Prospects in neutron transverse spin study

with a polarized 3He Target at 12 GeV JLab

Haiyan Gao (高海燕 )

Duke University/TUNL

Durham, NC, U.S.A.

A Third Joint meeting of Division of Nuclear Physics of American Physical Society and the Japanese Physical Society

Oct 13-17, 2009 Waikaloa, Hawaii

(

Outline• Introduction• First experiment at 6 GeV in Hall A @ JLab (Xiaodong Jiang)

• Transversity with 12 GeV at JLab • Summary

QCD Nucleon Structure• Strong interaction, running coupling ~1

-- QCD: the theory of strong interaction

-- asymptotic freedom (2004 Nobel)

pQCD works at high energy

-- interaction significant at

intermediate energy

quark-gluon correlations

-- confinement

interaction strong at low energy

coherent hadron

-- Chiral symmetry

-- theoretical tools:

pQCD, OPE, Lattice QCD, ChPT

E

• Charge and magnetism (current) distribution– Nucleon: Electric GE

and magnetic GM form factor

• Spin distribution • Quark momentum and

flavor distribution• Polarizabilities• Strangeness content• …..

Leading-Twist Quark Distributions

non-vanishing integrating

over

K - dependent, T-odd

K - dependent, T-even

( Eight parton distributions functions)

Transversity:

K

Transversity• Three twist-2 quark distributions:

– Momentum distributions: q(x,Q2) = q↑(x) + q↓(x)

– Longitudinal spin distributions: Δq(x,Q2) = q↑(x) - q↓(x)

– Transversity distributions: δq(x,Q2) = q┴(x) - q┬(x)

• Some characteristics of transversity:

– δq(x) = Δq(x) for non-relativistic quarks

– δq and gluons do not mix → Q2-evolution simpler

– Chiral-odd → not accessible in inclusive DIS

• Rapidly developing field, worldwide efforts: BNL, Belle at KEK, CERN,

DESY, JLab, FAIR project at GSI, … • It takes two chiral-odd objects to measure transversity

Access Parton Distributions through Semi-Inclusive DIS

...]})cos(1[

...]1[

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...)()sin(

)sin([

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...)2cos(

...{

)1(2

)cos(2

2

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)sin(

)sin(

)2sin(

)2cos(

,

2

2

2

2

Sh

Sh

Sh

Sh

h

h

LTSheT

LLeL

UTSh

ULSh

UTShT

ULhL

UUh

TUU

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FS

FS

F

F

FS

FS

F

F

y

xyQdPdzddxdyd

d

Unpolarized

PolarizedTarget

PolarizedBeam andTarget

SL, ST: Target Polarization; e: Beam Polarization

Boer-Mulder

Sivers

Transversity

Pretzelosity

Separation of Collins, Sivers and pretzelocity effects through angular dependence

1( , )

sin( ) sin( )

sin(3 )

SiversU

Pretzelos

TColli

ity

l lUT h S

h S h ST

UT h S

nsU

N NA

P N

A

N

A A

1

1 1

1

1 1

sin( )

sin(3 )

sin( )Co

PretzelosityU

SiversUT

llins

T h S T

h S

UT

UT h S

TU

UT

TA

H

f

A

D

A h H

h

AUTsin() from transv. pol. H target

Simultaneous fit to sin( + s) and sin( - s) `Collins‘ moments

• Non-zero Collins asymmetry

• Assume q(x) from model, then

H1_unfav ~ -H1_fav

• H1 (BELLE) (arXiv:0805:2975)

`Sivers‘ moments

•Sivers function nonzero (+) orbital angular momentum of quarks

•Regular flagmentation functions

M. Anselmino et al, PRD75,05032(2007)

Latest Results on Sivers

From HERMES

arXiv:0906.3918

Positive Sivers amplitude

For

~zero for

~zero from COMPASS data

On D target

0, , , , - K K

0

Negative Sivers

For u quark and

Positive for d quark

Sivers asymmetries from COMPASS deuteron

Collins asymmetries from COMPASS deuteronPhys. Lett. B 673 (2009) 127-135

Transverse Target SSA Measurement at Jefferson Lab Hall A Using a Polarized 3He Target (Neutron)

First Experiment Completed Recently!

