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Transverse spin physics at RHIC

Transverse spin physics at RHIC. Rencontres de Moriond, March 8 - March 15 Ralf Seidl (RBRC) for the RHIC SPIN collaboration (BRAHMS, STAR, PHENIX ). The RHIC ring(s) with polarized protons. RHIC pC Polarimeters. Absolute Polarimeter (H jet). Siberian Snakes. B RAHMS & PP2PP.

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Transverse spin physics at RHIC

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  1. Transverse spin physics at RHIC Rencontres de Moriond, March 8 - March 15 Ralf Seidl (RBRC) for the RHIC SPIN collaboration (BRAHMS, STAR, PHENIX) R.Seidl: Transverse spin measurements at RHIC

  2. The RHIC ring(s) with polarized protons RHIC pC Polarimeters Absolute Polarimeter (H jet) Siberian Snakes BRAHMS & PP2PP PHOBOS Siberian Snakes Spin Flipper PHENIX STAR Spin Rotators Partial Snake Helical Partial Snake Strong Snake 2  1011 Pol. Protons / Bunch e = 20 p mm mrad LINAC AGS BOOSTER 200 MeV Polarimeter Rf Dipole AGS Internal Polarimeter AGS pC Polarimeter R.Seidl: Transverse spin measurements at RHIC

  3. Relativistic Heavy Ion Collider 3Spin Experiments • PHENIX • STAR • BRAHMS • PHOBOS (heavy-ion) • Characteristics • 2 counter-circulating rings • 3.8 km in circumference • Top Energies (each beam): • 100GeV / Au-Au • 250GeV / p-p • Mixed Species (d+Au) R.Seidl: Transverse spin measurements at RHIC

  4. Local polarimetry:Forward Neutron Asymmetries IP12’s first asymmetry Zero Degree Calorimeterbehind Dx magnet neutron  shower max AN = 0.110±0.015 PLB650:325-330,2007 localasymmetriesat PHENIX vertical polarization radial polarization monitoring of polarization alignment when using spin rotators R.Seidl: Transverse spin measurements at RHIC

  5. Cross sections in (semi)inclusive DIS and pp, Factorization k’ k Q fq(x1) fq(x2)  s̃ Dh(z) fq(x1) s̃ Dh(z) • Hard scales PT and Q2 • Convolution integrals over all involved momenta • Factorization of involved distribution and fragmentation functions • (kT)-dependent distribution and fragmentation functions R.Seidl: Transverse spin measurements at RHIC

  6. Cross sections well understood at √s=200 GeV PHENIX:arXiv:0704.3599 [hep-ex] BRAHMS,PRL.98:252001,2007 |h| < 0.35 R.Seidl: Transverse spin measurements at RHIC

  7. Transverse single spin asymmetries AN Look at left-right asymmetries relative to one transversely polarized proton beam To cancel acceptance effects use square root formula R.Seidl: Transverse spin measurements at RHIC

  8. E704 Asymmetries Adams et al. (E704), PLB 264, 462 (1991). Adams et al. (E704), PRD 53, 4747 (1996). BNL-AGS √s = 6.6 GeV 0.6 < pT < 1.2 perturbative QCD predicted nearly vanishing single spin asymmetries Huge asymmetries seen in E704 at √s=20 GeV Higher twist effect? R.Seidl: Transverse spin measurements at RHIC

  9. Single spin asymmetries also at higher scales: Confirmed at RHIC at √s=200 GeV STAR:arXiv:0801.2990v1 [hep-ex] STAR: PRL.92:171801,2004 R.Seidl: Transverse spin measurements at RHIC

  10. Recently also PT dependence STAR:arXiv:0801.2990v1 [hep-ex] Prediction by: (Sivers): D’Alesio and F. Murgia, PRD 70, 074009 (2004) and (twist-3): C. Kouvaris, J. Qiu, W. Vogelsang, F. Yuan, PRD74, 114013 (2006). higher twist  1/PT dependence Not really seen in lower PT data, maybe at higher PT though R.Seidl: Transverse spin measurements at RHIC

  11. Single Spin Asymmetries at mid rapidity PHENIX, PRL. 95, 202001 (2005) 0 (2001/02) pt (GeV/c) pt (GeV/c) P=15% in 2002, P=47% in 2005 polarization scaling uncertainty: 30%(2002), ≈ 20%(2005) residual polarization in unpolarized beam: < 10% and small AN May provide information on gluon-Siverseffect • gg and qg processes are dominant • Transversity+ Collins is suppressed R.Seidl: Transverse spin measurements at RHIC

  12. Brahms asymmetries at √s=200 GeV J. H. Lee and F. Videbaek (BRAHMS), AIP Conf. Proc. 915, 533 (2007) 2.3 degrees 2.3 degrees K- and p asymmetries puzzling p 4 degrees 2.3 degrees R.Seidl: Transverse spin measurements at RHIC

  13. Asymmetries also seen at √s=62 GeV PHENIX, Chiu et al., nucl-ex/0701031 R.Seidl: Transverse spin measurements at RHIC

