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Simonetta Marcello Torino University Seminar @ JAEA Tokai- mura , October 26, 2010

Hypernuclear Weak Decay Measurements with FINUDA Experiment. Simonetta Marcello Torino University Seminar @ JAEA Tokai- mura , October 26, 2010. OUTLINE. FINUDA Experiment Study of Hypernuclear Weak Decays Mesonic Weak Decays (MWD) Non- Mesonic Weak Decays (NMWD)

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Simonetta Marcello Torino University Seminar @ JAEA Tokai- mura , October 26, 2010

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  1. HypernuclearWeakDecayMeasurements with FINUDA Experiment Simonetta Marcello.Torino University -Seminar @ JAEA-October 2010 Simonetta Marcello Torino University Seminar @ JAEA Tokai-mura, October 26, 2010

  2. OUTLINE • FINUDA Experiment • Study of Hypernuclear Weak Decays • Mesonic Weak Decays (MWD) • Non-Mesonic Weak Decays (NMWD) • Two body Rare Non-Mesonic Weak Decays Simonetta Marcello.Torino University -Seminar @ JAEA-October 2010

  3. DAFNE e+-e- Collider e+ e- e+- e- Beams of 510 MeV at the c.m. energy ofF (1020) meson circulating in two different rings collide in two interaction regions Simonetta Marcello.Torino University -Seminar @ JAEA-October 2010 DAFNE is a high luminosity F Factory L ~ 2.2x1032 cm-2s-1 ~ 900 F/s  8 pb-1/day

  4. Φ Decays • neutral andcharged kaons • collinear (Back-to-Back) and tagged • monochromatic andlow energy Low Energy kaons can be stopped in Nuclear Targets Ekin 16 MeV SIDDHARTA K-N scattering rp 13% K+K- 49% Simonetta Marcello.Torino University -Seminar @ JAEA-October 2010 KLOE CP, CPT violation chiral dynamics … FINUDA Strangeness Nuclear Physics KSKL 34%

  5. DAFNE e+-e- Collider DAFNE PeakLuminosityhistory 2001-2007 FINUDA RUN-2 FINUDA RUN-1 Simonetta Marcello.Torino University -Seminar @ JAEA-October 2010

  6. DAFNE e+-e- Collider DAFNE PeakLuminosityhistory 2000-2009 Simonetta Marcello.Torino University -Seminar @ JAEA-October 2010 FINUDA FINUDA In the last years further improvement in the Luminosity has been achieved L ~ 3÷4x1032 cm-2s-1 peak luminosity

  7. RUN-2: October 2006 – June 2007 Daily integrated luminosity [nb-1] Integrated luminosity [nb-1] Average dailyintegrated luminosity ~7 pb-1 Stable Data Taking Integrated Luminosity ~ 1 fb-1 HYP events: ~ 5 millions Simonetta Marcello.TorinoUniversity -Seminar @ JAEA-October 2010

  8. FINUDA Spectrometer @ DAΦNE Structure of a collider experiment • Large acceptance:> 2 p sr • B=1T omogeneous magnetic field within 2% TOFONE detector Mechanical frame Vertex/target Drift Chambers, Straw tubes Magnet end-caps

  9. π- 6Li 6Li π- L p 7Li 12C K- K+ 12C 12C μ+ 51V 27Al Fixed TARGET Experiment FINUDA is a target experiment with cylindrical geometry 127 MeV/c 16 MeV 12.5 mrad e+ e-Φ K+ K- e+ K- are stopped in very thin targets Different Targets at the same time Φ e- Simonetta Marcello.Torino University -Seminar @ JAEA-October 2010 Not exactly at rest boost of 12.3 MeV/c

  10. FINUDA Physics • HYPERNUCLEAR PHYSICS • Spectroscopy • Weak Decays • HADRON PHYSICS with STRANGENESS • Bound Kaonic Clusters K-stop + AZ ALZ + p- • Very thinnuclear targets (0.1 ÷ 0.3 g/cm2) • High Resolution Spectroscopy Dp/p = 0.6% • • Detection and full reconstruction of particles • • Coincidence measurement with large acceptance SIMULTANEOUSLY ON DIFFERENT TARGETS Simonetta Marcello.Torino University -Seminar @ JAEA-October 2010 • Detection and full reconstruction of particles • Very goodL identification

