Investigation of the lowenergy kaons hadronic interactions in light - PowerPoint PPT Presentation

C onclusions PART 1 - K-pp search: *The signal from the decay of a K-pp bound state is masked by the Σ / Λ conversion process. *No clear peak structure excludes the possibility of a high formation rate and/or narrow width resonance. - Λ d, Λ t *3- and 4-nucleon absorption processes clearly seen. *Additional structures must be investigated. Σ 0 contamination? Bound state?

PART 2 Nature of the Λ (1405) investigated through Σ 0 π 0 / Σ + π − correlation

Scientific case of the Λ(1405) Λ(1405) : mass = 1405.1 +1.3 ­1.0 MeV, width = 50 ± 2 MeV I = 0, S = ­1 , J p = 1/2 ­ , Status: **** , strong decay into Σπ Its nature has been a puzzle for decades: three quark state, unstable KN bound state, penta­quark, two poles?? First experimental evidence: M. H. Alston, et al., Phys. Rev. Lett. 6 (1961) 698 → πππΣ K ­ p Λ(1405) Λ(1116)

Scientific case of the Λ(1405) ­ The three quark model picture: Λ(1405) mass?? Similar to the nucleon sector N(1535), the expected mass of the Λ * is around 1700 MeV. ­ Energy splitting between the Λ(1405) and the Λ(1520) ( spin­orbit partner ( J p = 3/2 ­ )) ??. R. Dalitz and collaborators first suggested to interpret Λ(1405) as an KN quasibound state.

Scientific case of the Λ(1405) Chiral unitary models: Λ(1405) is an I = 0 quasibound state emerging from the coupling ● between the KN and the Σπ channels. Two poles in the neighborhood of the Λ(1405): 4) t wo poles : (z 1 = 1424 +7 ­23 – i 26 +3 ­14 ; z 1 = 1381 +18 ­6 – i 81 +19 ­8 ) MeV (Nucl. Phys. A881, 98 (2012)) mainly coupled to KN mainly coupled to Σπ → line­shape depends on production mechanism Akaishi­Esmaili­Yamazaki phenomenological ● potential Phys. Lett. B 686 (2010) 23­28 Confirmation of single pole ansatz?

Scientific case of the Λ(1405) Chiral unitary models: Λ(1405) is an I = 0 quasibound state emerging from the coupling ● between the KN and the Σπ channels. Two poles in the neighborhood of the Λ(1405): 4) t wo poles : (z 1 = 1424 +7 ­23 – i 26 +3 ­14 ; z 1 = 1381 +18 ­6 – i 81 +19 ­8 ) MeV (Nucl. Phys. A881, 98 (2012)) HADES mainly coupled to KN mainly coupled to Σπ → line­shape depends on production mechanism Akaishi­Esmaili­Yamazaki phenomenological ● potential Phys. Lett. B 686 (2010) 23­28 Confirmation of single pole ansatz?

Scientific case of the Λ(1405) K ­ nuclear absorption experiments .. long history .. BUT 1) m πΣ spectra CUT AT THE ENERGY LIMIT AT­REST 2) ( Σ ± π ∓ ) Σ(1385) CONTAMINATION “A study of K − 4 He → ( Σ ± π ∓ ) + 3 Η using slow instead of stopping K − would be very useful in eliminating some of the uncertainties in interpretation” D. Riley, et al. Phys. Rev. D11 (1975) 3065 Esmaili et el., Phys.Lett. B686 (2010) 23­28 In flight K ­ absorption allows to explore the higher mass region

Scientific case of the Λ(1405) Λ(1405) is I = 0 Σ 0 π 0 (I =0) golden decay channel (free from Σ(1385) background I=1) The Σ 0 π 0 spectrum was only observed in 3 experiments … with different line­shapes ! I. Zychor et al., Phys. Lett. B 660 (2008) 167 K. Moriya, et al., (Clas Collaboration) Phys. Magas et al. PRL 95, 052301 (2005) 034605 S. Rev. C 87, 035206 (2013) Prakhov, et al., Phys. Rev. C70 (2004)

