Transcript 幻灯片 1 - Jefferson Lab

Neutron (e,e’π±) Target Single-Spin Asymmetry in Semiinclusive 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:
Characteristics of Transversity
Nucleon Structure
• Nucleon anomalous magnetic
moment (Stern, Nobel Prize
1943)
 Beam
- 6Gev, 15 microA electron beam
Reasonable Known with 20 years effort.
Transversity, business just started.
 Target
HALL-A 3He Target
40-cm long Rb-K spinexchange hybrid cell at 10 atm
. HRS
• Some characteristics of transversity :
HRS
– h1T = g1L for non-relativistic quarks
• In non-relativistic case, boosts and rotations commute.
Understanding the underlying nucleon structure (Spin,
flavor, charge, current distribution)
from quantum chromodynamics (confinement region) is
essential.
 ~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.
– Important inequalities:
|h1Tq| ≤ f1q ; |h1Tq| ≤ (f1q + g1Lq )/2.
q
q
Helicity
– h1T and gluons do not mix
state
Electronuclear Scattering
– Q2-evolution for h1T and g1L are different
– Chiral-odd →
• not accessible in inclusive DIS
------ A powerful tool to study nuclear structure
Spectrum:
Inclusive:
Detector system & 3He Target
Well Known, since first measurement at 70s.
• 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)
A
N
Target Polarimetry
N
+
-
 NMR and EPR will be
used to measure the target
polarization.
(the main tool)
 Hall-A Setup
detecting electron only
Semi-inclusive: (providing
• It takes two Chiral-odd objects to measure
transversity
additional information)
detecting electron and one of the
hadrons coincidently
– 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
Scattering
plane
Parton distribution
Function (PDF)
• Artru model
• Based on LUND
fragmentation
picture.
 Charged pion detection
- Hall-A High Resolution Spectrometer, at -160
Projections
DXs~PDF*FF
 First direct data on neutron AUT
Fragmentation
function (FF)
 At high-x
Clear separation of Collins and Sivers effect.
Statistical uncertainty dominates.
The kinematics and coordinate
• Sivers effect ( Sin(φh- φS) )
• E’ is the energy of
scattered electron
• θe is the scattering
angle
• ν =E-E’ is the energy
transfer.
• kT: quark transverse
momentum
– A new type of PDF, T-odd, depends on intrinsically
quark transverse momentum
quark orbital
momentum
 Kinematics comparable to the HERMES
experiment.
HERMES: 3 years
Beam direction
DIS: Q2 (1/λ) and ν is large,
but x is finite.
COMPASS: 1 year
Into the page
HALL A: 29 days