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Overview of Jefferson Lab’s Spin Physics Programme. Introduction Experimental Setup Asymmetry Measurement Moments of Structure Functions Outlook. Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007. Spin structure vs distance scale.

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Overview of jefferson lab s spin physics programme

Overview of Jefferson Lab’s Spin Physics Programme

  • Introduction

  • Experimental Setup

  • Asymmetry Measurement

  • Moments of Structure Functions

  • Outlook

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Spin structure vs distance scale
Spin structure vs distance scale

Q2

Bjorken Sum Rule

Asymptotic freedom

single partons

multiple partons

Perturbative QCD

constituent

quarks, N*

photon interacts with

pions, nucleon

Chiral Perturbation Theory

magnetic

moment

(GDH SR)

GDH Sum Rule

Q2=0

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


The cebaf accelerator
The CEBAF Accelerator

  • Electron beam

  • Energy up to 5.7 GeV

  • Current 1 - 100 µA (Hall B 50 nA)

  • Polarization > 0.8

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Experimental halls
Experimental Halls

Hall C HMS + SOS

Polarized Targets:

H2 and D2 (Hall B + C)

3He (Hall A)

Hall B CLAS

Hall A HRS + HRS

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Polarized targets in halls b c
Polarized Targets in Halls B & C

  • Dynamically polarized targets of solid (deuterated) ammonia

  • 5 Tesla magnetic field

  • 140 GHz polarizing microwaves

  • 1 Kelvin superfluid helium

  • Longitudinal polariztion

  • P1 < 0.9 P1 ave = 0.7 - 0.8

  • P2 < 0.4 P2 ave = 0.2 - 0.3

  • measured by NMR

  • Also transverse polarization in Hall C

  • Current

  • 3 nA in Hall B

  • 100 nA in Hall C

  • Luminosity < 1035 cm-2 sec-1

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Polarized target in hall a
Polarized Target in Hall A

  • Polarized 3He gas target

  • Optical pumping and spin exchange

  • Longitudinal and transverse polarization

  • P3 < 0.5 P1 ave = 0.4

  • measured by NMR and EPR

  • Current 12 µA

  • Luminosity < 1036 cm-2 sec-1

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Clas detector in hall b
CLAS Detector in Hall B

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Dis of lepton off nucleon

k’

k

k’

Elastic

k

q

p’

q

p’

xP=

p

xP=p

P

P

W

DIS of lepton off nucleon

Virtual photon scatters off parton

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Kinematic coverage
Kinematic Coverage

EG1

EG4

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Status of g 1 x q 2
Status of g1(x,Q2)

  • Existing data mostly for DIS and low x

  • Remaining

    • G (RHIC, COMPASS)

    • L (COMPASS, HERMES, Jlab)

    • Transversity (HERMES, Jlab, RHIC)

    • Large x precision measurements (Jlab)

    • Measurement in non-perturbative region (Jlab)

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Asymmetry Measurement

A1 A2

e’

qe

A1

A2

e

the asymmetries A1 and A2 can be extracted by varying the direction of the nucleon polarization

where D, , d,  are function of Q2, W, E0, R

Pe

Pt

y

nucleon

the structure functions g1andg2are linear combination of A1andA2

g1(x,Q2)

g2(x,Q2)

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Asymmetry measurement
Asymmetry Measurement

Simultaneous extraction of A1 and A2 from measured asymmetry

1 -  E’ / E

 √ Q2

A|| = D ( A1 +  A2 ) with = and D =

E -  E’

1 +  R

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


A 1 a 2 for proton
A1+A2 for proton

1.7 GeV (proton)

5.7 GeV (proton)

Parametrization of previous world data (including CLAS) by S. Kuhn , L. Stuart, et al. including “AO” and “MAID2000” for resonance region

Blue solid line = Estimated contribution from A2 to A1+A2

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


G 1 for the p roton

F1

g1(x,Q2) =

[(A1+´ A2)+(°-´)A2]

1+°2

g1(x,Q2) for the proton

g1forthe proton

Parameterization of previous world data (including CLAS)

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Proton deuteron comparison
Proton/Deuteron Comparison

In the ¢(1232) region and at low Q2, g1d/2 is consistent with g1p

At high Q2, g1p is significantly larger than g1d/2 , indicating a negative contribution from the neutron

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Asymmetry measurement1
Asymmetry Measurement

  • Very preliminary result

  • A2is larger than previously used EG1 model, basing on MAID and AO

  • Same result reported by RSS experiment from JLab Hall C (2007)

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Asymmetry measurement in hall c rss
Asymmetry Measurement in Hall C (RSS)

  • Polarized longitudinal and transverse ammonia target

  • 100 nA electron beam

  • Both polarizations average between 0.6 and 0.7

  • HMS spectrometer at 13.5º

  • 160 million events

Q2 range from 0.8 to 1.4 GeV2/c2

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Asymmetry a 1
Asymmetry A1

Proton

Deuteron

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


G 2 from hall c rss
g2 from Hall C (RSS)

Twist-2 Wandzura-Wilcek approximation

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


G 2 from hall c rss1
g2 from Hall C (RSS)

Twist-3 matrix element d2 representing quark-gluon correlation

d2 = 0.0057 ± 0.0009 stat. ± 0.0007 sys. for 0.29 < x < 0.84

d2 = 0.0029

at Q2 = 5 GeV2/c2

Compared to SLAC

d2 = 0.0032 ± 0.0017

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Polarized pdf s
Polarized PDF’s

