spin physics results from rhic

M. Grosse Perdekamp, UIUC

Spin Physics Results from RHIC

International Workshop on Hadron Structure and Spectroscopy

CRNS, ParisApril 4th -6th , 2011 

STARSTAR

pp2pp

AnDY

Preliminaries: Facility Status QCD & PDFs vs Data

Gluon spin distribution Inclusive hadron and jet results QCD analysis Low x & x-dependence with di-jets and rapidity separated di-hadrons

W-production in polarized p-p First results from pp W eν

Transverse Spin Inclusive AN

Channels isolating Collins or Sivers effects Drell Yan measurements in Akio Owaga’s talk

Spin Physics Results from RHIC

RHIC Status: Running Polarized p-p at √s= 500 GeV through 4-8/15

3

Lu

min

osit

y in

Rela

tive U

nit

es

Time in Store [days]

impact from3rd collisionpoint

4 RHIC fills, last week of March First full length 500 GeV run

P ~ 45 % (max above 50%)goal is P ~ 50%

L ~ 5 x 1031 cm-2s-1

goal is L ~ 10 x 1031 cm-2s-1

o AnDY commissioned successfullyo muon-W trigger in PHENIX in operation

o ∫Ldt ~ 40% of planned, due to major hardware failure in cryo-system (repaired).

4

NLO pQCD Cross Sections vs RHIC data for Different √s and Rapidity Intervals

√s = 200 GeV

∆ PHENIX π0, η = 0∙ Brahms π+ ,η = 2.95 ⌷ STAR π0 ,η =

3.7- - - - - NLO pQCD

√s = 62.4 GeV

See analysis in De Florian, Vogelsang, Wagner PRD 76,094021 (2007) and Bourrely and Soffer Eur.Phys.J.C36:371-374 (2004)

o PHENIX π0, η = 0-------- NLO pQCD

Good agreement between inclusivehadron cross sections from RHIC data and pQCD calculations !

pT [GeV]pT [GeV]

(I) Gluon Spin Distribution Inclusive hadron and jet results

QCD analysis

Low x & x-dependence with di-jets and rapidity separated di-hadrons

6

ALL for Inclusive Hadrons & Jets at mid-Rapidity η ~ 0 : constrain ΔG(x) at 0.05 < x < 0.2

ALL for neutral pions and jets vs DSSVde Florian, Sassot, Stratmann,Vogelsang PRD 80:034030,2009 

x-range for ALLπ0 in 3 pT bins

Courtesy Swadhin Taneja, Stony Brook

other channels in STAR andPHENIX: eta, charged hadrons,ALL(“charm”) at mid-rapidityALL(J/ψ) for η~ 2.

7

ΔG(x) from DSSV Global QCD Analysis

RHIC

Range

0.05<x<0.2

Large-x

x≥0.2

Small-x

x≤0.05

ΔGtrunc[0.05,0.2] ≈ 0 since node at x≈0.1

Data constrains only truncated first moment of ΔG(x) in x-interval [0.05,0.2], but not functional form at low or high x

ΔGtrunc in large-x region constrained to be small by requirement that ΔG(x) ≤ G(x); at Q2=10 GeV2: ΔGtrunc[0.3,1.0] ≤ 0.03

At small x, ΔG(x) can differ from DSSV beyond errors without violating funda-mental constraints

ΔGtrunc[0.05,0.2] = ∫ ΔG(x) dx = 0.0050.2

0.05

+0.051

-0.058-0.058-0.058-0.058

x ΔG(x)

de Florian, Sassot, Stratmann,Vogelsang PRD 80:034030,2009 

Next steps: ALL for di-jets in STAR resolve xq, xgprojections for 500 GeV and ∫Ldt = 300 pb-1 P=70%

o Information on x1 and x2, forward jets

give access to lower x !

o

De Florian, Frixione, Signer and VogelsangNPB 539 (1999) 455 and PC for present calc.

