High-Precision Measurements of g A and g V in Neutron and Nuclear - - PowerPoint PPT Presentation

High-Precision Measurements of g A and g V in Neutron and Nuclear β - Decay d d l Brad Plaster, University of Kentucky σ   g g A A n θ p θ e p e n  e FNAL Project X Physics Study June 16 2012 June 16, 2012 B. Plaster 1

Neutron β -decay form factors u d e ― W ― W  e g V = g V (0) = 1 [CVC] g P negligible Experiments probe : g A = g A (0) (0) SCC SCC g S , g T = 0 0 G A = G F V ud g A G G V under G-parity G V = G F V ud g V g WM (0) = κ p – κ n [CVC] [but broken in SM by isospin-symmetry breaking] isospin symmetry breaking] B. Plaster 2

Neutron β -decay observables Lifetime :       2 5 1 G    G m g        2 2   1 1 3 3 1 1 RC RC F e A A V ud V f f   3 3 d 2  G g V V n [Czarnecki et al. (2004)] = 1 0390(4) = 1.0390(4) [Marciano and Sirlin (2006)] Correlation coefficients : [Jackson, Treiman, Wyld (1957)]                  dW p p m J p p p p     2          ( ) 1   e e n e e p E E E a b A B D   0   e e e     d d dE E E E J E E E E       e e e e n e e   2 1  a 0   2 1 3 b, D sensitive , A greatest A 0 greatest       ( ( 1 1 ) ) to beyond SM   2 A sensitivity to  0   2 1 3 physics    ( 1 ) [and most straightforward T 0 = 782 keV  2 [beyond recoil-order] B to measure] to measure] 0     2 1 1 3 3 T p ~ 750 eV Recoil-order terms : Holstein (1974) Gudkov et al. (2006) B. Plaster 3 Harrington (1960) Gardner and Zhang (2001) Bhattacharya et al. (2012)

Nuclear β -decay observables Superallowed 0 + -> 0 + ft values : Experimental observables : half-life branching ratio branching ratio Q-value   ft    F ( 1 δ )( 1 δ δ ) t R NS C  3 ln 2 1    5 2 2 2 ( 1 ) V m G g V e F V ud R CVC: g V = 1,  2   / 0 . 29 [Saxon-Woods] CVC CVC independent of medium    2 2 / / 0 . 93 [Hartree-Fock] Hardy and Towner (2009) B. Plaster 4 Towner and Hardy (2010)

V ud from nuclear β -decay Assuming CVC, g V = 1 : |V ud | 2 = 0.94916 ± 0.00016 ± 0.00035 ± 0.00020 ± 0.00004 exp’t ∆ R δ C , δ NS δ ’ R V Experimental error below theoretical error Significant effort on testing validity of δ C , δ NS corrections [e.g., Melconian (2011, 2012)] [ g , ( , )] CKM unitarity satisfied at present, using g V = 1 nuclear β -decay V ud and V us : 0.9999 ± 0.0004 ± 0.0004 d V 0 9999 0 0004 0 0004 Experimentalist question to theorists : Are there Experimentalist question to theorists : Are there V ? prospects for reducing the error on ∆ R Hardy and Towner (2009) B. Plaster 5 Towner and Hardy (2010)

Status of neutron β -decay: g A Decay of polarized neutrons :                    dW dW p p p p m m J J p p p p p p p p       2          ( ) 1   e e n e e p E E E a b A B D   0   e e e     d d dE E E E J E E E E       e e e e n e e [ [Results for  from a and B not competitive at present] 0.2% determination g A /g V = g A = –1.2726(24) / 1 2 26(24) [from A 0 values and one combined A 0 /B 0 result included in PDG] Error subject to large  2 /  = 5.1 g  H. Abele et al. (2002) J. Liu et al. (2010) B. Plaster 6 R.W. Pattie et al. (2009) D. Mund et al. (2012)

Status of neutron β -decay: τ n PDG Average PDG A * Pre-2011 : 885.7 ± 0.8 s 2011 – 2011 : : 881 5 ± 1 5 s 881.5 ± 1.5 s  2 2   / / 2 2 . 7 7 2 5       1 G m           2 2 1 1 3 3 1 1 RC RC F e V V ud f f   3 2  n Compare τ n with g A treating 0 +  0 + V ud as input p ud * New self-corrected result : B. Plaster 7 Arzumanov et al., JETP Lett. 95, 224 (2012) : 881.6 ± 0.8 ± 1.9 s

Experimental techniques for g A PERKEO II: Cold Neutron Beam Cold Neutron Beam ~50 μ eV – 25 meV   glancing angles l i l High Statistics J J p  n e A J E n e S:B ~ 8:1 B 8 1 S:B ~ 8:1 B 8 1    N N    cos  ( ) i i A E P A meas    e e N N i i H. Abele et al. (2002) D. Mund et al. (2012) B. Plaster 8 H. Abele (2008)

Experimental techniques for g A UCNA: Stored Ultracold Neutrons (UCN) Low L UCN  7 m/s Backgrounds storage  350 neV [esp. n-induced] High Polarization S:B ~ 40:1 R.W. Pattie et al. (2009) B. Plaster et al. (2012) B. Plaster 9 J. Liu et al. (2010)

