observables with the Nab...

50
Stefan Baeβler The measurement of neutron beta decay observables with the Nab spectrometer 1 Inst. Nucl. Part. Phys.

Transcript of observables with the Nab...

Page 1: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

Stefan Baeβler

The measurement of neutron beta decay

observables with the Nab spectrometer

1 Inst. Nucl. Part. Phys.

Page 2: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

The neutrino electron correlation coefficient 𝒂

2

𝑑Γ ∝ 1 + 𝑎𝑝𝑒𝐸𝑒

cos 𝜃𝑒𝜈 + 𝑏𝑚𝑒

𝐸𝑒

n

e-

𝜈𝑒

p 𝜃𝑒𝜈

Page 3: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

Novel approach to determine cos 𝜃𝑒𝜐:

Kinematics in Infinite Nuclear Mass Approximation:

1. Energy Conservation: 𝐸𝜐 = 𝐸𝑒,𝑚𝑎𝑥 − 𝐸𝑒,𝑘𝑖𝑛

2. Momentum Conservation:

𝑝𝑝2 = 𝑝𝑒

2 + 𝑝𝜐2 + 2𝑝𝑒𝑝𝜐 cos 𝜃𝑒𝜐

The neutrino electron correlation coefficient 𝒂

2

𝑑Γ ∝ 1 + 𝑎𝑝𝑒𝐸𝑒

cos 𝜃𝑒𝜈 + 𝑏𝑚𝑒

𝐸𝑒

n

e-

𝜈𝑒

p 𝜃𝑒𝜈

Page 4: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

𝐸𝑒,𝑘𝑖𝑛 = 450 keV

1 + 𝑎𝑝𝑒𝐸𝑒

cos 𝜃𝑒𝜈 𝑝𝑝2

pp2 [MeV2/c2]

pp

2 d

istr

ibuti

on

0.0 0.5 1.0 1.5

Novel approach to determine cos 𝜃𝑒𝜐:

Kinematics in Infinite Nuclear Mass Approximation:

1. Energy Conservation: 𝐸𝜐 = 𝐸𝑒,𝑚𝑎𝑥 − 𝐸𝑒,𝑘𝑖𝑛

2. Momentum Conservation:

𝑝𝑝2 = 𝑝𝑒

2 + 𝑝𝜐2 + 2𝑝𝑒𝑝𝜐 cos 𝜃𝑒𝜐

The neutrino electron correlation coefficient 𝒂

2

𝑑Γ ∝ 1 + 𝑎𝑝𝑒𝐸𝑒

cos 𝜃𝑒𝜈 + 𝑏𝑚𝑒

𝐸𝑒

n

e-

𝜈𝑒

p 𝜃𝑒𝜈

Page 5: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

𝐸𝑒,𝑘𝑖𝑛 = 450 keV

1 + 𝑎𝑝𝑒𝐸𝑒

cos 𝜃𝑒𝜈 𝑝𝑝2

pp2 [MeV2/c2]

pp

2 d

istr

ibuti

on

0.0 0.5 1.0 1.5

Novel approach to determine cos 𝜃𝑒𝜐:

Kinematics in Infinite Nuclear Mass Approximation:

1. Energy Conservation: 𝐸𝜐 = 𝐸𝑒,𝑚𝑎𝑥 − 𝐸𝑒,𝑘𝑖𝑛

2. Momentum Conservation:

𝑝𝑝2 = 𝑝𝑒

2 + 𝑝𝜐2 + 2𝑝𝑒𝑝𝜐 cos 𝜃𝑒𝜐

J.D. Bowman, Journ. Res. NIST 110, 40 (2005)

The neutrino electron correlation coefficient 𝒂

2

𝑑Γ ∝ 1 + 𝑎𝑝𝑒𝐸𝑒

cos 𝜃𝑒𝜈 + 𝑏𝑚𝑒

𝐸𝑒

n

e-

𝜈𝑒

p 𝜃𝑒𝜈

Properties of 𝑝𝑝2 distribution for fixed 𝐸𝑒:

Edges 𝑝𝑝2

𝑚𝑖𝑛,𝑚𝑎𝑥= 𝑝𝑒 ± 𝑝𝜐

2

Slope ∝ 1 + 𝑎𝑝𝑒

𝐸𝑒cos 𝜃𝑒𝜈 𝑝𝑝

2

cos 𝜃𝑒𝜈 𝑝𝑝2 = +1

cos 𝜃𝑒𝜈 𝑝𝑝2 = −1

Page 6: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

Electron spectrum:

0 2 0 0 4 0 0 6 0 0 8 0 0

𝐸𝑒,𝑘𝑖𝑛 (keV)