→ Σ 0 π 0 K - ”p” bound proton in 4 He / 12 C

Σ 0 π 0 channel Λ (1405) signal searched by K ­ interaction with a bound proton in Carbon → Σ 0 π 0 detected via: (Λγ) (γγ) K ­ p Strategy : K ­ absorption in the DC entrance wall, mainly 12 C with H contamination (epoxy) 2005 AR + IF N. U. N. U. 2012 2012 Carbon target Carbon target AR only AR only m lim in 12 C at­rest p Σ0π0  (MeV/c 2 ) m Σ0π0  (MeV/c 2 ) m π0Σ0 resolution σ m ≈ 32 MeV/c 2 ; p π0Σ0 resolution : σ p ≈ 20 MeV/c. Negligible (Λ π 0 + internal conversion) background = (3±1) % → no I=1 contamination

Σ 0 π 0 channel K ­ nuclear absorption experiments .. long history .. BUT 1) m πΣ spectra always cut at the AT­REST limit 2) ( Σ ± π ∓ ) spectra suffer Σ(1385) contamination P. J. Carlson, et al. Nucl. Phys. 74 642 D. Riley, et al. Phys. Rev. D11 (1975) 3065 N. U. n o i t a 2005 AR + IF z i l m r 2012 2012 o n Carbon target Carbon target y r a AR only AR only r t i b m lim in 12 C r a at­rest p Σ0π0  (MeV/c 2 ) m Σ0π0  (MeV/c 2 )

Σ 0 π 0 channel 2005 AR + IF N. U. N. U. 2012 2012 Carbon target Carbon target AR only AR only m lim in 12 C at­rest p Σ0π0  (MeV/c 2 ) m Σ0π0  (MeV/c 2 ) In­flight component … FIRST EVIDENCE IN K ­ ABSORPTION MASS SPECTROSCOPY opens a higher invariant mass region

→ Σ + π − K - ”p” bound proton in 4 He / 12 C

Σ + π ­ invariant mass spectra → Σ + π − detected via: (p π 0 ) π − K ­ p Possibility to disentangle: Hydrogen, in­flight, at­rest, K − capture if resonant production contribution is important a high mass component appears! T otal T otal H IF H IF 4He IF 12C AR 4He AR 12C

Resonant VS non­resonant Another unsolved question .. π K ­ N → (Y* ?) → Y how much comes from resonance ? Investigated using: → Λπ − direct formation in 4 He K ­ ”n” In collaboration with Prof. S. Wycech

Channel: K − 4 He → Λ π − 3 He … the idea Bubble chamber experiments exhibit two components: → Low momentum Λ π − pair S­wave, I=1, non­resonant transition amplitude. ● High momentum Λ π − pair → P­wave resonant formation ? ● Also exsists in S­state K­mesic atom as a result of the ) three body structure of the system V e M 2 ( / s t n u (K = 1, n=2, 3 He = 3) o C K. Brunnel et al., Phys.Rev. D2 (1970) 98

→ Λ π − 3 He … the idea Channel: K − 4 He K − (s=0) 4 He(s=0) n(s=1/2) Σ ∗− (s=3/2) → resonance p­wave only atomic s­state capture: s s n n consequence of 3­body effect s (K − n) s­state interaction p (K − n) p­state interaction + p s 3 He 3 He Σ ∗− not allowed s s Σ ∗− allowed NON­RES only K − K − (K − 4 He → Λ π − 3 He) absorptions from (n s) ­ atomic states are assumed → ● 4 He bubble chamber data (Fetkovich, Riley interpreted by Uretsky, Wienke) Coordinates recupling enables for P­wave resonance formation ●

→ Λ π − 3 He … the strategy Channel: K − 4 He ● Fit of the p Λπ−  observed distribution using calculated distributions : s (p Λπ ) = | Ψ N (p Λπ )| 2 |f s (p Λπ )| 2 ρ non­resonant P s p (p Λπ ) = | Ψ N (p Λπ )| 2 c 2 |2f Σ∗ (p Λπ )| 2 ρ/3 ( kp Λπ ) 2 resonant P s To determine for the first time the ratio resonant/non­res. ● |f N­R Λπ | given the fairly well known |f Σ∗ Λπ |

Channel: K − 4 He → Λ π − 3 He … calculated reactions Calculated primary hadronic interactions: At­rest : S­wave non­Res / P­wave Σ (1385) Res K − 4 He → Λ π − 3 He In­flight : S­wave non­Res / P­wave Σ (1385) Res At­rest : S­wave non­Res / P­wave Σ (1385) Res K − 4 He → Σ 0 π − 3 He In­flight : S­wave non­Res / P­wave Σ (1385) Res At­rest : S­wave non­Res / S­wave Λ (1405) Res / P­wave Σ (1385) Res K − 4 He → ( Σ π) 0 3 H In­flight : S­wave non­Res / S­wave Λ (1405) Res / P­wave Σ (1385) Res

