Collins effect ( Sin(fh fS) )

1
Neutron (e,ep) Target Single-Spin Asymmetry in
Semi-inclusive DIS on a Transversely Polarized
3He Target
-
Kalyan Allada, Chiranjib Dutta, Mitra Shabestari,
Xin Qian On the behalf of Transversity
Collaboration Two experiments with the highest
scientific rate
A
Nucleon Structure
Characteristics of Transversity
Detector system 3He Target

• Beam
• - 6Gev, 15 microA electron beam
• Target

Well Known, since first measurement at 70s.

• 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)

Reasonable Known with 20 years effort.
Transversity, business just started.
HALL-A 3He Target

• 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.

• Some characteristics of transversity
• h1T g1L for non-relativistic quarks
• In non-relativistic case, boosts and rotations
  commute.
• Important inequalities h1Tq f1q
  h1Tq (f1q g1Lq )/2.
• h1T and gluons do not mix
• Q2-evolution for h1T and g1L are different
• Chiral-odd ?
• not accessible in inclusive DIS

HRS
HRS
Understanding the underlying nucleon structure
(Spin, flavor, charge, current distribution) from
quantum chromodynamics (confinement region) is
essential.
q
q
Helicity state
Electronuclear Scattering ------ A powerful tool
to study nuclear structure

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

N
N
-

Spectrum
Inclusive (the main tool) detecting electron
only Semi-inclusive (providing additional
information) detecting electron and one of the
hadrons coincidently

• Hall-A Setup

• 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)

Asymmetry in Semi-Inclusive DIS with polarized
target

• Collins and Sivers Asymmetry

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

What is Semi-Inclusive Deep Inelastic Scattering
(SIDIS)

• Collins effect ( Sin(fh fS) )
• Access to transversity
• Artru model
• Based on LUND fragmentation
• picture.

Scattering plane
Parton distribution Function (PDF)

• Charged pion detection
• - Hall-A High Resolution Spectrometer, at -160

Projections

• 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.

Fragmentation function (FF)
DXsPDFFF
The kinematics and coordinate

• Sivers effect ( Sin(fh- fS) )
• A new type of PDF, T-odd, depends on
  intrinsically quark transverse momentum
  quark orbital momentum

• E is the energy of scattered electron
• ?e is the scattering angle
• ? E-E is the energy transfer.
• kT quark transverse momentum

HERMES 3 years
COMPASS 1 year
Beam direction
Into the page
DIS Q2 (1/?) and ? is large, but x is finite.
HALL A 29 days