  11. Hypernuclear Event K-stopAZ ALZ p- p- Forward track K+m+ nm Simonetta Marcello.Torino University -Seminar @ JAEA-October 2010 p- 6Li m+ K- F K+ Forward p-track

  12. Detector capabilities • Selective triggerbased on fast scintillation detectors • CleanK-vertexidentification • ISIM P.ID.+x,y,zresolution + K+ tagging • p, K, p, d, t … Particle Identification (dE/dx) • High momentum resolution(6‰ FWHM) • tracker resolution+He bag+thin targets • 6‰ for - @270 MeV/c for spectroscopy • 1% for p- @270 MeV/c for decay study • 6% for - @110 MeV/c for mesonic decay study • 2% for p @400 MeV/c for non-mesonic decay study • Time-Of-Flight (TOF system) • Neutron detection (external Scintillator barrel) Simonetta Marcello.TorinoUniversity -Seminar @ JAEA-October 2010

  13. FINUDA Data Takings RUN-1 2003-2004 Integrated Luminosity:190 pb-1one million of HYP events Targets: 2x6Li, 1x7Li, 3x12C, 1x27Al, 1x51V • 12Creference target for detector performance tuning • 27Al-- 51Vmedium-heavy nuclei for spectroscopic studies • 6Li-- 7Lisources of light hypernuclei RUN-2 2006-2007 Integrated Luminosity:~1 fb-1five millions of HYP events Simonetta Marcello.Torino University -Seminar @ JAEA-October 2010 Targets: 2x6Li, 2x7Li, 1x13C, 1x9Be, 1x16O Medium-light targets to allow a wider spectrum of physics: • hypernuclear spectroscopy • NRH spectroscopy • hypernuclear decay modes • bound kaonic states

  14. Hypernuclear Weak Decays: Mesonic channels Free Space p + p- B.R. 63.9 % Gp-free n+ p0B.R. 35.8 % Gp0free Q ~ 38 MeV ; pN = pp~ 100 MeV/c Hamiltonian describes transitions with Δ I of 1/2 and 3/2 with comparable strengths BUT an enhancement in Δ I = 1/2 component is observed in free Y decays and K decays Δ I = ½ Rule ExpGp-free / Gp0free= 1.78 Gp-free / Gp0free= 2 pure Δ I = 1/2 Strong interaction corrections are added But not enough to account for such an enhancement Gp-free / Gp0free= 1/2 pure Δ I = 3/2 In the Nuclear Medium L  p + p- Gp- QM < 38 MeV ; pN ~ 100 MeV/c < kF = 270 MeV/c Mesonic mode (MWD) is Pauli Blocked But still possible in finite nuclei L  n + p0 Gp0

  15. Hypernuclear Weak Decays: Non-Mesonic channels One-Nucleon induced Decays L p  n p Gp QM ~ 176 MeV ; pN ~ 415 MeV/c > kF = 270 MeV/c Nucleon pairs mainly emitted back-to-back Difficult to measure neutrons, low efficiency L n  n n Gn Two-Nucleon induced Decay L N N n N N G2N QM ~ 176 MeV pN ~ 340 MeV/c QM shared among the three Nucleons • Nucleons can escape the nucleus • Non-Mesonic mode (NMWD) is not Pauli Blocked • NMWD dominates over the Mesonic one for all hypernuclei, • but the lighter ones, where is in competition with the MWD • Final State Interaction (FSI) cannot be neglected in NMWD

