Measurement of Parity-Violation in Cold Neutron Capture M. Dabaghyan for the NPDGamma Collaboration...

Measurement of Parity-Violation in Cold Neutron Capture

Mikayel Dabaghyan for the NPDGamma Collaboration

M. Dabaghyan for the NPDGamma Collaboration The n + p → d + γ Experiment at LANL

Outline

1. Hadronic Weak Interaction

What…

Why…

How…

2. Experiment

Hardware and measurements

3. Analysis and Results

Asymmetry, Errors

4. Summary and Outlook

Present and Future


Why…

Z0 = 91.2 GeV W± = 80.4 GeV

range - ≤ 2×103 fm . π, ρ, ω ≤ 300 MeV.

range - ≤ 1 fm .

Bosons are too heavyNN

N N

Z0, W± ?ρ, ω, π±


Explore weak interaction at low energies.

The ΔI = ½ rule: Γ(Ks0 → π0π0) » Γ(K+ → π+π0).

Probe strong interaction at low energies.

Study the weak interaction between hadrons

Weak Interaction

μ → e- + υμ + υe

n → p + e- + υe

n + p → n + p

Weak processes

μ-

νμW-

e-νe

d

u

W-

e-νe

dun

dup

u

d

W+

udp

udn duu

dud n

p

π+


Weak Interaction

ΔS = 0 : strong

Use Parity!

Weak vs. Strong NN

N N

π±, ρ, ω PCPV𝑺𝑻𝑹𝑶𝑵𝑮𝒘𝒆𝒂𝒌 ~ 𝟏𝟎𝟕


Parity Violation

Two nucleon system: n + p → d + γ

ΔS = 0, ΔI = 1 channel

Study the weak interaction between hadrons

real world

mirror world

P(x) = - x P(y) = - y P(z) = - z

Parity

P(sn) = sn P(kγ) = - kγ


Why PV in n+p → d+γ ?

Parity Violation|𝜓𝐽=0𝑖𝑛𝑖𝑡𝑖𝑎𝑙 =ۄ | 𝑆01 ,1 +ۄ 𝛼0| 𝑃03 ,1 𝜓𝐽=1𝑖𝑛𝑖𝑡𝑖𝑎𝑙| ۄ =ۄ | 𝑆13 ,0 +ۄ 𝛼0| 𝑃11 ,0 +ۄ 𝛼1| 𝑃13 ,1 𝜓𝐽=1𝑓𝑖𝑛𝑎𝑙| ۄ | = ۄ 𝑆13 ,0 +ۄ 𝛼0| 𝑃11 ,0 +ۄ 𝛼1| 𝑃13 ,1 ۄ


3S1, I=0 3P1, I=1 1P1, I=0

3S1, I=0 3P1, I=1 1P1, I=0 1S0, I=1 3P0, I=1

M1

E1E1

M1

E1

E1E1

E1E1

Hindered transition

n + p excited and ground states

How…

n p d

ϑ

𝑑𝜎𝑑Ω= 1+ 𝐴𝛾 ∙𝑐𝑜𝑠ሺ𝜗ሻ

𝐴𝛾 = 2ξ2∙ 𝐸1ۃ ۄ𝑀1ۃ ۄ


-2 -1 0 1 2 3 4

Goal:DDH: 𝑯𝝅𝟏,𝑯𝝆𝟎,𝑯𝝆𝟏,𝑯𝝆𝟏′ ,𝑯𝝆𝟐,𝑯𝝎𝟎,𝑯𝝎𝟏 𝑯𝝅𝟏 𝑨𝜸 = −𝟎.𝟎𝟒𝟓∙

DDH: Desplanques, Donoghue, Holstein, Annals of Physics 124, 1980, 449.M. Dabaghyan for the NPDGamma Collaboration The n + p → d + γ Experiment at LANL

