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Single-spin asymmetries in two hadron production of polarized deep inelastic scattering at HERMES

Single-spin asymmetries in two hadron production of polarized deep inelastic scattering at HERMES. Tomohiro Kobayashi Tokyo Institute of Technology for the HERMES collaboration. Contents The HERMES experiment Quark distribution functions

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Single-spin asymmetries in two hadron production of polarized deep inelastic scattering at HERMES

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  1. Single-spin asymmetries in two hadron production of polarized deep inelastic scattering at HERMES Tomohiro Kobayashi Tokyo Institute of Technology for the HERMES collaboration • Contents • The HERMES experiment • Quark distribution functions • Single-spin asymmetry in 2-hadron semi-inclusive DIS • Conclusion and outlook Second Joint Meeting of the Nuclear Physics Divisions of APS and JPS, Hawaii (Sep. 22nd, 2005 Session JE-9)

  2. HERMES experiment at DESY Target magnet HERA positron (electron) beam 27.6 [GeV] current ~ 30[mA] Transversely polarized hydrogen target(2002~2005) polarization ~ 75[%]

  3. ＨＥＲＭＥＳ Spectrometer Internal gas target H(pol)、D（pol）、 He、Ne、Kr、Xe • acceptance : 40 mrad ≦Q≦ 220 mrad • Tracking resolution： dP/P = (0.7-1.3)%、dQ = 0.6 mrad • PID： Hodoscope、Calorimeter、TRD and RICH Lepton ID efficiency > 97%, Hadron contamination < 1% Hadron ID(p, K, P) at 2‐15 GeV/c e+ beam 27.6GeV 8m

  4. Quark distribution functions At leading twist quark spin Quark momentum distribution: proton spin Quark Helicity: Quark Transversity: unknown chiral odd • quark’s relativistic nature • positivity bound : • Soffer bound ：

  5. d q ( x ) : Access to transversity chiral odd Need another chiral odd objects. Inclusive DIS Semi-inclusive DIS Not accessible accessible • Transversity couples to … • Collins fragmentation function (FF) • 2-hadron interference FF • Polarized Lambda FF • Spin-1 FF • :

  6. H ( z ) 1 d q ( x ) H ( z ) 1 Single-spin asymmetry of 2-hadron production (data taken in 2002…2004) Azimuthal single-spin asymmetries beam spin target spin f + f d q ~ sin( ) sin q ( x ) H ( z ) ^ 1 R S TransversityInterference FF (chiral odd) can be extracted using measured by e+ e- collider, BELLE describes interference between different production channels of pion pairs

  7. : s-p wave interference in scattering theory Partial wave expansion R. L. Jaffe, Xuemin Jin, and Jian Tan, Phys. Rev. Lett. 80, 1166 (1998) P. Estabrooks and A. D. Martin, Nucl. Phys. B79, 301 (1974) Sign of the phase shift changes at might depend strongly on

  8. Spectator model for fragmentation Partial wave expansion M. Radici et al., hep/ph-0110252 No strong dependence.

  9. Single-spin asymmetry in 2-hadron production Single-spin asymmetries (no binning) First observation of transverse asymmetries in interference process

  10. Single-spin asymmetry in 2-hadron production Single-spin asymmetries Fit with Amplitude of the asymmetry modulation

  11. Single-spin asymmetry in 2-hadron production If we look at dependence, ( : invariant mass of pion pair) Asymmetry is fitted with Positive asymmetry is observed around

  12. Spectator model for fragmentation Partial wave expansion Marco Radici at Como, 7 - 10 Sept 2005

  13. Conclusion • Conclusion • Single-spin asymmetry in production is measured • with transversely polarized hydrogen target at HERMES. • This is the first observation of transverse target spin asymmetry • in interference process. • modulation of is observed at 4 sigma level. • Positive asymmetry is observed for measured invariant • mass range. ( =0.25 - 2.0 [GeV/c2])

  14. Outlook • Outlook • 4~5 M more DIS events are • expected in 2005, • compared to 3.5 M DIS • events in 2002~2004.

  15. backup

  16. Event selection Data set : 2002~2004 SIDIS events with at least pion pair( ) appeared were analyzed. Kinematic cuts : ≥ 1 GeV2 ≥4 GeV2 ≥0.023 0.1 < < 0.85 > 2.5 GeV (for DIS lepton) > 1 GeV (for Hadron) > 2 GeV, where To cut exclusive channel.

  17. Evaluate What is measured where is the average target polarization. ( )

  18. Single-spin asymmetry in 2-hadron production : invariant mass of pion pair Asymmetry is fitted with Positive asymmetry is observed around binning :0.25, 0.40, 0.55, 0.77, 2.0 [GeV]

  19. spectrum With or without cut

  20. spectrum With or without cut

  21. double spin asymmetry Fit for both beam polarization. No double spin asymmetry Beam polarization (%) Beam polarization don’t affect to the asymmetry

  22. Polarized cross section for 2 hadron SIDIS 2 hadron semi-inclusive DIS Single spin asymmetries

  23. Polarized cross section for 2 hadron SIDIS 2 hadron semi-inclusive DIS In Wandzura-Wilzcek approx., function with tilde vanish.

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