1 Spin Physics with STAR at RHIC , Introduction STAR longitudinal spin program: results and future STAR transverse spin program: results and future Summary STAR 2 Quark spin, (~30%)-DIS Gluon spin, Poorly known Orbital Angular Momenta Little known Spin sum rule (longitudinal case): Spin structure of nucleon Little known in the transverse case: Proton spin Proton spin Helicity distribution: Transversity: 3 Detailed knowledge on q(x), g(x) (before RHIC) x 4 RHIC- the first polarized pp collider in the world 5 pp Run Year (200/500) % / 35* L max [ s -1 cm -2 ] / 85* L int [pb -1 ] at STAR (Long./Transverse) 0 / / / 03.1 / / 3.40 /3.122 /10.5* *first 500 GeV run 6 The STAR spin program Longitudinal spin program: determination of the helicity distributions: Gluon polarization g(x) in the nucleon -- results & status (inclusive jet, hadrons) -- status & future plan (di-jets, +jet, heavy flavor) Flavor separation: quark & anti-quark polarization -- RHIC 500 GeV program (W prodction) -- (anti-)hyperons spin transfer Transverse spin program: Single spin asymmetry A N (SSA) on 0, QCD mechanisms (Sivers, Collins, high-twist) -- forward +jet production on Sivers effects 7 MRPC ToF barrel 100% ready for run 10 PMD FPD FMSFMS EMC barrel EMC End Cap DAQ1000 Complete Ongoing TPC FTPC BBC STAR Detector (current) 8 COMPASS, PLB676,31(2009) g determination from DIS Recent measurements from DIS: 9 f2f2 f1f1 Longitudinal spin asymmetry: Accessing g(x) in pp collision 10 STAR PRL 97, STAR PRL 97, pQCD works at RHIC energies-unpolarized cross sections Mid-rapidity jet cross section is consistent with NLO pQCD over 7 orders of magnitude Forward rapidity 0 cross section also consistent with NLO pQCD Many other examples 11 STAR inclusive 0 A LL at various rapidities During Run 6, STAR measured A LL for inclusive 0 for three different rapidity regions Mid-rapidity result excludes large gluon polarization scenarios Larger rapidity correlates to stronger dominance of qg scattering with larger x quarks and smaller x gluons Expect A LL to decrease as increases | | < < < 2 = 3.2, 3.7 12 STAR inclusive 0 A LL at various rapidities During Run 6, STAR measured A LL for inclusive 0 for three different rapidity regions Mid-rapidity result excludes large gluon polarization scenarios Larger rapidity correlates to stronger dominance of qg scattering with larger x quarks and smaller x gluons Expect A LL to decrease as increases | | < < < 2 = 3.2, 3.7 PHENIX, arXiv: | | < 0.35 13 PRL 97, (2006) Results on jet X-section and spin asymmetry PRL 97, (2006) Experimental cross section agrees with NLO pQCD over 7 orders of magnitude 14 Experimental cross section agrees with NLO pQCD over 7 orders of magnitude PRL 97, (2006) PRL 100, (2008) Results on jet X-section and spin asymmetry 15 RHIC constraints Impact of RHIC early results on g(x) de Florian et al., PRL101(2008) Early RHIC data (2005, 2006) included in a global analysis along with DIS and SIDIS data. Evidence for a small gluon polarization over a limited region of momentum fraction (0.050.55 STAR 2006 PRELIMINARY ~ 3.66 Run 6 inclusive A N at large x F = / = /- 0.02 33 E704 Nucl. Phys. B 510 (1998) 3 ++ -- 200 GeV 62.4 GeV BRAHMS,PRL101(2008) Large SSA of different hadrons in different experiments 34 Separating Sivers and Collins effect in pp collisions Collins effect: spin and k correlation in fragmentation process (related to transversity) For hadron SSA, both Sivers and Collins effects can contribute. Forward jets and photon may provide separation of them. SPSP k ,q p p Sivers effect: spin and k correlation in initial state (related to orbital angular momentum) SPSP p p SqSq k,k, Sensitive to transversity Sensitive to orbital angular momentum 35 Mid-rapidity jet A N ~0, different as the conventional calculations with Sivers function fitted from SDIS. Sivers distribution, is process dependent (not universal), A N of jet production - Sivers effect STAR, PRL99,142003(2007) A N of mid-rapidity consistent with zero: An example: attractive color interactionrepulsive color interaction 36 Probing Sivers effect with + mid-rapidity jet Bacchetta et al., PRL 99, Conventional calculations predict the asymmetry to have the same sign in SIDIS and +jet Calculations that account for the repulsive interactions between like