The NPDGamma Experiment at the SNS

Hadronic Weak Interaction

NPDGamma expt. Setup

LANSCE Results

Commissioning at the SNS

Madison Spencer

Christopher CrawfordUniversity of Kentucky

for the NPDGamma Collaboration

The 19th Particles and Nuclei International Conference (PANIC11)

Cambridge, MA

2011-07-26

N N

N N

Meson exchange

STRONG(PC)

WEAK(PV)

Motivation

The Hadronic Interaction is dominated by the strong force,

But the weak component can be isolated due to parity violation

W,Z range = 0.002 fm – probe short-range quark correlations in QCD nonperturbative regime

nuclear PV – test of nuclear structure models

test of EFT in S = 0 sector(I=1/2 rule not understood)

physics input to PV electron scattering experiments

0 decay – matrix elements of 4-quark operators

DDH picture

DDH Potential

isos

pin

rang

e

Desplanques, Donoghue, Holstein, Annals of Physics 124, 449 (1980)

EFT approach

Zhu, Maekawa, Holstein, Ramsey-Musolf, van Kolck, NP A748, 435 (2005)

C.-P. Liu, PRC 75, 065501 (2007)

p-p and nuclei

Pion-less EFT Couplings

Ramsey-Musolf, Page, Ann. Rev. Nucl. Part. Sci. 56:1-52,2006

p-p scat. 15, 45 MeV Azpp

p- scat. 46 MeV Azpp

p-p scat. 220 MeV Azpp

n+pd+ circ. pol. Pd

n+pd+ asym. Ad

n- spin rot. dn/dz

18F asym. I =1 19F, 41K, 175Lu, 181Ta asym. 133Cs, 205Tl anapole moment 21Ne (even-odd)

GOAL – resolve couplingconstants from few-bodyPV experiments only

NPDGamma parity-violating observable A

Experimental setup at the FnPB

Supermirror polarizer

FNPB guide

CsI Detector Array

Liquid H2 Target

H2 Vent Line

Beam Stop

Magnetic Field Coils

Magnetic Shielding

H2 Manifold Enclosure

Spallation neutron source – cold moderator

spallation sources: LANL, SNS• pulsed -> TOF -> energy

LH2 moderator: cold neutrons• thermal equilibrium in ~30 interactions

Spallation neutron source – cold moderator

spallation sources: LANL, SNS• pulsed -> TOF -> energy

LH2 moderator: cold neutrons• thermal equilibrium in ~30 interactions

Neutron Flux at the SNS FnPB

SNS TOF window

15 m

eV L

H2

thre

shol

d

Flux = 6.5x1010 n/s/MW 2.5 Å < λ < 6.0 Å

FnPB supermirror polarizer

Fe/Si on boron float glass, no Gd

m = 3.0 critical anglen = 45 channelsr = 9.6 m radius of curvaturel = 40 cm lengthd = 0.3mm vane thickness

T=25.8% transmissionP=95.3% polarizationN=2.2£1010 n/s output flux (chopped)

simulations using McStas / ROOT ntuple

RF spin rotator

• essential to reduce instrumental systematics- spin sequence: cancels drift to 2nd order- danger: must isolate fields from detector- false asymmetries: additive & multiplicave

• works by the same principle as NMR- RF field resonant with Larmor frequency rotates spin- time dependent amplitude tuned for all energies- compact, no static field gradients

holding field

sn

BRF

3He Ion chamber – Beam Monitors

• Larger beam cross section

• Use wires rather than plates

• Reduce absorption and scattering of beam

• Reduce micro-phonic noise pickup

• Neutron Flux monitor

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

• Monitor ortho/para ratio in the target

16L liquid para-hydrogen target

15 m

eV

ortho

para

capture

En (meV)

(b

)

30 cm long 1 interaction length

99.97% para 1% depolarization

super-cooled to reduce bubbles

SAFETY !!

pp pp

para-H2

pp pp

ortho-H2

E = 15 meV

16L liquid para-hydrogen target

Installation of the LH2 target in the FnPB

CsI(Tl) Detector Array

4 rings of 12 detectors each• 15 x 15 x 15 cm3 each

VPD’s insensitive to B field

detection efficiency: 95%

current-mode operation• 5 x 107 gammas/pulse• counting statistics limited

LH2 run at LANSCE – Fall 2006

Number of good runs 5401 / 750 h

Average delivered proton current 89 A at 80 kW

Average beam pol. (3He spin filter)55 +/- 7.5 %

Spin-flip efficiency 98 +/- 0.8%

Para-hydrogen fraction in LH2 target 99.98 %

Beam depolarization in target2 %

Data loss (cuts, bad events)~1 %

A γ,UD=(-1.2±1.9±0.2)x10-7

A γ,LR=(-1.8±2.1±0.2)x10-7

Installation and Commissioning at the FnPB

Commissioning Measurements

Calibrated CsI detectors

Mapped out the holding field

Measured beam flux and profile

Tuned the spin flipper

Measured beam polarization

Measured Cl asymmetry

Measured Al asymmetry

Measured background rates from mock-up target

Ready to install LH2 target

Improvements at SNS

Higher moderator brightness( 40x more neutrons )

Supermirror polarizer instead of 3He ( 4x figure of merit )

Higher duty factor, and longer run time

Better control of systematics

Estimated Run Time at SNS

2200 hr at 1.4 MW to achieveδA = 1 x 10-8 statistics

Measurement of Beam Flux and Profile

Time of Flight

NPDGamma Collaboration

R. Alarcon1, S. Balascuta1, L. Barron-Palos2, S. Baeßler3, D. Bowman4, J. Calarco ,R. Carlini5, W. Chen6, T. Chupp7, C. Crawford8, M. Dabaghyan9, A. Danagoulian10, M. Dawkins11, N. Fomin10, S. Freedman13, T. Gentile6, M. Gericke14 C. Gillis11, G. Greene4,12, F. Hersman9, T. Ino15, G. Jones16, B. Lauss17, W. Lee18, M. M. Leuschner11, W. Losowski11, R. Mahurin12, Y. Masuda15, J. Mei11, G. Mitchell19, S. Muto15, H. Nann11, S. Page14, D. Pocinic, S. Penttila4, D. Ramsay14,20, A. Salas Bacci3, S. Santra21, P.-N. Seo22, E. Sharapov23, M. Sharma7, T. Smith24, W. Snow11, W. 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

7Univeristy of Michigan, Ann Arbor8University of Kentucky

9University of New Hampshire10Los Alamos National Laboratory

11Indiana University12University of Tennessee

13University of California at Berkeley

14University of Manitoba, Canada15High Energy Accelerator Research

Organization (KEK), Japan16Hamilton College

17Paul Scherer Institute, Switzerland 18Spallation Neutron Source

19University of California at Davis20TRIUMF, Canada

21Bhabha Atomic Research Center, India22Duke University

23Joint Institute of Nuclear Research, Dubna, Russia

24University of Dayton