Status and Perspective of the high-energy polarized proton ...high-energy polarized proton-proton program at RHIC. Bernd Surrow BNL PAC Meeting, BNL, Department of Physics Upton, NY,

Bernd Surrow

BNL PAC Meeting, BNL, Department of PhysicsUpton, NY, May 08, 2008 Bernd Surrow

1

Status and Perspective of the high-energy polarized proton-

proton program at RHIC

Bernd SurrowBNL PAC Meeting, BNL, Department of PhysicsUpton, NY, May 08, 2008

Outline

Summary and Outlook

Theoretical foundation

2

!p !p

Highlights of recent results and achievements

Future polarized p-p physics program

Gluon polarizationQuark / Anti-Quark PolarizationTransverse spin dynamics

Future polarized p-p collider performance



General

3

Mom

entu

m

cont

ribu

tion

Spin contribution

f(x) =

f+(x) + f−(x)

+

∆f(x) =

f+(x)− f−(x)

−

p

p

pTx1

x2

dσpp ∝ f1 ⊗ f2 ⊗ σh ⊗Dhf Factorization

e′

X

e

p

xQ2

W 2 ! Q2/x

dσep ∝ F2 =∑

q

xe2qfq(x)

Universality

0

0.2

0.4

0.6

0.8

1

-410 -310 -210 -110 10

0.2

0.4

0.6

0.8

1

HERA I PDF fit (prel.)

CTEQ6.1M

HERA I PDF fit (prel.)

CTEQ6.1M

x

xf 2 = 10 GeV2Q

vxu

vxd

0.05)×xS (

0.05)×xg (

vxu

vxd

0.05)×xS (

0.05)×xg (

0

0.2

0.4

0.6

0.8

1

HER

A S

truct

ure

Func

tions

Wor

king

Gro

upA

pril

2008

H1 and ZEUS Combined PDF Fit


Theoretical foundation4

Precision measurements (e.g. F2) ⇒ Precision on quark/gluon structure

Strong violation of scaling at low x and high Q2

In contrast to:

Low Q2 high x!

Evolution

xg ∝(

dF2

d lnQ2

)

H1 and ZEUS Combined PDF Fit

HER

A S

truct

ure

Func

tions

Wor

king

Gro

upA

pril

2008

x = 0.000032, i=22x = 0.00005, i=21

x = 0.00008, i=20x = 0.00013, i=19

x = 0.00020, i=18x = 0.00032, i=17

x = 0.0005, i=16x = 0.0008, i=15

x = 0.0013, i=14x = 0.0020, i=13

x = 0.0032, i=12x = 0.005, i=11

x = 0.008, i=10x = 0.013, i=9

x = 0.02, i=8

x = 0.032, i=7x = 0.05, i=6

x = 0.08, i=5x = 0.13, i=4

x = 0.18, i=3

x = 0.25, i=2

x = 0.40, i=1

x = 0.65, i=0

Q2/ GeV2

!r(x

,Q2 ) x

2i

HERA I e+p (prel.)Fixed TargetHERA I PDF (prel.)

10-3

10-2

10-1

1

10

10 2

10 3

10 4

10 5

10 6

10 7

1 10 10 2 10 3 10 4 10 5

e (kµ)

e (k /)

γ* (qµ)

P (p µ)X (pµ /)



Gluon polarization - Extraction

5

ALL =d∆σ

dσ

long-range short-range long-range

∆f2∆f1 aLL =∆σh

σh

Extract Δg(x,Q2) through

Global Fit (Higher Order

QCD analysis)!

