in the Neutron Decay Direct Search for Scalar and Tensor Couplings - PowerPoint PPT Presentation

Transverse Electron Polarization in the Neutron Decay Direct Search for Scalar and Tensor Couplings in Weak Interaction Kazimierz Bodek for nTRV Collaboration Institute of Physics, Jagiellonian University, Cracow, Poland

Electron polarization in  -decay      ( | ) J E dE d n e e e e J n           J p p          n  e e  1   ... R N G dE d P p e e     E J E   e n e J.D. Jackson et al., Phys. Rev. 106, 517 (1957)  e p e p   G -coefficient can be deduced from the longitudinal electron polarization component  N -coefficient can be deduced from the transverse electron polarization component contained in the plane parallel to the parent polarization  R -coefficient can be obtained from the transverse electron polarization component perpendicular to the plane spanned by the neutron polarization and electron momentum K. Bodek, PANIC11 2

Electron polarization in  -decay  Assuming maximal parity violation C V = C’ V = Re C V = 1, C’ A = C A = Re C A =  and neglecting terms quadratic in C S and C T :          2 1 ' ' m C C m C C         P -odd, T -even 1 Im  S S  Im  T T  G     2 2 1 3   1 3   p C p C e V e A                  2 1 2 1 ' ' m C C C C       P -even, T -even  S S  T T Re Re   N       2 2 2 1 3 1 3   1 3   E C C e V A                   2 1 2 1 ' ' m C C C C P -odd, T -odd        S S   T T  Im Im R       2 2 2 1 3 1 3   1 3   p C C e V A  EM contributions are driven by C V and C A couplings and scale with the decay asymmetry parameter A :       ' ' m C C C C        0.2175 Re  S S  0.3350 Re  T T  N A SM     E C C e V A  0.05        ' ' m C C C C        0.2175 Im  S S  0.3350 Im  T T  R A SM     p C C e V A  0.001 K. Bodek, PANIC11 3

Scalar and tensor couplings  SM contributions:  Mixing phase  CKM gives contribution which is 2 nd -order in weak interaction: < 10 -10   -term contributes through induced NN PVTV interactions: < 10 -9  Candidate models for scalar couplings (at tree-level):  Charged Higgs exchange  Slepton exchange (R-parity violating super symmetric models)  Vector and scalar leptoquark exchange  The only candidate model for tree-level tensor contribution (in renormalizable gauge theories) is:  Scalar leptoquark exchange K. Bodek, PANIC11 4

Mott scattering  Mott scattering: – Analyzing power caused by spin-orbit force – Parity and time reversal conserving (electromagnetic process) – Sensitive exclusively to the transversal polarization K. Bodek, PANIC11 5

FUNSPIN – Polarized Cold Neutron Facility at PSI    10 1 10 s 80 I P % n n K. Bodek, PANIC11 6

Mott polarimeter  Challenges: o Weak and diffuse decay source o Electron depolarization in multiple Coulomb scattering o Low energy electrons (<783 keV ) o High background (n-capture) Pb-foil Pb-foil  Solutions: o Tracking of electrons in low- 50 cm mass, low- Z MWPCs o Identification of Mott- scattering vertex (“V - track”) o Frequent neutron spin flipping o “foil - in” and “foil - out” measurements scintillator MWPC scintillator K. Bodek, PANIC11 7

Neutron polarization from decay asymmetry N ( ,   P )  N ( ,   P ) A n =  0.1173  P n  A n      ( ) n n P A cos E n n N ( ,   P )  N ( ,   P ) n n o Average neutron polarization from decay rate asymmetry (“ single-track ” events) E (  ) o Averaging super-mirror polarimeter data:  P n  = 0.87 ± 0.01 o Offset in data well understood  2 /dof = 1.15 and corrected for (spin flipper  P n  = 0.776 ± 0.003 related deadtime)  cos  K. Bodek, PANIC11 8

Two-parameter fit      ( , ) ( , ) n P n P   A ( )      ( , ) ( , ) n P n P (2) F  G H             A ( ) ( ) ( ) ( ) R ( ) ( ) AP P S N N R   N = 0.062 ± 0.012 A (  )- AP  (  ) F (  ) R = 0.004 ± 0.012   ˆ – normal to Mott n ˆ ˆ ˆ F G H           ˆ ˆ ˆ ˆ ( ) , ( ) , ( ) J p n J n J p scattering plane e e K. Bodek, PANIC11 9

