Experimental Status of the Weak Decay of Λ hypernuclei

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1 Experimental Status of the Weak Decay of Λ hypernuclei Stefania Bufalino INFN-Sezione di Torino XI International Conference on Hypernuclear and Strange Particle Physics

2 Outline of the talk Why weak decay of hypernuclei? Experimental results: - two nucleon induced non mesonic weak decay (NMWD) - single particle spectra from NMWD - mesonic weak decay What about the future of this field? 2

3 FINUDA Scientific Program Hypernuclear physics Hypernuclear spectroscopy: PLB 622 (2005) 32: 12 ΛC PLB 698 (2011) 219: 7 ΛLi, 9 ΛBe, 13 ΛC, 16 ΛO Weak Decay: NPA 804 (2008) 151: NMWD 5 Λ He, 7 Λ Li, 12 Λ C PLB 681 (2009) 139: MWD ( 5 Λ He,) 7 Λ Li, 9 Λ Be, 11 Λ B, 15 Λ N PLB 685 (2010) 247: NMWD & 2N 5 Λ He, 7 Λ Li, 9 Λ Be, 11 Λ B, 12 Λ C, 13 Λ C, 15 Λ N, 16 Λ O PLB 701 (2011) 556: NMWD & 2N 5 Λ He, 7 Λ Li, 9 Λ Be, 11 Λ B, 12 Λ C, 13 Λ C, 15 Λ N, 16 Λ O NPA 881 (2012) 322 : (n, n, p) events from 2N Rare Decays: NPA 835 (2010) 439; 4 Λ He, 5 ΛHe 2-body decays Neutron-rich Hypernuclei: PLB 640 (2006) 145: upper limits 6 ΛH, 7 ΛH and 12 ΛBe PRL 108 (2012) , NPA 881 (2012) 269: 6 Λ H observation 3 A complete review on these items: E. Botta, T. Bressani and G. Garbarino, EPJA 48 (2012) 41

4 Mesonic Weak Decay Measurements A Λ Z A (Z+1) + π - Γ π Γ M (p π 100 MeV/c) A Λ Z A Z + π 0 Γ π0 Pauli blocking 4 Experimental observables τ, Γ π, π0 / Γ Λ, (single) particle decay spectra s-shell: Λ-N potential central repulsion p-shell: π distortion effect and MWD enhancement π -nucleus optical potential J π assignment: new indirect spectroscopic tool

5 Non-Mesonic Weak Decay Measurements A Λ Z A-2 (Z-1) + p + n Γ p A Λ Z A-2 Z + n + n Γ n A Λ Z A-3 (Z-X) + N + N + N X=0,1,2 Γ 2N Γ NM (~420 MeV/c, ~340 MeV/c) s-shell: ΔI = 1/2 rule (Schumacher 92: 4 Λ H/4 Λ He/5 Λ He π Λ R n0 /R p0 =0.23±0.17 (0.5)) heavy hypernuclei and ΔI = 1/2 rule (Cassing 03: τ Λ =145±11 ps A~ Rn/Rp>2 ΔI = 3/2 contr. ΔI = 1/2 C.L. ) momentum 270 MeV/c N N N observables (p-shell): - Γ NM = Γ n + Γ p + Γ 2N - Γ n /Γ p puzzle (solved? systematics) 5 - Γ 2N, FSI contributions

NMWD: 2N induced decay evidence Triple coincidence (n+n+p) events @ FINUDA exclusive Λnp nnp 7 ΛLi 4 He+p+n+n decay event M. Agnello et al., Nuclear Physics A 881 (2012) 322 338 p π = 276.9 ± 1.