∆G(Q2) =∫ 1

0∆g(x,Q2)dx ∆f1

∆f2

∝∆f1 ⊗∆f2 ⊗ σh · aLL ⊗Dh

f

f1 ⊗ f2 ⊗ σh ⊗Dhf

Input

σh

xT = 2pT /√

s

Inclusive Jet production (200GeV: Solid line / 500GeV: Dashed line)

00.10.20.30.40.50.60.7

0 10 20 30 40 50 60 70 80 90 100pT

σij/σ

tot

-1<η<1 gg qg qq

00.10.20.30.40.50.60.7

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5XT

σij/σ

tot

-1<η<1 gg qg qq



Gluon polarization - Inclusive Measurements

6

part

onpa

rtic

lede

tect

or

Jet

π0π+

g

q

€

Δg

€

Δq



Gluon polarization - Correlation Measurements

Correlation measurements provide access to partonic

kinematics through Di-Jet/Hadron production and Photon-Jet

production

Di-Jet production / Photon-Jet production

Di-Jets: All three (LO) QCD-type processes contribute: gg, qg and

gg with relative contribution dependent on topological coverage

Photon-Jet: One dominant underlying (LO) process

Larger cross-section for di-jet production compared to photon

related measurements

Photon reconstruction more challenging than jet reconstruction

Full NLO framework exists ⇒ Input to Global analysis

7

p

p

pTx1

x2

p

p

pTx1

x2

M =√

x1x2s η3 + η4 = lnx1

x2

gg, qg, qq

qg

Di-Jet production

Photon-Jet production

AWL =

1P

N+(W )−N−(W )N+(W )−N−(W )

RHICBOS W simulation at 500GeV CME

00.10.20.30.40.50.60.70.80.9

1

0 20 40pT (GeV)

dσ/d

p T (pb

/GeV

)

W+ for CTEQ5M

Total cross-section: 14.41<ye<2

00.10.20.30.40.50.60.70.80.9

1

0 20 40pT (GeV)

dσ/d

p T (pb

/GeV

)

W- for CTEQ5M

Total cross-section: 8.01<ye<2’

0123456789

10

0 20 40pT (GeV)

dσ/d

p T (pb

/GeV

)

W+ for CTEQ5M

Total cross-section: 134.7No cuts

0123456789

10

0 20 40pT (GeV)

dσ/d

p T (pb

/GeV

)

W- for CTEQ5M

Total cross-section: 42.0No cuts

∆d + u→W+

∆u + d→W+

W− → e− + νe

W+ → e+ + νe



Quark / Anti-Quark Polarization - W production

8

∆d + u→W−

∆u + d→W−

∆d + u→W+

∆u + d→W+

W∓

Key signature: High pT lepton (e-/e+ or

μ-/μ+) (Max. MW/2) - Selection of

W-/W+ : Charge sign discrimination of

high pT lepton

Required: Lepton/Hadron

discrimination

AW+

L = −∆u(x1)d(x2)−∆d(x1)u(x2)u(x1)d(x2) + d(x1)u(x2)

x1 =MW√

seyW x2 =

MW√s

e−yW

Leptony

-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5

LA

-0.4

-0.2

0

0.2

0.4

0.6 GRSV std

GRSV val

>20 GeVT P-W

Leptony

-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5

LA

-0.8

-0.6

-0.4

-0.2

-0

0.2 GRSV std

GRSV val

>20 GeVT P+W



Quark / Anti-Quark Polarization - Sensitivity in W production

9

Large uncertainties for polarized anti-quarks reflected in leptonic asymmetries!

Theoretical framework for leptonic

asymmetries exists (RHICBOS) ⇒ Basis for

input to global analysis!

Reconstruction of W-rapidity only possible

in approximative way in forward direction

Important contribution from forward and

mid-rapidity region

0.1 0.2 0.3 0.4 0.5 0.6-0.15

-0.1

-0.05

-0

0.05

0.1

0.15

0.2

0.25

0.3

0.35Graph

+l

-l0.1 0.2 0.3 0.4 0.5 0.6

-0.06

-0.04

-0.02

-0

0.02

0.04

Graph

GRSV std

GRSV val

-l

+l

Graph

∆u ∆u

∆d∆d



Transverse spin dynamics

10

AN =σ↑ − σ↓σ↑ + σ↓

Single transverse-spin asymmetry Basic, naive QCD calculations (leading-twist,

zero quark masses) predict: AN=0 (AN ~ mq/

√s)

Qiu and Sterman (Initial-state twist-3)/

Koike (final-state twist-3)

Sivers: k⊥ in initial state (Correlation of

quark k⊥ and transverse proton spin):

