Experimental study of strange tribaryons in the reaction

Heejoong YimSeoul National University

For E549 collaboration

),(4 nKHe stop

KEK-PS E549 CollaborationH. Bhang, J. Chiba, S. Choi, H. 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

nucl-ex/0310018

higher statistics with better resolution is required to confirm the peak structure.

2

1,2

100 pST

2

1,2

1

3

2

2

1,2

3

3

1

2

1,2

11,10

1 pST

pSHeK stom )( 4

nSHeK atom )( 4

2

1,2

10

nST

2

1,2

1

3

1

2

1,2

3

3

2

2

1,2

10,11

nST

Difference between

),(4 nKHe stop ),(4 pKHe stop

and

No structure at around 3140 MeV/c2 on the proton spectrum

T=0

KEK PS-E549 experiment• Further study of S0 state in the 4He(K-

stop, p) reaction

• Search for other kind of strange tribaryon in the 4He(K-

stop, n)

(2) Inclusive spectroscopy of S0

(1) Determination width with high resolution

E471 upper limit E549 finite value

Statistics x 20

Formation rate

(3) Search for excited state

(2) Confirmation of S+ (T=0) (statistics ~3 times higher)

(1) Study of isospin dependence (T=0,1 state)

K- + 4He → S0[T=1] + p | 1/2 -1/2 > |1 -1> + |1/2 1/2>K- + 4He → S+[T=1] + n | 1/2 -1/2 > |1 0> + |1/2 -1/2>

Formation ratio = 2:1

- 4He(K-stop, p) spectroscopy

- 4He(K-stop, n) spectroscopy

TC

TC

NC

NC

T0

VDC

BLC

TOF analysis for neutral particles

0TTNCT

tkaon_flighT

NCtargetTOF

flightkaonTNCNCtarget TTTTOF _0

1. TNC-TT0

2. Determine vertex point TOFtarget->vertex

3. Tkaon_flight

K

Stopping kaon selection by T0 ADC

z

z

K -

K -

T0ADC (a.u.)

T0ADC (a.u.)

Stop kaon selection region

Target cellTarget region

Z

BLC

VDC

Target cellK

Beam direction

Zcos

σ ~295ps

σ ~380ps

Z-vertex correction for kaon flight time from T0 to it’s stop

NC ADC (MeVee)

1/b

eta

Separation for NC

n

n/

Previous result (E471) Present preliminary result (E549)

/1

S/N Improvement

Improvement

S/N ratio is much improved.

10 MeVee

3 MeVee

5 MeVee

n

n

NC time calibration and resolution

σ~0.040

Previous result (E471)

/1

Now the resolution is comparable with E471 result. But, TOF analysis is still progressing.

So, the resolution will be more improved.

Present E549 result (very preliminary)

10 MeVee threshold

E MeVee

The resolution variation on ADC energy range(10 MeVee threshold)

/1

~185MeV/c

nstopped

Check of neutron TOF analysis using Σ decay

Monochromatic neutron source from

is expected in the stopped K - reaction

at 185 MeV/c

We can say neutron momentum scale is

reasonable.

3MeVee threshold &

1 charged hit on TC &

1 charged hit on the opposite NC arm

3MeVee threshold &

1 charged hit on the opposite NC arm

~185MeV/c

Particle identification by TC

Previous TC setup (E471)

Present TC setup (E549)

CBE

dE/d

x of

TC_

A (a

.u.)

TC_D layer

TC_A layer

TC_C layer

TC_B layer Upgrade

TC_thin layer

(a.u.)

TC_thick layer

TC_thick MeVee/cm

TC_t

hin

MeV

ee/c

m

Semi-inclusive neutron momentum distribution

Previous result (E471)

7 MeVee threshold

10 MeVee threshold

Present result (E549)

summary

• Neutron S/N ratio is much improved.• Now, missing mass resolution is

comparable with previous E471 result.• Neutron statistics is increased.• Analysis is in progress.

z

y

z (mm)

Target cell

Carbon degrader

Al cap

y

x

Vertex image by VDC and BLC tracking

Degrader & Al cap

),(4 nKHe stopResult of previous experiment

E471 for Indication of strange trybaryon S+ (T=0)

Stopping kaon selection by reaction time

Reaction time of

100ps

),( XK

Zcos

reactionT

Reaction time of ),( XK

cLTTTT flightkaonTNCreaction /_0

Unit :100ps

reactionT

Blue : cut by stop kaon selection

Red : remainder after stop kaon selection

In-flight decay

stop decay

Beam direction cosine distribution of Decay particle by VDC chamber

7MeVee

Stop event Passing through event

PID by TC (2)

cMeV /

Blue : Accidental neutron

Red : After rejecting accidental neutron

With 10 MeVee threshold

NC ADC (MeVee)

1/b

eta

threshold

Accidental neutron

Cell structure of VDC