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Decay pion spectroscopy of electro-produced hypernuclei

APFB2011 22-26 Aug, 2011 Seoul, Republic of Korea. Decay pion spectroscopy of electro-produced hypernuclei. Tohoku Univ. Kyo Tsukada. Introduction Hypernucleus Concept of decay pion spectroscopy Physics of decay pion spectroscopy. Hypernucleus. Nucleus

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Decay pion spectroscopy of electro-produced hypernuclei

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  1. APFB2011 22-26 Aug, 2011 Seoul, Republic of Korea Decay pion spectroscopy of electro-produced hypernuclei Tohoku Univ. Kyo Tsukada

  2. Introduction • Hypernucleus • Concept of decay pion spectroscopy • Physics of decay pion spectroscopy

  3. Hypernucleus • Nucleus • many-body system of proton and neutron • Hypernucleus • Hyperon (Y=L here) in a nucleus • a new degree-of-freedom, “strangeness”, • L can be introduced deep-inside nucleus (no Pauli effect) • energy level can be measured directly • Y-N interaction can be investigated • Impurity effect for nucleus; shrinkage, clustering, deforming, … <-> N-N interaction n p L Y-N interaction should be investigated carefully and precisely for light hypernuclei. high resolution, high accuracy various nuclei ; wide range, new finding

  4. measurements of L(Y) Hypernucleus examples of processes reaction spectroscopy (BL ,mass) JLab MAMI J-PARC (e-’ K+), K+, π- e-, π+, K- γ-ray γ-ray spectroscopy (level splitting) J-PARC a, p weak decays (π-, NN) emulsion (L,LL) (mass) J-PARC L p- spectroscopy (mass) JLab MAMI We can measure the mass of various hypernucei by using completely different way with past experiments.

  5. p- spectra of past experiments • It is difficult to achieve both high statistics and resolution. 7ΛLi 11ΛB KEK-E287, E326 high rate and high quality primary electron beam (1013-14Hz, 100mmf) + thin target (̴10 mg/cm2) beam : stop K- target : 7Li decay p- spectroscopy with high resolution and high accuracy FINUDA Coll. and A. Gal et al., Phys Rev. B 681 (2009) 139 A. Gal, Nucl. Phys. A 828 (2009) 72

  6. Concept of decay pion spectroscopy ] e- beam Kaon tag p Fragments ] two body decay after stop pion spectroscopy π- Λ Absolute mass of various L hypernuclei pion momentum resolution ̴ 100 keV/c -> mass resolution ̴100 keV goal of accuracy ̴ a few 10 keV

  7. Hypernuclei from 9Be target Other targets, 7Li or 12C or so, should be measured in future.

  8. Physics of decay pion spectroscopy • High resolution and accuracy of mass for various light hypernuclei • 3LH, 4LH, …, 11LB, 12LB, i.e. A=3-12 • Spin-parity (JP) of the ground state • Charge symmetry breaking (CSB) • (4LH<->4LHe), (6LHe<->6LLi), (7LHe<->7LLi* <->7LBe), … • Search for hypernucleus near the neutron drip line • 6LH, 7LH, 8LH … • important information for L-S coupling • …

  9. Experiment • Facilities • Experimental apparatus • Estimations • Run summary • Some analysis plots of present conditions

  10. Electron beam facility MAMI-C JLab We started the feasibility study for the decay pion spectrometer experiment at Mainz in this year.

  11. MAMI-C (Mainz Microtron) Spec-B Spec-A Spec-C Frankfurt Mainz KAOS beam A1 collaboration 1st beam time : 24/May/2011-14/Jun/2011 KAOS and SpekC 2nd beam time : 19/Jul/2011-1/Aug/2011 KAOS and SpekA+SpekC 3rd beam time : near future ̴20 km southwest from Frankfurt

  12. spectrometers for decay p spectroscopy • 1500 MeV beam energy • zero-degree kaon tagged byKAOS • decay-pion detection with Spectrometer A & C (dp/p <10-4) 2m Beam dump K+ KAOS target KAOS SpekC SpekA p- p- SpekC SpekA pre-target beam chicane

  13. KAOS • Some detectors were newly introduced. • TOF wall (H-Wall) • Aerogel Cherenkov detectors (AC) • n = 1.015 • Tagger counters Tagger AC H-Wall G-Wall MWPC KAOS Magnet beam H-Wall Trigger=H ⊗G ⊗Tagger G-Wall

