T-violating observables in neutron decay experimental opportunities - - PowerPoint PPT Presentation

T-violating observables in neutron decay – experimental opportunities

Kazimierz Bodek

Marian Smoluchowski Institute of Physics, Jagiellonian University, Krakow, Poland „Theoretical issues and experimental opportunities in searches for time reversal invariance violation using neutrons”, Dec. 6-8, 2018, Amherst MA

Outline

 T-odd correlations in neutron -decay  D- and R-correlations  Experiments in the past: emit, Trine and nTRV  emit+Trine+nTRV together (?)  BRAND  Potential benefits of BRAND  T-odd correlation in radiative neutron decay  Challenges and strategy  Conclusions

T-violating observables in neutron decay – experimental opportunities 07.12.2018

2

TRV tests

T-violating observables in neutron decay – experimental opportunities 07.12.2018

3 Initial Final Initial Final (a) (b) t  -t

 If interaction violates TR symmetry: (a) ≠ (b)

1 2 3 4 3 4 1 2 Scattering, binary reaction: 1 3 4 1 3 4 Particle decay:

 True TRV tests require (i) reversal of motion and (ii) exchange of initial and final states  In particle decay exchange of initial and final states is impossible

D- and R-correlations

 D-correlation (C-odd, P-even, T-odd)

T-violating observables in neutron decay – experimental opportunities

 R-correlation (C-even, P-odd, T-odd)

07.12.2018

4

  1

e e e e e e e e e e e

m d S E a b A B D dE d d E E E J E E E E

      

                        J p p p p p p

D

  1

e e e e e e e e e e e e e e e e

m d S E b A G Q N R dE d E J E E J E E m E                            J J p p σ p p σ p σ σ

R

  1

;

e e e e e e e e e e

m d S E b A N R dE d E J E E

  

                      J p p σ σ σ p

R

 In ordinary neutron decay, two observables are particularly interesting

D  <J>/J (pep) D R  <J>/J (pe) R

D-correlation

 For left-handed V-A interactions ( ), defining  = CA/CV , neglecting terms quadratic in CS and CT, point charge, no recoil:

T-violating observables in neutron decay – experimental opportunities

   

* * * 2 2 2 * * * * 2 *

Im Im ' ' 1 2 1 3 ' ' 1 Re 1 3

V A S T S T T V V S S T T e A V

C C C C C C D C C C C C C m p C C                                ' , '

V V A V

C C C C  

 

 

* * 2

' ' 1 2sin Im ; , 1 3

S S T T AV T V A

C C C C D S T S T S T C C  

     

       

0.435 sin

VA AV T

D  

5

1.2 10

FSI T T

D D D D



    

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J.D. Jackson et al., Phys. Rev. 106, 517 (1957); J.D. Jackson et al.,

• Nucl. Phys. 4, 206 (1957); M.E. Ebel et al., Nucl. Phys. 4, 213 (1957)

D-correlation, emit-II

 emiT-II (NIST):

• NG6 cold neutron beam
• Longitudinally polarized (~0.95) in the fiducial volume
• Compact, symmetric setup with azimuthally alternating

electron- and proton-detectors

• Proton detectors segmented (4x4 cm2) SBD, accelerating

potential ~25 kV

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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D-correlation, emit-II

 Acquired information

• e-p coincidences, ToF
• Electron energy
• (Accelerated) proton energy

 Isolation of D using:

• Symmetry of detectors
• Periodic neutron spin flip

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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T-violating observables in neutron decay – experimental opportunities 07.12.2018

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D-correlation, emit-II

 Result

T-violating observables in neutron decay – experimental opportunities

(68% C.L.)