K − 4 He → Λ π − 3 He preliminary fit Simultaneous fit (p Λπ− ­ m Λπ− ­ θ Λπ− ) leaving the ratio At­rest /In­flight and 12 C contamination to vary around the estimated values within errors: Global fit ) c / V Λ π − At­rest N­R e M 0 Λ π − At­rest RES 1 ( s t n Λ π − In­flight N­R u o C Λ π − In­flight RES Λ π − events from K − 12 C → Λ p/n conversion Σ p/n p Λπ−  (MeV/c)

K − 4 He → Λ π − 3 He preliminary fit Simultaneous fit (p Λπ− ­ m Λπ− ­ θ Λπ− ) leaving the ratio At­rest /In­flight and 12 C contamination to vary around the estimated values within errors: χ 2 / (ndf – np) = 1.4 ● ● (At­rest RES)/(At­rest N­R) = 0.9 ± (0.2stat)± (0.4sys) ● (In­flight RES)/(In­flight N­R) = 0.9 ± (0.2stat)± (0.4sys) (In­flight) / (At­rest) = 1.9 ± 0.4 ● Σ p/n → Λ p/n conversion = (10 ± 1)% ● Λ π − events from K − 12 C = (53 ± 2)% ●

C onclusions PART 2 Σπ spectra show a high invariant mass component → associated to in­flight K − m Σπ m ● capture PRELIMINARY Λπ ­ first measurement of RES/N­R ratio in nuclear K − absorption. ● Next steps … Same analysis is ongoing for Σ 0 π ­ → extraction of |f N­R Σ0π− (I=1)| ● Similar description of Σ + π ­ and Σ ­ π + production → extraction of |f N­R Σ+π− | and ● |f N­R Σ−π+ |, a comparison of these could give an estimate of |f N­R Σ+π− (I=0) + f N­R Σ+π− (I=1)| against |f N­R Σ+π− (I=0) ­ f N­R Σ+π− (I=1)| Branching ratio modifications in different targets (see A. Ohnishi et al., Phys. Rev. ● C 56 5 (1997) 2767) & Density dependence of m and p (see L. R. Staronski, Σπ and m Σπ p Σπ Σπ S. Wycech, Nucl. Phys. 13 (1987) 1361 / A. Cieplý, E. Friedman, A. Gal, V. Krejčiřík ­ Phys.Lett.B698 (2011) 226­230)

Perspectives .. AMADEUS experiment: Implementation of dedicated solid targets & cryogenic gaseous targets (H, d, 3 He, 4 He) inside the KLOE DC. R&D activity is ongoing

:­) Thanks

Spare Slides

Experimental program of AMADEUS Unprecedented studies of the low­energy charged kaons interactions in nuclear matter: solid and gaseous targets (d, 3 He, 4 He, 8 Be, 12 C … ) in order to obtain unique quality information about: 1) Possible existence of kaonic nuclear clusters (deeply bound kaonic nuclear states) Single & multi – nucleon K ­ absorption 2) Nature of the controversial Λ (1405)  Low­energy charged kaon cross sections for momenta lower than 100 MeV/c (still not measured)  Many other processes of interest in the low­energy strangeness QCD sector → implications from particle and nuclear physics to astrophysics (dense baryonic matter in neutron stars)

Carbon target inside KLOE Advantages: ● gain in statistics ● K ­ absorptions occur in Carbon ● absorptions at­rest. ● MC simulation: 26% of K ­ stopped in C, 2% of K ­ stopped in Al hence aluminium contamination from 19% → 7% ! ● Thickness optimazied (based on MC simulations) to maximize the number of stopping K − in the targed, minimizing the charged particles energy loss. (~90 pb ­1 ; analyzed 37 pb ­1 , x1.5 statistics)

p / d / t masses obtained by time of flight

→ Σ 0 π 0 K - ”p” bound proton in 4 He / 12 C

Scientific case of the Λ(1405) The three quark model picture has some difficulties to reproduce the Λ(1405) . According to its negative parity, one of the quarks has to be excited to the l = 1 orbit. Similar to the nucleon sector, where one of the lowest negative parity baryon is the N(1535), the expected mass of the Λ * is around 1700 MeV (since it contains one strange quark). Another difficulty is the energy splitting observed between the Λ(1405) and the Λ(1520) , if is interpreted as the spin­orbit partner ( J p = 3/2 ­ ). R. Dalitz and collaborators first suggested to interpret Λ(1405) as an KN quasibound state.