6 NMWD: 2N induced decay evidence Triple coincidence (n+n+p) FINUDA exclusive Λnp nnp 7 ΛLi 4 He+p+n+n decay event M. Agnello et al., Nuclear Physics A 881 (2012) p π = ± 1.2 MeV/c p miss = 217 ± 44 MeV/c E tot = 178 ± 23 MeV MM= 3710± 23 MeV/c 2 E(n1) = 110 ± 23 MeV E(n2) = 16.9± 1.7MeV E(p) = ± 0.85 MeV θ (n1 n2) = 94.8 ±3.8 θ (n1 p) = ±3.4 θ (n2 p) = 154 ±19 no n-n or p/n scattering 6 First direct experimental evidence of 2N-induced NMWD!!

7 ..if we release the cut on E p Triple coincidence (n+n+p) FINUDA exclusive Λnp nnp 7 ΛLi 4 He+p+n+n decay event p π = ± 1.2 MeV/c p miss = 447 ± 18 MeV/c E tot = 147.1± 4.2 MeV MM= ± 4.7 MeV/c 2 E(n1) = 21 ± 2.0 MeV E(n2) = 35.3 ± 3.6 MeV E(p) = ± 0.50 MeV θ (n1 n2) = ± 5.4 θ (n1 p) = 53.5 ±4.3 θ (n2 p) = ±3.9 no n-n or p/n scattering M. Agnello et al., Nuclear Physics A 881 (2012) First direct experimental evidence of 2N-induced NMWD!!

Triple coincidence (n+n+p) events @ FINUDA exclusive Λnp nnp 9 ΛBe 3 He+ 3 H+n +n+ p decay event M. Agnello et al.

9 MeV MM= 5617.3± 5.0 MeV/c 2 E(n1) = 20.2 ± 2.5 MeV E(n2) = 31.5 ± 4.2 MeV E(p) = 71.77 ± 0.80 MeV θ (n1 n2) =133.

8 Triple coincidence (n+n+p) FINUDA exclusive Λnp nnp 9 ΛBe 3 He+ 3 H+n +n+ p decay event M. Agnello et al., Nuclear Physics A 881 (2012) p π = ± 1.2 MeV/c p miss = 253 ± 18 MeV/c E tot = ± 4.9 MeV MM= ± 5.0 MeV/c 2 E(n1) = 20.2 ± 2.5 MeV E(n2) = 31.5 ± 4.2 MeV E(p) = ± 0.80 MeV θ (n1 n2) =133.6 ± 7.5 θ (n1 p) = ± 5.5 θ (n2 p) = 95.4 ± 3.6 no n-n or p/n scattering 8 First direct experimental evidence of 2N-induced NMWD!!

Background evaluation K - np Σ - p absorption of two correlated nucleons followed by the in-flight Σ - n π - Target θ (π p) Ep (MeV) 7 Li 33.4 ± 3.7 51.11 ± 0.85 7 Li 121.7 ± 3.2 90.83 ± 0.

9 Background evaluation K - np Σ - p absorption of two correlated nucleons followed by the in-flight Σ - n π - Target θ (π p) Ep (MeV) 7 Li 33.4 ± ± Li ± ± Be ± ± 0.80 M. Agnello et al., Nuclear Physics A 881 (2012) significant back-to-back correlation this feature rules out completely the first event on 7 Li - the correlation between cosθ(π p) and Ep was studied for the simulated background major contribution of this background channel for π and p emitted in a quasi back-to-back topology and for Ep > 100 MeV. - Evaluation of the number of simulated events surviving to a 3σ cut on cosθ (π p) and Ep for the 7 Li and 9 Be target ~10 3 events was found for both targets 9 The two Λnp nnp real events do not arise from background to a confidence level larger than 99%.

