Nucleon Spin Structure 30 Years of Experiment: What have we learned?

Nucleon Spin Structure

30 Years of Experiment: What have we learned?

M. Grosse Perdekamp, University of Illinois and RBRC

Nucleon Spin Structure 2 June 6 th

Overviewo Scientific Motivation and Early Beginnings

The Rabi School of Physics The SLAC – Bielefeld -- Tsukuba – Yale Collaboration Modern Experiments

o Nucleon Helicity Structure Quark spin ΔΣ Gluon spin ΔG Orbital angular momentum Lz GPDs !

o Transverse Spin

Transverse spin in hard scattering QCD Transversity and Collins Quark Fragmentation The Sivers Effect


ondistributiquark dependent spin

(x)q - (x) qq(x)

ondistributi momentumquark )( xq

ondistributi gluondependent spin

(x)G - (x) GG(x)

proton

quark

p

px

Scientific Motivation: Proton Structure Including Spin Degrees of Freedom

Constituents: quarks = u, d, s and gluons

(x)

:SpinQuark Total

,

1

0

qq

x

x

q

(x)

:SpinGluon Total 1

0

x

x

GG


Proton Spin Structure from Inclusive Deep Inelastic Lepton-Nucleon

Scattering

electron or

muon probe

spin

proton target

spin

qq

Qdxxq

xqxqxqQxg

,

21

0

21

0at )(

)()()(),(Extract spin dependent quarkdistribution functions from thespin structure function g1(x,Q2)

Large Q2: measure photon-quark absorption cross section doublespin asymmetry

),( 211 QxgAA

qq

qqqLL


The Rabi School of Physics N. F. Ramsey, Eur. J. Phys. 11 (1990) 137J. Rigden, Physics World, Nov. 1999

(I) Molecular beam laboratory at Columbia University with strong emphasize on the development of new experimental technology.

(II) Field new, precise instrumentation to study fundamental questions of physics.

Example: Precision Measurements of “Hydrogen Spin Structure”

g-2 of the electron, P. Kusch Lamb shift, W. E. Lamb

Dirac Theory QED Tomonaga, Schwinger, Feynman

Nobel Prize 1955

Rabi, Nobel Prize 1944

Nobel Prize 1965


SLAC: Quark Structure of the Proton

Nucleon Quantum Chromo

Dynamics

Experiment: Deep inelastic electron nucleon scattering

Theory: quark structure of hadrons, QCD

Friedman,Kendall, TaylorNobel Prize 1990

Gell MannNobel Prize 1969

also Nakano, Nishijima

New instrumental method & fundamental physics !


Polarized Deep Inelastic Scattering

(I) Molecular beam technology as starting point for the development of polarized electron beams at Yale starting 1959.

(II)Physics:

(a) Proton spin structure (b) Test the Bjorken sum rule as fundamental QCD prediction

Experiments E80+E130 at SLAC

Bielefeld – CUNY – SLAC – Nagoya – Tsukuba – Yale (Coward, Kondo, Hughes)

EMC experiment at CERN (Gabathuler, Sloan, Hughes)

Vernon W. Hughes

a contribution from the Rabi School of Physics !


The Quark Spin Contribution ΔΣ

Quark Spin Contribution to the Proton Spin.

SLAC: 0.10 < xSLAC <0.7 CERN: 0.01 < xCERN <0.5

0.1 < xSLAC < 0.7A1(x)

x-Bjorken

EMC, Phys.Lett.B206:364,19881338 citations in SPIRES

1.005.007.0 CERNSLAC

0.01 < xCERN < 0.5“Proton Spin Crisis”

First Thesis on Nucleon SpinStructure E80/Yale, 1977:Noboru Sasao


DIS

Nucleon Spin Structure: 30 Years of Experiment

2000

ongoing

1995

2007

ongoing

ongoing

polarized pp

semi inclusive + exclusive processes, luminosity

Quark Spin – Gluon Spin – Transverse Spin – GPDs – Lz

SLAC E80-E155

CERN EMC,SMC COMPASS

FNAL E704

DESY HERMES

JLAB Halls A, B, C

RHIC BRAHMS, PHENIX, STAR

polarized proton beams, polarized proton collider

major experimental innovations

Nucleon Spin Structure June 6 th

AGSLINACBOOSTER

Polarized Source

Spin RotatorsPartial Snake

Siberian Snakes

200 MeV Polarimeter

Rf Dipole

RHIC pC Polarimeters Absolute Polarimeter (H jet)