Scientific case Λ(1405) Distribution shape depends TO TEST THE HIGHER POLE: on the decay channel: production in KN reactions (only ● chance to observe the high mass pole) decaying in Σ 0 π 0 (free from Σ(1385) ● background I=1)

Scientific case of the Λ(1405) TO TEST THE HIGHER POLE: production in KN reactions (only chance to observe the high mass ● pole) decaying in Σ 0 π 0 (free from Σ(1385) background I=1) ●

Scientific case Λ(1405) K ­ nuclear absorption experiments .. long history .. BUT 1) m πΣ spectra CUT AT THE ENERGY LIMIT AT­REST 2) ( Σ ± π ∓ ) Σ(1385) CONTAMINATION P. J. Carlson, et al. Nucl. Phys. 74 642 “A study of K − 4 He → ( Σ ± π ∓ ) + 3 Η using slow instead of stopping K − would be very useful in eliminating some of the uncertainties in interpretation” D. Riley, et al. Phys. Rev. D11 (1975) 3065 Esmaili et el., Phys.Lett. B686 (2010) 23­28 p πΣ (MeV/c) The Σ 0 π 0 spectrum was only observed in 3 experiments … with different line­shapes ! I. Zychor et al., Phys. Lett. B 660 (2008) 167 K. Moriya, et al., (Clas Collaboration) Phys. Magas et al. PRL 95, 052301 (2005) 034605 S. Rev. C 87, 035206 (2013) Prakhov, et al., Phys. Rev. C70 (2004)

Σ 0 π 0 channel In­flight component … FIRST EVIDENCE IN K ­ ABSORPTION MASS SPECTROSCOPY opens a higher invariant mass region p π0 resolution : σ p ≈ 12 MeV/c ) m lim 12 C ) m lim 12 C c c / / in filght At rest V V at­rest e e M M In flight 0 0 1 1 ( ( / / s s t t n n u u o o C C 2005 DATA 2012 DATA ) ) 2 2 c c / / in­flight component V V e e M M ( (   0 0 0 0 π π π π 0 0 0 0 Σ Σ Σ Σ m m p π0  (MeV/c) p π0  (MeV/c)

Σ 0 π 0 channel Acceptance corrected m π 0 Σ 0 spectra, DC wall (left) DC gas (right) Acceptance function evaluated in 8 intervals of p π 0 Σ 0 (between 0 and 700 MeV/c) 8 intervals of θ π 0 Σ 0 (between 0 and 3.15 rad) 30 intervals of m π 0 Σ 0 (between 1300 and 1600 MeV/c 2 ) Arbitrary normalization Arbitrary normalization 2005 DATA 2005 DATA Carbon Helium

Σ + π ­ HYDROGEN contamination → from → Σ + π − detected via: (p π 0 ) π − K ­ p ) c / V → Σ π is peaked at around K ­ H e M ( 2005 DATA − −  1430 MeV !!! π π p DC wall K ­ H interaction probability estimate based on K ­ interaction AT­REST in p Σ+  (MeV/c) hydrocarbons mixture data (Lett. Nuovo Cimento, C 1099 (1972)) ) order of 1% !!! c / V e M 2012 DATA (  − − NOW π π p Thanks to the excellent p π− resolution < 1 MeV ... p Σ+  (MeV/c)

Σ + π ­ HYDROGEN contamination → from → Σ + π − detected via: (p π 0 ) π − K ­ p K ­ H absorption in­flight (MC) ) c / V K ­ 12 C absorption in­flight (MC) e M ( 2005 DATA − −  π π p AND K ­ 12 C absorption at­rest (MC) K ­ H contribution ~ 20% p Σ+  (MeV/c) … in­flight absorption is extremely different ) c / V e M 2012 DATA (  − − π π p K ­ 12 C absorption at­rest (MC) ONLY ! p Σ+  (MeV/c)

Σ 0 π 0 channel Invariant mass spectra with mass hypotesis on Σ 0 and π 0 non resonant misidentification background subtracted (right) σ m ≈ 17 MeV/c 2 ( 12 C) σ m ≈ 15 MeV/c 2 ( 4 He) Similar m π 0 Σ 0 shapes due to the similar kinematical thresholds for 4 He and 12 C. 2005 DATA 12 C 12 C 4 He 4 He n.r.m. 4 He n.r.m. 12 C

