Hypernuclear g-ray spectroscopy via the (K-, p0) reaction

1
Hypernuclear g-ray spectroscopy via the (K-, p0)
reaction

• K. Shirotori
• Tohoku Univ.

2
Motivation

• Mirror hypernuclei
• Neutron-rich hypernuclei
• sd-shell hypernuclei

3
Mirror hypernuclei

• Charge symmetry breaking in hypernuclei
• ?Systematic data by precise measurement by g ray
  spectroscopy
• Target
• 4He 4LH ? 4LHe
• 12C 12LB ? 12LC

4
Neutron-rich hypernuclei

• 7LHe
• Disappearance of neutron-halo

Drastic B(E2) change
6He
7LHe
E2
Calc. by E. Hiyama
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sd-shell hypernuclei

• Even-even core hypernuclei
• Even-even core B(E2) transition 4? 2, 2?0
• ? Moment of inertia ErotI(I1)/2J

E(4)
4
E(4)/ E(2) 3.3 Rotation 2.0 Vibration
E2
E(2)
2
E2
Small Eg
0
Large Eg

• The energy of those transition has the
  information of the nuclear deformation/collectivit
  y.
• Energy spacing and B(E2) measurement
• ?Effects of L on the collective motion

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Even-even core hypernuclear production-Advantages
of the (K-, p0) reaction-

• (K-, p-) reaction (NCX)
• Difficult to produce hypernuclei with even-even
  core
• Direct 25Mg(10), 29Si(4.7) enrich target
• ?Hyperfragment (need unique identification method
  and how about DSAM difficulty ?)
• (K-, p0) reaction (SCX)
• Possible direct production
• ?Systematic study of 2?0 transition
• 23Na(23LNe), 27Al(27LMg), 31P(31LSi),
• 35,37Cl(35,37LS), 39K(39LAr), 45Sc(45LCa)

4?2?0 of core nuclei
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Experiment
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Past experiment BNL E907
NMS

• 12LB reaction spectroscopy via the (K-stop, p0)
  reaction
• NMS
• Neutral Meson Spectrometer
• Pre-shower BGO detector
• Shower tracking DC
• CsI calorimeter
• DEmass 2.2 MeV (12LB g.s)

p0 energy spectrum
M. W. Ahmed et al
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Requirements of the (K-, p0) reaction spectroscopy

• Mass resolution A few MeV _at_ E1E2
• Position resolution and Vertex resolution
• Energy resolution by measuring opening angle
• Doppler correction
• Angular selection
• qlt 5(DL 0) substitutional states ?
  Hyperfragment
• qgt 515(DL 1 or 2) bound states ?s, p,
  sd-shell
• Spin-flip cross section at large angles (q gt10)
• Good efficiency
• To keep large production rate (/beam) order of
  mb

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Detector type

• Size Beam momentum
• 0.9, 1.1, 1.5, 1.8 GeV/c ?
• Energy resolution
• Inorganic-scintillator CsI
• Position resolution
• With position detector ?
• Homogeneous inorganic-scintillator
• OR
• Inorganic-scintillator with position detectors

SCISSORS III _at_ LNS
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Beam momentum

• Large production
• 0.9 GeV/c or 1.8 GeV/c
• Spin-flip and non-spin-flip
• 1.1 GeV/c or 1.5 GeV/c
• ? K1.1 or K1.8 ?
• Deeply-bound for sd-shell K1.8
• Both NCX and SCX with spin-flip K1.1
• ?Both K1.1 and K1.8 are available.

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Acceptance of both two decay g rays

• No large difference by changing the beam momentum
• Hit position of two g rays are averaged within p0
  scattering angles.
• The size of detector cannot be optimized to each
  beam momentum.
• The detector can be used at both K1.1 and K1.8.

- 1.1 GeV/c - 1.5 GeV/c - 1.8 GeV/c
qlt10o
10oltqlt25o
g-ray hit position on the detector _at_
E1-E2/(E1E2) lt0.3 (1 m from the target, w/o
the angular correlation of the cross section)
Size 1000 mm1000 mm (with beam through hole)
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Detector thickness
Energy deposit of both two g rays from the p0 of
1.0 GeV/c.
15X0 280 mm

• The simulation shows that the thickness of
  detector is needed to be more than 20X0 by using
  the CsI crystal.
• CsI X0 18.6 mm
• The scattered p0 has large energy because the (K,
  p) reaction is the endoergic reaction.

20X0 370 mm
25X0 470 mm
30X0 560 mm
Thickness 300400 mm
35X0 650 mm
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Choice of detector type

• Large target size
• Wide scattering angle
• ?Homogeneous crystal colorimeter
• Shower Tracker ?(to determine the precise
  position)
• Pre-shower detector
• Converter BGO, PWO
• ? Tracker DC
• ? Calorimeter CsI
• Segmented target sandwiched by scintillation
  counter
• ?Need to study

Charge veto
Crystal
Hole
g
Hyperball-J (half)
g
SksMinusSks?
K-
50 cm
Rough setup figure
Cost of the crystal 1 cm3/5 ? 100 cm100
cm40 cm 4105 cm3 ? \ 2.4108 _at_ 1 \120
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Future plan

• Detector type selection
• Homogeneous crystal Vertex resolution ?
• Pre-shower tracker Efficiency ?
• Target segmentation
• Realistic simulation
• Vertex resolution
• Energy resolution
• Doppler correction
• Background estimate
• Trigger, DAQ ..

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Summary

• Purposes of g-ray spectroscopy via the (K-, p0)
  reaction
• Mirror hypernuclei Charge symmetry breaking
• neutron-rich hypernuclei Disappearance of
  neutron-halo
• sd-shell hypernuclei The effects of L on the
  collective motion
• Detector for the (K-, p0) reaction spectroscopy
• Both K1.1 and K1.5 can be available.
• Large CsI detector array a
• Need to study the experimental feasibility