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  

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

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

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

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

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

The Importance of Low x : Example Quark Spin  ΔΣ Quark Spin Contribution to the Proton Spin. Measurements at SLAC: 0.10 < xSLAC <0.7 vs CERN: 0.01 < 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

Quark and Gluon Spin Structure of the Proton Quark Spin Contribution from Analysis of Spin Dependent Lepton-Nucleon Scattering COMPASS Phys.Lett. B693 (2010) 227-235 Proton Neutron Fraction of proton spin carried by quarks: ΔƩ = 0.33 ± 0.025(exp) ± 0.030 (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

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

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 1995-2005 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

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

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

Unpolarized Cross Sections and pQCD Calculations in pp at √s = 200 GeV PHENIX pp 0 X PRD76, 051106 STAR: ppjet X PRL 97, 252001 PHENIX pp X PRL 98, 012002 ||<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

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

Double Spin Asymmetries ALL for Inclusive Jets Observed with STAR 10 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

ALL for Inclusive 0 with PHENIX Process Fraction PHENIX Run5+6 √s = 200 GeV: PRL103, 012003 5 10 pT(GeV) 0 pT wBG 2 GeV/c 20% 5 8% 10 5% March 16th Quark and Gluon Spin Structure of the Proton 16

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, 012003 (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

G: Global QCD Based Fit DSSV: Daniel de Florian Rodolfo Sassot Marco Stratmann Werner Vogelsang G: Global QCD Based Fit Phys. Rev. Lett. 101, 072001(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

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

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

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

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

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

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

0 at s=62 and 500 GeV Unpolarized Cross Sections s=62 GeV: PHENIX, PRD79, 012003 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

Quark and Gluon Spin Structure of the Proton PHENIX ALL for π0 s=62 GeV PHENIX, PRD79, 012003 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

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

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

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 ~ 10-4-10-3 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 p0 3.1 < η < 3.9 p0 trigger p0 or h+/- |η|<0.35 Backward direction (South)  Forward direction (North)  Side View

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

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, 152302 pQCD seems working even at forward rapidities March 16th Quark and Gluon Spin Structure of the Proton

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

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

Flavor Separation of Quark- Anti-Quark Polarizations DSSV: PRL 101, 072001 (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

W-Production: Sensitivty of AL vs l STAR Central (barrel) region (We , ||<1) First data from 2009: PRL106, 062002 (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, 062001 (2011) Forward Arms (W , 1.2<||<2.4) : Trigger upgraded, first data from 2011 March 16th Quark and Gluon Spin Structure of the Proton

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

Central region: W  e from Run9 Cross section P=0.39 L=8.6/12 pb-1 in PHENIX/STAR PHENIX: PRL106, 062001 (2011) STAR: PRL106, 062002 (2011) STAR AL PHENIX AL e- e+ e- e+ March 16th Quark and Gluon Spin Structure of the Proton

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

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

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

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

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~0.02-0.03 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 2009 run First AL results from W   in forward rapidity at s=500 GeV from 2011 runc oming soon March 16th Quark and Gluon Spin Structure of the Proton

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

Transition form Soft to Hard PRD76, 051106 (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

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

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

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

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

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

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