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9

• T. E. Chupp, R. L. Cooper, K. P. Coulter, S. J. Freedman, B. K. Fujikawa, A. Garcia, G. L. Jones, H. P. Mumm,
• J. S. Nico, A. K. Thompson, C. A. Trull, F. E. Wietfeldt, and J. F. Wilkerson, Phys. Rev. C 86, 035505 (2012)

curtesy of H.P. Mumm

(10-4)

T-violating observables in neutron decay – experimental opportunities 07.12.2018

10 Most of systematic effects were MC modelled

emiT-II+NGC

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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D-correlation, emit-III+NGC

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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D-correlation, Trine

T-violating observables in neutron decay – experimental opportunities

 Trine (ILL):

• PF1 cold neutron beam
• Longitudinally polarized (~0.97) in the fiducial volume
• Compact setup with planar geometry
• Electron- and proton-detectors in perpendicular planes
• Proton detectors PIN diodes on ground potential
• Accelerating potential: 25 kV
• MWPC for gamma suppression and selection of angular ranges

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• T. Soldner, L. Beck, C. Plonka,
• K. Schreckenbach, O. Zimmer,
• Phys. Lett. B 581 (2004) 49

D-correlation, Trine

 Excellent S/B ratio of 23  Systematic effects and corrections

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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• T. Soldner, L. Beck, C. Plonka,
• K. Schreckenbach, O. Zimmer,
• Phys. Lett. B 581 (2004) 49

D-correlation with ep/n + MagSpec ?

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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 ep/n-spectrometers adiabatically coupled to n-decay channel (PERC, ANNI)  Conserve particle energy and angular (polar) distributions  Reconstruct pepp using decay kinematics (?)

RB NoMoS

 No definite plans yet (B. Maerkisch, TUM)

• X. Wang, G. Konrad, H. Abele, NIMA (2012) 254

e.g. G. Konrad et al., J. Phys.: Conf. Series 340 (2012) 012048

R-correlation

T-violating observables in neutron decay – experimental opportunities

   

* * * * * * 2 2 2

Im ' ' Im ' ' 1 4 2 1 3

T A T A S A S A V T V T T V V

C C C C C C C C C C C C R C C                   ' , '

V V A V

C C C C  

 

 

 

2 2

1 2 ' ' Im Im ; , 1 3 1 3

S S T T T V A

C C C C R S T S T C C     

   

         

4

9 10

FSI SM T T T e

m R R R R A R p 



      

 

2

1 Re 2 1 1 3

FSI e

m R p            

 For left-handed V-A interactions ( ), defining  = CA/CV , neglecting terms quadratic in CS and CT , point charge, no recoil:

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   

0.218 Im 0.335 Im

T

R S T

 

  

N-correlation

T-violating observables in neutron decay – experimental opportunities

 

 

 

2 2

1 2 ' ' Re Re ; , 1 3 1 3

S S T T T V A

C C C C N S T S T C C     

   

         

2

7.9 10

T SM T SM T e

m N N N N A N E



      

 

2

1 Re 2 1 1 3

SM e

m N E           

 N is C-even, P-even and T-even

e pe p Pp Jn

N R

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   

0.218Re 0.335Re

T

N S T

 

  

Electron spin analysis

T-violating observables in neutron decay – experimental opportunities

 Mott scattering:

• Analyzing power caused by spin-orbit force
• Parity and time reversal conserving (electromagnetic process)
• Sensitive exclusively to the transverse polarization

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nTRV@PSI – Mott polarimeter

 Challenges:

• Weak and diffuse decay source
• Electron depolarization in multiple Coulomb scattering
• Low energy electrons (<783 keV)
• High background (n-capture)

MWPC scintillator scintillator Pb-foil Pb-foil

50 cm

 Solutions:

• Tracking of electrons in low-

mass, low-Z MWPCs

• Identification of Mott-

scattering vertex (“V-track”)

• Frequent neutron spin

flipping

• “foil-in” and “foil-out”

measurements

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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Limits on S and T contributions

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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• A. Kozela, G. Ban, A. Bialek,
• K. Bodek, P. Gorel, K. Kirch, St.

Kistryn, O. Naviliat-Cuncic,

• N. Severijns, E. Stephan, and J. Zejma,
• Phys. Rev. C 85, 045501 (2012).

Systematic uncertainties in nTRV@PSI

 Dominating systematic uncertainties

1. Combined error from uncertainties of:

a) Neutron polarization b) Low energy cut c) Decay asymmetry A measurement (R, N were measured relatively to A) d) Statistical precision of geometry factors

2. Mott target thickness nonuniformity 3. Guiding field map 4. High background (to be subtracted) due to guiding neutron beam in He atmosphere 5. Properties of Front End electronics and DAQ

1. 2. 3. 4. 5.

