the npdgamma experiment at the snsweb.mit.edu/panic11/talks/tuesday/parallel-3g/5... · christopher...
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The NPDGamma Experiment at the SNS
Hadronic Weak Interaction
NPDGamma expt. Setup
LANSCE Results
Commissioning at the SNS
Madison Spencer
Christopher Crawford University 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 ΔS = 0 sector (ΔI=1/2 rule not understood)
physics input to PV electron scattering experiments
0νββ 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-α scat. 46 MeV Azpp
p-p scat. 220 MeV Azpp
n+p→d+γ circ. pol. Pγd
n+p→d+γ asym. Aγd
n-α spin rot. dφnα/dz
18F asym. ΔI =1 19F, 41K, 175Lu, 181Ta asym. 133Cs, 205Tl anapole moment 21Ne (even-odd) GOAL – resolve coupling
constants from few-body PV experiments only
NPDGamma parity-violating observable Aγ
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 t
hres
hold
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 angle�n = 45 channels r = 9.6 m radius of curvature l = 40 cm length d = 0.3mm vane thickness
T=25.8% transmission P=95.3% polarization N=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)
σ (b
)
30 cm long → 1 interaction length 99.97% para → 1% depolarization
super-cooled to reduce bubbles
SAFETY !!
p p
para-H2
p p
ortho-H2
ΔE = 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 target 2 %
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 achieve δA = 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 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 16Hamilton College
17Paul Scherer 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