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Search for neutron rich -hypernuclei with the FINUDA spectrometer

Search for neutron rich -hypernuclei with the FINUDA spectrometer. Barbara Dalena ( Bari University and INFN Bari, Italy ) on behalf of the FINUDA Collaboration. Outline. The scientific case: N eutron R ich  - H ypernuclei Production of NRH in FINUDA

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Search for neutron rich -hypernuclei with the FINUDA spectrometer

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  1. Search for neutron rich -hypernuclei with the FINUDA spectrometer Barbara Dalena(Bari University and INFN Bari, Italy)on behalf of the FINUDA Collaboration

  2. Outline • The scientific case: Neutron Rich -Hypernuclei • Production of NRH in FINUDA • Upper Limits of the NRH production rate results of the first FINUDA data taking • Expected events for next FINUDA run 2006/2007 • Summary

  3. Neutron rich -hypernuclei stable nuclei neutron rich nuclei proton rich nuclei 8B 10B 11B 12B 13B 14B 15B 7Be 9Be 11Be 12Be 14Be 10Be 6Li 7Li 8Li 11Li 9Li 3He 4He 6He 8He 1H 2H 3H Hypernuclei with a large neutron excess. Z N

  4. Neutron rich -hypernuclei 8B 10B 11B 12B 13B 14B 15B 7Be 9Be 11Be 12Be 14Be 10Be 6Li 7Li 8Li 11Li 9Li 3He 4He 6He 8He 1H 2H 3H Hypernuclei with a large neutron excess. Their existence has been theoretically predicted (L. Majling, NP A 585 (1995) 211c). Z N

  5. Neutron rich -hypernuclei 9B 10B 11B 12B 13B 14B 15B observed not observed 7Be 8Be 9Be 10Be 11Be 12Be 13Be Finuda 1° run 7Li 8Li 9Li 10Li 11Li 12Li 6Li N = Z 8B 10B 11B 12B 13B 14B 15B 4He 5He 6He 7He 8He 9He 7Be 9Be 11Be 12Be 14Be 10Be 3H 4H 5H 6H 7H 6Li 7Li 8Li 11Li 9Li 3He 4He 6He 8He 1H 2H 3H Hypernuclei with a large neutron excess. Their existence has been theoretically predicted (L. Majling, NP A 585 (1995) 211c). The Pauli principle does not apply to the  inside the nucleus + extra binding energy ( “glue-like” role)  a larger number of neutrons can be bound S Z -1 N

  6. Motivations • Hypernuclear physics: N interactions at low densities, the role of 3-body forces

  7. Motivations • Hypernuclear physics: N interactions at low densities, the role of 3-body forces • Neutron drip-line: response of neutron halo on embedding of  hyperon, hypernuclear species with unstable nuclear core T. Yu. Tretyakova and D. E. Lanskoy, Nucl. Phys. A 691: 51c, 2001.

  8. Y. Akaishi et al., Phys. Rev. Lett. 84: 3539,2000 Motivations • Hypernuclear physics: N interactions at low densities, the role of 3-body forces • Neutron drip-line: response of neutron halo on embedding of  hyperon, hypernuclear species with unstable nuclear core T. Yu. Tretyakova and D. E. Lanskoy, Nucl. Phys. A 691: 51c, 2001. • Astrophysics: Feedback with the astrophysics field: phenomena related to high-density nuclear matter in neutron stars. S. Balberg and A. Gal, Nucl. Phys. A 625: 435, 1997. Y. Yamamoto, S.Nishizaki and T. Taktsuka, Nucl. Phys. A 691: 432, 2001.

  9. ; ; ; ; Calculated Production Rate of is  3 order of magnitude less than the measured one of (  10-3) . Production of Neutron Rich -hypernuclei T. Yu. Tretyakova and D.E. Lanskoy, Proc. Of Workshop “Recent progress in Strangeness nuclear physics”, H. Outa et al. eds., KEK (2003) 80.

  10. e+ KLOE KSKL (34.1%) FINUDA  K+K- (49.1%)  (15.5%) DEAR e- FINUDA(FIsica NUcleare at DANE) DANE:DoubleAnnulare+-e- -factory forNiceExperiments: Beam Energy 510 MeV L5 1031cm-2s-1- 250 ’s s-1 • The decay of the  is an intense source of: • couples of neutral and charged kaons • collinear and tagged • monochromatic and low energy (16 MeV)