10 Weak decay: analysis strategy in FINUDA Inclusive production π - spectra K - np background corrected NMWD magnetic analysis!! MWD NMWD decay π - and p spectra (Λ qf decay)/k - np background subtracted & acceptance corrected 10

11 Mesonic decay ratio: Γ π- / Γ Λ Γ π- / Γ Λ = Γ tot / Γ Λ BR π Γ tot / Γ Λ = (0.990±0.094) + (0.018±0.010) A fit from measured values for A=4-12 hypernuclei M. Agnello PLB 681 (2009) 139 / "! " # /2 + 1/2 + strong nuclear structure effects FINUDA data T. Motoba PTPS 117 (1994) 477 previous data A.Gal NPA 828 (2009) 72 1/2 + 5/2 + 3/ A A

12 NMWD total width Lifetime measurements + MWD BRs Y. Sato et al., PRC 71 (2005) Ramos, et. al., PRC 50 (1994) 2314 (OPE + local density approx.) A Γ nm /Γ Λ Reference Itonaga, et. al., PRC 65 (2002) (DQ+OPE (π K)+2π/ρ+2π/σ ) Alberico, et. al., PRC 61 (2000) (Γ 1N only) Sato, et. al., PRC 71 (2005) saturation 5 Λ He 0.404±0.020 KEK PS E462, E508: Kameoka, Okada NPA Λ C 0.953±0.032 KEK PS E462, E508: Kameoka, Okada NPA ±0.14 COSY COSY-13: Cassing 2003

NMWD: Γ n /Γ p ratio Single nucleon measurements Measurements of NMWD p spectra and Γ p : Γ n deduced as Γ tot Γ p Γ M Γ n /Γ p increased by missing p considered as n p missing due to rescattering

13 NMWD: Γ n /Γ p ratio Single nucleon measurements Measurements of NMWD p spectra and Γ p : Γ n deduced as Γ tot Γ p Γ M Γ n /Γ p increased by missing p considered as n p missing due to rescattering inside the residual nucleus (FSI) and/or 2N induced decays Γ n /Γ p puzzle : 2 (Γ n /Γ p ) exp 0.5 vs (Γ n /Γ p ) th ~ KEK PS E307 p spectra 12 Λ C, 28 Λ Si, Λ Fe Y. Sato et al., PRC 71 (2005) Noumi 1995 n measurements needed!! Szymanski

14 NMWD: Γ n /Γ p ratio neutron spectra measurements KEK PS E369 high resolution spectroscopy 12 Λ C, 89 Λ Y J.H. Kim et al., PRC 68 (2003) n spectra as by-product E369/E307 Γ n /Γ p ~ ΛC high statistics n and p spectra KEK PS E462/E508 NMWD n & p spectra 5 ΛHe, 12 ΛC S. Okada et al., PLB 579 (2004) 249 Γ n /Γ p =

15 NMWD: Γ n /Γ p ratio n +p and n+n spectra FSI correction needed, based on calculations 2N-induced contributions? measurement of n & p in coincidence!! Λp np, Λn nn 2-body decays (b-t-b correlation) & (E p + E n = Q value) if not FSI and not 2N KEK PS E462 NMWD n & p spectra in coincidence 5 Λ He B.H. Kang et al., PRL 96 (2006) Γ n / Γ p ( 5 Λ He) N nn / N np = 0.45 ± 0.11 ± 0.03 KEK PS E508 NMWD n & p spectra in coincidence 12 ΛC M.J. Kim et al., PLB 641 (2006) 28 Γ n / Γ p ( 5 ΛHe) N nn / N np = 0.51 ± 0.13 ± n & p detection in coincidence b-t-b removes ambiguities of FSI and 2N NMWD

16 Single proton spectra from FINUDA 15 MeV threshold! 5 Λ He 7 Λ Li 12 Λ C 16 Similar shape for 5 ΛHe, 7 ΛLi and 12 ΛC Peak at ~ 80 MeV (Q/2 value), broadened by N Fermi motion, visible even for 12 Λ C no strong FSI effect in low energy region FSI & 2N contribution in the low energy region?

