Nab: precise experimental study of unpolarized neutron beta decay - - PowerPoint PPT Presentation

Nab: precise experimental study of unpolarized neutron beta decay

Dinko Poˇ cani´ c, (for the Nab collaboration)

University of Virginia

2015 Fall Meeting of the APS Division of Nuclear Physics Santa Fe, NM 28 – 31 October 2015

Neutron beta decay observables (SM)

dw dEedΩedΩν ≃ peEe(E0 − Ee)2 ×

• 1 + a

pe · pν EeEν + b m Ee + σn ·

• A

pe Ee + B pν Eν

• + . . .
• where in SM:

a = 1 − |λ|2 1 + 3|λ|2 A = −2|λ|2 + Re(λ) 1 + 3|λ|2 B = 2|λ|2 − Re(λ) 1 + 3|λ|2 λ = GA GV (with τn ⇒ CKM Vud) also proton asymmetry: C = κ(A + B) where κ ≃ 0.275 .

• D. Poˇ

cani´ c (UVa) The Nab experiment: Basic definitions 30 Oct ’15/DNP2015 2 / 14

Neutron beta decay observables (SM)

dw dEedΩedΩν ≃ peEe(E0 − Ee)2 ×

• 1 + a

pe · pν EeEν + b m Ee + σn ·

• A

pe Ee + B pν Eν

• + . . .
• where in SM:

a = 1 − |λ|2 1 + 3|λ|2 A = −2|λ|2 + Re(λ) 1 + 3|λ|2 B = 2|λ|2 − Re(λ) 1 + 3|λ|2 λ = GA GV (with τn ⇒ CKM Vud) also proton asymmetry: C = κ(A + B) where κ ≃ 0.275 . ⇒ SM overconstrains a, A, B observables in n β decay! Fierz interf. term b brings add’l. sensitivity to non-SM processes!

• D. Poˇ

cani´ c (UVa) The Nab experiment: Basic definitions 30 Oct ’15/DNP2015 2 / 14

Goals of the Nab experiment (at SNS, ORNL)

◮ Measure the e–ν correlation a in neutron decay with precision

∆a/a ≃ 10−3

• r ∼ 50× better than:

current results:

−0.1054 ± 0.0055 Byrne et al ’02 −0.1017 ± 0.0051 Stratowa et al ’78 −0.091 ± 0.039 Grigorev et al ’68

• D. Poˇ

cani´ c (UVa) The Nab experiment: Goals and motivation 30 Oct ’15/DNP2015 3 / 14

Goals of the Nab experiment (at SNS, ORNL)

◮ Measure the e–ν correlation a in neutron decay with precision

∆a/a ≃ 10−3

• r ∼ 50× better than:

current results:

−0.1054 ± 0.0055 Byrne et al ’02 −0.1017 ± 0.0051 Stratowa et al ’78 −0.091 ± 0.039 Grigorev et al ’68

◮ Measure b (Fierz interf. term) in n decay with

∆b ≃ 3 × 10−3 current results: none (not yet reported for n decay)

• D. Poˇ

cani´ c (UVa) The Nab experiment: Goals and motivation 30 Oct ’15/DNP2015 3 / 14

Goals of the Nab experiment (at SNS, ORNL)

◮ Measure the e–ν correlation a in neutron decay with precision

∆a/a ≃ 10−3

• r ∼ 50× better than:

current results:

−0.1054 ± 0.0055 Byrne et al ’02 −0.1017 ± 0.0051 Stratowa et al ’78 −0.091 ± 0.039 Grigorev et al ’68

◮ Measure b (Fierz interf. term) in n decay with

∆b ≃ 3 × 10−3 current results: none (not yet reported for n decay)

◮ Nab will be followed by the ABba/PANDA polarized program to

measure A, electron, and B/C, neutrino/proton, asymmetries with ≃ 10−3 relative precision.

