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Future Investigations of the Flavor Dependence of Sea Quark Helicities at STAR

STAR. Future Investigations of the Flavor Dependence of Sea Quark Helicities at STAR. J. Sowinski for the Collaboration. How is the Sea Generated?. Perturbative picture implies that u(x)~d(x). _. _. Virtual p ’s imply an excess of d over u. _. _. u. u. d. u. d. u. d. p +. ¯.

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Future Investigations of the Flavor Dependence of Sea Quark Helicities at STAR

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  1. STAR Future Investigationsof theFlavor Dependenceof Sea QuarkHelicitiesatSTAR J. Sowinski for the Collaboration

  2. How is the Sea Generated? Perturbative picture implies that u(x)~d(x) _ _ Virtual p’s imply an excess of d over u _ _ u u d u d u d p+ ¯ d n “Middle Ground” chiral symmetry + large Nc models p’s = Goldstone bosons nucleons = solitons p J. Sowinski RHIC Spin Collab. Mtg.

  3. Flavor Asymmetry of the Sea NMC and • Gottfried Sum Rule in DIS • DIS on nuclei • SIDIS • Drell-Yan • Quantitative calculations of Pauli blocking not sufficient • Non-perturbative processes seem to be needed in generating the sea Phys.Rev.Lett. 80 (1998) 3715 J. Sowinski RHIC Spin Collab. Mtg.

  4. _ ¯ ¯ ¯ • d(x)-u(x)andDu(x)-Dd(x)better for Q2 evolution • E866Results are qualitatively consistent with pion cloud models, instanton models, chiral quark soliton models, etc. ¯ ¯ x(Du-Dd) ¯ ¯ ¯ x(d-u) E866 Results Polarized q Flavor Asymmetry • pQCD motivated models predict • [Du(x)-Dd(x)]dx[[d(x)-u(x)]dx • Chiral motivated models tend to disagree ¯ ¯ ¯ ¯ B. Dressler et al., Chiral Quark Soliton Model Predictions m2 = (5 GeV)2 m2 = (600 MeV)2 J. Sowinski RHIC Spin Collab. Mtg.

  5. One example of global fit: DSSV • Except for DG main constraints from (SI)DIS • Flavor and valence distributions well determined • Du and Dd best fit distributions asymmetric • But error bands allow flavor symmetric sea Current Constraints on the Polarized Sea D. De Florian et al. Phys. Rev. Lett. 101, 072001 (2008) J. Sowinski RHIC Spin Collab. Mtg.

  6. _ _ ALW - ~u(x1)Dd(x2)+d(x1)Du(x2) W+(-) Production in p-p at  s = 500 GeV/c2 Dressler et al. predict large sensitivity Parity violating single spin asymmetry AL (Helicity flip inone beamwhile averaging overother) • V-A coupling • only LH u and RH d couple to W+ • Likewise LH d and RH u to W - • Only LH W’s produced • Neutrino decay gives preferential directionality in decay _ _ Allows kinematic separation especially for W- in EEMC J. Sowinski RHIC Spin Collab. Mtg.

  7. NLO Theory Calculations NLO theoretical framework with NNLL resummation accuracy allows interpretation of AL(ye) and Monte Carlo calculations.Nucl. Phys. B666, 31 (2003)RHICBOS J. Sowinski RHIC Spin Collab. Mtg.

  8. STAR • Need to detect e+ e- and measure pT • Need to find in huge hadronic background • Need to separate e+ and e- charge Large solid angle of STAR h EM Calorimetry e Forward GEM Tracker J. Sowinski RHIC Spin Collab. Mtg.

  9. Tracking Upgrade at STAR TPC Only Add FGT • Charge sep. in forward region essential • TPC tracking degrades in forward dir. • Add FGT allows >80% c.s. separation • Isolation cut based on tracks for h>2 J. Sowinski RHIC Spin Collab. Mtg.

  10. EndcapElectroMagneticCalorimeter Pb Scint sampling calorimeter 21 radiation lengths 720 projective towers Depth Segmentation 2 preshower layers, e/h p0/g disc. High position resol. SMD p0/g disc. Postshower layer e/h discc. L0 trigger- high tower, jet patches J. Sowinski RHIC Spin Collab. Mtg.

  11. e/h Discrimination Examples (3 of many) cuts • Shower shape in calo. • Isolation about electron • Veto on energy opposite in f J. Sowinski RHIC Spin Collab. Mtg.

  12. e/h discrimination • Full cuts strongly suppress (~1000) hadrons while preserving ~80% of electron/positrons • Full Pythia/GEANT simulation • Isolation cone about electron • Awayside veto • Calorimeter shower shapes J. Sowinski RHIC Spin Collab. Mtg.

  13. Projected Signal to Background Ratios • Succesfully suppress hadronic background to give S/B >1 for pT> 28 GeV • Allows for 30% conversion of neutrals before tracking Full neutral rejection 30% neutrals convert to tracks J. Sowinski RHIC Spin Collab. Mtg.

  14. Projections vs pT • 1 < h < 2 • 300 pb-1 • Realistic BG subtraction • Recent PDFs ~representing current allowed Du/Dd range • Dd and Du isolated J. Sowinski RHIC Spin Collab. Mtg.

  15. Projections vs. Pseudorapidity • Du sensitivity spread over h J. Sowinski RHIC Spin Collab. Mtg.

  16. Summary • First 500 GeV run planned for February • Over next 5 yrs. of full operation could expect 300 pb-1 of pol. pp collsiions • W program at STAR and RHIC should provide new constraints on the flavor (a)symmetry of the sea quarks J. Sowinski RHIC Spin Collab. Mtg.

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