Transcript A search for deeply-bound kaonic nuclear states in (in

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
4He(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 K1.1
Beam: 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
Beam
K- from K1.8BR or K1.1
Magnet
neutron
Aerogel Cherenkov
(beam π veto)
1.0 GeV/c
15m
Missing-mass resolution nTOF (E549 14×8)
~20MeV/c2 (FWHM)
1.2 ~ 1.5 GeV/c
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)
Λand ∑channel
• Invariant mass of pπp system (perfect detector,
kpp mass width =0, binding energy=100 MeV)
∑channel
( γ missing)
Λchannel
pπp
Momentum resolution of charged track in CDC
Invariant mass of Kpp (GeV/c2)
Parameter for CDC
L ( Arm length), B( Magnetic Field)
N (number of measured point)
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
Λ channel
Invariant mass of Λp (MeV)
∑ channel
Λ channel
Invariant mass of Λp (MeV)
CDS at JPARC (CDS-J)
980
200
20
• 3He target in the middle of CDC
• Trigger scintilator surrounding CDC
• He based chamber gas need to be
used
Event display Simulation using GEANT4
Detector simulation
works fine.
Test-2; Λ reconstruction efficiency
• Λ produced @ (0,0,0) with emitted angle q = 90 degree
Two or more hits on CDH
Λ mass resolution
Λ momentum (MeV/c)
σ（MeV）
σ（MeV）
reconstructed mass resolution
of L and Kpp state
Kpp state
momentum (MeV/c)
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
Yield estimation (K-pp)
• neutron detection (efficiency~30%) : 300ev/day
• 1/3 of Kpp decay to Λ+p or Σ0+p
+Λ
+ (Λ+p)
coincidence (CDS) : 50ev/day
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)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.
Detectors
Already exist
• Neutron Counter
• Beam sweeping magnet
– ( any dipole will be OK,
but required large Bdl )
－ SKS???
Future upgrade
Neutron Counter
Forward proton spectrometer
need to construct
• Beam line chambers:
• Liquid 3He target
• CDS
– Solenoid magnet
– CDC (chamber + electronics)
– Cylindrical Hodoscope
• Scintilator hodoscpe
• Beam ID counter
KURAMA
CDC
DC3
DC4
DC1
DC2
Energy loss correction
Plot : Δp (generate-Reconstruct) vs. Generated momentum
Before correction
Afterc orrection
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 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.
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