PHENIX

PHOBOS BRAHMS & PP2PP

STAR

Siberian Snakes

AGS pC Polarimeter

Helical Partial Snake

Strong Snake

Spin Flipper

RHIC Spin InstrumentationRHIC Spin InstrumentationDevelopment 1995-2005Development 1995-2005

A novel experimental method: Probing Proton Spin Structure in High Energy Polarized Proton Collisions

Instrumentation

High current polarized proton source High energy proton polarimetry Control of spin coherence during acceleration + storage Spin sorted luminosity measurements

Physics

Probes directly sensitive to color charge Utilize Parity violation in W-production Large Q2 clean pQCD interpretation US-Japanese

collaboration at Brookhaven National Laboratory

RIKEN Radiation LaboratoryRIKEN BNL Research Center

Nucleon Spin Structure 11

June 6 th

at ultra-relativistic energiesthe proton represents a jetof quark and gluon probes

For example, direct photon production ~ probe gluon content with quark probes

)()(

)()( 21

1

1 xAxG

xGqqga

NN

NNA

LL

LL

The related double spin asymmetry:

RHIC SPIN: Proton Structure with Quark and Gluon Probes

quark

gluonquark

photon

experimental doublespin asymmetry

pQCD DIS?

12Nucleon Spin Structure June 6 th

Nucleon Helicity Structure

Quark spin ΔΣ , Δq(x) Gluon spin ΔG(x), ∫ ΔG(x)dx Orbital angular momentum Lz GPDs ?


June 6 th

Inclusive Measurements of g1p, g1

d and g1

n

Proton Neutron

HERMESΔƩ = 0.33 ± 0.011(th) ± 0.025 (exp) ± 0.028 (evo) at 5 GeV2

COMPASSΔƩ = 0.35 ± 0.03 (stat) ± 0.05 (syst) at 3 GeV2

Bjorken sum

S. Paul, X. Lu, H. Gao, INPC 2007

0.1821 ∓ 0.0019 (NNNLO)


June 6 th

Semi-Inclusive DIS: e+p e+ h +X Quark & Anti-Quark Helicity Distributions

u quarks large positive polarization

d quark have negative polarization

sea quarks (u, d, s ,s) compatible with 0in the measured x-range 0.02 < x < 0.6.

[HERMES, PRL92(2004), PRD71(2005)]

0.0430.002 u -

0.0350.054 d -

0.0340.028 s

x

Future:Precision DIS at JLAB-12 and at apossible electron – ion collider!

xΔu(x)

xΔd(x)

xΔu(x)

xΔd(x)

xΔs(x)

How well do we know hadron fragmentation functions ? new analysis of e+e- data, Hirai, Kumano, Nagai, Sudo hep-ph/0612009, INPC 2007

Possible Improvements

include e-p, p-p and e+e- in fragmentation function analysis done! De Florian, Sassot, Stratmann hep-ph/0703242

“add data” from b-factories e+e- hadrons


June 6 th

Belle MC

<1% of data sample work in progress

Possible Impact on the Knowledge of Hadron FFs from Analysis of b-Factory Data

z 2/

s

Ez

h

FF

FF

Compilation of dataavailable for the char-ged hadron FF

Belle MC: Charged h+/-, pions, kaons, protons

precision at high z!

h+,- pions kaons protons

Input for precision measurements of quark helicity distributions in SIDIS, with JLab-12 and a possible future electron- polarized proton collider.


