The NPDGamma Experiment at the SNS

Christopher Crawford University of Kentucky for the NPDGamma Collaboration The 19th Particles and Nuclei International Conference (PANIC11) Cambridge, MA 2011-07-26     Hadronic Weak Interaction NPDGamma expt. Setup LANSCE Results Commissioning at the SNS Madison Spencer

Motivation

The Hadronic Interaction is dominated by the strong force, But the weak component can be isolated due to parity violation

N STRONG (PC) N

DDH picture

N WEAK (PV) N

     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 Potential

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

EFT approach

C.-P. Liu, PRC 75, 065501 (2007) Zhu, Maekawa, Holstein, Ramsey-Musolf, van Kolck, NP A748, 435 (2005)

Pion-less EFT Couplings

      p-p scat. 15, 45 MeV A z pp p  scat. 46 MeV A z pp p-p scat. 220 MeV n+p  d+  A circ. pol. P  z d pp n+p  d+  n  asym. spin rot.

A  d d  n  /dz     18 F asym.  I =1 19 F, 41 K, 175 Lu, 181 Ta asym.

133 Cs, 205 Tl anapole moment 21 Ne (even-odd) GOAL – resolve coupling constants from few-body PV experiments only p-p and nuclei Ramsey-Musolf, Page, Ann. Rev. Nucl. Part. Sci.

56

:1-52,2006

NPDGamma parity-violating observable A



Experimental setup at the FnPB

CsI Detector Array Liquid H 2 Target H 2 Vent Line H 2 Manifold Enclosure Supermirror polarizer Magnetic Shielding Beam Stop Magnetic Field Coils FNPB guide

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

Flux = 6.5x10

10 n/s/MW 2.5 Å < λ < 6.0 Å SNS TOF window

FnPB supermirror polarizer

Fe/Si on boron float glass, no Gd m = 3.0 n = 45 r = 9.6 m l = 40 cm d = 0.3mm critical angle channels radius of curvature length vane thickness T=25.8% P=95.3% N=2.2

£ 10 10 n/s transmission polarization output flux (chopped)

simulations using McStas / ROOT ntuple

RF spin rotator

• • essential to reduce instrumental systematics - spin sequence:   cancels drift to 2 nd 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 s n B RF

3 He Ion chamber – Beam Monitors

• • • Neutron Flux monitor Neutron Polarization (in conjunction with 3 He 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

16L liquid para-hydrogen target

    30 cm long  1 interaction length 99.97% para  1% depolarization super-cooled to reduce bubbles SAFETY !!

p p 

E = 15 meV

p p para-H 2 ortho-H 2 ortho para capture E n (meV)

16L liquid para-hydrogen target

Installation of the LH 2 target in the FnPB

CsI(Tl) Detector Array

    • 4 rings of 12 detectors each 15 x 15 x 15 cm 3 each VPD ’ s insensitive to B field detection efficiency: 95% • • current-mode operation 5 x 10 7 gammas/pulse counting statistics limited

LH 2 run at LANSCE – Fall 2006

       7 A γ,UD =(-1.2

± 1.9

± 0.2)x10 A γ,LR =(-1.8

± 2.1

± 0.2)x10 7 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 target 2 % Data loss (cuts, bad events) ~1 %

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 LH 2 target Improvements at SNS

 Higher moderator brightness ( 40x more neutrons )  Supermirror polarizer instead of 3 He ( 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 achieve δA = 1 x 10 -8 statistics

Measurement of Beam Flux and Profile

Time of Flight

NPDGamma Collaboration

R. Alarcon 1 , S. Balascuta 1 , L. Barron-Palos 2 , S.

Baeßler 3 , D. Bowman 4 , J. Calarco ,R. Carlini 5 , W. Chen 6 , T. Chupp 7 , C. Crawford 8 , M. Dabaghyan 9 , A. Danagoulian 10 , M. Dawkins 11 , N. Fomin 10 , S. Freedman 13 , T. Gentile 6 , M. Gericke 14 C. Gillis 11 , G. Greene 4,12 , F. Hersman 9 , T. Ino 15 , G. Jones 16 , B. Lauss 17 , W. Lee 18 , M. M. Leuschner 11 , W. Losowski 11 , R. Mahurin 12 , Y. Masuda 15 , J. Mei 11 , G. Mitchell 19 , S. Muto 15 , H. Nann 11 , S. Page 14 , D. Pocinic, S. Penttila 4 , D. Ramsay 14,20 , A. Salas Bacci 3 , S. Santra 21 , P.-N. Seo 22 , E. Sharapov 23 , M. Sharma 7 , T. Smith 24 , W. Snow 11 , W. Wilburn 10 , V. Yuan 10 1 Arizona State University 2 Universidad Nacional Autonoma de Mexico 3 University of Virginia 4 Oak Ridge National Laboratory 5 Thomas Jefferson National Laboratory 6 National Institute of Standards and Technology 7 Univeristy of Michigan, Ann Arbor 8 University of Kentucky 9 University of New Hampshire 10 Los Alamos National Laboratory 11 Indiana University 12 University of Tennessee 13 University of California at Berkeley 14 University of Manitoba, Canada 15 High Energy Accelerator Research Organization (KEK), Japan 16 Hamilton College 17 Paul Scherer Institute, Switzerland 18 Spallation Neutron Source 19 University of California at Davis 20 TRIUMF, Canada 21 Bhabha Atomic Research Center, India 22 Duke University 23 Joint Institute of Nuclear Research, Dubna, Russia 24 University of Dayton