Ongoing fit of Σ 0 π 0 8 component fit : Resonant component K ­ C at­rest/in­flight. (M, Γ ) = (1405 ÷ 1430 , 5 ÷ 52 ) ● Non resonant Σ 0 π 0 K ­ H production at­rest/in­flight ● Non resonant Σ 0 π 0 K ­ C production at­rest/in­flight ● Λπ 0 background ( Σ (1385) + I.C.) ● non resonant misidentification ( n.r.m. ) background ●

Fit of Σ 0 π 0 spectrum in C /ndf ~ 1.7 corresponding to (M min , Γ min ) = (1426 , 52) MeV/c 2 χ 2 min Global fit Resonant component K ­ C at­rest ● n. r. K ­ C at­rest n. r. K ­ C in­flight n. r. K ­ H in­flight ● Λ 0 π 0 background + n. r. m. ● Preliminary .. more next weeks m Σ0π 0 p Σ0π 0

Oton Vázquez Doce KN interactions with KLOE Issues Is there room for a 2NA pionic mode? K-NN → YπN The preliminary fits find «a place» for this processes (~ 5%) and... Λpπ-events in 12C Λp events in 12C Λγ (MeV/c2)

6 Oton Vázquez Doce KN interactions with KLOE 8 Events with Cos(th-lambda-t)<-0,97 - Clear back-to-back enhacement lambda-triton signal - Events in Carbon not showing this feature - 3NA features also seen in the momentum correlations

6 Oton Vázquez Doce KN interactions with KLOE KLOE: Study of Σπ in 12C 9 Mass of π 0 reconstructed: σ m ~ 18 MeV/c2

Channel: K − 4 He → Λ π − 3 He … calculated reactions Calculated secondary hadronic interactions: EACH INTERNAL CONVERSION PROCESS: → Λ p/n Σ p/n was calculated for both P­wave and S­wave produced Σ s. ) c / V e M ( − −  π π p p Λ  (MeV/c)

Channel: K − 4 He → Λ π − 3 He … calculated reactions Calculated secondary hadronic interactions: EACH INTERNAL CONVERSION PROCESS: → Λ p/n Σ p/n was calculated for both P­wave and S­wave produced Σ s. Some Carbon from Isobutane Λ π − direct production In­flight At­rest Σ 0 p conversion ) c / V e M Σ 0 n conversion ( − −  π π p Σ + n conversion p Λ  (MeV/c)

K − 4 He → Λ π − 3 He events selection ) c / V e M ( − −  π π p p Λ  (MeV/c)

K − 4 He → Λ π − 3 He events selection Λ π − direct production In­flight RES + N­R ) c Λ π − direct production / V e At­rest RES + N­R M ( − −  π π p p Λ  (MeV/c) CUT based on MC simulations used to select Λ π − direct production events ● → At­rest CAN NOT be separated from In­flight global fit performed ● → Λ p/n conversion Background sources: ­ Λ π − events from Σ p/n ● ­ Λ π − events from K − 12 C absorptions in Isobutane

K − 4 He → Λ π − 3 He background Σ p/n → Λ p/n conversion: ● Each possible conversion channel was simulated Σ 0 p / Σ 0 n / Σ + n / At­rest / In­flight / from RES and N­R produced Σ s Λ π − events from K − 12 C absorptions in Isobutane (90% He, 10% C 4 H 10 ): ● K − 12 C DATA in the KLOE DC wall are used estimated contribution: N KC /N KHe = ( n KC / n KHe ) ∙ ( σ KC / σ KHe ) ∙ (BR KC ( Λ π − )/BR KHe ( Λ π − )) Nuovo Cimento 39 A 338­347 (1977) K − 12 C still not calculated: ­ uncertain initial state of K meson l Κ = 1, 2, 3 ­ 4 nucleons in s­orbit , 8 nucleons in p­orbit ­ final state hyperon interactions

K − 4 He → Λ π − 3 He fit Simultaneous fit (p Λπ− ­ m Λπ− ­ θ Λπ− ) leaving the ratio At­rest /In­flight and 12 C contamination to vary around the estimated values within errors: ) c / 2 V . 0 e / M s t n 3 u ( o s C t n u o C cos( θ Λπ− m Λπ−  (MeV/c 2 )  ) Global fit Λ π − At­rest N­R Λ π − At­rest RES Λ π − In­flight N­R Λ π − In­flight RES Λ π − events from K − 12 C Σ p/n → Λ p/n conversion

