Semiinclusive L polarization study at CLAS

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Semi-inclusive L polarization study at CLAS

• Marco Mirazita
• I.N.F.N. Laboratori Nazionali di Frascati

For the CLAS Collaboration
International Workshop on Strangeness
polarization in semi-inclusive and exclusive L
production Trento, 27-31 October, 2008
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The nucleon spin
NAÏVE PROTON SPIN SUM RULE
experiments
Need for more contributions

• Valence quark angular momentum ?
• - measured in exclusive reactions (DVCS, DVMP)
  through GPDs and the Jis sum rule
• - small?

• Gluon spin ?
• - several measurements (SMC, HERMES, COMPASS,
  RHIC)
• - indication that the net size is small

• Sea quark angular momentum ?
• - DIS experiments (COMPASS, HERMES) Ds ? -0.1
• - analysis of SIDIS data (HERMES) Ds ? 0 within
  errors

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Why polarized L ?
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Lepton-nucleon scattering
e p ? e L X
For exclusive channels X K, K(892), .
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Measuring the L polarization
Proton yield with polarized L
Parity-violating weak decay amplitude ?
asymmetry in the proton angular distributions
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Exclusive or inclusive L?
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A model for polarization transfer
lepton-nucleon scattering
Quantitative predictions in the Intrinsic
Strangeness Model Ellis et al., EPJ C52,283(2007)

• What happens for strongly correlated final
  states as for L K?
• Will the connection between s and L spin be
  spoiled?
• What for different final mesons?

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Jefferson Lab - Newport News, USA
Continuous Electron Beam Accelerator Facility
Imax 200 mA Duty Factor 100 sE/E 2.5
10-5 Beam Pol 80 L 1034 cm-2 s-1
Emax 6 GeV
Hall B

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The CLAS detector

• Toroidal magnetic field (6 supercond. coils)
• Drift chambers (argon/CO2 gas, 35000 cells)
• Time-of-flight scintillators
• Electromagnetic calorimeters
• Cherenkov Counters (e/p separation)

• Performances for charged particles
• large acceptance
• 8ltqlt142 in LAB frame
• 60-80 of f
• good momentum and angular resolution
• Dp/p 0.5- 1.5,
• Dq 1 mrad
• Df 4 mrad

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The e1f experiment at CLAS

• data taken in april-july 2003
• beam energy E5.5 GeV
• beam current 7 nA
• target liquid H2 L 5cm
• average beam polarization PB 0.74 0.03
• number of triggers (e- X) 200 billions
• integrated luminosity L 2.1 1039 cm-2 21
  fb-1
• torus field 1.5 T m (forward)
• acceptance for charged particles
• p(e-) gt 0.5 GeV/c
• p(p) gt 0.3 GeV/c
• p(p-) gt 0.1 GeV/c

PRELIMINARY RESULTS FROM 15 OF THE STATISTICS
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Event Display
SECTOR 6
SECTOR 4
EC
SC
CC
DC3
DC2
DC1
SECTOR 3
SECTOR 1
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Event Display
SECTOR 6
SECTOR 4
EC
SC
CC
DC3
DC2
DC1
SECTOR 3
SECTOR 1
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Particle ID

• Track reconstruction in DC
• b measurement with TOF scintillators

log-z axis
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e/p rejection
measured b
electrons
pions
log-z axis
P GeV/c
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Electron vertex
Vz(electron) cm
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Event Selection e p p- X
electrons
protons
P GeV/c
p-
qLAB deg
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Inclusive e p p- events

• e p p- X events
• electron cuts
• p(e) gt 0.8 GeV
• Vz(e) cut

15 of the full statistics
Missing Mass GeV/c2
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L selection

• e p p- X events
• electron cuts
• p(e) gt 0.8 GeV
• Vz(e) cut

M 1115.90.1 s 1.16 0.02
IM(p p-) GeV/c2
15 of the full statistics
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Inclusive L events

• e p p- X events
• electron cuts
• p(e) gt 0.8 GeV
• Vz(e) cut
• L cuts

Missing Mass GeV/c2
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DIS Cuts L X events
W2 GeV2
Q2 GeV2
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Inclusive DIS L events

• e p p- X events
• electron cuts
• p(e) gt 0.8 GeV
• Vz(e) cut
• L cuts
• DIS cuts

• exclusive K dominating in the CLAS kinematics
• clear signal of K(892)

Missing Mass GeV/c2
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Kinematics distributions DIS LX events
Q2 gt 1 GeV2 W gt 2 GeV MM gt 0.6 GeV/c2
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Kinematic distributions
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Polarization measurement in CLAS

• CLAS electron beam
• average polarization PB 0.74 0.03
• beam helicity flip rate 30 Hz

• acceptance effects largely cancel in the ratio
• fast beam spin flip ensures that possible
  detector response unstability affects in the same
  way N and N-

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Fitting the L yield vs xF
IM(p p-) in xF binning

• e p p- X events
• electron cuts
• p(e) gt 0.8 GeV
• Vz(e) cut
• DIS cuts
• MM cut
• no helicity separation

Target fragmentation xF lt 0 Current
Fragmentation xF lt 0
15 of the full statistics
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Fitting the L yield vs MM
IM(p p-) MM binning

• e p p- X events
• electron cuts
• p(e) gt 0.8 GeV
• Vz(e) cut
• DIS cuts
• no helicity separation

Different final state contributions can be
selected
15 of the full statistics
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Fitting the L yield vs zL
IM(p p-) zL binning

• e p p- X events
• electron cuts
• p(e) gt 0.8 GeV
• Vz(e) cut
• DIS cuts
• MM cut
• no helicity separation

lower zL ? more target fragmentation
15 of the full statistics
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Projected results
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Systematic studies - BKG
Two possible options
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Systematic studies detector acceptance
Non uniform detector response can produce false
asymmetries in the decay proton angular
distributions

• Monte Carlo simulation of SIDIS L events
• - no asymmetry is generated ? no asymmetries
  must be reconstructed

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Systematic studies - MC

• - LEPTOLUND event generator for SIDIS
• - GEANT based simulation of the CLAS response
• check that no asymmetries are produced in the
  reconstructed events
• asymmetry from acceptance-corrected yields

Good agreement CLAS is in the DIS regime
e L X events
histogram MC points data
Relative weight of LK has to be tuned
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Systematic studies detector acceptance
Non uniform detector response can produce false
asymmetries in the decay proton angular
distributions

• Monte Carlo simulation of SIDIS L events
• - no asymmetry is generated ? no asymmetries
  must be reconstructed

• Study K0 SIDIS electroproduction
• - the Kaon has spin 0 ? no asymmetries must be
  found

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Systematic studies K0
e p ? e p p- X events

• similar experimental acceptance

• higher BKG but factor 2 more statistics

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Conclusions