An Experimental Search for Deeply Bound Kaonic Nuclei with Stopped

Kaons

Takatoshi Suzuki(U-Tokyo), for KEK-E471 collaboration

Outline:1. Introduction2. Experiment and devices3. Low level analysis4. 4He(K-

stopped, p) spectra and discovery of S0(3115)5. 4He(K-

stopped, n) spectra and indication of S+(3140)

6. Discussion and Conclusion

1. Introduction1-0 Does deeply bound kaonic nuclear states with narrow widths

exist ?-> Yes they do! * Wycech (cf. NPA 450 (1986) 399c )

coupled channel potential and in-medium t-matrix (from Martin) * Kishimoto (PRL 83 (1999) 4701)

Atomic DD potential + SU(3) Chiral Lagrangian (from Batty-Friedmann-Gal) (from Waas-Kaiser-Weise)

* Akaishi-Yamazaki (PRC 65 (2002) 044005)

low energy KN scattering + (from Martin + Iwasaki) -> No, they don’t! They must be shallow and broad. * Many authors.

1-3. AY predictions3 - Isospin dependence of the kbar-nuclear states

State gI=0 gI=1 Un-contracted

(MeV)

EK

Contracted

(MeV)

EK

3KH(T=0) 3/2 3/2 -76 82 -108 20

3KH(T=1) 1/2 5/2 - - -21 95

4KHe(T=1/2) 1 3 -69 66 -86 34

First prediction of a strongly bound narrow kbar-NNN state with T=0.Shallow and broad state with T=1

Y. Akaishi and T. Yamazaki,PRC 65 (2002) 044005

1-4. 4He(K-stopped, n/p) reactions - population of the kbar - NNN states

4He(K-stopped, n) T=0,1 formation channel -> (K- - 3He)T=0, (K- - 3He)T=1,Tz=0

Appearance of a narrow peak was expected. 4He(K-

stopped, p) T=1 formation channel -> (K- - 3H)T=1,Tz=-1

No narrow peaks were expected.

1-5. Experimental principle• Kaonic helium4 formation

from stopped K-

• Kaonic nuclear formation via nuclear Auger effect

• Neutron(proton) emission as a spectator

• Strong decay into mesonic or non-mesonic final states

Triple coincidence of

1. Incident kaon

2. Auger nucleon

3. Secondary charged particleMissing mass spectroscopy.

2. Experiment

Stopped K- method.

1. Incident K- and its track

by beamline detectors -

2. secondary charged particle and

its track by TC-VDC -

3. nucleon and its stop

timing(TOF) by NC -

are measured in coincidence.

Those 3 signals are required hardwarewise

K-beam & VTCOR &NCOR

semi-inclusive spectra

2-1. Experiment - an overviewM. Iwasaki et al., NIM A 473 (2001) 286

2-2. kaon beam line Secondary K- beam extracted through

KEK-PS K5

* 2TP(Tera Proton)/spill(1.6 sec

duration with 4 sec cycle)

* 6cm thick Pt production target

* pK ~ 650 MeV/c

p/p ~ 4 %

* Wedge-Shaped-Degrader

(stopped K+ yield: 1.5 times enriched)

2-3. Beam line devices 1 - a side view

Beam definition -> ScinitllatorsK/separation -> Lucite Cherenkov Counters … Kratio at T0: 0.005

Kaon track detection -> Beamline Drift Chamber (BDC) ~ 4.7 k/spill

~ 0.88 M/spill

2-5. Beam line devices 3 - Liquid helium4 target Only a brief summary……

* 0.145 g/cm3 super fluid helium 4 * Cell structure: cylindrical tube

* 15 cm thickness (2.18 g/cm2)

* 23.5 cm diameter

* Stable operation below 2.0 K

2-7. Neutron detector system - cross sections of NC and NCV

Plastic scintillator segments to detectnucleon stop timing and position.

* Two arms(32(E471)+ 24(SKS)segments)* 8.3 % of total solid angle* NCV to cover NC

segments * Fe plate between NC and NCV to induce

e+ e-

Reaction vertex is defined

by the two pre-defined

tracks.

Vca: vector connects two

closest- approaching

points, which represent

final state hyperon motion

DCA : |Vca|

3-3. Reaction vertex and DCA

With two-dimensional correlation between T0 pulse height and

Vertex z position…..

3-4. Stopped K selection

K+ K-

With reaction vertex

position…..

Events originate

from outer materials

are omitted.

3-5. Target fiducial cut

We measure the time difference between kaon injection onto T0 and nucleon detection on NC.

With ray events….1. Slewing correction factors

2. z-vertex correction factor(Flight time of K from T0 to its stop:)

3. Time origin in order to adjust 1/for events

are determined.

3-7. TOF analysis on NC (1)

spectrum for neutral particles….

3-8. TOF analysis on NC (2)

Variation of the center and of 1/ distribution...

Procedure…• Charged particle is Selected by NCV hit.

2. Total light output,

is obtained.

3. The proton events appear on the two-dimensional correlation between and ENC.

3-9. Proton PID on NC

PID of secondary charged

Particle:

Stage 1

TCthin dE/dx vs TOF

Stage 2 (Fig.)

dE/dx vs dE/dx

Proton and pion are

separated.

3-10. PID of secondary charged particle

For the events(pion) within the

polygon, momentum value can

be defined.

3-11. Secondary pion momentum cut

We divide the pion events at 125 MeV/c -255 MeV/c (hypernuclear formation)exclusively appear on -decay side.

