RHIC-Spin:Results and Outlook

KEK Workshop on High-Energy Hadron Physics with Hadron Beams

January 7, 2010

Yuji Goto (RIKEN/RBRC)

January 7, 2010 2

Outline

• Longitudinal-spin asymmetry measurement– Collinear (spin) structure of the nucleon

• gluon-spin contribution to the nucleon spin• sea-quark contribution (with weak boson measurement)

• Transverse-spin asymmetry measurement– Multi-dimensional (spin) structure

• orbital angular momentum inside the nucleon

gq LLg 2

1

2

1

g

ssdduu

gq LL

January 7, 2010 3

RHIC

January 7, 2010 4

RHIC polarized proton-proton collider

BRAHMS& PP2PP

STAR

PHENIX

AGS

LINACBOOSTER

Pol. H- Source

Spin Rotators

200 MeVPolarimeter

AGS InternalPolarimeter

rf Dipole

RHIC pCPolarimeters

Absolute Polarimeter(H jet)

AGS pC PolarimetersCold PartialHelical Siberian Snake

Warm PartialHelical Siberian Snake

PHOBOS

Spin Rotators

Full HelicalSiberian Snakes

Partial Solenoidal Snake

January 7, 2010 5

RHIC runs (PHENIX data sets)• Longitudinal-polarization runs

• Transverse-polarization runs

January 7, 2010 6

RHIC performance

(from slides shown by Thomas Roser at RHIC Retreat 2009)

January 7, 2010 7

RHIC runs• 200-GeV program

– gluon polarization measurement (almost) achieved in 2006– 1st stage program to be done in 2009 (+ another run) by

more statistics and more variety of data for gluon polarization

• 500-GeV program– started in 2009 for sea-quark polarization measurement

with weak boson– Production run will start in 2011

• 3/4 longitudinal-spin & 1/4 transverse-spin

January 7, 2010 8

PHENIX and STAR

• STAR detector• 2 coverage for

jet measurement• barrel TPC and EMC• endcap EMC

• PHENIX detector• limited acceptance• high resolution central EMCal• high-rate trigger and DAQ• forward muon detectors

January 7, 2010 9

Longitudinal-spin asymmetries

• Gluon-spin contribution to the nucleon spin• Sea-quark spin contribution

– with weak boson measurement

gq LLg 2

1

2

1

g

ssdduu

January 7, 2010 10

Double-helicity asymmetries

• Comparison with GRSV model with different gluon polarization

Midrapidity jet at STAR Midrapidity 0 at STAR

GRSV: NLO pQCD calculation by Gluck, Reya,Stratmann and Vogelsang, PRD 63, 094005 (2001).

January 7, 2010 11

Double-helicity asymmetries

• Comparison with GRSV model with different gluon polarizationMidrapidity 0 at s = 200 GeVPRL103, 012003 (2009).

0

Midrapidity 0 at s = 62.4 GeVPRD79, 012003 (2009).

January 7, 2010 12

Gluon spin contribution - results• GRSV-std [g = 0.4 at Q2 = 1 (GeV/c)2] rejected on more

than 3-sigma level• Strong constraints for gluon-spin contribution to explain

remaining part of the nucleon spinMidrapidity jet at STAR Midrapidity 0 at PHENIX

January 7, 2010 13

Global analysis result• New analysis by DSSV

– PHENIX + STAR + SIDIS + DIS– Smaller g than GRSV-std [g = 0.4 at Q2 = 1 (GeV/c)2]– Strong constraint on the size of g(x) for 0.05 < x < 0.2

by the RHIC data

de Florian, Sassot, Stratmannand Vogelsang, PRL 101, 072001 (2008).

January 7, 2010 14

Gluon spin contribution - plan

• 2009 run (+ another run?)– Correlation channel: jet-jet at STAR

• better constraint on parton scattering kinematics

East Barrel+ Endcap

East Barrel+ West Barrel

East + East& West + West

West Barrel+ Endcap

January 7, 2010 15

Gluon spin contribution - plan• PHENIX upgrades

– VTX silicon vertex tracker• inclusive jet

• open charm

• correlation channels

– better constraint on parton scattering kinematics

– jet + jet / jet + photon

• barrel VTX to be installed in 2010

January 7, 2010 16

Sea-quark polarization - introduction• Large uncertainty in anti-quark polarization

