The NPD ExperimentDavid Bowman

I Scientific goals

II Status

NPD Collaboration

• Institutions– Dayton, Dubna, Hamilton, Indiana, Jlab, KEK,

LANL, NIST, ORNL, TRIUMF, Berkeley, Manitoba, Michigan, New Hampshire, Tennessee

• Sponsors– DoE, NSF, NSERC, LANL, collaborating

institutions

Scientific goal of the experiment

€

• Measure Aγ ±10-8 , the σn ⋅kγ asymmetry in

r n + p → d +γ

• Aγ = 0 if parity is conserved in the NN interaction

• The NN interaction violates parity due to the small

weak interaction between nucleons

• The hadronic weak interaction can be described by

a meson - exchange potential

• Aγ determines the weak πNN coupling, fπ1

Hadronic weak interaction

• Weak NN force interferes with the strong NN force.

• Changes parity of the NN pair.• Changes INN by 0, 1, or 2.• Produces parity-violating admixtures in

nuclear wave functions and PV asymmetries• HWI is described by a meson exchange

potential

The value of is controversial

• 18F gamma circular polarization experiments give 0. Haxton interprets result to give =0±1.0 10-7.

• 133Cs anapole moment gives non-zero value. Flambaum interprets result to give =7±3 10-

7.• The goal of the NPD experiment is to

measure with an accuracy of 0.5 10-7.• Goal error is 5% of the DDH reasonable

range.

€

fπ1

€

fπ1

€

fπ1

€

fπ1

Status of NPD experiment

• 04-5 commissioning run complete

• 06 production at LANSCE– Measure A to ±10-7

• Move to SNS in 06-7– Measure A to ±10-8

Apparatus to measure A

Neutron Intensity Monitors

3He neutron polarizer

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The r n +3 r

H e → p+3H reaction

is polarization dependent.

σ parallel = 2.3 barns

σanti -parallel =1696 barnsEn

=TOF vthermal σthermal

LThe anti -parallel state is

removed leaving a polarized

beam.

Determine 3He polarization

€

Tpol Tun =Cosh P3 n3 σ 3( ) =

CoshP3 n3 σthermal vthermal t

l

⎛ ⎝ ⎜

⎞ ⎠ ⎟

P3 = .4678 ± .19% stat.

• Stable operation for

several weeks

• 3He polarization = 46±2%

Commissioning the RFSR

FP12 neutron guide

RF Spin Rotator

3He Spin Filter

M1 M2

Spin-flipper efficiency

Preliminary

Liquid Para-Hydrogen Target• 20 liter liquid volume, 30 cm diameter and 30 cm long

• Absorbs 65% of neutron beam

• 1% neutron depolarized at 17K (0.05% of LH2 in ortho-state) due to large scattering cross section

• No false asymmetries from target material

• Use 6Li to shield CsI from neutrons

Ortho (total)

Para (total)

Capture cross section

CsI detector 48 (15cm)3 modules

noise/counting statistics

• Electronic noise << counting statistics• Experiment operates close to counting

statistics limit€

σ exp =1.07

number of γ' s

Electronic asymmetries(beam off)

• Time to determine electronic asymmetries << run time

• False asymmetries are 10-8

Asymmetry

(10-8)

Time

(hours)

Additive -0.1±.3 5

Multiplicative -0.8 ±.5 11

Measured asymmetries

• Time to determine background asymmetries << run time• False asymmetries ~ asymmetry f-bkg are 5 10-8

MaterialTime

(shifts)f-bkg (%)

U-D (PV)

Asy.(10-6)

L-R (PC)

Asy.(10-6)

Al 21. 6. 0.0±0.3 0.2±0.3

Cu .5 2. 1.2±2.5 -0.3±2.5

B .5 0.7 1.3±2.3 -4.5±3.3

In .5 0.4 -3.2±2.3 -3.0±2.5

Cl 1. 0.0 19.2±2.0 0.6±2.0

Spin interactions

Estimated sizes of false asymmetries

Apparatus performance

• All components of the apparatus performed as designed

• Several physics measurements have been

LH target must be finished, tested, and installed

• We request a thorough-going safety review to insure a safe target.

Beam time request

• The estimate is based on measured performance– 3He polarization = .55– Cell diameter = 10 cm

• Projected FPNB projected intensity• 7000 MWh for data and systematics• 1000 h at > ,14 MW for tuning and

systematics

Schedule

• We request that NPD run after the beam line is commissioned– 9/06 Move to SNS– 9/07 Beam line ready– 12/07 Experiment installed– 3/08 Commissioning complete– 6/08 Start production

Geoff’s questions

• Technical issues - hydrogen target• Funding $K 2500 already spent for apparatus at LANL

– 20 transport to SNS– 160 shielding– 20 supports and stands– 20 Air conditioning– 130 target infrastructure– 30 instrumentation/cabling

• Safety - hydrogen target• Complex installation - one block• ~ 40 users• 3 PhD’s to date, trained several undergraduate students, Expect

several PhD’s from SNS run