June 6 th

Another Alternative:

W-production at RHIC

SIDIS: large x-coverage uncertainties from knowing fragmentation functions

Ws in polarized p-p: limited x-coverage high Q2 theoretically clean no FF-info needed

Hermes – 243 pb-1

PHENIX – 800 pb-1


June 6 th

Gluon Spin Contribution ΔG(x)

from scaling violation of world g1(x,Q2):Hirai, Kumano, SaitoPhys.Rev.D74:014015,2006

gP1(x,Q2)

ΔG=∫ΔG(x) dx = 0.47 ∓ 1.08 , Q2=1GeV2


June 6 th

Gluon Polarization from Photon Gluon Fusion in DIS

“direct” measurements

Photon-Gluon Fusion (PGF)

• golden channel: charm productiongolden channel: charm production

• hadron production at high Phadron production at high PTT

S. Paul, X. Lu INPC 2007

Favors small ΔG(x≈0.1)


June 6 th

2005 data

ALL also for , , J/

K.Aoki, R. Fatemi, B. SurrowINPC 2007

Gluon Polarization from Inclusive Hadrons and Jets in Polarized pp


June 6 th

2006: 7.5 pb-1 @ 60% polarisation

projections



June 6 th

NLO QCD Analysis of DIS A1 + ALL(π0)

DIS A1 + ALL(π0)

ACC03

x

0.14 0.21 1.27 0.5 AAC03

10.0 0.25 1.08 0.47 A DIS

0.070.27 0.320.31 )(A DIS

)(

1

01

LLA

dxxG

Only DIS ∫ΔG(x) dx = 0.47 ∓ 1.08 , Q2=1GeV2

Hirai, Kumano, SaitoPhys.Rev.D74:014015,2006

DIS + pp ∫ΔG(x) dx = 0.31 ∓ 0.32 , Q2=1GeV2


June 6 th

PHENIX π0 ALL vs GSA-LO and GSC-NLO

ALL

pT[GeV]

GSA-LO

GSC-NLO

PHENIX-2005

GSA-LO: ΔG = ∫ΔG(x)dx = 1.7

GSC-NLO: ΔG = ∫ΔG(x)dx = 1.0

Large uncertainties resultingfrom the functional form usedfor ΔG(x) in the QCD analysis!

GSA-LO and GSC-NLOcourtesy Marco Stratmannand Werner Vogelsang


June 6 th

ΔG(x) A, B and C from Gehrmann Stirling

present x-range

Much of the first momentΔG = ∫ΔG(x)dx might emerge from low x!

Some theoretical guidance:

ΔG(x) ≤ x G(x)

but G(X) diverges fasterthan x-1 !

NEED TO EXTENDMEASUREMENTS TOLOW x !!


June 6 th

Increase integrated luminosity by factor 10 (2008)

Extend measurements to low x Di-hadron Production extends (2008) measurements to x 0.01

NLO treatment available: Marco Stratmann -- INPC 2007

(EMC forward calorimeters available in STAR and PHENIX!)

Forward detector upgrades for direct (2011)photons and heavy flavor + electron cooling reach x 0.001

Polarized Electron Ion Collider measure ΔG(x) through scaling violations

Next Steps for ΔG(x) at RHIC


June 6 th

1

1

)0,,q()0,,q(2

1 xE xHxdxJ q

X. Ji, Phy.Rev.Lett.78,610(1997)

Generalized Parton Distributionsvs Orbital Angular Momentum ?

GPDs Hu, Hd, Eu, Ed provide access to total quark contribution to proton angular momentum in exclusiveprocesses l + N l’ + N + γ

½ = ½ (u+d+s) + Lq + Jg

J q

Proton spin sum


June 6 th

First Model Dependent Constraint of Ju vs JdE. Burtin, P. Bertin, X. Lu, INPC 2007

27Nucleon Spin Structure June 6 th

Transverse Spin

Transverse spin in hard scattering QCD Transversity and Collins Quark Fragmentation The Sivers Effect


June 6 th

Transverse Spin Phenomena in Hard Scattering QCD

QCD: Asymmetries for transverse spin are small at high energies (Kane, Pumplin, Repko, PRL 41, 1689–1692 (1978) )

Xpp π+

π-

π0

LR

N

LR

PA

1 :Observable

GeV 20s

Is QCD the correct theory of the strong interaction?

Experiment (E704, Fermi National Laboratory):

4q 10,20,3m example, N

qN AGeVsMeV

s

mA

QCD Test !


