# Presentation: 823649

## Proposed measurement of the Parity-Violating Neutron Spin Rotation in Liquid-4He

- Proposed measurement of the Parity-Violating Neutron Spin Rotation in Liquid-4He

**Anna Micherdzinska**
**I****ndiana ****U****niversity ****C****yclotron ****F****acility**

- PANIC							             27 Oct 2005

## Collaboration

- C.D. Bass2, B.E. Crawford1, J.M. Dawkins2, B.R. Heckel5, P.R. Huffman4,
- D. Luo2, D.M. Markoff4, A.M. Micherdzinska2, H.P. Mumm3, J.S. Nico3,
- M.G. Sarsour2, W.M. Snow2, H.E. Swanson5
- Gettysburg College1
- Indiana University / IUCF2
- National Institute of Standards and Technology (NIST)3
- North Carolina State University / TUNL4
- University of Washington5
- NSF PHY-0100348

## Seminar overview

**Motivation **
- Why study parity violation (**PV)** in neutron spin rotation
- What is spin rotation?
**Experiment**
- Experimental challenges
- Design of apparatus
**Summary/Goals**

## Motivation

- Parity Violation (PV) neutron spin rotation is a probe of the NN weak interaction
-     		     after ~ 40 years of study hadronic weak interaction is not understood
- 						   ( data + theory is inconsistent)
- Why this is important to understend NN weak interactions ?
- needed to interpret PV in atomic, nuclear and hadron physics
- sensitive to q-q correlation in nucleon

- Relative weak/strong amplitudes: ~[e**2**/m**W****2**]/[g**2**/m******2**]~10**-7**

##     The NN weak interaction: Theoretical description

- assumes , and exchange dominate the low-energy PV NN potential as they do for strong NN

- Weak meson exchange coupling constants
*f**********h******************h****************h****************h****************h*************

**DDH**** meson exchange model**

## n-4He orthogonal to 133Cs, p-4He n-4He spin rotation in terms of weak couplings (=10-7rad/m, Dmitriev)   DDH “best values” =-(0.97f+0.32h0-0.11h1+0.22h0-0.22h1) rad/mn+p->D+ asymmetry determines f fDesplanques) plot: =310-7 rad/m, =510-9

- n-**4**He orthogonal to **133**Cs, p-**4**He n-**4**He spin rotation in terms of weak couplings (=10**-7**rad/m, Dmitriev)   DDH “best values” =-(0.97*f*******+0.32*h**********0***-0.11*h**********1***+0.22*h**********0***-0.22*h**********1***) rad/mn+p->D+ asymmetry determines *f********* *f*Desplanques) plot: =3****10**-7** rad/m, =5****10**-9**

- Current knowledge about weak NN amplitudes**  **

## transversely polarized neutrons corkscrew due to weak NN interaction [opposite helicity components of |>z=1/2(|>x+ |>x) accumulate different phases from snpn term in forward scattering amplitude]

PV rotation angle per unit length d/dx related to PV amplitude [=(n-1)px, n-1=2f/p2] 

 d/dx ~1x10-7 rad/m (DDH), 3x10-7 rad/m goal at NIST 06 in n+4He

Parity Violating  d/dx independent on vn

Parity Conserving  d/dx  (due to B field) dependent of vn

- transversely polarized neutrons corkscrew due to weak NN interaction [opposite helicity components of |>**z**=1/2(|>**x**+ |>**x**) accumulate different phases from snpn term in forward scattering amplitude]
- PV rotation angle per unit length d/dx related to PV amplitude [=(n-1)px, n-1=2f/p**2**]
-  d/dx ~1x10**-7** rad/m (DDH), _3x10__**-7**__ rad/m goal at NIST 06 in n+__**4**__He_
- Parity Violating  d/dx independent on v**n**
- Parity Conserving  d/dx  (due to B field) dependent of v**n**

- Parity Violation in Neutron Spin Rotation

**x**

**z**

- polarizer

- analyzer

##    Suppression of B in target

- All possible systematic effects have to be reduced...  Magnetic field is responsible for all of these !
- (Earth field ~50T cause rotation of 5A neutrons ~ 10rad/m) 		             We have to reduce B field:
- Magnetic shields                                                                                        fluxgates, trim coils
-   2nT in target region still not good enough (rotation 100 times bigger than **pv**)
- _Target design_ – to extract tiny PV signal from much bigger due to magnetic field

##    Target design to further suppress B rotation

- 3He n-detector
- Analyzer
- Target Chamber – back position
-  **** – Coil
- Target Chamber – front position
- Polarizer

******F****+**** ********PV**

- -******F ****-**** ********PV**

******B**-******F****)**** ****-**** ********PV**

******mag**** ****-**** ********PV**

- A

- B

- B – A = 2******PV**

- z

- y

- x

## Target design

- 3He n-detector
- Analyzer
- Target Chamber – back position
-  **** – Coil
- Target Chamber – front position
- Polarizer

- Cold Neutron Beam

- A

- B

- B – A = 2******PV**

**** – Coil

##    Cross section of Spin Rotation Apparatus

-    Cross section of Spin Rotation Apparatus

## Associated with residual longitudinal B (B< 10 nT )

			effect				               estimate of size

He diamagnetism		      (BHe ≠ Bvac)		~10-8 rad/m

He optical potential	 	      (VHe ≠ Vvac)		~10-8 rad/m

small angle scattering in He				~10-8 rad/m

LHe 	superfluid LHe: decrease small angle scattering by ~(5)

PV spin rotation independent of neutron energy, B rotation depends on neutron energy. 
At NIST we will amplify effects by increasing B in separate measurements. However, no
TOF... (future SNS !) 

previous version (1996): upper bound on systematic effects < 210-7 rad/m
our goal: systematic effects < 110-7rad/m

We will amplify systematic effects using ~ 100T field

- 	_	__	__effect__	__	__	__	__               estimate of size_
**He diamagnetism****	****	****      ****(B****He **≠ **B****vac****)****	****	****~10****-8**** rad/m**
**He optical potential****	**** ****	****      (V****He**** **≠** V****vac****)****	****	****~10****-8**** rad/m**
**small angle scattering in He****	****	****	****	****~10****-8**** rad/m**
- LHe 	superfluid LHe: decrease small angle scattering by ~(****5)
- PV spin rotation independent of neutron energy, B rotation depends on neutron energy.
- At NIST we will amplify effects by increasing B in separate measurements. However, no
- TOF... (future SNS !)
- previous version (1996): upper bound on systematic effects < 210**-7** rad/m
- our goal: systematic effects < 1****10**-7**rad/m
- We will amplify systematic effects using ~ 100T field

-    Systematic Effects in PV Spin Rotation

##    Summary and plans

- We will perform challenging search for neutron spin rotation in LHe at NIST at the beginning of 2006
- Experimental apparatus was updated since 1996 measurement (receiving ******PV**(n,a) = ( 8.0 ±14 (stat) ± 2.2 (syst) )**** 10**-7** rad/m)
- New target, additional CRYOPERM magnetic shield, monitoring magnetic field outside and in the target region, active trim coils, all nonmagnetic materials, use of superfluid LHe.
- NIST: increase the detected beam flux by a factor of 1.5, monitoring magnetic field outside of our apparatus.
- Successful measurement  (sensitivity goal ******PV**=3****10**-7** rad/m in 3 months of data taking + ~1 month of systematic study) will broaden our knowledge about NN weak interaction
- letter of intent approved to perform PV neutron spin rotation in LHe at SNS