absorption on few-nucleon systems with FINUDA at LNF S. Piano - PowerPoint PPT Presentation

Results on K - absorption on few-nucleon systems with FINUDA at LNF S. Piano INFN Trieste FINUDA Collaboration Meson2010 – June 11 2010 – Results on K - absorption on few-nucleon systems with FINUDA at LNF – S.Piano – INFN Trieste – FINUDA Collaboration

K - absorption by few nucleons (on nuclei) • Study of hypernuclei and their decays: – One nucleon absorption (pion-emission) N → π Y ⇒ K - A → Λ ( Σ ) π X – K - • Search for possible deeply bound kaon states: – Two nucleon absorption (no-pion emission) (2N) → N Y ⇒ K - A → Λ ( Σ ) pX, K - A → Λ ( Σ ) nX – K - – Three nucleon absorption (no-pion emission) (3N) → NN Y ⇒ K - A → Λ ( Σ ) dX – K - – Four nucleon absorption (no-pion emission) (4N) → NNN Y ⇒ K - A → Λ ( Σ ) tX – K - Meson2010 – June 11 2010 – Results on K - absorption on few-nucleon systems with FINUDA at LNF – S.Piano – INFN Trieste – FINUDA Collaboration

Λ identification with FINUDA FINUDA FRONTAL VIEW VERTEX REGION Meson2010 – June 11 2010 – Results on K - absorption on few-nucleon systems with FINUDA at LNF – S.Piano – INFN Trieste – FINUDA Collaboration

6 Li(K - , Λ )X Phase Space Simulations stop To measure the non-mesonic K - A → Σ 0 p A ′ gs channels it is necessary to detect Σ 0 → Λγ K - A → Λ p A ′ gs p (n,d,t) and Λ with high resolution in the high momentum region (mesonless Λ -production region) FINUDA DATA: K - 6 Li → Λ X stop K - NN →Λ N K - N →Λπ not acceptance corrected K - A → Λπ - p A ′ gs Meson2010 – June 11 2010 – Results on K - absorption on few-nucleon systems with FINUDA at LNF – S.Piano – INFN Trieste – FINUDA Collaboration

Λ momentum from K - stop FINUDA DATA: K - 6 Li → Λ X stop Simulations: K - A →Λπ X stop K - A →Λ pX stop K - NN →Λ N K - N →Λπ 4 He 12 C not acceptance corrected Katz et al.,: K - 4 He →Λ X stop K - N →Λπ K - NN →Λ p No Data absorption absorption Meson2010 – June 11 2010 – Results on K - absorption on few-nucleon systems with FINUDA at LNF – S.Piano – INFN Trieste – FINUDA Collaboration

2NA: K - pp identification with FINUDA Λ p Invariant Mass to measure K - pp: 1. Data taking 2003-2004: – 200 pb -1 2 2. reconstruction of Λ ’s – p Λ > 300 MeV/c 1 – 6 MeV FWHM cos θ YN < -0.8 3. Λ and p angular correlation – Events with a Λ -p coincidence: ~ 5% – Light targets only (3x 12 C, 2x 6 Li, 1x 7 Li) – Λ p should be emitted in opposite directions, apart from FSI Meson2010 – June 11 2010 – Results on K - absorption on few-nucleon systems with FINUDA at LNF – S.Piano – INFN Trieste – FINUDA Collaboration

Λ p invariant mass in FINUDA SEMI- -EXCLUSIVE ANALYSIS EXCLUSIVE ANALYSIS SEMI • High resolution tracks only • A bump is observed ~ 200 events in the published paper – Two nucleon absorption m K +2m p + (pp) → Λ p • K - Acceptance correction peak expected at 2.34 GeV + (pp) → Σ 0 p → Λγ p • K - 74 MeV lower distribution, and broadened fit region – Kaon nuclear bound state formation (pp) → X → Λ p M = (2255 ± 9) MeV/c 2 • K - → Σ 0 p → Λγ p B = 115 +6 -5 (stat) +3 -4 (sys) MeV Γ = 67 +14 (stat) +2 -3 (sys) MeV -11 FINUDA Coll., PRL 94(2005)212303 Meson2010 – June 11 2010 – Results on K - absorption on few-nucleon systems with FINUDA at LNF – S.Piano – INFN Trieste – FINUDA Collaboration

Alternative interpretations of the Λ p bump • K - pp → [K-pp] →Λ p: [K-pp] bound state (FINUDA) • QF-2NA K - pp →Λ p followed by FSI (Magas et al.) • Dominance of Σ 0 production over Λ : QF-2NA K - pp →Σ 0 p followed by Σ 0 → Λγ decay • QF-2NA K - NN →Σ N followed by Σ N →Λ N conversion reaction: K - A →Σ 0,+ π 0,- X K - A →Σ 0,+ nX K - A →Σ 0,- pX Σ 0 p →Λ p Σ 0 p →Λ p Σ 0 n →Λ n Σ + n →Λ p Σ + n →Λ p Σ - p →Λ n • Decay of heavier kaonic nuclei (Mares et al.) QF-2NA = Quasi Free Two Nucleon Absorption Meson2010 – June 11 2010 – Results on K - absorption on few-nucleon systems with FINUDA at LNF – S.Piano – INFN Trieste – FINUDA Collaboration