DDH TheoreticalEstimate

n+p→d+γCavaignac et al.Phys.Lett.B., 67148, 1977

18FEvans et al.; Bini et al.Phys.Rev.Lett. 55

133CsWood et al.Science 275, 1753, 1997 Flambaum and MurrayPhys. Rev. C 56, 1641, 1997

Compound NucleiBowman et al. LANL 2002

-2 -1 0 1 2 3 4

Hπ1 so far…

Hπ1(×10-6)

0.5× 10−8 𝑜𝑟𝑑𝑒𝑟 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑚𝑒𝑛𝑡

Hπ1(×10-6)

Experiment - Overview


Flight Path

Neutron Guide

Shielding

Holding Field

Beam Monitors

Detector Array

RF Spin Flipper

Polarizer

Analyzer

Hydrogen Target

Compound Targets


800 MeV Protons from ½ mile linac (~100μA) Protons hit the W spallation target to produce neutrons Neutrons are moderated by LH2 to ~100meV 20Hz pulses – 50ms frames – time of flight informationNeutrons are delivered by an ~20m “supermirror” guide

Flight – Path

Experiment – Flight Path

Apparatus


𝜆= ℎ𝑡𝑚𝐿

Apparatus – Flight Path Length


Bragg Transmission𝑛𝜆= 2𝑑∙𝑠𝑖𝑛𝜃

Flight Path Length𝐿0 = 21.10± 0.03 𝑚 𝐿1 = 21.11± 0.03 𝑚 𝐿2 = 21.49± 0.03 𝑚 𝐿3 = 22.81± 0.04 𝑚

L1 L2 L3

Tn

3π acceptance

4 rings of 15×15×15 cm3 CsI crystals

VPD: insensitive to magnetic field

High event rate: use current mode

Low-noise preamps: < 0.1 mV RMS

Operate at counting statistics

95% γ’s stopped in crystals

Aligned with B0 better than 1o

Measure Neutron Flux

Experiment – γ-ray Detectors


Experiment – Polarizer

3He cellUnpolarized

Neutrons

Polarized

Neutrons

Helmholtz Coils

Polarized Laser Light

12 cm in diameter, 5 cm thick

4.9 atm·cm

Relaxation time of 500 hrs

Typical polarization ~ 55%

Boo-Boo


- 3 barns

- 5333 barns!

Transmission

3He as a Neutron Spin Filter

n 3He

n 3He

𝑻↑↓ = 𝒆− 𝒏𝒍𝝈∙ሺ𝟏∓𝑷𝟑ሻ 𝑻𝒏 = 𝒄𝒐𝒔𝒉(𝒏𝝈𝒍𝑷𝟑) 𝑷𝒏 = ඨ𝟏 −൬

𝑻𝟎𝑻𝒏൰𝟐

Experiment – Polarizer


Tn/

To

TOF [ms]

Experiment – Polarizer Performance


Experiment – Analyzer

Measure Neutron Beam polarization

Measure RFSF efficiency

Optimize RFSF parameters

Function



PEEK/glass components

Uniform Temperature (165o C)

Non-metallic parts

Polarized light from 2 sides

30 W Laser

Oven

Laser Optics


Transport Suitcase 2.5 cm in diameter

6.2 atm·cm

Relaxation time of 130 hrs

Typical polarization ~ 47%


Helmholtz coils create 12 Gauss fieldRunning on batteriesLoss of polarization: ~10%/hr

TS - 12


Experiment – RF Neutron Spin Flipper

Limit systematic effects

2 mm Al housing enough to isolate RF field

20 Hz pulse pattern: ↑↓↓↑↓↑↑↓

Resonant Radio Frequency Spin Rotator


Optimization is performed using the Analyzer

Normalized population difference between ↑↓

RFSF Efficiency Optimization

RFSF – Parameter Optimization


OffNo=No++No- N1=N1++N1- N1=N1++N1- N2=N2++N2-

Pol Anl

RFSFOn

RFSF

OffPol AnlNo=No++No- N1=N1++N1- N1=N1++N1- N2=N2++N2-

RFSF

OffPol AnlNo=No++No- N1=N1++N1- N1=N1++N1- N2=N2++N2-

RFSF

OnPol AnlNo=No++No- N1=N1++N1- N’1=N’