  16. Hypernuclear Weak Decays GTot = GM +GNM GM = Gp-+Gp0 ; GNM = Gp+ Gn+G2N t =ℏ / GTot hypernucleus lifetime • Hypernuclear decays: only way to get information on LN NN • Extension of NN  NN weak interaction with ΔS = 0, in particular on the • parity conserving part of the Hamiltonian (masked by strong interaction) • No experimental observation of L N  NN using L beams. • Possible to study the reverse reaction pn  p L, • but not feasible  very low s ~ 10-12mb Simonetta Marcello, JSPS Fellow, Kyoto University-Intensive Lectures-July 29-31, 2009

  17. Hypernuclear Weak Decays: Non-Mesonic channels One Pion Exchange Model Not enough to explain Gn / Gp ratio Massive mesons (r, K, K*, h and w) have been included to explain interaction at short distances N N One Meson Exchange Model p, r, w, h, K , K* One-Nucleon induced Decays N N N Simonetta Marcello, JSPS Fellow, Kyoto University-Intensive Lectures-July 29-31, 2009 p, r, w, h, K , K* L N Two-Nucleon induced Decay Hybrid models adopting direct quark mechanisms in addition to meson-exchange potential have been used L N N

  18. PHYSICS MOTIVATIONS • Mesonic Weak Decays • p-nucleus optical potential, the low energy p probes the nuclear structurepossibile to discriminate among different potential models • (instead of studying p-nucleus scattering or X-rays from pionic atoms) • Enhancement of the p-mesonic decay rates due to the pion wave distortion  higher momentum available for the Nucleon • Jpassignment hypernuclei, strong dependence of the two-body p- decay Branching Ratios on the ground state spin: new indirect spectroscopic tool

  19. PHYSICS MOTIVATIONS • Non-Mesonic Weak Decays • 4-baryon strangeness changing weak interaction give the possibility to investigate both the parity violating and the parity conserving contributions to the Hamiltonian (in NN  NN the latter one is masked by the strong interaction) • DI=1/2 rule • Gn/Gppuzzle • G2N and Final State Interactions (FSI) contributions

  20. p - Study of Weak Decays with FINUDA Coincidence measurement charged Mesonic channel charged Non-Mesonic channel K-stop + AZ  ALZ + p- ALZA(Z+1) + p- K-stop + AZ  ALZ+p- ALZA-2(Z-1) + p + n S-EX 260-280 MeV/c MWD 80-110 MeV/c NMWD 170-600 MeV/c - - Simonetta Marcello.TorinoUniversity -Seminar @ JAEA-October 2010

  21. Mesonic Weak Decays

  22. Mesonic weak Decays p-shell hypernuclei • MWD strictly forbidden in infinite nuclear matter (pN~ 100 MeV/c) • p feels attraction in nuclear medium due to the p-wave part of the optical potential (p distortions) •  dispersion relation modified inside the nucleus •  pioncarries lower energy for fixed momentum q: Ep ≤ √(q2+mp2) •  Energy conservation: highermomentumavailablefor the final nucleonwhichhas more chance toovercome the Fermi momentum • theoretical calculations with pion distorted wave predict MWD to be less suppressed for p-shell (A~10) • Enhancementof MWD due topionwavedistortion: • Bando et al., Progr. Theor. Phys. Suppl. 72 (1984) 109 • Osetet al., NPA 443 (1985) 704 • Extensivecalculations: • Motobaet al., Prog. Theor. Phys. Suppl. 117 (1994) 477 • Gal Nucl. Phys. A 828 (2009) 72 Pauli Blocking is less effective in the medium ! Simonetta Marcello.TorinoUniversity -Seminar @ JAEA-October 2010

  23. StudyofMesonicDecays • Not Pauli blocked in Light p-shell Hypernuclei • Can provide information on spin-parity of the • initial hypernuclear ground state K- + AZ ALZ + p– Hypernucleus Formation high p– momentum ~ 270 MeV/c In the bound region from the ground state peak Δp/p =1% FWHM Cuts are reduced ALZ A(Z + 1) + p– Hypernucleus Decay low p– momentum ~ 100 MeV/c Simonetta Marcello.KyotoUniversity-IntensiveLectures-July 29-31, 2009 Short track reconstructed by means of 2 layers of Si-Microstrips and 1 layer of Low Mass Drift Chambers Δp/p =6% FWHM Only 3 points ALZ AZ + p0 p0 not detected in FINUDA

