First results from the NPDGamma

experiment at the Spallation Neutron Source

Nadia Fomin

Los Alamos National Laboratory

June 1st, 2012

St. Petersburg, FL

ϑ

Outline

•NPDGamma - Hadronic weak interaction -

• Theoretical Motivation

• Experimental Setup

• Results of LANSCE run

• Current SNS run

•Aluminum, Chlorine, and for the

first time Hydrogen

ϑ

N

N N

N

Weak NN couplings are largely unknown: non-

perturbative regime makes calculations and

experiments challenging

Why do we care?

• Weak interaction is manifested in long range nuclear

interactions

• Inconsistent results from previous measurements (ex: fπ)

• weak NN couplings => allows for a quantitative interpretation

of PV phenomena at nuclear and atomic scales

• probe of QCD – nuclear properties at short range

Studying the Weak Interaction through Parity Violation

ρ,π, ω

W±,Z0

Hadronic Weak Interaction Models 1. DDH model – uses valence quarks to calculate effective PV meson-nucleon

coupling directly from SM via 7 weak meson coupling constants

• Observables can be written as their combinations

102'1101 ,,,,,, hhhhhhf

110022110011

hahahahahafaA

111.0 fA fπ~4.5x10-7

p-4He Δσ/σ

(ppm)

fπ

hρ0

hρ1

hρ2

hω0

hω1

-0.107

-0.001

0.003

-0.92

-0.50

0.103

0.053

-0.160

0.002

-3.12

-0.23

-0.25

-0.23

-0.97

-0.32

0.11

-0.22

0.22

0.079

0.079 0.079

0.032

-0.073

0.073

-0.340

0.140

0.079 0.047

0.059

0.059

n+p d+γ

Aγ (ppm)

n+d t+γ

Aγ (ppm)

n-p φPV

(μrad/m)

n-4He φPV

(μrad/m)

p-p Δσ/σ

(ppm)

Weak π–nucleon coupling (long range)

HWI Models - Continued

2. Effective Field Theory

– developed by Holstein, Ramsey-Musolf, van Kolck, Zhu and Maekawa

– model-independent

NN potentials are expressed in terms of 12 parameters, whose linear

combinations give us 5 low energy coupling constants

connect to 5 parity-odd S-P NN amplitudes

)1(

)0(

)2,1,0(

1

3

1

3

1

1

1

3

0

3

0

1

IPS

IPS

IPS

t

I

st ,, 2,1,0Corresponding to

tN6 09.0~

27.0 mCA pn

3. Lattice QCD (NEW)

-- J. Wasem, PRC C85 (2012)

h1πNN=1.099 ±0.505 [x10-7]

+0.058

-0.064

fπ could be very small

• Experiments suggest a small fπ (nearly zero)

– corresponds to ΔI=1 transition (should be large)

– ΔI=0,2 do not contribute to Aγ

– Observations are not well understood (ΔI=0 contribution appears to

be large, and ΔI=1 appears to be small)

fπ could be very small

• Experiments suggest a small fπ (nearly zero)

– corresponds to ΔI=1 transition (should be large)

– ΔI=0,2 do not contribute to Aγ

– Observations are not well understood (ΔI=0 contribution appears to

be large, and ΔI=1 appears to be small)

Lattice QCD

fπ could be very small

• Experiments suggest a small fπ (nearly zero)

– corresponds to ΔI=1 transition (should be large)

– ΔI=0,2 do not contribute to Aγ

– Observations are not well understood (ΔI=0 contribution appears to

be large, and ΔI=1 appears to be small)

Lattice QCD

NPDgamma

111.0 fA DDH

Reaction of interest: dpn

+

Eγ=2.2MeV

+

We measure Aγ, the PV asymmetry in the distribution of emitted gammas.

