HYPERNUCLEI AT PANDA PerErik Tegnr, Stockholm University

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HYPERNUCLEI AT PANDAPer-Erik Tegnér, Stockholm
University

• Hypernucleus A nucleus with a bound hyperon
• Hyperon baryon with strangeness (-1, -2 or -3)
• The ? hyperon strangeness -1, spin ½,
• isospin 0, mass 1116 MeV/c2

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• Extension of the nuclear chart in a new
  dimension, strangeness S

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First hypernucleus discovered 51 years ago,
cosmic rays in nuclear emulsion
Now production reactions of S-1 hypernuclei
Primary interaction at A Created fragment
f Fragment decay at B Into three charged particles
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High-resolution production of ? hypernucleus
states
An example, 89?Y at KEK (Japan), resolution
?E1.65 MeV (Hotchi et al, PRC 64 (2001) 044302
A text book demonstration of the nuclear shell
model (no states are forbidden for ? due to the
Pauli principle)
1f

• - N strong interaction?
• One pion exchange does not contribute
• Spin-orbit splitting?

1d
1p
1s
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High-precision gamma-ray spectroscopy
Example 7?Li (6Li and a ?) produced in KEK
E419 experiment
Four transitions identified, excited states of
the 6Li core
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Medium effects!! B(E2 5/2?1/2) 1/3 of B(E2)
in 6Li May be interpreted as a shrinkage of the
6Li core by 20 (density increase by a factor of
2)
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The decay of a ? hypernucleus
Weak decay
The baryon baryon weak interaction!
at least in heavier nuclei
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Double hypernuclei (S -2)
Only six(?) ?? hypernuclei known
New physics (in addition to S -1
physics) Baryon baryon forces in the ? - ?
channel Search for the H particle (six-quark
system uuddss) Composition of neutron stars
Challenges Abundant production of ?? hypernuclei
is difficult Identification of produced system
is problematic ?-ray measurements in coincidence
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At PANDA, high production rate in antiproton
annihilations

In primary target
In secondary target, e.g. Li, Be, B, C
and
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Expected rates
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Germanium detectors at PANDA
Challenges for high-resolution ?-ray spectroscopy
with germanium detectors Operated in a high
magnetic field, B 2T Large hadronic
background Resolution of 3 5 keV desirable
(implies high granularity)
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Present activities (within the HadronPhysics EU
project) Stockholm University and Royal Institute
of Physics (Bo Cederwall et al) Investigation of
germanium detector properties in magnetic
fields Use of pulse shape analysis Pilot study
at DAPHNE (Frascati), single hypernucleus studies
Test of a Euroball cluster detector at GSI in a
magnetic field Three crystals (C, D, F)
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More possibilities production of ?- atoms!
One topic
? has J3/2, hyperfine splitting of the atomic
states ?electric quadrupole moment?
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CONCLUSION
Studies of hypernuclei hadron physics and
nuclear structure physics
TOPICS

• Shell model for hyperons
• The strong ?N and ?? interaction
• The four-baryon weak interaction
• Six-quark states the H particle
• Medium effects the properties of hyperons in
  nuclear medium
• Medium effects the response of the medium to the
  presence of hyperons
• Cosmological objects

TECHNIQUES

• High production yield antiprotons at HESR
• Detection and identification of hadrons PANDA
• High-resolution gamma-ray spectroscopy segmented
  germanium detectors