Experiments on polarized ``neutron’’ important!!

Jefferson Lab Hall A E06-010/E06-011

e

e’

HRSL

BigBite

16o

30o

Polarized3He Target

Jefferson Lab E06-010: Single Target-Spin

Asymmetry in Semi-Inclusive n↑(e, e’±) Reaction on a

Transversely Polarized 3He Target

• Performed in Jefferson Lab Hall A from 10/24/08-2/6/09

• Exceeded the approved goal• 7 PhD students• First measurement of the neutron

Collins and Sivers asymmetries x = 0.1 - 0.4

• Upgraded polarized 3He target 20 min fast spin-flip vertical polarization improved performance

• BigBite for e and HRSL for and K.• BigBite detectors working well• Commissioned RICH in HRSL

Nucleon Transversity at 11 GeV Using a Polarized 3He Target and SOLid in Hall A

(

(Hall A Collaboration proposal)

Beijing U., CalState-LA, CIAE, W&M, Duke, FIU, Hampton, Huangshan U.,

Cagliari U. and INFN, INFN-Bari and U. of Bari, INFN-Frascati, INFN-Pavia,

Torino U. and INFN, JLab, JSI (Slovenia), Lanzhou U, LBNL, Longwood U,

LANL, MIT, Miss. State, New Mexico, ODU, Penn State at Berks, Rutgers,

Seoul Nat. U., St. Mary’s, Syracuse, Tel aviv, Temple, Tsinghua U, UConn,

Glasgow, UIUC, Kentucky, Maryland, UMass, New Hampshire, USTC, UVa

and the Hall A Collaboration

Strong theory support,

Over 130 collaborators, 40 institutions, 8 countries

including all 6 GeV transversity collaboration

Solenoid detector for SIDIS at 11 GeV

GEMs

(study done with Babar magnet, 1.5T)

Experimental Overview• SoLID (proposed for PVDIS)

– GEMs (tracking+vertex), – Calorimeter (trigger/pid), – CO2 gas cerenkov, aerogel (trigger/pid)– Heavy gas cerenkov (pid)– Scintillator (trigger)– Kinematics

• Forward angle region (8.5o – 16o) (electron and pion)

• Large angle region (16o – 25o) (electron only)

• High pressure polarized 3He target – 10 amags, 40 cm long, 60% polarization, spin flip

• 11 GeV beam,15 µA (unpolarized/polarized) – 8 GeV

• Polarized luminosity 1036/(cm2s)• Unpolarized H/D/3He factorization test & dilution

corrections

3 ( , ' )He e e

GEMs: tracking device6 GEMs in total: positioned inside magnet (momentum, angle and vertex reconstruction);Forward angle: 8.5o to 16o (5 layers of GEM)Large angle: 16o to 25o to (4 layers GEM, 3 in common with Forward angle)

GEANT3 simulations show background rates in GEMs much less than the limit

Particle identificationParticle identification

• Electron identification

– Forward angle: CO2 gas Cerenkov/EM calorimeter

• 2 m long, 1 atm CO2,,,threshold for pion 4.8 GeV/c

• Shower plus Cerenkov provides better than 104:1 for pion rejection for 1.5 to 4.8 GeV/c momentum region

• 200:1 for pion rejection for momentum greater than 4.8 GeV/c (pion/e ratio < 1.5)

• Multi-bounce mirror system for CO2 Cerenkov counter

– Large angle

• Electron momentum 4-6 GeV/c, expected pion/e ratio <

1.5

• ``Shashlyk''-type calorimeter, pion rejection 200:1,

efficiency for electron detection 99%

Electromagnetic Calorimeter

Pion rejection factor 200:1 for E> 2.0 GeV

Pion identification

5.3793.802p

2.8402.0K

0.8030.565

Pthreshold GeV/c

n=1.015

Pthreshold GeV/c

n=1.03

Particle

Combination of 1 atm CO2

Cerenkov, a heavy gas Cerenkov, and an aerogelCerenkov can reduce kaonBackground to < 1%

