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

),(4 nKHe stopResult of previous experiment

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

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

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 >8)

(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

n_targetreaction_iNCtargetflightkaonTNC TTOFTTT _0

)0(

1. TNC-TT0

2. Determine vertex point TOFtarget->vertex

3. Tkaon_flight

K

Stopping kaon selection by T0 ADC

Reaction time of ),( XK

cLTTTT flightkaonTNCreaction /_0 z

z

K -

K -

T0ADC (a.u.)

T0ADC (a.u.)

Stop kaon selection region

Target cell

Degrader & Al cap

Target region

Unit :100ps

reactionT

Blue : cut by stop kaon selection

Red : remainder after stop kaon selection

Stopping kaon selection by reaction time

In-flight

Stop kaon

Reaction time of

100ps

),( XK

Zcos

Z

BLC

VDC

Target cellK

Beam direction

reactionT

NC ADC (MeVee)

1/b

eta

Separation for NC

n

Background level ~ 7MeVee

n/

Previous result (E471) Present preliminary result (E549)

n

3 MeVee

10 MeVee

5 MeVee

/1

S/N Improvement

Improvement

Even 5MeVee threshold, S/N ratio is about 10:1

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

cMeV /

nstopped

3MeVee threshold &

1 charged hit on TC &

1 charged hit on the opposite NC arm

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.

Particle identification by TC

Previous TC setup (E471)

Present TC setup (E549)

CBE

dE/d

x of

TC_

A (M

eVee

/cm

)

TC_D layer

TC_A layer

TC_C layer

TC_B layer Upgrade

TC_thin layer

TC_thick layer

(MeVee)

Semi-inclusive neutron momentum distribution

cMeV /

Blue : Accidental neutron

Red : After rejecting accidental neutron

With 10 MeVee threshold

NC ADC (MeVee)

1/b

eta

threshold

Only about 5% of E549 data was used

Accidental neutron

Previous result (E471)

summary

• Neutron S/N ratio is much improved.• Now, 1/beta resolution is comparable

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

z

y

z (mm)

Target cell

Carbon degrader

Al cap

y

x

Vertex image by VDC and BLC tracking

In-flight decay

stop decay

Beam direction cosine distribution of Decay particle by VDC chamber

Semi-inclusive Neutron momentum with 7MeVee threshold