longitudinal polarization of and in dis at compass
DESCRIPTION
Longitudinal polarization of and in DIS at COMPASS. M.G.Sapozhnikov Joint Institute for Nuclear Research, Dubna On behalf of the COMPASS Collaboration. Physical motivation. Longitudinal polarization of and in DIS is sensitive to: s(x), s(x) polarization of strange quarks s - PowerPoint PPT PresentationTRANSCRIPT
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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
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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
NM.Sapozhnikov, JINR
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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
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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
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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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