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Prospects on Hypernuclear Physics

Prospects on Hypernuclear Physics. Hypernuclear physics: state of the art DA Φ NE: an efficient hypernuclear factory FINUDA physics program Future prospects Conclusions. Paola Gianotti LNF. d. d. p. u. u. p. w,h. u. u. p(r). u. d. S. L N. a. u. s. W. a. L. n. d. L. d.

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Prospects on Hypernuclear Physics

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  1. Prospects on Hypernuclear Physics • Hypernuclear physics: state of the art • DAΦNE: an efficient hypernuclear factory • FINUDA physics program • Future prospects • Conclusions Paola Gianotti LNF

  2. d d p u u p w,h u u p(r) u d S LN a u s W a L n d L d +  p(r) L d d LN NL 6Li K p S p LN NLN Hypernuclear Physics: state of the art • Hypernuclear physics is a good tool to match nuclear and particle • physics. The study of this field may help in understanding some • crucial questions: • four baryon weak • interaction vertex; • YN and YY strong interactions; • change of hyperon and meson properties in the nuclear medium; • existence of di-baryon particles; • the role played by the quark degrees of freedom, • flavor symmetryand chiral models in nuclear and hypernuclear field.

  3. The 1st round 1953 Discovery of Λ hypernuclei Emulsion detectors --- CERN PS, BNL AGS K- beam Λ potential depth about 1/2 The 2nd round First Counter Experiments CERN & BNL 1973 Stopped (K-,π-) at CERN 1974 in-flight (K-,π-) at CERN PS and BNL AGS very small spin-orbit splitting • The 3rd round • New reactions with New Detectors • 1985 (π+,K+) started at AGS • 1990 S=-2 searches at AGS and KEK (Emulsion-counter hybrid technique) • 1993 S=-1 Λ Spectroscopy, Weak decay, SKS spectrometer • 1998g ray spectroscopy (Hyperball) • ΛN potential definition • Γn/ Γp puzzle in the non-mesonic decays 50 years of Hypernuclear Physics

  4. θL= 0o Hyperon recoil momentum [MeV/c] Projectile momentum pLab [GeV/c] Production of Λ-Hypernuclei Different production mechanisms can be used to form an hypernuclei: strangeness exchangereaction(in flight, stopped) σ≈ 100 mb ; Ibeam = 104 s-1 associated production σ ≈ 1 mb ; Ibeam = 107 s-1 real and virtual photo- production σ ≈ μb ; Ibeam = 1010 s-1

  5. Production of Λ-Hypernuclei (K+,π+),and(K-stop,π-) are similar, both give to the hyperon a large momentum transferred, but not identical. Many excited hypernuclear states DWIA calculations a 12C(K-,π-) pK=800 MeV/c Saclay-Lyon amplitude 12C(g,K+)12ΛB Eg=1.1GeV θ=10o b 12C(π+,K+) pπ=1040 MeV/c θ=0o c 12C(K-stop,π-) T.S.H. Lee et al., Phys. Rev. C 58 (1998) 1551. Electroproduction mainly populates streched and unnatural parity nuclear states. K.Itonaga et al., Prog. Theor. Phys 84 (1990) 291.

  6. Production of Λ-Hypernucleiexp. results 12C(g,K+)12ΛB pΛ sΛ pΛ 12C(K-,π-) sΛ HNSS(E89-009) high resolution (900MeV FWHM) spectrometer FINUDA experiment high resolution (1.4 MeV FWHM) spectometer

  7. Hypernuclear Spectroscopy • GOAL: understanding Baryon-Baryon interactions • NN interaction: experimentally well known from elastic • scattering data • phenomenologically well reproduced by • meson-exchange and quark-cluster models • YN, YY interaction: poor scattering data low yield, • short lifetime (ct < 10 cm) information from hypernuclei are important mostly Λ-hypernuclei  ΛN interaction In Λ-hypernuclei: No Pauli effect, weak coupling  simple structure  extraction of ΛN interaction is rather straightforward

