atsushi tokiyasu (for leps collaboration)

Atsushi Tokiyasu(for LEPS collaboration)

Experimental Nuclear and Hadronic Physics Laboratry,

Department of Physics, Kyoto University

Search for Kaonic nuclei at SPring8/LEPS

GCOE Symposium12th – 14th .Feb.2013 @ Kyoto University

GCOE Symposium @ Kyoto University

strangeness in nuclei

2013/2/13 2 / 11

ds us,

SU(3) octet baryon SU(3) nonet meson

L K?Hyper nucleiShrinkage impurity effect.

nuclear force in SU(3)

Kaonic nuclei

new form of the nuclei

whether exist or not?

What happens in nuclei?

uds

hyperon kaon


dependent on the models of KN interaction the calculation methods.

Formation of Cold (T=0) and Dense (r > 2r0) nuclei.

2013/2/13 3 / 11

K can be bound in the nuclei by strong interaction.

K N interaction (I=0) is strongly attractive !X-ray shift of Kaonic HydrogenK- p scattering data

2-body: KN : L(1405) ?

3-body: KNN : lightest nucleus. K-pp the strongest bound state in 3-body systems

Theoretical prediction (All theory support the existence)B.E. = 20-100 MeVG = 40- 110 MeV

If G > B.E, it is difficult to observe experimentally.

Ref: Particle Data Group

Kaonic nuclei


Experiments

2013/2/13 4 / 11

）（）（ syststat 34

65115


141167



FINUDA @ DAFNE (2005) DISTO@ SATURNE(2010)stropped K- on (6Li, 7Li, 12C, 27Al and 51V) p p L p K+

B.E. =B.E. =

G =G =

invariant mass (L + p) Missing mass (K)

MeV

MeVMeV

MeV

M.Agnello, Nagae and Fujoka et al., PRL 94, 212303 (2005) T.Yamazaki et al., PRL 104, 132502 (2010)

K-pp L p , S0 p, S n (non-mesonic decay) easy to identify experimentally S p p (mesonic decay)


Summary of the introductionK-pp is the lightest kaonic nuclei.

Existence of K-pp is not established.

Experimental search using different reactions are awaited!

Forthcoming experiments3He(K-, n)X E15 @ J-PARC D(p+, K+)X E27 @ J-PARCg D K+ p- X LEPS @ SPring-8

2013/2/13 5 / 11

Prof.Nagae’s talk


g D K+ p - X reaction

2013/2/13 6 / 11

K+

p-

g

“K” exchanged in t-chanel unique for g-induced reaction g ( J = 1)polarization observables are available.

K-pp is “soft” object. small momentum transfer detect K+ and p- at forward angle

Search for a bump structure in the missing mass spectrum Mx

2 = (Eg + MD – EK- Ep)2 - (pg – pK - pp)2

independent of decay chanel.

K, K*Y*

p

npK-

p

Y*

(Eg, pg) (EK, pK)

(Ep, pp)

(MD,0) Y* door-way.


SPring-8 “Super Photon ring-8 GeV”

2013/2/13 7 / 11

Data take:2002/2003, 2006/2007 7.6 x 1012 photons on LD2 target

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

Back-word Compton Scattering

e

e

Detect withTagging counter

Eg=1.5 - 2.4 GeVexperimentalhatch

355nm laser8 GeV

LEPS

DEg=12 MeV


LEPS spectrometer

2013/2/13 8 / 11

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+


particle identification

2013/2/13 9 / 11

K+

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

TOF (Time of flight)

m2 = p2(1/β2 - 1)

line tracking + Runge-Kutta method.

mass p = 938.3 MeVmass K+ = 493.7 MeVmass p- = 139.6 MeV

c.f.

p

p+

K-

0


Missing Mass Spectrum

2013/2/13 10 / 11

Error Bar : statistical uncertainty (~5%)Red Box : systematic uncertainty (~20%)Hatched : discrepancy between datasets (~12%)

preliminary

No bump structure was observed!upper limit of cross section

L S

n

search region: Mass = 2.22 - 2.36 GeV/c2

B.E. = 150 - 10 MeV

acceptance was corrected with Monte-Carlo simulation

expected signal


Upper Limits of differential cross section

2013/2/13 11 / 11

preliminary

-G= 20 MeV 0.05 - 0.25 mb

-G = 60 MeV 0.15 - 0.6 mb

-G =100 MeV 0.15 - 0.7 mb

a few % of typical hadron production cross section.

g N L K p (~8 mb )g N S K p (~4 mb)

B.E. 15 points (10-150 MeV)G 3 points

upper limits of cross section were determined log likelihood ratio method


Conclusion and future prospect

The existence of Kaonic nuclei is not established.

K-pp was searched for using g D K+ p - X reaction

No bump structures were found, and the upper limits of differential cross section were determined to be a few % of typical hadron production cross section.

Future prospectdetect the decay products from K-pp. increase S/Nsearch for other charge states using gDK+ K-pn , gDK+p+ K-nn

2013/2/13 12 / 11


Collaborators

2013/2/13 13 / 15


Appendix

2013/2/13 14 / 15


Appendix

Meritdeuteron small nuclear effect(FSI).additional p- emission reduce the momentum transfer.K can be exchanged.polarization observable is available.

Demeritsmall cross section (~nbarn).many background sourcelimited information on hadron resonance.necessary to detect the decay product.

2013/2/13 15 / 15


Calculation of Upper Limits

2013/2/13 16 / 15

preliminary

preliminary

Upper Limit was calculated with log Likelihood ratio method

Background proces g p K+ p- L g p K+ p- S g p K+ p- S(1385) g p K+ p- S(1385)- g p K+ p- p Lconstant offset

Signal Breit Wigner distribution

-2DlnL = 3.841 upper limit (95% C.L.)

Signal Yield


Theoretical calculation

2013/2/13 17 / 15

Binding Energy DecayWidth

Method

Yamazaki and Akaishi 48 MeV 61 MeV PhenomenologicalVariatioal Method

Dote, Hyodo and Weise 20±3 MeV 40-70 MeV Chiral SU(3)Variational Method

Ikeda and Sato 60 – 95 MeV 45 - 80 MeV Chiral SU(3)Fadeev Calculation

Shevchenko, Gal and Mares

50 – 70 MeV 90 – 110 MeV PhenomenologicalFadeev Calculation

S. Wycech and A. M. Green

56.5~78 MeV 39~60 MeV

Uchino, Hyodo and Oka

depend on L* NVariational Method

All calculations predict that K-pp can exist!!

However… B.E. = 20 – 100 MeV G = 40 – 110 MeV Depending on the K N interaction model and Calculation Method.


Background processes

2013/2/13 18 / 15

preliminary

15 quasi- free processes were considered for fitting.gN Y K+ Y K+ p- Y* K+ p- Y K+ p- p

The main background (~20 %)gn K+ L(1520) Sp Lpp

g N K+ p- XMM(K+)

MM(K+,p-)

MM(K+)

MM(K+,p-)

c2/ndf ~ 1.3

Yhyperon (L,S)Y* hyperon resonance (L(1405),S(1385)…)

atsushi tokiyasu (for leps collaboration)

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