Λ (1116) the signature of K ­ hadronic interaction starting point of the performed analysis reconstruction of the Λ decay p π − (BR ∼ 64 % ) vertex: Λ(1116) → requests: ● vertex with at least two opposite charged particles ● spatial position of vertex inside DC, or in DC entrance wall ● negative tracks with dE/dx < 95 ADC counts. Positive tracks are requested to have an associated cluster in the calorimeter and the correct E ­ p relation. (KLOE Memo 330 September 2006)

Λ (1116) the signature of K ­ hadronic interaction Correction for low momentum positive tracks (due to the kinetic energy threshold of the calorimeter ∼ 20 MeV) Clear separation with respect to pions (from K + two body decay) Excellent fianal p π − invariant mass spectrum.

Λ p/ Λ d/ Λ t and Λ p + π − channels

Λ p/ Λ d/ Λ t and Λ p + π − scientific case How hadron masses and interactions change in nuclear medium .. approach by means of kaonic nuclear clusters. Deeply Bound Kaonic Nuclear States (ex. K ­ pp – K ­ ppn) predicted due to the strong KN interaction in the I=0 channel. Wycech (1986) ­ Akaishi & Yamazaki (2002) Search for signal of bound states in the Λ p channel: candidate to be a K ­ pp cluster. Observed (FINUDA, KEK, DISTO) and very debated HADES, L. Fabietti, Status of the ppK­ analysis and last words about the Lambda(1405) interpretation strongly depends on single and multi – nucleon absorption process: → Λ / Σ π single nucleon PIONIC, most probable process K ­ N → Λ / Σ N (K ­ NNN → Λ / Σ NN) multi­nucleon NON­PIONIC, (BR ≈ 20% in 4 He ) K ­ NN

Tools for identifying Λ N events Interaction vertex identified backward extrapolating Λ + N, also using: Trunc ADC ­ dE/dx ­ EMC: Time, Energy, Mass by TOF p (MeV/c) Counts/30(MeV/c 2 ) Quality checks using distances: π ­ Tracked K ­ in 12% of events ­ Backwards extrapolated K + used instead p (possible in 95% of events d when the K ­ is missing) ­ Λ decay path m(MeV/c 2 )

Excellent DC resolution π − from Λ decay (MeV/c) p from Λ decay (MeV/c) Λ ­ p invariant mass (MeV/c 2 ) Distributions: MC­Reconstructed Minv pπ- (MeV) Tracks connected by KLOE vtx (left) Tracks NOT connected by KLOE vtx (right) p (MeV/c) r vertex (cm)

Good acceptance ... Projection of acceptance function depending on (P Λ ,P p , m Λ p ) on the Invariant mass plane. True phase space MC Reconstructed MC Acc. Corrected MC Normalization 1:1 (no efficiency evaluation) KEK

… allows to perfectly disentangle 1N­absorption in Λ p correlation study K ­ pp cluster ?? → Λπ − (p from residual nucleus) Background: 1NA: K ­ N → Λ N (pionless) 2NA: K ­ NN Λp events KLOE In 4 He Λ p all events Λπ − (p) events (arbitrary normalization) Λ ­ p invariant mass (MeV/c 2 ) acceptance in Λ ­ p invariant mass (MeV/c 2 ) (arbitrary normalization) The Λ p missing mass for the Λπ − (p) events lies exactly in the 2N+ π − masss region m 2N +m π KEK-E549 Λ ­ p missing mass (MeV/c 2 ) Mod.Phys.Lett.A23, 2520 (2008)

Λ d/ Λ t analyses Search for signal of bound states in the Λ d channel. Candidate to be a K ­ ppn cluster. Observed spectra from FINUDA and KEK again showing possible bound states in the high invariant mass region . Λ d events deuterons In 4 He m Λ d (MeV/c 2 ) low accept. region TOF particle mass (MeV/c 2 ) FINUDA Nucl.Phys.A835, 43 (2010)

