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Single-spin asymmetry of charm di-jet in longitudinally polarized pp collisions at STAR. Introduction and motivation Reconstruction of W and Z signals Single-spin asymmetry of di-jet Summary and outlook. Orbital Angular Momentum. Introduction and motivation. Nucleons’ spin structure. - PowerPoint PPT Presentation
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Single-spin asymmetry of charm di-jet in longitudinally polarized pp collisions at STAR
Introduction and motivation
Reconstruction of W and Z signals
Single-spin asymmetry of di-jet
Summary and outlook
Nucleons’ spin structure
• Spin sum rule for nucleon:
• In naive Quark Model, the nucleon is made up of three quarks, its spin (½) is carried by the three quarks’ spin.
“Spin Crisis” : In 1988, EMC experiment found proton spin carried by quarks’ spin is 20%-30%.
1 1
2 2 q gG L L
Quark spin
u u d d s sGluon spin
Orbital Angular Momentum
Introduction and motivation
Introduction and motivation
Longitudinal spin program at RHIC
( , )
LLjets and leading hadrons A etc
G prompt photons
heavy flavor production
, ( , )LLs s hyperons D etc
, ( , , )
,L LL
u uweak bosons A A etc
d d
Introduction and motivation
SSA of W bosons
p p W X p p W XWL
p p W X p p W X
A
- ( ) 0 -:
p p W Xthe cross section for W bosons production when
helicity of the polarized beam is - (+) .
: W ud W Leading order diagrams for
Introduction and motivation
SSA of W bosons
: ++ - +
In weak interaction, parity is vialated.
W is only left - hand u d W
1 2 1 2( ) ( ) ( ) ( )p p W u d W u d W
d u x d x d d x u x d
1 2 1 2( ) ( ) ( ) ( )p p W u d W u d W
d u x d x d d x u x d
1 2 1 2
1 2 1 2
( ) ( ) ( ) ( )
( ) ( ) ( ) ( )W
L
u x d x d x u xA
u x d x d x u x
Introduction and motivation
SSA of W bosons
1 2 1 2
1 2 1 2
( ) ( ) ( ) ( )
( ) ( ) ( ) ( )W
L
u x d x d x u xA
u x d x d x u x
To abtain asymmetry of , one interchanges and .-W u d
0 :
0 : -
WLW
WLW
uy A approaches
u
dy A approaches
d
1 2, W Wy yW WM Mx e x e
s s
Motivation-----1
Introduction and motivation
Reconstruction of W
Leptonic channel :
eW e
t almost all high P electrons
come from this process,
the background is small
neutrinos can not be detected,
there is missing energy,
the kinematics
Advantages :
Disadvantages:
of W can not be claimed clear
Hadronic channel :
W di jet
/ 0
the branching ratio is 6 times
larger than leptonic channel,
the kinematics of W can be claimed
the background is big,
QCD 2 2 process
Z
di - jet
Advantages :
Disadvantages:
Introduction and motivation
Leptonic channel
: t
P distribution of electron in W e+
: (10.72 0.16)%Branching ratio
* lab *e e W e
Relation between electron rapidity and W rapidity : y = y + y where y is lepton rapidity in W rest frame
Introduction and motivation
Hadronic channel
2 2 - Di jets from QCD process di jets from W bosons
(67.96 0.35)Branching ratio: %
0
supress the QCD di- jets very much
supress Z di- jet more than W di- jet
Charm di- jet ( at least one charm jet )
Motivation-----2
& the kinematics of W can be claimed directly
Introduction and motivation
0
0( ) ( ) ( )
( ) ( ) ( )
di jet W W Z
L L L L
W W ZA A A A
tot tot tot
0( ) ( ) ( ) ( */ ) ( )tot W W Z QCD
( ) ( )
( ) ( )di jetL
p p di jet p p di jetA
p p di jet p p di jet
+ -
0
W ,W
production of di - jet Z
QCD 2 2 process
LQCD 2 2 process : A = 0 Parity conservation
SSA of di-jet
Reconstruction of W and Z signals
UA2 experiment
-1
630GeV p p collisions
Luminosity : 0.73 pb
mass resolution : 10%
630 190 0
signals are observed in
the mass region of W and Z
R.Ansari et al [UA2 Collaboration], Phys. Lett. B 186, 452 (1987)
Reconstruction of W and Z signals
Fast Simulation of the invariant mass distribution of di-jet in pp collision at STAR.
Mass resolution : 5%
Fast simulation of the invariant mass distribution of charm di-jet in pp collision at STAR.
Reconstruction of W and Z signals
Mass resolution : 5%
From W+ From W- From Z0 QCD 2->2 W+/total
common di-jet 59256 19764 4200 7.04E+6 0:0083
charm di-jet 29236 9924 704 1.92E+5 0:126
cross section:-6
0 -7
-3
:1.133 10
:3.278 10
2 2 : 2.381 10
pp W mb
pp Z mb
QCD process mb
comparison:
1
s = 500GeV; luminosity = 400pb ; E > 20GeV; < 1t
mass resolution = 5%; mass window= [75GeV - 85GeV]
Reconstruction of W and Z signals
Reconstruction of W and Z signals
di-jet charm di-jet
6
1+(-)W 1 210Z 1
1QCD 1 30
Single-spin asymmetry of di-jet
SSA of pure W bosons
PDF : GRV98polarized PDF : GRSV2000
Single-spin asymmetry of di-jet
SSA of di-jet
PDF : GRV98polarized PDF : GRSV2000
Single-spin asymmetry of di-jet
SSA of charm di-jet
PDF : GRV98polarized PDF : GRSV2000
Single-spin asymmetry of di-jet
SSA of charm di-jet events & the charge of charm can be determined
PDF : GRV98polarized PDF : GRSV2000
Summary and outlook
Summary
L L
L
• q, q of light flavor A of W bosons A of di - jet
• W from di- jet significance is not good W from charm di- jet improve significance
• A of pure W signal is large with
L
L
GRV98 & GRSV2000
• A of di- jet is too small, not very hopeful large background
• A of charm di- jet improve significance 4 times hopeful, need further work
Summary and outlook
Outlook
0L
L
• Contribution of Z bosons ( production and A )
• Detail study of QCD background ( different sub process )
• Behavior in different resolution and acceptance
• A with other polarized PDF
• Kin tematic and topological cuts ( E , , etc. )
• Comparison between leptonic channel and hadronic channel
Why DLL of (anti-)lambda in STAR?
P is more sentive to s model
0 0
0 0
p p H X p p H X
LL
p p H X p p H X
D
f D
Longitudinal spin transfer in polarized proton-proton collisions:
Pol. frag. func. model
models s
Q. X, E. Sichtermann, Z. Liang, PRD 73,2006
GeV 8
GeV 200
Tp
s
Theory prediction on polarization of anti-lambda in RHIC energy:
into LL
D may give new insights s at high pT
P is more sentive to s model
<pT> ~ 1.3 GeV <|xF|> ~ 0.0075
Data sample:
Minbias data from run 2005 About 3M events
Kinetics range:
Qinghua Xu for STAR
Jet define algorithms:
Kt algorithms and cone algorithms
See Salam’s talk
RHIC : Relativistic Heavy Ion Collider
STAR : The Solenoidal Tracker at RHIC
TPC : time projection chamber
EMC : E-M calorimeter