sMxx /21

Courtesy STAR

9

Extending ΔG(x) to Lowest x with Forward di-Jets or High pT di-

HadronsE.g. back-to-back neutral pion pairs in the PHENIX forward EMC

Associate particle, pT,2

Trigger particle, pT,1

dφ

back-to-back: selects di-jets

Back-to-back hadrons: trigger (pT,1) and associate (pT,2<pT,1) in separate jets: large forward boost

Central Arm

(|η|<0.35)

x1 >> x2

Jet -1 (π0, pT,1)

forward EMC (3.1<|η|<3.9)

Jet 2 (π0, pT,2)

500M PYTHIA events ≈ 0.014 pb-1 , only hard QCD processes, soft processes eliminated by

pT cuts (study by Cameron McKinney, UIUC)

enhances q-gfraction to ~ 60%

Selecting x2 with pT Cuts: x2 Decreases and q-g Fraction Increases with Magnitude of pT

cut

pT,1>1.0 GeV/c, pT,2>0.5 GeV/c<x2> ≈ 0.014

x2x1

pT,1>2.0 GeV/c, pT,2>1.0 GeV/c<x2> ≈ 7.2*10-3

pT,1>3.0 GeV/c, pT,2>1.5 GeV/c<x2> ≈ 4.8*10-3

log x

di-hadron pT cuts and resulting <x2>

11

pT,1>3 GeV, pT,2 > 1.5 GeV error bars are statistical only

Projected ALL(π0) in MPC for different ΔG(x) at low x

for ∫Ldt = 300 pb-1, √s = 500 GeV (RHIC W program, 2011 to 2015)

Increasing Δgtrunc [10-4,0.05]

ΔGtrunc= -.1 ΔGtrunc= -.2 ΔGtrunc= -.5

ΔGtrunc [10-4,0.05] = -0.1 will be observable

First Forward EMC ALL , Run 2009 at √s=200 GeV and Projections for Run 2011, √s=500

GeV

12

ALL forward EMC clusters run 2009

DSSV NLO

DSSV-MAX PYTHIA

GSC NLO

ALL forward clusters, projected 2011

First step towards acquisition of large integrated luminosity for ΔG(x) at small x !

(II) W-production in polarized p-p pp W eν first results

pp W μν look at ongoing run

Quark and Anti-Quark Helicity Distributions from Inclusive AL

e,μ in W-Production

• Large Q2, knowledge of FFs not needed

• pQCD analysis of inclusive lepton AL

• DSSV analyzed MC data of 200 pb-1 and 800 pb-1 from STAR and PHENIX

• Significant improvement of knowledge with 200 pb-

1

De Florian at Berkely RSC meeting Nov, 2009

First exploratory run at√s=500 GeV in 2009P ~ 35%∫Ldt ~ 9 pb-1

15

Jacobian Peak for e- and e+

STAR, run 2009, √s= 500 GeV: Parity Violating AL in p+p high pT e

AL for e- and e+

Not yet (!) sensitive to quark andanti-quark helicity distributions

Phys.Rev.Lett. 106 (2011) 062002 

16

W-Cross Sections for p-p: PHENIX  & ATLAS

Consistent with NNLO QCD

 Phys.Rev.Lett. 106 (2011) 062001  arXiv:1012.5382 [hep-ex]

17

News from Present p-p Run at √s = 500 GeV

First full length 500 GeV run

P ~ 45 % (max above 50%)goal is P ~ 50%

L ~ 5 x 1031 cm-2s-1

goal is L ~ 10 x 1031 cm-2s-1

o AnDY commissioned succesfullyo muon/W trigger in PHENIX in operation

o ∫Ldt ~ 40% of planned, due to major hardware failure in cryo system (repaired).

