review of g in dis and pp … a lot has happened since kyoto frank ellinghaus university of mainz /...

Review of G in DIS and pp… a lot has happened since Kyoto

Frank Ellinghaus

University of Mainz / University of Colorado

October 2008

SPIN’08, Charlottesville, USA

Frank Ellinghaus, Spin’08, Charlottesville

e-p Spins antialigned

In the beginning….

– Electron polarization transfers to virtual photons– Compare DIS cross sections with aligned and antialigned ep spins

e-p Spins aligned~

g1 (proton) > 0-> Larger cross section for anti-aligned ep Spins -> Higher probability for aligned quark-proton Spins

212( , )B

B

dg x Q

dx dQ

• Polarize electrons and nucleons (started in mid 1970s at SLAC)

G. Baum et al, PRL 51, 1983

Frank Ellinghaus, Spin’08, Charlottesville

Results from Inclusive Polarized DIS

• Analogous to unpolarized (F2) case, g1 can be used to fit polarized PDFs:

Polarized PDFs extracted from fits to g1(proton, deuteron)

• Result: Quarks carry only 30% of the nucleon spin (0.3)

HERMES: PRD 75:012007 (2007)

COMPASS: PLB 647:8 (2007)

• Gluon contribution G not well constrained due to small range in xB,Q2 (no polarized ep collider)

( ), ( ), ( )B B Bq x q x G x

…try DIRECT measurements ->

Frank Ellinghaus, Spin’08, Charlottesville

G via direct measurement in DIS

||

1 1~ ( ) ...PGF PGF BG BGG

A

f a fGf A A

Photon-Gluon Fusion: * g -> qqbar

• ccbar production, detect D-mesons, hard scale provided by charm mass, clean channel (low BG), statistically limited

• detect hadrons (or hadron pairs) with Q2>1 GeV2(hard scattering) More BG sources with difficult to determine or/and model-dependent fractions and asymmetries. Larger sample…

• detect hadrons (or hadron pairs) using all Q2

Even more BG sources with difficult to determine or/and model-dependent fractions and asymmetries. Largest sample…

Frank Ellinghaus, Spin’08, Charlottesville

Fixed Target DISBeam: 27.6 GeV e+/e-; Beam: 27.6 GeV e+/e-; 50-55% polarization50-55% polarization

Target: H, D Target: H, D 80-85% polarization80-85% polarization

6/30/07

Beam: 160 GeV Beam: 160 GeV ; ; 75-80% polarization75-80% polarization

Target: Target: 66LiD; LiD; 50% polarization50% polarization

Frank Ellinghaus, Spin’08, Charlottesville

The “golden” channel

D*->D0 soft

2002-2004 analysis: hep-ex/0802.2160

F. KunneTuesday

2002-2006 preliminary analysis:

“tagged D0”

Frank Ellinghaus, Spin’08, Charlottesville

COMPASS: Hadron Pairs, Q2 > 1 (GeV/c)2

LEPTO with JETSET tuned to data…

• pT>0.7 GeV/c for both hadrons increases PGF contr.• Q2 > 1 (GeV/c)2 provides hard scale• At least two add. subprocesses to be considered

500k events

K. KurekTuesday

Frank Ellinghaus, Spin’08, Charlottesville

COMPASS: Hadron Pairs, Q2 < 1 (GeV/c)2

0.080.040.095gx

PYTHIA

Add. Sensitivity to G, but polarized PDFs of photon unmeasured

• pT>0.7 GeV/c for both hadrons increases PGF contr.• pT

2 > 2.5 (GeV/c)2 provides hard scale

• Add. contr. (about 50%) from resolved-photon processes

PGF

QCDC

LO

PLB 633 (2005) 25

preliminary2 23( / )GeV c

Frank Ellinghaus, Spin’08, Charlottesville

HERMES, hadrons, all Q2

PYTHIA (tuned to data)

2 0.1250.082/ ( , ) 0.078 0.034 0.011g g x

20.204 1.35 2 GeVx

Results from different (proton, deuterium) data samples and different event topologies are consistent.

Good sensitivity, but model dependentg/g=0 -> contribution of quarks

Frank Ellinghaus, Spin’08, Charlottesville

Summary Direct DIS measurements

g/g=0 is likely small with unknown sign!

Frank Ellinghaus, Spin’08, Charlottesville

RHIC @ BNL

STARSTAR

Relativistic Heavy Ion Collider also provides longitudinally and transverselypolarized proton beams at s = 200 GeV, 62.4 GeV, (500 GeV, 2009+)

Polarimeter (H jet) pC Polarimeters

Spin Rotators Siberian Snakes

Frank Ellinghaus, Spin’08, Charlottesville

PHENIX and STAR

Large acceptanceAzimuthal symmetry

High rate capabilityLimited acceptance

Frank Ellinghaus, Spin’08, Charlottesville

PHENIX longitudinally polarized pp Runs

Year s [GeV] Recorded L Pol [%] FOM (P4L)

2003 (Run-3) 200 .35 pb-1 27 1.5 nb-1

2004 (Run-4) 200 .12 pb-1 40 3.3 nb-1

2005 (Run-5) 200 3.4 pb-1 49 200 nb-1

2006 (Run-6) 200 7.5 pb-1 57 690 nb-1

2006 (Run-6) 62.4 .10 pb-1 48 5.3 nb-1

(Similar numbers for STAR. Experiments can separately choose longitudinal or transverse polarization.)