17 Comparisons with theory and KEK results 15 MeV threshold! 12 Λ C FINUDA NPA 804 (2008),151 Garbarino PRC 69 (2004), KEK E462/E508 PLB 597 (2004), 249 FINUDA NPA 804 (2008),151 5 Λ He FINUDA NPA 804 (2008),151 FINUDA NPA 804 (2008),151 KEK E462/E508 PLB 597 (2004), 249 Garbarino PRC 69 (2004),

18 NMWD 2N-induced contribution KEK PS E Λ C M. Kim et al., PRL 103 (2009) quenching of low energy N due to FSI & 2N which share the same phase space no kinematical separation Γ 2N from measured spectra by accurate accounting of FSI FSI from INC introduces uncertainties FSI by varying INC strength to fit measured inelastic total cross section data: 12 C(p, p ) 18 Γ 2N /Γ NM = 0.29 ± 0.13 Γ 2N = 0.27 ± 0.13 Γ 1N = 0.68 ± 0.13 Γ n = 0.23 ± 0.08 Γ p = 0.45 ± 0.10

NMWD: Γ 2N LNF FINUDA Coll. and G. Garbarino, PLB 685 (2010) 247 Γ 2N /Γ NMWD & Γ n /Γ p independent on A assumption W.Alberico and G.Garbarino, Phys. Rev. 369 (2002) 1.

19 NMWD: Γ 2N LNF FINUDA Coll. and G. Garbarino, PLB 685 (2010) 247 Γ 2N /Γ NMWD & Γ n /Γ p independent on A assumption W.Alberico and G.Garbarino, Phys. Rev. 369 (2002) 1. NMWD p gaussian fit free µ µ from fit 12 Λ C A low A high 19 A low : spectrum area below µ 1N + 2N + FSI A high : spectrum area above µ 1N + FSI 2N(>70 MeV) ~ 5% 2N tot assumption G.Garbarino, A.Parreno and A.Ramos, Phys.Rev.Lett. 91 (2003) Phys.Rev. C 69 (2004)

20 NMWD: Γ 2N FSI & ΛNN contribution evaluation: systematics 20

5 + Γ 2 /Γ p R(A) = a + b A = + b A 1 + Γ 2 /Γ p Assumption: Γ 2 /Γ 1 and Γ n /Γ p indipendent from A supported by exp and theory FSI linear on A up to A=16 Γ 2 = 0.43 ± 0.

21 FSI & ΛNN contribution evaluation Γ np : Γ pp : Γ nn = 0.83 : 0.12 : 0.04 Γ np /Γ p ~ Γ 2 /Γ p assumption E. Bauer and G.Garbarino, Nucl.Phys. A 828 (2009), 29. R = A low = A low + A high 0.5 N(Λp np) + N(Λnp nnp) + N p FSI-low N(Λp np) + N(Λnp nnp) + N p FSI-low + N p FSI-high Γ 2 /Γ p R(A) = a + b A = + b A 1 + Γ 2 /Γ p Assumption: Γ 2 /Γ 1 and Γ n /Γ p indipendent from A supported by exp and theory FSI linear on A up to A=16 Γ 2 = 0.43 ± 0.25 Γ p 21 Bauer et al., NPA 828 (2009) 29 Bhang et al., EPJ A33 (2007) 259: ~ ΛC M. Kim et al., PRL 103 (2009) : 0.29 ± ΛC J.D.Parker et al., PRC 76 (2007), : 0.24 (95% CL) 4 Λ He Γ 2 = Γ NM Γ 2 /Γ p = 0.24 ± 0.10 Γ n /Γ p Γ 2 /Γ p Bhang et al., EPJ A33 (2007) 259.

NMWD: Γ 2N p-n coincidences R(A) = N n (cos θ - 0.8, E p < µ-20 MeV) N p ( E p >µ p single spectra fit) = N(Λnp nnp) + N FSI 0.5 N(Λp np) + N FSI R(A) = a + b A = Γ 2 0.

