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Yongjiang Li. Supervisor: Prof. Wang Xu Shanghai Institute of applied physics, CAS , China Collaborator: Prof. W.M. Snow Indiana university, USA. Outline. Section 0 collaborators Section I introduction of ( the motivation, apparatus, preliminary results ) Section II Introduction of

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Yongjiang Li

Supervisor: Prof. Wang Xu

Shanghai Institute of applied physics, CAS,China

Collaborator: Prof. W.M. Snow

Indiana university, USA


Section 0 collaborators

Section I introduction of

(the motivation, apparatus, preliminary results)

Section II Introduction of

(the motivation, proposed apparatus, SLEGS, systematic effect,plan)

Section III Conclusion of NPD Gamma and


section 0 npdgamma collaborators
Section 0 NPDGamma collaborators

J.David Bowman,1 Roger D. Carlini,2 Timothy E. Chupp,3 Wangchun Chen,4, Silviu Corvig,6 Mikayel Dabaghyan,6 Dharmin Desai,7 Stuart J. Freedman,8 Thomas R. Gentile,5 Michael T. Gericke,9 R. Chad Gillis,9 Geoffrey L. Greene,7,10

F. William Hersman,6 Takashi Ino,11 Takeyasu Ito,7 Gordon L. Jones,12 Martin Kandes,3 Bernhard Lauss,8 Mark Leuschner,4

Bill Losowki,13 Rob Mahurin,7 Mike Mason,6 Yasuhiro Masuda,11 Jiawei Mei,4 Gregory S. Mitchell,1 Suguro Muto,11 Hermann Nann,4 Shelley Page,9 Seppo Pentilla,1 Des Ramsay,9,14 Satyaranjan Santra,15 Pil-Neyo Seo,16 Eduard Sharapov,17 Todd Smith,18 W.M. Snow,4 W.S. Wilburn,1 Wang Xu,19 Vincent Yuan,1 Hongguo Zhu,6

1 Los Alamos National Laboratory, Los Alamos, NM 87545

2 Thomas Jefferson National Accelerator Facility, Newport News, VA 23606

3 Dept. of Physics, Univ. of Michigan, Ann Arbor, MI 48109

4 Dept. of Physics, Indiana University, Bloomington, IN 47408

5 National Institute of Standards and Technology, Gaithersburg, MD 20899

6 Dept. of Physics, Univ. of New Hampshire, Durham, NH 03824

7 Dept. of Physics, Univ. of Tennessee, Knoxville, TN 37996

8 Univ. of California at Berkeley, Berkeley, CA 94720

9 Dept. of Physics, Univ. of Manitoba, Winnipeg, Manitoba, R3T 2N2 Canad

10 Oak Ridge National Laboratory, Oak Ridge, TN 37831

11 High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki, Japan

12 Dept. of Physics, Hamilton College, Clinton, NY 13323

13 Indiana University Cyclotron Facility, Bloomington, IN 47408

14 TRIUMF, Vancouver, British Columbia V6T2A3 Canada

15 Bhabha Atmoic Research Center, Mumbai, India

16 Dept. of Physics, North Carolina State University, Raleigh, NC 27695

17 Joint Institute of Nuclear Research, Dubna, Russia

18 Dept. of Physics, Univ. of Dayton, Dayton, OH 45469-2314

19Shanghai Institute of applied physics, Shanghai, China

section i
Section I
  • NN weak interaction

~1 fm

outside=QCD vacuum

|N>=|qqq>+|qqqqq>+…=valence+sea quarks+gluons+…

interacts through strong NN force, mediated by mesons |m>=|qq>+…

Interactions have long (~1 fm) range, QCD conserves parity

If the quarks are close, the weak interaction can act, which violates parity. Relative strong/weak amplitudes: ~ [g2/m2] / [e2/m2W]~106

Quark-quark weak interaction induces NN weak interaction

Visible using parity violation

q-q weak interaction: an “inside-out” probe of strong QCD

~1/100 fm range



The Hadronic Weak Interaction

W and Z boson exchange

Nucleon interaction takes place on a scale of 1 fm -- short range repulsion. Due to the heavy exchange particles, the range of W± and Z0 is 1/100 fm, weak interaction probes quark-quark interaction and correlations at small distances.

At low energies N-N weak interaction modeled as meson exchange with one strong PC vertex, one weak PV vertex.


The weak PV couplings contribute in various mixtures and a variety of observables:

W and Z boson exchange

DDH - Model

Desplanque, Donohue, Holstein 1980







NPDGamma aims to measure the correlation between the neutron spin and the direction of the emitted photon in neutron-proton capture at low momentum transfer.

  • is a clean measurement of fπ:

fp1 - 0.12 hr1 - 0.18 hw1 x 107

  • •Negligible contributions from ρ, ω, 2π exchanges less than 1% contribution
  • •No uncertainty from nuclear wave functions
3 he polarizer
3He polarizer

Polarized Laser Light

  • The method of neutron polarization relies upon the spin dependence of the interaction of neutrons with 3He nuclei.
  • The 3He nuclei are polarized by shining circularly polarized laser light on a glass cell containing 3He atoms and a small amount of rubidium.





3He cell

Helmholtz Coils

rf spin flipper
RF Spin Flipper

The rapid reversal of the neutron spin is important in the reduction of systematic effects.

