• Collins effect ( Sin(φh+ φS) )– Access to transversity

• Artru model• Based on LUND

fragmentation picture.

Neutron (e,e’Neutron (e,e’ππ±±) Target Single-Spin Asymmetry in ) Target Single-Spin Asymmetry in Semi-inclusive DIS on a Transversely Polarized Semi-inclusive DIS on a Transversely Polarized 33He He

Target Target Kalyan Allada, Chiranjib Dutta, Mitra Shabestari, Xin

QianOn the behalf of Transversity Collaboration

Two experiments with the highest scientific rate: Nucleon StructureNucleon Structure

• Nucleon anomalous magnetic moment (Stern, Nobel Prize 1943)

• Electromagnetic form factor from electron scattering (Hofstadter, Nobel Prize 1961)

• Deep-in-elastic scattering, quark underlying structure of the nucleon (Freedman, Kendell, Taylor, Nobel Prize 1990)

Understanding the underlying nucleon structure (Spin, flavor, charge, current distribution)from quantum chromodynamics (confinement region) is essential.

Electronuclear ScatteringElectronuclear Scattering------ A powerful tool to study nuclear structure

Inclusive: (the main tool)

detecting electron only Semi-inclusive: (providing additional information) detecting electron and one of the hadrons coincidently

Spectrum:

What is Semi-Inclusive Deep What is Semi-Inclusive Deep Inelastic Scattering (SIDIS)Inelastic Scattering (SIDIS)

• E’ is the energy of scattered electron

• θe is the scattering angle

• ν =E-E’ is the energy transfer.

• kT: quark transverse momentum

Characteristics of TransversityCharacteristics of Transversity

• Some characteristics of transversity :– h1T = g1L for non-relativistic quarks

• In non-relativistic case, boosts and rotations commute.

– Important inequalities: |h1Tq| ≤ f1

q ; |h1Tq| ≤ (f1

q + g1Lq )/2.

– h1T and gluons do not mix

– Q2-evolution for h1T and g1L are different– Chiral-odd →

• not accessible in inclusive DIS

N

q q

N

Helicity state

- +

• It takes two Chiral-odd objects to measure transversity– Drell-Yan (Doubly transversely polarized p-p collision)– Semi-inclusive DIS

Chiral-odd distributions function (transversity)Chiral-odd fragmentation function (Collins function)

-

Detector system & Detector system & 33He TargetHe Target

HRS

HALL-A 3He Target

ProjectionsProjections

HRS

Collins and Sivers Asymmetry

Parton distribution Function (PDF)

Fragmentationfunction (FF)DXs~PDF*FF

The kinematics and coordinateThe kinematics and coordinate

DIS: Q2 (1/λ) and ν is large, but x is finite.

Scatteringplane

Beam direction

Into the page

• Sivers effect ( Sin(φh- φS) )– A new type of PDF, T-odd, depends on intrinsically

quark transverse momentum quark orbital momentum

Asymmetry in Semi-Inclusive DIS with polarized Asymmetry in Semi-Inclusive DIS with polarized targettarget

40-cm long Rb-K spin-exchange hybrid cell at 10 atm .

~42% target polarization with spin-flip frequency of 20 minutes.

A third set of Helmholtz coil will be added together with the laser optics to allow vertical polarization of the 3He target.

Target Polarimetry

NMR and EPR will be used to measure the target polarization.

First direct data on neutron AUT

At high-x

Clear separation of Collins and Sivers effect.

Statistical uncertainty dominates.

Kinematics comparable to the HERMES experiment.

Hall-A Setup

Beam

- 6Gev, 15 microA electron beam

Target

Electron detection - BigBite spectrometer, solid angle = 64msr, at 300

Charged pion detection

- Hall-A High Resolution Spectrometer, at -160

Transversity, business just started.

HALL A: 29 days

HERMES: 3 years

COMPASS: 1 year

Well Known, since first measurement at 70s.

Reasonable Known with 20 years effort.

A