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A search for deeply-bound kaonic nuclear states in (in-flight K - , N) reaction

A search for deeply-bound kaonic nuclear states in (in-flight K - , N) reaction. Hiroaki Ohnishi RIKEN. Physics motivation. Detail study of the structure seen in 4 He(Kstop,N) reaction ( KEK-PS E471) Is that really signal from deeply bound K-nucleus? If so, Cross section? Decay Branch?.

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A search for deeply-bound kaonic nuclear states in (in-flight K - , N) reaction

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  1. A search for deeply-bound kaonic nuclear states in (in-flight K-, N) reaction Hiroaki Ohnishi RIKEN

  2. Physics motivation • Detail study of the structure seen in4He(Kstop,N) reaction ( KEK-PS E471) • Is that really signal from deeply bound K-nucleus? If so, • Cross section? • Decay Branch? Using 3He with improved detector apparatus

  3. Basic parameters for the experiment • (K-,N) elementary process cross sectionhas peak structure about Kbeam~ 1.0 GeV No magic momentum exist in (K,N) reaction Beamline: K1.8BR or K1.1 Beam: 1.0GeV/c K− Intensity: 0.8x106 /spill

  4. Concept of the detector system • Liquid 3He target • Neutron counter in 0. degree • Kaon beam sweeping magnet Beam K- from K1.8BR or K1.1 Magnet neutron 15m Aerogel Cherenkov(beam π veto) Missing-mass resolution ~20MeV/c2 (FWHM) nTOF (E549 14×8) 1.2 ~ 1.5 GeV/c 1.0 GeV/c

  5. Requirement on the detector around target system • Target branch mode for this experiment • 3He(K-,n) Kpp, Kpp-> Λp-> pπp • All charged particle. • We will be able to measure this channel with both missing mass and invariant mass, if we have GOOD tracking detector around target Cylindrical Detector System (CDS) • There is another channel which might be interesting • 3He(K-,n) Kpp, Kpp-> ∑ｐ->Λｐ（γ）->pπp+(γ)

  6. Λand ∑channel • Invariant mass of pπp system (perfect detector, kpp mass width =0, binding energy=100 MeV) Momentum resolution of charged track in CDC Λchannel pπp ∑channel ( γ missing) Invariant mass of Kpp (GeV/c2) Parameter for CDC L ( Arm length), B( Magnetic Field) N (number of measured point)

  7. Test Simple simulation; Generate Kpp bound state. Generated particle momentum is smeared with expected resolution curve. • In case of B=0.5T, N=16 L = 18cm L = 30cm ∑ channel ∑ channel Λ channel Λ channel Invariant mass of Λp (MeV) Invariant mass of Λp (MeV)

  8. 75 20 60 CDS at JPARC (CDS-J) 980 400 200 • 3He target in the middle of CDC • Trigger scintilator surrounding CDC • He based chamber gas need to be usedto minimize material

  9. Event display -Simulation using GEANT4 Detector simulationworks fine.

  10. Test-2; Λ reconstruction efficiency • Λ produced @ (0,0,0) with emitted angle q = 90 degree Two or more hits on CDH

  11. reconstructed mass resolutionof L and Kpp state Kpp state Λmass resolution σ（MeV） σ（MeV） momentum (MeV/c) Λmomentum (MeV/c)

  12. Estimation of event rate • Forward neutron counter acceptance~ 0.0194 sr • Cross section of kpp = 10 μｂ • Coincidence rate between CDC hit and forward neutron ( more than 1 particle hit on CD-Hodoscope ) • fraction of the neutron detected event with Λ reconstructed in CDC ~ 50 % • fraction of the neutron detected event with Λ+p reconstructed in CDC ~ 47 % 0.0194 0.049

  13. Yield estimation (K-pp) • neutron detection (efficiency~30%) : 300ev/day • 1/3 of Kpp decay to Λ+p or Σ0+p + Λ coincidence (CDS) : 50ev/day + (Λ+p) coincidence (CDS) : 47ev/day • tracking eff., DAQ eff., analysis eff. etc. • 1 month ~ 100 shifts will be necessary to have enough (~1500 ) statistics.

  14. Need to be done • Background estimation again • Elastic scattering, charge exchange reaction • p(K-, p)K- , n(K-, n)K-, p(K-, n)K0, p(K-, K0L)n • Quasi-free hyperon production • p(K-, Λ)π0, n(K-, Λ)π-, N(K-, Σ)π • Two-nucleon absorption ? • K- + “pn” → Λ+n, Σ0+n, Σ-+p • Other backgrounds are in unbound region.

  15. Detectors need to construct Already exist • Neutron Counter • Beam sweeping magnet • ( any dipole will be OK, but required large Bdl ) • Beam line chambers: • Liquid 3He target • CDS • Solenoid magnet • CDC (chamber + electronics) • Cylindrical Hodoscope • Scintilator hodoscpe • Beam ID counter － SKS??? Future upgrade Forward proton spectrometer KURAMA CDC Neutron Counter DC1 DC3 DC2 DC4

  16. Energy loss correction Plot : Δp (generate-Reconstruct) vs. Generated momentum Before correction Afterc orrection

  17. Λ reconstructed mass resolutionbefore and after e-loss correction

  18. Test-1; Momentum resolutionSimulation and simple calculation Point ; Proton generated at (0,0,0) emitted angle q=90. degree momentum reconstruction done using hot position on CDC with position resolution Line; Expected momentum resolution Calculated with B, arm length, Material budget etc.

  19. Some concerns • Beam sweeping magnet • Now we (still) considered KAMAE magnet • CDS magnet will be designed and producing in JFY18 • CDC construction will be start during JFY19

  20. 0.5 • 0.5M / 0.7s

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