  14. Brahms asymmetries at √s=62 GeV BRAHMS, arXiv:0801.1078 [nucl-ex] p R.Seidl: Transverse spin measurements at RHIC

  15. What creates these single spin asymmetries? Sivers function unpol FF Transversity Collins function • Transverse momentum dependent distribution function: Sivers effect • Transversity with transverse momentum dependent fragmenation function: Collins effect • Higher twist effect on the distribution function or fragmentation function side : Description found to be equivalent to TMDs at intermediate PT R.Seidl: Transverse spin measurements at RHIC

  16. Naïve Sivers interpretation • Attractive rescattering of hit quark by gluon creates transverse momentum • M.Burkardt [hep-ph0309269] – impact parameter formalism • Orbital angular momentum at finite impact parameter • observed and true x differ • Observable left/right asymmetry Taken from H. Tanaka in Trento’04 > R.Seidl: Transverse spin measurements at RHIC

  17. Recent theoretical progress in understanding the ANs • Fitting HERMES and COMPASS Sivers data, • Take Collins contribution into account and • Calculate phases to describe RHIC AN results STAR asymmetries: Boglione, D’Alesia, Murgia e-Print: arXiv:0712.4240 [hep-ph] Reasonable well agreement vs xF Not so well agreement at lower PT R.Seidl: Transverse spin measurements at RHIC

  18. Brahms asymmetries J. H. Lee and F. Videbaek (BRAHMS), AIP Conf. Proc. 915, 533 (2007) √s=200 GeV • Pion asymmetries fairly well described • At least same sign for both K asymmetries as in data R.Seidl: Transverse spin measurements at RHIC

  19. Heavy flavor related single spin asymmetries • Open charm single spin asymmetrie s most sensitive to gluon Sivers function (d’Alesio et al,….) • J/y slightly more involved due to questions concerning production • new calculations for charmonium from F.Yuan, arXiv:0801.4357 [hep-ph] R.Seidl: Transverse spin measurements at RHIC

  20. Sivers Back-to-back jets D. Boer and W. Vogelsang, Phys. Rev. D 69, 094025 (2004) • Idea: Jets should be sensitive to initial kt of quarks and gluons • No sensitivity to final kt of hadrons • Possibility to pin down Sivers effect in pp collisions • Measure spin depentent deviation of dijets R.Seidl: Transverse spin measurements at RHIC

  21. Emphasizes (50%+ ) quark Sivers • VY 1, VY 2 are • calculations by • Vogelsang & Yuan, • PRD 72 (2005) • 054028 • -Bomhof et al PRD • 75, (2007) 074019 AN consistent with zero in central region Partial cancellation of SIDIS –like and DY –like contributions from Sivers function Sivers back-to-back jet measurements STAR,PRL,99(2007)142003 R.Seidl: Transverse spin measurements at RHIC

  22. Experiment SIDIS vs Drell Yan: Sivers|DIS= − Sivers|DY *** TestQCD Prediction of Non-Universality *** RHIC II Drell Yan Projections HERMES Sivers Results 0 Sivers Amplitude Markus Diefenthaler DIS Workshop Műnchen, April 2007 0 Feng Yuan Werner Vogelsang 0.1 0.2 0.3 x R.Seidl: Transverse spin measurements at RHIC

  23. Other future measurements • Direct access to transversity via Interference Fragmentation function • No Sivers –like contributions • kT integrated, evolution understood • Open charm single spin asymmetries • Direct photon – jet Sivers asymmetries • Drell Yan for Sivers function and Boer-Mulders function R.Seidl: Transverse spin measurements at RHIC

  24. Summary • Single spin asymmetries confirmed at higher √s • Increasing with xF for pions and kaons • Compatible to zero for small and negative xF • PT dependence only falling for higher PT ,lower not well understood • First heavy quark single spin asymmetries compatible with zero • Sivers Back-to-back measurements compatible with zero due to partial cancellations of DY type and SIDIS type contributions • More exciting results in the future R.Seidl: Transverse spin measurements at RHIC

  25. Backup slides R.Seidl: Transverse spin measurements at RHIC

  26. Transversity • In helicity basis: helicity distribution and momentum difference and sum of diagonal amplitudes • Transversity contains helicity flip and is not diagonal • Helicity is conserved quantity for (nearly) massless quarks • All interactions conserve helicity/chirality  Transversity cannot be observed in DIS R.Seidl: Transverse spin measurements at RHIC

  27. Quark distributions in spin bases q(x),G(x) Sum of quarks with parallel and antiparallel polarization relative to proton spin (well known from Collider DIS experiments) Unpolarized distribution function q(x) Difference of quarks with parallel and antiparallel polarization relative to longitudinally polarized proton (known from fixed target (SI)DIS experiments) Dq(x), DG(x) Helicity distribution function Dq(x) Difference of quarks with parallel and antiparallel polarization relative to transversely polarized proton (first results from HERMES and COMPASS – with the help of Belle) dq(x) Transversity distribution function dq(x) R.Seidl: Transverse spin measurements at RHIC

  28. Transversity and friends q(x) Unpolarized DF helicity DF Transversity DF Dq(x) dq(x) Sivers function Boer-Mulders function R.Seidl: Transverse spin measurements at RHIC

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