  8. Hypernuclear Spectroscopy Textbook example of Single-particle orbits in nucleus Hotchi et al., PRC 64 (2001) 044302 The peak positions iswell described by a Wood-Saxon potential Phenomenological NN, YN potential, mainly based on OBE mechanism, improves (Nijmegen ESC02, 03) thanks to hypernuclear physics

  9. DSLSNT Recent improvements (1998~2003) g spectroscopy • 7LLi, 9LBe, 10LB, 11LB, 15LN, 16LO KEK E419, E509, E518; BNL E930 • 13LCBNL E929NaI array Hyperball p shell: 4 radial integrals for pN,sΛ w.f.

  10. Towards hyper-fine splitting understanding N- LS interaction SN~ -0.4 MeV KEK E419 (π+,K+) 7ΛLi spin-spin interaction D = 0.50 MeV HYPERBALL SL= - 0.01 MeV BNL E930 (K-, π-) 9ΛBe BNL E929 (K-,π-) 13ΛC SL = 152 ± 54(stat) ± 36(syst) keV NaI The experimental measurements on SΛ are in agreement but smaller than the values given by the meson exchange models BNL E930 (K-, π-) 13ΛC T ~ 30 keV (prelim.)First info. on T OBEP predictions agree with the experimentalvalue ND NF NSC89 NSC97f T (keV) 18 33 36 54

  11. ΛΛinteraction • Unique channel in SU(3) BB interaction classification • Repulsive core may vanish in this channel • possibile existense of H-dibaryon (uuddss, J=I=0) • Original prediction by Jaffe (PRL38 (1977) 195) • - H is predicted80 MeV below ΛΛmass • No experimental evidence so far • - at least, deeply bound H is rejected • ΛΛ - Ξ N (- ΣΣ) coupling important (ΔE = 28 MeV) • ΛΛ interaction study performed by • - ΛΛ hypernuclei • - ΛΛ final state interaction in (K-,K+) reaction • (J. K. Ahn et al., PLB444 (1998) 267 ) • Present data suggests ΛΛ interaction is weakly attractive

  12. Hybrid emulsion experiment (KEK-PS E373) K+ K- - • Track #1 is the • Binding energy of • is obtained to be • BLL = 7.3±0.3 MeV • (from a+2L) • In order to extract LL • interaction, we take • DBLL = BLL - 2BL( ) • = 1.0±0.3 MeV •  weakly attractive 6 He LL 6 He LL 5 He L • Hybrid emulsion -- (K-,K+) reaction to produce Ξ- • then stop it in emulsion • The best event found (H. Takahashi et al., PRL87(2001)212502)

  13. Chain of π- decays (BNL E906) D6 line CDS detector: (K-,K+) Ξ-, Ξ- + 9Be -> ΛΛZ+ X First production of ΛΛhypernuclei by a counter experiment • 4 ΛΛH →4 ΛHe* + π-(104) • →3 ΛH + p • →3He + π-(114.3) 3LH 4LH 3LH 4LLH PRL 87(2001) 132504

  14. Neutron rich Λ-Hypernuclei A new branch of nuclear physics is studyng light nuclei with extended spatial distribution giving rise to a neutron halo. Superheavy elements number of protons • Proton-rich nuclei solar burning Neutron-rich nuclei number of neutrons Better candidates to study matter with extreme N/Z ratio are neutron rich Λ-hypernuclei 7ΛH, 6ΛH, 12ΛBe,... Here more extended mass distribution are expected thanks to the “gluing role” of the Λ Interesting also for astrophysics studies on high density nuclear matter in neutron stars

  15. Neutron rich Λ-HypernucleiTretyakova et al., Nucl. Phys, A691 (2001) 351c, Akaishi et al., Frascati Phys. S. XVI, (1999) 59 Two different production mechanisms have been invoked: • Double charge exchange K-p → Λπ0 ; π0 p → n π+ π-p → π0 n ; π0 p → K+Λ • Strangeness exchange with Λ-Σ coupling K-p → Σ-π+; (Σ-nΛ p) π-p → Σ-K+; (Σ-nΛ p) FINUDA KEK E521 10B

