Slide 1

Schleching 2008 4.1 Przisionsphysik mit Neutronen / 4. Experimente diesseits SM Many processes have the same Feynman diagram as neutron decay: Primordial element formation n + e + p + ' e ~ 1/ ( 2 H, 3 He, 4 He, 7 Li) p + e n + e ~ 1/ n p + e + ' e Solar cycle p + p 2 H + e + + e p + p + e 2 H + e etc. ~ (g A /g V ) 5 Neutron star formation p + e n + e Pion decay 0 + e + ' e Neutrino detectors ' e + p e + + n Neutrino forward scattering e + n e + p etc. W and Z production u' + d W e + ' e etc. precision data of weak interaction parameters today only from neutron decay Neutron decay data are useful u e W d e e e W d u' d e W u e Slide 2 Schleching 2008 4.2 Przisionsphysik mit Neutronen / 4. Experimente diesseits SM calculated gains in neutron count rates ILL-Millenium program Slide 3 Schleching 2008 4.3 Przisionsphysik mit Neutronen / 4. Experimente diesseits SM 2001 S-DH GmbH: Neutron optics, H. Hse 2006 CASCADE GmbH : large fast n-detectors, M. Klein, C. Schmidt Start-ups Slide 4 Schleching 2008 4.4 Przisionsphysik mit Neutronen / 4. Experimente diesseits SM t History of the universe: a succession of phase transitions TP NP AP FKP Slide 5 Schleching 2008 4.5 Przisionsphysik mit Neutronen / 4. Experimente diesseits SM n-decay rate: 1 = const (|g V | 2 + 3|g A | 2 ) = const G F 2 |V ud | 2 (1+3|| 2 ) Only 2 parameters needed: CKM matrix element V ud, (G F from muon decay)ratio of c.c. = 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 Slide 6 Schleching 2008 4.6 Przisionsphysik mit Neutronen / 4. Experimente diesseits SM Standard model: axial to vector coupling c.c. = g A /g V CKM- matrix element |V ud | unitarity test of CKM-matrix = V ud 2 + V us 2 + V ub 2 1 = 0 ? weak magnetism p n all - p,... weak cross-sections p /E = 0.6710 38 cm 2 /GeV number of -families N = 2.5(6) baryonic matter in universe/ 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 < < 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 Slide 7 Schleching 2008 4.7 Przisionsphysik mit Neutronen / 4. Experimente diesseits SM. . ... ... . . UCN best measured with stored ultracold-neutrons ('UCN', T n ~ 1mK) short history: neutrons 'in-beam':1960: = (1010 30) s 1982: = (925 11) s stored UCN: 1989: = (888 3) s 2004: = (885.7 0.8) s N = N o exp( t/) decay rate: 1 = const |V ud | 2 (1 + 3 2 ) History of neutron lifetime R. Picker, Mo Abend Slide 8 Schleching 2008 4.8 Przisionsphysik mit Neutronen / 4. Experimente diesseits SM History: = g A /g V : derived from -asymmetry A: =g A /g V = 1.19 0.02 1960 = 1.25 0.02 1975 = 1.261 0.004 1990 = 1.26950.0039 2005 = 1.27390.0015 2006 Slide 9 Schleching 2008 4.9 Przisionsphysik mit Neutronen / 4. Experimente diesseits SM upper row, combined: = 0.0040 0.0012 first column, with V cd, V td : ' = 0.00150.0054 Unitarity tests of upper row of CKM matrix upper row, with: V ud = 0.97170.0013 n V ud = 0.97400.0005 Nuclei V ud = 0.97280.0030 V us = 0.219600.0023 K V ub = 0.00360.0009 B if due to right-handed currents: phase = 0.0020 0.0006 |V ud | 2 + |V us | 2 + |V ub | 2 = 1 Standard Model: = 0 0.0000 i.e. test of cos 2 C + sin 2 C Aim: all entries in CKM matrix from particle decays Slide 10 Schleching 2008 4.10 Przisionsphysik mit Neutronen / 4. Experimente diesseits SM Nuclear super-allowed 0 + 0 + -transitions (plus corrections) with half life t, phase space factor f J.C. Hardy, I.S. Towner, PR C 71, 055501 (2005) before nuclear corrections: after nuclear corrections: 1 band (from > 100 measurements) Slide 11 Schleching 2008 4.11 Przisionsphysik mit Neutronen / 4. Experimente diesseits SM new neutron lifetime measurement reestablishes unitarity when using old V us 0 0.001 Slide 12 Schleching 2008 4.12 Przisionsphysik mit Neutronen / 4. Experimente diesseits SM = by-product of '/-analysis: 2002 2005 B.R. K L e , reestablishes unitarity when using old n : PDG 2006, all