1. Quark- and Gluon-Spin Structure of the Proton from High Energy Polarized Proton-Proton Collisions at RHIC
M. Grosse Perdekamp
University of Illinois, Urbana Champaign
STAR
Seminar Saclay, March 16th, 2012  

2. Quark and Gluon Spin Structure of the Proton
Overview
Scientific Motivation
Studying Nucleon spin structure
in polarized proton-proton collisions at RHIC
Gluon Spin
Experimental results from RHIC
Global analysis
Future Steps
W-production?
First results with W → e  at mid-rapidity
Status of Measurements W → μ  at forward rapidity
With input and slides from
Alexander Bazilevsky!
March 16th
Quark and Gluon Spin Structure of the Proton

3. Quark and Gluon Spin Structure of the Proton
Motivation: The Nucleon as QCD Laboratory
The proton is the fundamental bound
state of QCD; Quarks and gluons are
the Consituents:
Can we understand the wave
function of the nucleon from
first principles QCD ?
Present (modest) status:
Description of proton in hard
scattering processes with parton
distribution functions.
March 16th
Quark and Gluon Spin Structure of the Proton

4. Quark and Gluon Spin Structure of the Proton
Motivation: Proton Spin Structure
Constituents:
quarks = u, d, s and gluons
March 16th
Quark and Gluon Spin Structure of the Proton

5. Quark and Gluon Spin Structure of the Proton
Motivation: Spin Sum Rule
De-composition of the Proton Spin
Orbital Angular
momentum
Quark Spin
Gluon Spin
March 16th
Quark and Gluon Spin Structure of the Proton

6. Quark and Gluon Spin Structure of the Proton
Proton Spin Structure from Inclusive Deep Inelastic Lepton-Nucleon Scattering
spin
Large Q2: measure photon-quark
absorption cross section double
spin asymmetry
spin
electron or
muon probe
proton target
Extract spin dependent quark
distribution functions from the
spin structure function g1(x,Q2)
March 16th
Quark and Gluon Spin Structure of the Proton

7. The Importance of Low x : Example Quark Spin  ΔΣ
Quark Spin Contribution to the Proton Spin.
Measurements at SLAC: < xSLAC <0.7
vs CERN: < xCERN <0.5
A1(x)
0.1 < xSLAC < 0.7
Note:
evaluation of ΔG=∫01G(x)dx
may require large x coverage
in particular towards low x
QPM expectation !
E130, Phys.Rev.Lett.51:1135,1983: >400 citations.
Spin Crisis !
EMC, Phys.Lett.B206:364,1988: >1400 citations in SPIRES
EMC, Nucl.Phys.B328:1,1989, >1200 citations in SPIRES
0.01 < xCERN < 0.5
x-Bjorken
March 16th
Quark and Gluon Spin Structure of the Proton

8. Quark and Gluon Spin Structure of the Proton
Quark Spin Contribution from Analysis of Spin Dependent Lepton-Nucleon Scattering
COMPASS Phys.Lett. B693 (2010)
Proton
Neutron
Fraction of proton spin
carried by quarks:
ΔƩ = 0.33 ± 0.025(exp) ± (th)
Deuteron
Limitation: lepton probes couple to electric charge,
sensitivity to gluons from scaling violations
March 16th
Quark and Gluon Spin Structure of the Proton

9. Nucleon Spin Structure: 30 Years of Experiment
Quark Spin – Gluon Spin – Transverse Spin – GPDs – Lz
SLAC E80-E155
CERN EMC,SMC COMPASS
FNAL E704
DESY HERMES
JLAB Halls A, B, C
RHIC BRAHMS, PHENIX, STAR
2000
ongoing
1995
2007
ongoing
ongoing
experimental innovations
polarized pp
high current polarized proton sources,
high energy proton polarimeters, polarized collider
March 16th
Quark and Gluon Spin Structure of the Proton

10. A novel experimental method: Probing Proton Spin
Structure in High Energy Polarized Proton Collisions
Instrumentation
High current polarized proton source
High energy proton polarimetry
Control of spin coherence during acceleration + storage
Spin sorted luminosity measurements
Physics
Probes directly sensitive to color charge
Utilize Parity violation in W-production
Large Q2  clean pQCD interpretation
Absolute Polarimeter (H jet)
RHIC pC Polarimeters
Siberian Snakes
BRAHMS & PP2PP
PHOBOS
RHIC Spin Instrumentation
Development
Siberian Snakes
PHENIX
Spin Flipper
STAR
Spin Rotators
Helical Partial
Snake
Partial Snake
Polarized Source
Strong Snake
LINAC
AGS
BOOSTER
200 MeV Polarimeter
Rf Dipole
AGS pC Polarimeter
March 16th
Quark and Gluon Spin Structure of the Proton

