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