Nab: precise experimental study of unpolarized neutron ...

Nab: precise experimental study ofunpolarized neutron beta decay

Dinko Pocanic, (for the Nab collaboration)

University of Virginia

4th Joint Meeting of the Nuclear Physics Divisionsof the Am. Phys. Soc. and Phys. Soc. of Japan

Kona, HI6–11 Oct 2014

Neutron beta decay observables (SM)

dEedΩedΩν' peEe(E0 − Ee)2

1 + a~pe · ~pνEeEν

Ee+ 〈~σn〉 ·

(A~peEe

+ B~pνEν

)+ . . .

]where in SM:

a =1− |λ|2

1 + 3|λ|2A = −2

|λ|2 + Re(λ)

1 + 3|λ|2

B = 2|λ|2 − Re(λ)

1 + 3|λ|2λ =

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. Pocanic (UVa) The Nab experiment: Basic definitions 10 Oct ’14/DNP2013 2 / 14

Neutron beta decay observables (SM)

dEedΩedΩν' peEe(E0 − Ee)2

1 + a~pe · ~pνEeEν

Ee+ 〈~σn〉 ·

(A~peEe

+ B~pνEν

)+ . . .

]where in SM:

a =1− |λ|2

1 + 3|λ|2A = −2

|λ|2 + Re(λ)

1 + 3|λ|2

B = 2|λ|2 − Re(λ)

1 + 3|λ|2λ =

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. Pocanic (UVa) The Nab experiment: Basic definitions 10 Oct ’14/DNP2013 2 / 14

Goals of the Nab experiment (at SNS, ORNL)

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

∆a/a ' 10−3 or ∼ 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

I Measure b (Fierz interf. term) in n decay with ∆b ' 3× 10−3

current results: none (not yet reported for n decay)

I Nab will be followed by the ABba/PANDA polarized program tomeasure 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. Pocanic (UVa) The Nab experiment: Goals and motivation 10 Oct ’14/DNP2013 3 / 14

Motivation:

Electron–neutrino angle from Ee and Ep

p Conservation of momentum in n beta decay,

~pp + ~pe + ~pν = 0 ,

yields

p2p = p2

e + 2pepν cos θeν + p2ν .

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).

D. Pocanic (UVa) The Nab experiment: Principles of measurement 10 Oct ’14/DNP2013 4 / 14

Nab measurement principles: proton phase space

e (MeV)

2 /c2 )

θ eν =

cos θ eν = 1

cos θeν = 0

proton phase spaceYield (arb. units)

100 keV

300 keV

500 keV

700 keV

0 0.2 0.4 0.6 0.8

NB: For a given Ee , cos θeν is a function of p2p only.

Slope ∝ aAAAAAAAK

AAAAAAAAK

AAAAAAAAAAAAAK

Numerous consistency checks are built-in!

Nab measurement principles: proton phase space

e (MeV)

2 /c2 )

θ eν =

cos θ eν = 1

cos θeν = 0

proton phase spaceYield (arb. units)

100 keV

300 keV

500 keV

700 keV

0 0.2 0.4 0.6 0.8

NB: For a given Ee , cos θeν is a function of p2p only. Slope ∝ a

AAAAAAAK

AAAAAAAAK

AAAAAAAAAAAAAK

Numerous consistency checks are built-in!

I Collect and detectboth electrons andprotons from neutronbeta decay.

I Measure Ee and TOFp

and reconstruct decaykinematics

I Segmented Si det’s:

PPPPPq

LANL/Micron development

CCOCCO

CCOCCOCCO

Nab principles of measurement

Spectrometer Coil design and ~B field profile

upper detector

lower detector

TOF TOF’

NBU’

NBL’

UDET’UDET

LDET’

neutron beam

0 0.2 0.4

3.5 m flight path omitted

-1 0 1 2 3 4 5

fiducialvolume

lowerdetector

upperdetector

z [cm]

fiducialvolume

B (on axis)z

B (off axis)z

Filter

-30-20 -10 0 10 20 30

Nab Si detectors (LANL-Micron development)

I 15 cm diameter

I full thickness: 2 mm

I dead layer ≤100 nm

I 127 pixels

I 15 cm diameter

I 127 pixels

These look lovely, buthow well do they work?

I 15 cm diameter

I 127 pixels

0 10 20 30 40 50 60 70 80Channels

20 25 30

1mm thick Si det.A. Salas-Bacci et al., NIM A 735 (2014) 408

35 kV15

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

21/t ’ [1/μs ]p

0 0.002 0.004 0.006 0.008

E = 150 keVe

E = 300 keVe

E = 450 keVe

E = 600 keVe

E = 750 keVe

I Use edges to determine andverify shape of detectionfunction Φ(pp, 1/tp);

I Use central part of Pt(1/t2p)

(∼ 70%) to extract a.

