Recent Studies of Hypernuclei Formationwith Electron Beams at MAMI
Patrick AchenbachU Mainz
Sept. 2o13
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13P Achenbach, U Mainz
Theoretical calculationsCluster model, shell model, mean field…
Hypernuclear spectroscopy
Unique laboratory to investigate the YN interaction
Nuclear forceLarge base of NN
scattering data
Nuclear Structure
Normal / exotic nuclei
Hyperon forceLimited YN/YY scattering data
Nuclear StructureHypernuclei
Baryon interaction
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13P Achenbach, U Mainz
The A = 4 isospin doublet
Nucleon-hyperon interaction can be studied by strange mirror pairs
Coulomb corrections are < 50 keV for the 4
ΛH - 4ΛHe pair
Energy differences of strange mirror pair are much larger than for 3H - 3He pair
With precise spectroscopy details of NY-interaction inferred
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13P Achenbach, U Mainz
The A = 7 isospin triplet
Assumed CSB potential may be too naïve Further study on A = 4 hypernuclear systems necessary
[E. Hiyma, NPA 914, 130 (2013).]7Li(e,e’K+)7ΛHe
[N. Nakamura et al., PRL 110, 12502 (2013).]
7BeΛ(T=1)7LiΛ
7HeΛ
5.36
(with
out C
SB)
(with
CSB
)
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13P Achenbach, U Mainz
Hypernuclear production methods
two regimes for hypernuclear and hyperfragment production:
- bound hypernuclear states- highly excited quasi-free region
hypernucleus quasi-free L[O. Hashimoto and H. Tamura, Prog. Part. Nucl. Phys. 57, 564 (2006).]
[From J-Lab Hall-A]
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13P Achenbach, U Mainz
Hypernuclear decay-pion spectroscopy
p
e’
e9Be
9LLi*
K+
7Li
-
d7LHe
fragmentation
two-body decay mono-energetic
pions
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13P Achenbach, U Mainz
Examples of - spectroscopy
KEK-E287, E326
beam: stopped K-
target: thick 7Li
7ΛLi 11
ΛB
FINUDA Coll. and A. Gal, Phys Rev. B 681 (2009) 139
A. Gal, Nucl. Phys. A 828 (2009) 72
intense and high quality primary electron beam(R > 1014 Hz, < 100 mm)
+thin target (~10 mg/cm2)
decay π- spectroscopywith high resolutionand high accuracy
Severe limitations by statistics or momentum resolution
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13P Achenbach, U Mainz
Goals of decay pion spectroscopy
• Masses with high accuracy for light hypernuclei:3LH, 4
LH, …, 11LB, 12
LB
Determination of charge symmetry breaking (CSB) effects: (4
LH ↔ 4LHe), (6
LHe ↔ 6LLi), (7
LHe ↔ 7LLi* ↔ 7
LBe), …
• Search for hypernuclei near the neutron drip line:6LH, 7
LH, 8LH …
important information for L-S coupling [cf Hiyama]
6LH: the “superheavy hyper-hydrogen – puzzle” [cf Fukuda and Feliciello]
pion momentum resolution ~ 100 keV/c → mass resolution ~100 keV/c2 (FWMH) → accuracy of a few 10 keV/c2
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13P Achenbach, U Mainz
Decay-pion spectroscopy at MAMI
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13P Achenbach, U Mainz
Accessible hypernuclei
missing mass sepctroscopy
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13P Achenbach, U Mainz
TOF system
tracking system
Cherenkov system
Particle detection system in KAOS
time-of-flight reso-lution with TOF walls
FWHM = 400 ps
pion detection ε > 95% by aerogel Cherenkov
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13P Achenbach, U Mainz
Kaon identification using TOF system
protons
pions
kaons
pions
kaons
protons
low / high momentum setting
• KAOS can cover 200–1300 MeV/c in only 2
settings
• clean kaon identification by TOF at low momenta
• Cherenkov information used for high momenta
low / high momentum setting
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13P Achenbach, U Mainz
Pioneering experiment 2o11
• KAOS can be operated at zero-degree scattering angle
• PID suffers from high positron background
positrons
hadrons
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13P Achenbach, U Mainz
Dedicated experiment 2o12
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13P Achenbach, U Mainz
Decay pion detection
Decay pions from strange hadrons
(K,π)
(K,μ)(K,e)
(K,π)
(K,μ)(K,e)
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13P Achenbach, U Mainz
Signal interpretation
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13P Achenbach, U Mainz
Examples of decay-pion spectra
To minimize human bias two independent analyses performed:Final spectra to be released by end of year
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13P Achenbach, U Mainz
Conclusions
- Two current questions in few-body physics:
- Decay pion spectroscopy gives access to ground-state masses of hypernuclei and could answer the questions!
- At MAMI pioneering experiments were followed by an experiment with a dedicated setup:
Clean tag on strangeness production at zero-degreeClean pion sample from weak decays of hyperons retrievedCurrent analysis limited by statistics → continuation with luminosity increase by one order of magnitude planned
How can we understand the A = 4 and A = 7 hypernuclei?Is the superheavy hyper-hydrogen nucleus bound?
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13P Achenbach, U Mainz
A1 Hypernuclear Collaboration