Sample of analyzed data

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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R- and D-correlation in one setup ?

T-violating observables in neutron decay – experimental opportunities

MWPC scintillator scintillator Pb-foil Pb-foil

BRAND

concept

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 Neutron beam in vacuum  Axial geometry  Electron tracking  Electron spin analysis with Mott scattering  Proton ToF  Alternating position sensitive e- and p-detectors

BRAND concept

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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Transverse electron polarization

1 ˆ ˆ

e e e e e e e e e e e e e e e e

m d a b A B D E E E J E E E E H L N R E E E J J E S U V J E E E J E E J J p p p p p p J J p p p p σ J J J p p p p p σ

a b A B D H L N  V U S R 

 Measuring electron- and proton-momentum and transverse electron polarization:

Re Re Im Im

' ' , , , , , functions of and kinematical quantities

S S T T S T S T A V V A

C C C C S T c c c c C C C C       

S T

• FSI

Re Re Im Im

Re Re Im Im

V A S T S T

X X X c S c T c S c T      

S S T T

 All correlation coefficients can be expressed as combinations of real and imaginary parts of exotic (scalar and tensor) couplings:

T-violating observables in neutron decay – experimental opportunities 07.12.2018

24 pe – electron momentum p – neutrino momentum  – electron spin projection direction

Sensitivity factors for scalar and tensor couplings

(leading order, no recoil, point charge)

SM () FSI () c(ReS) c(ReT) c(ImS) c(ImT)

a

• 0.1048
• 0.1714†

0.1714†

• 0.0007

+0.0012

b

+0.1714 +0.8286

A

• 0.1172
• 0.0009

+0.0014

B

+0.9876

• 0.1264

+0.1945

D

+0.0009

• 0.0009

H

+0.0609

• 0.1714

+0.2762

L

• 0.0004

+0.1714

• 0.2762

N

+0.0681

• 0.2176

+0.3348

R

+0.0005

• 0.2176

+0.3348

S

• 0.0018

+0.2176

• 0.2176

U

• 0.2176

+0.2176

V

• 0.2176

+0.2172

† (|CS|2+|C’S|2)/2 instead of ReS and (|CT|2+|C’T|2)/2 instead of ReT

, respectively * Kinematical factor averaged over electron kinetic energy Ek = (200,783) keV

 Cancellation effects are insignificant for transverse electron polarization related correlation coefficients ! ! !

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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BRAND – kinematical sensitivity maps

Figure 4: Sensitivity maps for the N, R, H, L, S, U and V coefficient as a function of the polar electron angle e or the relative electron-proton angle and the azimuthal spin projection angle s (arbitrary units). Irregularities in contours are due to limited statistics in simulations. The kinematical acceptance is defined by

   

   

kin kin e p e p

200,782 keV, 50,760 eV, 45 ,135 , 30 ,150 .

• E

E      

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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Impact of H, L, N, R, S, U and V measurement with anticipated accuracy of 510-4

Leptoquark exchange model RPV MSSM

 Constraints on real scalar contributions dominated by:

• Super-allowed 0+0+
• Correlations in mirror

transitions

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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Impact of H, L, N, R, S, U and V measurement with anticipated accuracy of 510-4

 Translated into EFT parameters

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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https://home.cern/news/news/accelerators/lhc-report-lhc-full

• M. Gonzalez-Alonso et al., Ann. Phys. 525 (2013)

 Electrons and missing transverse energy (MET) channel

V-correlation

T-violating observables in neutron decay – experimental opportunities

   

* * * 2 2 2 * * 2

Im Im ' ' 1 2 1 3 ' ' 1 Im 1 3

V A S T S T T e V V S S T T V A

C C C C C C m V E C C C C C C C C                             

 

* * 2

1 2sin Im Im Im 1 3

AV T e

m V S T S T S T E   

     

                   

 

5

10 ?

