1 / 15-14np

Λ

A deeply bound Ξ N system
detected in nuclear emulsion
Kazuma Nakazawa
for the E07 (J-PARC) collaboration
Phys. Dept., Gifu Univ., JAPAN
30th Nov., 2014

Outline1. Ξ-N interaction
2. “Overall scanning” method
3. The KISO event showing
a deeply-bound Ξ-N system
4. SummaryJ-PARC
Hadron2014

2 / 15n

１．Ξ-N interactionpΛStudy of hadron-hadron interaction,

In S=-2 sector,

J-PARC
Hadron
2014

Baryon octet YY-mixing [ΛΛΞNΣΣ(H)]･ m(ΞN) – m(ΛΛ) = (23~28) MeV<= m(ΣN) – m(ΛN) = 80 MeV

 Uniquely available source of information;
H-dibaryon, double-Λ hypernucleus, Ξ hypernucleus

ΞN interaction,

 can be studied a Ξ-nucleus potential via Ξ hypernucleus and Ξ atoms
However non conclusive measurement has been made, so far.
@ BNL, KEK ・Any peak structures for Ξ-nuclear state were not observed.
・Attractive potential on 1Ξ2Be was suggested to be 14 MeV.
・Two events (E176) … 3D atomic or nuclear p bound state?
one event (E373) … consistent with the Ξ- capture in 3D orbit.
@ J-PARC (coming soon)
・E03 & E07 … X-ray measurement from Ξ atoms.
・E05 ………… High reso. spectr. of Ξ hypernuclei.

For the emulsion experiment,

it has been a key point to develop fully automated and fast scanning system.

3 / 15

2. Development ofnpΛ“Overall-scanning”

Primary motivation;
fast detection of α decay verticesof natural isotopes to calibrate
range-energy relation.

① fast image capture
Developed systemwith CCD camera：Win2000 sp4：3.0 GHz
1.57GB RAM
Camera ：100Hz (CCD)
Obj. lens：x 50
emulsion： 500μmarea：0.1x0.08mm2# of image：~100/cycle
Time：3sec/cycle[～ hard limit]
OSCPUJ-PARC
Hadron2014

4 / 15

2. Development ofnpJ-PARC
Hadron2014

Λ“Overall-scanning”② fast image processing for event detection
Until April. 2013,
α decay VTX
8 M images by test operation (1.46 cm )3using E373 emulsion (55 liters)
Double-Λ3 vertices

2 vertices (single-Λ cand.)

NAGARA event

was detected by this method

more5 / 15

3. A new event by the “Overall-scanning”,
named“KISO”
p Λn

Emitted back-to-back direction

J-PARCHadron2014 Topology seems to be consistent with the past events of twin hypernuclei (E176).

Results of KEK-E176: S.Aoki et al., NP. A828 (2009) 191-232

np

A new event by the “Overall-scanning”,
named“KISO”
Λ6 / 15J-PARC
Hadron2014

E176 results; S.Aoki et al., NP. A828 (2009) 191-232
Ξ− binding energy (MeV) in nucleus : 12C [most probable]

Coulomb assisted
nuclear p bound state.
==> VΞ- = 18 MeV
Y. Yamamoto, Few-Body Syst.
Suppl. 9 (1995) 145

BΞ- = 3.75 MeV (Γ = 2.7 MeV)
for nuclear p state
Y. Akaishi,Nucl. Phys. A 547 (1992) 217c

BΞ−(3D) = 0.13 MeV for 12C  not inconsistent!!
(= 0.17 MeV for 14N)

Range-Energy relation

was calibrated in good accuracynΛpProtonfor Std. emulsion(Ilford G5 : 0 = 3.815 g/cm3);
ref.[1] W.H.Barkas, N.C. VIII (1958) pp.201-214
data fitted by polynomial expression
under the Bethe-Bloch formula.

Calc. Our 7th order polynomial fitting to the ref.[1]7 / 15J-PARC
Hadron2014

Density of our emulsion;= 3.621 +/- 0.105 g/cm3by measurement of α rays
with monochromatic K.E.
from 212Po and 228Th.
Consistent with= 3.667 +/- 0.066 g/cm3
by measurement ofits size and weightat the E373 beam exposure.

