The NPDGamma ExperimentA measurement of the parity violating directional γ-asymmetry in polarized cold neutron capture on hydrogen.

Nadia Fomin

University of Tennessee

for the NPDGamma Collaboration

St. Petersburg, Russia

June 13th, 2008

Outline

Introduction and Motivation

Experiment

Analysis and Preliminary Results from y yfirst run

Next run at SNS

PC PVM

N N

Weak interaction at low momentum transfer between nucleons is accessible through measurements of small parity-odd amplitudes

Natural scale ~x10-7, set by relative size of meson vs boson exchange amplitudes

Weak NN couplings are largely unknown: non-perturbative regime makes calculations and experiments challenging

Introduction

N Nand 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

Introduction - continued 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

Introduction - continuedEFT– 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

)210(31 IPS

Additionally, a long-range pion-nucleon coupling constant (~fπ)

)1(

)0(

)2,1,0(

13

13

11

13

03

01

IPSIPSIPS

tIst ,, 2,1,0

Corresponding to

– In a proton-neutron system, nucleons are loosely coupled, and fπ is believed to be the dominant coupling (same as in DDH model)

tN6 09.0~27.0 mCA pn

Reaction of interest: dpn

+

Eγ=2.2MeV

cos1

41 A

dd

isolates the ∆I=1 part of the weak interaction

A predicted to be -5x10-8

ks n

γ

+

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

111.0 fA DDH

A p

Note That EFT Gives about same value

Experimental Setup

NDPGamma on FP12

10G magnetic guide field coils to preserve neutron polarization

3He Spin Filter (Run 1 only)• 3He gas is polarized via spin exchange with laser-polarized Rb

• σsinglet/σtriplet~104 – neutrons with spins || to 3He pass through (filter)

• 3He Polarization ~ 55%

• Relaxation time ~500hrs

TOF 1/λ

At the pulse source, a simple relationship exists between energy and arrival time of the neutrons

Resonant RF Spin Flipper

• 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

LH2 target and CsI detector array

30 cm

30 c

m

•3π acceptance

C t d i t

16L vessel of liquid parahydrogen

Ortho-hydrogen scatters the neutrons and leads to beam depolarization

•Current-mode experiment

•γ-rate ~100MHz (single detector)

•Low noise solid-state amplifiers

New Wire Chamber Beam Monitors

• Neutron Flux

• Neutron Polarization (in conjunction with 3He analyzer – once)

• Monitor ortho/para ratio in the target

• Larger beam cross section

• Use wires rather than plates

•Reduce absorption and scattering of beam

•Reduce micro-phonic noise pickup

• Currently being tested at LANSCE

Data Summary from 2006 run

Number of good runs (8.5min long)

Neutron Polarization (ave)

Spin Flip Efficiency

Para fraction in LH2 target

Al background

~5000

53±2.5%

98.8±0.5%

99.98±0.2%

~25% (ave)

Depolarization

Stern-Gerlach steering Asym

γ-ray circ.pol. Asym

2%

10-10

10-10

Raw asymmetry is formed between each pair of detectors {i,j} for each spin sequence, for each time bin via

Analysis Procedure

iiθ

),,(),()]()()(),(1[4det xfEzhEEEPgAVY dnnnsfnndd

Detector geometry SF efficiency

Neutron depolarization

Capture Locus

γ energy depositionNeutron Polarization

ijji YYYYA 1

Raw asymmetry for a detector pair {ij}, time bin t, is related to physics asymmetry via:

j

)()()()()(

)()()()(tttP

AtAAtAtGtAtGtA

sfn

noisebeamgainrawLRLRUDUD

BGUDPHYSUDUD AAA ,,

ij

j

ji

jraw YYYY

A2

•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 A

sincos LRUDraw AAA

Analysis Procedure - continuedCalibration Target: 35Cl

-target with a large and well-known γ-asymmetry (26±7)x10-6

AUD is extracted from a fit of Arawto θ, the angle of detector pair

ii

j

θ

Preliminary Hydrogen ResultA γ,UD=(-1.9±2.0±0.2)x10-7

A γ,LR=(-1.1±2.1±0.2)x10-7

Continuing NPDGamma at the SNS in Oak Ridge, TN

LANSCE SNSSensitivity 2x10-7 1x10-8

Polarizer 3He polarizer SuperMirror (average 55% NP)

Polarizer(98% NP)