⇒ Orbital momentum

Collins: k⊥ in final state (Correlation of

transverse quark spin and k⊥ of hadron):

⇒ Transversity

Study transverse spin effects:



Cross Section Results

11

Good agreement between data and NLO

calculations for neutral pion production at

forward and central rapidity



Cross Section Results

12

Good

agreement

between data

and NLO

calculations for

jet production

and prompt

photon

production at

central rapidity



ALL Results - Inclusive Jet Production

13

-0.7 < η < 0.9

RUN 6 results: GRSV-MAX / GRSV-MIN ruled out - ALL result favor a gluon polarization in the measured x-region which falls in-between GRSV-STD and GRSV-ZERO

Consistent with RUN 5 result (Factor 3-4 improved statistical precision for pT>13GeV/c)

0.2

0.4

0.6

0.82/c2=100GeV2Q

-310 -210-110 1

0

X gluon

p =28 GeV/cT

p = 5.6 GeVT

/c

a)

1

∆G

x10 5

0.25

0.5

0.75

1.0

0

frac

dN/d

(log

x)

-410

-310

-210

10

CL

/c ) 2 = 0.4 GeV2 G (Q∆ 20

-1 -0.5 0 0.5 1

-1

1

STARjet+X→pp

g=-g

∆G

RSV

g=0

∆G

RSV

GRS

V-st

d g=g

∆G

RSV

b)

Pol. uncertainty

xparton ! 2pT /√

s



ALL Results - Neutral pion production

14

Consistent RUN 5/6 results

RUN 6 results: ALL result favor a

gluon polarization in the

measured x-region which falls in-

between GRSV-STD and GRSV-

ZERO



Global analysis incl. RHIC pp data

15

TABLE I: Data used in our analysis [2, 3], the individualχ2 values, and the total χ2 of the fit. We employ cuts ofQ, pT > 1GeV for the DIS, SIDIS, and RHIC high-pT data.

experiment data data points χ2

type fitted

EMC, SMC DIS 34 25.7

COMPASS DIS 15 8.1

E142, E143, E154, E155 DIS 123 109.9

HERMES DIS 39 33.6

HALL-A DIS 3 0.2

CLAS DIS 20 8.5

SMC SIDIS, h± 48 50.7

HERMES SIDIS, h± 54 38.8

SIDIS, π± 36 43.4

SIDIS, K± 27 15.4

COMPASS SIDIS, h± 24 18.2

PHENIX (in part prel.) 200 GeV pp, π0 20 21.3

PHENIX (prel.) 62GeV pp, π0 5 3.1

STAR (in part prel.) 200 GeV pp, jet 19 15.7

TOTAL: 467 392.6

spond to the maximum variations for ALL computed withalternative fits consistent with an increase of ∆χ2 = 1 or∆χ2/χ2 = 2% in the total χ2 of the fit.

Our newly obtained antiquark and gluon PDFs areshown in Fig. 2 and compared to previous analysis [4, 6].For brevety, the total ∆u+∆u and ∆d+∆d densities arenot shown as they are very close to all other fits [4–6].Here, the bands correspond to fits which maximize thevariations of the truncated first moments,

∆f1,[xmin−xmax]j (Q2) ≡

∫ xmax

xmin

∆fj(x, Q2)dx, (8)

at Q2 = 10 GeV2 and for [0.001 − 1]. As in Ref. [6]they can be taken as faithfull estimates of the typicaluncertainties for the antiquark densities. For the elusivepolarized gluon distribution, however, we perform a moredetailed estimate, now discriminating three regions in x:0.001-0.05, 0.05-0.2 (roughly corresponding to the rangeprobed by present RHIC data), and 0.2-1.0. Within eachregion, we scan again for alternative fits that maximizethe variations of the truncated moments ∆g1,[xmin−xmax],sharing evenly to ∆χ2. In this way we can produce alarger variety of fits than for a single ([0.001−1]) moment,and, therefore, a more conservative estimate. Such a pro-cedure is not necessary for antiquarks whose x-shape isalready much better determined by DIS and SIDIS data.One can first of all see in Fig. 2 that ∆g(x, Q2) comes outrather small, even when compared to fits with a “moder-ate” gluon polarization [4, 6], with a possible node in thedistribution. This is driven by the RHIC data which puta strong constraint on the size of ∆g for 0.05 ! x ! 0.2

-0.02

-0.01

0

0.01

0.022 4 6 8

A!