• D. Poˇ

cani´ c (UVa) The Nab experiment: Goals and motivation 30 Oct ’15/DNP2015 3 / 14

Goals of the Nab experiment (at SNS, ORNL)

◮ Measure the e–ν correlation a in neutron decay with precision

∆a/a ≃ 10−3

• r ∼ 50× better than:

current results:

−0.1054 ± 0.0055 Byrne et al ’02 −0.1017 ± 0.0051 Stratowa et al ’78 −0.091 ± 0.039 Grigorev et al ’68

◮ Measure b (Fierz interf. term) in n decay with

∆b ≃ 3 × 10−3 current results: none (not yet reported for n decay)

◮ Nab will be followed by the ABba/PANDA polarized program to

measure A, electron, and B/C, neutrino/proton, asymmetries with ≃ 10−3 relative precision. Motivation:

• multiple independent determinations of λ (test of CKM unitarity),
• independent and competitive limits on S, T currents (BSM).
• D. Poˇ

cani´ c (UVa) The Nab experiment: Goals and motivation 30 Oct ’15/DNP2015 3 / 14

Electron–neutrino angle from Ee and Ep

− ν

ν

e θ e n p

Conservation of momentum in n beta decay,

• pp +

pe + pν = 0 , yields p2

p = p2 e + 2pepν cos θeν + p2 ν .

Neglecting proton recoil energy, Ee + Eν = E0, so that pν = E0 − Ee. Therefore: cos θeν is uniquely determined by mea- suring Ee and Ep (or pp ⇒ TOFp).

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cani´ c (UVa) The Nab experiment: Principles of measurement 30 Oct ’15/DNP2015 4 / 14

Nab measurement principles: proton phase space

e (MeV) p 2 (MeV2/c2)

E p cos θeν = -1 cos θeν = 1 cos θeν = 0 proton phase space Yield (arb. units) Ee = 100 keV 300 keV 500 keV 700 keV

0.5 1 1.5 0.2 0.4 0.6 0.8

NB: For a given Ee, cos θeν is a function of p2

p only.

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cani´ c (UVa) The Nab experiment: Principles of measurement 30 Oct ’15/DNP2015 5 / 14

Nab measurement principles: proton phase space

e (MeV) p 2 (MeV2/c2)

E p cos θeν = -1 cos θeν = 1 cos θeν = 0 proton phase space Yield (arb. units) Ee = 100 keV 300 keV 500 keV 700 keV

0.5 1 1.5 0.2 0.4 0.6 0.8

NB: For a given Ee, cos θeν is a function of p2

p only.

Slope ∝ a

❆ ❆ ❆ ❆ ❆ ❆ ❆ ❑ ❆ ❆ ❆ ❆ ❑ ❆ ❆ ❆ ❆ ❆ ❆ ❆ ❆ ❑ ❆ ❆ ❆ ❆ ❆ ❆ ❆ ❆ ❆ ❆ ❆ ❆ ❆ ❑

Numerous consistency checks are built-in!

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cani´ c (UVa) The Nab experiment: Principles of measurement 30 Oct ’15/DNP2015 5 / 14

◮ Collect and detect

both electrons and protons from neutron beta decay.

◮ Measure Ee and TOFp

and reconstruct decay kinematics

◮ Segmented Si det’s:

PPPP P q

LANL/Micron development

P ✐ ✛ P P ✐ ❆ ❑ ❈ ❈ ❖ ❈ ❈ ❖ ❈ ❈ ❖ ❈ ❈ ❖ ❈ ❈ ❖ ✻

Nab principles of measurement

✟✟✟✟✟✡ ✡ ✡ ✡ ✡ ✡ ✡ ✡ ✡ ✡ ✣

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cani´ c (UVa) The Nab experiment: Principles of measurement 30 Oct ’15/DNP2015 6 / 14

Spectrometer Coil design and B field profile

upper detector lower detector

NBL NBU F TOF

TOF’

NBU’ NBL’ UDET’ UDET LDET LDET’

neutron beam z [m] r [m]

0.2 0.4 5

• 1

3.5 m flight path omitted Magnetic field B [T] 1 2 3 4

• 1

1 2 3 4 5 fiducial volume lower detector upper detector

z [m] z [cm] Magnetic field B [T]

1 2 3 4 fiducial volume B (on axis)

z

B (off axis)

z

Filter

• 30-20 -10 0

10 20 30

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cani´ c (UVa) The Nab experiment: Principles of measurement 30 Oct ’15/DNP2015 7 / 14

Nab Si detectors (LANL-Micron development)

◮ 15 cm diameter ◮ full thickness: 2 mm ◮ dead layer ≤100 nm ◮ 127 pixels

Front Back

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cani´ c (UVa) The Nab experiment: Principles of measurement 30 Oct ’15/DNP2015 8 / 14

Nab Si detectors (LANL-Micron development)

◮ 15 cm diameter ◮ full thickness: 2 mm ◮ dead layer ≤100 nm ◮ 127 pixels

Front Back

How well do they work?