Frank Ellinghaus, Spin’08, Charlottesville

G via direct measurement in pp

2 2~LL gg qg qqA a a q G aG q

Access to polarized gluon distribution function via double helicity asymmetry in inclusive polarized pp scattering, e.g.,

Invariant mass spectrum of 2 photons in EMCal(M=135MeV)

Measure from DISpQCD, fragmentation fcts.

0p p X

NRN

NRN

PPA

YBLL

1

L

LR Relative Luminosity R using

beam-beam counters

Frank Ellinghaus, Spin’08, Charlottesville

First: Check unpolarized case!

Using a set of unpolarized PDFs ( + fragmentation functions in case of hadron (0) production) the cross section agrees with NLO pQCD calculations.

PHENIX -- 0

PRD76:051106,2007

STAR -- jets

PRL 97, 252001 (2006)

Frank Ellinghaus, Spin’08, Charlottesville

STAR -- jetsRun 6 preliminary

Run 5 (2005): PRL 100, 23 (2008)

• G = G(x), -G(x) excluded;• GRSV-std excluded with 99% CL

Run 6 preliminary

M. SarsourFriday

• No inconsistency with DIS data due to generally large uncertainties on Dg(x).• Small or negative gluon contribution to nucleon spin favored in this model.• Data also consistent with GS-C ->

Frank Ellinghaus, Spin’08, Charlottesville

Model dependence of G

g integral between

GRSV

- 0

GRSV

- std

GS-C

0<x<1 0 0.4 1

0.02<x<0.3 0 0.25 0

• Measurement averages over certain x range• Shape of G(x) cannot be extracted -> Value for first moment model dependent

Frank Ellinghaus, Spin’08, Charlottesville

PHENIX --0 at 200 GeV

Run 5: Phys.Rev.D76:051106,2007Run 6: arXiv:0810.0694

GRSV: Glueck et al., PRD 63 (2001)

G = G(x), -G(x) excluded; GRSV-std slightly disfavored

K. NakanoTuesday

Run 5 + Run 6

Frank Ellinghaus, Spin’08, Charlottesville

STAR – 0, PHENIX – PHENIX J/Psi

PHENIX excludes G= G(x), -G(x)

J. Seeletoday

STAR 0 consistent with PHENIX

X. WangFriday

A. Hoffman

today

Frank Ellinghaus, Spin’08, Charlottesville

+, –, 0 and the sign of G

0

0 LL LL LLG A A A

0

d d dD D D

0

0 LL LL LLG A A A

Especially in the region where qg scattering is dominant (pT > 5 GeV),the increasing contribution of d quarks (d<0) leads to:

“Model independent” conclusion possible once enough data is available.

Fraction of pion production

s=62.4 GeV

PHENIX Preliminary

A. Dattatoday

A. MorrealeTuesday

Frank Ellinghaus, Spin’08, Charlottesville

Charged hadrons at STAR A. Kocoloskitoday

Frank Ellinghaus, Spin’08, Charlottesville

Direct Photons at s=200 GeV

Run-5

At the end of the day all these (and the DIS, SIDIS) asymmetry data need to go into a “global” QCD fit in order to extract G! ->

q

g q-> small unc. from FFs-> better access to sign of G (q times G)

Theoretically clean “Golden Channel” is luminosity hungry…

Dominated by qg Compton:

R. Bennetttoday

Frank Ellinghaus, Spin’08, Charlottesville

First pol. PDF extraction using pp data

DSSV, arXiv: 0804.0422First “global” (DIS+SIDIS+pp) analysis!

G small in measured range (0.05 < x< 0.2).Contribution at small or large x?

Different ranges in x can be probed in:• 500 GeV (2009+, lower x) and 62 GeV running (larger x, larger scale unc.) ->• different rapidities ->

• Strong impact of Star jets and Phenix 0 in measured range. • Shape of G(x) cannot be extracted -> All “missing” spin can be at low x…. • Next step: Mapping of x-dependence via di-jets, di-hadrons and gamma-jet

M. StrattmannTuesday

Frank Ellinghaus, Spin’08, Charlottesville

• At fixed xT = 2pT/sqrt(s) cross-section is 2 orders of magnitude higher at 62.4GeV than at 200GeV

• Significant result at high xT from small data set at 62.4 GeV (0.04 pb-1) when compared to 200 GeV data (1.8pb-1)

• pQCD applicable for pT > 2 GeV/c…

Accessing different x-rangesPHENIX: 0 ALL at s=62.4 GeV

Increased sensitivity to larger x

K. NakanoTuesday

STAR: 0 ALL at forward rapidity

Increased sensitivity to smaller x

• Also: step towards gamma-jet correlation measurements to map out the x-dependence• STAR Di-Jet measurements promising

T. SakumaFriday

S. WissinkFriday

arXiv: 0810.0701

Frank Ellinghaus, Spin’08, Charlottesville

Summary & Outlook• PHENIX and STAR data provided a significant constraint on the

polarized gluon PDF in a global QCD fit to “all” DIS, SIDIS and pp data

-> G(x) small in measured range (0.05 < x < 0.2)• Direct measurements by HERMES+COMPASS support this finding with

somewhat larger uncertainties.• No sensitivity to shape of G(x)

-> all the “missing” spin can still be at smaller x.

• HERMES: – final word (long paper) soon

• COMPASS: – Open Charm: Add 2007 data (small improvement)

– High-pT hadrons, Q2>1 (GeV/c)2: Add 2006+2007 data (significant improvement)

• PHENIX+STAR: – Different beam energies (500 GeV, 2009+) and rapidities will give access to an

order of magnitude smaller x

– Correlation measurements will provide sensitivity to shape of G(x)