June 6 th

STARSTAR

Single Transverse Spin Asymmetries AN

at √=62.4 GeV and 200 GeV

Large single spin asymmetries persist at higher √s=62.4 and 200 GeV

√s=62.4 PHENIX and BRAHMS √s=200 GeV STAR

ANAN

xF

xF

M. ChiuINPC 2007


June 6 th

Inspect Factorized Expression for Cross Section

2P

)( 1xqi

)( 2xq j

11Px

22PxijLLa

1ps

Jet

Proton Structure

hard scattering reaction

fragmentationprocess

),(

)(ˆ)(),( ,

21

3

2,121

3

. Thqlkji

Tqi pzFFdxdx

qqqqdxqkxq

dzdxdx

Xppdlkj

fragmentationfunction

pQCD Proton Structure

small spindependence

(aLL~10-4)

Can initial and/or final state effects generate large transverse spin asymmetries? (ALL ~10-1)


June 6 th

Transverse Spin in QCD: Two Solutions

π+

π-

π0

(I) “Transversity” quark-distributions and Collins fragmentation

Correlation between proton- und quark-spin and spin dependent fragmentation

),()( 221

kzHxq

(II) Sivers quark-distribution

Correlation between proton-spin and transverse quark momentum

)(),( 21 zDkxf h

qq

T

AN

xF

Collins FFQuark transversespin distribution

Sivers distribution


June 6 th

Collins Effect in the Quark- fragmentation into the Final State

sq

π

qq

π sqp

p

= 0 AN =

NL - NR

NL + NR

Collins Effect NL : pions to the left

NR : pions to the right

q

qs

k

hph

,

hp

Collins Effect:Fragmentation of a transversely polarizedquark q into spin-less hadron h carries anazimuthal dependence:

sin

qh spk


June 6 th

π+ picks up L=-1 tocompensate for thepair S=1 and is emittedup.

u-quark absorbsphoton/gluon and flips it’s Spin.

Proton spin is pointing up!

String breaks anda dd-pair with spin1 is inserted.

A simple model to illustrate that spin-orbital angularmomentum coupling can lead to left right asymmetriesin spin-dependent fragmentation:

Artru Model for Collins Fragmentation

L = -1


June 6 th

Measurements of Quark Transversity Distributionsand Collins Fragmentation Functions (I) SIDIS

Collins Asymmetries in semi-inclusive deep inelastic scattering

e+p e + π + X

~ Transversity (x) x Collins(z)

New HERMES results for Collins AsymmetriesDiefenthaler, DIS 2007, Lu INPC 2007

AUT sin(s)


June 6 th

Collins Asymmetries in e+e-

annihilation into hadrons

e++e- π+ + π- + X

~ Collins(z1) x Collins (z2)

New Belle Collins AsymmetriesSeidl, DIS 2007

Measurements of Quark Transversity Distributionsand Collins Fragmentation Functions (II) e+e-

1hP

2hP

e-

e+

A12 cos(2)

PRELIMINARY


June 6 th

Anselmino, Boglione, D’Alesio,Kotzinian, Murgia, Prokudin, TurkPhys. Rev. D75:05032,2007

HERMES SIDIS

+ COMPASS SIDIS

+ Belle e+e-

transversity dist.

+ Collins FF

Fit includes:

First Extraction of Quark Transversity Distributionsand Collins Fragmentation Functions SIDIS + e+e-


June 6 th

The Sivers Effect

proton

Sp

Sp

proton

Sivers function:D. Sivers 1990

Sivers:

Correlation between the transverse spin of theproton and the transverse momentum kT of quarks and gluons in the proton (link to orbitalangular momentum?)

M

SkPkxfxqA PTq

TN

)ˆ(

),()( 2211Observed asymmetry:


June 6 th

Sivers Asymmetries at HERMES and COMPASS

implies non-zero Lq


June 6 th

Sivers Effect and Orbital Angular Momentum

M. Burkardt

>


June 6 th

The Sivers Effect : Needs Final State Soft Gluon Exchange

M. Burkardt


June 6 th

What have we learned from this?

The Sivers effect arises from soft gluon interactions in thefinal state (SIDIS) or initial state (Drell Yan).

