HYPERNUCLEI

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HYPERNUCLEI
Postgraduate seminar

• Author Luka Debenjak
• Adviser doc. dr. Simon Širca

University of Ljubljana Faculty of mathematics
and physics
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Contents

• Introduction
• The baryon-baryon interaction
• Production of the hypernuclei
• The hypernuclear g-ray spectroscopy
• Weak decays of hypernuclei
• The (e,eK ) setup at MAMI
• Conclusion

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Introduction
First hypernucleus found in photoemulsions by
Danysz and Pniewski (1952)
p cosmic ray A nucleus f track of
hypernucleus B decay of hypernucleus Identified
reaction
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Introduction

• Hypernucleus nucleus with A and Z with one or
  more hyperons
• Hyperons (Y) baryons with strangeness
• p, n, Y distinguishable particles
• placed in independent potential
• well with Pauli exclusion principle
• Shell model
• Produced hypernucleus can be in an excited state
• Hypernucleus in its ground state the hyperon
  occupies the lowest shell (1s)

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The 3D nuclear landscape
Double L-hypernuclei S-2 Studied with
Single L-hypernuclei S-1 Studied with
Ordinary nuclei with protons and neutrons S0
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The baryon-baryon interaction

• Why study hypernuclei
• hyperon inside nucleus as a unique probe of
  nuclear interior
• enables us to study direct baryon-baryon or
  meson-baryon interactions

• Difficult to study the YY and NY no hyperon
  beams and targets
• Hypernuclei as a
  micro-laboratory for YY and NY interactions

Hypernucleus nuclear core with hyperon in
hyperonnucleus effective potential
V(r) Gaussian shape, depend on the model
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Radial integrals of two-body matrix elements
Parameters depend on the model of and
Once the potential (parameters) is set
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Hypernuclear spectroscopy
Reaction is identified by reaction products
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Production of the hypernuclei

• Strangeness exchange reaction, a)
• Associated production reaction, b)
• Photo-production
• Electro-production, c)

Low recoil momentum hyperon bound inside the
nucleus
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The (e,eK ) reaction

• Excellent energy resolution
• Well described by first order
• perturbation calculation
• (one photon exchange)

Experiments done under small angles
Two spectrometers are needed for e and K at
extremely forward angles
Excellent trajectory reconstruction and particle
identification
Excellent resolution of the energy spectrum
Jefferson Lab, MAMI,
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An example of excitation energy
spectrum
Best fit solid line Theory dashed line
Ls, Lp after replacing s- or p-shell
proton
Hard to distinguish the finer structure! g-ray
spectroscopy
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The hypernuclear g-ray spectroscopy
Energy released by neutrons or protons or g-rays
when Y lower shells Limited up
to the L p-orbit!
The region of high excitation energy in
hypernuclei can not be explored with g-ray
spectroscopy
Excellent resolution with Ge detectors (Hyperball)
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An example of the g-ray spectroscopy of
Small spacing in twin peaks spin dependent YN
Contribution to the energy spacings
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Weak decays of hypernuclei
Strangeness, isospin, parity, are not conserved.
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The (e,eK ) setup at MAMI

• At MAMI spectrometer Kaos is used
• Bmax 1.95 T pmax 1.6 GeV/c
• pmax/pmin 2
• Trajectories measured by
• MWPCs
• Time of flight and trigger information
• segmented scintillator array
• High momentum particle identification (p /K
  separation)
• aerogel threshold Cerenkov detector
• Electron detection
• Scintillation fibres with MAPMT read-out

double spectrometer
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2 TOF Walls
Cerenkov detector (prototype)
2 MWPCs
Fibre detector
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Conclusion

• The main properties of the hypernuclei physics
  was shown, mostly L-hypernuclei
• Hyperon as a deep nuclear probe for NN, YN, YY
  interactions
• Studied by
• production mechanisms (small recoil momentum)
• g-ray spectroscopy (limited up to the L p-orbit)
• Effective potential as a function of five
  parameters

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• Thank you
• happy holidays