Λ d/ Λ t analyses Search for signal of bound states in the Λ d channel. Candidate to be a K ­ ppn cluster. Observed spectra from FINUDA and KEK again showing possible bound states in the high invariant mass region . deuterons Λ d events In 4 He tritons m Λ d (MeV/c 2 ) Only FINUDA and M. Roosen, J.H. Wickens, Il Nuovo Cimento 66 (1981), 101. (4 events) have shown Λ ­ t spectra from K ­ absorption! TOF particle mass (MeV/c 2 ) Preliminary FINUDA Phys.Lett.B 229, 229 (2008) Filled histogram= data Λ t events Open histogram = Phase space simulation In 4 He Cos(θ Λt )

Conclusions Λ p/ Λ d/ Λ t and Λ p + π − analyses KLOE excellent acceptance and resolution! Λ p and Λ p + π − analyses completed, show important differences revealing the mesonic absorption characteristics. Good statistics in Λ t.

→ Σ 0 π 0 / Σ + π − channels K - ”p” bound proton in 12 C

Scientific case Λ(1405) Λ (1405): ( m , Γ ) = (1405.1 +1.3 ­1.0 , 50 ± 2 ) MeV, I = 0, S = ­1 , J p = 1/2 ­ , Status: ****, strong decay into Σπ Its nature is being a puzzle for decades: 1) three quark state : expected mass ~ 1700 MeV 2) penta quark : more unobserved excited baryons 3) unstable KN bound state 4) two poles : (z 1 = 1424 +7 ­23 – i 26 +3 ­14 ; z 1 = 1381 +18 ­6 – i 81 +19 ­8 ) MeV (Nucl. Phys. A881, 98 (2012)) mainly coupled to KN mainly coupled to Σπ → line­shape depends on production mechanism Line­shape also depends on the decay channel TO TEST THE HIGHER POLE: production in KN reactions (only chance to observe the high mass pole) Complementary to HADES measurement decaying in Σ 0 π 0 (free from Σ(1385) background) See L. Fabietti's talk

Scientific case Λ(1405) K ­ nuclear absorption experiments .. long history .. BUT 1) m πΣ spectra always cut at the at­rest limit 2) ( Σ ± π ∓ ) spectra suffer Σ(1385) contamination P. J. Carlson, et al. Nucl. Phys. 74 642 “A study of K − 4 He → ( Σ ± π ∓ ) + 3 Η using slow instead of stopping K − would be very useful in eliminating some of the uncertainties in interpretation” D. Riley, et al. Phys. Rev. D11 (1975) 3065 Esmaili et el., Phys.Lett. B686 (2010) 23­28 p πΣ (MeV/c) The Σ 0 π 0 spectrum was only observed in 3 experiments … with different line­shapes ! I. Zychor et al., Phys. Lett. B 660 (2008) 167 K. Moriya, et al., (Clas Collaboration) Phys. Magas et al. PRL 95, 052301 (2005) 034605 S. Rev. C 87, 035206 (2013) Prakhov, et al., Phys. Rev. C70 (2004)

Photon clusters identification → Σ 0 π 0 → (Λ(1116) γ 3 ) (γ 1 γ 2 ) → ( p π − ) 3γ K - ”p” → π + π 0 ) 1) 3 neutral clusters selection (E c l > 20 MeV) not from K + decay (K + 2 = t 2 / σ 2 2) photon clusters selection: χ t t where t = t i – t j time of flights in light speed hypothesis. Selects three photon clusters in time from the Λ decay vertex r Λ → γ 1 γ 2 distinctioncay 3) photon clusters identification: γ 3 from π 0 i , j and k represent one of the previously selected candidate photon cluster. 4) Cuts on χ t 2 and χ πΣ 2 optimized on MC simulations & splitted clusters rejection The algorithm has (from true MC information) an efficiency (98±1) % to identify photons and (78±2) % to select the correct triple of neutral clusters.

Photon clusters identification: Σ 0 invariant mass m γ1γ 2 , m γ1γ3 , m γ2γ3 MC m γ1γ3 , m γ2γ3 m γ1γ 2 DATA 2012 DATA m γ1γ 2 , m γ1γ3 , m γ2γ3 2012 m γ1γ3 , m γ2γ3 m γ1γ 2 m Λγ3

