Strangeness production from kaon two-nucleon absorption on light nuclei

Transcription

1 Strangeness production from kaon two-nucleon absorption on light nuclei S. Piano INFN Trieste FINUDA Collaboration

2 Λ identification with FINUDA FINUDA FRONTAL VIEW VERTEX REGION

3 Proton and Λ purity with FINUDA proton purity > 98% All π - p pairs PID: at least 3 out of 4 layers (i.e., ISIM, OSIM, LMCD1 and LMDC2) deliver similar de/dx values. Proton purity > 98% Topological cut on π-pp sample: K - stop p primary vertex π- p secondary vertex S/N > 8 All π - p pairs: π - p IM no topological cut π - pp sample: π - p IM after topological cut FWHM 6 MeV/c 2 S/N 8.3

4 not acceptance corrected FINUDA: 6 Li(K - stop,λp)x Data Taking 8x statistics on: 6 Li, 7 Li, 9 Be, 13 C, 16 O - Improved tracking efficiency and secondary vertex reconstruction - Extended range of the reconstructed momentum - Improved selections (missing mass) - Statistics large enough to study single tgt spectra : 3x 12 C+2x 6 Li+1x 7 Li : 2x 6 Li

5 not acceptance corrected FINUDA: 6 Li(K - stop,λp)x Data Taking 8x statistics on: 6 Li, 7 Li, 9 Be, 13 C, 16 O - Improved tracking efficiency and secondary vertex reconstruction - Extended range of the reconstructed momentum - Improved selections (missing mass) - Statistics large enough to study single tgt spectra FINUDA Coll., PRL 94(2005) : 3x 12 C+2x 6 Li+1x 7 Li : 2x 9 Be+2x 6 Li+2x 7 Li Analyzed statistics comparable to data analysis cuts among them: Cos θ Λp < : 2x 6 Li No angular cut in the present analysis

6 not acceptance corrected FINUDA: 6 Li(K - stop,λp)x Acceptance Correction - FINUDA lower momentum thresholds: p π > 70 MeV/c and p p >130 MeV/c - Large Correction for p p < 300 MeV/c and p Λ < 300 MeV/c - Present analysis p p > 300 MeV/c and p Λ > 300 MeV/c - No angular cut : 2x 6 Li Λp Finuda Acceptance

7 not acceptance corrected FINUDA: 6 Li(K - stop,λp)x Acceptance Correction - FINUDA lower momentum thresholds: p π > 70 MeV/c and p p >130 MeV/c - Large Correction for p p < 300 MeV/c and p Λ < 300 MeV/c - Present analysis p p > 300 MeV/c and p Λ > 300 MeV/c - No angular cut - Error bars take in to account statistical and systematic uncertainties : 2x 6 Li Before acceptance correction After acceptance correction

8 acceptance corrected FINUDA: 6 Li(K - stop,λp)x Spectra

9 acceptance corrected K -6 Li Σ 0,+ na K -6 Li Σ 0,+ π 0,- A FINUDA: 6 Li(K - stop,λp)x Spectra Composition K -6 Li Σ 0 pa Σ 0 Λγ K -6 Li ΛnA FSI: na npa K -6 Li ΛpA FSI: ΛA ΛnA K -6 Li ΛpA K -6 Li Σ 0,- pa Σ 0 n Λn Σ - p Λn K -6 Li ΛpnA Quasi-Free simulations with nucleon pairs Fermi mom. and A residual nucleus (ground state) [Heusi, NPA 407 (1983) 429] Simulations filtered by FINUDA and acceptance corrected

10 acceptance corrected K -6 Li Σ 0,+ na K -6 Li Σ 0,+ π 0,- A FINUDA: 6 Li(K - stop,λp)x Spectra Composition K -6 Li Σ 0 pa Σ 0 Λγ K -6 Li ΛnA FSI: na npa K -6 Li ΛpA FSI: ΛA ΛnA K -6 Li ΛpA K -6 Li Σ 0,- pa Σ 0 n Λn Σ - p Λn K -6 Li ΛpnA How to evaluate the best FIT taking into account simultaneously IM, Cos, MM, p p, p Λ spectra???

