NPDgamma Liquid Hydrogen Target Safety Review At LANL November 29-30, 2005.
The NPDGamma Experiment
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The NPDGamma Experiment
Christopher Crawford
University of Tennessee
2007-05-30
• hadronic PV formalism
• experimental setup
• LANSCE ) SNS Madison Spencer
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Simple Level Diagram of n-p System; is primarily sensitive to the ∆I = 1 component of the weak interaction
Low-energycontinuum states
Bound states
E1 E1M1
E1
E1
€
3S1,I =0
€
3P1,I =1
€
1P1,I =0
€
3S1,I =0
€
3P1,I =1
€
1P1,I =0
€
1S0,I =1
€
3P0,I =1
€
3S1 VW3P1 ;ΔI =1
€
3S1 VW1P1 ;ΔI =0
€
1S0 VW3P0 ;ΔI =2
€
r n +p→ d+γ
• Weak interaction mixes in P waves to the singlet and triplet S-waves in initial and final states.• Parity conserving transition is M1.• Parity violation arises from mixing in P states and interference of the E1 transitions.• A is coming from 3S1 - 3P1 mixing and interference of E1-M1 transitions - I = 1 channel
Mixing amplitudes:
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Meson exchange model
• DDH formalism:– 6+1 meson-nucleon coupling constants– pion channel dominated by neutral current (Z0)– PV effects: interference between strong and weak vertex
N N
N N
Meson exchange
STRONG(PC)
WEAK(PV)
Desplanques, Donoghue, Holstein, Ann. Phys. 124 449 (1980)
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EFT approach
Zhu, Maekawa, Holstein, Ramsey-Musolf, van Kolck, Nucl. Phys. A748, 435 (2005)
Liu, nucl-th/0609078
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Danilov Parameters
Zero range limit:
Ramsey-Musolf, Page, Ann. Rev. Nucl. Part. Sci. 56:1-52,2006
PV NN-interaction
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Why study hadronic PV?• probe of atomic, nuclear,
and hadronic systems– map out coupling constants– resolve 18F, 133Cs discrepancy– probe nuclear structure effects– anapole and qq contributions
to PV electron scattering
np A nD A np n pp Az p Az
f-0.11 0.92 -3.12 -0.97 -0.34
h0 -0. 50 -0. 23 -0.32 0.08 0.14
h1 -0.001 0.10 0.11 0.08 0.05
h2 0.05 -0.25 0.03
h0 -0. 16 -0. 23 -0.22 0.07 0.06
h1 -0.003 -0.002 0.22 0.07 0.06
• probe of QCD in low energy non-perturbative regime– confinement, many-body
problem
– sensitive to qq correlations
– measure QCD modification of qqZ coupling
n + p d +
A = -0.11 f
+ -0.001 h1
+ -0.003 h1
n-capture elastic scatteringspin rotationBowman
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Why study hadronic PV?
Liu, nucl-th/0609078
Ramsey-Musolf, Page, Ann. Rev. Nucl. Part. Sci. 56:1-52,2006
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p-p and nuclei
Existing measurements
Anapole
Nuclear anapole moment(from laser spectroscopy)
Light nuclei gamma transitions(circular polarized gammas)
Polarized proton scattering asymmetries
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p-p and nuclei
Existing measurements
D
ed Spin rot/A Anapole
Circular components
Medium withcircular birefringence
Linear Polarization
?