• Weak boson measurement– Parity-violating asymmetry

at forward rapidity at backward rapidity

)()()()(

)()()()(

baba

babaWL xuxdxdxu

xuxdxdxuA

January 7, 2010 17

Sea-quark polarization - introduction

• Uncertainty and yield of lepton– W- l- at backward rapidity

• sensitive to anti-u quark polarization

– W+ l+ at midrapidity• sensitive to anti-d quark polarization

January 7, 2010 18

2009 RHIC Run s = 500 GeV run started• Sea-quark polarization measurement started

– midrapidity W+ e+ measurement

midrapidity positron yield at PHENIX midrapidity e+/e- yield at STAR

January 7, 2010 19

Sea-quark polarization - plan

• PHENIX plan– Muon-trigger upgrade

• muon tracker FEE• RPC

Central arm W+ e+ measurementfrom 2009 run

Muon arm measurement withmuon-trigger upgrade from 2011

RPC1(a,b)RPC2 RPC2RPC3 RPC3

Muon tracker FEE

70 & 300 pb-1

anti-d quark pol

anti-u quark polanti-d quark pol

300 & 1300 pb-1

January 7, 2010 20

Sea-quark polarization – plan

• STAR plan– FGT upgrade

• Forward GEM Tracker• e+/e- separation

Barrel EMC W+ e+ measurementfrom 2009 run

Endcap measurement withFGT upgrade from 2011

300 pb-1 300 pb-1

January 7, 2010 21

Transverse-spin - introduction

gq LL • Multi-dimensional structure of the nucleon

– Orbital angular momentum inside the nucleon– Shape of the nucleon

direction ofnucleon spin

quark distributionwith parallel spinto the nucleon

quark distributionwith anti-parallel spinto the nucleon

NSAC Long Range Plan arXiv:0809.3137

G. A. Miller, PRC68, 022201(R) (2003)

January 7, 2010 22

Transverse-spin - results

+

K

p

p

Forward rapidity 0 at STARat s = 200 GeV

Forward identified particlesat BRAHMS

Forward rapidity 0 at PHENIXat s = 62.4 GeV

Transverse-spin - results

• Results at forward rapidity– Explained as a mixture of Sivers effect, Collins effect, and

higher-twist effect– Why similar asymmetry on K+ (valence+sea) and K-

(sea+sea)?– Why large asymmetry on anti-proton?

• How to distinguish Sivers effect?– Back-to-back jet

• How to separate initial-state and final-state interaction with remnant partons?– Forward photon + jet– Drell-Yan process

January 7, 2010 23

January 7, 2010 24

Transverse-spin - results

• Back-to-back jet at STAR– Sensitive to the Sivers effect,

but no asymmetry measured even in kinematic region sensitive to the polarized-quark scattering

• Initial-state and final-state interaction with remnant partons– Different sign

• attractive or repulsive

– Cancellation of both effect– (Cancellation of u and d

quarks, too)

0

2

h

January 7, 2010 25

Forward photon + jet• Sivers effect only with initial-state interaction

(repulsive only)– Higher yield can be obtained– STAR forward photon measurement with FMS (Forward

Meson Spectrometer) and Endcap EMC– PHENIX forward photon measurement with MPC (Muon

Piston Calorimeter) and possible forward calorimeter upgrade (FOCAL)

A. Bacchetta et al.,PRL 99, 212002 (2007).AN in photon+jet production

forward photon η > 2jet -1 < η < 0

NSAC milestone for transverse spin (HP13, 2015)

no process dependence

correct process dependence

Summary• Polarized proton-proton collision

– Complementary to the polarized DIS• Longitudinal-spin asymmetry measurement at RHIC

g measured in RHIC 200-GeV program• small to explain remaining part of the nucleon spin• correlation channel for better constraint on parton scattering

kinematics– Sea-quark polarization with weak-boson measurement in RHIC

500-GeV program started from 2009• detector upgrades underway for production runs from 2011• for better precision of and g

• Transverse-spin asymmetry measurement at RHIC– Multi-dimensional structure of the nucleon

• related to the orbital angular momentum inside the nucleon & shape of the nucleon

• Important role of initial-state and final-state interaction with remnant partons inside the nucleon

• forward photon+jet and Drell-Yan process

January 7, 2010 26

Backup Slides

January 7, 2010 28

Introduction• Origin of the nucleon spin 1/2 ?

– Polarized DIS experiments• Virtual-photon - quark scattering• EMC experiment at CERN

– total quark spin constitutes a small fraction of the nucleon spin

– integration in x = 0 ~ 1 makes uncertainty– more data to cover wider x region with more precise data

necessary• SLAC/CERN/DESY/JLAB experiments

– Polarized proton-proton collision• quark-quark + quark-gluon + gluon-gluon scatterings

– sensitive to the gluon• RHIC polarized proton-proton collider experiments

– perturbative QCD applicable– sea-quark with weak boson measurement

)%syst(14)stat(912 “proton spin crisis”

%30~

Lg 2

1

2

1

January 7, 2010 29

FNAL-E704• Longitudinal-spin asymmetry measurement

– Double-helicity asymmetry

– For g: gluon-spin contribution s = 19.4 GeV• low statistics• applicability of perturbative QCD questionable to extract the

gluon-spin contribution from the asymmetry data

ALL(0): PLB 261 (1991) 197. ALL(multi-): PLB 336 (1994) 269.

dd

ddALL

January 7, 2010 30

FNAL-E704

• Transverse-spin asymmetry measurement– Left-right asymmetry

– Large asymmetries discovered at forward rapidity

• no large asymmetry expected at this “high energy”

