Longitudinal ? and ?? polarizations in DIS at COMPASS

1
Longitudinal ? and ?? polarizations in DIS at
COMPASS

• M.G.Sapozhnikov
• Joint Institute for Nuclear Research, Dubna
• On behalf of the COMPASS Collaboration

2
Physics motivation

• ? production in DIS, target fragmentation
• Polarized strangeness model
• J.Ellis, D.Kharzeev, A.Kotzinian, Z.Phys. 1995,
  C65, 189
• Large negative longitudinal polarization was
  predicted

3
Strangeness of the vacuum

• The vacuum strange quark condensate is as large
  as the light quark condensate
• Ioffe B.L., Nucl.Phys. 1981, B188, 317, erratum
  1981, B191, 591.
• Reinders L.J., Rubinstein H.R., Phys.Lett., 1984,
  B145, 108.

4
Strangeness of the nucleon

• S.Brodsky
• Extrinsic connected with gluons perturbative
• Intrinsic connected with valence quarks
  nonperturbative
• The strange quarks contribution in the nucleon
• could be small or large, depending on the matrix
  element
• Ioffe B.L., Karliner M., Phys.Lett., 1990, B247,
  387
• Small vector, tensor
• Large scalar, pseudoscalar, axial vector

5
Strangeness of the nucleon small

• Momentum fraction Ps 4 at Q220 GeV2
• (CCFR)
• Electric and magnetic form factors at Q20.48
  (GeV)2 (HAPPEX)
• GE 0.39 GM 0.025 ?0.020 ? 0.014
• Contribution to the nucleon magnetic moment is
  -0.1 ? 5.1 (SAMPLE)

6
Strangeness of the nucleon large

• Scalar part
• Old ?N data y0.2?0.2
• Lattice y0.36 ?0.03
• Recent ?N data y0.36-0.48
• (Meissner U.-G., Smith G., hep-ph/0011277)

7
Strangeness of the nucleon axial-vector part

• Inclusive DIS
• Semi-inclusive DIS, positive polarization of the
  strange sea
• HERMES, hep/ex-0307064
• criticism of the procedure A.Kotzinian.
  Phys.Lett. B552 (2003) 172
• E.Leader, D.Stamenov PRD67 (2003) 037503
• non-negative polarization is almost impossible

8
Polarization of nucleon strangeness

• Sz-1

9
Polarized intrinsic strangeness model

• J.Ellis, M.Karliner,D.Kharzeev, M.Sapozhnikov,
  Phys.Lett., 1995, v.B353 , p. 319 Nucl.Phys.
  A673 (2000) 256
• antiproton annihilation at rest, predictions
  for NN
• M.Alberg, J.Ellis, D.Kharzeev, Phys.Lett. 1995,
  B356, 113
• Spin transfer Dnn in
• J.Ellis, D.Kharzeev, A.Kotzinian, Z.Phys. 1995,
  C65, 189
• J.Ellis, A.Kotzinian, D.Naumov , Eur.Phys.J. C25
  (2002) 603
• Longitudinal polarization of ?-hyperons in DIS
• For recent review V.P.Nomokonov,
  M.G.Sapozhnikov,
• hep-ph/0204259, 2002,
• Phys. of Elementary Particles and Atomic
  Nuclei, 34 (2003) 184

10

• production in DIS, target fragmentation
• NOMAD Collaboration
• Nucl. Phys. B588 (2000) 3
• Nucl. Phys. B605 (2001) 3
• D.Naumov, COMPASS data analysis at Dubna, 2003

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? production in DIS, current fragmentation

• NQM no spin transfer from u,d quarks to ?
• Cu(?) 0 , Cs(?)1, P(?) 0
• M.Burkardt,R.Jaffe
• Cs(?)0.6, Cu(?)-0.2
• P(?) -0.22
• Phys.Rev.Lett. 70 (1993)2537
• HERMES
• S(?) P(?)/Pb D(y) 0.11 0.17 0.03

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? production in DIS, current fragmentation - 2

• J.Ellis, A.Kotzinian, D.Naumov no spin transfer
  from any quark,
• ? is from the diquark fragmentation
• P(?) (-0.004) (-0.073)
• for COMPASS kinematics
• Eur.Phys.J. C25 (2002) 603

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COMPASS Detector
SAS
Muon filter 2
MWPCs
ECal2 HCal2
LAS
SM2
Muon filter 1
ECal1 HCal1
GEM MWPCs SciFi
RICH
Drift. Ch.
SM1
Silicon SciFi
GEM MWPCs
Scintillating fibers
GEM Straws
Beam
Micromegas
Polarized target
2002 run 160 GeV µ beam 2.8 . 108 µ/spill (4.8
s)
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Polarized 6LiD target
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Data taking in 2002 run

• 260 TB data, 5?109 events
• Present results are from 4 weeks of 8 of the 2002
  run
• Averaged on the target polarization
• No PID for ?
• Pb -0.75?0.02

16
Events selection
?
V1
p
V2
?

?
?-

• Cuts
• Primary vertex in the target
• Secondary vertex
• zgt35 cm or Dgt6??D
• pT gt 23 MeV/c
• ? lt 0.01 rad
• Q2 gt1 (GeV/c)2
• 0.2ltylt0.8

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• Comparison of experimental data with the MC for
• momenta of V0
• ltp?gt ? 12 GeV/c
• ltp?gt ? 2 GeV/c

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• COMPASS kinematics
• ltxFgt ? 0.21
• ltQ2gt ? 1.9 (GeV/c)2
• ltxBjgt ? 0.02

19
Experimental data
N(?) N(??)
E665 750 650
NOMAD 8087 649
HERMES, 1996-2000 10568 1687
COMPASS 10800 5900
20
Two vertex cuts and two methods of analysis

• Vertex cuts
• Zgt35 cm cleanest sample
• Ratio B/S 12
• Dgt6?D largest sample
• Ratio B/S 25
• Analysis methods
• sidebands subtraction
• bin-by-bin fitting

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• Sidebands subtraction
• Width of the region - 2?

22

• Bin-by-bin fit of the invariant mass
  distributions of (p?-) in different bins in cos ?x

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nX e? nY e? ? et nZ nX ? nY
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• Conclusions
• Clear demonstration of the COMPASS potential for
  study of ? production in DIS
• Only 4 weeks of data taking
• Longitudinal polarization of ? and?? are small
  and similar.