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Prospects of hypernuclear experiments at MAMI-C

Prospects of hypernuclear experiments at MAMI-C. Tohoku University Sho NAGAO. Contents. Introduction Decay pion spectroscopy Experimental setup Results Future plan Summary. L ight hypernuclei. Expansion of S=-1 floor Emulsion (K - ,π - ),(π + ,K + ),( e,e’K + ) etc.

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Prospects of hypernuclear experiments at MAMI-C

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  1. 3rd Korea-Japan Workshop Prospects of hypernuclear experiments at MAMI-C Tohoku University Sho NAGAO

  2. 3rd Korea-Japan Workshop Contents • Introduction • Decay pion spectroscopy • Experimental setup • Results • Future plan • Summary

  3. 3rd Korea-Japan Workshop Light hypernuclei • Expansion of S=-1 floor • Emulsion • (K-,π -),(π+,K+),(e,e’K+) etc. • ΛN interaction • Effective ΛN interaction • ΛN-ΣN coupling • Three body ΛNN force • Charge symmetry breaking • Impurity effect • Deeply bound state • Shrinkage effect hypernuclear chart Z N

  4. 3rd Korea-Japan Workshop Λ-N charge symmetry breaking (CSB) 350 keV H He 4 4 Λ Λ p p n ΔB = 760keV p p p n p ≃ n n Λ Coulomb force n n Λ -BΛ (MeV) -BΛ (MeV) 3H + Λ 3He + Λ -1.00±0.06 -1.24±0.06 1+ 1+ -2.04±0.04 0+ -2.39 ±0.03 0+ 3H 3He CSB effect : 71 keV R.A.Brandenburg et al., Phys. Rev. C 37 781-785 (1988). Exp. Exp. M. Juric et al., Nucl. Phys. B 52 (1973) 1 M. Bedjidian et al., Phys. Lett B 83 (1979) 252

  5. 3rd Korea-Japan Workshop Decay pion spectroscopy of Λ hypernuclei ~20 μA ~20 mg/cm2 e - Kaon tag p K+ Λ π- Fragments Δp/p ~ 10-4 Pion spectrometer Z • New experimental technique • Hypernuclear mass spectroscopy • with high precision • (~30 keVaccuracy) • Fragmentation probability N

  6. 3rd Korea-Japan Workshop Experimental setup Target Spek-B Spek-A Spek-C π- π- Kaos (Kaon tagger) Target thickness optimization Background suppression in Kaos e- 9Be Spek-A, C (Pion spectrometer) K+ Kaos

  7. 3rd Korea-Japan Workshop Target thickness The optimization of target thickness is quite important Too thin → Less stopping probability Too thick → More energy struggling Worse accuracy The estimation of target thickness effect using Geant4 Simulation Stopping prob. (%) Resolution (MeV/c) Target thickness (mg/cm2)

  8. 3rd Korea-Japan Workshop Setup in Kaos Top view TOF2 (H) AC1 AC2 TOF1 (G&I) 1m e+, π+, K+, p Lead wall Kaos Magnet

  9. 3rd Korea-Japan Workshop Setup in Kaos (Lead wal) Geant4 Simulation of Lead wall Top view TOF2 (H) K+ 50 % AC1 π+ AC2 p TOF1 (G&I) Survival ratio 1m 0.2 % e+ e+, π+, K+, p Lead wall Lead thickness (cm) Kaos Magnet • e+ background : Seriously high (~100 MHz/20 μA beam) • Momentum resolution : No relation with mass resolution

  10. 3rd Korea-Japan Workshop Kaos setup (Aerogel Cherenkov) π+ veto in offline analysis NPE distribution in J-PARC T44 • 6 segments • Hamamatsu 5” PMT • Teflon diffused reflector • Panasonic 3 cm • Refractive index = 1.05 π+ p Counts K+ 0 5 10 15 20 25 30 NPE 0.5 m Rejection efficiency (NPE<2) 1.5 m

  11. 3rd Korea-Japan Workshop Decay pion experiment in 2012 • 2nd decay pion experiment terms : 24 Oct. ~ 11 Nov. in 2012 • Typical condition

  12. 3rd Korea-Japan Workshop Identification of decayed pion events Coincidence time = Time at target of K+ - Time at target of π - Cuts in Kaon tagger Cuts in Pion spectrometer TOF wall : beta, energy deposit Momentum : mass reconstruction Aerogel Cherenkov : pion rejection Gas Cherenkov : electron rejection 2011 2012 “K+,π-” Coincidence & Accidental b.g. “K+,μ-” counts / 500 ps Accidental background Coincidence time (ns) Coincidence time (ns)

  13. 3rd Korea-Japan Workshop K+ tagged π-momentum spectrum Preliminary 133 MeV/c peak : 4ΛH width : ~200 keV/c (FWHM) stat. err. : <30 keV/c QF hyperon background accidental background

  14. 3rd Korea-Japan Workshop Formation probability of 4ΛH [2,3] 2.0×10-4 [1] [1] Phys. Rev. D 86 (2012) 1328 [2] M.M Bloch et al. Proceedings of Int. Conf. on Hyperfragments, CERN-Report 64-1 pp.63 [3] D. Bertrand et al. Nucl. Phys. B16 (1970) 77.

  15. 3rd Korea-Japan Workshop Detection ratio of Λ (Simulation) 1 3 2 Kaos 4 Spek-C • Virtual Photon distribution M. Sotona private communication • Fermi motion of proton A. Bodek and J.L. Ritchie, Phys. Rev. D 23 1070-1091 (1981). • N(γ,K+)Y cross section : Isobar model (K-MAID) • Acceptance of Kaos & Spek-C http://wwwkph.kph.uni-mainz.de/MAID/kaon/ Decayed pion mom. dist. Decayed pion 2D dist. Pion momentum (MeV/c) QF Λ QF Σ - Stopped QF Σ- Pion angle (degree) Pion momentum (MeV/c)

  16. 3rd Korea-Japan Workshop Future plan • Taking data with better S/N ratio • Higher yield → Longer beam time & Higher beam intensity • Suppression of background Accidental b.g Optimization of Lead wall : rate→~1/4 (already checked) Trigger upgrade in Spek-C QF hyperonb.g End of May in 2014 Hyperfragments simulation w/ collimator target QF hyperons ~2cm ~ 70% reduction Collimator Pion spectrometer

  17. 3rd Korea-Japan Workshop Future plan Material : Tungsten Heavyalloy Size : 40H×70L×30T mm3 Tungsten Collimator & Frame

  18. 3rd Korea-Japan Workshop Summary • Decay pion spectroscopy • new technique • ~ 30 keV mass accuracy in light hypernuclei • Hypernuclear formation probability • Pilot experiment • The experiments have performed in 2011 & 2012 • 4ΛH peak with small statistical err. • Formation probability • Future plan • Aiming to better S/N ratio • Position optimization of lead wall • Collimator to suppress QF hyperon b.g. • Next beam time : The end of May (2014) ~

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