Overview of the n3He Experiment and Target Chamber Mark McCrea University of Manitoba for the n3He Collaboration January 30, 2017 1 / 21
n3He Introduction The n3He experimental goal is to make a high precision measurement of the parity violating directional asymmetry in the proton emission direction from the reaction n + 3 He → p + T + 765 keV � The asymmetry is expected to be small, of order 10 − 7 , and our goal is to measure it to 2 × 10 − 8 . 2 / 21
Theoretical Motivation u d d u d d N N π, ρ, ω ? PC PV Strong Weak u d d u d d N N Uncertain HWI DDH Parameterization DDH Meson Exchange Parameters: ω + a 1 ′ ω h 1 ′ O pv = a 1 π h 1 π + a 0 ρ h 0 ρ + a 1 ρ h 1 ρ + a 2 ρ h 2 ρ + a 0 ω h 0 ω + a 1 ω h 1 ω q q q q Z 0 , W ± g q q q q Strong Interaction Weak Interaction 3 / 21
FnPB Schematic • Located at the Oak Ridge National Laboratory in Tennessee • 60 Hertz pulsed spallation source • n3He was located at the FnPB • 20K liquid hydrogen moderator for cold neutron beam lines 4 / 21
n3He Schematic Diagram 5 / 21
Neutron Pulse m1(V) m1(V) 0.35 Unchopped 0.35 Chopped 0.3 0.3 0.25 0.25 0.2 0.2 0.15 0.15 0.1 0.1 0.05 0.05 0 0 0 16.6 33.3 50.0 66.6 83.3 100 116 133 0 16.6 33.3 50 66.6 83.3 100 116 133 time(ms) time(ms) 1 Hz Pulse 60 Hz Pulses 6 / 21
Target/Detector Chamber • 0 . 47 atm He-3 fill gas • 144 signal wires • − 350 V bias voltage • Aluminum housing 7 / 21
n3He Target Chamber Schematic 33 . 8 30 . 4 1 . 9 Beam 16 25 . 4 y / ˆ ˆ x HV Signal ˆ z 8 / 21
Signal Formation in Chamber n + 3 He → p + T + 765 keV � neutron proton Triton Electron Collection Ion Collection Objects are to scale. 9 / 21
Measured Charge Distribution in the Chamber i 1 h g Wire Letter f 10 -1 Beam e d c 10 -2 b a 4 6 8 12 14 2 10 16 Layer Number 10 / 21
Asymmetry Calculation For an ideal target and detector: Y ↑ / ↓ = I 0 ǫ k (1 ± P cos θ A PV ± P sin θ A PC ) (1) k For a real target and detector: Y ↑ / ↓ = I 0 ǫ k (1 ± PG PV A PV ± PG PC A PC ) (2) k S13.00008 : Simulation of ion chamber signals in the n+3Hep+t experiment (next talk) To calculate the asymmetry: Y ↑ − Y ↓ 1 A PV = (3) Y ↑ + Y ↓ PG PV J12.00006 : A measurement of the parity violating asymmetry in the neutron capture on 3He at the SNS 11 / 21
Preliminary Asymmetry Results LR Raw Asymmetry A+ B × -6 10 2 1.5 1 Raw asymmetry 0.5 0 -0.5 -1 -1.5 0 10 20 30 40 50 60 70 80 90 11 x Layer number + wire number J12.00006 : A measurement of the parity violating asymmetry in the neutron capture on 3He at the SNS (January 29) 12 / 21
Summary • n3He Data taking completed end of 2015 • Asymmetry calculations underway • We expect to reach the goal statistical accuracy 13 / 21
n3He Collaboration • Geoff Greene Arizona State University Western Kentucky University • R. Alarcon • Ivan Novikov • Serpil Kucuker • D. Blyth • Chris Coppola University of Manitoba Duke University, Triangle • Michael Gericke • Chris Hayes Universities Nuclear Laboratory • Mark McCrea • Irakli Garishvili • Pil-Neo Seo • Carlos Olguin • Eric Plemmons Istituto Nazionale di Fisica Universidad Nacional Aut´ onoma • Noah Birge Nucleare, Sezione di Pisa de M´ exico • Michele Viviani • Connor Gautham • Libertad Baron Oak Ridge National Laboratory • Mae Scott • Andr´ es Ramirez-Morales • David Bowman University of Tennessee at University of New Hampshire • Vince Cianciolo Chattanooga • John Calarco • Paul E. Mueller • Josh Hamblen • Seppo Penttil¨ University of Nevada at Los Vegas a • Jeremy Watts • Jack Thomison • Caleb Wickersham • A. Barzilov • T. Tong Middle Tennessee State University of South Carolina University of Indiana University • Vladimir Gudkov • Chad Gillis • Robert Mahurin • Matthias Schindler University of Kentucky University of Virginia • Young-Ho Song • Chris Crawford • Stefan Baessler • Latiful Kabir University of Tennessee • Aaron Sprow • Nadia Fomin • Septimiu Balascuta 14 / 21
Spare Slides 15 / 21
Parity Transformation A parity transformation, P inverts the spatial coordinates, inverting polar vectors, such as momentum , P ( � k ) = − � k , but not axial vectors, such a spin, P ( � σ ) = � σ . � σ n � k p Original state: θ s ,� � σ n k p n 3 He Beam T � σ n Parity transformed: � σ n p n 3 He T Beam θ s ,� k � k p � k p Spin flipped: θ s ,� k p n Beam 3 He T σ n � � σ n 16 / 21
FnPB CAD Model 17 / 21
n3He In FnPB 18 / 21
Collimator • 4 independent haws • Cd and Li-6 neutron absorbing layers used to stop beam 19 / 21
Assembled Frame Stack • 144 signals to read out • 0.02” diameter wires • 17 HV frames • 16 signal frames 20 / 21
Chamber Assembly • 1mm aluminum windows • 4 signal feed thrus • 2 gas feed thrus • 2 HV feed thrus • 0.47 atm He-3 fill gas • operated at -350V • 4 point kinematic mount allows the target to be aligned to the magnetic field and neutron beam 21 / 21
Recommend
More recommend
