A search for strange tribaryonic states

in the reaction

Heejoong YimSeoul National University

For KEK-PS E549 collaboration

),(He stopped4 nK

KEK-PS E549 Collaboration

H. Bhang, J. Chiba, S. Choi, Y. Fukuda, T. Hanaki, R. S. Hayano, M. Iio, T. Ishikawa, M. Iwai, S. Ishimoto, T. Ishiwatari, K. Itahashi, M. Iwasaki, P. Kienle, J. Kim, Y. Matsuda, H. Ohnishi, S. Okada, H. Outa, M. Sato, S. Suzuki, T. Suzuki, D. Tomono, E. Widmann, T. Yamazaki, H. Yim

Y. Akaishi & T. Yamazaki : PRC 65 (2002) 044005

・ Deep!

・ Narrow!

～ 100 MeV

～ 20 MeV= meta-stable

・ Shrink!

cf: BN ～ 10 MeV

= high density?

Embedding Ｋ in nucleus ？

4He

p p n K- n

Z : +1T : 0 or 1

pp n n K-

Z : 0Ｔ　：　１

predicted

unpredicted

Missing mass measurement

3

How to produce ？

),(He stopped4 pK

),(He stopped4 nK

Possible states of the reaction

Neutron spectrum

Hard to confirm the structure due to low statistics

Search for state (T=0) with 8 times better statistics than E471

Aim of

),(He stopped4 nK

Reaction Z T TZ

+1 1,0 0 Predicted by Akaishi

),(He stopped4 nK spectroscopy

He3K

E471 nucl-ex/0310018

Y. Akaishi & T. Yamazaki : PRC 65 (2002) 044005

Motivation of E549 Neutron Measurement

Stopped K- method.

① Incident K- and its track

by beamline detectors

(K-/π- ratio ~ 1/200, K- ~ 5000/spill)

② Nucleon and its stop

timing(TOF) by NC

③ Secondary charged particle and

its track by TC-Tracking Chamber

Same condition with previous experiment

(Semi-Inclusive condition)

① ②

③

TC

TC

NC

Overview of Experiment Setup

T0 & BDC

TOF Analysis for Neutral Events

Beam

1. TT0 : Measured time by T0

2. Tkaon_flight : Beam (K-) flight time from T0 to it’s stop

3. TNC : Measured time by NC

Track viewed by VDC&BDC

Liq. He

veto

TOFtarget→NC : Flight time from target vertex to NC

TOF targetNC

TNC

TT0

Tkaon_flight

1.5 times Improved Missing Mass Resolution

1/β

ADC (MeVee)

n

E471

Time Calibration and Resolution for Neutron Counter (NC)

E threshold=7 MeVee

1/β

σ =0.030E549

E471

Missing Mass [MeV/c2]

Mis

sin

g M

ass

reso

luti

on

in

σ [

MeV

/c2 ]

Black – previous (E471)

Red – Present (E549)

Resolution variation on a Missing Mass

Momentum scale and slewing correction are well tuned

Σ+ n

π+

cos θ < -0.99

(~185 MeV/c)

(~185 MeV/c)

(~0 MeV/c)

K- N

ΣQF πQF

Check of TOF Analysis

Threshold=2MeVee

ADC (MeVee)

MeV/c

Σ decay

Pn ~ 185MeV/c

Threshold=2MeVee

Σ decay

1/β ~ 5.18

1/β

Co

un

ts /

(5

MeV

/c)

Neutron momentum

E471 E549

Much improved S/N ratio

ThresholdE471 = 10 MeVee

ThresholdE549 = 7 MeVee

10 MeVee

n

1/β

Co

un

ts/0

.025

Background Level Check

5 MeVee

Co

un

ts/0

.025

1/β

Semi-Inclusive Neutron Spectrum

E471 (nucl-ex/0310018)

About 8 times higher statistics

Neutron momentum (MeV/c)

Co

un

ts /

(10

MeV

/c) E549

Neutron momentum (MeV/c)

Semi-inclusive Semi-inclusive

Missing Mass Spectrum

Co

un

ts /

(5 M

eV/c

2)

Black – Data

Red – Estimated background

Missing Mass [MeV/c2]

Semi-inclusive neutron

Background subtracted

Pion coincidence is required to estimate upper limit of kaonic state

Co

un

ts/(

5MeV

/c2 )

Missing Mass

[1] R. C. Byrd et al. Nucl. Inst. Meth. A313 (1992) 437.

Missing mass spectrum with pion coincidence

Missing Mass [MeV/c2]

Black – 7 MeVee threshold

Red – 10 MeVee threshold

Blue – 13 MeVee threshold

Missing Mass [MeV/c2]

Eff

icie

ncy

[ra

tio

]

Neutron detection efficiency estimation by

DEMON code [1]

Arb

itra

ry U

nit

Efficiency corrected Missing Mass

Missing Mass [MeV/c2]

Mis

sin

g M

ass

reso

luti

on

in

σ [

MeV

/c2 ]

Black – previous (E471)

Red – Present (E549)

Resolution variation on a Missing Mass

Λπ NNΛnp ΣNN

•Develop a simulation for the semi-inclusive measurement with pion coincidence.

