Analysis of Hydrogen Data from CLAS Hall B at JLab

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Analysis of Hydrogen Data from CLAS Hall B at
J-Lab

• Early Methods of Particle Identification

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Kinematics of Electron Scattering
Scattered Electron, 4-momentum p-prime (measured)
This is a diagram of the process that occurs in
electron scattering experiments.
Beam Electron, 4-momentum p Here energy 4.462
GeV
Angle Theta (measured)
Target (nucleon) proton for hydrogen target
(stationary)
Products of Scattering- Invariant Mass W
(calculated)
The interaction takes place via the exchange of a
virtual photon of momentum q and energy nu.
These quantities are found by subtracting the
scattered electrons 4-vector from the incident
electrons 4-vector. Addition of the resulting
4-vector to the target 4-vector gives the
4-vector of the outgoing products, from which
their invariant mass W of the products may be
calculated.
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Previous Cuts

• Sampling Fraction Cut
• Inner EC Cut
• Y-Value Cut
• Z-Vertex Cut
• Time Of Flight Cut

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EC Fiducial Cut

• We already require electrons to register in the
  electromagnetic calorimeter. The edges of the
  calorimeter are regions of nonuniform acceptance,
  so they are cut away.

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EC Fiducial Cut Graphs
Before After
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CLAS Fiducial Cuts

• General fiducial cuts are also made to exclude
  particles found in regions of the CLAS detector
  too near the sector boundaries and cryostats.

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CLAS Fiducial Cuts e-
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CLAS Fiducial Cuts p
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CLAS Fiducial Cuts pi-plus
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CLAS Fiducial Cuts pi-minus
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Momentum Corrections
Kinematic corrections have been made to the data.
The package used was developed specifically for
the hydrogen data that we are analyzing it is
the PittsMomCorr package in the CLAS software.
We have no better set of corrections for the
carbon data, so we are using the same package
the experimental setup was fairly similar, and
beam energy and torus current the same, so this
is acceptable for now.
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Momentum Corrections for Hydrogen
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Momentum Corrections for Carbon
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W Values H2 vs. C.Why the difference?
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Q2 H2 versus C.Dotted Line Hydrogen, Solid
Line Carbon
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Missing Mass Squared resonance e, pSolid Line
Hydrogen, Dotted Line Carbon (note change)
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Missing Mass Squared resonance e, pi-plus Solid
Line Hydrogen, Dotted Line Carbon
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Missing Mass Squared resonance e, p, pi-plus
Solid Line Hydrogen, Dotted Line Carbon
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Missing Mass Squared resonance e, p, pi-minus
Solid Line Hydrogen, Dotted Line Carbon(note
lower stats)
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Further Questions

• Why the differences in W and Q2? Inelastic
  scattering? Nuclear effects?
• Why the smeared carbon missing mass plots,
  especially in ep?
• e/p/pi-minus missing mass vs. e/p/pi-plus missing
  mass similar in hydrogen, very different in
  carbon. Why?

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References

• D.Carman and B.Raue (Hyperon Electroproduction at
  CLAS, 2002).
• S.Stepanyan, correspondence.