The measurement of Parity Violating asymmetry in

and n p d d n p

Yongjiang Li

Supervisor: Prof. Wang XuShanghai Institute of applied physics, CAS ， China

Collaborator: Prof. W.M. SnowIndiana university, USA

Outline

Section 0 collaboratorsSection 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 GammaDNP

d n p n p d

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 208996 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 2769517 Joint Institute of Nuclear Research, Dubna, Russia

18 Dept. of Physics, Univ. of Dayton, Dayton, OH 45469-231419Shanghai Institute of applied physics, Shanghai, China

Section I The capture of polarized neutron by parahydrogen n p d

• NN weak interaction

|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

outside=QCD vacuum

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 interactionVisible using parity violation

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

~1 fm

~1/100 fm range

weak

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.

classical

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

DDH - ModelDesplanque, Donohue, Holstein 1980

1 0 1 1' 2 0 1, , , , , ,f h h h h h h

N

N

PV

PC

W and Z boson exchange

W and Z boson exchange

The Hadronic Weak Interaction

why we choose ?n p d

n p

d

205 133

z

18 21

19

Observables on this plot :

•Nuclearanapolemoment : Tl, Cs

•Longitudinal analyzing powerA : p p, p

•Photon polarization P : F, Ne, d np

•Directional gamma asymmetry A : F,np d

is a clean measurement of fπ: dpn

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

NPD

Goal

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.

f - 0.12 h

- 0.18 hx 107

80.11 5 10 (predicted value)A f

NPDgamma apparatus on FP12 at LANSCE

3He polarizer

• 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.

33He cellHe cellUnpolarizedUnpolarized

NeutronsNeutrons

PolarizedPolarized

NeutronsNeutrons

Helmholtz CoilsHelmholtz Coils

Polarized Laser LightPolarized Laser Light

RF Spin FlipperRF Spin Flipper

• 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.

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

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 Target16-liter Liquid Para-Hydrogen Target

• To maintain neutron spin in scattering a para- hydrogen target is required.

• The Φ 30cm×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)

Point target and point detector:

Detector yield:

Detector Geometry:Detector Geometry:Neutron Polarization:Neutron Polarization:Spin Flip Efficiency:Spin Flip Efficiency:Neutron DepolarizationNeutron Depolarization ：：Capture LocusCapture Locus：：Gamma Energy DepositionGamma Energy Deposition ：：

Measured Asymmetries

Asymmetry analysis and results(2)

Neutron time-of-flight from pulsed source (msec, En1/t2)

Aγ,UD = (−1.1 ± 2.1(stat.) ± 0.2(sys.)) × 10−7 Aγ,LR = (−1.9 ± 2.0(stat.) ± 0.2(sys.)) × 10−7

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

Systematics, e.g:● activation of materials,e.g. cryostat windowsStern-Gerlach steering

● in magnetic field gradientsL-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

Simulation of the systematic effects1. Mott schwinger Scattering( ( ))f is p p

R-L asymmetry

2. Scattering of polarized gamma rays by magnetized iron

Neutron Spin = +/-

MagnetizedIron Roof

LH Target

MagnetizedIron Floor

ElectronPolarization

CP=+/-

CP=-/+

•In the (polarized)n+p->D+gamma reaction, the gamma has a small circular polarization•the scattering cross section is spin dependent.

NPDgamma at SNS at ORNL

Supermirror polarizer

FNPB guide

CsI Detector Array

Liquid H2 Target

H2 Vent Line

Beam Stop

Magnetic Field Coils

H2 Manifold Enclosure

Spin Flipper

Goal：statistical statistical

error=1x10error=1x10−8−8

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 .

1 0 1 2 0 11 2 3 4 5 6

0 2 0 3

0 2 0

( ) ( ) ( ) ( ) ( ) ( ) ( )

( ) 0.70 0.17 ( 8.85 17.34 3.13 ) 10

( 12 ) 0.037 0.022 ( 1.159 2.244 1.584 ) 10

N t N s

N t N s

A c h c h c h c h c h c h

A threshold m m h h h

A MeV m m h h h

3

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

d n p Why we choose the ?d n p

0 0 2 2 0 0 1 1 1 1 1( ) ( )A E a g h a g h a g h a g h g h a g h a g h

0 2 0 3

2 0 3

2 0 3

0

0.4

10

( ) (4.82 7.43 0.99 ) 10

( ) (3.13 0.67 ) 10

( ) 0.211 ( ) 10

thr

thr

thr

E E

E E MeV

E E MeV

A g h g h g h

A g h g h

A g h h

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

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

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

0 0

0

here ( ) denotes the total cross section of

when the state of gamma ray

is right(left) circularly polarized.

, ,

is the total reaction cross section

exc

d np

pol pol

A

d np

ept the cross section depend

on the gamma polarization.

pol

The theory predicted value of A γ is :8( 2.2 ) 2.53 10d npA E MeV

8( 2.2 ) 1 10d np

d np

AE MeV

A

(ref: Liu2004 ， PRC69 ， 065502)

1016 counts

What is observable?

D2O target

Graphite

Collimator

4He gas ion chamber

γ detector

3He gas ion chamber

6Li

γ detector

Pb wall

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.

Proposed apparatus

3 3

4 4

0.764 ( 5000 )

( 4 )

n He p H MeV b

n He n He b

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

apparatusdesign

Geant4simulation

geometry

results

In the near future, we will construct the SLEGS.

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

Electron energy 3.5GeV

Laser energy 0.117eV

Gamma ray energy ≤22MeV

Beam intensity 108-1010 photons/s

Wavelength 10.4-10.8 μm

Peak power 500 MW

Rise/fall time ＜ 90 μs

Stabilization of power (%)

±8

Using a polarized laser, a polarized γ ray can be generated.When we change the polarization of the laser, the polarization of γ ray reverse .

e Laser γ ray

e

We preliminarily list some of the systematic effects :

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 ……▶

♣ ……

0 1

( , , , , , , , , , , , )

( ) ( )

( , , , , , , , , , , , , )

n n p p D D e e

m n

n n p p D D e e

P S P S P S P S P S P S

A B S A B P A B

A B P S P S P S P S P S P S

… …

we will find out the corresponding physics processes.

What is the next for GammaDNP ?

1. Find the relationship between the Asymmetry and the coupling constants at the neutron energy of ~20MeV.

2. Do the Monte Calro simulation of GammaDNP

3. Analysis the source of systematic effects, the corresponding physics process

4. 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 h2

ρ. 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.