  24. MWD Measurements: strategy Inclusive production p-spectrum background corrected LONG TRACKS (4 points) Dp/p ~ 1% in the region 260-280 MeV/c 11LB Background under formationpeak K-(np)  S- p S-  n p- 12LC Branching Ratio BR p–= Gp– / G TOT BR p–= Np-decays/ NHYP SHORT TRACKS (in Si-Microvertex) Detection of p-down to ~ 80 MeV/c 11LB Decayp-spectrum background & acceptancecorrected p- Background under decaypeak Lqfdecay Simonetta Marcello.TorinoUniversity -Seminar @ JAEA-October 2010

  25. StudyofMesonicDecays 7Li Target K- + 7Li  5LHe + d + p– K- + 7Li  5LHe + p + n + p– K- + 7Li 7LLi + p– (276 MeV/c) Mesonic Decay Mesonic Decay 7LLi 7Be + p– (107.7 MeV/c) 5LHe5Li + p– (99.3 MeV/c) Simonetta Marcello.KyotoUniversity-IntensiveLectures-July 29-31, 2009 MesonicWeakDecayofHypernucleiisimportantbecauseittakesplacedeeply inside the nucleus (since the Lis in s-shells1/2 ) and involves a low energyp, so it can sensitivelyprobe the structureofnuclearinterior

  26. Jp assignment: 7LLi Agnello PLB 681 (2009) 139 7Be: 3/2-gs & 1/2- (429keV) • Correspondencewith the calculatedstrengthfunctions • T. Motobaet al, Progr. Theor. Phys. Suppl. 117 (1994) 477 • A. Gal, Nucl. Phys. A 828 (2009) 72 • Formationofdifferentexcitedstatesof the daughternucleus • Initialhypernucleusspin • Jπ(7LLig.s.) = 1/2+ Sasao, PLB 579 (2004) 258 3-body decays BR p–= 0.315 ± 0.041 T. Motoba (Private Communication)) Gal NPA 828 (2009) 72

  27. Jp assignment: 9LBe 9B: 3/2-gs & 1/2-(2.75 MeV) DT ~ 4 MeV FWHM @38 MeV • Correspondencewith the calculatedstrengthfunctions • T. Motobaet al, Progr. Theor. Phys. Suppl. 117 (1994) 477 • A. Gal, Nucl. Phys. A 828 (2009) 72 • Initialhypernucleusspin • Jπ(9LBeg.s.) = 1/2+ • O.Hashimoto NPA 639 (1998) 93c Agnello PLB 681 (2009) 139 BR p–= 0.154 ± 0.040 T. Motoba (Private Communication))

  28. Jp assignment: 11LB Agnello PLB 681 (2009) 139 • Correspondence with the calculated strength functions • H. Bando et al, Pers. Meson Science (1992) 571 • A. Gal, Nucl. Phys A 828 (2009) 72 • Two contributions of 11C 5/2- ground state • and 7/2- excited state • Initial hypernucleus spin • Jπ(11ΛBg.s.) = 5/2+: experimental confirmation • Sato et al., PRC 71 (2005) 025203 by different observable 11C: 3/2-gs & 7/2- (~6.5 MeV) BR p–= 0.199 ± 0.039 T. Motoba (Private Communication)

  29. Jp assignment: 15LN Agnello PLB 681 (2009) 139 • Correspondence with the calculated strength functions • T. Motoba et al, Nucl. Phys. A 489 (1988) 683 • A. Gal, Nucl. Phys. A 828 (2009) 72 • 15ΛNg.s spin not known. Jπ(15ΛNg.s.) = 3/2+ • D.J.Millener, A.Gal, C.B.Dover Phys. Rev. C 31 (1985) 499 • Spin ordering not obtained from g-rays of 16LO • M.Ukai et al. Phys. Rev.C 77 (2008) 054315. • First experimental determination of • Jπ(15ΛNg.s.) = 3/2+ from decay rate value and spectrum shape 15O: 1/2-gs & sd(~6 MeV) BR p–= 0.085 ± 0.028 T. Motoba NPA 489 (1988) 683.

