Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Patrick Achenbach U Mainz Sept. 2o13
Jan 04, 2016
Recent Studies of Hypernuclei Formationwith Electron Beams at MAMI
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. 2o13
P Achenbach, U Mainz
Theoretical calculations
Cluster model, shell model, mean field…
Hypernuclear spectroscopyHypernuclear 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. 2o13
P Achenbach, U Mainz
The A = 4 isospin doublet 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. 2o13
P Achenbach, U Mainz
The A = 7 isospin tripletThe 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. 2o13
P Achenbach, U Mainz
Hypernuclear production methodsHypernuclear 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. 2o13
P Achenbach, U Mainz
Hypernuclear decay-pion spectroscopyHypernuclear decay-pion spectroscopy
p
e’
e
9Be
9Li*
K+
7Li
-
d7He
fragmentation
two-body decay mono-energetic
pions
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13
P Achenbach, U Mainz
Examples of p- spectroscopyExamples of p- 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. 2o13
P Achenbach, U Mainz
Goals of decay pion spectroscopyGoals of decay pion spectroscopy
• Masses with high accuracy for light hypernuclei:3LH, 4
LH, …, 11LB, 12
LB
Determination of charge symmetry breaking (CSB) effects:
(4LH ↔ 4
LHe), (6LHe ↔ 6
LLi), (7LHe ↔ 7
LLi* ↔ 7LBe), …
• 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. 2o13
P Achenbach, U Mainz
Decay-pion spectroscopy at MAMIDecay-pion spectroscopy at MAMI
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13
P Achenbach, U Mainz
Accessible hypernucleiAccessible hypernuclei
missing mass sepctroscopy
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13
P Achenbach, U Mainz
TOF system
tracking system
Cherenkov system
Particle detection system in KAOSParticle 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. 2o13
P Achenbach, U Mainz
Kaon identification using TOF systemKaon 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. 2o13
P Achenbach, U Mainz
Pioneering experiment 2o11Pioneering 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. 2o13
P Achenbach, U Mainz
Dedicated experiment 2o12Dedicated experiment 2o12
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13
P Achenbach, U Mainz
Decay pion detectionDecay 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. 2o13
P Achenbach, U Mainz
Signal interpretationSignal interpretation
Recent Studies of Hypernuclei Formation with Electron Beams at MAMI Sept. 2o13
P Achenbach, U Mainz
Examples of decay-pion spectraExamples 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. 2o13
P Achenbach, U Mainz
ConclusionsConclusions
- 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-degree
Clean pion sample from weak decays of hyperons retrieved
Current 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. 2o13
P Achenbach, U Mainz
A1 Hypernuclear CollaborationA1 Hypernuclear Collaboration