Y i e

l d (

a r b

. u

n i t

s )

b = +0.1

SM

The Fierz Interference Term 𝒃

3

𝑑Γ ∝ 𝜚 𝐸𝑒 1 + 𝑎𝑝𝑒𝐸𝑒

cos 𝜃𝑒𝜈 + 𝑏𝑚𝑒

𝐸𝑒

n

e-

𝜈𝑒

p 𝜃𝑒𝜈

Page 7: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

d

n = (ddu)

p = (udu)

u

e-

νe gV , gA

Coupling Constants in Neutron Decay

𝑛 → 𝑝 + 𝑒− + 𝜈 𝑒

Coupling Constants of the Weak Interaction

gV = GF·Vud·1

gA = GF·Vud·λ

5

Page 8: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

d

n = (ddu)

p = (udu)

u

e-

νe gV , gA

Coupling Constants in Neutron Decay

𝑛 → 𝑝 + 𝑒− + 𝜈 𝑒

Coupling Constants of the Weak Interaction

gV = GF·Vud·1

gA = GF·Vud·λ 𝜏𝑛−1 ∝ 𝑔𝑉

2 + 3𝑔𝐴2

5

Page 9: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

d

n = (ddu)

p = (udu)

u

e-

νe gV , gA

Coupling Constants in Neutron Decay

𝑛 → 𝑝 + 𝑒− + 𝜈 𝑒

Coupling Constants of the Weak Interaction

gV = GF·Vud·1

gA = GF·Vud·λ 𝜏𝑛−1 ∝ 𝑔𝑉

2 + 3𝑔𝐴2

𝜆 =𝑔𝐴𝑔𝑉

5

Page 10: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

d

n = (ddu)

p = (udu)

u

e-

νe gV , gA

Coupling Constants in Neutron Decay

e-

νe n

p

n + νe ↔ p + e-

Primordial Nucleosynthesis Solar cycle

e+

νe

p + p

2H+

p + p → 2H+ + e+ + νe

𝑛 → 𝑝 + 𝑒− + 𝜈 𝑒

Coupling Constants of the Weak Interaction

Start of Big Bang Nucleosynthesis,

Primordial 4He abundance Start of Solar Cycle, determines amount of

Solar Neutrinos

gV = GF·Vud·1

gA = GF·Vud·λ 𝜏𝑛−1 ∝ 𝑔𝑉

2 + 3𝑔𝐴2

𝜆 =𝑔𝐴𝑔𝑉

5

Page 11: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

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Neutron Lifetime Measurements

Beam: Decay rate: 𝑑𝑁

𝑑𝑡=

𝑁

𝜏𝑛

12

Page 12: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

6

Neutron Lifetime Measurements

UCN from source

UCN

Storage

bottle(s)

Shutter UCN

detector

Beam: Decay rate: 𝑑𝑁

𝑑𝑡=

𝑁

𝜏𝑛

Bottle: Neutron counts : 𝑁 = 𝑁0𝑒−

𝑡

𝜏𝑒𝑓𝑓

with 1

𝜏𝑒𝑓𝑓

=1

𝜏𝑛+

1

𝜏𝑤𝑎𝑙𝑙

13

Page 13: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

875

880

885

890

895

1985 1990 1995 2000 2005 2010 2015 2020

Neu

tro

n l

ifet

ime

[s]

Experiment publication

material bottle not used beam

6

Neutron Lifetime Measurements

UCN from source

UCN

Storage

bottle(s)

Shutter UCN

detector

Beam: Decay rate: 𝑑𝑁

𝑑𝑡=

𝑁

𝜏𝑛

Bottle: Neutron counts : 𝑁 = 𝑁0𝑒−

𝑡

𝜏𝑒𝑓𝑓

with 1

𝜏𝑒𝑓𝑓

=1

𝜏𝑛+

1

𝜏𝑤𝑎𝑙𝑙

14

Page 14: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

875

880

885

890

895

1985 1990 1995 2000 2005 2010 2015 2020

Neu

tro

n l

ifet

ime

[s]

Experiment publication

material bottle not used beam

6

Neutron Lifetime Measurements

UCN from source

UCN

Storage

bottle(s)

Shutter UCN

detector

Beam: Decay rate: 𝑑𝑁

𝑑𝑡=

𝑁

𝜏𝑛

Bottle: Neutron counts : 𝑁 = 𝑁0𝑒−

𝑡

𝜏𝑒𝑓𝑓

with 1

𝜏𝑒𝑓𝑓

=1

𝜏𝑛+

1

𝜏𝑤𝑎𝑙𝑙

15

875

880

885

890

895

1985 1990 1995 2000 2005 2010 2015 2020

Neu

tro

n l

ifet

ime

[s]

Experiment publication

material bottle not used magnetic bottle beamUCNtau

Page 15: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

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Motivation for Nab

Determination of ratio 𝜆 = 𝑔𝐴 𝑔𝑉 from

𝐴 = −2 Re 𝜆 + 𝜆 2 1 + 3 𝜆 2 or

𝑎 = 1 − 𝜆 2 1 + 3 𝜆 2 :

−1.30 −1.28 −1.26 −1.24

UCNA (2010) ( )

PERKEO II (1997) ( )

Stratowa (1978)

PERKEO I (1986)

Liaud (1997)

( ) PERKEO II (2002)

PERKEO II (2013)

UCNA (2013) ( )

Mostovoi (2001)

Yerozolimskii (1997)

Byrne (2002)

My average:

𝜆 = −1.2756(11)

Δ𝜆 𝜆 = 0.03%

(Nab goal)

𝜆 = 𝑔𝐴/𝑔𝑉

aCORN (2017)

UCNA (2017)

Page 16: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

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Motivation for Nab

Most recent 2+1+1 flavor Lattice-QCD result from

PNDME: T. Bhattacharya et al., PRD 94, 054508 (2016)

Note: 𝜆 should be fixed by standard model.

