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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 +. ¯. - PowerPoint PPT Presentation
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STARSTAR
Future Investigations of the Flavor Dependence of Sea Quark
Helicities at STAR
J. Sowinski
for the
Collaboration STARSTAR
STARSTAR 10/4/2008 J. Sowinski RHIC Spin Collab. Mtg. 2
u u
d
p u d
d
u
d̄
n+
Virtual ’s imply an excess of d over u
_ _
Perturbative picture implies that u(x)~d(x)
_ _
How is the Sea Generated?
“Middle Ground” chiral symmetry +
large Nc models
’s = Goldstone bosons nucleons = solitons
STARSTAR 10/4/2008 J. Sowinski RHIC Spin Collab. Mtg. 3
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
STARSTAR 10/4/2008 J. Sowinski RHIC Spin Collab. Mtg. 4
B. Dressler et al., Chiral Quark Soliton Model Predictions
m2 = (600 MeV)2
m2 = (5 GeV)2
x(d-u)̄¯
x(u-d)¯ ¯
• d(x)-u(x) and u(x)-d(x) better for Q2 evolution
• E866 Results are qualitatively consistent with pion cloud models, instanton models, chiral quark soliton models, etc.
¯ ¯ ¯¯
E866 Results Polarized q Flavor Asymmetry_
• pQCD motivated models predict
[u(x)-d(x)]dx [d(x)-u(x)]dx
• Chiral motivated models tend to disagree
¯ ¯¯ ¯1
01
0
STARSTAR 10/4/2008 J. Sowinski RHIC Spin Collab. Mtg. 5
Current Constraints on the
Polarized Sea
D. De Florian et al. Phys. Rev. Lett. 101, 072001 (2008)
• One example of global fit: DSSV• Except for G main constraints
from (SI)DIS• Flavor and valence distributions
well determined• u and d best fit distributions
asymmetric• But error bands allow flavor
symmetric sea
STARSTAR 10/4/2008 J. Sowinski RHIC Spin Collab. Mtg. 6
• 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)
ALW - ~ u(x1)d(x2)+d(x1)u(x2)
_ _
Allows kinematic separation especially for W- in EEMC
Dressler et al. predict large sensitivity
W+(-) Production in p-p at s = 500 GeV/c2
STARSTAR 10/4/2008 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
STARSTAR 10/4/2008 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
Forward GEM Tracker
EM Calorimetry
h
e
STARSTAR 10/4/2008 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 >2
STARSTAR 10/4/2008 J. Sowinski RHIC Spin Collab. Mtg. 10
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
STARSTAR 10/4/2008 J. Sowinski RHIC Spin Collab. Mtg. 11
Examples (3 of many) cuts
• Shower shape in calo.• Isolation about electron• Veto on energy opposite in
e/h Discrimination
STARSTAR 10/4/2008 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
STARSTAR 10/4/2008 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
30% neutrals convert to tracks
Full neutral rejection
STARSTAR 10/4/2008 J. Sowinski RHIC Spin Collab. Mtg. 14
Projections vs pT
• 1 < < 2• 300 pb-1
• Realistic BG subtraction
• Recent PDFs ~representing current allowed u/d range
• d and u isolated
STARSTAR 10/4/2008 J. Sowinski RHIC Spin Collab. Mtg. 15
Projections vs. Pseudorapidity
• u sensitivity spread over
STARSTAR 10/4/2008 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