• D. Poˇ

cani´ c (UVa) The Nab experiment: Principles of measurement 30 Oct ’15/DNP2015 8 / 14

Nab Si detectors (LANL-Micron development)

◮ 15 cm diameter ◮ full thickness: 2 mm ◮ dead layer ≤100 nm ◮ 127 pixels

Front Back

10 20 30 40 50 60 70 80 Channels 5000 10000 15000

Proton normalized yield Noise 20 25 30 1mm thick Si det.

• A. Salas-Bacci et al., NIM A 735 (2014) 408

35 kV 15

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cani´ c (UVa) The Nab experiment: Principles of measurement 30 Oct ’15/DNP2015 8 / 14

Analysis strategy (methods “A” and “B”)

2

1/t ’ [1/μs ]

p 2

Yield

0.002 0.004 0.006 0.008

E = 150 keV

e

E = 300 keV

e

E = 450 keV

e

E = 600 keV

e

E = 750 keV

e

◮ Use edges to determine and

verify shape of detection function Φ(pp, 1/tp);

◮ Use central part of Pt(1/t2 p)

(∼ 70%) to extract a.

• A. parametrize edges and width of Φ(pp, 1/tp) by fitting; use central part
• f Φ (∼ 70%) to extract a in a multiparameter fit, and
• B. specify accessible parameters of Φ by direct measurement; ⇒ treat a,

µ = 1/t2

p(pp), and Ndecays as free parameters in a two-step fit, ◮ as well as a HYBRID OF THE TWO METHODS.

• D. Poˇ

cani´ c (UVa) The Nab experiment: Principles of measurement 30 Oct ’15/DNP2015 9 / 14

Analysis strategy (methods “A” and “B”)

2

1/t ’ [1/μs ]

p 2

Yield

0.002 0.004 0.006 0.008

E = 150 keV

e

E = 300 keV

e

E = 450 keV

e

E = 600 keV

e

E = 750 keV

e

◮ Use edges to determine and

verify shape of detection function Φ(pp, 1/tp);

◮ Use central part of Pt(1/t2 p)

(∼ 70%) to extract a.

• A. parametrize edges and width of Φ(pp, 1/tp) by fitting; use central part
• f Φ (∼ 70%) to extract a in a multiparameter fit, and
• B. specify accessible parameters of Φ by direct measurement; ⇒ treat a,

µ = 1/t2

p(pp), and Ndecays as free parameters in a two-step fit, ◮ as well as a HYBRID OF THE TWO METHODS.

• D. Poˇ

cani´ c (UVa) The Nab experiment: Principles of measurement 30 Oct ’15/DNP2015 9 / 14

Analysis strategy (methods “A” and “B”)

2

1/t ’ [1/μs ]

p 2

Yield

0.002 0.004 0.006 0.008

E = 150 keV

e

E = 300 keV

e

E = 450 keV

e

E = 600 keV

e

E = 750 keV

e

◮ Use edges to determine and

verify shape of detection function Φ(pp, 1/tp);

◮ Use central part of Pt(1/t2 p)

(∼ 70%) to extract a.

• A. parametrize edges and width of Φ(pp, 1/tp) by fitting; use central part
• f Φ (∼ 70%) to extract a in a multiparameter fit, and
• B. specify accessible parameters of Φ by direct measurement; ⇒ treat a,

µ = 1/t2

p(pp), and Ndecays as free parameters in a two-step fit, ◮ as well as a HYBRID OF THE TWO METHODS.

• D. Poˇ

cani´ c (UVa) The Nab experiment: Principles of measurement 30 Oct ’15/DNP2015 9 / 14

Projected statistical uncertainties for a and b

Statistical uncertainties for a

Ee,min 100 keV 100 keV 100 keV 300 keV tp,max – – 40 µs 30 µs 40 µs σa 2.4/√Nu 2.4/√Nu 2.6/√Nu 2.8/√Nu 3.1/√Nu σa† 2.6/√Nu 2.6/√Nu 2.8/√Nu 3.1/√Nu 3.5/√Nu σa§ 3.3/√Nu 3.4/√Nu 3.6/√Nu 4.0/√Nu 4.6/√Nu

† with Ecalib and LTOF variable; § using inner 75% of p2

p data.