However, precision of its calculation from

first principles is insufficiently precise:

PNDME’16

LHPC’12

LHPC’10

RBC/UKQCD’08

Lin/Orginos’07

RQCD’14

QCDSF/UKQCD’13

ETMC’15

CLS’12

RBC’08

1.00 1.25 1.50 1.75

𝑁𝑓=2

𝑁𝑓=2+1

𝑁f=

2+1+1 𝜆 = 𝑔𝐴/𝑔𝑉

Determination of ratio 𝜆 = 𝑔𝐴 𝑔𝑉 from

𝐴 = −2 Re 𝜆 + 𝜆 2 1 + 3 𝜆 2 or

𝑎 = 1 − 𝜆 2 1 + 3 𝜆 2 :

−1.30 −1.28 −1.26 −1.24

UCNA (2010) ( )

PERKEO II (1997) ( )

Stratowa (1978)

PERKEO I (1986)

Liaud (1997)

( ) PERKEO II (2002)

PERKEO II (2013)

UCNA (2013) ( )

Mostovoi (2001)

Yerozolimskii (1997)

Byrne (2002)

My average:

𝜆 = −1.2756(11)

Δ𝜆 𝜆 = 0.03%

(Nab goal)

𝜆 = 𝑔𝐴/𝑔𝑉

aCORN (2017)

UCNA (2017)

Page 17: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

7

Motivation for Nab

Most recent 2+1+1 flavor Lattice-QCD result from

PNDME: T. Bhattacharya et al., PRD 94, 054508 (2016)

Note: 𝜆 should be fixed by standard model.

However, precision of its calculation from

first principles is insufficiently precise:

PNDME’16

LHPC’12

LHPC’10

RBC/UKQCD’08

Lin/Orginos’07

RQCD’14

QCDSF/UKQCD’13

ETMC’15

CLS’12

RBC’08

1.00 1.25 1.50 1.75

𝑁𝑓=2

𝑁𝑓=2+1

𝑁f=

2+1+1 𝜆 = 𝑔𝐴/𝑔𝑉

Determination of ratio 𝜆 = 𝑔𝐴 𝑔𝑉 from

𝐴 = −2 Re 𝜆 + 𝜆 2 1 + 3 𝜆 2 or

𝑎 = 1 − 𝜆 2 1 + 3 𝜆 2 :

−1.30 −1.28 −1.26 −1.24

UCNA (2010) ( )

PERKEO II (1997) ( )

Stratowa (1978)

PERKEO I (1986)

Liaud (1997)

( ) PERKEO II (2002)

PERKEO II (2013)

UCNA (2013) ( )

Mostovoi (2001)

Yerozolimskii (1997)

Byrne (2002)

My average:

𝜆 = −1.2756(11)

Δ𝜆 𝜆 = 0.03%

(Nab goal)

𝜆 = 𝑔𝐴/𝑔𝑉

aCORN (2017)

UCNA (2017)

2. Goal: Test of unitarity of Cabibbo-

Kobayashi-Maskawa (CKM) matrix from

𝑉𝑢𝑑2𝜏𝑛 1 + 3𝜆2 = 4908.7 19 s and

𝑉𝑢𝑑2 + 𝑉𝑢𝑠

2 + 𝑉𝑢𝑏2 = 1

For neutron data to be competitive, want:

Δ𝜏𝑛 𝜏𝑛 ~0.3 s Δ𝜆 𝜆 ~0.03%

0+→0+

neutron (λ, τStorage)

neutron (λ, τBeam)

Kl3 (Nf=2+1+1)

Kl2

tau →hadrons

mirror nuclei

0.968

0.97

0.972

0.974

0.976

Vud

Page 18: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

What if the test of CKM unitarity fails?

𝑑′𝑠′𝑏′𝐷′

=

𝑉𝑢𝑑 𝑉𝑢𝑠 𝑉𝑢𝑏 𝑉𝑢𝐷𝑉𝑐𝑑 𝑉𝑐𝑠 𝑉𝑐𝑏 𝑉𝑐𝐷𝑉𝑡𝑑 𝑉𝑡𝑠 𝑉𝑡𝑏 𝑉𝑡𝐷𝑉𝐸𝑑 𝑉𝐸𝑠 𝑉𝐸𝑏 𝑉𝐸𝐷

𝑑𝑠𝑏𝐷

Like all precision measurements, a failure of the unitarity test would not point to a single cause: Various possibilities exist, among those are: 1. Heavy quarks:

2. Exotic muon decays: All determinations of 𝑉𝑢𝑑 use 𝐺𝐹 from muon lifetime. If the muon had additional decay modes (𝜇 → 𝑋 + 𝑌 +⋯), 𝐺𝐹 (and 𝑉𝑢𝑑) would be determined wrong. E.g., 𝜇+ → 𝑒+ + 𝜈 𝑒 +𝜈𝜇 (wrong

neutrinos) would be very relevant for neutrino factories.