11 Arb. Unity FINUDA: 6 Li(K - stop,λp)x GLOBAL FIT Λp data fitted by GLOBAL FIT which requires 5 distributions (Inv Mass, Miss Mass, Cosθ Λp, p Λ and p p ) to be reproduced at same time by (sum of)10 reactions Binned Maximum Likelihood Fit Cos θ Λp Inv Mass Miss Mass p Λ p p Bin Number

12 acceptance corrected FINUDA: 6 Li(K - stop,λp)x GLOBAL FIT Sum of 10 bck reactions explain 90% of the spectra χ ν2 3.1

13 acceptance corrected K -6 Li Σ 0,+ na K -6 Li Σ 0,+ π 0,- A FINUDA: 6 Li(K - stop,λp)x GLOBAL FIT K -6 Li Σ 0 pa Σ 0 Λγ K -6 Li ΛnA FSI: na npa K -6 Li ΛpA FSI: ΛA ΛnA K -6 Li Σ 0,- pa Σ 0 n Λn Σ - p Λn K -6 Li ΛpnA K -6 Li ΛpA Excess of data around 2300 MeV/c 2 Cos Λp ~ -1

14 acceptance corrected FINUDA: 6 Li(K - stop,λp)x K - A Σ 0,+ na K - A Σ 0,+ π 0,- A On 6 Li data around 2300 MeV/c 2 not explained... nor Cos Λp ~ -1 K - A ΛnA FSI: na npa K - A ΛpA FSI: ΛA ΛnA K - A Σ 0 pa Σ 0 Λγ 6 Li Different configurations for residual nucleus are all within 10 MeV/c 2 : t+n ~ 3748 MeV/c 2 4 H ~ 3751 MeV/c 2 d+2n ~ 3755 MeV/c 2 p+3n ~ 3757 MeV/c 2 K - A Σ 0,- pa Σ 0 n Λn Σ - p Λn K - A ΛpnA K - A ΛpA

15 acceptance corrected 6 Li(K - stop,λp)x: Test the [K - pp] hypothesis K -6 Li [K - pp] m,σ A m = 2255 MeV/c 2 σ = 28 MeV/c 2 Main Idea: Try to include the [K-pp] resonance state in the global fit But which central value and width? Scan them on a discrete grid and find the best fit K - A Σ 0 pa Σ 0 Λγ K - A Σ 0,+ na K - A Σ 0,+ π 0,- A K - A Σ 0,- pa Σ 0 n Λn Σ - p Λn K - A ΛpnA K - A ΛnA FSI: na npa K - A ΛpA FSI: ΛA ΛnA K - A ΛpA K - A [K - pp] m,σ A

16 acceptance corrected 6 Li(K - stop,λp)x: Test the [K - pp] hypothesis K -6 Li [K - pp] m,σ A m = 2255 MeV/c 2 σ = 28 MeV/c 2 K -6 Li [K - pp] m,σ A m = 2276 MeV/c 2 σ = 28 MeV/c 2 K - A Σ 0 pa Σ 0 Λγ K - A Σ 0,+ na K - A Σ 0,+ π 0,- A K - A Σ 0,- pa Σ 0 n Λn Σ - p Λn K - A ΛpnA K - A ΛnA FSI: na npa K - A ΛpA FSI: ΛA ΛnA K - A ΛpA K -6 Li [K - pp] m,σ A m = 2298 MeV/c 2 σ = 28 MeV/c 2 K - A [K - pp] m,σ A

17 acceptance corrected 6 Li(K - stop,λp)x: Test the [K - pp] hypothesis K -6 Li [K - pp] m,σ A m = 2298 MeV/c 2 σ = 05 MeV/c 2 K -6 Li [K - pp] m,σ A m = 2298 MeV/c 2 σ = 20 MeV/c 2 K - A Σ 0 pa Σ 0 Λγ K - A Σ 0,+ na K - A Σ 0,+ π 0,- A K - A Σ 0,- pa Σ 0 n Λn Σ - p Λn K - A ΛpnA K - A ΛnA FSI: na npa K - A ΛpA FSI: ΛA ΛnA K - A ΛpA K -6 Li [K - pp] m,σ A m = 2298 MeV/c 2 σ = 36 MeV/c 2 K - A [K - pp] m,σ A