  16. Weak decay of hypernuclei • In free space... • Λ p + π- (63.9%, Q = 38 MeV) • n + π0 (35.8%, Q = 41 MeV) • ΔI=1/2 rule holds • - initial state: I=0, final state: I=1/2 or 3/2 • if If = 1/2, branch is 2:1 • 3/2, 1:2 • -this is a general rule in strangeness decay, • but no one knows why • This decay (called mesonic decay) is suppressed in hypernuclei • due to Pauli blocking for the final state nucleon. • Therefore, non-mesonic decay occurs in hypernuclei • p + Λ p + n, • n + Λ  n + n, .... • - Is the ΔI=1/2 still valid? • We need to measure Γn and Γp

  17. OPE 0.05  0.2 OME (with heavy meson ) Quark models … observables: Γn / Γp 1.5 0.5 1 0 Exp. Value 0.5  2 Weak decay of hypernuclei mesonic decay non- mesonic decay Do we need quarks to describe non-mesonic decay or the OBE description is good?

  18. Experimental measurements (past) Past experiments only measured Γtot asymmetry of the weak decay of polarized Hypernuclei Λlifetime is almost constant for A > 10 non-mesonic decay dominate  short range nature of non-mesonic decay

  19. Experimental measurements (present) Modern experiments can measure Γp andΓn at the same time: KEK SKS FINUDA En+Ep First results are coming from KEK En+En 5LHe (E462) :Γn/ Γp0.45±0.11±0.03 systematic error : neutron efficiency(6%) + acceptance (3%) To be compared with the old data: 0.93±0.55 (Szymanski et al. PRC 43 (1991)849) Is the puzzle ofΓn/ Γp solved? Stay tuned....

  20. FINUDAFIsica NUcleareaDAΦNE The Φprovide a unique “K- beam” : • monochromatic low momentum (127 MeV/c) • triggertaggingK-stop event through the associate K+ • no hadronicbackground that can be stopped in thin targets to produce hypernuclei K-stop +AZ AΛZ+π-

  21. FINUDA scientific program • comparison with the 6Li; available data of poor quality 7Li • source of Λ4Heand Λ5He( Λ6Li unstable) to study of the decay of light hypernuclei 6Li

  22. reference target for spectroscopy and weak decay studies • expected over 105 events in the excitation spectrum • search for weakly excited states, ≤ 10-5/Kstop • (present limit 10-4/Kstop) • weak decays: Γp (Λp → n p) • Γn (Λn → n n) • Γpn (Λ n p → n n p) New • Γnn (Λ n n → n n n) New • Γπ- (Λ→ p π-) 12C 27Al • never studied before • measurement of the capture rate in medium A hypernuclei • no measurements available with K- at rest, useful for weak • decay studies • important to assess the capture rate for medium and heavy • A hypernuclei 51V

  23. DAΦNE Complex KLOE FINUDA Accelerator Complex

  24. FINUDA Detector TOFONE detector Magnet end-cap Magnet yoke B=1.0 T Mechanical support (clessidra) Straw tubes, LMDC, Vertex/target

  25. FINUDA Interaction Region Targets 3 12C 1 51V 1 27Al 2 6Li 1 7Li 44.10 210.00 44.10 Carbon target profile 26.0 1.700.03 4.700.03 200.00 27.10 27.10 244.00 4.70 2.60 3.70 1.00 Lithium target profiles 27.10 244.00 27.10 4.70 2.60 4.10 0.60 44.10 210.00 44.10 Vanadium target profile 2.60 0.625 3.3250.03 200.00 44.10 210.00 44.10 Aluminum target profile 1.00 2.60 3.70.03 200.00 2mm Sci. Be 500μm