color charges predict opposite sign Critical test of our basic theoretical understanding 37 STAR Detector - future MRPC ToF barrel 100% ready for run 10 FMSFMS FGT Ongoing MTD R&D HFT TPC FHC Forward jet reconstruction with FMS+FHC =2.8 FPD 38 SSA with forward jets and photons Projected precision of A N for p +p jet + X : Jet energy profile from FHC+FMS: Collins effects(spin and k correlation in fragmentation process ): Accessed via spin-dependent correlations of hadrons within forward jet Sivers effect(spin and k correlation in initial state): Accessed by symmetric azimuthal integration of hadrons from forward jet Accessed by forward direct photons 39 Transverse spin transfer of hyperons and q(x) Transverse spin transfer of hyperons transverse spin can provide access to transversity, via channel ->n+ : transversity distribution : f(x) = f (x) - f (x) pQCD Transversely polarized fragmentation function : Measurement at BELLE ? - Transverse spin transfer can provide access to transversity, which is still poorly known so far. 40 Large polarization with unpolarized beam p + p + X, observed in different experiments. Still not fully understood. target produced production plane Transverse hyperons polarization in unpolarized pp How about at RHIC energy? ( = 2p L / s) 41 Longitudinal spin physics at STAR: Determination of gluon polarization G : Currently inclusive probes with jets, are providing important constraints on G. Early results have been included in global analysis. Near future probes: Increased statistics and higher energy for inclusive jets will provides additional constraints with better precision and wider x-range. Correlation measurements (di-jet, photon-jet) with access to partonic kinematics will provide better resolution in x and direct probe to G. Determination of sea quark polarization: With 500 GeV collisions, W-production provide unique tool to study the anti-quark polarization. Spin transfer of hyperons provides sensitivity to strange quark polarization. Summary & Outlook - I 42 Transverse spin physics at STAR: STAR has observed large transverse single-spin asymmetries for forward particle production. Study Collins and Sivers effects in pp reaction with Single-spin asymmetry with forward jet. STAR transverse +jet measurements will provide a direct illustration of attractive vs. repulsive color-charge interactions Transverse hyperon polarization at forward region at STAR Summary & Outlook -II 43 FMS: expanding STARs forward acceptance Expanded p T range for inclusive 0 A N during Run 8 STAR Forward Meson Spectrometer 2.5 < < 4.0 STAR 44 What is the FHC? Two identical 9x12 enclosures of E864 hadron calorimeter detectors X100X117 cm 3 Refurbished and used by PHOBOS collaboration as forward hadron multiplicity detectors for run- 3 d+Au Recycle 45 PHENIX, arXiv: 46 47 World efforts for spin physics Current running Lepton-nucleon scattering: COMPASS, JLAB Polarized proton-proton scattering, RHIC Future facilities EIC (BNL) JPARC (Japan) GSI-FAIR (Germany) DESY e + Jefferson LabSLAC E CERN Finished experiments: SLAC, EMC, SMC, HERMES All these experiments have their unique coverage on q, g, Lq,g, and they are complementary as well 48 49 Hyperon spin transfer at forward region Forward hyperons, reconstructed via n+ channel, and polarization can be determined through decay product, i.e, dN/dcos * = N 0 (1+ P cos *) Provide access to pol.p.d.f. and fragmentation functions Longitudinal spin transfer D LL : Model evaluation shows D LL provide sensitivity to pol. parton distributions. s(x) models 50 Jet Finding in STAR Jet reconstructed with TPC tracks and EMC energy deposits, using midpoint Cone Algorithm: 51 The STAR Detector Magnet 0.5 T Solenoid Triggering & Luminosity Monitor Beam-Beam Counters 3.4 < | | < 5.0 Zero Degree Calorimeters Central Tracking Large-volume TPC | | < 1.3 Calorimetry Barrel EMC (Pb/Scintilator) | | < 1.0 Shower-Maximum Detector Endcap EMC (Pb/Scintillator) 1.0 < < 2.0 52 Transverse spin asymmetry - spin structure of nucleon Large single transverse-spin asymmetry observed at RHIC: STAR, Phys. Rev. Lett. 92 (2004)171801STAR, Phys. Rev. Lett. 97 (2006) Basic QCD calculations (leading- twist, zero quark mass) predict A N ~0, while cross sections are found to be in agreement with pQCD evaluations.