Single parameter fit                      , , , , n P n P n P n P   S                        , , , , n P n P n P n P   (3) G  PS  N N     F       2 2 2 2 ( ) 1 ( ) A P                      , , , , n P n P n P n P   U                        (4) , , , , n P n P n P n P         F H        R AP R PS K. Bodek, PANIC11 10

Final results R SM = 0.5 × 10 3 N SM = (68 ± 1) × 10 3 K. Bodek, PANIC11 11

Limits on S and T contributions K. Bodek, PANIC11 12

RPV MSSM contributions to n-decay R = (  1) 2j+3B+L . R -parity violating super-symmetric contributions to the neutron beta decay Nodoka Yamanaka et al 2010 J. Phys. G: Nucl. Part. Phys. 37 055104 From R -coefficient From 0 +  0 +  100 GeV m e L K. Bodek, PANIC11 13

What next? K. Bodek, PANIC11 14

Transverse electron polarization a b D B A ^ R H N L U S V K. Bodek, PANIC11 15

Sensitivity factors for scalar and tensor couplings Re S Re T Im S Im T SM (  ) FSI (  ) @  0.104793  0.171405 †  0.000727 0.171405 † 0 +0.001171 a 0 0 +0.171405 +0.828595 0 0 b  0.117233  0.000923 0 0 0 +0.00142 A  0.126422 +0.987560 0 +0.194539 0 0 B  0.000923 0 0 0 0 +0.000923 D  0.171405 0 +0.060888 +0.276198 0 0 H  0.000444  0.276198 0 0 0 +0.171405 L  0.217582 0 +0.068116 +0.334815 0 0 N  0.217582 0 +0.000497 0 0 +0.334815 R  0.001845  0.217582 0 +0.217582 0 0 S  0.217582 0 0 +0.217582 0 0 U  0.217582 0 0 0 0 +0.217582 V * Kinematical factor averaged over E k = (200,783) keV † (| C S | 2 +| C’ S | 2 )/2 instead of Re S and (| C T | 2 +| C’ T | 2 )/2 instead of Re T , respectively @ 1 st order, static field, point charge, no recoil K. Bodek, PANIC11 16

Impact of H , L , N , R , S , U , V measurement with anticipated accuracy of 5  10 -4  Constraints on real scalar contributions dominated by: – Super-allowed 0 +  0 + – Correlations in mirror transitions  n-decay correlations could join the game ! K. Bodek, PANIC11 17

2 nd -generation experiment with CN beam  General features of the experimental setup: o Axial polarimeter geometry (instead of planar)  2.5 m long beam acceptance o Multi Wire Drift Chambers (instead of MWPC):  Hexagonal cell geometry  x - , y - coordinates from drift time (  x =  y = 0.5 mm)  z -coordinate from charge division (  z = 1.0 mm)  Reduced pressure (0.2-0.3 bar) WORKS ! K. Lojek at al., NIMA 611 (2009) 284 o Additional background suppression and higher polarization:  Pulsed beam (?) 3 He spin filter (?)   Overall gain factor in the rate of reconstructed V-track events: 20 – 30 (as compared to the present setup)  Expected sensitivity for all coefficients: 5 × 10 -4 K. Bodek, PANIC11 18

2 nd -generation experiment with CN beam He, 0.2-0.3 bar scintillator Pb-foil 0.0 0.5 1.0 m MWDC CN beam (He+isobutane, 0.2-0.3 bar) K. Bodek, PANIC11 19

With detection of electrons and recoil protons … Grounded vacuum window: 6 µm Longitudinal neutron polarization, Mylar, reinforced with Kevlar fibers Axial guiding field B = 0.1  0.5 mT Mott scattering foil Plastic scintillator e  MWPC, 1 layer p + Grounded grid p-e conversion foil LiF (20nm) + Al (10nm) + 6F6F(100nm), -25 kV [S. Hoedl et al., J. Appl. Phys. 99, 084904 (2006)] MWDC, hexagonal, 5 layers K. Bodek, PANIC11 20

Electron-proton kinematics p e  e-p p p p  K. Bodek, PANIC11 21

Electron-proton kinematics 700 ns 700 ns 100 keV 100 eV (200 keV for Mott scat.)  Measured electron energy, reconstructed proton flight path and measured proton time-of-flight must match !  Constraints from 3-body kinematics will considerably reduce coincidence time  With 10 5 decays per second: single rate (per wire) < 1 kHz K. Bodek, PANIC11 22