1++N’1- N’

2=N’2++N’

2-

NMR Flip – 100%

Compare NMR and RFSF flips

Scan off-axis by moving

collimator+analyzer+M3

εon axis = 99.69 ± 0.12

ε1.3” beam left = 94.06 ± 0.11

ε1.3” beam right = 93.83 ± 0.11

RFSF Efficiency Measurement

RFSF – Efficiency

൫𝑇𝑜𝑓𝑓↑↑ − 𝑇𝑜𝑛↑↑൯൫𝑇𝑜𝑓𝑓↑↑ − 𝑇𝑜𝑓𝑓↓↑ ൯ൗ� = 1+ 𝜀2


PV in Compound Nuclei – Not so simple, so why bother?

Some materials are in the beamline – Al, Cu, In …

Reason 1.

Study PV in nuclear targets – has not been done for this A-range

Reason 2.


Large capture cross-section

Small scattering cross-section

Small incoherent cross-section

Close level spacing

Selection Criteria

Compound Solid Targets

Al

Mn

Co

Cu

Ti

Cl

In

V

Sc

List of Solid Targets


Compound Solid Targets


Targets – LH2

LH2 Target

Aluminum cylinder

Diameter of 26.62 cm

16L of LH2

kept at ~ 17 K

σcap « σscatt

Para-H2: capture and coherent scatter

Ortho-H2: coherent and incoherent scatter

𝜎𝑖𝑛𝑐𝑜ℎ𝑜𝑟𝑡ℎ𝑜 = 20.052± 0.014 𝑏 𝜎𝑐𝑜ℎ𝑜𝑟𝑡ℎ𝑜 = 0.439± 0.003 𝑏

Cross sections


Cro

ss S

ectio

n

meV

σsortho

σspara

σa

Ortho-Para conversion - 1030 hrs

Two FeO2 OPCs – 112 hrs

OPC #1

OPC #2

LH2 target

Neutron Beam

Targets – LH2

𝐾𝑂𝑃𝐶 = 6.09 %ℎ𝑟

𝐾𝑛𝑎𝑡𝑢𝑟𝑎𝑙 = 1.94 %ℎ𝑟

Ortho-to-Para Conversion


Targets – LH2

M2 M3

LH2 Full measurement:

Empty measurement:

Resulting in

Transmission Through LH2

𝑆𝑀3𝐸𝑚𝑝𝑡𝑦𝑆𝑀2𝐸𝑚𝑝𝑡𝑦 = 𝐾3𝐾2 ∙𝑇𝑜𝑡ℎ𝑒𝑟

𝑆𝑀3𝐹𝑢𝑙𝑙𝑆𝑀2𝐹𝑢𝑙𝑙 = 𝐾3𝐾2 ∙𝑇𝑜𝑡ℎ𝑒𝑟 ∙𝑇𝐻2

𝑇𝐻2 = 𝑆𝑀3𝐹𝑢𝑙𝑙 𝑆𝑀2𝐹𝑢𝑙𝑙Τ𝑆𝑀3𝐸𝑚𝑝𝑡𝑦 𝑆𝑀2𝐸𝑚𝑝𝑡𝑦ൗ�


Para: 99.98%

Data Analysis

n p d

ϑ

𝑑𝜎𝑑Ω= 1+ 𝐴𝛾 ∙𝑐𝑜𝑠ሺ𝜗ሻ


Raw Asymmetry

Physics Asymmetryθ

Data Analysis

𝐴𝛾𝑟𝑎𝑤 = 𝑈− 𝐷𝑈+ 𝐷

U

D

𝐴𝛾𝑟𝑎𝑤 = 𝐴𝛾𝑈𝐷𝐺𝑖𝑈𝐷 + 𝐴𝛾𝐿𝑅𝐺𝑖𝐿𝑅

𝐴𝛾 = 𝐴𝛾𝑟𝑎𝑤𝑃ሺ𝑡ሻ∙𝑇ሺ𝑡ሻ∙𝑆ሺ𝑡ሻ

𝑨𝜸𝒕𝒐𝒕𝒂𝒍 = σ 𝑨𝜸𝒊𝝈𝒊,𝜸𝟐𝒊σ 𝟏𝝈𝒊,𝜸𝟐𝒊 ± 𝟏

ඨσ 𝟏𝝈𝒊,𝜸𝟐𝒊

Sequence Asymmetry


Table Motion Measurements

Reconstructed Angles

Detector Geometry

RC

R

XC -R

XC

YC

Crystal

Source

𝑺ሺ𝒙,𝒚ሻ∝ 𝟏𝑹𝟐 ⇒ 𝝏𝑺𝝏𝒚ൗ�𝝏𝑺𝝏𝒙ൗ�= 𝒕𝒂𝒏ሺ𝝑ሻ


Error from Left-Right Mixing into Up-Down

Ideally cosϑ and sinϑ

Neutron absorption probability

Energy left by a γ in the crystal

Geometry Factors

Detector Geometry

𝑨𝜸′𝒓𝒂𝒘 = 𝒄𝒐𝒔𝝑𝑨𝜸𝑼𝑫+ 𝜹𝝑𝟐 𝑨𝜸𝑳𝑹൨+ 𝒔𝒊𝒏𝝑𝑨𝜸𝑼𝑫+ 𝜹𝝑𝟐 𝑨𝜸𝑳𝑹൨

𝝑′ = 𝒔𝒊𝒏−𝟏ۏێێۍ 𝑮𝑳𝑹𝒊

ට൫𝑮𝑳𝑹𝒊 ൯𝟐 +൫𝑮𝑳𝑹𝒊 ൯

𝟐ے

ۑۑې


Depolarization in the targets

Neutron Beam Depolarization𝝈𝒕𝒐𝒕 = 𝝈𝒂+𝝈𝒄+ 𝝈𝒊

𝑷𝒂 = 𝝈𝒂𝝈𝒕𝒐𝒕 ,𝑷𝒇𝒍𝒊𝒑 = 𝟏𝟑𝝈𝒊𝝈𝒄+𝝈𝒊


Backgrounds and false asymmetries

Electronic pick-up

Activation

Scattered neutrons

Frame overlap

γ’s from spallation

Few percent for solids

More for LH2

ABkg = 0

Sources of Backgrounds

𝑨𝒔𝒊𝒈 = 𝑨𝒔𝒊𝒈+𝒃𝒌𝒈൫𝑺𝒔𝒊𝒈 + 𝑺𝒃𝒌𝒈൯𝑺𝒔𝒊𝒈 = 𝑨𝒔𝒊𝒈+𝒃𝒌𝒈ሺ𝟏 + 𝜷ሻ− 𝑨𝒃𝒌𝒈𝜷

𝝈𝑨𝒔𝒊𝒈 = ටሺ𝟏 + 𝜷ሻ𝟐𝝈𝑨𝒔𝒊𝒈+𝒃𝒌𝒈𝟐 + 𝜷𝟐𝝈𝑨𝒃𝒌𝒈𝟐


Cuts

Neutron beam current

Detector sums/diff’s

Beam fluctuations

Detector saturation

Valid spin sequences

Cuts on the Data


Systematics

Multiplicative noise

Additive noise

Non-hydrogen target Aγ

Mott – Schwinger LR

Stern – Gerlach steering

Sources


Huge known UD asymmetry

Calibrate the experiment

Chlorine

𝑨𝜸𝒓𝒂𝒘 = 𝑨𝜸𝑼𝑫𝒄𝒐𝒔ሺ𝝑′ሻ+ 𝑨𝜸𝑳𝑹𝒔𝒊𝒏ሺ𝝑′ሻ Fit to

Asymmetry Results - Chlorine

AγUD = (19.62)×10-6

AγLR = (0.087)×10-6

RIN

G

4RIN

G

3RIN

G

2RIN

G

1


Aγ = (19.47 ± 2.02)×10-6

-3.0E-05

-2.0E-05

-1.0E-05

0.0E+00

1.0E-05

2.0E-05

3.0E-05

0 2.5 5 7.5 10 12.5 15 17.5 20 22.5

Aγ

raw

θdetector [rad]

Cl Data A=UD*COS(x) + LR*SIN(x)

Para-Hydrogen, Aγ

More statistics

Better knowledge of

background