VN : a unit vector along with detected hyperon motion

VcaVN ~ 0 -> Quasi-free hyperonproduction or hypernuclear formation << 0 -> non-pionic absorption or kaonic nuclear formation and its non-mesonic decay >>0 -> hyperon decay

3-12. Study of the hyperon motion in the final state - VcaVN

4. 4He(K-stopped, p) spectra

4-1. Semi-inclusive momentum spectrum

A significant peak structureExists just below 500 MeV/c, on a continuum due to

1. Formation of a strange tribaryon via

2. Hypernuclear formation and its non-mesonic two-body decay

3. A fake due to instrumental bias?

Discovery of a strange tribaryon S0

4-2. Classification of the momentum spectrum 1 - by secondary charged particle ID and momentum

(a) pion cut

(b) proton cut

(c) fast(decay) pion cut

(d) slow(decay) pion cut

4-3. Classification of the momentum spectrum 2 - VcaVp selection

Under pi-cut condition-(a) VcaVp : -6 ~ 0 -> hyper nuclear two-body decay

(b)VcaVp : 0~+6 -> hyper nuclear two-body decay

(c) VcaVp : -60~-6 -> Formation of a strange tribaryon and its non-mesonic decay

(d)VcaVp: 6~60

-> nothing to generate mono-chromatic structure…

4-5. Summary of the analysis

a): event topology of hypernuclear cascadeb),c): indication of analysis 1,2

4-6. 4He(K-stopped, p) missing mass spectrum and S0(3115)

Event-by-event energy loss correction ->

Function fitting with P3 BG + Gaussian signal->DOF = 8.76/12Gaussian center: 3117.7 MeV/c2

Gaussian sigma: 8.7 MeV/c2

Statistical significance: S/S = 2441/297= 8.2

(Unexpected) Discovery of a Starnge Tribaryon S0(3115)

T. Suzuki et al., PLB 597 (2004) 263

5. 4He(K-stopped, n) spectra

5-1 Momentum referential peakMonochromatic neutron source from

stoppedn

is expected in the stopped K- reaction at 185 MeV/c (1/).

The peak position is exactly adjusted even for the events with small pulse height, and it also ensure the proton momentum scale as well as neutron.

5-2. Semi-inclusive neutron momentum spectrum

Neutron semi-inclusive momentum spectrum at 10 MeVee thresholdAfter constant BG subtraction….The overall shape is well reconstructed by Monte-Carlo simulation.No clear peak-like structure is found in.

The intensity over400 MeV/c is exclusivelydue to non-pionic absorptionprocess….

5-3. Classification of the spectrum by pion momentum

An indication of a peak structure is found only in -decay cut spectrum

-> indication of another kind of strange tribaryon S+ mainly decays into ?

-> further study by VcaVn selection is required…...

5-4. Classification by VcaVn and indication of S+

Once decay mode and mass value hasbeen estimated, we can set relevant VcaVn window to enhance the signalusing Monte-Carlo.

Comparison between(a)-25<VcaVn<-5 (HSN) AND-5<VcaVn<-2 or -60<VcaVn<-25 (LSN)

(b)5<VcaVn<25 AND2<VcaVn<5 or 25<VcaVn<60

We find a clear enhancement of HSN spectrum on (a) -> Indication of S+

5-5. 4He(K-stopped, n) missing mass spectrum and S+(3140)

A enhancement of the HSN missing mass spectrum at around 3140 MeV/c2

-> An indication of another kind of strange tribaryon S+(3140) state. * No structure at around 3140 MeV/c2 on the proton spectrum-> T=0.A global fitting to the HSN data points of1 exponential BG + 2 Gaussian (S+(3140) and S+(3115)) DOF = 28.52/31Gaussian center: 3140.5 MeV/c2

Gaussian sigma: 7.3 MeV/c2

Statistical significance:S/S=120/32= 3.7

Consistent yield with S0(3115)

M. Iwasaki et al., nucl-ex/0310018 v2

6. Discussion and conclusion6-1 Comparison between kaonic nuclear calculation

S0(3115) = K-pnnT=1,Tz=-1,S+(3140) = K-ppnT=0 (=3

KH)kaonic nuclear state?

Problem?:1. level reversing2. large deviation of kbar binding energy up to 100 MeV.

Other possibilities?

Experiment: nucl-ex/0310018 (v2) , PLB 597 (2004) 263.Non-relativistic calc.: PRC 65 (2002) 044005 , PLB 535 (2002) 70.

6-2. Experiments for kaonic nuclear study in year 2005For B=3….

1. KEK E549(Iwasaki) - Study of 4He(K-

stopped, p) inclusive spectrum - Extension of E471 for 4He(K-

stopped, n) 2. KEK P570(Hayano) - Kaonic 4He 3d->2p X-ray measurement - Extension of E471 for 4He(K-

stopped, n)

For other baryon numbers…1. FINUDA at Frascati(Nagae) - Invariant mass spectroscopy for B=2,3 - Missing mass spectroscopy for heavier nuclei2. KEK E549(Kishimoto) - Missing mass spectroscopy via 16O(K-, p) reaction

6-3. Conclusion

1. We have discovered a new kind of strange tribaryon

S0(3115) with total isospin T=1 in the 4He(K-stopped, p)

reaction.2. An indication of another kind of strange tribaryonS+(3140) with total isospin T=0 has been obtained in

the 4He(K-stopped, n) spectrum.