  30. Mesonic decay ratio: Gp- / GL Gp- / GL= Gtot / GL BRp- Gtot/GL= (0.990±0.094) + (0.018±0.010) A BRp- = Np-decays/ NHYP present data T. Motoba PTPS 117 (1994) 477 previous data fit from measured values for A=4-12 hypernuclei [Sasao et al., PLB579(2004)258] A.Gal NPA 828 (2009) 72 p distortion, MWD enhancement proved ! strong nuclear structure effect A

  31. Non Mesonic Weak Decays

  32. Hypernuclear Weak Decays: Gn / Gp Ratio What about ΔI = ½ rule for L decay in the medium ? L n  n n L p  n p L N N n NN Gn/ Gp= 1/2 for pure ΔI = 1/2 Gn/ Gp= 2 for pure ΔI = 3/2 Most studied systems: 5LHe and12LC For a long time large experimental values have been measured (1 ÷ 2) indicating a possible violation of ΔI = ½ rule in hypernuclear decays and small theoretical values have been predicted (OPE model 0.1 ÷ 0.2) The analysis of Gn / Gp ratio is influenced by the two-nucleon induced process, whose experimental identification is rather difficult

  33. Hypernuclear Weak Decays: Gn /Gp Ratio New experimental measurements and progress in theoretical models contributed to solve the Gn / Gp ”Puzzle” 5LHe 12LC First measurement of nucleon-coincidence spectra and angular correlation (BtoB) Gn / Gp≈ 0.4 - 0.5 Outa et al., NPA754 (2005) 157c, Kang et al., PRL96(2006)062301 L n  n n L p  n p L N N n N N Significant contribution of two-Nucleon induced decay and FSI (non-BtoB kinematics)quenching of N yields ~ 40% Bhang et al., EPJ A33 (2007) 259 Theoretical improvements: havier mesons, interaction terms which violate ΔI=1/2 rule, quark degree of freedoms for the short range baryon-baryon interactionGn / Gp≈ 0.3-0.7 Sasaki et al., NPA669 (2000) 331 Parreno and Ramos, PRC65(2002)015204

  34. π- and proton spectra from 12ΛC NMWD 12C Spectrum of negative pions for events with a proton detected in coincidence red peak at 272 MeV/c (12ΛC ground state) π- spectrum in coincidence with p Simulation of the background reaction K- n p Σ- p followed by the decayΣ-  nπ- Fermi momentum distribution for nucleons selection criteria and quality cuts as for real data RUN-1 Acceptance corrected Not acceptance corrected Not acceptance corrected 339 events 339 events proton spectra in coincidence with π- peak Simulated background

  35. π- and proton spectra from 12ΛC NMWD 12C proton spectrum in coincidence with π- peak π- spectrum in coincidence with p simulation + reconstruction + selection + normalization RUN-1 background subtracted proton spectrum in coincidence with π- peak normalization region coincidence K- npS-p S-n π- Short tracks protonThreshold = 15 MeV M. Agnello et al., NPA 804 (2008), 151 15 MeV

  36. 269 MeV/c 275 MeV/c π- and proton spectra from 7ΛLi NMWD π- spectrum in coincidence with p • K- stopped in 7Li target can produce: 7ΛLi, (6ΛHe+p), (5ΛHe+d), (4ΛHe+t), (3ΛHe+α) • 275 MeV/c peak is consistent with 7ΛLi g.s. • 269 MeV/c peak is consistent with 5ΛHe+d pmax = 272,67 MeV/c ΔBΛ = 3.98 MeV 7Li RUN-2 Simulation of the background K- np → Σ-p followed by Σ- → nπ- proton spectrum in coincidence with π- peak (275MeV/c) background subtracted proton spectrum in coincidence with π- peak (275MeV/c) Simulated background Acceptance Corrected