[ Nu . . . number of protons detected in upper detector. ]

Statistical uncertainties for b

Ee,min 100 keV 200 keV 300 keV σb 7.5/ √ N 10.1/ √ N 15.6/ √ N 26.3/ √ N σb†† 7.7/ √ N 10.3/ √ N 16.3/ √ N 27.7/ √ N

†† with Ecalib variable.

[ N . . . number of n-decay electrons detected in either detector. ]

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cani´ c (UVa) The Nab experiment: Uncertainties 30 Oct ’15/DNP2015 10 / 14

Projected statistical uncertainties for a and b

Statistical uncertainties for a

Ee,min 100 keV 100 keV 100 keV 300 keV tp,max – – 40 µs 30 µs 40 µs σa 2.4/√Nu 2.4/√Nu 2.6/√Nu 2.8/√Nu 3.1/√Nu σa† 2.6/√Nu 2.6/√Nu 2.8/√Nu 3.1/√Nu 3.5/√Nu σa§ 3.3/√Nu 3.4/√Nu 3.6/√Nu 4.0/√Nu 4.6/√Nu

† with Ecalib and LTOF variable; § using inner 75% of p2

p data.

[ Nu . . . number of protons detected in upper detector. ]

Statistical uncertainties for b

Ee,min 100 keV 200 keV 300 keV σb 7.5/ √ N 10.1/ √ N 15.6/ √ N 26.3/ √ N σb†† 7.7/ √ N 10.3/ √ N 16.3/ √ N 27.7/ √ N

†† with Ecalib variable.

[ N . . . number of n-decay electrons detected in either detector. ]

• D. Poˇ

cani´ c (UVa) The Nab experiment: Uncertainties 30 Oct ’15/DNP2015 10 / 14

Nab systematic uncertainties: Method B

Experimental parameter (∆a/a)SYST Magnetic field: curvature at pinch 5 × 10−4 ratio rB = BTOF/B0 2.5 × 10−4 ratio rB,DV = BDV/B0 3 × 10−4 LTOF, length of TOF region (*) U inhomogeneity: in decay / filter region 5 × 10−4 in TOF region 1 × 10−4 Neutron beam: position 4 × 10−5 width 2.5 × 10−4 Doppler effect small unwanted beam polarization small Adiabaticity of proton motion 1 × 10−4 Detector effects: Ee calibration (*) Ee resolution 5 × 10−4 Proton trigger efficiency 2.5 × 10−4 Accidental coinc’s (will subtract out of time coinc) small Residual gas

• ngoing parametric studies

small Background

• ngoing parametric studies

small Overall sum 1 × 10−3 (*) Free fit parameter

• D. Poˇ

cani´ c (UVa) The Nab experiment: Uncertainties 30 Oct ’15/DNP2015 11 / 14

Nab systematic uncertainties: Method B

Experimental parameter (∆a/a)SYST Magnetic field: curvature at pinch 5 × 10−4 ratio rB = BTOF/B0 2.5 × 10−4 ratio rB,DV = BDV/B0 3 × 10−4 LTOF, length of TOF region (*) U inhomogeneity: in decay / filter region 5 × 10−4 in TOF region 1 × 10−4 Neutron beam: position 4 × 10−5 width 2.5 × 10−4 Doppler effect small unwanted beam polarization small Adiabaticity of proton motion 1 × 10−4 Detector effects: Ee calibration (*) Ee resolution 5 × 10−4 Proton trigger efficiency 2.5 × 10−4 Accidental coinc’s (will subtract out of time coinc) small Residual gas

• ngoing parametric studies

small Background

• ngoing parametric studies

small Overall sum 1 × 10−3 (*) Free fit parameter

• D. Poˇ

cani´ c (UVa) The Nab experiment: Uncertainties 30 Oct ’15/DNP2015 11 / 14

Nab systematic uncertainties: Method B

Experimental parameter (∆a/a)SYST Magnetic field: curvature at pinch 5 × 10−4 ratio rB = BTOF/B0 2.5 × 10−4 ratio rB,DV = BDV/B0 3 × 10−4 LTOF, length of TOF region (*) U inhomogeneity: in decay / filter region 5 × 10−4 in TOF region 1 × 10−4 Neutron beam: position 4 × 10−5 width 2.5 × 10−4 Doppler effect small unwanted beam polarization small Adiabaticity of proton motion 1 × 10−4 Detector effects: Ee calibration (*) Ee resolution 5 × 10−4 Proton trigger efficiency 2.5 × 10−4 Accidental coinc’s (will subtract out of time coinc) small Residual gas

• ngoing parametric studies

small Background

• ngoing parametric studies

small Overall sum 1 × 10−3 (*) Free fit parameter

• D. Poˇ

cani´ c (UVa) The Nab experiment: Uncertainties 30 Oct ’15/DNP2015 11 / 14

Nab apparatus in FnPB/SNS

extends:

• ∼6 m above beam height,
• ∼2 m below beam height (pit).

