in collaboration with :V.K. Magas, E. Oset, R. Molina, L. Tolós, J. Yamagata-Sekihara, S. Hirenzaki

A. Ramos University of Barcelona

(JPS+SPHERE meeting, Vila Lanna, Prague 4-6 September, 2010)

Strange mesons in nucleiS=-1 mesons:- K (Jp=0-)- K* (Jp=1-)

Evidences of deeply bound K- nuclear states (BK ~ 100 MeV) from slow kaon reactions on nuclei has been claimed

Pseudoscalar K mesons in nuclei

Understanding the properties of Kbar mesons has been one of the major goals in strange nuclear physics.

How attractive is the Kbar-nucleus optical potential? May kaon condensation occur in neutron star interiors?

Phenomenological fits to kaonic atom data preferred UK(r 0) ~ -200

MeV

Self-consistent theoretical calculations that use realistic Kbar N interactions(KN data reproduced, chiral dynamics) obtain UK(r 0) ~ -50 to -70 MeV

OKX

The observed peaks in nuclear reactions using slow kaons:

1. (K-stop, p) (bump)

2. (K-stop, Lp)

3. (K-stop, Ld)

can be explained in terms of conventional input that combines:

a) an absorption mechanism

K-NN L N (in 1. and 2.)

K-NNN L d (in 3.)

b) nuclear medium effects:Fermi motion/recoil

(direct reaction peaks broaden)FSI of the emitted particles (if daughter nucleus is big enough)

( secondary peaks/structures may appear)

E. Oset, H. Toki, Phys. Rev. C74, 015207 (2006)

M. Agnello et al. Phys. Lett. B654, 80 (2007)

V.K. Magas, E. Oset, A. Ramos and H. Toki, Phys. Rev. 74 (2006) 025206

M. Agnello et al. Phys. Rev. Lett. 94, 212303 (2005)T. Suzuki et al., Mod. Phys. Lett. A23, 2520 (2008)

V.K. Magas, E. Oset and A. Ramos, Phys. Rev C77, 065210 (2008)

T. Suzuki al. Phys. Rev .C76, 068202 (2007)

V.K. Magas, E. Oset, A. Ramos and H. Toki, Nucl.Phys. A804, 219 (2008)

Another “evidence” for a very deeply attractive K- nucleus potential:

The (K-,p) reaction on 12C at KEK

T. Kishimoto et al., Prog. Theor. Phys. 118 (2007) 181

pK = 1 GeV/c

qp < 4.1o forward nucleons (the most energetic)

in-flight kaons

plus “coincidence requirement”:(at least one charged particle in decay counters surrounding the target)claimed not to affect the spectrum shape

J. Yamagata, H. Nagahiro and S. Hirenzaki, Phys.Rev. C74, 014604 (2006)

shallow deep

Analysis of T. Kishimoto et al., Prog. Theor. Phys. 118 (2007) 181

Process: quasielastic scattering K- p K- p in nuclei

Green’s function method Normalization: fitted to experiment Background: fitted to experiment

Re UK=−60 MeV Im UK=−60 MeV

Re UK=−160 MeV Im UK=−50 MeV

Re UK=−190 MeV Im UK=−40 MeV

The only mechanism for fast proton emission in the Green’s function method isthe quasielastic process K- p K- p where the low-energy kaon in the final state feels a nuclear optical potential and can occupy stable orbits (no width) , unstable orbits, or be in the continuum (quasifree process)

However, there are other mechanisms that can contribute:

Taken from J. Yamagata and S. Hirenzaki, Eur. Phys. J. A 31, 255{262 (2007)

Multistep processes:K- and/or N undergo secondary collisions as they leave the nucleus

One-nucleon absorption:K- N p L and K- N p Sfollowed by decay of L or S into p p

Two-body absorption:K- N N S N and K- N N L N followed by hyperon decays

We implement these processes in a Monte Carlo simulation of K- absorption in nuclei

Monte Carlo simulation

Further collisions of the emitted particles as they cross the nucleus. We follow: the K- until it leaves the nucleus or gets absorbed all energetic p and n (until they leave the nucleus) all energetic L and S (until they leave the nucleus and decay into pN)

Finally, we represent the spectra of the emerging protons

The incoming K- will experience a certain process (quasielastic, one-nucleon or two-nucleon absorption) at a point r with a probability given by sqe r dl, s1N r dl or s2N r dl where dl is a typical step size.

