Spin Physics at RHIC Towards Precision QCD Physics, KEK, March 10, 2007 Naohito SAITO (KEK)
Why Spin? Fundamental Concept in Physics Appears in Many Different Levels Galaxy to Space-Time Structure Fundamental Quantum Number for Elementary Particles Important in Symmetry Test Parity Time Reversal
Proton Spin Crisis Anomaly SLAC：Pol’ electron scattering Consistent with QM CERN：Pol’ muon Discovery of Anomaly Q-Spin Cont: DS ~ 0 DESY：Pure Proton Confirm Anomaly SLAC＆CERN：Hi Precision Establish Anomaly DS ~ 0.1-0.3 >> ~
First Crisis? Proton has gone through many crisis Spin Mass : mu~5 MeV/c2, md~10 MeV/c2 Saved by constituent quark model Momentum : Saved by gluon momentum Spin Helicity SR: Theory guideline for separation (nf=3) (Ji, Tang, and Hoodboy)
Probing the Proton Structure EM interaction Photon Sensitive to electric charge2 Insensitive to color charge Strong interaction Gluon Sensitive to color charge Insensitive to flavor Weak interaction Weak Boson Sensitive to weak charge ~ flavor Insensitive to color
Spin Structure Studies: Exp’mt COMPASS Pol.m HERMES Pol.e± JLab Exp’s Pol.e- RHIC Spin Pol. pp BELLE e+e- Pol.m Beam: RICH-1 Pol.Target SM1 SM2 2-stage spectrometer LAS (Large angle) Kp SAS(Small angle) SAS LAS Ecal1 & Hcal1 m filter 1 m filter 2 Ecal2 & Hcal2 RICH-2
RHIC at BNL Two independent rings: 3.83 km Max Energy Luminosity NY City Two independent rings: 3.83 km 120 bunches/ring 106 ns bunch intvl Max Energy p-p 250 + 250 GeV Au-Au 100/N + 100/N GeV Luminosity p - p 2x1032 cm-2s-1 (Polarized) Au-Au 2x1026 cm-2s-1 RHIC
RHIC:First Polarized pp Collider
Gluon Polarization
Gluon is expected to be Polarized To compensate the Spin SR: (not necessarily) To recover QM expectation thru axial anomaly Through Q2 evolution: DS and Dg mix Dg~0.3 would be enough Dg~2 required Q2 evolution of the 1st Moment
History of Dg Hunting Hunting for Dg Direct Probe Indirect Probe FNAL E704 High-pT p0 High-mass Multi-g pair DESY HERMES High-pT hadron pair Indirect Probe NLO Analysis by SMC PRL 84(00)2584 PLB261(1991)197 PRD58(1998)112002 PLB336(1994)269
Status of Dg/g(x) from Lepton Scat. Or w/o RHIC Spin Photon-Gluon Fusion Process for 2-”jet” Open Charm New COMPASS results! Gluon Pol. Can be +, 0, - Courtesy Vogelsang and Stratmann
Constraints on Dg(x) w/ p0 Prod. pp p0 X is sensitive to gggg and gqgq
“Standard” value of DG from pre-RHIC DIS data Constraints on DG “Standard” value of DG from pre-RHIC DIS data Assuming DG = 0
AAC updates (S.Kumano, M. Hirai, NS, PRD (2006) Include J-Lab, HERMES, COMPASS new data Trial inclusion of PHENIX p0 ALL data K-factor method a la CTEQ Gluon Uncertainty significantly reduced!
Gluon Polarization Dg>0 preferred at large-x Dg=0.3±0.3 HERMES and COMPASS A1d data Higher-twist effects? Dg=0.3±0.3 Additional scale error of ~20% previously 0.5±1.3 If no p0 data 0.5±1.1 Additional scale error ~20%
Improved Constraints Newly obtained 1st moments (Q2=1 GeV2) Dg = 0.3±0.3 With additional scale error of ~20% DS = 0.27±0.07 Still need to improve precision Dg Lq and Lg, too! GPD Compare with Ji, Tang,Hoodboy Expectation
Extend x Range ALL(p0) from Run 6/7 (65 pb-1) will extend x range to larger x STAR jet measurement also provides precision data 500 GeV run will cover smaller x-range FWD rapidity coverage also useful for smaller-x region W. Vogelsang
Prompt Photon Production Gluon Compton Dominates 10% Contamination from Annihilation No fragmentation contribution in LO k2 P1 P2 k1 i ) ( 2 1 g q gq a x e A LL ® Ä D = å 1 0.001
Direct photon in Run-2006/7 W. Vogelsang k2 P1 P2 k1
Uncertain Unpolarized Glue Valence-Q well determined Sea is uncertain at large-x Gluon is unknown at large and small-x Need direct measurement Not only for Dg but also for LHC
Sea Polarization
Sea Constraints: SDIS and QCD fit QCD fit often assumes SU(3) symmetric sea Need to include SIDIS data Flavor separation by HERMES (talk by L. de Nardo) important progress! Still compatible with QCD fit Significant constraints observed by de Florian et. al. Small-x issue remains
W Production in pp Collisions W is produced through pure V-A Chirality is fixed ideal for spin structure studies W couples to weak charge ~ flavor Flavor is (almost) fixed ideal for flavor structure studies Parity Violating Asymmetry AL : J. Soffer et al.
Sea Constraints: RHIC W Prospects Clear flavor separation Weak charge ~ flavor Clear spin information Left handed current only Start in 2009! The 1st Commission starts tomorrow! Projected statistical precision
Transverse Spin Physics
Single Transverse Spin Asymmetries Fermilab E-704 reported Large Asymmetries AN Could be explained as Transversity x Spin-dep fragmentation (Collins effect), Intrinsic-kT imbalance (Sivers effect) , or Twist-3 (Qiu-Sterman, Koike) Or combination of above Left Right
BRAHMS Results on AN BRAHMS observed Large AN in charged pion production Similar Trend to E704, but deviation from ZERO starts earlier? Need to explore further!
More from BRAHMS p+ K+ K- p p- Pion Kaon Proton “+”>0 “-” <0 “-” >0 !! Proton “+” = 0 “-” > 0
RHIC Spin Roadmap submitted to DOE, Feb. 11, 2005 http://spin. riken Year P(%) Weeks (Com/Ph) Lumi CM Energy Goals 2002 15 8 (5/3) 0.5 pb-1 200 GeV Transverse Spin 2003 30 0.35 pb-1 Longitudinal Spin Gluon Polarization? 2004 40 5(5/0) 0.15 pb-1 RHIC Commissioning Pol. Gas Jet Target 2005 50 10 3.8 pb-1 410 GeV Gluon Pol/Transv. Commissioning 2006/7 70 13+10 ~120 pb-1 0.1 pb-1 62.4 GeV 500 GeV 2008/9 10+10 ~150 pb-1 ~180 pb-1 W-Physics/Transv.
Past and Future of RHIC Spin Luminosity Lost Future
Asymmetries calculated for RHIC RHIC Luminosity should be improved to realize these measurements…
Summary No final answer yet… but qualitatively new picture of spin structure is emerging! RHIC is still catching up Kodaira-san’s prediction We would like to contribute to precision QCD physics by providing experimetal results from RHIC, and J-PARC.