1. Neutron (e,e’π±) 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
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)
Well Known, since first measurement at 70s.
Beam
- 6Gev, 15 microA electron beam
Target
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
state
Helicity
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(φh+ φS) )
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)
DXs~PDF*FF
The kinematics and coordinate
Sivers effect ( Sin(φh- φS) )
A new type of PDF, T-odd, depends on intrinsically quark transverse momentum quark orbital momentum
E’ is the energy of scattered electron
θe is the scattering angle
ν =E-E’ is the energy transfer.
kT: quark transverse momentum
HERMES: 3 years
COMPASS: 1 year
Beam direction
DIS: Q2 (1/λ) and ν is large, but x is finite.
Into the page
HALL A: 29 days