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An Experimental Search for Deeply Bound Kaonic Nuclei with Stopped Kaons

An Experimental Search for Deeply Bound Kaonic Nuclei with Stopped Kaons. Outline: 1. Introduction Experiment and devices Low level analysis 4 He( K - stopped , p ) spectra and discovery of S 0 (3115) 4 He( K - stopped , n ) spectra and indication of S + (3140)

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An Experimental Search for Deeply Bound Kaonic Nuclei with Stopped Kaons

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  1. An Experimental Search for Deeply Bound Kaonic Nuclei with Stopped Kaons Outline: 1. Introduction Experiment and devices Low level analysis 4He(K-stopped, p) spectra and discovery of S0(3115) 4He(K-stopped, n) spectra and indication of S+(3140) Discussion and Conclusion Takatoshi Suzuki(U-Tokyo), for KEK-E471 collaboration

  2. 1. Introduction 1-0 Does deeply bound kaonic nuclear states with narrow widths exist ? -> Yes they do! * Wycech(cf. NPA 450 (1986) 399c ) coupled channel potential and in-medium t-matrix (from Martin) * Kishimoto(PRL 83 (1999) 4701) Atomic DD potential + SU(3) Chiral Lagrangian (from Batty-Friedmann-Gal) (from Waas-Kaiser-Weise) * Akaishi-Yamazaki(PRC 65 (2002) 044005) low energy KN scattering + L(1405) (from Martin + Iwasaki) -> No, they don’t! They must be shallow and broad. * Many authors.

  3. Y. Akaishi and T. Yamazaki, PRC 65 (2002) 044005 1-3. AY predictions3 - Isospin dependence of the kbar-nuclear states First prediction of a strongly bound narrow kbar-NNN state with T=0. Shallow and broad state with T=1

  4. 1-4. 4He(K-stopped, n/p) reactions - population of the kbar - NNN states 4He(K-stopped, n) T=0,1 formation channel-> (K- - 3He)T=0, (K- - 3He)T=1,Tz=0 Appearance of a narrow peak was expected. 4He(K-stopped, p)T=1 formation channel -> (K- - 3H)T=1,Tz=-1 No narrow peaks were expected.

  5. 1-5. Experimental principle • Kaonic helium4 formation from stopped K- • Kaonic nuclear formation via nuclear Auger effect • Neutron(proton) emission as a spectator • Strong decay into mesonic or non-mesonic final states Triple coincidence of 1. Incident kaon 2. Auger nucleon 3. Secondary charged particle Missing mass spectroscopy.

  6. 2. Experiment 2-1. Experiment - an overview M. Iwasaki et al., NIM A 473 (2001) 286 Stopped K- method. 1. Incident K- and its track by beamline detectors - 2. secondary charged particle and its track by TC-VDC - 3. nucleon and its stop timing(TOF) by NC - are measured in coincidence. Those 3 signals are required hardwarewise K-beam & VTCOR &NCOR semi-inclusive spectra

  7. 2-2. kaon beam line Secondary K- beam extracted through KEK-PS K5 * 2TP(Tera Proton)/spill(1.6 sec duration with 4 sec cycle) * 6cm thick Pt production target * pK ~ 650 MeV/c * Dp/p ~ 4 % * Wedge-Shaped-Degrader (stopped K+yield: 1.5 times enriched)

  8. 2-3. Beam line devices 1 - a side view Beam definition -> Scinitllators K/p separation -> Lucite Cherenkov Counters … K/p ratio at T0: 0.005 Kaon track detection -> Beamline Drift Chamber (BDC) ~ 4.7 k/spill ~ 0.88 M/spill

  9. 2-5. Beam line devices 3 - Liquid helium4 target Only a brief summary…… * 0.145 g/cm3 super fluid helium 4 * Cell structure: cylindrical tube * 15 cm thickness (2.18 g/cm2) * 23.5 cm diameter * Stable operation below 2.0 K

  10. 2-7. Neutron detector system - cross sections of NC and NCV Plastic scintillator segments to detect nucleon stop timing and position. * Two arms(32(E471)+ 24(SKS)segments) * 8.3 % of total solid angle * NCV to cover NC segments * Fe plate between NC and NCV to induce g->e+ e-

  11. 3-3. Reaction vertex and DCA Reaction vertex is defined by the two pre-defined tracks. Vca: vector connects two closest- approaching points, which represent final state hyperon motion DCA : |Vca|

  12. 3-4. Stopped K selection K- K+ With two-dimensional correlation between T0 pulse height and Vertex z position…..

  13. 3-5. Target fiducial cut With reaction vertex position….. Events originate from outer materials are omitted.

  14. 3-7. TOF analysis on NC (1) We measure the time difference between kaon injection onto T0 and nucleon detection on NC. With g-ray events…. 1. Slewing correction factors 2. z-vertex correction factor (Flight time of K from T0 to its stop:) 3. Time origin in order to adjust 1/b =1 for g events. are determined.

  15. 3-8. TOF analysis on NC (2) 1/b spectrum for neutral particles…. Variation of the center and s of 1/b distribution...

  16. 3-9. Proton PID on NC Procedure… • Charged particle is Selected by NCV hit. 2. Total light output, is obtained. 3. The proton events appear on the two- dimensional correlation between 1/b and DENC.

  17. 3-10. PID of secondary charged particle PID of secondary charged Particle: Stage 1 TCthin dE/dx vs TOF Stage 2 (Fig.) dE/dx vs dE/dx Proton and pion are separated.