  • Inclusion of large amount of low-Q2 data from CLAS EG1 by Leader, Siderov, and Stamenov

  • Simultaneous extraction of polarized parton densities and higher twist corrections

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Polarized pdf s1
Polarized PDF’s

  • Error envelopes

  • LSS05

  • LSS06 (EG1)

  • CLAS12

overall improved by EG1 data

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Test of quark hadron duality

S11 (1535)

D (1232)

Global

F15 (1680)

Test of Quark-Hadron Duality

Proton

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


G 1 from hall c rss
g1 from Hall C (RSS)

Integration over resonance region 1.09 GeV < W < 1.91 GeV

of NLO PDFs and comparison with measurement gives a ratio of

1.17 ± 0.08

Q2 range from 0.8 to 1.4 GeV2/c2

Global duality only at 2 sigma level

Local duality not observed

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Q 2 dependence of g 1 f 1
Q2 dependence of g1/F1

  • Q2 dependence of g1 at fixed x is very similar to F1 in the DIS region

  • EG1 data show a decrease in g1/F1 even in the DIS region

  • Resonance region  different Q2 dependence  goes negative at 

  • High Q2 results agree with SLAC data

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Quark polarization in the valence region
Quark polarization in the valence region

Assuming the naïve parton model with no sea contribution, quark polarizations in the valence region can be estimated directly from the data:

¢u/u = [5g1p-2g1d/(1-1.5wD)]/[5F1p-2F1d]

¢d/d = [8g1d/(1-1.5wD)-5g1p]/[8F1d-5F1p]

¢u /u ! 1 as x ! 1

Consistent with pQCD and QM

Disagrees with SU(6)

¢d /d < 0 up to the highest x ~0.6

Consistent with Hyperfine Perturbed QM

Disagrees with pQCD w/o orbital angular momentum

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Moments and sum rules
Moments and Sum Rules

QPM

Ellis-Jaffe Sum Rule

3

1

4

a0

a3 +

1p =

a8 +

= 0.186 +QCD corr

36

36

36

3

1

4

a0

= - 0.025 +QCD corr

a3 +

1n = -

a8 +

36

36

36

Bjorken Sum Rule (pre QCD)

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Gdh sum rule

1

Q2 (GeV2)

GDH Sum Rule

IGDH

  • relates the difference of the photo-absorption cross section for helicity 1/2 and 3/2 to the nucleon magnetic moment, i.e. a connection between dynamic and static properties. Recent measurements at Bonn and Mainz, ongoing efforts at other labs

  • based on very general principles, as gauge invariance, dispersion relation, low energy theorem

  • at finite Q2 can be related to

    the integral of the spin structure

    function g1

  • strong variation of nucleon spin

    properties as a function of Q2

G1

DIS

pQCD

Transition Region

GDH sum rule

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Generalized gdh integral
Generalized GDH Integral

A generalization of the GDH sum rule has been suggested by Ji and Osborne by relating the virtual-photon forward Compton amplitude S1to the nucleon structure function G1

X.Ji et al., Phys.Lett.B472 (2000) 1

GDH sum rule and Chiral Perturbation Theory

- — + cQ2 + O (Q4)

Lattice?

Ellis-Jaffe Sum rule and Operator Product Expansion

~

Q2 < 0.1 GeV2

S1(0,Q2)

 2

M2

x0

ò

16pa

Q2

IGDH (Q2) = dx g1(x,Q2)

0.1 < Q2 < 0.5 GeV2

Q2 > 0.5 GeV2

Measurable

Calculable

mt(Q2)

Qt-2

t=2,4,…

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


1 for the proton and deuteron
1 for the proton and deuteron

proton

deuteron

1

1

Q2(GeV2)

Q2(GeV2)

  • Xmin=0.001, x_max= pion production threshold

  • shows strong Q2 dependence varying from negative to positive values as Q2 increases

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Low q 2 behavior of 1 pt
Low Q2 behavior of 1-PT

deuteron

proton

preliminary

preliminary

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Eg4 projection
EG4 projection

  • Extends to very low Q2 of 0.015 GeV2 both proton and deuteron

  • Data taken earlier this year

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Hall a measurement on 3 he
Hall A Measurement on 3He

1n

E94-110

Q2 range 0.1 - 1 GeV2

Preliminary

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Hall a measurement on 3 he e01 012
Hall A Measurement on 3He E01-012

  • g1/g2 and A1/A2 (3He/n) in resonance region, 1 < Q2 < 4 GeV2

  • Study quark-hadron duality in spin structure

1n

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Bjorken sum q 2 evolution
Bjorken Sum Q2 Evolution

Combined data from

EG1a and Hall A E94-010

A. Deur, et al., PRL 93, 212001 (2004)

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Jlab upgrade eg12 projections
JLab Upgrade: EG12 projections

W > 2; Q2 > 1

Allows access to higher x values

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


Summary
Summary

  • A wealth of new data on the nucleon spin structure in the non-perturbative regime has been produced at Jefferson Lab as part of a broad spin physics program, still in progress

  • These measurements provide new information for understanding the transition between hadronic and partonic degrees of freedom by investigating spin structure functions, related sum rules and moments, asymmetries, …

  • A new measurement to cover the very low momentum transfer region and provide a bridge to the GDH sum rule at the photon point has just been completed recently

  • 12 GeV program at Jlab will offer the opportunity to extend these measurements into new kinematic regions

Stephen Bültmann - ODU RHIC/AGS Users Meeting, June 2007


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