FSI T T

V V V V



   

ˆ 1 ... d V dE d E J J p σ

V 

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0.261 sin

VA AV T

V  

 

200 keV

e

T 

BRAND – methods, expected performance, strategy

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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 Experimental methods:

• Measure decay electrons and e-p coincidences
• Electron tracking in hexagonal, low Z, low pressure MWDC
• p-e conversion followed by e detection in scintillator (ToF, position)
• Decay vertex reconstruction
• Electron spin analysis by Mott scattering (vertex reconstruction)

 Overall systematic uncertainty floor achieved in nTRV@PSI:

• N correlation:

410-3

• R correlation:

510-3

 Gradual improvement of exp. accuracy (systematic uncertainty):

nTRV (PSI) BRAND I (ILL) BRAND II (ILL) BRAND III (ESS)

410-3  210-3  110-3  510-4

 BRAND is based on experimentally proven methods (nTRV@PSI)

FUNDED !!!

Theoretical corrections (SM)

 Final State Interaction (FSI)

• Exist calculations sufficient for a, b, A, B, D, R and N

coefficients measurements with accuracy of 10-4

• For H, L, S, U and V coefficients FSI correction exist only in

lowest order (point charge) approximation

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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 Recoil order corrections (ROC)

• Main contribution from Weak Magnetism
• No ROC exist for H, L, S, U and V
• V. Gudkov, et al., 77, 045502 (2008).

A.N. Ivanov et al., Phys. Rev. C 95, 055502 (2017). A.N. Ivanov et al., Phys. Rev. C 98, 035503 (2018).

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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Radiative Neutron Decay:

Motivation:

• Improve measurement of branching ratio and measure energy spectrum.
• Investigate a basic process in the fundamental semileptonic decay.
• Test QED in a weak process at 1% level.

curtesy of J. Nico

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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RDK II Experiment: Precision BR and Spectrum

RDK II Results:

• Measured radiative spectrum over 3 decades of energy using two detectors (400 eV to endpoint
• f 782 keV).
• Improved measurement of the branching ratio. Results consistent with theory.
• First measurement of the shape of the photon energy spectrum (≈1% level)

curtesy of J. Nico

34

T-violating observables in neutron decay – experimental opportunities 07.12.2018

Prospects with Radiative Decay

Future Possibilities:

• Improve precision to test chiral perturbation theory calculation and recoil order

corrections.

• Determination of other correlations using photon as a tag.
• Novel ideas in radiative neutron decay:
• photon polarization, i.e., non V-A currents (Bernard et al., PLB 2004)
• examine new class of angular correlations

curtesy of J. Nico

T-odd Momentum Correlation:

• Measure triple-product correlation of decay-product momenta
• Correlation is P and T odd but spin independent; sensitive to sources of CP violation

not constrained by EDMs (Gardner and He, PRD 86 (2012) and PRD 87 (2013))

• Possible experiments in neutron and nuclear (Ne-19, Ar-35) decay systems
• Experimentally, design annular detector (emiT-style) to detect neutron decay products

with high efficiency and good solid angle coverage

• Mount experiment at high-flux beam line (e.g., NG-C gives x10 increase over NG-6)
• Avoid incremental improvements: investigate new detector technologies

(e.g., bolometers)

ke(kpK)

T-odd landscape in n-decay

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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 In neutron decay correlation experiments, three major projects are expected to deliver T-odd observables:

• Observable: D (AV, ImS, ImT)
• Anticipated improvement x40 (compared

to emiT-II) – entering sensitivity of <10-5 (FSI will be visible)

• Basic techniques as in emit-II
• Possible development of detectors:

cryogenic particle detection – join efforts with T-oddRDK

• Observable: ke(kpK) (CPV not

constrained by EDMs)

emiT-III+T-oddRDK @NGC(NIST)

• Observables: V (AV, ImS, ImT),

R (ImS, ImT), L (ImS, ImT), D (AV, ImS, ImT)

• Gradual improvement up to x30

(compared to nTRV) – (FSI will be visible)

• Basic techniques: combination of emiT-II,

Trine and nTRV

• Systematic effects assessment via

mapping, calibration and direct measurement (MC confirmed)

• Development of proton detectors
• T-even obs.: a, A, B, H, N, S, U

(ReS, ReT),

BRAND @PF1B(ILL)/ESS

Conclusions

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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 Complementarities and synergies:

• BRAND has main competition from: (i) HE pp  e + MET and (ii) spectrum shape

(Fierz term) in n-decay

• emiT-III and BRAND apply different strategies for assessment of systematic errors
• Some of systematic effects in emiT-III and BRAND can be compared for e.g.