22 NMWD: Γ 2N p-n coincidences R(A) = N n (cos θ - 0.8, E p < µ-20 MeV) N p ( E p >µ p single spectra fit) = N(Λnp nnp) + N FSI 0.5 N(Λp np) + N FSI R(A) = a + b A = Γ Γ p + b A Γ 2 /Γ p not dependent on A N_n/N_p systematics: all p-shell Γ 2 /Γ p 0.39±0.16 stat sys sys Γ 2 /Γ NM 0.21±0.07 stat sys sys M. Kim et al., PRL 103 (2009) : 0.29 ± Λ C FINUDA Coll. et al., PLB 685 (2010) 247: 0.24± A 22 FINUDA Coll. and G. Garbarino, PLB 701 (2011) 556 low statistics direct measurement reduced error

23 WD in heavy ion collisions First interesting results achieved by RHIC New results from ALICE experiment will be presented by R. Lea (today at parallel VIII) in the future: JPARC 23 E18: Coincidence Measurement of the Weak Decay of 12 Λ C and the three-body weak interaction process

24 24 Thanks for your attention!

25 25 Backup

26 NMWD 2N-induced contribution KEK PS E508 reanalysis 12 Λ C H. Bhang et al., PRL 96 (2006) Single spectra quenching of high energy N due to Γ 2N Coincidence spectra Γ 2N /Γ NM ~ 0.4 strong contribution of 2N induced NMWD 26

FINUDA @ DAFNE e + + e - φ (1020) K + + K - (127 MeV/c) K - stop + A Z A Λ Z + π-

TOFONE) Clean K - vertex identification (ISIM P.ID.

(OSIM&LMDs de/dx, TOF) High momentum resolution (6 FWHM for π- @270 MeV/c for

@110 MeV/c for decay study) (2% FWHM for p @400 MeV/c for decay study) (tracker

27 DAFNE e + + e - φ (1020) K + + K - (127 MeV/c) K - stop + A Z A Λ Z + π- Detector capabilities: Selective trigger based on fast scintillation detectors (TOFINO, TOFONE) Clean K - vertex identification (ISIM P.ID.+ x,y,z resolution + K + tagging) π, K, p, d, P.I.D. (OSIM&LMDs de/dx, TOF) High momentum resolution (6 FWHM for MeV/c for spectroscopy) Solenoid: B=1T (1% FWHM for MeV/c for decay study) (6% FWHM for MeV/c for decay study) (2% FWHM for MeV/c for decay study) (tracker resolution + He bag + thin targets) Solid angle ~ 2π srad data taking: 190 pb -1 (2x 6 Li, 7 Li, 3x 12 C, 27 Al, 51 V) 2006 data taking: 966 pb -1 (2x 6 Li, 2x 7 Li, 2x 9 Be, 13 C, D 2 O)

Λ Z A (Z+1) + π - K - stop + A Z A Λ Z + π- A Λ Z A-2 (Z-1) + p + n

28 charged Mesonic channel MWD & NMWD studies in FINUDA Coincidence measurement charged Non-Mesonic channel K - stop + A Z A Λ Z + π- A Λ Z A (Z+1) + π - K - stop + A Z A Λ Z + π- A Λ Z A-2 (Z-1) + p + n S-EX MeV/c MWD MeV/c NMWD MeV/c π - p π - π - 28

