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: Neutron Rich -Hypernuclei FINUDA Production of NR H in FINUDA Upper Limits of the NR H production rate FINUDA results of the first FINUDA data taking FINUDA Expected events for next FINUDA run 2006/2007 Summary

stable nuclei neutron rich nuclei proton rich nuclei N 1H1H 2H2H 3H3H 3 He 4 He 6 He 6 Li 7 Li 8 Li 9 Li 7 Be 9 Be 10 Be 11 Li 11 Be 12 Be 8B8B 10 B 11 B 12 B 13 B 14 B 8 He 15 B 14 Be Z Neutron rich -hypernuclei Hypernuclei with a large neutron excess.

N 1H1H 2H2H 3H3H 3 He 4 He 6 He 6 Li 7 Li 8 Li 9 Li 7 Be 9 Be 10 Be 11 Li 11 Be 12 Be 8B8B 10 B 11 B 12 B 13 B 14 B 8 He 15 B 14 Be Neutron rich -hypernuclei Hypernuclei with a large neutron excess. Their existence has been theoretically predicted (L. Majling, NP A 585 (1995) 211c ). Z

observed N = Z not observed Finuda 1° run 1H1H 2H2H 3H3H 3 He 4 He 6 He 6 Li 7 Li 8 Li 9 Li 7 Be 9 Be 10 Be 11 Li 11 Be 12 Be 8B8B 10 B 11 B 12 B 13 B 14 B 8 He 15 B 14 Be N S 6 Li 3 H 4 H 5 H 6 H 7 H 4 He 5 He 6 He 7 He 8 He 9 He 7 Li 8 Li 9 Li 10 Li 7 Be 8 Be 9 Be 10 Be 11 Be 11 Li 12 Li 12 Be 13 Be 9 B 10 B 11 B 12 B 13 B 14 B 15 B Neutron rich -hypernuclei 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 Z

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

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.

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, 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, Y. Yamamoto, S.Nishizaki and T. Taktsuka, Nucl. Phys. A 691 : 432, Y. Akaishi et al., Phys. Rev. Lett. 84: 3539,2000

; ; ; ; Calculated Production Rate of is 3 order of magnitude less than the measured one of ( ). 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.

FINUDA (FI sica NU cleare at DA NE ) DA NE: Double Annular e + - e - -factory for Nice Experiments: Beam Energy 510 MeV L cm -2 s s s -1 K S K L (34.1%) (15.5%) K + K - (49.1%) e+e+ e-e- FINUDA DEAR KLOE The decay of the is an intense source of: couples of neutral and charged kaons collinear and tagged monochromatic and low energy ( 16 MeV ) The decay of the is an intense source of: couples of neutral and charged kaons collinear and tagged monochromatic and low energy ( 16 MeV )

The FINUDA detector Apparatus designed for a typical collider experiment : Cylindrical geometry large solid angle (> 2 sr) multi-tracking analysis Detector capabilities: Selective trigger based on fast scintilla- tion detectors (TOFINO, TOFONE) Clean K - vertex identification (ISIM P.ID.+ x,y,z resolution + 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) Simultaneous study of formation and decay of strange hadronic systems by full event reconstruction 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

Neutron Rich production in FINUDA K - stop + 12 C 12 Be + + K - stop + 6 Li 6 H + + K - stop + 7 Li 7 H momentum is related to the binding energy (B ) B (MeV) p (MeV/c) 12 Be H H FINUDA FINUDA data taking : Event selection: Reconstruction of a + with a momentum value in the hypernucleus bound region P.ID. made using d E /d x from OSIM and TOF from TOFINO & TOFONE ; ; ELEMENTARY

Inclusive spectra K - + p n (130 < p < 250 MeV/ c ) K - + pp + + n n (100 < p < 320 MeV/ c ) Background : Contaminations : + K + decay 235MeV/c) p / decay

Background reduction Simulated NR H production event (FINUDA vertex view) K - + pp + + n n Simulated event of : 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).

Final spectra and U.L. evaluation N R H Rate / stopped K - (90% C.L. Upper Limit) FINUDA PLB 640 (2006) pp ( ) Previous best published value 12 Be 2.0± 0.4(stat) (sys) H 2.5± 0.4(stat) – (sys) NEW 7 H 4.5 ± 0.9(stat) – (sys) NEW

Expected events for next run HYPER- NUCLEUS TARGET B (MeV) p (MeV/c) PRODUCTION RATE / k - stop EVS ROI U.L. 90% C.L. 6 H 6 Li4.1 [1]252 < [3] H 7 Li5.2 [2]245 < [3] He 9 Be8.5 [2]257 < [4] Be 13 C11.7 [2]259(?) C 16 O 7.3(2 + ) [5]264 < (0 + )[4] (2 + ) [5] (0 + ) [5] (0 + )[2] [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 [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.

Summary The search for hypernuclei with large neutron excess is a field of interest in modern nuclear physics FINUDA FINUDA spectrometer can study NR H states FINUDA The first FINUDA data 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 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.

Back-up slides

Neutron rich -hypernuclei 1953: Discovery of hypernuclei by M. Danysz e J. Pniewski (Philos. Mag. 44: 348, 1953) 1985: Evidence of production of 11 Li e 11 Be (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: , 2005) 40 events of 10 Li

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

Momentum resolution in our track selection conditions + stop + + n p 0.9% MeV/c 1 MeV/c [ MeV/c]

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 ). Green line select 10% of background vs 50% of signal Noise to signal ratio improved of a factor 5.

Rate /K - stop in the ROI N = number of + in the region of interest. N = number of +. = number of stopped kaons. D ( + ) D ( + ). G ( + )=, MC/RC. BR ( K 2 ) = ROI = 2 p 2MeV/c

3 S = signal, B = background :. 3 maximum fraction of N ROI that may be ascribed to NR H at fixed C.L. (90%). 3 Upper Limit (U.L.) N ROI

Background estimation 2 /ndf = 145.7/95=1.5 p0 = p1 = Fit range: GeV/c 2 /ndf = 107.8/92=1.2 p0 = p1 = p2 = = Mean = hypothesis 1 hypothesis 2 1)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. 2)Any evaluation of S = N-B gives values lower than the maximum not significant signal at 90% C.L. hypothesis N tot ROI S=N-B R/K - stop (U.L.) U.L Li