3. (Semi-)leptonic decays of nuclei through something other than exchange of 𝑊± bosons:

𝑉𝑢𝐷2 = 1 − 𝑉𝑢𝑏

2 − 𝑉𝑢𝑠2 − 𝑉𝑢𝑑

2

W. Marciano, A. Sirlin, PRL 56, 22 (1986) P. Langacker, D. London, PRD 38, 886 (1988)

K.S. Babu and S. Pakvasa, hep-ph/0204236

Specific models: E.g. W. Marciano, A. Sirlin, PRD 35, 1672 (1987). R. Barbieri et al., PLB 156, 348 (1985) K. Hagiwara et al., PRL 75, 3605 (1995) A. Kurylov, M. Ramsey-Musolf, PRL 88, 071804 (2000) 12

Energy scale of new physics: Λ ≥ 11 TeV V. Cirigliano et al., NPB 830, 95 (2010)

Page 19: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

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Other searches for Beyond Standard Model Physics: S,T interactions (fermions with “wrong”

helicity), e.g. through W’ bosons; weak magnetism; second class currents; …

LHC-Search for 𝑝𝑝 → 𝑒 + 𝜈 + other stuff and 𝑝𝑝 → 𝑒 + 𝑒 + other stuff

Scalar(S) and tensor(T) interactions in beta decay

LHC:

8 TeV, 20 fb-1

Low-energy experiments (mostly 0+ → 0+,

𝜋 → 𝑒𝜈𝛾); 𝑔𝑆,𝑇 from quark model

Low-energy experiments,

𝑔𝑆,𝑇 from Lattice QCD

Low-energy experiments (add 𝑏 < 10−3

in n, 6He); 𝑔𝑆,𝑇 from quark model

Low-energy experiments,

𝑔𝑆,𝑇 from Lattice QCD

LHC:

14 TeV, 10,300 fb-1

Page 20: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

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Nab spectrometer @ FNPB @ SNS

Fundamental Neutron Physics Beamline (FNPB)

@ Spallation Neutron Source (SNS)

Cold Neutron Beam

decay volume

0 kV

0-1 kV

- 30 kV

magnetic filter

region (field

maximum)

Neutron

beam

TOF region

(low field)

4 m flight path skipped

1 m flight path skipped

Page 21: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

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Segmented

Si detector Ø 81 mm

decay volume

0 kV

0-1 kV

- 30 kV

magnetic filter

region (field

maximum)

Neutron

beam

TOF region

(low field)

4 m flight path skipped

1 m flight path skipped

Nab spectrometer operation

Page 22: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

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Segmented

Si detector Ø 81 mm

decay volume

0 kV

0-1 kV

- 30 kV

magnetic filter

region (field

maximum)

Neutron

beam

TOF region

(low field)

4 m flight path skipped

1 m flight path skipped

Original configuration: D. Počanić, S. Baeßler, D. Bowman, V. Cianciolo, G. Greene, S. Penttilä et al., NIM A 611, 211 (2009)

Asymmetric configuration: S. Baeßler, D. Počanić, D. Bowman, S. Penttilä et al., arXiv:1209.4663

Nab spectrometer operation

• Measurement of 𝐸𝑒,𝑘𝑖𝑛 and tp for each event; protons

only in upper detector

→ 1 tp2 gives an estimate for 𝑝𝑝

2, magnetic field

shape gives a narrow detector response function

• Long TOF region improves proton TOF resolution

• Two detector geometry allows to suppress electron

backscattering

Page 23: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

Nab spectrometer principle: measurement of Ee and tp

16

decay volume

0 kV

0-1 kV

- 30 kV

magnetic filter

region (field

maximum)

Neutron

beam

TOF region

(low field)

4 m flight path skipped

1 m flight path skipped

• Measurement of 𝐸𝑒,𝑘𝑖𝑛 and tp for each event; protons

only in upper detector

→ 1 tp2 gives an estimate for 𝑝𝑝

2, magnetic field

shape gives a narrow detector response function

• Long TOF region improves proton TOF resolution

• Two detector geometry allows to suppress electron

backscattering

Proton Trajectory

Magnetic Field

Adia

bat

ic

conver

sion

𝑝∥

𝑝⊥

𝑝∥

𝑝⊥

Page 24: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

Electron energy measurement with backscattering

suppression

detected Ee [keV]

Yie

ld

1

10 1

10 2

10 3

10 4

10 5

0 50 100 150 200 250 300

detected Ee for e- in lower detector

detected Ee with only lower detector

Detector response for

incoming Ee = 300 keV

• Measurement of 𝐸𝑒,𝑘𝑖𝑛 and tp for each event; protons

only in upper detector

→ 1 tp2 gives an estimate for 𝑝𝑝

2, magnetic field

shape gives a narrow detector response function

• Long TOF region improves proton TOF resolution

• Two detector geometry allows to suppress electron

backscattering

decay volume

0 kV

0-1 kV

- 30 kV

magnetic filter

region (field

maximum)

Neutron

beam

TOF region

(low field)

4 m flight path skipped

1 m flight path skipped

17

Page 25: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

18

Nab data analysis

𝐸𝑒,𝑘𝑖𝑛 = 450 keV

cos 𝜃𝑒𝜈 𝑝𝑝2 = +1

1 + 𝑎𝑝𝑒𝐸𝑒

cos 𝜃𝑒𝜈 𝑝𝑝2

pp2 [MeV2/c2]

pp2 d

istr

ibuti

on

0.0 0.5 1.0 1.5

cos 𝜃𝑒𝜈 𝑝𝑝2 = −1

Page 26: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

18

Full GEANT4 spectrometer simulation:

Nab data analysis

𝑡𝑝 =𝑚𝑝 ∙ spectrometer length

𝑝𝑝−component along 𝐵

𝐸𝑒,𝑘𝑖𝑛 = 450 keV

cos 𝜃𝑒𝜈 𝑝𝑝2 = +1

1 + 𝑎𝑝𝑒𝐸𝑒

cos 𝜃𝑒𝜈 𝑝𝑝2

pp2 [MeV2/c2]

pp2 d

istr

ibuti

on

0.0 0.5 1.0 1.5

cos 𝜃𝑒𝜈 𝑝𝑝2 = −1

0 0.002 0.004 0.006

Yie

ld

Inverse squared proton TOF 1 𝑡𝑝2 [1/μs2]

0

4000

8000

12000

𝐸𝑒,𝑘𝑖𝑛 = 450 keV

𝐸𝑒,𝑘𝑖𝑛 = 300 keV

𝐸𝑒,𝑘𝑖𝑛 = 150 keV

𝐸𝑒,𝑘𝑖𝑛 = 600 keV

𝐸𝑒,𝑘𝑖𝑛 = 750 keV

Page 27: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

18

Data analysis: Use edge to determine or verify the spectrometer TOF response function.

Then, use central part to determine slope and

correlation coefficient a.

Full GEANT4 spectrometer simulation:

Nab data analysis

𝑡𝑝 =𝑚𝑝 ∙ spectrometer length

𝑝𝑝−component along 𝐵

𝐸𝑒,𝑘𝑖𝑛 = 450 keV

cos 𝜃𝑒𝜈 𝑝𝑝2 = +1

1 + 𝑎𝑝𝑒𝐸𝑒

cos 𝜃𝑒𝜈 𝑝𝑝2

pp2 [MeV2/c2]

pp2 d

istr

ibuti

on

0.0 0.5 1.0 1.5

cos 𝜃𝑒𝜈 𝑝𝑝2 = −1

0 0.002 0.004 0.006

Yie

ld

Inverse squared proton TOF 1 𝑡𝑝2 [1/μs2]

0

4000

8000

12000

𝐸𝑒,𝑘𝑖𝑛 = 450 keV

𝐸𝑒,𝑘𝑖𝑛 = 300 keV

𝐸𝑒,𝑘𝑖𝑛 = 150 keV

𝐸𝑒,𝑘𝑖𝑛 = 600 keV

𝐸𝑒,𝑘𝑖𝑛 = 750 keV

Page 28: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

19

Statistical uncertainty budget for 𝒂 coefficient

Planned statistical uncertainty budget:

3.6×108 events can be detected in 6 weeks (Decay volume V = 246 cm3, 12.7% of decay

protons go to upper detector, 50% efficiency in use of beam time, 1600 decays/s),

corresponding to Δ𝑎

𝑎 𝑠𝑡𝑎𝑡∼ 2.4 ⋅ 10−3 for this period.

→ 𝚫𝒂

𝒂 𝒔𝒕𝒂𝒕∼ 𝟕 ⋅ 𝟏𝟎−𝟒 can be reached, but it requires 70 weeks of data taking.

lower 𝑬𝐞,𝒌𝒊𝒏 cutoff none 100 keV 100 keV 100 keV

upper 𝒕𝒑 cutoff none none 40 μs 30 μs

𝚫𝐚 (𝑵, 𝒂, 𝒃 variable) 2.4/√N 2.5/√N 2.7/√N 3.0/√N

𝚫𝐚 (𝑵, 𝒂, 𝒃, 𝑬𝒄𝒂𝒍, 𝑳 variable) 2.6/√N 2.7/√N 2.9/√N 3.2/√N

𝚫𝐚 (𝑵, 𝒂, 𝒃, 𝑬𝒄𝒂𝒍, 𝑳 variable, inner 75% of data) 3.4/√N 3.5/√N 3.8/√N 4.3/√N

As above, 10% bg 4.2/√N 4.4/√N 4.6/√N 5.0/√N

Compare to Δ𝑎 𝑎 = 4 % of best existing experimental results (ACORN 2017),

and ∼ 1 % planned for ACORN and aSPECT

Page 29: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

20

Experimental parameter Main specification Systematic

uncertainty Δa/a

Magnetic field

... curvature at pinch Δ𝛾/𝛾 = 2% with 𝛾 = 𝑑2 𝐵𝑧(𝑧)/𝑑𝑧2/𝐵𝑧(0) 5.3·10-4

… ratio rB = BTOF/B0 (Δ𝑟𝐵)/𝑟𝐵 = 1% 2.2·10-4

… ratio rB,DV = BDV/B0 (Δ𝑟𝐵,𝐷𝑉)/𝑟𝐵,𝐷𝑉 = 1% 1.8·10-4

Length of the TOF region none

Electrical potential inhomogeneity:

… in decay volume / filter region 𝑈𝐹 − 𝑈𝐷𝑉 < 10 mV 5·10-4

… in TOF region 𝑈𝐹 − 𝑈𝑇𝑂𝐹 < 200 mV 2.2·10-4

Neutron Beam:

… position Δ𝑧𝐷𝑉 < 2 mm 1.7·10-4

… profile (including edge effect) Slope at edges < 10%/cm 2.5·10-4

… Doppler effect small

… Unwanted beam polarization 𝑃𝑛 ≪ 10−4 can be small

Adiabaticity of proton motion 1·10-4

Detector effects:

… Electron energy calibration Δ𝐸𝑒,𝑘𝑖𝑛 < 0.2 keV 2·10-4

… Shape of electron energy response fraction of events in tail to 1% 5.7·10-4

… Proton trigger efficiency 𝜖𝑝 < 100 ppm/keV 3.4·10-4

… TOF shift due to detector/electronics Δ𝑡𝑝 < 0.3 ns 3·10-4

Residual gas 𝑝 < 2 ⋅ 10−9 torr 3.8·10-4

Background / Accidental coincidences small

Sum 1.2·10-3

Systematic uncertainty budget for 𝒂 coefficient

Page 30: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

Goal: 𝚫𝐛 ≤ 𝟑 ⋅ 𝟏𝟎−𝟑

Systematic uncertainties:

1. Electron energy determination

2. Most stringent requirement: Non-linearity of 0.01%

3. Background

2% of events in tail

(deadlayer, bremsstrahlung) Y

i e l d

1

10 1

10 2

10 3

10 4

10 5

detected Ee [keV]

0 50 100 150 200 250 300

Detector response to decay

electron with 𝐸𝑒 = 300 keV

decay volume

0 kV

- 30 kV

+1 kV

magnetic filter

region (field

maximum)

Neutron

beam

TOF region

(low field)

4 m flight path skipped

1 m flight path skipped

0 V

-30 kV

Electron spectrum:

0 2 0 0 4 0 0 6 0 0 8 0 0

𝐸𝑒,𝑘𝑖𝑛 (keV)

Y i e

l d (

a r b

. u

n i t

s )

b = +0.1

SM

The measurement of the Fierz Interference Term 𝒃

21

𝑑Γ ∝ 𝜚 𝐸𝑒 1 + 𝑎𝑝𝑒𝐸𝑒

cos 𝜃𝑒𝜈 + 𝑏𝑚𝑒

𝐸𝑒

n

e-

𝜈𝑒

p 𝜃𝑒𝜈

Page 31: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

Goal: 𝚫𝐛 ≤ 𝟑 ⋅ 𝟏𝟎−𝟑

Systematic uncertainties:

1. Electron energy determination

2. Most stringent requirement: Non-linearity of 0.01%

3. Background

2% of events in tail

(deadlayer, bremsstrahlung) Y

i e l d

1

10 1

10 2

10 3

10 4

10 5

detected Ee [keV]

0 50 100 150 200 250 300

Detector response to decay

electron with 𝐸𝑒 = 300 keV

Electron spectrum:

0 2 0 0 4 0 0 6 0 0 8 0 0

𝐸𝑒,𝑘𝑖𝑛 (keV)

Y i e

l d (

a r b

. u

n i t

s )

b = +0.1

SM

The measurement of the Fierz Interference Term 𝒃

21

𝑑Γ ∝ 𝜚 𝐸𝑒 1 + 𝑎𝑝𝑒𝐸𝑒

cos 𝜃𝑒𝜈 + 𝑏𝑚𝑒

𝐸𝑒

n

e-

𝜈𝑒

p 𝜃𝑒𝜈

Page 32: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

22

Status of Nab experiment

Fundamental Neutron Physics Beamline

@ Spallation Neutron Source

Page 33: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

22

Status of Nab experiment

Magnet system tested successfully at manufacturer, is

expected to arrive at ORNL this Friday.

Fundamental Neutron Physics Beamline

@ Spallation Neutron Source

Page 34: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

22

Status of Nab experiment

Magnet system tested successfully at manufacturer, is

expected to arrive at ORNL this Friday.

Fundamental Neutron Physics Beamline

@ Spallation Neutron Source

𝐵 measured 𝐵 calculated

-200 -100 0 100 300 400 500 600

1

2

3

4

𝑧/cm 200

Page 35: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

Nab (and UCNB) detector properties

• DAQ system (A. Sprow, C. Crawford et al.): All

waveforms recorded. Risetime ∼ 40 ns, fall time

∼ 4 µs.

• Energy resolution a few keV, threshold ≤ 10 keV

• Noise low enough to detect protons (average

deposited energy: 18 keV)

• Bad pixels need investigation

Ø 81 mm

Back side

LabVIEW controller C++ coincidence logic

LabVIEW FPGA low-threshold trapezoid trigger on ADC Optical fiber bus, clock & sync 23

Page 36: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

Nab (and UCNB) detector properties

• DAQ system (A. Sprow, C. Crawford et al.): All

waveforms recorded. Risetime ∼ 40 ns, fall time

∼ 4 µs.