FOM (NP2) 8.9x107/s X200 improvement

Target 16L, LH2New and improved, thinner windows

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

L t t t b d

Improved Understanding of systematic effects

Last two must be measured

• 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

Spallation Neutron Source at ORNL

•1.4 GeV protons, 60Hz

•LHg Spallation target -> neutrons•H2 moderator

•17m SM guide, curved

5 - Cold Neutron Chopper13 - Fundamental

11A - Powder Diffractometer Commission 2007

12 - Single Crystal Diffractometer Commission 2009

7 - Engineering Diffractometer IDT CFI Funded Commission 2008

6 – EQ SANS Commission 2007

9 –VISION

Spallation Neutron Source at ORNL

1B - Disordered Mat’lsCommission 2010

2 - Backscattering Spectrometer Commission 2006

3 - High Pressure Diffractometer Commission 2008

4A - Magnetism Reflectometer Commission 2006

4B - Liquids ReflectometerCommission 2006

Chopper Spectrometer Commission 2007

18 - Wide Angle Chopper Spectrometer Commission 2007

17 - High Resolution Chopper SpectrometerCommission 2008

13 Fundamental Physics Beamline Commission 2008

14B - Hybrid Spectrometer Commission 2011

15 – Spin Echo

FNPB – cold beamline commissioned on Sep 12th, 2008

ortho

para

captureuseful range 1-15 meV

Getting cave ready for NPDGamma

After

Before

Supermirror polarizer

CsI Detector Array

Liquid H2 Target

H2 Vent Line

H2 Manifold Enclosure

Conceptual design of Experiment

FNPB guide

Beam Stop

Magnetic Field Coils

Spin Flipper

SummarySuperMirror Polarizer replaces the 3He Polarizer (x4.1)

Higher moderator brightness (x12) => more cold neutrons

New LH2 target – thinner windows, smaller background contribution

Predicted size -5x10-8 (DDH) - NPDGamma will make a ( )20% measurement (1x10-8)

Installation is currently under way

Production Hydrogen Data – early 2010

P. Alonzi3, R.Alracon1, S. Balascuta1, L. Barron-Palos2, S. Baeßler3, J.D. Bowman4,J.R.Calarco9, R.D.Carlini5, W.C. Chen6, T.E. Chupp7, C. Crawford8, M. Dabaghyan9, J.Dadras12,A. Danagoulian10, M.Dawkins11, N. Fomin12, S.J. Freedman13, T.R. Gentile6, M.T. Gericke14 R.C. Gillis11, G.F. Greene4,12, F. W.Hersman9, T. Ino15, G.L. Jones16, B. Lauss17, W. Lee18, M. Leuschner11, W. Losowski11, R. Mahurin12, Y.Masuda15, J. Mei11, G.S. Mitchell19, S. Muto15, H. Nann11, S. Page14, D.Počanic3,S.I. Penttila4, D.Ramsay14,20, A. Salas Bacci10, S. Santra21, P.-N. Seo22, E. Sharapov23, M. Sharma7, T. Smith24, W.M. Snow11,W.S. Wilburn10 V. Yuan10

1Arizona State University2Universidad Nacional Autonoma de Mexico

3University of Virginia 4Oak Ridge National Laboratory

5Thomas Jefferson National Laboratory6National Institute of Standards and Technology

7U i i t f Mi hi A A b

The NPDGamma collaboration

7Univeristy of Michigan, Ann Arbor8University of Kentucky

9University of New Hampshire10Los Alamos National Laboratory

11Indiana University12University of Tennessee

13University of California at Berkeley14University of Manitoba, Canada

15High Energy Accelerator Research Organization (KEK), Japan16Hamilton College

17Paul Scherrer Institute, Switzerland 18Spallation Neutron Source

19University of California at Davis20TRIUMF, Canada

21Bhabha Atomic Research Center, India22Duke University

23Joint Institute of Nuclear Research, Dubna, Russia24University of Dayton

Systematic Effects

Interaction Vectorcorrelation

UD/LR

PV/PC

Time of flight dependence

Size ofasymmetry

n+pd+NPDGamma) sn k ud pv no 5x10-8(*)

n+pn+p (scattering shift) k’n sn kn lr pc 1/t 1x10-9(*)

n+pd+ (#) k’ sn kn lr pc 1/t2 1x10-10(*)

n+pd+ (magnetized iron) sn k ud pc no 1x10-10(*)

np+e+ne (beta decay) sn ke ud pv no 3x10-11(*)

d (D i i ) k d 1 10 10(*)n+dt+ (D2 contamination) sn . k ud pv no 1x10-10(*)

n+pn+p (Mott-Schwinger) k’n sn kn lr pc 1/t2.8 5x10-10 (**)

n+6Li+t (Li-shield) sn . k’n ud pv no 2x10-11(*)

(n.)B (Stern-Gerlach) (sn )B ud pc t1 1x10-10(**)

n+A(A+1)+e+ne sn ke ud pv varies <10-10(*)

n+A(A+1)+ sn k ud pv no <10-9(**)

n+27Al28Al+ sn k ud pv no < 210-7(**)

(#) see Ref. [30]sn is the neutron spin and k is momentum of particle. (*) size calculated(**) size measured

What gives rise to parity violation in ?

Low-energycontinuum states

M1 (PC)

3S1, I 0 1S0,I 13P1,I 1 1P1,I 0 3P0,I 1

E1E1

E1

E1

dpn

11

ME

A

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

exchange

Bound states3S1,I 0 3P1,I 1 1P1,I 0

)1(

)0(

)2,1,0(

13

13

11

13

03

01

IPSIPSIPS

1M