The density error of 0.105 g/cm3
gives rise inaccuracies,

ΔR / R : 1.1%
ΔE / E : 0.7%
for proton to 12C
with their energy
less than several tens’ MeVnp

8 / 15Outline of the KISO event

J-PARCHadron2014Λ1) Ξ- hyperon can be produced in the target (8 mm from top the Em.)
2) Auger electron  make the capture point clear.
3) MIPS track from the decay point D.
E373 setup
4) TK #4  went out of the emulsion stack.
5) Consistent with Ξ- capture reaction occurred on C, N or O.
6) The charge of #2 should be 2 or more.
7) The charge of #1 should be ≦ 5.
8) Hummer track : 8He, 8Li or 8B  8Be*(2+).

Vertices A & BAB#4#4

Ranges and angles
track range (µm) theta (deg.) phi (deg.)#1
8.0 ± 0.3 133.0 ± 3.0 13.2 ± 3.2#2
69.1 ± 0.5 40.4 ± 0.9 193.1 ± 1.2#3
13.3 ± 0.4 102.3 ± 2.3 340.4 ± 1.6#4> 4990.7 145.0 ± 0.9 85.4 ± 1.3#56.7 ± 0.3 49.6 ± 4.2 132.6 ± 4.3#65.8 ± 0.3 131.0 ± 4.5 318.9 ± 4.7#7 2492.0 ± 3.9 43.1 ± 1.3 191.8 ± 1.5#837.3 ± 0.7 131.9 ± 1.3 29.2 ± 1.3

comments
Single-hypernucleus
77.1 ± 0.3 µm : B ~ C
Out of the emulsion stack8
α from Be8
α from Be

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Analysis of the KISO eventnVertexp Λ D

0510 (μm)(a)(b)

5Vertex BReconstructed mass
(MeV/c2)
7458.531 ± 0.307  Using measured data
7458.540 ± 0.308  Under the momentum balance

8Be*(2+) → 2α at VTX. DD0

Mass of 8Be∗(2+)(MeV/c2 )7457.890(Γ = 1.5 MeV)

J-PARC
Hadron2014

10 (μm)Possibility of mesonic decay of #1
π- possibility (#4) is nothing in comparison with Energy-loss(Grain density ~ x1.41[+/- 0.08]) of π- in the NAGARA event.
K.E. of #4 (34.8MeV, if it’s a proton ) was too large to understandthe decay mode with a π0 meson at the decay point of #1.

B#4

Non-mesonic decay at VTX. B

Vertex Bnp

The case of 8B : denied under charge conservation

ΛBJ-PARCHadron
2014

Total A ≦ 17, total Z ≦ 7 (even for Ξ− + 16O)
・TK #2 … must be non-mesonic … Z(≧2)
 TK #1 (Z≦5)  if TK #4 Z=1, TK #3(Z≦4)  8＝
B

The case of 8He : denied momentum imbalance at VTX.A
Assuming 8He (#3) / p or d (#4)  ΛLi (#1),
only the process is considered;Ξ- + 16O => 1Λ0Li (#1) + 7ΛBe(#2), 1Λ0Li => 8He (#3) + p (#4) + n
Momentum imbalance (373.1 +/- 13.4 MeV/c) at point A#4

The particle (#3) should be 8LiVertex BB

10 / 15

Possibility of 8He or 8B for TK #3

Possible process at VTX. B

Consistent with an association of a MIPS from VTX. D.

Mc : Mass of a core nucleus + M(Λ)
Mr : reconstructed minimum mass
Mc ‑ Mr : BΛmax. should be plus value.

#4

The particle (#1) is1 0Be, 1 1Be or 1 2Be.
ΛΛΛ

There is no bound hyperfragment for track #2

11 / 15nVertex A Possible process at VTX. ApΛAThe mode :Ξ− + 14N  1Λ0Be + 5ΛHe
was uniquely identified

J-PARCHadron
2014Vertex A Possiblities of in-flight decay of hypernuclei (#1 and/or #2)
npΛ

12 / 15J-PARC
Hadron2014

BΞ− = M(Ξ−+14N) – E(1Λ0Be) – E(5ΛHe)– ΔK.E.(1Λ0Be + 5ΛHe)
Assuming BΞ− = 0.00 MeV, ΔK.E. = 4.43 MeV.

