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 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
Basic parameters for the experiment• (K-,N) elementary process cross section
has peak structure about Kbeam~ 1.0 GeV
No magic momentum exist in (K,N) reaction
Beamline: K1.8BR or K1.1Beam: 1.0GeV/c K−Intensity: 0.8x106 /spill
Concept of the detector system
• Liquid 3He 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/c2 (FWHM)
Beam
Magnet
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 ->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/c2)
∑channel( γ missing)
Λchannelpπp
Momentum resolution of charged track in CDC
Parameter for CDCL ( Arm length), B( Magnetic Field)N (number of measured point)
Test
• In case of B=0.5T, N=16
∑ channelΛ channel
L = 18cm
Invariant mass of Λp (MeV)
L = 30cm
Invariant mass of Λp (MeV)
∑ channelΛ channel
Simple simulation; Generate Kpp bound state. Generated particle momentum is smeared with expected resolution curve.
980
400
75
6020
200
• 3He target in the middle of CDC• Trigger scintilator surrounding CDC • He based chamber gas need to be usedto minimize material
CDS at JPARC (CDS-J)
Event display -Simulation using GEANT4
Detector simulationworks fine.
Test-2; Λ reconstruction efficiency
• Λ produced @ (0,0,0) with emitted angle = 90 degree
Two or more hits on CDH
reconstructed mass resolutionof and Kpp state
Λ mass resolution
Λ momentum (MeV/c) momentum (MeV/c)
Kpp state
σ(
MeV
)
σ(
MeV
)
Estimation of event rate• Forward neutron counter acceptance~ 0.0194 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 %
0.0194
0.049
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 e
nough (~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)K0, p(K-, K0
L)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.
Detectors
• Beam line chambers:• Liquid 3He target• CDS
– Solenoid magnet– CDC (chamber + electronics)
– Cylindrical Hodoscope• Scintilator hodoscpe
• Beam ID counter
CDCKURAMA
DC1DC2
DC3
DC4
Neutr
on
Counte
rneed to construct
Already exist• Neutron Counter• Beam sweeping magnet
– ( any dipole will be OK, but required large Bdl )
- SKS???
Future upgradeForward proton spectrometer
Energy loss correction
Before correction Afterc orrection
Plot : Δp (generate-Reconstruct) vs. Generated momentum
Λ reconstructed mass resolutionbefore and after e-loss correction
Test-1; Momentum resolutionSimulation 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
0.5
• 0.5M / 0.7s