A different interpretation of the M p Λ bump • Magas, Oset et al, PRC74 (2006), 0252006 – The peak is due to ~90% FSI of p and Λ , no DBKS – The bump is a result of the angular cuts applied in the analysis (i.e., a deformation of a flat distribution) – 115 MeV as a binding energy is quite too much! • …but: – Analysis of the higher statistics data shows that the deformation of the spectrum is not due to angular cuts – No strong dependence on angular distribution from A=6 to A=16 – FSI alone cannot explain the full spectrum – Back-to-back correlation belongs to the data themselves Meson2010 – June 11 2010 – Results on K - absorption on few-nucleon systems with FINUDA at LNF – S.Piano – INFN Trieste – FINUDA Collaboration

FINUDA: 6 Li(K - , Λ p)X stop 2006-2007 Data Taking • 8x statistics on: 6 Li ( 7 Li, 9 Be) - Improved tracking efficiency - Extended range of the reconstructed momentum not acceptance corrected - Improved selections (missing mass) - Statistics large enough to study single tgt spectra not acceptance corrected not acceptance corrected unphysical region Meson2010 – June 11 2010 – Results on K - absorption on few-nucleon systems with FINUDA at LNF – S.Piano – INFN Trieste – FINUDA Collaboration

FINUDA: 6 Li(K - , Λ p)X stop New A= 6 Li, 7 Li, 12 C inv mass spectra not acceptance corrected A= 6 Li not acceptance corrected compatible with published one New data Old data Same cuts applied FINUDA Coll., PRL 94(2005)212303 not acceptance corrected not acceptance corrected unphysical region Meson2010 – June 11 2010 – Results on K - absorption on few-nucleon systems with FINUDA at LNF – S.Piano – INFN Trieste – FINUDA Collaboration

FINUDA: 6 Li(K - , Λ p)X stop Final States are separated by reconstructing the not acceptance corrected Missing Mass: not acceptance corrected 1) QF-TNA K - A →Λ pX 2) QF-TNA K - A →Σ 0 pX 3) QF-TNA K - A →Λπ pX not acceptance corrected not acceptance corrected K - 6Li →Λ p 4 H gs Meson2010 – June 11 2010 – Results on K - absorption on few-nucleon systems with FINUDA at LNF – S.Piano – INFN Trieste – FINUDA Collaboration

FINUDA: 6 Li(K - , Λ p)X stop Simulation: K -6 Li →Λ p 4 H gs not acceptance corrected not acceptance corrected K - 6Li →Λ p 4 H gs Meson2010 – June 11 2010 – Results on K - absorption on few-nucleon systems with FINUDA at LNF – S.Piano – INFN Trieste – FINUDA Collaboration

FINUDA: 6 Li(K - , Λ p)X stop Final States are separated by reconstructing the not acceptance corrected Missing Mass: not acceptance corrected 1) QF-TNA K - A →Λ pX 2) QF-TNA K - A →Σ 0 pX 3) QF-TNA K - A →Λπ pX K - 6Li →Σ 0 p 4 H gs Σ 0 →Λγ not acceptance corrected not acceptance corrected K - 6Li →Λ p 4 H gs Meson2010 – June 11 2010 – Results on K - absorption on few-nucleon systems with FINUDA at LNF – S.Piano – INFN Trieste – FINUDA Collaboration

FINUDA: 6 Li(K - , Λ p)X stop Final States are separated by reconstructing the not acceptance corrected Missing Mass: not acceptance corrected 1) QF-TNA K - A →Λ pX 2) QF-TNA K - A →Σ 0 pX 3) QF-TNA K - A →Λπ pX K - 6Li →Σ 0 p 4 H gs Σ 0 →Λγ not acceptance corrected not acceptance corrected K - 6Li →Λ p 4 H gs K - 6Li →Λπ 0,+,- p 4 H gs Meson2010 – June 11 2010 – Results on K - absorption on few-nucleon systems with FINUDA at LNF – S.Piano – INFN Trieste – FINUDA Collaboration

FINUDA: 6 Li(K - , Λ p)X stop Only a minor fraction of the bump can be associated to K - pp →Σ 0 p →Λγ No K - 6Li →Σ 0 p 4 H gs Σ 0 →Λγ Σ 0 →Λγ not acceptance corrected not acceptance corrected K - 6Li →Λ p 4 H gs K - 6Li →Λπ 0,+,- p 4 H gs But …the Missing Mass selection cannot exclude Σ N →Λ N conversion reactions: K - A →Σ 0,+ π 0,- X K - A →Σ 0,+ nX K - A →Σ 0,- pX Σ 0 p →Λ p Σ 0 p →Λ p Σ 0 n →Λ n Σ + n →Λ p Σ + n →Λ p Σ - p →Λ n Meson2010 – June 11 2010 – Results on K - absorption on few-nucleon systems with FINUDA at LNF – S.Piano – INFN Trieste – FINUDA Collaboration

FINUDA: Σ N →Λ N conversion reactions Simulations: Λ p Invariant Mass Σ N →Λ N cannot explain K -6 Li →Σ 0,+ π 0,-5 He gs the FINUDA Λ p bump: Σ 0 p →Λ p K -6 Li →Σ 0 p 4 H gs Σ + n →Λ p Σ 0 →Λγ Inv Mass Spectra is out of range and/or K -6 Li →Σ 0,+ n 4 H gs ( 4 He gs ) K -6 Li →Λ p 4 H gs Angular Distribution Σ 0 p →Λ p has a different shape Σ + n →Λ p Simulations: Λ p angular distribution K -6 Li →Σ 0,- p 4 He gs ( 4 H gs ) Σ 0 n →Λ n Σ - p →Λ n Meson2010 – June 11 2010 – Results on K - absorption on few-nucleon systems with FINUDA at LNF – S.Piano – INFN Trieste – FINUDA Collaboration