Σ 0 π 0 channel Λ (1405) signal searched by K ­ interaction with a bound proton in Carbon → Σ 0 π 0 detected via: (Λγ) (γγ) K ­ p Strategy : K ­ absorption in the DC entrance wall, mainly 12 C with H contamination (epoxy) N. U. N. U. 2005 2012 2012 Carbon target Carbon target m lim in 12 C at­rest p Σ0π0  (MeV/c 2 ) m Σ0π0  (MeV/c 2 ) m π0Σ0 resolution σ m ≈ 32 MeV/c 2 ; p π0Σ0 resolution : σ p ≈ 20 MeV/c. Negligible (Λ π 0 + internal conversion) background = (3±1) % → no I=1 contamination

Σ 0 π 0 channel K ­ nuclear absorption experiments .. long history .. BUT 1) m πΣ spectra always cut at the at­rest limit 2) ( Σ ± π ∓ ) spectra suffer Σ(1385) contamination P. J. Carlson, et al. Nucl. Phys. 74 642 D. Riley, et al. Phys. Rev. D11 (1975) 3065 2005 N. U. N. U. 2012 2012 Carbon target Carbon target m lim in 12 C at­rest p Σ0π0  (MeV/c 2 ) m Σ0π0  (MeV/c 2 )

Σ 0 π 0 channel N. U. Mass momentum correlatation m lim in 12 C at­rest m Σ0π0  (MeV/c 2 ) 2005 N. U. 2012 2012 Carbon target Carbon target p Σ0π0  (MeV/c 2 )

Σ 0 π 0 channel in­flight component … FIRST EVIDENCE IN K ­ ABSORPTION MASS SPECTROSCOPY open a higher invariant mass region p π0 resolution : σ p ≈ 12 MeV/c ) m lim 12 C ) m lim 12 C c c / / in filght At rest V V at­rest e e M M In flight 0 0 1 1 ( ( / / s s t t n n u u o o C C 2005 DATA 2012 DATA ) ) 2 2 c c / / in­flight component V V e e M M ( (   0 0 0 0 π π π π 0 0 0 0 Σ Σ Σ Σ m m p π0  (MeV/c) p π0  (MeV/c)

Σ 0 π 0 channel Invariant mass spectra with mass hypotesis on Σ 0 and π 0 non resonant misidentification background subtracted (left) σ m ≈ 17 MeV/c 2 (DC wall) σ m ≈ 15 MeV/c 2 (DC gas) Similar m π 0 Σ 0 shapes due to the similar kinematical thresholds for 4 He and 12 C. 2005 DATA DC wall DC wall DC gas DC gas n.r.m. gas n.r.m. wall

Σ 0 π 0 channel Acceptance corrected m π 0 Σ 0 spectra, DC wall (left) DC gas (right) Acceptance function evaluated in 8 intervals of p π 0 Σ 0 (between 0 and 700 MeV/c) 8 intervals of θ π 0 Σ 0 (between 0 and 3.15 rad) 30 intervals of m π 0 Σ 0 (between 1300 and 1600 MeV/c 2 ) Arbitrary normalization Arbitrary normalization

Σ + π ­ channel → Σ + π − detected via: (p π 0 ) π − K ­ p ) c / V e M ( 2005 DATA − −  π π p in­flight components clearly evidenced by the excellent p π− p Σ+  (MeV/c) resolution ... ) c / V e M 2012 DATA (  − − π π p p Σ+  (MeV/c)

Σ + π ­ channel → Σ + π − detected via: (p π 0 ) π − K ­ p K ­ H absorption in­flight (MC) ) c / V K ­ 12 C absorption in­flight (MC) e M ( 2005 DATA − −  π π p K ­ 12 C absorption at­rest (MC) … in­flight components clearly evidenced by the excellent p π− p Σ+  (MeV/c) resolution ) c / V e M 2012 DATA (  − − π π p K ­ 12 C absorption at­rest (MC) ONLY ! p Σ+  (MeV/c)

Σ + π ­ channel → Σ + π − detected via: (p π 0 ) π − K ­ p 2005 data K ­ H absorption in­flight (MC) ) ) c c / / V K ­ 12 C absorption in­flight (MC) V e e M M ( 2005 DATA 3 ( − −  / π π s p t n u o K ­ 12 C absorption at­rest (MC) C m lim in 12 C at­rest m Σ+π−  (MeV/c 2 ) p Σ+  (MeV/c) 2012 Carbon target ) c / V ) c e / M V 2012 DATA e ( M  − − π π 3 p ( / s t n u K ­ 12 C absorption at­rest (MC) o m lim in 12 C C at­rest ONLY ! m Σ+π−  (MeV/c 2 ) p Σ+  (MeV/c)