cos1

4

1A

d

d

isolates the ΔI=1 part of the weak interaction

A predicted to be -5x10-8

ksn

DDH

1B - Disordered Mat’ls

Commission 2010

2 - Backscattering

Spectrometer

Commission 2006

3 - High Pressure

Diffractometer

Commission 2008

4A - Magnetism

Reflectometer

Commission 2006

4B - Liquids

Reflectometer

Commission 2006

5 - Cold Neutron

Chopper

Spectrometer

Commission 2007

18 - Wide Angle

Chopper Spectrometer

Commission 2007

17 - High Resolution

Chopper Spectrometer

Commission 2008

13 - Fundamental

Physics Beamline

Commissioned 2008

11A - Powder

Diffractometer

Commission 2007

12 - Single Crystal

Diffractometer

Commission 2009

7 - Engineering

Diffractometer

IDT CFI Funded

Commission 2008

6 – EQ SANS

Commission 2007

14B - Hybrid

Spectrometer

Commission 2011

15 – Spin Echo

9 –

VISION

Spallation Neutron Source at ORNL

Reached 1MW of power – September, 2009

Spallation Neutron Source at ORNL

•1.4 GeV protons, 60Hz

•Hg Spallation target neutrons

•H2 moderator

•17 m SM guide, curved

Spin octet

NPDGamma – Experimental Setup

Result from LANSCE run (2006) & Improvements for SNS

A γ,UD=(-1.2±2.0±0.2)x10-7

A γ,LR=(-1.8±2.1±0.2)x10-7

LANSCE SNS

Sensitivity 2x10-7 1x10-8

Polarizer 3He polarizer

(average 55% NP)

SuperMirror

Polarizer

(95% NP)

FOM (NP2) 8.9x107/s X200

improvement

Target 16L, LH2 New and

improved, thinner

windows

Result from LANSCE run (2006) & Improvements for SNS

A γ,UD=(-1.2±2.0±0.2)x10-7

A γ,LR=(-1.8±2.1±0.2)x10-7

SNS

Sensitivity 2x10-7 1x10-8

Polarizer 3He polarizer

(average 55% NP)

SuperMirror

Polarizer

(95% NP)

FOM (NP2) 8.9x107/s X200

improvement

Target 16L, LH2 New and

improved, thinner

windows

Pola

rization

Wavelength (Å)

Subject of M. Musgrave’s PhD thesis

LH2 target

30 cm

30 c

m

•16L vessel of liquid parahydrogen

•Ortho-hydrogen scatters the neutrons and

leads to beam depolarization

!NEW!

ASME code approved pressure vessel

See stamp!

Proton target - Parahydrogen

Orthohydrogen I=1 (aligned spins)

Parahydrogen I=0 (anti-aligned spin)

• No safety issues from sensors in the hydrogen system

• Energy dependence of the neutron transmission can be used

If En < 14.7meV, cannot flip

neutron spin

Para state dominates at low

temperatures, helped by a catalyst

(material with a solid paramagnetic

surface)

Parahydrogen Target

•3π acceptance

•Current-mode experiment

•γ-rate ~100 MHz (single

detector)

•Low noise solid-state

amplifiers

Detector

Array

i i

j

θ

•In principle, experiment can be done with just one detector, reversing the neutron

spin:

•Add opposite detector at same angle

(eliminates some systematic errors):

Asymmetry Extraction

YY

YYAraw

ij

ij

ji

ji

rawYY

YY

YY

YYA

2

1

i i

j

θ

Geometrical Factors

ykkiG nUDˆˆˆˆ)(

GUD

GLR

Generated via a combination of

MCNPX and measurements

with a gamma source

xkkkiG nnLRˆˆ)ˆ(ˆ)(

i i

j

θ

• 10.5 hours of data

– best measurement

to date

• Expect ~2% result

Allows for a rigorous check-out of

the entire system: DAQ, RFSF,

Detector Array, Analysis software

2011

2012

• 10.5 hours of data

– best measurement

to date

• Expect ~2% result

Allows for a rigorous check-out of

the entire system: DAQ, RFSF,

Detector Array, Analysis software

2011

2012

PV asymmetries

• Stern-Gerlach force 2x10-11

• Circularly polarized s 9x10-13

• In-flight decay 1x10-11

• Capture on 6Li 2x10-11

• Al ’s 1.3x10-8

• Al decay 1x10-10

Last two must be measured

Improved Understanding of systematic effects

• Mott-Schwinger in LH2 (must be modeled)

• Parity-allowed n+p d+γ 2x10-8

• Parity-allowed LR asymmetry in capture on Al=0

• These asymmetries can mix into the U-D channel if the detector and guide field are not aligned

PC LR asymmetries

•Largest source of

background in NPDGamma

•Need to measure asymmetry

to ~3x10-8

• Subject of S. Balascuta’s

PhD thesis.