D-coefficient

• Planned R&D for proton detection towards reduction of the accelerating field is

important for both projects  emiT-III@NGC(NIST) is oriented mainly towards better constraining AV  Relatively low-risk project; if funded, would improve current limit by factor of 5-10 in 4-5 years; further improvement depends on cryogenic particle detection  T-oddRDK@NGC(NIST) is a pioneering experiment to search for CPV that cannot be constrained by EDM  Largely depends on development of cryogenic particle detection – join efforts with emiT-III would be natural  BRAND@PF1B(ILL)/ESS is devoted mainly to search for scalar and tensor currents  Statistical sensitivity for D-correlation in full size BRAND will be comparable to emiT-III  Statistical sensitivity for H, L, N, R, S, U and V is 30 times lower than for D  “younger” than emiT – can be classified as nTRV-II

Backup slides

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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Neutron -decay correlations

1 ... ˆ ˆ ˆ

e e e e e e e e e e e e e e e e e e e e e e e e e e e e e e

m a b A B D E E E J E E E E G H K L N E E E m E E E E J Q R S T E m J E J E J E E E J E U V E J E E J p p p p p p J p p p p p p p σ J J J J p p p p p p p σ J p p p σ

e e e e e

W J E m J E E J J p p p a b A B D G H K L N Q  W V U T S R   pe – electron momentum p – neutrino momentum  – electron spin sensing direction

 For  transition with vector polarization of parent J/J (e.g. neutron decay):

J.D. Jackson et al., Phys. Rev. 106, 517 (1957); J.D. Jackson et al., Nucl. Phys. 4, 206 (1957); M.E. Ebel et al., Nucl. Phys. 4, 213 (1957) T-violating observables in neutron decay – experimental opportunities 07.12.2018

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Suppression of sensitivity to ReS and ReT

 May significantly decrease sensitivity to ReS, ReT (e.g. coefficient B – complete cancellation in pure transitions)

1 2 1 2

; , , , ASY

 

               p p q q J J σ σ

 Instead of X experiments deliver  If XV-A + XFSI  0, cancellation effects are insignificant !!!

SM FSI Re Re SM FSI Re Re SM FSI Im Im

Re 1 Re Im Im

X b S S e e X b X X T T S T

X X X X c c X X S m b E c c X X T c S c T

ReS ReT

b

ImS ImT  Experimental correlation coefficients related to p, q, J and are deduced form rate asymmetries:

σ

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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Systematic effects

 Depolarization by multiple Coulomb scattering

• From deviations between experimental data (120 keV, 14 MeV)

and theory (ELSEPA+Geant4) – presently on 1-2% level

• Can be improved by dedicated measurements with polarized

electron beam in the energy range 100-800 keVbe neglected

 „g-2 effect”

• 7 mrad per revolution de-synchronization between spin and

momentum

• For 1 mT magnetic field strength  can be neglected
• Transverse electron polarization related observables cannot

be measured in strong magnetic field !

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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Systematic effects (cont.)

• In uniform field step of 30 kV,

incident energy of 100 keV and angle of 45o, momentum vector rotates by about 12o

30 kV s p

 Momentum rotation in external electric field

• f pe-converter
• Effect decreases with increasing energy and decreasing inc. angle
• In symmetric barrier (e.g. 0300 kV) of uniform field the effect

cancels exactly

• It cancels also in asymmetric field barrier, if symmetrically

sampled by incidence angles of electrons

• Symmetric barrier appears, if recoil protons are detected using

pe conversion technique

T-violating observables in neutron decay – experimental opportunities 07.12.2018

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BRAND summary

 BRAND project offers systematic exploration of the transverse electron

polarization correlation coefficients R, N, H, L, S, U, V in neutron  decay (H, L, S, U, V were never measured before)