Hydrogen

Asymmetry Results - Hydrogen

RIN

G

4RIN

G

3RIN

G

2RIN

G

1

Aγ = (0.95 ± 2.01)×10-7


AγUD = (1.7)×10-7

AγLR = (1.1)×10-7

-1.5E-06

-1.0E-06

-5.0E-07

0.0E+00

5.0E-07

1.0E-06

1.5E-06

0 2.5 5 7.5 10 12.5 15 17.5 20 22.5

Aγ

raw

θdetector [rad]

DATA A=UD*COS(x) + LR*SIN(x)

Results – The other targets

Co 7.7 3.5 0.7 3.6

Cu -11.9 5.8 1.1 5.9

In 6.8 3 0.6 3.1

Mn -5.3 7.8 0.5 7.8

Sc 7 2.8 0.7 2.9

Ti -6.5 3 0.6 3.1

V 1.7 6.3 0.2 6.3

Targets Aγ(×10-7) σAγ,stat(×10-7) σAγ,syst(×10-7)


σAγ,TOT(×10-7)

Summary


Aγ = (0.95 ± 2.01)×10-7

Hπ1 = (-2.1 ± 4.5)×10-6

LANL 2006, Production Phase 1

Preliminary

Cavaignac et al.Phys.Lett.B., 67

148, 1977

Aγ = (0.6 ± 1.8)×10-7

Hπ1 = (-1.4 ± 4.0)×10-6

DDH TheoreticalEstimate

n+p→d+γCavaignac et al.Phys.Lett.B., 67148, 1977

18FEvans et al.; Bini et al.Phys.Rev.Lett. 55

133CsWood et al., Science 275, 1753, 1997 Flambaum and Murray, Phys. Rev. C 56, 1641, 1997

Compound NucleiBowman et al. LANL 2002

-4 -2 0 2 4Hπ

1(×10-6)

n + p → d + γLANL 2006, Preliminary

ORNLLANLJLABUniversity of MichiganIndiana UniversityIndiana Univ. CyclotronNISTUniversity of New HampshireUniversity of TennesseeUniv. of California, BerkeleyUniv. of California, DavisUniversity of ManitobaUniversity of ArizonaHamilton CollegeNorth Carolina State Univ.JINR, Dubna, RussiaUniv. of DaytonKEK, Japan

J.D. Bowman, S. Penttila S.Wilburn.T.Ito,A. Klein,V.Yuan,A.Salas-Bacci, S.SantraR.D. Carlini T.E. Chupp, M. SharmaM. Leuschner, J. Mei, H. Nann, W.M. Snow, R.C. GillisB. LosowkiT.R. GentileF.W. Hersman, M. Dabaghyan,H. Zhu,S. Covrig, M.MasonG.L. Greene, R. MahurinS.J. Freedman, B. LaussG.S. MitchellM.T. Gericke, S. Page, D. RamsayL. Barron-Palos, S. BalascutaG.L. JonesP-N. SeoE. SharapovT. SmithT. Ino, Y. Masuda, S. Muto

The NPDγ Collaboration


Measurement of Parity-Violation in Cold Neutron Capture M. Dabaghyan for the NPDGamma Collaboration...

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