Need to modify naïve concepts of factorization whichreduce hard scattering to partonic processes and neglect softgluon interactions in the initial or final state: hard scatteringmatrix elements are modified with gauge link integrals thataccount for initial and final state soft gluon exchange.

A modified concept of universality has been obtained which showshow the presence of initial or final state interactions can impacttransverse momentum dependent distribution; eg. the Siversfunction changes sign between SIDS and Drell Yan!

There may be exciting applications elsewhere, eg. other transversemomentum dependent effects or the understanding nuclear effects in hard scattering.


June 6 th

Goals for the Future

Quantitative understanding of transverse spin phenomena in QCD

Do Sivers and Collins mechanisms reconcile QCD with transverse spin phenomena?

Precision measurements of transversity distributions and Collinsfragmentation function measurements.

This will complete the experimental survey of the nucleon at leading twist. Determine sum of first moments (tensor charge) which can be compared to lattice calculations.

Survey Sivers and Boer Mulders effects in SIDIS and pp

Fundamental understanding of factorization and universality in hard scattering.

Relation to orbital angular momentum ?!

Future results expected from COMPASS, RHIC, JLAB, Belle, JLAB-12-GEV, JPARC FAIR and EIC. This includes high precision measurements in e-p, e-e and p-p possibly first systematic study of factorization + universality


June 6 th

Transversity : correlation between transverse proton spin and quark spin

Sivers : correlation between transverse proton spin and quark transverse momentum

Boer/Mulders: correlation between transverse quark spin and quark transverse momentum

Transversity, Sivers and Boer Muldersin the Proton Wavefunction

)( 2xq

),( 221

kxf qT

),( 211

kxh q

Sp– Sq – coupling ?

Sp- Lq– coupling ??

Sq- Lq– coupling ??


June 6 th

Summary

Bjorken sum rule holds

Integral quark spin contributions are well known

Δq(x), Δq(x) only well known for up-quarks only

Hints that ΔG(x) is small at x~0.1. ∫ΔG(x)dx remains largely unconstraint RHIC luminosity, low-x

Possible route to OAM through

Exp. Observation of Sivers and Collins asymmetriesTheoretical advance in understanding TMD + concepts of factorization and universality

Plenty of work for theory + existing and future experimental tools!


June 6 th

Sivers in SIDIS and Drell Yan vsFactorization and Universality


June 6 th

Transverse Spin Drell Yan at RHIC vs

π-Sivers Asymmetry in Deep Inelastic Scattering

• Important test at RHIC of the fundamental QCD prediction of the non-universality of the Sivers effect!

• requires very high luminosity (~ 250pb-1)


June 6 th

Simple QEDexample:

DIS: attractive Drell-Yan: repulsiveSame in QCD:

As a result:

Non-universality of Sivers Asymmetries:Unique Prediction of Gauge Theory !


June 6 th

0.1 0.2 0.3 x

Siv

ers

Am

plitu

de

0

Experiment SIDIS vs Drell Yan: Sivers|DIS= − Sivers|DY

*** Test QCD Prediction of Non-Universality ***

HERMES Sivers Results

Markus DiefenthalerDIS WorkshopMűnchen, April 2007

0

RHIC II Drell Yan Projections


June 6 th

I) Can one extract G(x,Q2) from pp?

II) NLO pQCD vs RHIC data

Is pQCD applicable at RHIC?


June 6 th

Global QCD Analysis for G(x,Q2) and q(x,Q2):

J. Pumplin et.al JEHP 0207:012 (2002)

3.16GeVQ at u

3.16GeVQ at d

10-410-3 10-2 10-1 0.5 x

gluon

down

up-quarks

anti-down

Quark and Gluon Distributions

error on G(x,Q2)

error for u(x,Q2)

+/- 10%

+/- 5% +/- 5%

error for d(x,Q2)

10-410-3 10-2 10-1 0.5 x

CTEQ6: use DGLAP Q2-evolution of

quark and gluon distributions to extract q(x,Q2)and G(x,Q2) from global fit to data sets at different scales Q2.

H1 + Zeus F2

CDF + D0 Jets

CTEQ5M1

CTEQ6M


June 6 th

G(x,Q2) and q(x,Q2) + pQCD beautifully agree Tevatron + HERA!