measurements: = 0.0008 (5) ud (9) us Other strategy: assume unitarity to hold strong-interaction physics New V us value Slide 13 Schleching 2008 4.13 Przisionsphysik 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 ep+ep+ Slide 14 Schleching 2008 4.14 Przisionsphysik mit Neutronen / 4. Experimente diesseits SM example for setup: example: B 0 =2T, B 1 =8T, B 2 =T: 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: hfor continuous unpolarized, 3 hfor continuous polarized, 10 hfor pulsed unpolarized, 4 dfor pulsed polarized 10m ILL user Slide 15 Schleching 2008 4.15 Przisionsphysik 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 orifice0.60.2 2. finite thickness of orificeeliminated 3. electron escape from orifice10.2 solid angle of p +, e emission: 4. non-uniformity of B 0 -field10.3 5. non-adiabatic variation of B 1 -field; adiabatic decoupling from B 2 -field0.50.5 (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 window10.2 10. from electron/proton beam dump20.4 11. from electron/proton detector (user's responsibility)61 neutron polarization: 12. polarisation measurement55 13. depolarisation in non-magnetic supermirror guide5 At present (for -asymmetry A, total, D. Mund (2005)):present: 34present: 39 Slide 16 Schleching 2008 4.16 Przisionsphysik mit Neutronen / 4. Experimente diesseits SM magnetic mirror limits beam divergence: cr B0B0 example: magnetic field: 2Tesla 8Tesla Tesla gyration radius: 2mm mm4mm critical angle: 30 0 90 0 15 0 beam width can be traded against beam divergence, with negligible spectral distortion B1B1 n-guidemagn. mirror to experiment = 'keyhole' B2B2 ~10m Slide 17 Schleching 2008 4.17 Przisionsphysik 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 Slide 18 Schleching 2008 4.18 Przisionsphysik mit Neutronen / 4. Experimente diesseits SM neutron beamstop: Charged neutron decay products can be guided anywhere (electro-)magnetically Example: n-guide n and e and p absorbers window frame B 0 =2TB 1 =8T B 2 =0.5T n-guide n and e and p absorbers window frame B 0 =2TB 1 =8T B 2 =0.5T cm Scale10 Slide 19 Schleching 2008 4.19 Przisionsphysik mit Neutronen / 4. Experimente diesseits SM EXAMPLES a) e spectroscopy (from pol., unpol. n's): orificeenergy sensitive detector ee B2B2 Slide 20 Schleching 2008 4.20 Przisionsphysik mit Neutronen / 4. Experimente diesseits SM b) magnetic p +, e spectroscopy: MAGNETIC SPECTROMETER e B 2 B 3 window- frame p + -shielding position- sensitive detectors Fig. 6: Sketch of a magnetic spectrometer for neutron decay products installed at the end of the beam line. Slide 21 Schleching 2008 4.21 Przisionsphysik mit Neutronen / 4. Experimente diesseits SM c) aSPECT retardation spectrometer: aSPECT orifice p+p+ Slide 22 Schleching 2008 4.22 Przisionsphysik mit Neutronen / 4. Experimente diesseits SM d) Mott scattering: MOTT SCATTERING APPARATUS orifice ee test of: electron helicity H e ~ e /c in hadron decay Slide 23 Schleching 2008 4.23 Przisionsphysik 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 Slide 24 Schleching 2008 4.24 Przisionsphysik mit Neutronen / 4. Experimente diesseits SM 2 nd order error sources of orifice: 1. neutron beam not uniform over edge of orifice: error 610 5 at E max for 10% change of n-flux over 1cm width 2. particles hit inner face of orifice: solution: oblique edge angle > 2 3. non-perfect absorption near edges: error 410 3 0.1 "active edge" N.B.: electron scattering effects can be calculated reliably to better than 10% 2mm Slide 25 Schleching 2008 4.25 Przisionsphysik mit Neutronen / 4. Experimente diesseits SM b) effect of mag. mirror field B 1 on p +, e : 00.20.40.60.81 0.2 0.4 0.6 0.8 1 A/ A 0 c)ASYMMETRY 00.20.40.60.81 0 0.2 0.4 0.6 0.8 1 1.2 N A 2 d)EFFICIENCY 00.20.40.60.81 0 20 40 60 80 c 0 a)CRITICALANGLE 00.20.40.60.81 B 0 /B 1 0 0.2 0.4 0.6 0.8 1 N/ N 0 b)COUNTRATE B 0 /B 1