  • Using the 20 Hz time scale set by the LANSCE source, the spin flipper reverse the neutron polarization direction periodically with a ↑↓↓↑↓↑↑↓ pattern.
  • This pattern eliminates the effects of first- and second-order time-dependent

drifts in detector efficiencies.

csi tl detector array
CSI(Tl) detector array

● 3π acceptance

● 48 crystals CsI (Tl) arranged in 4 rings

surrounding the LH2 target

● Current-mode experiment

● γ-rate ~100MHz (single detector)

● (15 ×15 × 15) cm3 CsI (Tl) crystals

16 liter liquid para hydrogen target
16-liter Liquid Para-Hydrogen Target
  • To maintain neutron spin in scattering a para- hydrogen target is required.
  • The Φ30cm×30cm target captures 60% of incident neutrons.
  • At 17 K only 0.05% of LH2 is in ortho state  1% of incident neutrons will be depolarized.
  • Target cryostat materials selected so that false asymmetries < 10-10.
  • Neutron mean free paths at 4 meV in
  • - ortho-hydrogen is = 2 cm,
  • - para-hydrogen is = 20 cm
  • for a n-p capture is = 50 cm.

useful range 1-15 meV

asymmetry analysis and results 1
Asymmetry analysis and results(1)

Point target and point detector:

Detector yield:

Detector Geometry:

Neutron Polarization:

Spin Flip Efficiency:

Neutron Depolarization:

Capture Locus:

Gamma Energy Deposition:

Measured Asymmetries

asymmetry analysis and results 2
Asymmetry analysis and results(2)

The first phase of the experiment was completed in 2006 at LANSCE.

Aγ,UD = (−1.1 ± 2.1(stat.) ± 0.2(sys.)) × 10−7

Aγ,LR = (−1.9 ± 2.0(stat.) ± 0.2(sys.)) × 10−7

Systematics, e.g:

● 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

Neutron time-of-flight from pulsed source (msec, En1/t2)

simulation of the systematic effects
Simulation of the systematic effects

R-L asymmetry


Iron Roof


2. Scattering of polarized gamma rays by magnetized iron

Neutron Spin = +/-

LH Target

•In the (polarized)n+p->D+gamma reaction, the gamma has a small circular polarization

•the scattering cross section is spin dependent.



Iron Floor




NPDgamma at SNS at ORNL



CsI Detector Array

Liquid H2 Target

H2 Vent Line

H2 Manifold Enclosure

Spin Flipper

FNPB guide

Magnetic Field Coils

Beam Stop


statistical error=1x10−8

section ii the photodisintegration of deuteron by circularly polarized gamma rays
Section II The photodisintegration of deuteron by circularly polarized gamma rays

1. The asymmetry is mainly defined by Δ I=0,2 parity-violating interactions.

2. The relationship between the asymmetry and the meson-nucleon coupling constants is energy dependent.

3.The best way to determine the ΔI=2 interaction h2ρ.





C.-P. Liu, PRC 69, 065502 (2004)


Ref : M. Fujiwara,PRC 69, 065503 (2004)

At present, there are not believable theory calculation for photon energy above12MeV.


What is observable?

  • We observe the asymmetry of the reaction cross section by measuring the generated neutron.

The theory predicted value of Aγis :

(ref: Liu2004,PRC69,065502)

1016 counts


Proposed apparatus


3He gas ion chamber

Pb wall


D2O target


γ detector

γ detector

4He gas ion chamber

Circular Polarized γ

♣ the detectors will operated in current model

♣ Graphite is used as neutron moderator.

♣ the 3He gas ion chamber Will absorb the most of neutrons, but 4He don’t. ♣ the gamma cross section on 3he and 4He is almost exactly the same.

♣ 6Li is used to prevent neutrons from going into the γ detector.

monte calro simulation
Monte Calro Simulation

We plan to simulate the GammDNP reaction in the Geant4 code. We are building the geometry in the code.








Shanghai Laser Electron Gamma Source (SLEGS) on SSRF at SINAP





In the near future, we will construct the SLEGS.

Using a polarized laser, a polarized γray can be generated.

When we change the polarization of the laser, the polarization of γray reverse .


List of systematic effects

♣laser beam:

▶ how close to “perfect” circular polarization

▶ beam flux

▶ frequency of helicity change

▶change of I(x, y,E, θx, θy) when switch

the polarization of the laser

▶ ……

♣electron beam:

▶ the polarized electrons in electron beam

▶ the efficiency of laser- electron collision

▶noise in intensity

▶ I(x, y,E, θx, θy)

▶ elliptical polarization

▶ ……

♣ Instrumental:

▶ windows laser pass through

▶the magnetic field

▶ ……

♣ ……

We preliminarily list some of the systematic effects :


What is the next for GammaDNP ?

  • Find the relationship between the Asymmetry and the coupling constants at the neutron energy of ~20MeV.
  • Do the Monte Calro simulation of GammaDNP
  • Analysis the source of systematic effects, the corresponding physics process
  • Simulate and calculate the systematic effects.

SectionIII Conclusion of N+P→Gamma+D and Gamma+D→N+P

★ the NPDGamma experiment have completed its first phase at LANSCE and will start its second data taking in early 2010 at ORNL.

★The GammaDNP experiment is essential to determine the constant of

h2ρ. And the relationship of parity-violating Asymmetry and coupling

constants is energy dependent.

★based on the SLEGS, it is possible to perform the GammaDNP experiment in the future.

★ The cooperation with NPDGamma group wil help us to draw valuable experience , and continue cooperation for the GammaDNP.