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Postgraduate seminar. HYPERNUCLEI. Author: Luka Debenjak Adviser: doc. dr. Simon Širca. University of Ljubljana Faculty of mathematics and physics. Contents. Introduction The baryon-baryon interaction Production of the hypernuclei The hypernuclear g -ray spectroscopy

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Hypernuclei

Postgraduate seminar

HYPERNUCLEI

Author: Luka Debenjak

Adviser: doc. dr. Simon Širca

University of Ljubljana

Faculty of mathematics and physics


Contents
Contents

  • Introduction

  • The baryon-baryon interaction

  • Production of the hypernuclei

  • The hypernuclear g-ray spectroscopy

  • Weak decays of hypernuclei

  • The (e,e’K) setup at MAMI

  • Conclusion

Hypernuclei


Introduction
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:

Hypernuclei


Introduction1
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)

Hypernuclei


The 3D nuclear landscape

Double L-hypernuclei

S=-2

Studied with

Single L-hypernuclei

S=-1

Studied with

Ordinary nuclei with protons and neutrons

S=0

Hypernuclei


The baryon baryon interaction
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 hyperon–nucleus effective potential

V(r): Gaussian shape, depend on the model

Hypernuclei


Radial integrals of two-body matrix elements

Parameters depend on the model of and

Once the potential (parameters) is set:

Hypernuclei


Hypernuclear spectroscopy
Hypernuclear spectroscopy

Reaction is identified by reaction products

Hypernuclei


Production of the hypernuclei
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

Hypernuclei


The e e k reaction
The (e,e’K) reaction

Experiments done under small angles

  • Excellent energy resolution

  • Well described by first order

    perturbation calculation

    (one photon exchange)

Two spectrometers are needed for e’ and K at extremely forward angles

Excellent trajectory reconstructionand particle identification

Excellent resolution

of the energy spectrum

Jefferson Lab, MAMI,…

Hypernuclei


An example of excitation energy spectrum
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

Hypernuclei


The hypernuclear g ray spectroscopy
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)

Hypernuclei


An example of the g ray spectroscopy of
An example of the g-ray spectroscopy of

Small spacing in twin peaks: spin dependent YN

Contribution to the energy spacings:

Hypernuclei


Weak decays of hypernuclei
Weak decays of hypernuclei

Strangeness, isospin, parity, are not conserved.

Hypernuclei


The e e k setup at mami
The (e,e’K ) 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 Čerenkov detector

  • Electron detection:

    Scintillation fibres with MAPMT read-out

double spectrometer

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2 TOF Walls

Čerenkov detector (prototype)

2 MWPCs

Fibre detector

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Conclusion
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 Lp-orbit)

  • Effective potential as a function of five parameters:

  • Hypernuclei


    Thank you

    &

    happy holidays

    Hypernuclei


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