the npdgamma experimentbattlestar.phys.utk.edu/wiki/images/e/e0/fomin_cipanp.pdf · • 10.5 hours...
TRANSCRIPT
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First results from the NPDGamma
experiment at the Spallation Neutron Source
Nadia Fomin
Los Alamos National Laboratory
June 1st, 2012
St. Petersburg, FL
ϑ
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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
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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
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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)
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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
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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)
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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
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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
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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
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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
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Spallation Neutron Source at ORNL
•1.4 GeV protons, 60Hz
•Hg Spallation target neutrons
•H2 moderator
•17 m SM guide, curved
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Spin octet
NPDGamma – Experimental Setup
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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
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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
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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!
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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)
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Parahydrogen Target
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•3π acceptance
•Current-mode experiment
•γ-rate ~100 MHz (single
detector)
•Low noise solid-state
amplifiers
Detector
Array
i i
j
θ
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•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
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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
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• 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
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• 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
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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
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•Largest source of
background in NPDGamma
•Need to measure asymmetry
to ~3x10-8
• Subject of S. Balascuta’s
PhD thesis.
Aluminum Target
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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
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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
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Production Data on Hydrogen – Typical Detector
• 1800 Runs
(approximately 8
days of data)
• Beam at 0.9 MW
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• Raw asymmetry
• No BG subtraction
• Fit to the
geometric factors
shows current
sensitivity of
5.6x10-8
Production Data on Hydrogen - so far
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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
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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
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The End
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ortho
para
capture useful range 1-15 meV
FnPB – cold beamline commissioned on Sep 12th, 2008
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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
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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
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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
![Page 36: The NPDGamma Experimentbattlestar.phys.utk.edu/wiki/images/e/e0/Fomin_cipanp.pdf · • 10.5 hours of data – best measurement to date • Expect ~2% result Allows for a rigorous](https://reader033.vdocuments.pub/reader033/viewer/2022042711/5f77ff9b184e2f7cb47972b3/html5/thumbnails/36.jpg)
•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