•Estimate number of stopped kaon in the target.

Obtain upper limit of the kaonic tribaryon state.

The further analysis is in progress !

Further analysis procedure

Goal

IF exist, → YNN or πΛNN Y → π±N

Study spectrum using decay particle - Σ± production by fast π (>~125 MeV/c)

- Λ production by slow π (<~125 MeV/c)

He3K

Event tagging can improve S/N ratio, selectively.

Event tagging by TC

He3K

neutron momentum [MeV/c] neutron momentum [MeV/c]

neutron momentum [MeV/c]Counts / (10 MeV/c) Counts / (10 MeV/c)

Counts / (10 MeV/c)

Neutron momentum spectra

E471(nucl-ex/0310018)

Co

un

ts /

(10

MeV

/c2 )

Neutron momentum [MeV/c]

Fast π tagged

E549

Co

un

ts /

(10

MeV

/c2 )

Neutron momentum [MeV/c]

Fast π tagged

At the present moment, the narrow (Γ~20 MeV/c2) structure wasn’t observed.

Summary•Neutron spectra was measured for the reaction with upgraded setup.

•At this stage, Narrow (Γ~20 MeV/c2) peak structure of kaonic state did not appear on present result.

•Now, in progress status, analysis for upper limit estimation of kaonic tribaryon state.

),(He stopped4 nK

Spare OHPs

Missing mass spectrum

MeV/c2

Pion triggeredSemi-inclusive

MeV/c2

Neutron spectra (5MeV/c binning)

Semi-inclusive Pion triggered

MeV/cMeV/c

Stopping kaon selection

z

K -

T0 (light output)

Stop kaon selection region

Target cell region

ZBLC

VDC

Target cell

Beam direction

Zsin

Stop kaon selection makes the acceptance to be correct

Sine distribution for scattered particle by VDC tracking.

T0Kaon at rest

In flight

z

Semi-inclusive neutron momentum distribution

Previous result (E471)

7 MeVee threshold

10 MeVee threshold

Present result (E549)

At 7 MeVee threshold, total statistics is about 8 times higher than E471 statistics.

IF exist, → YNN or πΛNN Y → π±N

Study spectrum using decay particle - Σ± production by fast π (>~125 MeV/c)

- Λ or Σ0 production by slow π (<~125 MeV/c)

He3K

π selection by using TC

Event Selection using TC (I)

He3K

E549 TC setup

TC_D layer

TC_A layer

TC_C layer

TC_B layer

Event Selection using TC (II)

Pion

E471 TC setup

TC_A layer

TC_B layer

Upgrade

Pion

Proton

Cut for Pi/P separation(1)

Eb+Ec (MeVee) Eb+Ec (MeVee)

Dire

ctio

n no

rmal

ized

EA

(MeV

ee)

Dire

ctio

n no

rmal

ized

EA

(MeV

ee)

Red - fast pion

Green - fast proton

Red - slow pion

Green - slow proton

Eb+Ec (MeVee)Dire

ctio

n no

rmal

ized

EA

(MeV

ee)

w/ D layer hit w/o D layer hit

w/ no cut

Pi/P separation for A-layer vs (B-layer + C-layer)

Eb+Ec (MeVee)

Eb+Ec (MeVee) Eb+Ec (MeVee)

Dire

ctio

n no

rmal

ized

EA

(MeV

ee)

Dire

ctio

n no

rmal

ized

EA

(MeV

ee)

Dire

ctio

n no

rmal

ized

EA

(MeV

ee)

no cut

fast pi or slow pi fast p or slow p

PID definition by TC

Pion

ProtonBlue – slow pion

Red – fast pion

TC 2nd layer [MeVee]

TC

1st [

MeV

ee]

TC 2nd layer [MeVee]

TC

1st [

MeV

ee]

TC 2nd layer [MeVee]

TC

1st [

MeV

ee]

TC 2nd layer [MeVee]

TC

1st [

MeV

ee]

E549

MeV/c

Co

un

ts /

(10

MeV

/c)

E471

Neutron spectrum with pion trigger

MeV/c

10 MeV/c binning

Detection efficiency correction

Efficiency curve by DEMONS

Efficiency corrected spectra

Less than 0.05%

Resolution variation

MeV/c

Mo

men

tum

res

olu

tio

n (

σ)

[MeV

/c]

Incoming K －

proton

4He target

Neutron counters

Iron plate

Charged particle vetocounter

E471 Setup Upgrade in E549

Incoming K －

proton

Neutron counters4 layers→7 layers

neutron

Proton TOF stop (σ ～ 70ps)Veto counter for neutrondetection

Smallertarget

TOFStart counter（ σ< 70ps)

Proton chamber

resolution improve 150ps→50ps

Both proton/neutronσ ～ 300ps

proton σ=100 ～ 150ps neutron σ=200ps

Upgraded feature of E549 setup

Introduction

Neutral event analysis

Results