• Energy resolution a few keV, threshold ≤ 10 keV

• Noise low enough to detect protons (average

deposited energy: 18 keV)

• Bad pixels need investigation

LANL test run with Ce-139 source, Analysis H. Li

Pulse height [ADC reading]

500 1000 1500 2000 2500 3000 3500

Even

ts

0

5

10

15

20

25

30

35

40

45

γ: 33 keV

Ce-139 source

β: 27 keV

β: 127 keV

β: 160 keV

Ø 81 mm

Back side

23

Page 37: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

Nab (and UCNB) detector properties

• DAQ system (A. Sprow, C. Crawford et al.): All

waveforms recorded. Risetime ∼ 40 ns, fall time

∼ 4 µs.

• Energy resolution a few keV, threshold ≤ 10 keV

• Noise low enough to detect protons (average

deposited energy: 18 keV)

• Bad pixels need investigation

LANL test run with Ce-139 source, Analysis H. Li

Pulse height [ADC reading]

500 1000 1500 2000 2500 3000 3500

Even

ts

0

5

10

15

20

25

30

35

40

45

γ: 33 keV

Ce-139 source

β: 27 keV

β: 127 keV

β: 160 keV

Ø 81 mm

Back side

Electron, ~ 100 keV, followed by

Proton, ~18 keV, in neighboring pixel

23

Page 38: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

Main electrode system: Simulation of the effect of openings

Symmetry axis Electric potential [V]

x

z

Assumption for simulation: Potential of bore tube different by 1 V from electrodes

24

Page 39: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

25

Top and bottom part of electrode system, before coating:

Parts are in hand, and are awaiting cleaning and coating.

Main electrode system: Fabrication

Symmetry axis

Page 40: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

26

Electrode surface coating: What is the issue?

Most undergraduate textbooks: No electric field in empty hole inside conductor…

Page 41: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

26

Electrode surface coating: What is the issue?

...and I have no objection if the conductor is homogenous. However, if not:

- +

E field

Most undergraduate textbooks: No electric field in empty hole inside conductor…

Page 42: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

26

_ _ _

+

+ +

Φ1

EF,1

V

Material 1 Material 2

Φ2

EF,2 Φ1 Φ2

EF,1 EF,2

Material 1 Material 2

VC

Electrode surface coating: What is the issue?

...and I have no objection if the conductor is homogenous. However, if not:

- +

E field

Most undergraduate textbooks: No electric field in empty hole inside conductor…

Page 43: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

26

_ _ _

+

+ +

Φ1

EF,1

V

Material 1 Material 2

Φ2

EF,2 Φ1 Φ2

EF,1 EF,2

Material 1 Material 2

VC

Electrode surface coating: What is the issue?

...and I have no objection if the conductor is homogenous. However, if not:

- +

E field

Most undergraduate textbooks: No electric field in empty hole inside conductor…

Consequence: Need to establish that electric field is known, or known to be absent, in flight path.

Page 44: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

0 50 100 150 200 250 300 350 0

5

10

15

20

25

30

35

40

Angle [°]

Hei

gh

t [m

m]

4900

4950

5000

5050

5100

Work Function [meV]

Work function measurements

In collaboration with Prof. I. Baikie, KP Technologies 27

Page 45: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

29

Main electrode system

We previously identified two coating methods that provide good homogeneity of the work function, and are compatible with UHV conditions. A copper/silver spray (which was good always when the coating looked good eye) and a graphite spray (which was mostly good when the coating looked good by eye). We decided to go with copper/silver.

But: Manufacturer changed recipe:

OLD AND GOOD NEW

Present status of testing: • New spray seems to be equally good in terms of work function

uniformity (𝜎 < 10 meV) • Vacuum test so far inconclusive • Cryogenic testing not yet done Next step: Align main electrode substrates, do coating, characterize

WF / meV

0.0 0.5 1.0 1.5 2.0 2.5 0.0

0.5

1.0

1.5

2.0

2.5

X [cm]

Y [cm

]

4600

4640

4680

4720

4760

4800

Page 46: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

a Department of Physics, Arizona State University, Tempe, AZ 85287-1504 b Department of Physics, University of Virginia, Charlottesville, VA 22904-

4714 c Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 d Department of Physics and Astronomy, University of Sussex, Brighton

BN19RH, UK e Department of Chemistry and Physics, University of Tennessee at

Chattanooga, Chattanooga, TN 37403 f Department of Physics and Astronomy, University of Kentucky,

Lexington, KY 40506 g Department of Physics, University of Manitoba, Winnipeg, Manitoba, R3T

2N2, Canada

h KIT, Universität Karlsruhe (TH), Kaiserstraße 12, 76131 Karlsruhe,

Germany i Department of Physics and Astronomy, University of Tennessee,

Knoxville, TN 37996 j Department of Physics and Astronomy, University of South Carolina,

Columbia, SC 29208 k Los Alamos National Laboratory, Los Alamos, NM 87545 l Department of Physics, University of Winnipeg, Winnipeg, Manitoba

R3B2E9, Canada m Department of Physics, North Carolina State University, Raleigh, NC

27695-8202 n Universidad Nacional Autónoma de México, México, D.F. 04510, México o University of Michigan, Ann Arbor, MI 48109

The Nab collaboration

R. Alarcona, S.B.b,c (Project Manager), S. Balascutaa, L. Barrón Palosn, K. Bassi, N. Birgei, A. Blosef, D.

Borissenkob, J.D. Bowmanc (Co-Spokesperson), L. Broussardc, A.T. Bryantb, J. Byrned, J.R. Calarcoc,i, T.