11. Quark and Gluon Spin Structure of the Proton
RHIC SPIN: Proton Structure with
Quark and Gluon Probes
At ultra-relativistic energies the
proton (roughly) represents a
jet of quarks and gluons
Example: Production of neutral pions
~ probe gluon content with
with quark probes!
experimental double
spin asymmetry R
Jet,π0
quark
gluon
gluon
quark
Jet,π0
DIS
QCD ?
March 16th
Quark and Gluon Spin Structure of the Proton

12. G Measurements at RHIC
Polarized Gluon Distribution Measurements :
Use a variety of probes with variety of kinematics
Access to different gluon momentum fraction x
Different systematics
Use different beam energies
March 16th
Quark and Gluon Spin Structure of the Proton

13. Unpolarized Cross Sections and pQCD Calculations in pp at √s = 200 GeV
PHENIX pp 0 X
PRD76,
STAR: ppjet X
PRL 97,
PHENIX pp X
PRL 98,
||<0.35
||<0.35
Good agreement between NLO pQCD calculations and data  pQCD can be used to extract spin dependent pdf’s from RHIC data.
March 16th
Quark and Gluon Spin Structure of the Proton

14. Probing G in Polarized pp Collisions
pp  hX
Double longitudinal spin asymmetry ALL is sensitive to G
March 16th
Quark and Gluon Spin Structure of the Proton

15. Double Spin Asymmetries ALL for Inclusive Jets Observed with STAR10 20
Process Fraction
STAR Preliminary Run6 , s=200 GeV
pT [GeV]
Good discriminative power between calculations with different assumption for G
March 16th
Quark and Gluon Spin Structure of the Proton

16. ALL for Inclusive 0 with PHENIX
Process Fraction
PHENIX Run5+6 √s = 200 GeV:
PRL103, 5 10
pT(GeV)
0 pT wBG
2 GeV/c 20% % %
March 16th
Quark and Gluon Spin Structure of the Proton 16

17. Quark and Gluon Spin Structure of the Proton
From ALL(pT) to G
Compare ALL(pT) data with calculated
ALL(pT) for a variety of
PRL103, (2009)
2(G)
From pQCD:
pT = 212 GeV/c 
xgluon = 0.02  0.3
March 16th
Quark and Gluon Spin Structure of the Proton

18. G: Global QCD Based Fit
DSSV:
Daniel de Florian
Rodolfo Sassot
Marco Stratmann
Werner Vogelsang
G: Global QCD Based Fit
Phys. Rev. Lett. 101, (2008)
First truly global analysis of all available polarized data including RHIC results
RHIC
data
Uncertainty estimation:
2=1
2/2=2%
A node?
March 16th
Quark and Gluon Spin Structure of the Proton

19. Run9 0 ALL : PHENIX Preliminary
Dataset
<PB> (%)
<PY> (%)
Lanalyzed (pb-1)
FOM (P4L)
Run5 50 49
2.5
0.15
Run6 56 57
6.5
0.66
Run9 14
1.5
Run5
Run6
Run9
Tendency to positive ALL?
March 16th
Quark and Gluon Spin Structure of the Proton

20. Global Fit Including PHENIX Run9 0 ALL
By S.Taneja et al (DIS2011) based on code from DSSV
xG(x)
xG(x)
DSSV
DSSV + PHENIX Run9 0 ALL
No node
Uncertainties decreased
node at x~0.1
March 16th
Quark and Gluon Spin Structure of the Proton

21. Run9 0 ALL : STAR Preliminary
3-4 smaller stat. uncertainties than in Run6:
Trigger upgrade
DAQ upgrade (increased rate, lower ET threshold)
Run9 data will have considerable impact
on G global fit and its uncertainty
March 16th
Quark and Gluon Spin Structure of the Proton

22. Quark and Gluon Spin Structure of the Proton
 Analysis similar to 0
Different flavor structure
Independent probe of G
PRD83,032001(2011)
PHENIX
Other probes of ΔG   ±
Preferred fragmentation
u+ and d -
u>0 and d<0
 different qg contri-butions for +, 0, -
 sensitivity to sign of G
March 16th
Quark and Gluon Spin Structure of the Proton

23. Quark and Gluon Spin Structure of the Proton
Other probes of ΔG
Direct Photon
Quark gluon scattering dominates
Direct sensitivity to size and sign of G
Need more P4L
~80%
Heavy Flavor
Production dominated by gluon gluon fusion
Measured via e+e-, +-, e, eX, X
Need more P4L
March 16th
Quark and Gluon Spin Structure of the Proton

24. Extend x-range  different s
2-2.5 GeV/c
4-5 GeV/c
9-12 GeV/c
0 at ||<0.35: xg distribution vs pT bin
s=500 GeV
s=62 GeV
s=200 GeV 
March 16th
Quark and Gluon Spin Structure of the Proton