The nucleus is described by a nuclear density profile r(r)

Once a process has been decided, we determine the local momenta of the emitted particles according to phase space

(details in next talk by V. Magas)

1N-absorption, rescattering

Proton spectrum

2N absorption, rescattering

No coincidence

-

V.K. Magas, J. Yamagata-Sekihara, S. Hirenzaki, E. Oset and A. Ramos, Phys. Rev. C81, 024609 (2010).

Comparison with KEK data:

“The experiment measures the proton PLUS at least one charged particle in the decay counters surrounding the target”

Our simulation should consider the coincidence requirement of KEK-PS E548

The simulation of such coincidence requirement is tremendously difficult, because it would imply keeping track of all charged particles coming out from all possible scatterings and decays.

The best we can do is to eliminate processes that, for sure, cannot have a coincidence: quasi-elastic K- p K- p events where neither the p nor the K- suffer secondary collisions. (In this type of processes the fast p moves forward and the K- escapes undetected through the back).

minimal coincidence requirement

The coincidence requirement removes a substantial fraction of events and changes the shape of the spectrum drastically

Comparison with KEK data:

Supp. ~0.7

Comparison with KEK data:

Low energy p – multiparticle final states should be less supressed!

Supp. ~ 1.0

- The results of the in-flight 12C(K-,N) reaction at KEK (PS-E548) can probably be explained with a conventional kaon optical potential (UK(r0) ~ -60 MeV)

- We have seen that the coincidence requirement introduces a non-negligible distortion in the spectrum

- This distortion is comparable in size (even bigger) than that produced by using a different kaon optical potential.

Vector K* mesons in nuclei From (K-,K*-) reaction in nuclei

(see V. Magas’ talk)

The study of vector meson properties in the nuclear medium has received a lot of attention, since they are tied to fundamental aspects of QCD

ρ meson: KEK325, CLAS-g7, CERES, NA60ω meson: NA60, CBELSA/TAPSϕ meson: KEK325, LEPS, COSY-ANKE

Less attention has been paid to the K* meson! (probably because it does not decay into dileptons).

K* N interaction in free space:(coupled-channels model)

Tij = Vij + Vil GlTlj

= +

transition potential

channels:K*NωΛ, ωΣρΛ, ρΣϕΛ, ϕΣK*Ξ

From local hidden gauge formalism

Bando et al. Phys. Rev. Lett. 54, 1215 (85); Phys. Rep. 164, 217 (88)

- Deals simultaneously with vector and pseudoscalar mesons

- Implements chiral symmetry naturally

- Leads to the same lowest order Lagrangian for pseudoscalar mesons

- Reproduces all the empirically successful low-energy relations of the r meson (KSFR) relation, vector meson dominance,…)

E. Oset, A. Ramos, Eur.Phys.J. A44 (2010) 431

VVV vertex

KSFR relation

BBV vertex

Bando et al, PRL 112 (1985)and Phys. Rep. 164 (1988) 217

Klingl, Kaiser, Weise,NPA 624 (1997) 527

transition potential VB->VB

Loop function G incorporates mass distribution (width) of vector meson

(same s-wave amplitude as in P B P B S-wave scattering)

L* S*

1783, Γ=9

1830, Γ=42

PDG:Λ(1690) 3/2-Λ(1800) 1/2-

PDG:Σ(1750) 1/2-

Our resonances are narrower thanknown PDG states because coupling to pseudoscalar-baryon channels isnot included

K* self-energy in the medium

a) K* K p and medium modifications

N N, D

MK*

free decay : G = -Im P/MK*= 50 MeV

medium corrections (absorption)

vertex corrections

The K* width increases substantially (factor 2)due to pion self-energy in nuclear matter

Tij = Vij + Vil GlTlj

= +

Tij(r) = Vij + Vil Gl(r) Tlj(r)

= +

Free space

Medium

Dressed K* meson: = +

Pauli blockingandbaryon dressing

meson dressing

+

b) K* N interaction in the medium: q.e. process K*N K*N , and also new absorption processes: K*N pKN, K*NN KNN

MK*

K* self-energy in the medium

Λ(1784)N-1 Σ(1830)N-1

free

K* width at normal nuclear matter density (r0) is 5-6 times larger than in free space!!

Can it be checked by some reaction in nuclei?? (V. Magas, next talk )

L. Tolos, R. Molina, E. Oset, and A. Ramos,arXiv:1006.3454 [nucl-th].

Thank you for your attention