  37. 269 MeV/c 275 MeV/c 7Li - π- and proton spectra from 5ΛHe NMWD K-stop + 7Li  5ΛHe + d + π- π- spectrum in coincidence with p 7Li • Enhancement of the low energy region FSI and 2 Nucleons induced effects • Bulk of the signal at 80 MeV • (~ Q/2 value of the reaction) RUN-2 Simulation of the background K- np → Σ-p followed by Σ- → nπ- proton spectrum in coincidence with π- peak (269MeV/c) background subtracted proton spectrum in coincidence with π- peak (269MeV/c) Simulated background Acceptance Corrected

  38. 6Li - π- and proton spectra from 5ΛHe NMWD K-stop + 6Li  5ΛHe + p + π- π- spectrum in coincidence with p 6Li Simulation of the background for the 2 Nucleons absorption take into account the cluster substructure of 6Li as (a + d) molecule 275 MeV/c RUN-2 Momentum distribution of the deuteron inside 6Li T. Yamazaki and Y. Akaishi NP A792 (2007 )229 background subtracted proton spectrum in coincidence with π- peak proton spectrum in coincidence with π- peak Simulated background Acceptance Corrected

  39. 5ΛHe, 7ΛLi and 12ΛCproton spectra 5LHe 7LLi • Similar shape for 5LHe, 7LLi and 12LC • Peak at ~ 80 MeV (Q/2 value), broadened by • N Fermi motion, visible even for 12LC • no strong FSI effect in low energy region • FSI & 2N contribution in the low energy region? 12LC

  40. Comparison with KEK experimental data FINUDA: NPA 804 (2008)151 KEK E462/E508: PLB 597 (2004)249 5ΛHe:FINUDA vs KEK 12ΛC:FINUDA vs KEK normalization beyond 35 MeV (KEK data threshold) Agreement for 5LHe, not for 12LC • KEK: thick targets  strong correction • FINUDA: thin targets & transparent detectors • KEK: p energy from TOF and range + dE/dx •  poorenergyresolutionabove 100 MeV, distortion • FINUDA: p momentum from magnetic analysis • 2% energy resolution FWHM @ 80 MeV, no distortion

  41. 12ΛC Theoretical curve Garbarino,(P.R.C 69 054603 [2004]) FINUDA proton spectra KEK 5ΛHe Theoretical curve (Garbarino,Phys. Rev. C 69 054603 [2004]) FINUDA proton spectra KEK Comparison with theoretical calculations normalization beyond 15 MeV (FINUDA data threshold) • New data important to constrain theories in low energy region • 12ΛC: FSI and two-nucleons induced NMWD appear to be too strong to reproduce the data (low energy peak + excess smearing) Comparison with theoretical models not satisfactory for 12LC Lnp  nnp strongly quenches the nucleon yields H. Bhang et al., EPJ A33 (2007) 259

  42. NMWD proton spectra p-shell hypernuclei Background subtracted & acceptance corrected M.Agnello et al., PLB 685 (2010) 247 5ΛHe 7ΛLi 9ΛBe 11ΛB Simonetta Marcello.Torino University -Seminar @ JAEA-October 2010 12ΛC 13ΛC 15ΛN 16ΛO

  43. NMWD: G2N L N N  n N N NMWD p FINUDA, PLB 685 (2010) 247 gaussian fit free m 12LC mfrom fit Alow Ahigh Alow: spectrum area belowm 1N + 2N + FSI assumption W.Alberico and G.Garbarino, Phys. Rev. 369 (2002) 1 Ahigh: spectrum area abovem 1N + FSI 2N(>70 MeV) ~ 5% 2Ntot G,Garbarino, A.Parreno and A.Ramos, Phys.Rev.Lett. 91 (2003) 112501. Phys.Rev. C 69 (2004) 054603 assumption G2N/GNMWD & Gn/Gp not depend on A