  18. 3-11. Secondary pion momentum cut For the events(pion) within the polygon, momentum value can be defined. We divide the pion events at 125 MeV/c -255 MeV/c (hypernuclear formation) exclusively appear on S-decay side.

  19. 3-12. Study of the hyperon motion in the final state - VcaVN VN : a unit vector along with detected hyperon motion VcaVN ~ 0 -> Quasi-free hyperon production or hypernuclear formation << 0 -> non-pionic absorption or kaonic nuclear formation and its non-mesonic decay >>0 -> hyperon decay

  20. 4. 4He(K-stopped, p) spectra 4-1. Semi-inclusive momentum spectrum A significant peak structure Exists just below 500 MeV/c, on a continuum due to 1. Formation of a strange tribaryon via 2. Hypernuclear formation and its non-mesonic two-body decay A fake due to instrumental bias? Discovery of a strange tribaryon S0

  21. 4-2. Classification of the momentum spectrum 1 - by secondary charged particle ID and momentum pion cut proton cut fast(S decay) pion cut slow(L decay) pion cut

  22. 4-3. Classification of the momentum spectrum 2 - VcaVp selection Under pi-cut condition- VcaVp : -6 ~ 0 -> hyper nuclear two-body decay VcaVp : 0~+6 -> hyper nuclear two-body decay VcaVp : -60~-6 -> Formation ofa strange tribaryon and its non-mesonic decay VcaVp: 6~60 -> nothing to generate mono- chromatic structure…

  23. 4-5. Summary of the analysis a): event topology of hypernuclear cascade b),c): indication of analysis 1,2

  24. 4-6. 4He(K-stopped, p) missing mass spectrum and S0(3115) Event-by-event energy loss correction -> Function fitting with P3 BG + Gaussian signal -> c2/DOF = 8.76/12 Gaussian center: 3117.7 MeV/c2 Gaussian sigma: 8.7 MeV/c2 Statistical significance: S/DS = 2441/297= 8.2 s T. Suzuki et al., PLB 597 (2004) 263 (Unexpected) Discovery of a Starnge Tribaryon S0(3115)

  25. The peak position is exactly adjusted even for the events with small pulse height, and it also ensure the proton momentum scale as well as neutron. 5. 4He(K-stopped, n) spectra 5-1 Momentum referential peak Monochromatic neutron source from S+stopped -> p+ + n is expected in the stopped K- reaction at 185 MeV/c (1/b=5.176).

  26. 5-2. Semi-inclusive neutron momentum spectrum Neutron semi-inclusive momentum spectrum at 10 MeVee threshold After constant BG subtraction…. The overall shape is well reconstructed by Monte-Carlo simulation. No clear peak-like structure is found in. The intensity over 400 MeV/c is exclusively due to non-pionic absorption process….

  27. 5-3. Classification of the spectrum by pion momentum An indication of a peak structure is found only in pS-decay cut spectrum -> indication of another kind of strange tribaryon S+ mainly decays into SNN ? -> further study by VcaVn selection is required…...

  28. 5-4. Classification by VcaVn and indication of S+ Once decay mode and mass value has been estimated, we can set relevant VcaVn window to enhance the signal using Monte-Carlo. Comparison between (a) -25<VcaVn<-5 (HSN) AND -5<VcaVn<-2 or -60<VcaVn<-25 (LSN) (b) 5<VcaVn<25 AND 2<VcaVn<5 or 25<VcaVn<60 We find a clear enhancement of HSN spectrum on (a) -> Indication of S+

  29. 5-5. 4He(K-stopped, n) missing mass spectrum and S+(3140) M. Iwasaki et al., nucl-ex/0310018 v2 A enhancement of the HSN missing mass spectrum at around 3140 MeV/c2 ->An indication of another kind of strange tribaryon S+(3140)state. * No structure at around 3140 MeV/c2 on the proton spectrum -> T=0. A global fitting to the HSN data points of 1 exponential BG + 2 Gaussian (S+(3140) and S+(3115)) c2/DOF = 28.52/31 Gaussian center: 3140.5 MeV/c2 Gaussian sigma: 7.3 MeV/c2 Statistical significance: S/DS=120/32= 3.7 s Consistent yield with S0(3115)

  30. 6. Discussion and conclusion Experiment:nucl-ex/0310018 (v2) , PLB 597 (2004) 263. Non-relativistic calc.: PRC 65 (2002) 044005 , PLB 535 (2002) 70. S0(3115) = K-pnnT=1,Tz=-1, S+(3140) = K-ppnT=0 (=3KH) kaonic nuclear state? Problem?: 1. level reversing 2. large deviation of kbar binding energy up to 100 MeV. Other possibilities? 6-1Comparison between kaonic nuclear calculation

  31. 6-2.Experiments for kaonic nuclear study in year 2005 For B=3…. 1. KEK E549(Iwasaki) - Study of 4He(K-stopped, p) inclusive spectrum - Extension of E471 for 4He(K-stopped, n) 2. KEK P570(Hayano) - Kaonic 4He 3d->2p X-ray measurement - Extension of E471 for 4He(K-stopped, n) For other baryon numbers… 1. FINUDA at Frascati(Nagae) - Invariant mass spectroscopy for B=2,3 - Missing mass spectroscopy for heavier nuclei • KEK E549(Kishimoto) - Missing mass spectroscopy via 16O(K-, p) reaction

  32. 6-3.Conclusion 1. We have discovered a new kind of strange tribaryon S0(3115) with total isospin T=1 in the 4He(K-stopped, p) reaction. 2. An indication of another kind of strange tribaryon S+(3140) with total isospin T=0 has been obtained in the 4He(K-stopped, n)spectrum.

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