Future neutron β -decay prospects Current published precision on A 0 : PERKEO II : 0.42% UCNA : 1.3% [later this summer: ~0.75%] Near-term projected precision : p j p PERKEO III : ~ 0.2% Precision on g A could approach UCNA :  0.5% [data in hand] ~0.05% in next several years y Longer-term projected precision : PERC :  0 1% on A a PERC :  0.1% on A, a Nab : 0.1% on a, 0.3% on b abBA : 0.1% on a, 0.08% on A abBA 0.1% on a, 0.08% on A also aCORN, aSPECT, etc. , , Neutron lifetime : Many world wide experiments aimed at  ± 1 0 s precision Many world-wide experiments aimed at  ± 1.0 s precision B. Plaster 10

Future neutron β -decay prospects Tests of CVC / Search for second-class currents in neutron β -decay [Holstein (1974), Gardner and Zhang (2001)] Recoil-order energy-dependence of the asymmetries (a, A)  n   ( ( ) ) cos θ θ ( ( ) ) A A E E P P A A E E meas bin all 6 form  A 0  ( ) recoil order term s A E factors examples A: best for  CVC Hypothesis Test CVC Hypothesis Test SCC Test SCC Test OR OR 0.1% on a : [assume SCC = 0] [assume CVC] 2.5% on g WM ; δ g T ~ 0 22  /2 δ g T 0.22  /2 B. Plaster 11

Future neutron β -decay prospects Extractions of g V *V ud in 0 +  0 + nuclear β -decay limited by theoretical errors What will it take for neutron β -decay to challenge nuclear β -decay ? Need δ A/A  0.11% AND Need δ τ n  0.4 s B. Plaster 12

Final notes Also recent theoretical work on searches for new physics (S, T) in neutron β -decay: b, B. [Bhattacharya et al. (2012)] Apologies for lack of time to discuss this, as focus was on g A , g V . Comment : FNAL source of UCN for β -decay studies would be very interesting UCNA limited by statistics at present Max ~60 Hz of β -decay rate from ~2/cm 3 in decay volume If could achieve, say, extracted UCN density of ~10/cm 3 -> 300 Hz ~500M counts for 0 1% statistics on A 500M counts for 0.1% statistics on A   2 2 . . 7 7  A A A -> ~0.025% on g A [V ud extraction] A N @ 300 Hz -> ~20 days of 100% running @ y f g B. Plaster 13

UCNA Collaboration H.O. Back, T.J. Bowles, L.J. Broussard, R. Carr, S. Clayton, S. Currie, B W Filippone A Garcia P Geltenbort S Hasan K P Hickerson J Hoagland B.W. Filippone, A. Garcia, P. Geltenbort, S. Hasan, K.P. Hickerson, J. Hoagland, G.E. Hogan, A.T. Holley, T.M. Ito, C.-Y. Liu, J. Liu, M. Makela, R.R. Mammei, J.W. Martin, D. Melconian, M.P. Mendenhall, C.L. Morris, R.W. Pattie, A Perez Galvan M L Pitt B Plaster J C Ramsey R Rios R Russell A. Perez Galvan, M.L. Pitt, B. Plaster, J.C. Ramsey, R. Rios, R. Russell, A. Saunders, S. Seestrom, W.E. Sondheim, E. Tatar, R.B. Vogelaar, B. VornDick, C. Wrede, A.R. Young, B. Zeck B. Plaster 14

The End B. Plaster 15

Why measure A with UCN ? Systematic Corrections [ % ] P l Polarization / i ti / Backgrounds Others Spin-Flip PERKEO I (1986) 2.6 ~ 3 ~13 magnetic mirroring strong cos θ g ILL (1997) ILL (1997) 2 9 2.9 ~ 3 ~ 3 variation PNPI (1997) 23 small ~3  cos θ   cos θ  PERKEO II (2002) 1.4 0.5 ~0.1  cos θ   cos θ  UCNA (2008–2009) 0.0 0.015 ~0.5 – ~1.0 backscattering +  cos θ  B. Plaster 16

Neutron lifetime experiments In-Beam Technique Cold neutron beam Cold neutron beam  N   / N  0 C Count N 0 and decay product(s) nt N nd d p d t(s) e.g.,, NIST Experiment Nico et al., PRC 71, 055502 (2005) Detector efficiencies, volume ! Dewey et al., PRL 91, 152302 (2003) Storage Technique Stored UCN: walls gravity B Stored UCN: walls, gravity, B   /  t ( )  N t N e 0 e.g., NIST Experiment Load then count “surviving” UCN Load, then count surviving UCN Ioffe Trap: Superposition of and/or decay products in “real time” 2x solenoid with quadrupole Losses other than β -decay ! β y Brome et al., PRC 63, 055502 (2001) O’Shaughnessy et al., arXiv: 0903.5509 B. Plaster 17

Most recent lifetime result 1 1 1   trap trap     storage loss (absorption, upscattering) measured measured extract extract must account must account for these extrapolated t l t d to zero loss UCN from detector source previous smallest extrapolation ~ 105 s t l ti 105 Serebrov et al PLB 605 72 (2005) Serebrov et al., PLB 605, 72 (2005) B. Plaster 18