Chuppo, T.V. Ciancioloc, J.N. Clementb, C. Crawfordf, W. Fanb, W. Farrarb, N. Fomini, E. Frležb, J. Fryb,

M.T. Gerickeg, M. Gervaisf, F. Glückh, G.L. Greenec,i, R.K. Grzywaczi, V. Gudkovj, J. Hamblene, C.

Hayesm, C. Hendruso, T. Itok, H. Lib, C.C. Lub, M. Makelak, R. Mammeig, J. Martinl, M. Martineza, D.G.

Matthewsf, P. McGaugheyk, C.D. McLaughlinb, P. Muellerc, D. van Pettenb, S.I. Penttiläc (On-site

Manager), D. Počanićc (Co-Spokesperson), G. Randalla, N. Roaneb, C.A. Roysem, K.P. Rykaczewskic, A.

Salas-Baccib, E.M. Scotti, S.K. Sjuek, A. Smithb, E. Smithk, A. Sprowf, E. Stevensb, J. Wexlerm, R.

Whiteheadi, W.S. Wilburnk, A.Youngm, B.Zeckm

30

Main project funding:

Active and recent collaborators:

Page 47: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

Goal: 𝚫𝐛 < 𝟑 ⋅ 𝟏𝟎−𝟑

Systematic uncertainties:

1. Electron energy determination

2. Background

2% of events in tail

(deadlayer, bremsstrahlung) Y

i e l d

1

10 1

10 2

10 3

10 4

10 5

detected Ee [keV]

0 50 100 150 200 250 300

Detector response to decay

electron with 𝐸𝑒 = 300 keV

decay volume

0 kV

- 30 kV

+1 kV

magnetic filter

region (field

maximum)

Neutron

beam

TOF region

(low field)

4 m flight path skipped

1 m flight path skipped

0 V

-30 kV

Electron spectrum:

0 2 0 0 4 0 0 6 0 0 8 0 0

E e , k i n ( k e V )

Y i e

l d (

a r b

. u

n i t

s )

b = +0.1

SM

The determination of the Fierz Interference term 𝒃

31

𝑑Γ ∝ 𝜚 𝐸𝑒 1 + 𝑎𝑝𝑒𝐸𝑒

cos 𝜃𝑒𝜈 + 𝑏𝑚𝑒

𝐸𝑒

n

e-

𝜈𝑒

p 𝜃𝑒𝜈

Page 48: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

Goal: 𝚫𝐛 < 𝟑 ⋅ 𝟏𝟎−𝟑

Systematic uncertainties:

1. Electron energy determination

2. Background

2% of events in tail

(deadlayer, bremsstrahlung) Y

i e l d

1

10 1

10 2

10 3

10 4

10 5

detected Ee [keV]

0 50 100 150 200 250 300

Detector response to decay

electron with 𝐸𝑒 = 300 keV

Electron spectrum:

0 2 0 0 4 0 0 6 0 0 8 0 0

E e , k i n ( k e V )

Y i e

l d (

a r b

. u

n i t

s )

b = +0.1

SM

The determination of the Fierz Interference term 𝒃

31

𝑑Γ ∝ 𝜚 𝐸𝑒 1 + 𝑎𝑝𝑒𝐸𝑒

cos 𝜃𝑒𝜈 + 𝑏𝑚𝑒

𝐸𝑒

n

e-

𝜈𝑒

p 𝜃𝑒𝜈

Page 49: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

• Main uncertainties in previous best experiment (PERKEO II): statistics, detector, background, polarization

• Superior detector energy resolution, good enough time resolution

• Keep coincidences to improve background

• Statistics @ SNS or NIST is an issue for 𝐴

• Polarization measurement seems manageable (XSM or He-3)

Segmented

Si detector

magnetic filter

region (field

maximum)

TOF region

(field r B · B 0 )

Polarizer:

Supermirror

or Helium-3

AFP

Spin

Flipper

• Beta asymmetry (to extract 𝐴) :

reflect all protons to bottom detector,

use top detector for electrons

• Proton asymmetry (to extract 𝐵):

detect protons at top

Planned continuation (SNS or NIST): Polarized neutrons

32

Polarimetry with

Helium-3

Page 50: observables with the Nab spectrometernab.phys.virginia.edu/slides/Nab_UKy_Baessler_2018.pdfMotivation for Nab Most recent 2+1+1 flavor Lattice-QCD result from PNDME: T. Bhattacharya

• The Nab collaboration is setting up the Nab spectrometer at the Spallation Neutron Source. Start of commissioning planned in summer 2018. Until tomorrow, the big reason for the delay has been the magnet.

• Goal: Δa/a ≤ 10-3 and Δb ≤ 3·10-3. This is in line with the requirements for standard model tests:

1) Compare renormalization constant 𝜆 = 𝑔𝐴/𝑔𝑉 to direct determination on lattice.

2) Unitarity test of Cabbibo-Kobayashi-Maskawa matrix in first row.

3) Search for new physics at above the TeV scale that manifests itself as S,T interaction.

Summary

33 Thank you for the attention!