ALL

0

pT [GeV]

PHENIX

PHENIX (prel.)

STAR

STAR (prel.)

DSSVDSSV "#

2=1

DSSV "#2/#

2=2%

Ajet

ALL

pT [GeV]

-0.05

0

0.05

10 20 30

FIG. 1: Comparison of RHIC data [3] and our fit. The shadedbands correspond to ∆χ2 = 1 and ∆χ2/χ2 = 2% (see text).

-0.04

-0.02

0

0.02

0.04

-0.04

-0.02

0

0.02

0.04

-0.04

-0.02

0

0.02

0.04

10-2

10-1

DSSV

DNS

GRSV

DSSV "#2=1

DSSV "#2/#

2=2%

x"u–

x"d–

x"s–

x

Q2 = 10 GeV

2 GRSV max. "g

GRSV min. "g

x"g

x

-0.2

-0.1

0

0.1

0.2

0.3

10-2

10-1

FIG. 2: Our polarized sea and gluon densities compared toprevious fits [4, 6]. The shaded bands correspond to alterna-tive fits with ∆χ2 = 1 and ∆χ2/χ2 = 2% (see text).

but cannot determine its sign as they mainly probe ∆gsquared. To explore this further, Fig. 3 shows the χ2

profile and partial contributions ∆χ2i of the individual

data sets for variations of the moment computed for thisx range. A nice degree of complementarity and consis-tency between is found. A small ∆g at x # 0.2 is alsoconsistent with data for ALL from lepton-nucleon scatter-ing [15], which still lack a proper NLO description. Thesmall x region remains still largely unconstrained.

We also find that the SIDIS data give rise to a ro-bust pattern for the sea polarizations, clearly deviating

395

400

405

410

-0.2 0 0.2

!2

"g1, [ 0.05-0.2 ]

all data setsx-range: 0.05-0.2

(a)

"!2"!i

"g1, [ 0.05-0.2 ]

PHENIXSTARSIDISDIS

(b) 0

5

10

15

-0.2 0 0.2

0.2

0.4

0.6

0.82/c2=100GeV2Q

-310 -210-110 1

0

X gluon

p =28 GeV/cT

p = 5.6 GeVT

/c

a)

1

∆G

x10 5

0.25

0.5

0.75

1.0

0

frac

dN/d

(log

x)-410

-310

-210

10

CL

/c ) 2 = 0.4 GeV2 G (Q∆ 20

-1 -0.5 0 0.5 1

-1

1

STARjet+X→pp

g=-g

∆G

RSV

g=0

∆G

RSV

GRS

V-st

d g=g

∆G

RSV

b)

Pol. uncertainty

hep-ph/0804.0422

Strong constraint on the size of Δg from RHIC

data for 0.05<x<0.2

Evidence for a small gluon polarization over a

limited region of momentum fraction

Important: Mapping x-dependence and extension

of x-coverage needed!

F x-0.6 -0.4 -0.2 0 0.2 0.4 0.6

NA

-0.4

-0.2

0

0.2

0.4 +!-!

BRAHMS Preliminary



AN results

16

Submitted to PRL, hep-ex/0801.2990

Precise measurement of AN as a function

of xF

AN calculations (Sivers / Twist-3) in

comparison to precise xF dependence of

measured AN ⇒ Constrain models!



AN results

17

Measured AN

is not found to

decrease in pT

in all xF bins

In contrast:

Theoretical

models predict

AN to

decrease with

pT

Submitted to PRL, hep-ex/0801.2990


Future polarized p-p collider performance

Polarized proton-proton operation at RHIC at 200 / 500 GeV

During last longest polarized proton-proton run (RUN 6):

Luminosity: ~1pb-1/day (~3pb-1/day design) delivered luminosity

Polarization: ~60% polarization (70% design)

18

500GeV development: Achieved 45%(*) beam polarization for single beam at 250GeV

Goal: At 70% beam

polarization

200GeV:

60⋅1030cm-2s-1

500GeV:

150⋅1030cm-2s-1

(*) Assumption: Analyzing power at 250GeV same as for 100GeV!



