search for the k - pp bound state via photon-induced reaction

Search for the K-pp bound state

via photon-induced reaction

“Hadron in nucleus” @ Kyoto University 1st. Nov. 2013

A. O. Tokiyasu (RCNP) for LEPS collaboration

ContentsWhat are Kaonic nuclei?

LEPS experiment at SPring-8

Results

Future work: search in LEPS2 experiment

Conclusion ☆ 　 This presentation is based on arXiv.1306.5320

2013/11/1 2Hadron in nucleus @ Kyoto University

What are Kaonic nuclei?


Kaonic nuclei KN interaction is strongly attractive (I=0) K bound state in nucleus → Kaonic nuclei

important to understand the sub-threshold KN interaction

KNN bound states are the simplest kaonic nuclei. K-pp bound state: largest B.E.

2013/11/1 Hadron in nucleus @ Kyoto University 4

KN L(1405) (KN + Sp)

CERN, LEPS, CLAS

KNN wide peak structure

FINUDA, DISTO

KNNN no narrow peak KEK PS-E471/E549

K + nucleus Kaon potential Osaka Group (KEK, BNL)

T. Yamazaki et al. PRC76, 045201

A.N. Ivanov, et al.arXiv:0512037v2

N. V. Shevchenko, et al. PRC76, 044004

Y. Ikeda et al. PRC76, 035203

A.Dote, et al.NPA804, 197

S. Wycech et al.PRC80, 045207

M. Bayar et al.arXiv:1207.1661v1

B.E. [MeV]

48 118 50~70 60~95 20±3 56.5~78

15~30

G[MeV]

61 58 ~100 45~80 40~70 39~60 75~80

K-pp bound state

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B.E = 10- 95 MeVG = 39 – 100 MeVdepending on- KN interaction- calculation methods

Hadron in nucleus @ Kyoto University

）（）（ syststat 34

65115

）（）（ syststat 23

141167

）（）（ syststat 53103 ）（）（ syststat 108118

B.E. =B.E. =G =G =

MeVMeV

MeVMeV

Theoretical prediction

Experiment

PRL 94, 212303 (2005) PRL 104, 132502 (2010)FINUDA @ DAFNE DISTO@ SATURNE

stopped K-

Lp invariant mass

↓ 　 inconsistent↓

pp→K+LpMM(K+)

search experiments via different reactions are awaited! → photon-induced reaction.

g-induced reaction

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K+

p

g

K-, K*-

pn

detect K+ at very forward angle→ t-channel reaction (on-shell meson exchange)→ virtual K- or K* beam ( p = 06-1.0 GeV/c)g (J=1, I=0, 1 )

N

NK

d (g, K+ p) X Eg=1.5- 2.4 GeV

p- X=K-pp ←This talk

p0 X=K-pn p+ X=K-nn

search for the peak structure in the inclusive missing mass spectrum MMd(K+p-)

search region: 2.22 – 2.36 GeV/c2

B.E. = 10 – 150 MeV


HADRON13(g, K+) K-pn(g, K+p+) K-nn

E, p measured

LEPS experiment at SPring-8


LEPS/SPring-8

Data take:2002/2003, 2006/2007 7.6 x 1012 photonss LD2 target (Total)

SPring-8: 8 GeV electron storage ringLEPS : hadron physics using g beam

Backword Compton Scattering

e

e

Detect withTagging counter

Eg=1.5 - 2.4 GeVexperimentalhatch

355nm laser

8 GeV

LEPS

DEg=12 MeV


LEPS spectrometer

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TOF

Dipole Magnet　 0.7 [Tesla]

Target

Start Counter DC2 DC3

DC1SVTX

AC(n=1.03)SSD(SVTX)Drift Chamber(DC 1~3)

position

Start Counter(SC)Time of flight wall(TOF)

time

Aerogel Cherencov counter(AC)Start Counter (SC)

trigger

g (1.52.4 GeV)

p-

K+


K+ and p- are detected at very forward angle(< 15 degree)

particle identification

K+

p- Dp ~ 6 MeV/c @ 1 GeV/c

DM ~ 10 MeV/c2

(2.22 - 2.36 GeV/c2 ) in MMd(K+p-)

TOF (Time of flight)

m2 = p2(1/β2 - 1)

Track reconstruction + Runge-Kutta method.

p

p+

K-

0


Analysis and Results


missing mass spectrum

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→No peak structure was observed!

expected signal

A: g n → S- K+

S- → n p-

B: g p → L K+ p-

C: g p/n → S-/0 K+ p-

B+ C : ~11 mbPeak structure was searched in 2.22 - 2.36 GeV/c2.

A

B

C


cut condition

-cosqlabK>0.95

-cosqlabp>0.95

-0.25<pK+<2.5-0.25<pp-<0.6

Determination of the upper limit of production cross section


log Likelihood ratio method.

DlnL = logL[Signal + BG] - logL[BG]

Signal : Breit-Wigner (fixed B.E., G)BG : quasi-free processes (listed in Figure)

The yields : -2DlnL=3.84 → upper limit at 95 % C.L.

upper limit of cross section

2013/11/1 14

-G= 20 MeV 0.17 - 0.55 mb

-G = 60 MeV 0.55 - 1.7 mb

-G =100 MeV 1.1 – 2.9 mb

1.5 - 26 % of YKp production cross section.

B.E. 15 points (10-150 MeV)G 3 points (20, 60 and 100MeV)


Background processes

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MMp(K+p-) and Mp(K) spectra were fitted simultaneously.Fitting function: quasi-free process gNY K+p

- gNY* K+

gNYp K+p

Main component:gp L(1520) K+

(~20%) → Sp → N pg N Y p K+ p

(~20%)

MMp(K+p-)

MMp(K+)


Search in LEPS-2 experiment


LEP2 facility

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acceptance: 5 -120 degree (charged particle)30 - 100 degree (g)p/Dp ~ 1% 　

beam intensity x10 of LEPS ( 107 cps)

4 p detector under construction for

the 1st experiment


LEPS 2-1 Exclusive search by tagging two protons

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accepted in LEPS2

Main Back ground process: quasi-free process (one nucleon is spectator)

To improvement of S/N: Non-mesonic decay modetwo high momentum proton

Tag

g d K+ + p- + K-

pp　 K-pp L + proton(p1) L proton (p2) + p-


Toy MC

Toy MC

accepted in LEPS2

LEPS 2 – 2 Search in the g+d→Ks L p


g+d→ Ks + K-ppK-pp → L + pー　 Ks (L) pー　 Ks L (p)ー　 (Ks) L pー　 Ks L p( ) ← ID with missing mass

g + d → Ks + K-ppK-pp → S0 + pS0 → L + g (50140 MeV) ← detectable

We can measure the B.R. (Lp/S0p)

Dalitz plot in the Center Mass system

K-pp production(B.E. = 60 MeV = 80 MeV = 100 MeV = 120 MeV)

Toy MC

Conclusion


Conclusion

K-pp bound state give us rich information on the sub-threshold KN

interaction. K-pp bound state was searched for via the g d

K+ p- X reaction at LEPS/SPring-8. Significant peak structures were not found in

MMd(K+p-) spectrum, and the upper limits of the production cross section were determined.

Main component of background processes were found to be quasi-free processes (g p→ L(1520) K+, g N→ L/S p K+p-).

LEPS2 has potential for more sensitive search experiments. 2013/11/1 21Hadron in nucleus @ Kyoto University

Collaborators

2013/11/1 22

Thank you for your attention!


search for the k - pp bound state via photon-induced reaction

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