J. Pumplin et.al JEHP 0207:012 (2002)

D0 Jet Cross Section ZEUS F2


June 6 th

and at RHIC ? q(x,Q2), G(x,Q2) and D(z,Q2) + pQCD are nicely consistent with experiment!

o Good agreement between NLO pQCD calculations and experiment can use a NLO pQCD analysis to extract spin dependent quark and gluon distributions from RHIC data!

PHENIX π0 cross section a |η|<0.35 Phys.Rev.Lett.91:241803,2003

STAR π0 cross section a 3.4<η<4.0 Phys.Rev.Lett.92:171801,2004

gluon fragmentation !?


June 6 th

• NLO-pQCD calculation– Private communication with

W.Vogelsang– CTEQ6M PDF.– direct photon + fragmentation photon– Set Renormalization scale and factorization scale pT/2,pT,2pT

Theory calculation show good agreement with the experimentalcross section.

Direct Photons: NLO pQCD vs RHIC data


June 6 th

W

Z

W Production in Polarized pp Collisions

Single Spin Asymmetry in the naive Quark Parton Model

GeV 20

for dominates

Tp

W

2121

21 ,

),(

),(xx

Mxu

MxuA

W

WWL

Experimental Requirements: tracking at high pT

event selection for muons difficult due to hadron decays and beam backgrounds

control of all backgrounds

Parity violation of the weakinteraction in combination withcontrol over the proton spin orientation gives access to theflavor spin structure in the proton!


June 6 th

Extraction of quark polarizations at LO

Machine and detector requirements:Machine and detector requirements:

– ∫Ldt=800pb-1, P=0.7 at √s=500 GeV

– trigger upgrade

– Control of backgrounds

contributions both from

FVTX and NCC!

2009 to 2012 running at √s=500 GeVis projected to yield ∫Ldt ~950pb-1


June 6 th

Run 5 ALL(): First constraints for ∆G(x)

¨

standard ∆G from DIS

∆G =0

PHENIX

max

∆G from

DIS

min ∆G possible curves: comparison with ALL obtained with ∆G from deep Inelastic lepton nucleon scattering

(M. Glück, E. Reya, M. Stratmann, und W. Vogelsang, Phys. Rev. D 53 (1996) 4775).

PANIC, October 2005

Asymmetries are consistentwith gluon spin contributionsfrom ʃ∆G(x)dx ~ 0 to 0.5


June 6 th

EMC-RICH Trigger (RBRC/UIUC, UCR, Tokyo)

Information from EMC (172 elements with4 energy thresholds) and RICH (256 ele-ments with one threshold) is used to tag high energy electrons and photons:

Physics (p-p, d-Au) :

/,,for ,, 000

Jdp

dAA

TLL N

EM

C T

rigge

r E

ffici

ency


June 6 th

Final results on ∆G will come from combined NLO analysis of RHIC and DIS

RHIC measurements will span broad range in x with good precision. Multiple channels with independent theo. and exp. uncertainties.

s=200 GeV incl. 0 prod’n s=500 GeV incl. jet prod’n

∆G Measurements by 2012 see Spin report to DOE http://spin.riken.bnl.gov/rsc/


June 6 th

Sivers Function in PHENIX: The Muon Piston Calorimeter (MPC)

Measure the Sivers function through the asymmetry AN in hadron-hadron correlationen, for neutral pions (Boer and Vogelsang Phys.Rev.D69:094025,2004) 0

0

AN Jets

Hadron Paare

∫Ldt = 0.35pb-1 (Run 3)


June 6 th

First attempt at lower x: ALL(2π0)

from Les Bland (for STAR FMS)Measure ALL for neutralpion pairs: one in the centralarm the second in the MPC

0.1 > x 0.001 !

MPC


June 6 th

NCC direct photons

ΔG(x) – x-range with Detector Upgrades


June 6 th

K.Aoki, R. Fatemi, B. SurrowINPC 2007


Nucleon Spin Structure 30 Years of Experiment: What have we learned?

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Transcript of Nucleon Spin Structure 30 Years of Experiment: What have we learned?