  11. Mechanical support (clepsydra) • For: • 2424 Straw Tubes (longitudinal + stereo) • 16 Low-Mass Drift Chambers • 18 m-strip vertex detectors (ISIM/OSIM) • Inner scintillator barrel – 12 slabs (TOFINO) • 8 Targets Simultaneous study of formation and decay of strange hadronic systems by full event reconstruction The FINUDA detector • Detector capabilities: • Selective triggerbased on fast scintilla- • tion detectors (TOFINO, TOFONE) • CleanK-vertexidentification • (ISIM P.ID.+x,y,zresolution + K+ tagging) • p, K, p, d, … P.ID. (OSIM dE/dx) • High momentum resolution(6‰ FWHM) • (tracker resolution + He bag + thin targets) • Neutron detection (TOFONE) • Time-Of-Flight (TOFONE-TOFINO) • Apparatus designed for a typical collider experiment: • Cylindrical geometry • large solid angle (> 2 sr) • multi-tracking analysis

  12. Event selection: • Reconstruction of a + with a momentum value in the hypernucleus bound region • P.ID. made using dE/dx from OSIM • and TOF from TOFINO & TOFONE p+ K- K+ Neutron Rich production inFINUDA ELEMENTARY ; ; FINUDAdata taking 2003-2004: K-stop + 12C  12Be + + K-stop + 6Li  6H + + K-stop + 7Li  7H + + + momentum is related to the  binding energy (B)

  13. Inclusive spectra Background: • K - + p   + +  -  +  + + n (130 < p < 250 MeV/c) • K - + pp   + + n  +  + + n (100 < p < 320 MeV/c) Contaminations: • + K+ decay (peak@235MeV/c) • p / decay

  14. Background reduction Simulated event of : K - + pp   + + n  +  + + n Simulated NRH production event (FINUDA vertex view) The reconstructed distance between the origin point of + and the K– stopping point it is broader (up to 8mm) for a + coming from + decay than for the signal (peaked at less than 1mm).

  15. Final spectra and U.L. evaluation

  16. Expected events for next run [4] Kubota et al., NPA 602 (1996) 327 [5] T. Yu. Tretyakova and D.E. Lanskoy, Proc. Of Workshop “Recent progress in Strangeness nuclear physics ”, H. Outa et al. eds., KEK (2003) 80. [1] Y. Akaishi et al., PRL 84 (2000) 3539 [2] L. Majling, NPA 585 (1995) 211c [3] M. Agnello et al. PLB 640 (2006) 145

  17. Summary • The search for hypernuclei with large neutron excess is a field of interest in modern nuclear physics • FINUDA spectrometer can study NRH states • The first FINUDAdata taking established the best published U.L. 90% C.L. value for 12Be and for the first time determined the same values for 6H and 7H. • FINUDA run 2006/2007 will improve its published U.L. values of a factor 4. At the same time we will search for 9He, 13Be and 16C.

  18. Back-up slides

  19. Neutron rich -hypernuclei • 1953: Discovery of hypernuclei by M. Danysz e J. Pniewski (Philos. Mag. 44: 348, 1953) • 1985: Evidence of production of 11Li e 11Be (Neutron Rich nuclei)  Halo phenomena • 1995: “ hypernuclei may be even better candidates to exhibit large values of N/Z and halo phenomena” L.Majling (Nucl. Phys. A 585: 211c,1995) • 2005: “Production of the Neutron-Rich Hypernucleus 10Li in the ( - , K+ ) Double Charge-Exchange Reaction” P.K. Saha et al. (Phys. Rev. Lett. 94: 052502, 2005) 40 events of 10Li

  20. Acceptance In the region 220-320 MeV/c acceptance is quite flat. 12C 6Li 7Li Final spectra acceptance corrected

  21. Momentum resolution in our track selection conditions +stop  + + n p  0.9% FWHM @235 MeV/c  1 MeV/c [220-300 MeV/c]

  22. Distance Selection • The reconstructed distance between the origin point of + and the K– stopping point is peaked at less than 1 mm for a + coming from the signal (red line). • Greenline select 10% of background vs 50% of signal  Noise to signal ratio improved of a factor  5.

  23. Rate /K-stop in the ROI ROI =  2p   2MeV/c • N = number of + in the region of interest. • N = number of +. • = number of stopped kaons. • D(+) D(+). • G(+)= , MC/RC. • G(+)= , MC/RC. • BR(K2) = 0.6343.

  24. Upper Limit (U.L.) • S = signal, B = background : . • maximum fraction of NROI that may be ascribed to NRH at fixed C.L. (90%). NROI NROI

  25. Background estimation Fit range: 0.190-0.250 0.256-0.320 GeV/c 6Li 2 /ndf = 145.7/95=1.5 p0 = 0.0043410.000649 p1 = 0.75250.0137 • Different background shapes give good 2 [1.2 – 1.5] (due to big error), but different value of B and S = N-B  Need to incorporate uncertainties in order to use Feldman & Cousins method. • Any evaluation of S = N-B gives values lower than the maximum not significant signal at 90% C.L. hypothesis 1 • 2 /ndf = 107.8/92=1.2 • p0 = 0.0042070.000630 • p1 = 0.73380.0138 • p2 = 0.0803 0.0152 • = 0.001092 0.000213 Mean = 0.2355 0.0002 hypothesis 2

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