HYPERNUCLEI

1. Postgraduate seminar HYPERNUCLEI Author: Luka Debenjak Adviser: doc. dr. Simon Širca University of Ljubljana Faculty of mathematics and physics

2. 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

3. 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

4. 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

5. 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

6. 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

7. Radial integrals of two-body matrix elements Parameters depend on the model of and Once the potential (parameters) is set: Hypernuclei

8. Hypernuclear spectroscopy Reaction is identified by reaction products Hypernuclei

9. 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

10. 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

11. 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

12. 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

13. An example of the g-ray spectroscopy of Small spacing in twin peaks: spin dependent YN Contribution to the energy spacings: Hypernuclei

14. Weak decays of hypernuclei Strangeness, isospin, parity, are not conserved. Hypernuclei

15. 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 Hypernuclei

16. 2 TOF Walls Čerenkov detector (prototype) 2 MWPCs Fibre detector Hypernuclei

17. 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

18. Thank you & happy holidays Hypernuclei