A

Decay rates R were estimated : R (1Λ0Be) = 0.6%, R (5ΛHe) = 2.9%
Thus, it is very unlikely for decays in flight on both nuclei.
It is also unlikely for in-flight decay for one of them due to well balance of momenta.
10Be and 5 He decayed after stopping.
ΛΛProcess of the KISO event
Ξ− + 14N  1Λ0Be + 5ΛHe,− )10Be  8Li + p + n, 8Li  2α + e- (+ νΛeex.

5 He  p(#7) + d(#8) + 2nΛBΞ− = 4.38 +/- 0.25 MeV (by Mom. balance [#1 and #2])

Measurement error : 0.09 MeV
Mass (1Λ0Be, 5ΛHe, Ξ−) error : 0.23 MeV

the KISO event
ΛTheoretical predictions

3.7σerr far from 3D level (σerr ~ 0.25 MeV)

0system
0.174

BΞ− = 03.27 (1+)
3.07 (0+)
2.41 (3--)
2.36 (22)3.228 (1-)
3.202 (0-)
2.585 (3--)
2.482 (2 )-0.110 (2 )0.08 (21)-BΛ = 9.11 +- 0.22(exp.)

10Be
Λ
g.s.

1.14

2
34

4.38±0.25

5Err.(meas.)=±0.09
Err.(mass)=±0.23

PTP. 105 (2001) 627

51.11±0.25

Yamaguchi, Yamamoto & Ueda

6.509 (4-)
6.433 (3-)

BΞ− (MeV)

110H & Y DJM

Ξ−14N

5.69

3D2p
The paper well presented thatthe past two event to be occurredin 2p nuclear bound state.

9Be + Λ0Energy (MeV)

J-PARCΞ− + 14N  1Λ0Be + 5ΛHe uniquely identified!! Hadron2014
BΞ− = 4.38 +/- 0.25 MeV (by Mom. balance for 1Λ0Be and 5ΛHe)np

13 / 15

The first evidence of a Ξ-14N system to be bound deeply. 1s

 submitted to PTEP

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np

4. Summary

J-PARCHadron2014

1. Λ We have performed experiments to study S=-2 systems with the nuclear
emulsion at KEK, however any conclusive information has not been obtained,so far.
2.

To get reliable information about S=-2 systems, we are developing fully
automated and fast scanning system, “Overall scanning” for theemulsion.

3.

During test operation of the system, a clear evidence of a deeply bound Ξ14N system, Ξ− + 14N  10Be + 5 He, has been detected and uniquely identifiedΛΛ3
in the emulsion of 1.46 cm volume among 55 liters.

4.

The detected event, named “KISO”, presents a deeply bound Ξ-14N systemwith Ξ− binding energy of 4.38 +/- 0.25 MeV, which is no longer theatomic 3D state (0.17 MeV for Ξ- atom on 14N). Even if the 1Λ0Be nucleus wasproduced in excited state, Ξ− binding energy is far from 3D atomic state bymore than 3.7 standard deviations.

5.

It was understood that ΞN interaction will be attractive!! To understandA-dependence of ΛΛ int. and ΞN interaction more in detail, we willcontinue development of “overall scanning” method to be applied in theE07 experiment, of which beam exposure can be carried out in Early 2016 (?).

New scanning systemfor the E07emulsionnp

15 / 15Λ

×300faster !!

with piezo stage
Present110 μm

Present system

130 μmJ-PARC
Hadron2014New

Obj. Lens

×50 (NA. 0.9)

×20 (NA. 0.35)

Camera100Hz XC_HR300

800Hz HXC20Pixel

512×440 pixel

2039×357 pixelArea

130 mm×110 mm

1140 mm×200 mm

0.3

55 sets

2 setsRate(Hz)200 μm1140 μm

Images of all of the emulsion plates can be obtained in a few years.