Production of Double Strangeness Hypernuclei in 12C(K-,K+) Reaction

at 1.67 GeV/c

Choi Bong Hyuk Pusan National University

For the E522 collaboration

summary outlook

Production of Hypernuclei

Data Analysis

Double HypernucleiDouble

Hypernuclei

Ξ- absorption

(K-,K+) reaction

summary outlook

Production of Hypernuclei

Data Analysis

Double HypernucleiTheoretical

prediction

Y.Yamamoto et al. Prog.Theor.Phys.Suppl.117(1994)

Y.Yamamoto -> DWIA (Distorted wave impulse approximation )

Woods-Saxon Potential

V0Ξ=-15MeV

W0Ξ= 1MeV

H.Maekawa et al. Eur.Phys.J 33, 269-272(2007)

pΞ

sΞ

H.Maekawa -> DWIA+LOFAt(Local Optimal Fermi Averaging t-matrix)

Previous experiment

E224 E885

E224, E885 resultPotential well depth ~ 14MeV : ( Woods-Saxon potential)

summary outlook

Production of Hypernuclei

Data Analysis

Double Hypernuclei

Image data

Measurement Hypernuclei

decay in SCIFI

Experiment Target Target size(cm3) material

KEK E224 SCIFI target 8×8×10 (CH)n

AGS E885 diamond target 8×1×5 C

KEK E373 hybrid emulsion

KEK E522 SCIFI target 10×10×20 (CH)n

1.67GeV/cK- beam

summary outlook

12C(K-,K+)X reaction

Data Analysis

Double HypernucleiE522

Experiment Setup

Outgoing particle mass

21

pm

cT

L

Reconstructed mass distribution

summary outlook

Production of Hypernuclei

Data Analysis

Double Hypernuclei

Cut condition-mass2-momentum cut-vertex cut-FTOF hit position cut-DChit- ToF cut

π+ & proton are contaminated

Backgroundrejection

pKabove 1.15 GeV/c

σ = 36.6 ± 3.6 MeV/c2

2 σ

2 σ : 19.9 %

summary outlook

12C(K-,K+)X reaction

Data Analysis

Double Hypernuclei

pKpK

3 σ

3 σ : 7.9 %

σ = 72.2 ± 2.0 MeV/c2

Backgroundrejection

Dotted line : before π+ and p contamination cutSolid line : after π+ and p contamination cut

(Carbon + Hydrogen) eventCarbon event

Hydrogen eventImage data

summary outlook

12C(K-,K+)X reaction

Data Analysis

Double Hypernuclei

Type Ⅰ Type Ⅱ Type Ⅲ Type Ⅳ TypeⅤ1.One prong at

vertex point2.One KINK at the

end of prong3.or ‘V’ topology

1.Only just one prong

at vertex point2. Stop or escape3. or ‘V’ topology

1.two prongs or

three prongs

2.many prongs

3. or ‘V’ topology

1. No prong at

vertex point

2. or ‘V’ topology

1. Another all Image

Image Categorization

Image datasummary

outlook

12C(K-,K+)X reaction

Data Analysis

Double Hypernuclei

Coplanarity angle

cut position : -1° ~ 1°

Carbon event : 19.6%

Hydrogen event : 80.4%

summary outlook

12C(K-,K+)X reaction

Data Analysis

Double Hypernuclei

)(cos2

1 KK

summary outlook

12C(K-,K+)X reaction

Data Analysis

Double Hypernucleip(K-,K+) missing

mass distribution

For Hydrogen target|Ψ| < 1

K+ momentum distribution

19.4% carbon events

p(K-,K+)X missing mass distribution

σ = 14.5 MeV/c2

12C(K-,K+) eventsummary

outlook

12C(K-,K+)X reaction

Data Analysis

Double Hypernuclei

no peak structure QF Ξ-

•one prong events at reaction point•one prong and one kink at the prong•one prong stop in the SCIFI•one prong and several kink at the prong

Quasi-free Ξ- event selection in the Image data

Quasi-free Ξ-

Excitation Energy [MeV]Excitation Energy [MeV] Excitation Energy [MeV]Excitation Energy [MeV]

12C(K-,K+) eventsummary

outlook

12C(K-,K+)X reaction

Data Analysis

Double Hypernuclei

Excitation energy spectrum with QF Ξ- function

Solid lineobtained by QF Ξ- distribution

(Excitation energy spectrum) - (QF Ξ- function)

Image check

below 0 MeV47 eventsQF Ξ- function17.27

Decay mode check

coun

t

coun

tExcitation Energy [MeV]Excitation Energy [MeV]

Excitation Energy [MeV]Excitation Energy [MeV]

Decay mode of 12

ΞBe

summary outlook

12C(K-,K+)X reaction

Data Analysis

Double Hypernuclei

Mesonic decay : Ξ decay inside the nucleus

Non-Mesonic decay : Ξ interact with bound nucleon No charged particle at vertex

ProductionCross-section

summary outlook

12C(K-,K+)X reaction

Data Analysis

Double Hypernuclei

angleacccoKKKK

fffd

d

d

d

),(C),(CBe 121212 N

N

Excitation Energy [MeV]Excitation Energy [MeV]

Some QF-Ξ- events

summary outlook

12C(K-,K+)X reaction

Data Analysis

Double HypernucleiProduction

Cross-section

90% confidence level upper limit

Below 0 MeV< 1.714 μb/sr

Excitation Energy [MeV]Excitation Energy [MeV]

Summary 12C(K-,K+)X reaction

Data Analysis

Double HypernucleiSummary

• (K-,K+) reaction investigate at KEK-PS K2 beamline

• E522 spectrometer mass resolution 14.5 MeV

• Decay mode of 12ΞBe (below 0 MeV)

- ratio of mosonic decay to total event : 0.7 - ratio of mesonic decay to non-mesonic decay : 2.5

• Production cross section 90% confidence level upper limit < 1.714 μb/sr below 0 MeV

Thank you for your attention!!!