18 6 Li(K - stop,λp)x: Test the [K - pp] hypothesis 2 2 (M K-pp, σ K-pp ) fitted by Chebyshev polynomials M K-pp Former FINUDA result: M K-pp = MeV σ K-pp = MeV The width (Γ ~70 MeV) is compatible but B moves from 115 to 80 MeV σ K-pp Minimum found at: M K-pp = MeV σ K-pp = MeV Avni, AJ 210 (1976) without [K - pp] = 291 Best 2 with [K - pp] = 219

19 acceptance corrected K -9 Be Σ 0,+ na K -9 Be Σ 0,+ π 0,- A FINUDA: 9 Be(K - stop,λp)x different A configurations K -9 Be ΛnA FSI: na npa K -9 Be ΛpA FSI: ΛA ΛnA K -9 Be Σ 0 p(2p+5n) Σ 0 Λγ K -9 Be Σ 0 p 7 He Σ 0 Λγ K -9 Be Σ 0,- pa Σ 0 n Λn Σ - p Λn K -9 Be ΛpnA K -9 Be Λp(2p+5n) K -9 Be Λp 7 He Daum, NPA 589 (1995) 553

20 acceptance corrected K -9 Be Σ 0,+ na K -9 Be Σ 0,+ π 0,- A FINUDA: 9 Be(K - stop,λp)x different A configurations K -9 Be ΛnA FSI: na npa K -9 Be ΛpA FSI: ΛA ΛnA K -9 Be Σ 0 p(2p+5n) Σ 0 Λγ K -9 Be Σ 0 p 7 He Σ 0 Λγ K -9 Be Σ 0,- pa Σ 0 n Λn Σ - p Λn K -9 Be ΛpnA K -9 Be Λp(2p+5n) K -9 Be Λp 7 He

21 acceptance corrected K -9 Be Σ 0,+ na K -9 Be Σ 0,+ π 0,- A FINUDA: 9 Be(K - stop,λp)x different A configurations K -9 Be Σ 0 pa Σ 0 Λγ K -9 Be ΛnA FSI: na npa K -9 Be ΛpA FSI: ΛA ΛnA K -9 Be Σ 0,- pa Σ 0 n Λn Σ - p Λn K -9 Be ΛpnA K -9 Be ΛpA Different A configurations: 1) 7 He ~ 6545 MeV/c 2 6 He+n ~ 6545 MeV/c 2 5 He+2n ~ 6547 MeV/c 2 4 He+3n ~ 6546 MeV/c 2 2) t+p+3n ~ 6567 MeV/c 2 3) d+p+4n ~ 6572 MeV/c 2 4) 2p+5n ~ 6574 MeV/c 2

22 acceptance corrected K -9 Be Σ 0,+ na K -9 Be Σ 0,+ π 0,- A FINUDA: 9 Be(K - stop,λp)x GLOBAL FIT K -9 Be Σ 0 pa Σ 0 Λγ K -9 Be ΛnA FSI: na npa K -9 Be ΛpA FSI: ΛA ΛnA K -9 Be Σ 0,- pa Σ 0 n Λn Σ - p Λn K -9 Be ΛpnA K -9 Be ΛpA Excess of data around 2300 MeV/c 2 explained Cos Λp ~ -1 well fitted

23 acceptance corrected 9 Be(K - stop,λp)x: Test the [K - pp] hypothesis K -9 Be [K - pp] m,σ A m = 2255 MeV/c 2 σ = 28 MeV/c 2 K -9 Be [K - pp] m,σ A m = 2276 MeV/c 2 σ = 28 MeV/c 2 K - A Σ 0 pa Σ 0 Λγ K - A Σ 0,+ na K - A Σ 0,+ π 0,- A K - A Σ 0,- pa Σ 0 n Λn Σ - p Λn K - A ΛpnA K - A ΛnA FSI: na npa K - A ΛpA FSI: ΛA ΛnA K - A ΛpA K - A [K - pp] m,σ A K -9 Be [K - pp] m,σ A m = 2298 MeV/c 2 σ = 28 MeV/c 2

24 acceptance corrected 9 Be(K - stop,λp)x: Test the [K - pp] hypothesis K -9 Be [K - pp] m,σ A m = 2255 MeV/c 2 σ = 28 MeV/c 2 K -9 Be [K - pp] m,σ A m = 2276 MeV/c 2 σ = 28 MeV/c 2 K - A Σ 0 pa Σ 0 Λγ K - A Σ 0,+ na K - A Σ 0,+ π 0,- A K - A Σ 0,- pa Σ 0 n Λn Σ - p Λn K - A ΛpnA K -9 Be [K - pp] m,σ A m = 2298 MeV/c 2 σ = 28 MeV/c 2 K - A ΛnA FSI: na npa K - A ΛpA Minima found for 7Li, 9Be,16O FSI: ΛA in the ΛnA range KM - A ΛpA K - A [K - K-pp and pp] σ K-pp m,σ A

