Spin Physics with High Energy Polarized pp Collisions Junji Tojo RIKEN Spin and Quantum Structure in Hadrons, Nuclei and Atoms (SQS04) Tokyo Institute of Technology February 20 th , 2004
Physics with Polarized pp Collisions • Spin structure of the proton – Understanding the proton spin 1/2 on the basis of quarks and gluons – Determination of polarized parton distribution functions with hard scattering processes • Spin effects in the fundamental reactions – Search for new phenomena caused by unexpected mechanisms • Physics beyond the standard model – Polarized partons as a tool to search for new physics Junji Tojo (RIKEN)
Spin Structure of the Proton • Understanding the proton spin 1/2 on the basis of quarks and gluons • Proton spin sum rule ∆Σ : quark polarizaion 1 1 ∆ = ∆Σ + ∆ + g :gluon polarization g L z 2 2 L :orbitalangular momentum z • Polarized DIS experiments at SLAC/CERN/DESY from ∆Σ − 0.1 0.2 1970’s showed • Looking for missing contributors to the proton spin ∆ ∆ ∆ – Measuring with polarized pp collisions at RHIC g , q , q Junji Tojo (RIKEN)
Tool : Hard Scattering Processes • Emitting Partons : f(x) • Hard interaction of partons : σ • Parton fragments into hadron : D(z) • Universality of f(x), σ , D(z) σ σ 3 ˆ d d = ∑∫ E f x ( ) f ( x ) D z dP ( ) i 1 j 2 3 dp dt i j , Junji Tojo (RIKEN)
Asymmetries • A LL : Double longitudinal spin asymmetry – Useful in extracting quark/gluon helicity distributions σ ++ − σ +− ( ) ( ) = A σ ++ + σ +− LL ( ) ( ) A N : Twist-3 or T A L : Parity Violation A TT : Transversity Junji Tojo (RIKEN)
Wide Variety of Reactions Available in pp Collisions Our Bible : “Prospects for Spin Physics at RHIC” G. Bunce, N. Saito, J. Soffer and W. Vogelsang Ann. Rev. of Nucl. And Part. Science 2000, 50 : 525 Junji Tojo (RIKEN)
Prompt photon production The Golden Channel for ∆ g Determination • Gluon Compton Dominates – At LO LO no fragmentation function – Small contamination from annihilation ∑ ∆ 2 e f (x ) ∆ i i 2 g( x ) = = ⊗ ⊗ → γ i u,d,s 1 ˆ A a (gq q ) ∑ LL LL 2 g(x ) e f ( x ) 1 i i 2 = i u,d,s A 1 Junji Tojo (RIKEN)
∆g Measurement by Prompt Photon ( ) ∆ G x GS95 prompt photon x Junji Tojo (RIKEN)
W Production in Polarized 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 ∆ −∆ u x d x ( ) ( ) d x u x ( ) ( ) + = W a b a b A + L u x d x ( ) ( ) d x u x ( ) ( ) a b a b Junji Tojo (RIKEN)
Physics beyond the Standard Model One of Expectations • Anomalous Parity Violation in Jet Production – Contact Interaction (Scale L) • CDF L>1.8 TeV • D0 L>2.4 TeV • RHIC Spin Reach L~3.3 TeV – New Gauge Boson Z’ Junji Tojo (RIKEN)
Relativistic Heavy Ion Collider at Brookhaven National Laboratory Junji Tojo (RIKEN)
RHIC Spin Collider Complex Junji Tojo (RIKEN)
MuID RICH PCs The PHENIX Detector MVD MuTr Junji Tojo (RIKEN) ZDC DC TEC/TRD BBC TOF EMCAL
The STAR Detector Junji Tojo (RIKEN)
RHIC Spin Run Since 2000 • Run1 : Sep. 2000 – The first polarized proton beam acceleration in one RHIC ring – One Siberian Snake, One p C CNI polarimeter • Run2 : Dec. 2001 - Jan. 2002 – The first spin run with transverse polarization – 4 Siberian Snakes, Two p C CNI polarimeters ∫ = = = -1 – s 200GeV, P 0.15, dt L 0.15pb (PHENIX) B • Run3 : Apr. – May 2003 – The first spin run with longitudinal polarization – 4 Spin rotators, AGS p C CNI polarimeter ∫ = = = – -1 200GeV, 0.25, 0.35pb (PHENIX) s P dt L B • Run4 : Apr. 2004, very soon ! – Commissioning for high P B and L – AGS warm snake, Absolute polarimeter, Spin flipper Junji Tojo (RIKEN)
Run2 and Run3 Results Highlight
A N in Forward Neutron Production (Run2) • Exp. for PHENIX Local Polarimeter at 12 O’clock • Unexpected observation ! • This neutron results used for PHENIX Local Polarimeter in Run3 Junji Tojo (RIKEN)
π 0 Cross Section (Run2) • π 0 measurement by PHENIX • Results consistent with NLO pQCD calculation NLO pQCD CTEQ6M PDF – Within the scale dependence µ = µ = p R F T ( µ = p T /2, p T , 2p T ) – Favors a larger gluon-to-pion fragmentation function (KKP) KKP FF • Important confirmation of theoretical foundations for Kretzer FF spin physics measurements – Applicability of pQCD PHENIX, PRL91, 241803 (2003) Junji Tojo (RIKEN)
A N in Forward π 0 Production (Run2) • Forward π 0 detection by STAR • Large spin effects observed, qualitatively consistent with models extrapolating from FNAL E704 data at √ s = 20 GeV. – Collins effect : Transversity – Sivers effect : Orbital motion – Twist-3 : quark-gluon correlation FNAL E704, √ s = 20 GeV STAR, hep-ex/0310058 Submitted to PRL Junji Tojo (RIKEN)
J/ ψ Cross Section (Run2) • J/ ψ detection in both ee and μμ channels by PHENIX • Cross sections are sensitive to the production mechanism – Color Octet Model (COM) describes cross sections with the present statistical precision. • Future high statistical measurement of J/ ψ polarization allows us to test the production mechanism. Junji Tojo (RIKEN)
A LL ( pp → π 0 X) (Run3) π 0 measurement by PHENIX • Solid line : B.Jagger et al ., PRD67, 054005 (2003) • Double long. asym. A LL sensitive to LL ∆ g(x) : Mixture of qq, qg and gg 0 A A from pp at s =200 GeV π LL 0.1 scattering PHENIX Preliminary σ ++ − σ +− ( ) ( ) GRSV-max = 0.05 A σ ++ + σ +− LL ( ) ( ) GRSV-std 0 • Assumption : Analyzing Power of RHIC CNI polarimeter -0.05 = A (100GeV) A (24GeV) N N -0.1 To be calibrated with the Absolute Polarization scaling error Polarimeter installed in Run4 ~30% is not included -0.15 0 1 2 3 4 5 6 • The first measurement of nonzero p (GeV/c) T A LL in the RHIC Spin Collider Junji Tojo (RIKEN)
Summary • Spin physics run in RHIC has started since Dec. 2001. • In two physics runs (Run2 and Run3), we obtained the results of – A N in Forward Neutron Production – π 0 Cross Section – A N in Forward π 0 Production – J/ ψ Cross Section – A LL ( pp → π 0 X) – And more • Performance of RHIC as the Spin Collider will be enhanced by new accelerator hardware installed in 2004-2005. Junji Tojo (RIKEN)
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