Kinematic coverage at 11 GeV

Kinematic coverage at 8 and 11 GeV

0.30 0.35z

0.45 0.50z

0.65 0.70z

Azimuthal angular coverage

Full spin angle coverage with a solenoid detection system

Large coverage for Collins, Sivers and Pretzelosity angle– Important in disentangle all three terms

Symmetry in azimuthal angular acceptance can help reduce systematic uncertainties significantly

1 2

1 2

1 2

1 2 1 2

1 2 1 2

( , ) ( , )1( , )

( ) ( , ) ( , )

2( , )

( , ) ( , ) ( , ) ( , )

( , ) ( , ) ( , ) ( , )

h h S h SUT h S

T h S h S

hUT h S

T T

h S h S h S h S

h S h S h S h S

N NA

P N N

AP P

N N N N

N N N N

With full azimuzhal coverage

),(

),,(

1

1

Sh

Sh

N

N

),(

),,(

2

2

Sh

Sh

N

N

Simultaneously measured

Better control of systematic error1, 2 refer to two different

Target spin directions in the lab

Acceptance

Incident beam energy 11 GeV

Resolutions

Rates

Incident beam energy 11 GeV

Projected results (ultimate precision in SSA)7 more bins in z

Incident beam energy 11 GeV, 8 GeV projection and updates soon

Positive pions

Negative pions

Power of SOLid

Trigger and DAQ

Option 1: Single electron rate ~ 110 kHz– Electron trigger: ECAL + GC + SC– DAQ will use the CODA3 and the pipeline technique

being developed for Hall D– Expect zero dead time with 100 – 200 kHz trigger

rate. Option 2: Coincidence rate ~ 90 kHz

– Pion trigger: ECAL + Aerogel + SC– Multi-DAQs to reduce trigger rate in each DAQ.– Will introduce some dead time.

Need further studies

Systematic Uncertainties

6.0-7.7%(relative)+1.1E-3(absolute)N/ATotal

3%relative3He Polarization

2%relativeRadiative Correction

2-3%relativeDiffractive Vector Meson

4-6%?relativeNuclear Effects

1.0%relativeBackground Subtraction

1.1 E-3absoluteRaw Asymmetry

SizeTypeSources

Average Stat: 1.8e-3, Collins asymmetry ~2%

Responsibilities• Aerogel Cerenkov detector: Duke, UIUC

• CO2 gas Cerenkov detector: Temple U.• Heavy Gas Cerenkov Temple U.• ECal: W&M, UMass, JLab, Rutgers, Syracuse• GEM detectors:UVa, Miss State, W&M, Chinese

Collaboration (CIAE, HuangshanU, PKU, LZU, Tsinghua, USTC), UKY, Korean Collaboration (Seoul National U)

• Scintillator: Chinese Collaboration, Duke• Electronics: JLab• DAQ: LANL, UVa and JLab• Magnet: JLab and UMass• Simulation: JLab and Duke

PAC decision: Defer with regretMore simulations and studies underway to address the Concerns raised by the PAC

blue: common withPVDISBlack: part in common with PVDISRed: This experiment only

Summary• The study of chiral-odd quark distribution function and

fragmentation function: an exciting, rapidly developing frontier, surprising flavor dependence observed in Collins and Sivers function,

Worldwide effort – Completed the 1st experiment at JLab

• Future 11 GeV with Solenoid and polarized 3He target allows for a precision 3-d mapping of neutron Collins, Sivers, and pretzelocity asymmetries, and the extraction of transversity, Sivers and pretzlocity distribution functions.

• Together with world proton results provides model independent determination of tensor charge of d quark. Provide benchmark test of Lattice QCD calculations

Supported by U.S. Department of Energy

DE-FG02 03ER41231

Transversity from JLab Hall A

• Linear accelerator provides

continuous polarized electron

beam

– Ebeam = 6 GeV

– Pbeam = 85%

• 3 experimental halls

42

A B C