PHENIX Muon Trigger Installed & Operating

RPCs in Urbana (NSF)

RPCs in PHENIX (NSF)

muTr trigger electronics(JSPS)

FPGA basedlevel-1 triggerprocessors

PHENIX Muon Trigger Performance

muTracker trigger efficiencies RPC-Inner Ring Efficiency

problems to be solved: RPC-gas -> mixture & pressure differentials timing -> RPC south is 1 beam clock late

Taking data with muTr part of trigger in run 2011, use RPCoffline for background rejection

First Look at Data from Fast Production (Ralf Seidl)

Arbitrary normalization

(III) Transverse Spin

Inclusive AN

Collins or Sivers effects

AN in Very Forward Neutron Productionusing the Zero Degree Calorimeter

neutron

Large negative SSA observed for xF>0

Diffractive physics Highly useful as local polarimeter for PHENIX

22

At Hard Scale: AN 0 , QCD Test !?

4q 10, 20,3m example, N

qN AGeVsMeV

s

mA

23

Experiment: Sizeable SSA Observed over Large Range of Scales !

Experiment: AN >> 10-4 for 4 GeV < √s < 200 GeV for charged pions !

from Christine Aidala, Spin 2008 andDon Crabb & Alan Krisch in then Spin 2008 Summary, CERN Courier, 6-2009

ZGS √s=4.7 GeV AGS √s=6.5 GeV FNAL √s = 20 GeV RHIC √s = 200 GeV

π+

π-

Soft effects due to QCD dynamics in hadronsremain relevant up to scales where pQCD canbe used to describe the scattering process!

24

AN vs xF almost unchanged for√s=19.4, 62.4 and 200 GeV

25

Origin of Large SSA for Hard Scattering --Two Solutions: Final State vs Initial State

(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

qqT

Collins FFQuark transversespin distribution

Sivers distribution

(III) Initial or final state twist-3+

Qiu/Sterman and Koike

STAR, PRL-92:171801, 2004

+ unified picture: Ji, Qiu, Vogelsang and Yuan in PRL-97:082002, 2006

First measurement atRHIC √s = 200 GeV

26

BRAHMS: AN for Charged Pions vs pT and xF at √s=62.4 GeV and √s=200 GeV

200 GeV

√s=200 GeV

√s=62.4 GeV

0.4<pT<0.6 GeV/c 0.5 pT<0.6 GeV/c 0.6 pT<0.8 GeV/c 0.8 pT<1.0 GeV/c 1.0 pT<1.2 GeV/c

0.5<pT<0.75 GeV/c1.0<pT<1.25 GeV/c 1.25<pT<1.5 GeV/c 1.5<pT<2.0 GeV/c 2.0<pT<2.5 GeV/c

AN increases withxF (valence quarks)

AN increases with pT ? Limited pT range!

Decrease as ~1/pT expected is not observed.AN constant from pT>2.5 GeV. Need more statistics to extend measurement to pT > 4 GeV !

Positive xF Negative xF

Consistent with zero for all pT

STAR Run 2008: pT Dependence of AN at √s=200 GeV Ogawa at CIPANP 2009

Expectations for AN with PHENIX MPC and Transverse Spin Running in 2012 or

2013

28

Red: Zhong-Bo Kang possible pT dependence if all even orders of twist expansion contributeBlue: pT dependence if sub-leading twist dominates

K p

Large AN for K- significant Sivers asymmetries for sea quarks ?!

Large AN for anti-Proton unexplained.

BRAHMS: AN for Charged Pions ,Kaons and Protons at √s=200 GeV

Another Surprise: AN for Eta Mesons larger than for Pions !

STARSTAR0.361 0.064NA

0.078 0.018NA

GeV 200

s

Xpp

AN(η) > AN(π0) for 0.55 < xF < 0.75

Possibly large effectsin the fragmentation foreta-mesons?

STAR arXiv:0905.2840 (Heppelmann, DIS08)

31

Understanding of AN in terms of Collins and Sivers Effect:

Work in Progress! Future goal: Extract Sivers and transversity quark distributions from global anlaysis to all SIDIS, pp and e+e- data!

