitive to all errors)correctionerror orifice:in units of 10 −4 1. non-uniform neutron beam profile over orifice finite thickness of orificeeliminated 3. electron escape from orifice10.2 solid angle of p +, e − emission: 4. non-uniformity of B 0 -field non-adiabatic variation of B 1 -field; adiabatic decoupling from B 2 -field (M-C- req.) background: 6. from neutron guide41 7. from n-beam shutter, pulsed neutron beamnon-existent from n-beam shutter, continuous neutron beam11 (exp. study req.) 8. from n-beam stop, pulsed neutron beamnon-existent from n-beam stop, continuous neutron beam21 e − /p + backscattering: 9. from beam window from electron/proton beam dump from electron/proton detector (user's responsibility)61 neutron polarization: 12. polarisation measurement depolarisation in non-magnetic supermirror guide≤5 At present (for β-asymmetry A, total, D. Mund (2005)):present: 34present: 39

16 Schleching Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM magnetic mirror limits beam divergence: θ cr B0B0 example: magnetic field: 2Tesla 8Tesla ½Tesla gyration radius: 2mm ½mm4mm critical angle: beam width can be traded against beam divergence, with negligible spectral distortion B1B1 n-guidemagn. mirror→ to experiment = 'keyhole' B2B2 ~10m

17 Schleching Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM … of variable beam divergence: guide field B 0 magnetic mirror field B1B1 high divergence low divergence n-decay products

18 Schleching Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM neutron beamstop: Charged neutron decay products can be guided anywhere (electro-)magnetically Example: ↑ n-guide ↑ n and γ e and p ↑ absorbers window frame B 0 =2TB 1 =8T B 2 =0.5T ↑ n-guide ↑ n and γ e and p ↑ absorbers window frame B 0 =2TB 1 =8T B 2 =0.5T cm Scale×10

19 Schleching Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM EXAMPLES a) e − spectroscopy (from pol., unpol. n's): orificeenergy sensitive detector e−e− B2B2

20 Schleching Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM b) magnetic p +, e − spectroscopy: MAGNETIC SPECTROMETER e − B 2 B 3 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.

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

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

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

24 Schleching Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM 2 nd order error sources of orifice: 1. neutron beam not uniform over edge of orifice: error 6·10 −5 at E βmax for 10% change of n-flux over 1cm width 2. particles hit inner face of orifice: solution: oblique edge angle >θ 2 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% 2mm

25 Schleching Präzisionsphysik mit Neutronen / 4. Experimente diesseits SM b) effect of mag. mirror field B 1 on p +, e − : A/ A 0 c)ASYMMETRY N A 2 d)EFFICIENCY c 0 a)CRITICALANGLE B 0 /B N/ N 0 b)COUNTRATE B 0 /B 1


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