SCALING LAW in single charged pion electroproduction

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SCALING LAW in single charged pion
electroproduction

• Weekly Report (Jul.17, 2006)

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Analysis procedures

• GSIM-GENOVA-EG ( single channel np )
• GSIM-GENEV (single, multi-pion channels)

• Based on EvntGen with Rad. effect on/off

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Analysis procedures

• single chan. currently GSIM evnt 200M
• single, multi-pion chan. REC evnt 81M

• Single chan. Rad effect on/off

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Impact of BG under mmx by misidentification
Q) BG contribution can be large due to
misidentification pion at p gt 2GeV ?
In the resonance region (Wlt1.8GeV,
Q21.874.52GeV2) Under 2.5s cut of ß BG
2
2.5s
ph
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Impact of BG under mmx by misidentification
Q) BG contribution can be large due to
misidentification pion at p gt 2GeV ?
In the resonance region (Wgt1.8GeV,
Q21.874.52GeV2) Under 2.5s cut of ß BG
1
2.5s
ph
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Missing mass
Missing mass distribution as function of Xbj at
fixed Q2, -t
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MMx plots in terms of Q2, pp
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BG Distribution
Q2 2.65GeV2 , -t 1.01.3GeV2 , Xbj 0.160.7
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BG subtraction

• Better understanding of background distribution
• Background contribution from particle
  misidentification at high momentum range (p gt
  2GeV) , and high W gt1.8GeV is small
• Apply the single gaussian function to describe
  the high mass
• Front tail from fit function would be a good
  description of BG contribution under neutron mass
  peak
• Only neutron signal and radiative effect are
  survived no fitting is necessary
• Systematic uncertainty check in cross section
  level among no cut, constant cut, 2rd order pol.
  function cut, gaussian cut for high mass (under
  way)

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Neutron mass

• How can we be free from background ? Detect the
  neutron directly on EC
• How we can separate between ? , n precisely ?
• Generally, we used the rough ß cut at the first
  time
• If we used very thin target, do we have better
  chance to separate the ?/n on ß distribution ?
• Do we have better understand neutron detection
  property from ß distribution ?
• How can we get better ß distribution to separate
  ?/n ?
• Better distance, timing resolution due to thin
  target ?

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Vertex distribution
1) Vertex distribution from LH2 target
2) Vertex distribution from empty target

• Choose the target window (left) as thin target
• Apply 3s cut of vz of electron
• Apply the constraint of vertex xy plane

-0.01ltvxlt0.19cm
-0.44ltvylt-0.24cm
-7.59ltvzlt-6.26cm
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E1-6 target
? Target materials
? Empty target Runs Run 30825, 30962, 31104, Run
31128, 31252, 31254, Run 31300, 31344
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Possibility of ?/n separation

• Distance from thin target to EC plane

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Possibility of ?/n separation
EC geometry
Inner 5 layers x 3(UVW) Outer 8 layers x
3(UVW)
Each layer BC 412 10.0mm Lead 2.2mm
? Inner dl 18.3 cm ? Outer dl 48.3 cm
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Possibility of ?/n separation

• The ß distribution

c1