Fully funded (NSF-MRI, plus DOE constr. + operating funds); Project so far on track to be ready for beam in 2016.

• D. Poˇ

cani´ c (UVa) The Nab experiment: Apparatus; drawings 30 Oct ’15/DNP2015 12 / 14

Status: some drawings of the Nab apparatus

CRYOGENIC LTD

`0.1

MM

THIRD ANGLE PROJECTION DWG No. OF SHEET

External View GA03 3658 1 1 1 24/06/2013 06/03/2014

3658 - 1 2 3 4 5 6 7 8 9 7 10 8 11 11 A A 16.50 7.93 11.50 9.75 29.26 7.63 18.13 24.75 3.95 16.50 7.93 5.38 11.50 5.63 SECTION A-A SCALE 1 : 4 D C B A A B C D 1 2 3 4 5 6 7 8 8 7 6 5 4 3 2 1

• DWG. NO.

P-25

• D. Poˇ

cani´ c (UVa) The Nab experiment: Apparatus; drawings 30 Oct ’15/DNP2015 13 / 14

Summary

◮ Nab is part of a broad experimental effort, to exploit the unparalleled

theoretical precision in electroweak processes in general. The program

• f precision studies is timely, complementary, and valuable for proper

interpretation of collider data.

• D. Poˇ

cani´ c (UVa) The Nab experiment: Summary 30 Oct ’15/DNP2015 14 / 14

Summary

◮ Nab is part of a broad experimental effort, to exploit the unparalleled

theoretical precision in electroweak processes in general. The program

• f precision studies is timely, complementary, and valuable for proper

interpretation of collider data.

◮ Nab is expected to resolve the longstanding consistency problem with

λ = GA/GV , and provide new constraints on non-SM processes; ABba will add independent constraints.

• D. Poˇ

cani´ c (UVa) The Nab experiment: Summary 30 Oct ’15/DNP2015 14 / 14

Summary

◮ Nab is part of a broad experimental effort, to exploit the unparalleled

theoretical precision in electroweak processes in general. The program

• f precision studies is timely, complementary, and valuable for proper

interpretation of collider data.

◮ Nab is expected to resolve the longstanding consistency problem with

λ = GA/GV , and provide new constraints on non-SM processes; ABba will add independent constraints.

◮ Nab is fully funded and all parts of the project are proceeding apace;

it is expected on the floor at SNS in 2016.

• D. Poˇ

cani´ c (UVa) The Nab experiment: Summary 30 Oct ’15/DNP2015 14 / 14

Summary

◮ Nab is part of a broad experimental effort, to exploit the unparalleled

theoretical precision in electroweak processes in general. The program

• f precision studies is timely, complementary, and valuable for proper

interpretation of collider data.

◮ Nab is expected to resolve the longstanding consistency problem with

λ = GA/GV , and provide new constraints on non-SM processes; ABba will add independent constraints.

◮ Nab is fully funded and all parts of the project are proceeding apace;

it is expected on the floor at SNS in 2016.

◮ Significant synergies and joint interest exist between the LANL UCNx

and Nab/ABba programs.

• D. Poˇ

cani´ c (UVa) The Nab experiment: Summary 30 Oct ’15/DNP2015 14 / 14

Summary

◮ Nab is part of a broad experimental effort, to exploit the unparalleled

theoretical precision in electroweak processes in general. The program

• f precision studies is timely, complementary, and valuable for proper

interpretation of collider data.

◮ Nab is expected to resolve the longstanding consistency problem with

λ = GA/GV , and provide new constraints on non-SM processes; ABba will add independent constraints.

◮ Nab is fully funded and all parts of the project are proceeding apace;

it is expected on the floor at SNS in 2016.

