# Presentation: 607992

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

- J. Sowinski
- for the
-                Collaboration

## p

- J. Sowinski  RHIC Spin Collab. Mtg.

- How is the Sea Generated?

- “Middle Ground”
- chiral symmetry +
- large Nc models
- ’s = Goldstone bosons nucleons = solitons

## Flavor Asymmetry of the Sea  

- J. Sowinski  RHIC Spin Collab. Mtg.

- 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

- Flavor Asymmetry of the Sea

## Polarized q Flavor Asymmetry

- J. Sowinski  RHIC Spin Collab. Mtg.

- B. Dressler et al., Chiral Quark Soliton Model Predictions

- m2 = (600 MeV)2

- m2 = (5 GeV)2

- E866 Results

- _

-  pQCD motivated models predict
***     ****[****u(x)-****d(x)]dx** ****   ** **[d(x)-u(x)]dx*
*** ***Chiral motivated models tend to disagree

*** ̄***

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## Current Constraints on the Polarized Sea

- J. Sowinski  RHIC Spin Collab. Mtg.

- D. De Florian et al.
- Phys. Rev. Lett. **101**, 072001 (2008)

## W+(-) Production in p-p at  s = 500 GeV/c2

- J. Sowinski  RHIC Spin Collab. Mtg.

-  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

- _

- _

- Parity violating single spin asymmetry AL
- (Helicity flip in one beam while averaging over other)

- Allows kinematic separation especially for W- in EEMC

- Dressler et al. predict large sensitivity

- W+(-) Production in p-p at ****** s = 500 GeV/c2

## NLO Theory Calculations

- J. Sowinski  RHIC Spin Collab. Mtg.

- NLO theoretical framework with NNLL resummation accuracy allows interpretation of AL(ye) and Monte Carlo calculations. *Nucl. Phys. B666, 31 (2003)**  **RHICBOS*

## STAR

- J. Sowinski  RHIC Spin Collab. Mtg.

- 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

- Forward GEM Tracker

- EM Calorimetry

- h

- e

## Tracking Upgrade at STAR

- J. Sowinski  RHIC Spin Collab. Mtg.

- 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 >2

## Endcap ElectroMagnetic Calorimeter

- J. Sowinski  RHIC Spin Collab. Mtg.

- Endcap ElectroMagnetic Calorimeter

- Pb Scint sampling calorimeter
- 21 radiation lengths
- 720 projective towers
- Depth Segmentation
- 2 preshower layers, e/h 0/ disc.
- High position resol. SMD 0/disc.
- Postshower layer e/h discc.
- L0 trigger- high tower, jet patches

## Examples (3 of many) cuts

- J. Sowinski  RHIC Spin Collab. Mtg.

- Examples (3 of many) cuts

- Shower shape in calo.
- Isolation about electron
- Veto on energy opposite in 

- e/h Discrimination

## e/h discrimination

- J. Sowinski  RHIC Spin Collab. Mtg.

- 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

## Projected Signal to Background Ratios

- J. Sowinski  RHIC Spin Collab. Mtg.

- Succesfully suppress hadronic background to give S/B >1 for pT> 28 GeV
- Allows for 30% conversion of neutrals before tracking

- 30% neutrals convert to tracks

- Full neutral rejection

## Projections vs pT

- J. Sowinski  RHIC Spin Collab. Mtg.

- Projections vs pT

- 1 <  < 2
- 300 pb-1
- Realistic BG subtraction
- Recent PDFs ~representing current allowed u/d range
-  d and           u isolated

## Projections vs. Pseudorapidity

- J. Sowinski  RHIC Spin Collab. Mtg.

-  u sensitivity spread over 

## Summary

- J. Sowinski  RHIC Spin Collab. Mtg.

- 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