Gluon polarization - Projection Run 9

19

-0.2

-0.1

0

0.1

0.2

0.3

GRSVDNS

x!g w/Run 6

GRSV max. !gGRSV min. !g

x!g w/Run 9

x

DSSV

-0.2

-0.1

0

0.1

0.2

0.3

10 -1 1

395

400

405

410

-0.2 0 0.2

0

5

10

15

-0.2 0 0.2

395

400

405

410

-0.2 0 0.2

!2

"g1, [ 0.05-0.2 ]

all data sets

x-range: 0.05-0.2 "!2"!i

"g1, [ 0.05-0.2 ]

PHENIXSTARSIDISDIS

!2

"g1, [ 0.05-0.2 ]

RUN 9"!2"!i

"g1, [ 0.05-0.2 ]

0

5

10

15

-0.2 0 0.2

Substantial improvement on gluon polarization from inclusive measurements

Complementary information from STAR and PHENIX

RUN 6

Bernd SurrowLattice QCD Club, MIT, Department of PhysicsCambridge, MA, May 02, 2008

M ∝√

x1x2

Results: Gluon Spin contribution20

Data/MC comparison complete - Good agreement in Di-Jet variables

First cross-section and ALL measurement in progress

η3 + η4 ∝ log(

x1

x2

)

Correlation measurements: Di-Jet production - Data Understanding

]2M [GeV/c20 30 40 50 60 70 80

LLA

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

0.06STAR: east barrel - endcap

< 0.04! < 2.0, -1.0 <

3!1.0 <

MCGRSV stdGRSV m03GRSV zeroGS-C(pdf set NLO)

(P = 60%)-150 pb

NLOGRSV stdDSSV

]2M [GeV/c20 30 40 50 60 70 80

LLA

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

0.06STAR: west barrel - endcap

+ X4 + jet3 jet" p + p = 200 GeVs

< 1.04! < 2.0, 0.0 <

3!1.0 <

]2M [GeV/c20 30 40 50 60 70 80

LLA

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

0.06STAR: east barrel - east barrel and west barrel - west barrel

< 0.04! < 0.0, -1.0 <

3!-1.0 <

< 1.04! < 1.0, 0.0 <

3! 0.0 <

]2M [GeV/c20 30 40 50 60 70 80

LLA

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

0.06STAR: east barrel - west barrel

< 0.04! < 1.0, -1.0 <

3!0.0 <

Scale uncertaintyGRSV stdDSSV



Gluon polarization - Di-Jets

21

Substantial improvement in

Run 9 from Di-Jet

production

Good agreement between

LO MC evaluation and full

NLO calculations

M =√

x1x2s η3 + η4 = lnx1

x2

0.200.07

0.610.22

x1x2

0.330.04

0.870.12

x1x2

0.200.07

0.610.22

x1x2

0.120.12

0.370.37

x1x2



Quark / Anti-Quark polarization program at PHENIX

Forward Muon Trigger layout

22

RPC1(a,b)RPC2 RPC2RPC3 RPC3

3 RPC planes for each muon chamber - Expected installation: Stations 2/3-North in 2009 - 2/3-South in 2010

FEE upgrade of muon tracking - Expected installation: North in Summer 2008 / South in Summery 2009




23

Main offline background: Low pT

hadrons decaying within muon

tracker volume mimicking a high pT

track

Tight cuts reduce S/B ratio to 1/3

Hadron absorber after central

magnet yoke to obtain 3/1 ratio




24

Large asymmetries dominated by

quark polarization - Important

consistency check to existing DIS

data with 100pb-1 (Phase I)

Strong impact constraining unknown

antiquark polarization requires

luminosity sample at the level of

300pb-1 for 70% beam polarization

(Phase II)



