Qinghua Xu, LBNL 1 Longitudinal Spin Transfer of in Polarized pp Collisi ons at 200 GeV Qinghua Xu, LBNL for the STAR Collaboration SPIN 2006, Oct 6, 2006 ) ( Λ Λ • Motivation • Proof-of-principle analysis at low p T with STAR • Preliminary results for D LL in inclusive production • Summary and outlook ) ( Λ Λ
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Longitudinal Spin Transfer of in Polarized pp Collisions at 200 GeV
Longitudinal Spin Transfer of in Polarized pp Collisions at 200 GeV. Qinghua Xu, LBNL for the STAR Collaboration SPIN 2006, Oct 6, 2006. Motivation Proof-of-principle analysis at low p T with STAR Preliminary results for D LL in inclusive production - PowerPoint PPT Presentation
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Qinghua Xu, LBNL 1
Longitudinal Spin Transfer of in Polarized pp Collisions at 200 GeV
Qinghua Xu, LBNL
for the STAR Collaboration
SPIN 2006, Oct 6, 2006
)(ΛΛ
• Motivation
• Proof-of-principle analysis at low pT with STAR
• Preliminary results for DLL in inclusive production
• Summary and outlook
)(ΛΛ
Qinghua Xu, LBNL 2
Why study ?
• Due to its self-analyzing weak decay, Λ polarization has been widely studied in different processes with many interesting results (following talks).
)(ΛΛ
decay parameter 0.642 0.013
)ˆ( 1d
dNppP ⋅+∝
Ω Λ
rα Unit vector along proton mom
entum in Λ rest frame.
Λ polarization vector
• What can we learn from polarization with polarized pp collider at RHIC?
)(ΛΛ
Qinghua Xu, LBNL 3
How sensitive is anti-Lambda DLL
to
• Longitudinal spin transfer in polarized proton-proton collisions:
• contains a strange quark, can it provide sensitivity to
?ss ΔΔ or
What can we learn with in polarized pp collisions ?
€
DLL ≡σ
p + p →Λ+X−σ
p + p →Λ−X
σp + p →Λ+X
+ σp + p →Λ−X
,
)(ΛΛ
Λ
?sΔ
ΛΛ &
measures the transfer of beam polarization to hyperon.
fraction production
fΔ DΔ
Δ
Λ production is expected to be dominated by u quark, while s_bar plays a dominate role for production at large pT!
Λ
[GeV]
)(ΛΛ
PYTHIA
€
s = 200 GeV
Qinghua Xu, LBNL 4
• Anti-Lambda DLL may give new insights into at high pT!sΔ
1)(PRD63,200 GRSV2000
standard
valence
Q2=5 GeV
-0.090.02 (Inclusive DIS)
0.010.03 (Semi-inclusive
DIS-HERMES)
GeV 8
GeV 200
>=
Tps
Q. X, E. Sichtermann, Z. Liang, PRD 73,2006
Pol. frag. func. model
x
models sΔ
:ss Δ+Δ
• Spin transfer of in pp collisionΛ
€
xΔs (x)
Qinghua Xu, LBNL 5
XppXpp
XppXppLLD
−+++
−+++
Λ→Λ→
Λ→Λ→
+
−≡
σσσσ
XppXpp
XppXppLLA
Λ→Λ→
Λ→Λ→
−+++
−+++
+
−≡
σσσσ
• Spin transfer versus double spin asymmetry
• DLL is ~ 4X more sensitive to than ALL.
• ~0.01 measurement will distinguish parameterizations.
sΔsΔ
models s with ΔLLA
models s with ΔLLD
standard GRSV00 valenceGRSV00
0<<1 for DLL
-1<<1 for ALL
[GeV]
Qinghua Xu, LBNL 6
RHIC- the first polarized pp collider
AGS Heclical Partial Snake
Stable polarization direction - transverseLongitudinal polarization at STAR/Phenix
4 spin orientations:++,+-,-+,--
Qinghua Xu, LBNL 7
STAR Detector
• primary vertex
p
V0_vertex
V0_DCA
Λ
rr
• is reconstructed by combining TPC tracks with opposite charges after particle identification from energy loss and applying topological cuts.