◮ Significant synergies and joint interest exist between the LANL UCNx

and Nab/ABba programs. Home page: http://nab.phys.virginia.edu

• D. Poˇ

cani´ c (UVa) The Nab experiment: Summary 30 Oct ’15/DNP2015 14 / 14

Active and recent Nab collaborators (as of Oct 2015)

• R. Alarcona, S. Baeßlerb,c∗, S. Balascutaa§, L. Barr´
• n Palosd, N. Birgee§,
• D. Borissenkob§, J.D. Bowmanc†, L. Broussardm,c, J. Byrnef , J.R. Calarcog,
• T. Chupph, V. Ciancioloc, C. Crawfordi, J. DuBoisb§, W. Fanb§, W. Farrarb§,
• N. Fomine, E. Frleˇ

zb, J. Fryb, M.T. Gerickej, F. Gl¨ uckk, G.L. Greenec,e, R.K. Grzywacze, V. Gudkovℓ, C. Hendrush§, F.W. Hersmang, T. Itom, H. Lib§, M.F. Makelam, J. Martinn, M. Martineza§, P.L. McGaugheym, C.D. McLaughlinb§,

• P. Muellerc, S.A. Pagej, D. van Petten§, S.I. Penttil¨

ac‡, D. Poˇ cani´ cb†, N. Roaneb§, K.P. Rykaczewskic, A. Salas-Baccib, E.M. Scotte§, A. Smithb§, A. Sprowi§,

• E. Stevensb§, J. Wexlero§, R. Whiteheade§, W.S. Wilburnm, A.R. Youngo.

aArizona State U.

• bU. of Virginia

cORNL dUNAM, Mexico

• eU. of Tennessee

f U. of Sussex

• gU. New Hampshire
• hU. of Michigan
• iU. of Kentucky
• jU. of Manitoba
• kUni. Karlsruhe

ℓU. of South Carolina mLANL

• nU. of Winnipeg
• N. Carolina State U.

∗Project Manager †Co-spokesmen ‡On-site Manager §Nab students, or recent Nab students

Home page: http://nab.phys.virginia.edu/

• D. Poˇ

cani´ c (UVa) The Nab experiment: Collaboration 30 Oct ’15/DNP2015 15 / 14

Current status of Vud and λ, from n decay

. . . remains an unresolved mess:

λ = gA/gV Vud PIBETA [Pocanic04] ft(0+→0+) [Hardy09] CKM unitarity [PDG 2012] τn [PDG 2012] PKO1 DD-ME2 ft(0+→0+) [Liang09] λ [PDG 2012] λ [UCNA 2010] λ [PERKEO II 2012]

0.96 0.965 0.97 0.975 0.98

• 1.29
• 1.28
• 1.27
• 1.26

✂ ✂ ✂ ✂ ✂ ✂ ✍

τ −1

n

∝ |Vud|2|gV |2(1 + 3|λ|2)

• 1.28
• 1.26
• 1.24

Stratowa (1997) PERKEO I (1986) Liaud (1997) PERKEO II (1997) ( ) ( ) PERKEO II (2002) PERKEO II (2013) UCNA (2010) ( ) UCNA (2013) Mostovoi (2001) Yerozolimskii (1997) Byrne (2002)

Average:

• 1.2724(21)

Δ λ/ = 0.03% (Nab goal) λ

Very low CL! ∆λ λ ≃ 0.27∆a a ≃ 0.24∆A A λ sensitivity to a, A is similar.

◮ Nab+abBA ⇒ several independent ∼ 0.03% determinations of λ, ◮ Combined with b ⇒ new limits on non-SM terms, esp. Tensor.

• D. Poˇ

cani´ c (UVa) The Nab experiment: Collaboration 30 Oct ’15/DNP2015 16 / 14

Limits on T, S couplings from beta decay

0.0010 0.0005 0.0000 0.0005 0.0010 0.02 0.01 0.00 0.01 0.02

T S

b 103 bΝ b 103 b0 2.2 4.3 103

0.0010 0.0005 0.0000 0.0005 0.0010 0.02 0.01 0.00 0.01 0.02

T S

b 103 bΝ 103 b0 2.2 4.3 103

Measurement of b with δb < 10−3 ⇒ > 4-fold improvement on the current limit for ǫT from π+ → e+νγ decay.

From T. Bhattacharya, V. Cirigliano, S.D. Cohen, A. Filipuzzi, M. Gonz´ alez-Alonso, M.L. Graesser, R. Gupta, H-W. Lin, Phys. Rev. D 85 (2012) 054512.

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cani´ c (UVa) The Nab experiment: Backup slides 30 Oct ’15/DNP2015 17 / 14