29 NMWD data References Exp. Measurement Szymanski PRC 43 (1991) 849 Noumi PRC 52 (1995) 2936 Hashimoto PLR 88 (2002) H.J.Kim PRC 68 (2003) Okada PLB 597 (2004) 249 Sato PRC 71 (2005) Kang PRL 96 (2006) M.J.Kim PLB 641 (2006) 28 Bhang EPJ A33 (2007) 259 Parker PRC 76 (2007) BNL AGS, LESB I (K -,! - ) 800 MeV/c KEK PS E160 (! +, K + ) 1.05 GeV/c KEK PS E307 (! +, K + ) 1.05 GeV/c KEK PS E369 (! +, K + ) 1.05 GeV/c KEK PS E462-E508 (! +, K + ) 1.05 GeV/c KEK PS SKS E307 (! +, K + ) 1.05 GeV/c KEK PS E462 (! +, K + ) 1.05 GeV/c KEK PS E508 (! +, K + ) 1.05 GeV/c KEK PS E462-E508 (! +, K + ) 1.05 GeV/c BNL AGS, LESB II (K -,! - ) 750 MeV/c p spectrum, " p, " n, " nm, " n /" p for 5 #He, " nm, " n /" p for 12 #C p spectrum for 12 #C, " p / "#, " nm / "#, " n /" p for 11 #B and 12 #C p spectrum and " n /" p for 12 #C and 28 #Si (theory) n spectrum for 12 #C and 89 #Y and " n /" p for 12 #C (theory) p, n spectra and " n /" p for 5 #He and 12 #C (exp) p spectrum and " nm / "# for 11 #B, 12 #C, 27 #Al, 28 #Si, #Fe (theory) p & n spectra, " n /" p for 5 #He p & n spectra, " n /" p for 12 #C re-analysis of p & n spectra for 5 #He and 12 #C, " n /" p for 12 #C " n, " p, " n /" p for 4 #He Agnello NPA 804 (2008) 151 LNF (K - stop,! - ) p spectrum for 5 #He, 7 #Li and 12 #C 29 M.Kim PRL 103 (2009) KEK PS E508 re-analysis of p & n spectra, " n, " p, " 2N for 12 #C Agnello PLB 685 (2010) 247 LNF (K - stop,! - ) p spectrum for 5 #He, 7 #Li, 9 #Be, 11 #B 12 #C, 13 #C, 15 #N and 16 #O, " 2 /" p Agnello PLB 701 (2011) 556 LNF (K - stop,! - ) np coinc. for 5 #He, 7 #Li, 9 #Be, 11 #B 12 #C, " 2 /" p 13#C, 15 #N and 16 #O

30 NMWD: p LNF LNF FINUDA NMWD p spectra 5 Λ He, 7 Λ Li, 12 Λ C M.Agnello et al., NPA 804 (2008) 151 Thin targets: 6 Li: 4 mm ~ 0.2 g/cm 2 7 Li: 4 mm ~ 0.2 g/cm 2 12 C: 1.7 mm ~ 0.4 g/cm 2 Coincidence of a proton with a π - (ground state) background evaluation and subtraction acceptance correction background reaction: K - np Σ - p Σ - n π - coincidence

counts / (2 MeV) J π assignment: 7 ΛLi (new) 300 250 200 150 100 Agnello PLB 681 (2009) 139 3-body decays 7 Be: 3/2 - gs & 1/2- (429keV) magnetic analysis!

31 counts / (2 MeV) J π assignment: 7 ΛLi (new) Agnello PLB 681 (2009) body decays 7 Be: 3/2 - gs & 1/2- (429keV) magnetic analysis!! Correspondence with the calculated strenght functions T. Motoba et al, Progr. Theor. Phys. Suppl. 117 (1994) 477. A. Gal, Nucl. Phys. A 828 (2009) 72. Formation of different excited states of the daughter nucleus kinetic energy (MeV) Initial hypernucleus spin J π ( 7 ΛLi g.s. ) = 1/2 + (Sasao, PLB 579 (2004) 258) / "! " # Gal NPA 828 (2009) /2 + 3/2 T. Motoba (Private Communication)) kinetic energy (MeV)

Hypernuclei: latest results from LNF and future programs at J-PARC

Hypernuclei: latest results from LNF and future programs at J-PARC n p p n p p n Λ p n n p p Λ n n Λ p Alessandro Feliciello I.N.F.N. - Sezione di Torino Outline 3 The FINUDA experiment at DAФNE hypernuclear