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? Using 3 He with improved detector apparatus

Basic parameters for the experiment (K-,N) elementary process cross section has peak structure about K beam ~ 1.0 GeV No magic momentum exist in (K,N) reaction Beamline: K1.8BR or K1.1 Beam: 1.0GeV/c K− Intensity: 0.8x10 6 /spill

Concept of the detector system Liquid 3 He target Neutron counter in 0. degree Kaon beam sweeping magnet K - from K1.8BR or K1.1 Aerogel Cherenkov (beam π veto) neutron nTOF (E549 14×8) 1.0 GeV/c 1.2 ~ 1.5 GeV/c 15m Missing-mass resolution ~20MeV/c 2 (FWHM) Beam Magnet

Requirement on the detector around target system Target branch mode for this experiment – 3 He(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 – 3 He(K-,n) Kpp, Kpp-> ∑ ｐ ->Λ ｐ（ γ ） ->pπp+(γ)

Λand ∑channel Invariant mass of pπp system (perfect detector, kpp mass width =0, binding energy=100 MeV) Invariant mass of Kpp (GeV/c 2 ) ∑channel ( γ missing) Λchannel pπp Momentum resolution of charged track in CDC Parameter for CDC L ( Arm length), B( Magnetic Field) N (number of measured point)

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

He target in the middle of CDC Trigger scintilator surrounding CDC He based chamber gas need to be used to minimize material CDS at JPARC (CDS-J)

Event display - Simulation using GEANT4 Detector simulation works fine.

Test-2; Λ reconstruction efficiency Λ (0,0,0) with emitted angle  = 90 degree Two or more hits on CDH

reconstructed mass resolution of  and Kpp state Λ mass resolution Λ momentum (MeV/c) momentum (MeV/c) Kpp state σ （ MeV ）

Estimation of event rate Forward neutron counter acceptance~ sr Cross section of kpp = 10 μ ｂ 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 %

Yield estimation (K - pp) neutron detection (efficiency~30%) : 300ev/day 1/3 of Kpp decay to Λ+p or Σ 0 +p + Λcoincidence (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.

Need to be done Background estimation again –Elastic scattering, charge exchange reaction p(K -, p)K -, n(K -, n)K -, p(K -, n)K 0, p(K -, K 0 L )n –Quasi-free hyperon production p(K-, Λ)π 0, n(K-, Λ)π -, N(K -, Σ)π –Two-nucleon absorption ? K - + “pn” → Λ+n, Σ 0 +n, Σ - +p –Other backgrounds are in unbound region.

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

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

Λ reconstructed mass resolution before and after e-loss correction

Test-1; Momentum resolution Simulation and simple calculation Point ; Proton generated at (0,0,0) emitted angle  =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.

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

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