25 Best Fit Parameters of [K - pp] μ Λp [MeV/c 2 ] Γ Λp [MeV/c 2 ] B [K-pp] [MeV] χ 2 ν S 6 Li Li Be O

26 Capture Rates (x 10-4 /K stop ) p Λ > 300 MeV/c, p p > 300 MeV/c Inclusive Λp Λp only QF Σ 0 p QF [K - pp] 6 Li Li Be O

27 Capture Rates (x 10-4 /K stop ) p Λ > 0 MeV/c, p p > 0 MeV/c (0-300 MeV/c extrapolation by simulations) Inclusive Λp Λp only QF Σ 0 p only QF [K - pp] 6 Li Li Be O

28 Katz, PRD 1(1970)1267 Capture Rates (x 10-4 /K stop ) p Λ > 0 MeV/c, p p > 0 MeV/c (0-300 MeV/c extrapolation by simulations) Inclusive Λp Λp only QF Σ 0 p only QF [K - pp] 6 Li Li Be O

29 FINUDA: 6 Li(K - stop,λp)x Missing Mass Sharp peak in Missing Mass spectra: K -6 Li ΛpA Close to Λpπ threshold Kinematics compatible with deeply bound pionic state Early predicted by J.Nieves and E.Oset, Deeply bound pionic states with the (Σ -, Λ) reaction Z. Phys. A 343 (1992) 477

30 FINUDA: 6 Li(K - stop,λp)x Missing Mass Sharp peak in Missing Mass spectra: K -6 Li ΛpA Close to Λpπ threshold Kinematics compatible with deeply bound pionic state Early predicted by J.Nieves and E.Oset, Deeply bound pionic states with the (Σ -, Λ) reaction Z. Phys. A 343 (1992) 477

31 FINUDA: 6 Li(K - stop,λp)x Missing Mass Sharp peak in Missing Mass spectra: K -6 Li ΛpA Close to Λpπ threshold p Λ

32 FINUDA: 6 Li(K - stop,λp)x Missing Mass Sharp peak in Missing Mass spectra: K -6 Li ΛpA Close to Λpπ threshold p Λ A π

33 FINUDA: 6 Li(K - stop,λp)x Missing Mass ( 4 He+π - ) (t+π - ) + p (d+π - ) + d Σ m i Sharp peak in Missing Mass spectra: K -6 Li ΛpA Close to Λpπ threshold Kinematics compatible with deeply bound pionic state Early predicted by J.Nieves and E.Oset, Deeply bound pionic states with the (Σ -, Λ) reaction Z. Phys. A 343 (1992) 477

34 Global Fit with deeply bound pionic state Included deeply bound pionic state in the global fit analysis K -6 Li Λp π A with π A = MeV/c 2 Best χ ν2 = 2.1 with π A = 3879 MeV/c 2 and σ << σ res Significance ~3

35 Outlook and Conclusions Evaluated spectra composition with 10 background reactions with the different configurations for the recoiling system for A= Global Fit: data simultaneously fitted to Inv Mass, Miss Mass, Cos θ Λp, p Λ and p p (TFractionFitter) Evaluated M [K-pp] and width on different targets A= by scanning χ 2 on a discrete grid Significant improvement of the fit quality including [K-pp] (A=6 16) and deeply bound pionic state (A=6) Yields and Capture Rates evaluated for the main channels

36 acceptance corrected not acceptance corrected Comparison with the former result K - A Σ 0,+ na K - A Σ 0,+ π 0,- A FINUDA Coll., PRL 94(2005) x 12 C+2x 6 Li+1x 7 Li : 3x 12 C+2x 6 Li+1x 7 Li : Cos θ Λp 2x < 9 Be+2x Li+2x 7 Li Analyzed statistics comparable to Present datadata analysis 2x cuts 9 Be+2x 6 Li+2x 7 Li among them: Cos θ Λp < Be K - A Σ 0 pa Σ 0 Λγ K - A ΛpA

37 p Λ A π