A. parametrize edges and width of Φ(pp, 1/tp) by fitting; use central partof Φ (∼ 70%) to extract a in a multiparameter fit, and

B. specify accessible parameters of Φ by direct measurement; ⇒ treat a,µ = 1/t2p(pp), and Ndecays as free parameters in a two-step fit,

I as well as a HYBRID OF THE TWO METHODS.

21/t ’ [1/μs ]p

0 0.002 0.004 0.006 0.008

E = 150 keVe

E = 300 keVe

E = 450 keVe

E = 600 keVe

E = 750 keVe

21/t ’ [1/μs ]p

0 0.002 0.004 0.006 0.008

E = 150 keVe

E = 300 keVe

E = 450 keVe

E = 600 keVe

E = 750 keVe

Projected statistical uncertainties for a and b

Statistical uncertainties for a

Ee,min 0 100 keV 100 keV 300 keV 100 keVtp,max – – 40µs 40µs 30µs

σa 2.4/√Nu 2.5/

√Nu 2.5/

√Nu 2.6/

√Nu 2.8/

σa† 2.5/

√Nu 2.6/

√Nu 2.7/

√Nu 3.1/

σa§ 4.1/

√Nu 4.1/

√Nu 4.4/

† with Ecalib and LTOF variable; § using inner 70% of p2p data.

Statistical uncertainties for b

Ee,min 0 100 keV 200 keV 300 keV

σb 7.5/√N 10.1/

√N 15.6/

√N 26.3/

σb†† 7.7/

√N 10.3/

√N 16.3/

√N 27.7/

†† with Ecalib variable.

D. Pocanic (UVa) The Nab experiment: Uncertainties 10 Oct ’14/DNP2013 10 / 14

Projected statistical uncertainties for a and b

Statistical uncertainties for a

Ee,min 0 100 keV 100 keV 300 keV 100 keVtp,max – – 40µs 40µs 30µs

σa 2.4/√Nu 2.5/

√Nu 2.5/

√Nu 2.6/

√Nu 2.8/

σa† 2.5/

√Nu 2.6/

√Nu 2.7/

√Nu 3.1/

σa§ 4.1/

√Nu 4.1/

√Nu 4.4/

† with Ecalib and LTOF variable; § using inner 70% of p2p data.

Statistical uncertainties for b

Ee,min 0 100 keV 200 keV 300 keV

σb 7.5/√N 10.1/

√N 15.6/

√N 26.3/

σb†† 7.7/

√N 10.3/

√N 16.3/

√N 27.7/

†† with Ecalib variable.

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 smallunwanted 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) smallResidual gas ongoing parametric studies smallBackground ongoing parametric studies small

Overall sum 1× 10−3

(*) Free fit parameter

width 2.5× 10−4

Nab apparatus in FnPB/SNS Apparatus extends:

• ∼6 m above beam height,

• ∼1.5 m below beam height.

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

D. Pocanic (UVa) The Nab experiment: Apparatus drawings 10 Oct ’14/DNP2013 12 / 14

Status: some drawings of the Nab apparatus

Parts List

DESCRIPTIONQTYITEM

Axial tie rod fixing41

16.5 inch US CF flange22

Axial tie rod fixing23

Sumitomo SRDK -415D 1.5W cryocooler44

Radial tie rod fixing45

Instrumentation flange26

CF 160 flange47

Magnet terminals 108

NW50KF evacuation valves29

Rotation plate210

Lifting eye211

Plain washers - Normal series - Product grade A12059

Hexagon Socket Head Cap Screw12060

Plain washers - Normal series - Product grade A7263

Hexagon head bolt - product grades A and B7264

CRYOGENIC LTD

QUANTITY

CUSTOM FINISHMATERIAL SPECIFICATION

DRAWN BY: REVIEWED BY:

JOB NUMBERTOLERANCE(UNLESS STATED) `0.1

DIMENSION

STD.PART No.

THIS DRAWING BELONGS TO CRYOGENIC LTD AND IS ISSUED ON THE CONDITION THAT IT IS NOT COPIED, REPRINTED OR DISCLOSED EITHER IN WHOLE OR IN PART TO A THIRD PARTY WITHOUT THE PRIOR CONSENT OF:CRYOGENIC LTD, ACTON PARK IND. ESTATE.THE VALE, LONDON W3 7QE

THIS DRAFT:

THIRD ANGLE PROJECTION

DWG No.