Present work: Extract Sivers + transversity from SIDIS and e+e- and predict AN in pp

Presently: Poor agreement with many problems to solve! Universality, evolution, pdf and fragmentation functions not sufficiently known.

For example, note the impact of un-polarized FFs thick line DSS thin line Kretzer

STAR π0

BRAHMS π+,-

Global analysis of SIDIS & e+e-

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

AN calculation from D’Alesio, 2008

Measurements to Isolate Different Mechanisms o Transversity & Collins o Sivers

33

Ideas for Measurements of Transversity Observables

at RHIC

][

][

Xpp

Xhjetpp

Xpp

Xllpp

hemisphere

hemisphere

Drell Yan:Required luminosity not available at RHIC.

Spin dependent Lambda-FF unknown.Measure Λ-FF in e+e- ?

Collins effect in jets; possible in STAR ? hadron ID at high p, z- and ϕ-resolution ?

Di-hadron intereference fragmentation function. IFF data available from e+e- Belle !

34

Interference Fragmentation –IFF- for Di-Hadrons at Mid-Rapidity in

PHENIX

AUT compatible ~0 withpresent statistics

Dilution from gg processes!

Future:

Update with more statistics from runs 2012 and 2013

extend measurements in the forward direction for smaller g-g process fraction and large x !

With 2012 & 2013 statistics

35

IFF Measurement in e+e- at BELLE

1 2( ) ( )jet jete e X

Artru and Collins,

Z. Phys. C69, 277 (1996)

Boer, Jakob, and Radici,

PRD67, 094003 (2003) q1

quark-1 spin

electron

positron

q2

quark-2 spinzpair-1

zpair-1

z1,2 relative pion-pair momenta

ϕpair-1ϕpair-21

1 2

2 θ

22 2

12 1 1 1 1 2 22

sin~ ( , ) ( , )

1 cos pair pair pair paira H z M H z M

PHENIX & STAR collaborators have joined Belle: BNL-Illinois-Indiana-RBRC-RIKEN

PreliminaryPreliminary

Preliminary

Preliminary

PreliminaryPreliminary

Preliminary

Preliminary

Preliminary

Belle IFF- Asymmetries vs Hadron Pair Momentum Fraction zi

9x9 z1 z2 binning

z1

a12

BNL-Illinois-Indiana-RBRC-RIKEN

to be publishedthis month …

37

Ideas for Measurements of Sivers Observables at RHIC

llpp

Xjetpp

Xpp

Xjetpp

Xflavorheavypp

Xjetjetpp

Xhpp

0

Precision measurement of AN at mid-rapidity.

Back-to-back correlations for jets.

AN for inclusive jets.

AN for heavy flavor.

AN for direct photons.

AN in jet-photon production.

AN in Drell Yan.

significant improve-ments from upgrades: forward calorimeters+ silicon vertex detectors

New Experiment: AnDY

38

AN from 0 and h+/- at Central Rapidity

PRL 95, 202001 (2005)

Anselmino et al, Phys. Rev. D 74 094011

Constrain gluon Sivers effect using PHENIX 2002 0 data !

Process Contribution to 0, η=0, s=200 GeV

39

AN from 0 Update

• pT range extended from 5 to 12 GeV/c

• Results consistent with previous PHENIX analysis• Statistical uncertainties reduced by more than

factor of 30

Impact of 2006 + 2008 Data Sets

u + d quarks Sivers w. no gluon or sea quark contribution.Low pT pi0 at mid-rapidity is not sensitive to valence quark Sivers function

Gluon Sivers parameterized to 1 sigma of data

Maximized Gluon Sivers functionViolates <kT> of partons = 0

Sea quark Sivers maximized + Gluon Sivers function

Naïve expected impact of new data.

0.02 < xSampled < 0.08

Theoretical analysis to be carried out.

