SIDDHARTA future precision measurement of kaonic atoms at DA F NE
An Experimental Search for Deeply Bound Kaonic Nuclei with Stopped Kaons
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Transcript of An Experimental Search for Deeply Bound Kaonic Nuclei with Stopped Kaons
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.