  14. Yield estimation • Model : Statistical decay model • Elementary cross section : 0.2-0.35mb/sr • Initial excited hypernucleus formation prob. : 0.7 • Hyperfragment stopping fractions : 0.87 • Two-body decay branch : 0.2-0.3 • Spectrometer acceptance : 28msr(SpekA,C), 12msr (KAOS) • Particle decay fractions in flight : 0.2 for p-, 0.3 for K+ 9Be target Phys.Lett.B697 (2011) 222 Kaon emission rate : 160-280Hz/mA Coincidence rate : 0.4-0.55 hyperfragments/day/mA

  15. Peak positions and momentum acceptance

  16. Run summary Kaon emission rate : 160-280Hz/mA Coincidence rate : 0.4-0.55 hyperfragments/day/mA

  17. Huge accidental positrons at KAOS accidental positron Covered by Tagger Covered by Tagger preliminary preliminary y-distribution at G-Wall [mm] The large acciedental events caused by positrons exists. Singles rate : 3MHz for G-Wall (H-Wall) for I=2.0uA We should avoid and/or remove positron efficiently. 1st + 2nd polinomial 2nd polinomial 1st polinomial

  18. Analysis • Analysis is ongoing. • Particle identification for KAOS and SpekA,C • Momentum reconstruction • Trace-back of particle tracks to target SpekC KAOS Dt=7.5ns (6.5ns for 110MeV/c) e+, p+ preliminary Dt=10.6ns (11ns for 110MeV/c) π- µ- proton e- time [nsec]

  19. summary • High resolution decay pion spectroscopy for light hypernuclei was proposed. • Mass resolution : ~100 keV • Mass accuracy : ~10 keV • Many light hypernulei including exotic states can be studied via the break-up of highly excited-states. • The 1st and 2nd commissioning run were performed at Mainz and the analysis is ongoing now. • The detectors should be improved in order to take data more efficiently with higher beam current.

  20. backup

  21. Nu ~ Nd ~ Ns Strangeness in neutron stars ( r > 3 - 4 r0 ) Strange hadronic matter (A → ∞) Strangeness LL, X Hypernuclei Z L, S Hypernuclei -2 N -1 0 World of matter made of u, d, s quarks “Stable” Higher density ３-dimensional nuclear chart by M. Kaneta inspired by HYP06 conference poster

  22. (e,e’K+) experiment at MAMI-C • Hypernuclear physics at MAMI-C • Upgrade of MAMI : 0.855 GeV -> 1.508 GeV (2006̴) • KAOS was introduced in MAMI-C (2008̴) Spec-B Kaos 縮尺

  23. (e,e’K+) experiment at MAMI MAMI JLab ~10 MeV (FWHM) ~2.5 MeV (FWHM)

  24. Experimental setup – target – 12C 45 mg/cm2 Al2O3 beam screen 9Be 22 mg/cm2 7Li (in future) beam SpecC SpecA 縮尺 target chamber Kaos

  25. 今回の実験のまとめ • 24 May 7:00 : start beam time • 25 May 18:00 ~ : start data taking • ~28 May 14:00 : calibration data for paddles • ~30 May 11:00 : coincidence data at 500 nA • ~1 June 10:00 : coincidence data at 300 nA with MWPC • ~1 June 22:00 : improvement of AC radiator (Matsushita -> Russian) • ~3 June 13:00 : coin data at 300 nA with MWPC • ~7 June 10:00 : coin data at 1500 nA w/o MWPC • ~8 June 11:00 : coin data at 2000 nA w MWPC • ~14 June 5:00 : coin data at 1500 nA w MWPC target : 125 μm 9Be Total Charge : 1.3 C Anselm : 1 counts / μA / day Sho : 170 counts / 10μA / 20days 10 counts stopping hyper fragments

  26. Target 横から ターゲットホルダー 上から Be 125 μm C 43.86 mg/cm2 Al2O3 beam screen Be 125×4 μm Li ? mg Scattering chamber empty 4 cm 冷却水ノズル

  27. Target x beam z y, x軸、合わせ mirror leveler2 mirror leveler2 ビームパイプ target マーカー マーカー leveler1 z軸合わせ

  28. trigger 124 deg Schematic view of Setup TOF ⊗ Tag ⊗ Scinti G-Wall e- H-Wall MWPC Kaos Kaon tag material : 9Be thickness : 125 μm tilt angle : 54 deg target AC Pion spectroscopy Pion spectroscopy SpecC SpecA VDC VDC 17 deg GC GC Scinti Scinti

  29. Kaos central momentum : 1000 MeV/c ] 0 degree (original beam direction) 17 deg 54 deg target (9Be 125mm) 107.95 deg 107.57 deg ] ] SpekA central momentum : 130 MeV/c momentum acceptance : 25% SpekC central momentum : 125 MeV/c momentum acceptance : 25% e- energy : 1508MeV

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