 Combined impact of R, N, H, L, S, U, V on BSM physics is comparable (or better) to Fierz term b and reveals completely different systematics  “HE approach” (tracking, vertex reconstructrion) allows to measure in low magnetic field which is necessary for transverse electron polarization)  Simultaneous measurement of “classical” coefficients a, A, B and D will provide consistency check and comparison of systematic effects specific to high and lowmagnetic field techniques  Experiment is challenging and not free of risks, however , most of critical techniques were experimentaly verified in pioneering project nTRV@PSI  Conservative planning and proposed step-by-step approach (3 subsequent phases) mitigate risk of failure

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Planning

BRAND I BRAND II BRAND III Site ILL Grenoble ILL Grenoble ESS Lund Time 3 – 4 years 3 – 4 years 5-6 years Pressure Ambient Ambient 300 mbar Mott target Pb (Au) Pb (Au) Depleted U Coverage of azimuthal angle 1/6 Full Full Statistical precision (goal) A 0.0008 0.00008 0.000016 a, B, D 0.005 0.0005 0.0001 R, N 0.01 0.001 0.0002 H, L, S, U, V 0.02 0.002 0.0004 Systematic errors R, N, H, L, S, U, V 0.002 0.001 0.0005

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Collaboration and commitments

 Presently BRAND collaboration consists of:

• JU Krakow: K. Bodek1), D. Rozpedzik, J. Zejma1), K. Lojek:

e- and p-detectors, front end electronics and DAQ, simulations

• INP PAS Krakow: A. Kozela1), K. Pysz & Co.:

mechanical structure, vacuum window, MWDC tracker, Mott target, Slow Control

• ILL Grenoble: T

. Soldner: polarized CN beam and infrastructure, vacuum

• KU Leuven: N. Severijns1) & Co.:

guiding magnetic field

• NCSU Raleigh: A.R. Young (?):

pe-converter film

• …

1) Members of nTRV@PSI

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BRAND - layout

MWDC (He+isobutane) Mott target (Pb, 238U) scintillator CN beam

500 1000 1500 mm

e-p conversion foil (LiF) He, 300 mbar (1 bar) Vacuum window Grounded grid

 BRAND I, II:

• ILL, DC beam, pressure 1 bar, Pb target

 BRAND III:

• ESS, pulsed beam, pressure 300 mbar, depleted U target

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n-decay kinematics

e-p

pe pp p

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Reconstruction of momenta

Assigned weight is proportional to the decay rate density Actual position of the decay vertex is not known

But:

It must be located on the electron trajectory segment coincident with the beam Neutron decay density distribution in the beam is known

Finally:

In extraction of correlation coefficients we sum over momenta – ambiguity in vertex position is not essential

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From charge division: z/z = 0.02

R&D: MWDC

hexagonal, low pressure, low Z, charge division

From drift time: r = 0.5 mm Efficiency = 99% r  (0,7) mm

 Expected Mott vertex position uncertainty: r = 2 mm, z = 2 cm; Mott (100o – 150o)  Expected significant reduction of uncertainty due to background subtraction (>10)

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R&D: Vacuum window prototype tests

 AMSYS simulations of mechanical stability  Windows sustain

• verpressure of 1.5 –

2.5 b before rapture  Long term stability and leakage rate tests ongoing

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R&D: „Proton” detector

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COMSOL simulations

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n-decay kinematics

1000 ns 1000 ns

100 keV (150 keV for Mott scat.) 50 eV

 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 105 decays per second: single rate (per wire) < 1 kHz

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Figure-of-Merit for Mott scattering

Electron energy thr.

• Max. scatt. angle

 

2 eff Mott Mott

FoM S   

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Electron and proton trajectories and ToF

Bending radii of protons and electrons are similar in the interesting energy ranges: 50800 eV for protons and 50800 keV for electrons p-e Time-of-Flight difference ranges from 20 to 100 ns (per 1 cm drift path) for interesting proton energy range 50800 eV

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DAQ

SCINTILLATOR (TRIGGER)

MWDC

Thin plastic scintillator, position sens.