– AN mq / s

• development of many models based on perturbative QCD

RightLeft

RightLeftN dd

ddA

January 7, 2010 31

2009 RHIC Run (Run-9)

s = 500 GeV run started– Lpeak = 9.6×1031 cm-2s-1

– Lave = 10 pb-1 / week• (as of April 2)

• Sea-quark polarization– central arm W+ e+ measurement at PHENIX from Run9

• Gluon polarization– lower x coverage x < 0.02

70 & 300 pb-1

anti-d quark pol

January 7, 2010 32

Cross section measurements• Applicability of NLO perturbative QCD

– Used for polarized measurementMidrapidity 0 at PHENIX Midrapidity jet at STAR

January 7, 2010 33

Cross section measurementsForward rapidity 0 at STAR

for transverse-spinasymmetry measurement

Midrapidity direct-photon at PHENIXfor gluon polarizationmeasurement in the future

January 7, 2010 34

Gluon spin contribution - introduction

• Scaling violation in polarized DIS– spanning a limited range of Q2

• Semi-inclusive DIS– high-pT hadron pairs

– open charm production

(th)(syst)(stat)99.0)GeV 1( :SMC 43.145.0

42.022.0

17.131.0

22

Qg

1.1(syst)(stat)8.06.1)GeV 5( :E155 22 Qg

lepton beam

or

or nucleon target

*

gluon

heavy flavor

B. Adeba et al., PRD 58, 112002 (1998).

P.L. Anthony et al., PLB 493, 19 (2000).

January 7, 2010 35

Gluon spin contribution - introduction• Polarized proton collision

• Double-helicity asymmetries of 0 and jet

][][][ qqgqgg

dd

ddA

qqgqgg

LL

proton beam

proton beam

or

or

gluon

photon

proton beam

proton beam

or

or gluon

gluonheavy flavor

direct photon production heavy-flavor production

gg + qg dominantsensitive tothe gluon reaction

January 7, 2010 36

Gluon spin contribution - results G constraint

– strong constraint of G as found by DSSV

– from s = 200 GeV 0 ALL results (0.02 < x < 0.3)

– constraint at 3 of -0.7 < G[0.02,0.3] < 0.5 is nearly shape independent

– other probes also will constrain G, and be used in future global fits

Midrapidity 0 at s = 200 GeVPRL103, 012003 (2009).

January 7, 2010 37

Transverse-spin - introduction• Extension of distribution functions

– GPD (Generalized Parton Distribution) and TMD (Transverse-Momentum Dependent) distribution

M. Diehl, Trento workshop, June 2007

January 7, 2010 38

TMD functions (and transversity)

Sivers function:correlation between nucleon transverse spinand parton transverse momentum (kT)

Transversity:correlation between nucleon transverse spinand parton transverse spin

Boer-Mulders function:correlation between parton transverse spinand parton transverse momentum (kT)

sign... oppositeor 0)( 0)( 11 dfuf TT0)( 0)( 11 dhuh

sign... same thehave to

expected )( and )( 11 dhuh

u-quark

d-quark

u-quark

d-quark

January 7, 2010 39

Transverse-spin - results

• Results at forward rapidity– Explained as a mixture of

Sivers effect, Collins effect, and higher-twist effect

– Why similar asymmetry on K+ (valence+sea) and K- (sea+sea)?

– Why large asymmetry on anti-proton?

• PHENIX 0 at midrapidity – Constraints on gluon Sivers

distribution

M. Anselmino, et al., PRD 74,094001 (2006)

January 7, 2010 40

DIS Drell-Yan

“toy” QED

QCD

attractive repulsive

Sivers function measurement• Sign of Sivers function determined by single transverse-

spin (SSA) measurement of DIS and Drell-Yan processes– Should be opposite each other

• Initial-state interaction or final-state interaction with remnant partons– Test of TMD factorization– Explanation by Vogelsang and Yuan…

• From “Transverse-Spin Drell-Yan Physics at RHIC,” Les Bland, et al., May 1, 2007

January 7, 2010 41

Sivers function measurement

• < 1% level multi-points measurements have already been done for SSA of DIS process

• comparable level measurement needs to be done for SSA of Drell-Yan process for comparison

January 7, 2010 42

Drell-Yan at RHIC

b-quark

Drell-Yan

“Transverse-Spin Drell-Yan Physics at RHIC,” Les Bland, et al., May 1, 2007

• Statistically limited due to the small yield of the Drell-Yan process– Large background from b-quark

January 7, 2010 43

Summary

• Polarized proton-proton collision– Complementary to the polarized DIS

• Longitudinal-spin asymmetry measurement at RHIC g measured in RHIC 200-GeV program

• small to explain remaining part of the nucleon spin

– Sea-quark polarization with weak-boson measurement in RHIC 500-GeV program started from 2009

• for better precision of and g

• Transverse-spin asymmetry measurement at RHIC– Multi-dimensional structure of the nucleon

• related to the orbital angular momentum inside the nucleon & shape of the nucleon

• Important role of initial-state and final-state interaction with remnant partons inside the nucleon