  26. FINUDA first run : October 2003 – March 2004 FINUDA FINUDA Daily integrated luminosity [nbarn-1] nb-1 From 14-Oct- 2003 to 22-Mar-2004 DAΦNE delivered 250 pb-1to IP2 33 pb-1 machine tuning 10 pb-1 FINUDA debugging 190 pb-1 useful data taking Integrated luminosity [nbarn-1] Integrated luminosity delivered to FINUDA Integrated luminosity delivered to FINUDA pb-1 DAΦNE peak luminosiy (cm-2s-1) 30∙106 events recorded

  27. FINUDA Detector performances • S.C. Solenoid: B = 1.0 Tfield homogeneity within 2% • Interaction/Target region: selection of K+- K-pairs , • production and detection of hypernuclei. • External tracking device: trajectories and momenta • of charged particles with high precision Δp/p = 0.3%. • External scintillator barrel:trigger purposes and • neutron detection (10% eff. , 8 MeV en. Resol.) • Helium gas chamber:reduction of particle multiple • scattering. sz =30 mm;en. res. 20% FWHM VDET z resolution LMDC:s(r,f)  150 mm; sz 1% wire length ST:s(r,f)  150 mm; sz = 500 mm Outer TOF time resolution FINUDA momentum resolution Dp/p is: 0.3% in He  1.5% in air Pid in VDET

  28. 6Li 6Li ISIM 2 7Li 12C ISIM 1 Φ ISIM 8 12C 12C ISIM 7 e+ 51V Φ 27Al e- Distribution of stopped K- • Reconstructed K- stopping points • external layer: 8 targets • inner layer: microstrip ISIM modules K-stopping in ISIM are about 10% of the total due to a boost (≈ 13 MeV) of the Φ in the x direction 12.5 mrad

  29. Experimental results π- spectra coming form different target materials π-spectrum contributions Clean hypernuclear structures can be seen in any target material Λ- hyp

  30. -1.8<BΛ<11.MeV Looking for protons from the Non-Mesonic Λdecay all positive from K- vertex 12C target Particles coming from background processes can be easily rejected requiring: dE/dx in the proton region; pπ- >240 MeV/c

  31. FINUDA future prospects The Segmented Clover Detector Ge crystals BGO Compton suppression shield active collimator (scintillator) Geometrical acceptance reduced to 72% @ L = 1033 cm-2 s-1 FINUDA can observe ~ 1.6 · 103 ev/h from YN g.s. • machine duty cycle: 75% • spectrometer acceptance: 72% • Ge acceptance: ~ 30% • εGe: ~ 30% ~ 1.87 · 103ev/d

  32. Conclusions • Hypernuclear Physics has reached the status of a mature science • It helps in understanding BB weak and strong force allowing a detailed study into a SU(3) flavor symmetry environment • Some open problems still remain: • precise measurements of the spin-observables; • double Lambda hyp. binding force B; • Existence of neutron rich hypernuclei; • Survey on different targets of Γn /Γp.

  33. Future activities • Jlab Hall A (HRS), Hall C (HKS) • DAΦNE FINUDA →DAΦNE2 with gspect. • KEK-PS, BNL-AGS (E930,E963,E964) SKS, Hyperball2,.. • J-PARC ・ Ξ hyp. Spectroscoy using K-K+ reaction ・ ΛΛ hyp. Study using π- seq. decay • GSI PANDA ΛΛ hyp. Ge spectroscopy

  34. Bhabha events e+ e- e+ e- e+ e- e+ e- e- Ks  + - e+ r0  + - e+ e- invariant mass (GeV/c)

  35. Ks  + -events - + - Ks +

  36. Hypernuclear typical event - + - K- F K+ +

  37. Momentum resolution K+ μ+νμ, π+πo From the width of the μ+ the spectrometer momentum resolution is evaluated. K+ +  (236 MeV/c) Δp/p 0.9% After mechanical alignment Δp/p 0.4% K+ + o (205 MeV/c)

  38. Background contributions TOT K- p+ - K- p-+ -  n - K- n0 - K- n- p - K- (NN)- N -  n -

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