25. 0 at s=62 and 500 GeV Unpolarized Cross Sections
s=62 GeV: PHENIX, PRD79,
s=500 GeV: PHENIX Preliminary
May need inclusion of NLL to NLO
Data below NLO at =pT by (3015)%
March 16th
Quark and Gluon Spin Structure of the Proton

26. Quark and Gluon Spin Structure of the Proton
PHENIX ALL for π0 s=62 GeV
PHENIX, PRD79,
Very limited data sample (0.04 pb-1, compared 2.5 pb-1 from Run2005 s=200 GeV)
Clear statistical improvement at larger x; extends the range to higher x (0.06<x< 0.4)
Overlap with 200 GeV ALL provides measurements at the same x but different scale (pT)
s=500 ALL results will be available soon (from Run2009 with L~10 pb-1 and P~0.4)
March 16th
Quark and Gluon Spin Structure of the Proton

27. Quark and Gluon Spin Structure of the Proton
G: Path Forward
Limitations in current data:
Limited x-range covered
Weak sensitivity to the shape of G(x)
Improve precision of current measurements
Get more data
Extend xg-range
Move to forward rapidities
Constrain kinematics: map G vs xg
More exclusive channels: pp   + jet and pp  jet + jet
March 16th
Quark and Gluon Spin Structure of the Proton

28. Impact of Additional Data for Jets and π0
PHENIX pp 0 X : projections
STAR pp jet X : projections
March 16th
Quark and Gluon Spin Structure of the Proton

29. Probing Low x Through Forward Di-Hadrons
PHENIX central spectrometer magnet
merged p0s
mid-fwd xgluon ~ 10-2
mid-fwd xgluon ~ 10-2
fwd-fwd xgluon ~ ϕ
Muon Piston Calorimeter (MPC)
trigger EM-cluster
3.1<η<3.9 p p
asssociated
p0 or EM-clusters
3.1 < η < 3.9
MPC
PbWO4
asssociated p < η < 3.9 p0
trigger
p0 or h+/-
|η|<0.35
Backward direction (South) 
Forward direction (North) 
Side View

30. PHENIX Muon Piston Calorimeter
Technology  ALICE(PHOS)
PbWO4
avalanche photo diode readout
Acceptance:
3.1 < η < 3.9, 0 < φ < 2π
-3.7 < η < -3.1, 0 < φ < 2π
Both detectors were installed for 2008 d-Au run.
Assembly at UIUC
PbWO4 + APD + Preamp
MPC integrated in the
piston of the muon
spectrometer magnet. 30

31. Forward Calorimetry: PHENIX MPC
Muon Piston Calorimeter (MPC): PbWO4
3.1 < || < 3.9, 2 azimuth
Gives access to lower: x10-3
Fully available from 2008
MPC 0 500 GeV
300 pb-1 P=0.55
STAR: 0 forward rapidity
PRL 97,
pQCD seems
working even
at forward rapidities
March 16th
Quark and Gluon Spin Structure of the Proton

32. Quark and Gluon Spin Structure of the Proton
STAR: di-Jet ALL
Run9 data
Projections for s=500 GeV
Constrains kinematics
 shape of G(x)
March 16th
Quark and Gluon Spin Structure of the Proton

33. PHENIX Silicon Vertex trackers VTX (2011) & FVTX (2012)
VTX barrel |h|<1.2 q g
jet
EMC and MPC: pT and photon
VTX: jet g Q
Q = c or b
Rejects hadronic background
c/b separated measurements
FVTX endcaps
1.2<|h|<2.7
mini strips
Luminosity and polarization hungry
March 16th
Quark and Gluon Spin Structure of the Proton

34. Flavor Separation of Quark- Anti-Quark Polarizations
DSSV: PRL 101, (2008)
Presently from
SIDIS:
Fragmentation functions to tag (anti)quark flavor
l +
p+p  W  e  /  + 
Parity violating W production:
Fixes quark helicity and flavor
No fragmentation involved
High Q2 (set by W mass)
March 16th
Quark and Gluon Spin Structure of the Proton

35. W-Production: Sensitivty of AL vs l
STAR
Central (barrel) region (We , ||<1)
First data from 2009: PRL106, (2011)
Forward (endcap) region (We , 1<||<2) :
Forward tracker upgrade, first data in 2012
PHENIX
Central Arms (We , ||<0.35)
First data from 2009: PRL106, (2011)
Forward Arms (W , 1.2<||<2.4) :
Trigger upgraded, first data from 2011
March 16th
Quark and Gluon Spin Structure of the Proton

36. Central region: W  e from Run9
Triggered by energy in EMCal
Momentum from energy in EMCal
Charge from tracking in B field
STAR: |e|<1
PHENIX: |e|<0.35 e- e+
L=12 pb-1
L=8.6 pb-1 e+ e-
March 165h
Quark and Gluon Spin Structure of the Proton