Spin rotation
Neutron spin rotation
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NPDGamma Collaboration
Measurement of the Parity - Violating Gamma Asymmetry A in the Capture of Polarized Cold Neutrons by Para-Hydrogen
J.D. Bowman (spokesman), G.S. Mitchell, S. Penttila, A. Salas-Bacci, W.S. Wilburn, V. Yuan
Los Alamos National Laboratory
M.T. Gericke, S. Page, D. RamsayUniv. of Manitoba
S. Covrig, M. Dabaghyan, F.W. HersmanUniv. of New Hampshire
T.E. Chupp, M. SharmaUniv. of Michigan
C. Crawford, G.L. Greene, R. MahurinUniv. of Tennessee
R. Alarcon, L. Barron, S. BalascutaArizona State University
S.J. Freedman, B. LaussUniv. of California at Berkeley
R.D. CarliniThomas Jefferson National Accelerator Facility
W. Chen, R.C. Gillis, J. Mei, H. Nann, W.M. Snow, M. Leuschner, B. Losowki
Indiana University
T.R. GentileNational Institute of Standards and
Technology
G.L. JonesHamilton College
Todd SmithUniv. of Dayton
T. Ino, Y. Masuda, S. MutoHigh Energy Accelerator Research Org. (KEK)
S. SantraBhabbha Atomic Research Center
P.N. SeoNorth Carolina State University
E. SharapovJoint Institute of Nuclear Research
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Overview of NPDG experiment
A = -0.11 f ¼ 5 £ 10-8
d / 1 + Pn A cos + Pn APC sin
A = 1 £ 10-8 for N ¼ 3 £ 1016 events
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Overview of NPDG experiment
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Pulsed neutron beam
~6x108 cold neutrons per 20 Hz pulse at the end of
the 20 m supermirror guide(largest pulsed neutron flux)
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Time-of-flight beam profile6
5
4
3
2
1
0
Neutron current (x10
5
neutrons/ms/cm
2
/pulse)
6050403020100
Time of Flight (ms)
Neutron current at the end of a 24.3 m long guide with 150 μ A proton current
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Time-of-flight beam profile
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Beam stability
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3He neutron polarizer• n + 3He 3H + p cross section is highly spin-dependent
J=0 = 5333 b /0
J=1 ¼ 0
• 10 G holding field determines the polarization anglerG < 1 mG/cm to avoid Stern-Gerlach steering
Steps to polarize neutrons:
1. Optically pump Rb vaporwith circular polarized laser
2. Polarize 3He atoms viaspin-exchange collisions
3. Polarize 3He nuclei viathe hyperfine interaction
4. Polarize neutrons by spin-dependent transmission
nn + nnpp
ppnnpp
nn +pp
P3 = 57 %
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Neutron Beam Monitors • 3He ion chambers• measure transmission
through 3He polarizer
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Beam Polarization
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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 to all energies
• compact, no static field gradients
holding field
sn
BRF
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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• pressurized to reduce bubbles• SAFETY !!
pp pp
para-H2
pp pp
ortho-H2
E = 15 meV
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Ortho-Para Conversion Cycle
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O/P Equilibrium Fraction
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Neutron Intensity on Target
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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– optimized for asymmetry
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Asymmetry Analysisyield (det,spin)
P.C. asym
background asym
geometry factor
P.V. asym
RFSF eff. neutron pol. target depol.
raw, beam, inst asym
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• activation of materials, e.g. cryostat windows
• Stern-Gerlach steering in magnetic field gradients
• L-R asymmetries leaking into U-D angular distribution (np elastic, Mott-Schwinger...)
• scattering of circularly polarized gammas from magnetized iron (cave walls, floor...)
estimated and expected to be negligible (expt. design)
Systematics, e.g:
A
stat. err.
systematics
(proposal)
Statistical and Systematic Errors
Systematic Uncertainties
slide courtesy Mike Snow
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Left-Right Asymmetries
• Parity conserving: • Three processes lead to LR-asymmetry
– P.C. asymmetry• Csoto, Gibson, and Payne, PRC 56, 631 (1997)
– elastic scattering• beam steered by analyzing power of LH2
• eg. 12C used in p,n polarimetry at higher energies• P-wave contribution vanishes as k3 at low energy
– Mott-Schwinger scattering• interaction of neutron spin with Coulomb field of nucleus• electromagnetic spin-orbit interaction• analyzing power: 10-7 at 45 deg
0.23 x 10-8
2 x 10-8
~ 10-8
at 2 MeV
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Detector position scans
5 mm resolution ~ 1 deg
target
detector
UP-DOWN LEFT-RIGHT
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Engineering Runs
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NPDG Asymmetry (Stat. Error)
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Spallation Neutron Source (SNS)Oak Ridge National Laboratory, Tennessee
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Spallation Neutron Source (SNS)
• spallation sources: LANL, SNS– pulsed -> TOF -> energy
• LH2 moderator: cold neutrons– thermal equilibrium in ~30 interactions
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FnPB Cold Neutron Beamline
Improvements for SNS:
• curved beamline
• 2 choppers (+ 2 unused)
• new shielding hut
• SM bender polarizer
• new LH2 vent line
• 60 Hz DAQ system
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Timeline
0
500
1000
1500
2000
2500
3000
3500
4000
2006-2 2007-1 2007-2 2008-1 2008-2 2009-1 2009-2 2010-1 2010-2 2011-1
Date
~Best Year for LANSCE Production
Early
Fin
ish D
ate
Fun
d. P
hys.
Beam
First
SNS
Beam
23 A
pr 2
006
• move NPDG to the SNS to achieve goal of A = 1£10-8
• possible follow-up experiment: n + d t +
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Conclusion
• the NPDG experiment had a successfulfirst phase at LANSCE
• project to determine A to 1£10-8 at the SNS– possible follow-up experiment: n + d t +
• hadronic parity violation is a unique probe of short-distance nuclear interactions and QCD– neutron capture is an important key to mapping
the long-range component of the hadronic weak interaction