Accessing Neutron Structure via BONUS Measurements of the Mirror Nuclei 3He 3H

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Accessing Neutron Structure via BONUS
Measurements of the Mirror Nuclei 3He /
3H Cynthia Keppel BONUSfest March 2005
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• I. R. Afnan, et al, PRC 68 035201 (2003),
  others
• Access F2n / F2p ratio from superratio of
  EMC-ratios F23He(H) / 2F2p(n) F2n(p), extract
  F2n / F2p ratio at 2 for x lt 0.85
• M.M. Sargsian et al, nucl-th/020503 (2002)
• Larger uncertainties expected in EMC effect,
  extract F2n / F2p ratio only at 12 for x lt 0.8
• JLab proposal for 6 GeV deferred by PAC 27, not
  high enough x, tritium target
• BONUS adds spectator tagging to reduce
  uncertainties
• Measure 3He, 3H, 3He/3H with tagged protons,
  deuterons
• Uses less tritium than proposed liquid, larger
  gas targets (2.2 mg for 10 cm x 4mm cylinder at
  7.5 atm - below DOE reportable limit)
• Still, get inclusive 3He/3H in CLAS

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3H possibilities
RTPC detects nothing, CLAS detects hard scatter
electron
n
n
n
n
n
p
p
p to RTPC
p
d to RTPC
n

• In all neutron target cases, detect spectator
  (except for RTPC acceptance, tracking efficiency,
  VERY low momentum protons, etc. - as with
  deuterium
• Just need to tag deuteron, dont need to
  differentiate from proton (more on this in a bit)
  - but, what if it breaks up? (need to look at
  momenta)
• Should not differ from deuterium measurement,
  check on technique plus additional information
  for wave function, EMC effect, etc.

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3He possibilities
RTPC detects 2 protons in coincidence
n
n
p
p
p
n
p
p to RTPC
p
d to RTPC
p

• In all cases, detect spectator(s) - except for
  RTPC acceptance, tracking efficiency, VERY low
  momentum protons, etc.
• Deuteron (p momentum) breakup question again,
  but here more likely due to Coulomb repulsion
• In this case, the answer is known from hydrogen
  measurements, so measurement provides excellent
  verification of BONUS technique (note deuteron
  easier) and data for 3He wave function studies

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Coulomb effects in 3He
Expect that the deuteron will often breakup due
to Coulomb repulsion between protons. The
Coulomb potential energy is 1.4 MeVfm, or 2.2
MeV per proton at a proton-proton separation of
dpp 1/3 fm. Breakup probability should depend
on fraction of time protons within 1/3 fm, ie the
protons nuclear wavefunction.
In an isospin symmetric world the difference in
deuteron/proton ratios from 3He and 3H should
depend entirely on proton nuclear wavefunction
in 3He!
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RTPC Penetration
GEANT model
Energy Deposited in each layer of material as
initial spectator momentum is varied.
60 MeV/c
70 MeV/c
80 MeV/c
D k He Cu k Cu
90 MeV/c
5 mm D2 gas 50 mm Kapton He... Field Plane RTPC
Gas GEMs, readout, etc.
100 MeV/c
110 MeV/c
120 MeV/c
Will measure 70 lt pproton lt 200 MeV/c
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Deuteron Eloss in RTPC
2.5 mm 4He gas 50 mm Kapton Dead Zone
(4He) Ground Plane (Al Mylar) Dead Zone (He
DME) HV Plane (Al Mylar) Sense Gas (He DME)
Higher minimum (100 MeV/c) momentum deuterons
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In conclusion

• Provides more information than proposed Jlab
  non-BONUS 6 and 12 GeV 3He / 3H experiments
• Less tritium safer, may be more acceptable to
  lab
• Need to pin down and elucidate where can help
  with A3 wavefunctions and other physics in
  addition to n/p at large x
• Provides nice verification of BONUS technique
  (proton from 3He should give hydrogen and neutron
  from 3H should give same answer as neutron from
  BONUS deuterium)
• But, at 6 GeV, still not at largest x