review of g in dis and pp … a lot has happened since kyoto frank ellinghaus university of mainz /...
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![Page 1: 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,](https://reader035.vdocument.in/reader035/viewer/2022062515/56649d165503460f949ece77/html5/thumbnails/1.jpg)
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
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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
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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 ->
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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…
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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
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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”
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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
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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
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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
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Frank Ellinghaus, Spin’08, Charlottesville
Summary Direct DIS measurements
g/g=0 is likely small with unknown sign!
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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
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Frank Ellinghaus, Spin’08, Charlottesville
PHENIX and STAR
Large acceptanceAzimuthal symmetry
High rate capabilityLimited acceptance
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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.)
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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
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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)
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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 ->
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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
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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
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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
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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
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Frank Ellinghaus, Spin’08, Charlottesville
Charged hadrons at STAR A. Kocoloskitoday
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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
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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
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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
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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)