Time-of-Flight dt1 dt2 dt3 dt4 dt5 Ee 1 µs

Quantity

• Exp. Information

Electron momentum Scintillation light & electron track* Proton momentum Time-of-flight & hit position

Electron track reconstructed with drift times (x, y) and charge division (z)

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BRAND 0 – test setup

Figure 8: Layout of the test experiment “BRAND 0”. a) Cross section in the plane perpendicular to the beam axis. b) Cross section in the plane containing the beam axis.

 Devoted for extensive on-line tests of critical components and beam

• ptimization

 Should be operational by late Summer 2018

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FUNSPIN – Polarized Cold Neutron Facility at PSI

10 1 n n

10 s 80 I P %



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nTRV@PSI – MWPCs, scintillators and electronics

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“V-track” events – on-line display

nTRV@PSI

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nTRV@PSI: Background subtraction

Absorption threshold Electronic threshold

 Observations:

• Spectral distribution of background depends weakly on the electron
• rigin
• Substantial contribution from prompt electrons

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nTRV@PSI: Neutron polarization from decay asymmetry

Pn = 0.80 ± 0.06

cos

Pn = 0.776 ± 0.003 2/dof = 1.15

A() cos

• Average neutron polarization

from decay rate asymmetry (“single-track” events) An = -0.1173

              

n n n n n n

( , ) ( , ) ( ) cos ( , ) ( , ) N P N P P A N P N P A

Pn An

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Effective kinematical factors

( , ) ( , ) ( ) ( , ) ( , ) ( ) ( ) ( ) ( ) ( ) ( ) n P n P n P n P R N S AP P                            A

F G H

N R A

N = 0.062 ± 0.012 R = 0.004 ± 0.012

A()-AP()F()

NSM = 0.068 RSM = 0.0005

A

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nTRV@PSI: Observables

 

               

       

, , , , , , , , n P n P n P n P n P n P n P n P AP R PS                                    U F H R

 

               

   

 

2 2 2 2

, , , , , , , , ( ) 1 ( ) n P n P n P n P n P n P n P n P PS N A P                                     S G F

N

( , ) ( , ) ( ) ( , ) ( , ) ( ) ( ) ( ) ( ) ( ) ( ) n P n P n P n P R N S AP P                            A

F G H

N R

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nTRV@PSI – final results

NSM×103 = 68 ±1 RSM×103= 0.5

• A. Kozela et al., Phys. Rev. C 85, 045501

(2012)

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Electron tracking, vertex reconstruction

 Unavoidable for electron spin analysis in Mott scattering  Allows for direct measurement of geometry factors  Improves diagnostics of beam in fiducial volume  Allows for implementation of corrections based on parameter maps (e.g. effective Sherman function corrected for target thickness variation and for angle of incidence)  Allows for accurate gain balance of large plastic scintillators  Reduces background in electron energy detector induced by gammas

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nTRV@PSI: Energy resolution

 Conversion electrons from 207Bi

Hodoscope 1 Counts Gaussian fit with fixed relative line positions Ei and intensities Ii i(E) = c1 + c2Ei Background b(E) = b0 + b1E + b2E2 600 600

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nTRV@PSI: beam profile

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T-violating observables in neutron decay – experimental opportunities

nTRV@PSI: Mott vertex

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nTRV@PSI: Projection of vertices onto XY-plane

x y z

Scint. Scint. M WP C Pb-foil Pb-foil

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• Spatial resolution: ~1 cm
• Relative thickness

accuracy: ~1%

• Absolute calibration: ~2%

Transport of polarized electrons in matter (multiple Coulomb scattering)

ELSEPA

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Effective Sherman function

• Exp. Data: PRL 82, 87 (1999)

Monte Carlo E = 14 MeV  = 34 mg/cm2

Pb

• Exp. Data: PR A 43, 207 (1991)

Monte Carlo E = 120 keV  = 135 µg/cm2

Au

 = 222 µg/cm2

At 120 keV (worst case): MC/Exp. :

ELSEPA

MC based on Geant4 + ELSEPA

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nTRV@PSI: Mott target thickness scan

X-ray lamp (35 kV) 2-axis driving system

• A. Kozela et al., NIMB 269 (2011) 1767

Pixel No. Relative difference (%)

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PLANAR AXIAL

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