  44. NMWD: G2N FSI & LNN contribution evaluation: systematics 5ΛHe 7ΛLi 9ΛBe 11ΛB 12ΛC 13ΛC 15ΛN 16ΛO

  45. NMWD: G2N FSI & LNN contribution evaluation Alow = 0.5 N(Lpnp) + N(Lnpnnp) + NpFSI-low Ahigh = 0.5 N(Lpnp) + NpFSI-high 12LC Alow assumption mfrom fit Alow N(Lnpnnp) Gnp G2N 0.5 = ≈ Ahigh Alow + Ahigh Gp Gnp : Gpp:Gnn= 0.83 : 0.12 : 0.04 E. Bauer and G.Garbarino, Nucl.Phys. A 828 (2009), 29. N(Lpnp) Gp N(Lnp nnp) + NpFSI-low N(Lpnp) + R = = N(Lnpnnp) + NpFSI-low + NpFSI-high N(Lpnp) +

  46. Rare Two-Body • Non Mesonic Decays

  47. Two body non mesonic decays of light hypernuclei • Non-mesonicdecaysof light hypernuclei (A<12) are not the favoureddecaychannels • Mesonicdecays play a largerrole • Two-body non mesonicdecay: largemomentum transfer (QVal~170 MeV) • Unlikelytooccur→ rare events • Expected branching ratios: at the levelof1.5% ofallnon-mesonicdecays • calculationsfor4ΛHe3He n, p t, d d [Rayet Nuovo Cim. 42B (1968), 238] • Veryfew and sparse observations • Mainlyfrombubblechamber/emulsionexperiments, for4ΛHe • Extremelypoorstatistics, a fewevents • No 4ΛHe→pt • A few4ΛHe→ 3He n : 8-14%ofallidentified NM decaysof4ΛHe • Corenmanset al. (1968), unpublished • Block PRL 3(1959), 291 • One4ΛHe→ddevent • Block et al. (1960) • One5ΛHe→dtevent • Keyeset al. Nuovo Cimento (1976)

  48. p d t d mips t p dE/dx p.id. TOF p.id. Light hypernuclei decays in FINUDA • large angular coverage (~4π) • Excellent particle identification for charged hadrons • Good momentum resolution • Capability to fully reconstruct the event topologies • Set of several targets allowing the production of different hypernuclei and hypernuclear fragments • 4ΛHe hyperfragments production, from all targets • 4ΛHe → d d • d momentum: 570 MeV/c • 4ΛHe → p t • p momentum: 508 MeV/c • 5ΛHe hypernucleus formation • From 6Li targets: K- 6Li → 5ΛHe + p + π-(π- momentum: 275.15 MeV/c) • From 7Li targets: K-7Li → 5ΛHe + d + π- • NM two-body decay: 5ΛHe → d t • d momentum: 597 MeV/c • 4ΛHe → n 3He • Not detectable

  49. Forward d Dp/p = 3% Backward d Dp/p = 4% 4ΛHe→dd decays Analyzed data: 954 pb-1, 2006-2007 data taking Expected event features: • 2 deuteron tracks of 570 MeV/c • Back-to-back deuteron tracks • possible 4ΛHe formation π- • for the formation of the 4ΛHe g.s. hypernucleus in 4He target: pπ=255 MeV/c π- d d

  50. 4ΛHe→pt decays • Lowerthresholdfortriton detection in FINUDA: 550 MeV/c • 508 MeV/c tritonscannotbeobserved ! • Missingtritonanalysis • oneprotonwithmomentum in the range (498-540) MeV/c • one high momentumπ- • Missing mass for the (A - 4ΛHe - p - π-) system compatiblewithone (missing) triton + residualnucleus • Large background contributionfromK-(np) → Σ-p: • capture rate 1.62%/K-stop in 6Li (NPA 775 (2006), 35) • Stringentcutstobeapplied on: • secondaryvertices • π- impact parameter (rejection 79%) • angulardistributions (backwardpeaked) • (pπ-) invariant mass torejectL fromconversionreactions

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