OFSHEETFIRST DRAFT:

External View

1 1 24/06/201306/03/2014

11:51:06

3658 -

7.93 11.50

7.63 18.13

16.50 7.93 5.38 11.50 5.63

SECTION A-ASCALE 1 : 4

12345678

8 7 6 5 4 3 2 1

WEIGHT:

Detector Assembly_nab

VARIED

RAMSEY 8/6/2014

COMMENTS:

SHEET 1 OF 3

MFG APPR.

ENG APPR.

CHECKED

DATENAMEDIMENSIONS ARE IN INCHESTOLERANCES UNLESS SPECIFIED:FRACTIONALANGULAR: MACH BEND TWO PLACE DECIMAL 0.01THREE PLACE DECIMAL 0.003

FINISH

MATERIAL

BDWG. NO.SIZE

SCALE:1:8

P-25SUBATOMIC PHYSICS

LOS ALAMOS NATIONAL LABORATORYLOS ALAMOS, NM, 87545 126Y-1766781 B1QUANTITY REQUIRED

PRELIMINARYNOT FOR

PRODUCTIOND. Pocanic (UVa) The Nab experiment: Apparatus drawings 10 Oct ’14/DNP2013 13 / 14

Summary

I Nab is part of a broad experimental effort, to exploit the unparalleledtheoretical precision in electroweak processes in general. The programof precision studies is timely, complementary, and valuable for properinterpretation of collider data.

I Nab is expected to resolve the longstanding consistency problem withλ = GA/GV , and provide new constraints on non-SM processes; ABbawill add independent constraints.

I Nab is fully funded and all parts of the project are proceeding apace;it is expected on the floor at SNS in 2016.

I Significant synergies and joint interest exist between the LANL UCNxand Nab/ABba programs.

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

D. Pocanic (UVa) The Nab experiment: Summary 10 Oct ’14/DNP2013 14 / 14

Summary

Current Nab collaboration

R. Alarcona, L.P. Alonzi2§, S. Baeßlerb∗, S. Balascutaa, A. Barkana, L. BarronPalosc , N. Birgei , J.D. Bowmand†, L. Broussardm, J. Byrnee , J.R. Calarcof ,

T. Chuppg , V. Cianciolod , C. Crawfordh, N. Fomini , E. Frlezb, M.T. Gerickej ,F. Gluckk , G.L. Greened,i , R.K. Grzywaczi , V. Gudkovl , D. Harrisonj ,

F.W. Hersmanf , T. Itom, H. Lib, M.F. Makelam, J. Martino , P.L. McGaugheym,S.A. Pagej , S.I. Penttilad‡, D. Pocanicb†, K.P. Rykaczewskid , A. Salas-Baccib,

E.M. Scotti , A. Sprowh, J. Thomisond , Z. Tompkinsb§, W.S. Wilburnm,A.R. Youngp, B. Zeckp.

aArizona State University bUniversity of VirginiacUNAM, Mexico dOak Ridge National LabeUniversity of Sussex f Univ. of New HampshiregUniversity of Michigan hUniversity of KentuckyiUniversity of Tennessee jUniversity of ManitobakUni. Karlsruhe/RMKI Budapest lUniversity of South CarolinamLos Alamos National Lab oUniversity of WinnipegpNorth Carlolina State Univ. †Co-spokesmen∗Project Manager ‡On-site Manager

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

Current status of Vud and λ, from n decay. . . remains an unresolved mess:

λ = gA/gV

PIBETA [Pocanic04]

ft(0+→0

+) [Hardy09]

CKM unitarity

[PDG 2012]

τ n [P

PKO1 DD-ME2ft(0

+) [Liang09]

-1.29 -1.28 -1.27 -1.26

τ−1n ∝ |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)

Very low CL!

λ' 0.27

a' 0.24

Aλ sensitivity to a, A is similar.

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

Limits on T , S couplings from beta decay

-0.0010 -0.0005 0.0000 0.0005 0.0010-0.02

b¤ < 10-3 bΝ - b¤ < 10-3

b0 + = -H2.2 ± 4.3L 10-3

-0.0010 -0.0005 0.0000 0.0005 0.0010-0.02

b¤ < 10-3 bΝ¤ < 10-3

b0 + = -H2.2 ± 4.3L 10-3

Measurement of b with δb < 10−3 ⇒ > 4-fold improvement on the currentlimit for εT from π+ → e+νγ decay.From T. Bhattacharya, V. Cirigliano, S.D. Cohen, A. Filipuzzi, M. Gonzalez-Alonso,

M.L. Graesser, R. Gupta, H-W. Lin, Phys. Rev. D 85 (2012) 054512.

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