DIS-09, Madrid 1
Longitudinal polarization of and in DIS at COMPASS
M.G.Sapozhnikov
Joint Institute for Nuclear Research, Dubna
On behalf of the COMPASS Collaboration
DIS-09, Madrid 2
Physical motivation
Longitudinal polarization of and in DIS is sensitive to:
• s(x), s(x)• polarization of strange quarks s
spin structure
)]()()()([ xsxsxsxsdxs
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production in DIS, quark fragmentation
•
Spin transfer from polarized quark
Quark fragmentation
Spin transfer from polarized muon
spin structure
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spin structure• SU(6) quark model: s = 1, u = d = 0
100% polarization to u or d quarks is no influence on polarization of P() - 0 (for u –quarks dominance)
• Burkardt-Jaffe: u = d = -0.23 P() – negative
• B.Q.Ma et al.: u = d =s
P() – positive • Lattice calculations: u = d ~0, s=0.68 P() ~ 0
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• Production and is mainly due to fragmentation of target remnant and u,d-quarks
• Spin transfer to and is mainly due to interaction with strange quark and antiquark
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COMPASS Detector
160 GeV µ+ beam
2.8 . 108 µ/spill (4.8 s)
Polarizedtarget
SM1Drift. Ch. RICH
ECal1 & HCal1
Muon filter 1
SM2
MWPCs
Micromegas
ECal2 & HCal2
Muon filter 2
GEM & MWPCsSciFi
GEM & MWPCs
GEM & Straws
SiliconSciFi
Scintillatingfibers
Beam
LAS
SAS
Pb = -0.760.04 - 2003Pb = -0.800.04 - 2004
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Polarized 6LiD target (2002-2004)
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Production of ()
p
Xd
No PID used
p
Xd
S
S
K
XKd
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Event selectionp
-
+
’+
•Primary vertex: in the target •Secondary vertex: 5 cm downstream the
target• pT > 23 MeV/c• < 0.01 rad•Q2 >1 (GeV/c)2
• 0.2<y<0.9
V1
V2
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Comparison with other experiments
N() N()
E665 750 650
NOMAD 8 087 649
HERMES, 1996-2000
7 300 1 687
RHIC 30 000 24 000
COMPASS, 2003,2004
70 000 42 000
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<xBj> = 0.05
<xF> = 0.23
<y> = 0.46
<Q2>=3.31 GeV2
Good agreement between data and MCM.Sapozhnikov, JINR
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<xBj> = 0.050
<xF> = 0.22
<y> = 0.48
<Q2>=3.27 GeV2
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Longitudinal polarization PL
=+(-)0.642 ±0.013 - () decay parameter
P - polarization vector
k - unit vector along the decay proton momentum
L-axis - along the momentum of virtual
photon
)1(4
kPN
d
dN tot
)cos1(2
1
cos
1
L
obs
obstot
Pd
dN
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Determination of the angular distribution:
• sidebands subtraction
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Angular distributions of and (run 2004)
Acceptance correction – using unpolarized MC
P(K0)=0.011±0.005
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Longitudinal spin transfer DLL
PL = DLL Pb D(y)
Pb – beam polarization, D(y) – depolarization factor
2
2
)1(1
)1(1)(
y
yyD
DLL’ - polarization of the struck quark along the axis L is transferred to the along the secondary axis L’
In our case: L=L’
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Comparison of and : x
DLL() DLL()
DIS-09, MadridThe results are averaged over target polarization
DLL() = -0.012 ± 0.047 ± 0.024
DLL() = 0.249 ± 0.056 ± 0.049
Preliminary
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Comparison of and : xF
The results are averaged over target polarizationDIS-09, Madrid
PL: dependence on the target polarization
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P= P--P+ =-0.010.04, = 0.010.05, DIS-09, Madrid
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Comparison with other experiments :
Preliminary
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Comparison with other experiments :
Preliminary
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Theory predictions for and
J.Ellis et al., Eur.Phys.J. C52 (2007) 603
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Preliminary
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Theory predictions for and
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Preliminary
J.Ellis et al., Eur.Phys.J. C52 (2007) 603
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Sensitivity to the strange distribution s(x)
CTEQ5L
GRV98
DLL(s)=0, BJ model
DLL(s)=0, SU(6) model
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Sensitivity to the strange distribution s(x)
CTEQ5L
GRV98
DLL(s)=0, BJ model
DLL(s)=0, SU(6) model
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Conclusions• Preliminary results on and spin transfer in DIS are
obtained on statistics 70000 and 42000 • DLL() DLL()
• DLL() ~ 0
• DLL() may be as large as 0.4-0.5
• First measurement of the () polarization for different target polarization. No significant dependence is found.
• Comparison with theory:– Spin transfer to is sensitive to s(x)
• Present statistics is only 25% of already accumulated.
More interesting things are coming.
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Backup slides
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• Influence to different PDF’s
Q2 = 4 GeV2
CTEQ5L
GRV98LO
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Polarization of from quark fragmentation
)()]()()([
)()]()()([2
2
zDxqyDPPxqe
zDxqPxqyDPeP
qTbqq
qTbqq
Spin transfer from polarized muon
Spin transfer from polarized quark
qqq DDD qqq DDDDIS-09, Madrid M.Sapozhnikov, JINR
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Polarization of : PT =0
)()(
)()()(2
2
zDxqe
zDxqyDPeP
qqq
qbqq
)()(
)()(
9
12 zDxqe
zDxsD
qqq
sLL
)()(
)()(
9
12 zDxqe
zDxsD
qqq
sLL
;0 du DD ;0
du DD
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DLL() > DLL()
)()(
)()(
9
12 zDxqe
zDxsD
qqq
sLL
)()(
)()(
9
12 zDxqe
zDxsD
qqq
sLL
Even if s(x)=s(x),DLL() > DLL() due to difference of the denominator:
Du,d() > Du,d()
Independent quark fragmentation: •DLL() > DLL()•Sensitivity to s(x)Are these conclusions still valid in a more advanced model?DIS-09, Madrid M.Sapozhnikov, JINR
Spin transfer from polarized quark to
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ssZee 0
91.0sPPolarized quarks, indeed, transfer the polarization to .
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Impact of LEP data
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D. de Florian, M.Stratmann, W.Vogelsang, PRD 57(1998)5811
1- SU(6)2 – BJ3 - u = d =s
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Theory predictions for /• Liang Zuo-tang et al. Phys.Rev.D72 (2005) 033006
-0.6 0 0.6 xFDIS-09, Madrid M.Sapozhnikov, JINR
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Transverse polarization PY
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- between virtual photon and p in c.m.s.
• Kaon background is important at large cos
• cut
-1 < cos <0.6
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