37. Central region: W  e from Run9
Cross section
P=0.39 L=8.6/12 pb-1 in PHENIX/STAR
PHENIX: PRL106, (2011)
STAR: PRL106, (2011)
STAR AL
PHENIX AL e- e+ e- e+
March 16th
Quark and Gluon Spin Structure of the Proton

38. Quark and Gluon Spin Structure of the Proton
Muon Trigger Upgrade for W-Physics
muTr trigger
electronics(JSPS)
Muon Trigger fully installed
for run 2012
RHIC 2012 Luminosity at 200 GeV
FPGA based
level-1 trigger
processors
RPCs in Urbana (NSF)
RPCs in PHENIX (NSF)
Run at √s = 510 GeV starts
next week!
March 165h
Quark and Gluon Spin Structure of the Proton

39. Quark and Gluon Spin Structure of the Proton
Last Component of the RPC based Muon Trigger:
Upstream Stations RPC-1 north & south installed
in October and November 2011
PHENIX RPC-1 north (~ 3m)
PHENIX RPC-3 north (diameter ~ 10 m)
March 165h
Quark and Gluon Spin Structure of the Proton

40. PHENIX Forward Arm: W  
First data collected in 2011:
L~15 pb-1 P~0.52
PHENIX Forward Arm: W  
Raw yields with different triggers and cuts
 trigger eff.
 trigger rejection
Expected W yield
More challenging than We at ~0
PHENIX 2kHz Bandwidth
March 165h
Quark and Gluon Spin Structure of the Proton

41. W  l : Projections for Quark Polarizations
PHENIX: We
STAR: We
PHENIX: W
March 16h
Quark and Gluon Spin Structure of the Proton

42. Quark and Gluon Spin Structure of the Proton
Summary
RHIC is the world’s first and only facility which provides collisions of high energy polarized protons
Allows to directly use strongly interacting probes (parton collisions)
High s  NLO pQCD is applicable
PHENIX&STAR continues producing results for different spin observables
Significant constraint on G for xg~ from inclusive 0 and jet ALL at s=200 GeV
Other ALL measurements to be included in G global fit with different systematics and x-coverage
First AL results from W  e in central rapidity at s=500 GeV from run
First AL results from W   in forward rapidity at s=500 GeV from runc oming soon
March 16th
Quark and Gluon Spin Structure of the Proton

43. Quark and Gluon Spin Structure of the Proton
Backup
March 16th
Quark and Gluon Spin Structure of the Proton

44. Transition form Soft to Hard
PRD76, (2007)
Exponent (e-pT) describes our pion cross section data perfectly well at pT<1 GeV/c (dominated by soft physics):
=5.560.02 (GeV/c)-1
2/NDF=6.2/3
Assume that exponent describes soft physics contribution also at higher pTs  soft physics contribution at pT>2 GeV/c is <10%
exponential
fit
pT>2 GeV/c – hard scale?
March 16th
Quark and Gluon Spin Structure of the Proton

45. Quark and Gluon Spin Structure of the Proton
From pT to xgluon
10-3
10-2
10-1 x
NLO pQCD: 0 pT=212 GeV/c  xgluon=0.020.3
GRSV model: G(xgluon=0.020.3) ~ 0.6G(xgluon =01 )
Each pT bin corresponds to a wide range in xgluon, heavily overlapping with other pT bins
These data is not much sensitive to variation of G(xgluon) within our x range
Any quantitative analysis should assume some G(xgluon) shape
March 16th
Quark and Gluon Spin Structure of the Proton

46. From ALL to G (with GRSV)
Generate g(x) curves for different (with DIS refit)
Calculate ALL for each G
Compare ALL data to curves (produce 2 vs G)
March 16th
Quark and Gluon Spin Structure of the Proton

47. G: theoretical uncertainties
Parameterization (g(x) shape) choice
Vary g’(x) =g(x) for best fit, and generate many ALL
Get 2 profile
At 2=9 (~3), consistent constraint:
-0.7 < G[0.02,0.3] < 0.5
 Our data are primarily sensitive to the size of G[0.02,0.3].
Theoretical Scale Dependence:
Vary theoretical scale :
=2pT, pT, pT/2
 0.1 shift for positive constraint
 Larger shift for negative constraint
March 16th
Quark and Gluon Spin Structure of the Proton

48. Quark and Gluon Spin Structure of the Proton
MPC: 0 cross section
March 16th
Quark and Gluon Spin Structure of the Proton

49. Quark and Gluon Spin Structure of the Proton
W cross section
March 16th
Quark and Gluon Spin Structure of the Proton

50. Quark and Gluon Spin Structure of the Proton
sPHENIX
March 16th
Quark and Gluon Spin Structure of the Proton