Aluminum Target

Aluminum Background

• The largest source of background at LANL (average of 25%)

• Goal for SNS measurement was to reduce it by a factor of 2

• Measured when the hydrogen was filled and converted to para

Detector 42

Sig

nal (V

)

Time (s)

• Fit results are consistent

with half-life of

Aluminum

• Useful for investigating

other beta-delayed

background

contributions

Aluminum Background

• The largest source of background at LANL (average of 25%)

• Goal for SNS measurement was to reduce it by a factor of 2

• Measured when the hydrogen was filled and converted to para

Aluminum background is

largest in the front ring, and

decreases with increasing

distance from the entrance

windows to the target

vessel

Production Data on Hydrogen – Typical Detector

• 1800 Runs

(approximately 8

days of data)

• Beam at 0.9 MW

• Raw asymmetry

• No BG subtraction

• Fit to the

geometric factors

shows current

sensitivity of

5.6x10-8

Production Data on Hydrogen - so far

Summary

• Numerous improvements to the experiment will allow for the first measurement

of Aγ that will test theoretical predictions

• Predicted size -5x10-8 (DDH) - NPDGamma will make a 20% measurement

(1x10-8)

• Analysis of Cl, Al data are ongoing

• Production Hydrogen Data is in progress

ϑ

P. Alonzi3, R.Alracon1, S. Balascuta1, L. Barron-Palos2, S. Baeßler3, A. Barzilov25, J.D. Bowman4,J.R.Calarco9, R.D.

Carlini5, W.C. Chen6, T.E. Chupp7, C. Crawford8, M. Dabaghyan9, A. Danagoulian10, M. Dawkins11, N. Fomin10, S.J.

Freedman13, T.R. Gentile6, M.T. Gericke14 R.C. Gillis11, K. Grammer12, G.F. Greene4,12, F. W. Hersman9, T. Ino15,

G.L. Jones16, S. Kucucker12, B. Lauss17, W. Lee18, M. Leuschner11, W. Losowski11, E. Martin8, R. Mahurin14, M.

McCrea14, Y. Masuda15, J. Mei11, G.S. Mitchell19, S. Muto15, M. Musgrave12, H. Nann11, I. Novikov25, S. Page14,

D.Počanic3,S.I. Penttila4, D. Ramsay14,20, A. Salas Bacci10, S. Santra21, P.-N. Seo3, E. Sharapov23, M. Sharma7, T.

Smith24, W.M. Snow11, W.S. Wilburn10 V. Yuan10

1Arizona State University 2Universidad Nacional Autonoma de Mexico

3University of Virginia 4Oak Ridge National Laboratory

5Thomas Jefferson National Laboratory 6National Institute of Standards and Technology

7Univeristy of Michigan, Ann Arbor 8University of Kentucky

9University of New Hampshire 10Los Alamos National Laboratory

11Indiana University 12University of Tennessee

13University of California at Berkeley 14University of Manitoba, Canada

15High Energy Accelerator Research Organization

(KEK), Japan

The NPDGamma collaboration

15High Energy Accelerator Research Organization

(KEK), Japan 16Hamilton College

17Paul Scherrer Institute, Switzerland 18Spallation Neutron Source

19University of California at Davis 20TRIUMF, Canada

21Bhabha Atomic Research Center, India 22Duke University

23Joint Institute of Nuclear Research, Dubna, Russia 24University of Dayton

25Western Kentucky University

The End

ortho

para

capture useful range 1-15 meV

FnPB – cold beamline commissioned on Sep 12th, 2008

Resonant Spin Rotator

• A resonant RF magnetic field (B1coswt) is applied for a time t to precess the neutron spin by π.

• B1(t) 1/TOF, for reversing neutron spin in wide energy range (~0.5-50 meV).

• Rapid spin reversal minimizes systematic effects

Challenging Example: Capture on Aluminum

•Neutrons capture on 27Al ->28Al*

•Gamma cascade follows as 28Al*->28Al (g.s.)

•Asymmetry correlated with σn

28Al Capture State

28Al G. S.

28Si*

28Si G. S.

P1

P2

10

2

8

1

101 2.

103.1 1.

kP

kP

Fraction that capture in Aluminum – small

Average over 8-step sequence is also small

What gives rise to parity violation in ?

n p d is primarily sensitive to the ∆I = 1 component of the weak interaction

exchange

Low-energy

continuum states

Bound states

M1 (PC)

3S1, I 0

3S1,I 0

1S0,I 1

3P1, I 1

1P1, I 0

3P1, I 1

1P1, I 0

3P0 ,I 1

E1 E1

E1

E1

dpn

)1(

)0(

)2,1,0(

1

3

1

3

1

1

1

3

0

3

0

1

IPS

IPS

IPS

1

1

M

EA

delete

•Time bins (40μs) are averaged

over with neutrons polarization and

other energy-dependent quantities

as weights.

•Asymmetry for a detector pair is

then given by

•AUD is extracted from a fit of Araw

to θ, the angle of detector pair

sincos LRUDraw AAA

Analysis Procedure – continued -

delete Calibration Target: 35Cl

-target with a large and well-known

γ-asymmetry (26±7)x10-6

i i

j

θ