Quark / Anti-Quark polarization program at STAR

25

Forward GEM Tracker: FGT

Charge sign identification for high momentum

electrons from W± decay (Energy determined

with EEMC)

Triple-GEM technology

FGT project:

ANL, IUCF, LBL, MIT, University of Kentucky,

Valparaiso University, Yale

Successful project review (Capital equipment

funding): January 2008

Expected installation: Summer 2010 FGTHFT


Future polarized p-p physics program26


e/h separation: Full PYTHIA QCD background and W signal sample including detector effects

e/h separation based on global cuts (isolation/missing ET) and EEMC specific cuts as

With current algorithm: ET > 25GeV yields S/B > 1 (For ET < 25GeV S/B ~ 1/5) used for AL

uncertainty estimates



Conclusion:

Charge sign reconstruction impossiblebeyond η = ~1.3

TPC + FGT Tracking, pT = 30 GeV/c

6 triple-GEM disks, assumed spatial resolution 60μm in x and y (Fairly insensitive for60-100μm)

Charge sign reconstruction probability above 90% for 30 GeV pT over the full acceptance ofthe EEMC for the full vertex spread


Reach of EEMCAcceptance



Mon May 5 23:40:44 2008

, Pol=0.7, including QCD background and detector effects-1STAR projections for LT=300 pb

lepton ET (GeV)20 25 30 35 40 45 50

-0.8

-0.6

-0.4

-0.2

-0

0.2

GRSV-STDGRSV-VALDNS2005-KKPDNS2005-KRETZERDSSV2008STAR projections

(W+) for positronL A Forward

lepton ET (GeV)20 25 30 35 40 45 50-0.2

0

0.2

0.4

0.6

0.8GRSV-STDGRSV-VALDNS2005-KKPDNS2005-KRETZERDSSV2008STAR projections

(W-) for electronL A Forward

lepton ET (GeV)20 25 30 35 40 45 50

-0.8

-0.6

-0.4

-0.2

-0

0.2

GRSV-STDGRSV-VALDNS2005-KKPDNS2005-KRETZERDSSV2008STAR projections

(W+) for positronLBackward A

lepton ET (GeV)20 25 30 35 40 45 50-0.4

-0.2

0

0.2

0.4

0.6GRSV-STDGRSV-VALDNS2005-KKPDNS2005-KRETZERDSSV2008STAR projections

(W-) for electronLBackward A


Large asymmetries dominated by

quark polarization - Important

consistency check to existing DIS

data with 100pb-1 (Phase I)

Strong impact constraining unknown

antiquark polarization requires

luminosity sample at the level of

300pb-1 for 70% beam polarization

(Phase II)




29

Conventional calculations predict the asymmetry to have the same sign in SDID and γ+ jet whereas

calculations that account for repulsive interactions between like color charges predict opposite sign

Critical test on Sivers effect

Bacchetta et al., PRL 99, 212002




30

Important test at RHIC of fundamental QCD

prediction of non-universality of Sivers effect 0.1 0.2 0.3 x

Siv

ers A

mpl

itude

0

HERMES Sivers Results

Markus DiefenthalerDIS WorkshopMűnchen, April 2007

0


Summary and Outlook31

Recorded Luminosity

Main physics Objective Remarks

~50pb-1 Gluon polarization using di-jets and precision inclusive measurements 200 GeV

~100pb-1W production (Important consistency

check to DIS results - Phase I)Gluon polarization (Di-Jets / Photon-Jets)

500 GeV

~300pb-1W production (Constrain antiquark

polarization - Phase II)Gluon polarization (Di-Jets / Photon-Jets)

500 GeV

~30pb-1 Transverse spin gamma-jet 200 GeV

~250pb-1 Transverse spin Drell-Yan (Long term) 200 GeV

Beam polarization: 70% / Narrow vertex region / Spin flipper for high precision asymmetry measurements

Critical: Sufficient running time!

Documents

Status and Perspective of the high-energy polarized proton ...high-energy polarized proton-proton program at RHIC. Bernd Surrow BNL PAC Meeting, BNL, Department of Physics Upton, NY,