41

AN in Di-Jet Production in STAR

zx

y

180º

proton spin

1S

Di-jet pT

Additional kT kick to jet axis from Sivers effect Boer & Vogelsang, PRD 69, 094025 (2004)

parton

kK

Gluon radiation

Di-jet pT

STAR: PRL-99:142003,2007

Di-jet AN consistent with 0

42

Summaryo Gluon Spin contribution constraint for 0.05 < x < 0.2 use di-jet and di-hadron measurements to probe x-dependence ΔG(x) and forward jet production to reach low x, x~0.001.

o W-program has started with electrons (STAR & PHENIX) and muons (PHENIX). Luminosity accumulation will take 3-4 runs.

o Precision data on AN are available. Exciting new Drell Yan experiment at IP2: AnDY (see Akio Ogawa’s talk). Initial measurements to isolate Collins -and Sivers- asymmetries. Much improvement from detector upgrades and increased statistics.

43

Backup

44

STAR Run 2006: pT Dependence of AN at √s=200 GeV PRL 101,222001

For given η strong correlation between xF and pT:

AN(pT)integratedover xF

AN(pT, xF)

AN increases with pT up topT ~ 3 GeV/c -- Models: AN ~ 1/pT

PHENIX: AN vs XF for 0’s at √s=62.4 GeV

AN = 0 for xF < 0 no sizeableasymmetries at small x!

Larger forward asymmetries at higher pseudo-rapidity, η ?

Limited by statistics and correlations between xF, pT and η !

Sivers Effect in Heavy Flavor Production

Heavy flavor production gives sensitivity to gluon Sivers effect . Significant improvement with vertex detector upgrades. Work needed to connect theory and experimental observable.

Anselmino et al, PRD 70, 074025 (2004)

Gluon Sivers=0

Gluon Sivers=Max

Calculations for D mesons

Measurement for -

47

A RHIC and US-Japan Contribution to Transverse SpinAnalysis: Measurement of the Collins Effect in e+e- Annihilation into Quarks at Belle BNL-Illinois-RBRC-RIKEN

q1

quark-1 spin

electron

positron

q2quark-2

spin

e++e- π+ + π- + X

~ Collins(z1) x Collins (z2)

Belle Collinsasymmetries & global fit

Collins FF extracted from Belle data.

Measurement of the Collinseffect in e+e- at Belle:

48

Collins Effect in Quark FragmentationJ.C. Collins, Nucl. Phys. B396, 161(1993)

q

momentum hadron relative : 2

z

momentum hadron e transvers:

momentum hadron :

spinquark :

momentumquark :

h

sE

EE

p

p

s

k

h

qh

h

h

q

qs

k

hph

,

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

hp

sin

qh spk

49

General Form of Fragmentation Functions

h

qhh

hqhqh

h

q zM

spkpzHzDpzD

ˆ ),()(),( 2,

1,

1

Number density for finding hadron h from a transversely polarized quark, q:

unpolarized FF Collins FF

IFF- a12 vs Invariant Mass8x8 m1 m2 binning

50

PreliminaryPreliminary

Preliminary

Preliminary

Preliminary Preliminary

Preliminary

PreliminarySystematic errors shown.a12 increases with m1 and m2

reaches |a12 | ~ 0.1 at large mi.

m1 [GeV/c2]

a12

51

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:

52

ANphoton+Jet : An Alternative Test of the

Process Dependence of the Sivers Effect at RHIC

Bachhetta, Bomhof, D’Alesio, Mulders, MurgiaPhys.Rev.Lett.99:212002,2007.

Weig

hte

d m

om

en

t of

AN

ph

oto

n+

Jet

no process dependence

Correct process dependence

Measurement: AN in jet-photon productionforward photon η > 2jet -1 < η < 0

Much less luminosity hungry …

NSAC milestone for transverse spin (HP-13, 2015) ! Reachable at STAR. Requires FOCAL upgrade in PHENIX.