Measurement of double-Measurement of double-polarized asymmetries in polarized asymmetries in quasi-elastic processes quasi-elastic processes

33He(e,e’d) and He(e,e’d) and 33He(e,e’p)He(e,e’p)

Miha MihoviloviMiha MihoviloviččFor the E05-102 CollaborationFor the E05-102 Collaboration

Why study Why study 33He?He?

- ProtonProton is well known and its properties are precisely measured.

- NeutronNeutron is relatively poorly understood. Only loose constraints on the charge, magnetism and spin distributionProblem:Problem: direct measurements not possible, no neutron target.

Solution:Solution: indirect measurements using appropriate targets:

1.) DeuteronDeuteron where neutron behaves almost as a free free particle due to the small binding energy (~2MeV)

2.) Polarized Polarized 33HeHe used as effective polarized neutron effective polarized neutron target.target. !!

!!!!

33He as effective nHe as effective n00 target target

Precision of this approximation depends on the understanding of the structure of the 3He.

Precise test of understanding of the 3He structure, nuclear forces between nucleons, FSI, MEC.

Understand the structure of the nn00

33He is a calculable nuclear He is a calculable nuclear systemsystem, where theoretical predictions of its nuclear structure can be compared with data to an increasingly accurate degree.

Error budget for An1: aside statistical error, leading source of error

is due to the uncertainty of the uncertainty of the polarizationpolarization of the

proton and neutron in polarized 3He.

- A bound state of p,p,np,p,n: S = ½, T = ½ (MS = ½, T = ½ (MTT = = +½)+½)

- Calculations predict three dominant components:

1.) Spatially symmetric state S (90%):Spatially symmetric state S (90%): Protons are in spin-singlet state. 3He spin is dominated by spin of n. n. Therefore 3He can be used as an effective nn target.

2.) State D (8%):State D (8%): Nucleon spins oriented in opposite to the 3He nuclear spin. Generated by tensor component of NN force.

3.) Mixed symmetry state S’ (2%):Mixed symmetry state S’ (2%): Arises from differences between T=0 and T=1 forces and hence reflects (spin-isospin)-space correlations.

33He ground-state wave-functionHe ground-state wave-function

SS

(L=0)(L=0)

np p

S’S’

(L=0)(L=0)

np p

DD

(L=2)(L=2)

np p

AAxx,A,Azz Asymmetry Measurement Asymmetry MeasurementExperiment E05-102 at Jefferson LabExperiment E05-102 at Jefferson Lab

- Understanding the role of the DD and S'S' states in 3He is a very important aspect of the few-body theory.

- Observables sensitive to the S'S' state constitute a stringent test of the theory. Among them are also asymmetries AAxx and AAz.z.

- For polarized beam and polarized target, the cross-section for the 3He(e,e’d) is:

The (±; ±) signs represent the beam helicities and the

projections of the target spin.

- Measuring asymmetries saves a lot of problems, because “all” the problems with normalization of cross-section problems with normalization of cross-section disappeardisappear.

!!

South

Lin

ac

North

Lin

ac

Inje

ctor

A B C

- CEBAFCEBAF center at JLabJLab was built to investigate the structure of nuclei and hadrons at intermediate energies and underlying fundamental forces.

TThomas homas JJefferson efferson NNational ational AAccelerator ccelerator FFacilityacility

6 GeV polarized continuous beam with currents up to 100uA is delivered to three experimental Halls A, B and C.

Experimental Setup in Hall A Experimental Setup in Hall A

Experiment E05-102 in Hall-A Experiment E05-102 in Hall-A

θL

p n

p

p

n

p

θqγ*

Incident polarized electron

Detected

Electron

Detected Deuterons and Protons

Az

Ax

Beam Helicity

Polarized Polarized 33He TargetHe Target

Beam Direction

Oven with Mirrors

Large Coil

12C Optics Target

Small Coil

Polarized 3He Cell

Vertical Coil

Polarization of the Polarization of the 33He TargetHe Target

• Five High-Power IR-Diode lasers (~30W) are used to polarize the target in all three directions

• Optical table with lenses, mirrors, λ-shifters is used to properly guide light from optical fibers to the target.

High Resolution SpectrometersHigh Resolution Spectrometers

2 Quadrupoles2 Quadrupoles

QuadrupoleQuadrupoleDipoleDipole

Detector packageDetector package

Particle Track

HRS - Detector PackageHRS - Detector Package

Scin

tilla

tor

s

Cere

nkov

Scin

tilla

tor

s

Pre-

Show

erSh

ower

VDCs

Electronics

Open Detector-Hut

BigBite Spectrometer BigBite Spectrometer

- Single normal-conducting dipole magnet spectrometer

- Combines a large solid large solid angleangle with a large large momentum acceptance.momentum acceptance.

- Two MWDCs for tracking; Each MWDC consists of 6 wire planes u,u’,v,v’,x,x’

-Two Scintillation planes E/dE for particle identification and Energy determination

Analysis of Measured DataAnalysis of Measured Data

- Experiment was done in June 2009. We accumulated ~15C~15C and collected 7TB7TB of data.

- Now Analysis is now underway. At the moment we are At the moment we are doing calibration of BigBitedoing calibration of BigBite. After the calibration the asymmetry determination will folow.

BigBite Optics CalibrationBigBite Optics Calibration

- Purpose of optics calibration is to determine target variables (yTg, φTg, θTg, δTg) from focal plane variables (xFp, yFp, θFp, φFp).

- There are many parameterizations possible. We use polynomials:

What are the theoretical expectations?What are the theoretical expectations?

S’S’ DD

DD

- The role of S’S’ is most evident in region of small recoil momenta where Ax is large. Az is close to zero at small pr.

- Much stronger variation of Az at high pr. This behavior is This behavior is governed by the D-state.governed by the D-state.

22H Results from NIKHEFH Results from NIKHEF

np

np

SS DD

(L=0)(L=0) (L=2)(L=2)

-This was observed in NIKHEF in the experiment with 2H polarized target

- Deuteron is S=1S=1 particle made of two S=1/2S=1/2 nucleons (p,n) -Sign-change of the Asymmetry is a clear sign that D-state component D-state component becomes important in the becomes important in the nucleus at high pnucleus at high pmissmiss..

ConclusionsConclusions

- Experiments with polarized target and polarized beam are important step forward in the experimental nuclear physicsimportant step forward in the experimental nuclear physics. .

- Asymmetries give an insight to the properties of the nucleons that were not measurable with unpolarized experimentsnot measurable with unpolarized experiments.

- Many 3He experiments were already done.

- Why is experiment E05-102 so special?Why is experiment E05-102 so special?

1.) Double polarized experiment (3He, e )

2.) Measured all three (p,d,n)(p,d,n) channels at same Q2 with ω covering the whole q-e peak and more.

3.) Measured asymmetries as function of peasured asymmetries as function of pmiss.miss.

It is the firstIt is the first, where D-wave and S’-wave contributions to 3He will be inspected in detail in order to understand Spin, Iso-Spin Spin, Iso-Spin structure of Nucleistructure of Nuclei, , MECMEC, , FSIFSI. Very important for all further Very important for all further experiments on experiments on 33He.He.

Thank you for listening!Thank you for listening!