Observation of neutron-rich -hypernuclei by the FINUDA experiment

Transcription

1 International Symposium on Strangeness Nuclear Physics 2014 December 12 nd -14 th, 2014, ChangSha, China Observation of neutron-rich -hypernuclei by the FINUDA experiment Alessandro Feliciello I.N.F.N. - Sezione di Torino

2 Outline the FINUDA DAΦNE physics motivations experimental results: INFN/LNF J-PARC 3

3 Mission accomplished! 20 years ago in Beijing 5

4 M. Agnello et al., PLB 40 (200) 145 M. Agnello et al., PRL 108 (2012) M. Agnello et al., NPA 881 (2012) 29 M. Agnello et al., PRC 8 (2012) nuclear models M. Agnello et al., PLB 22 (2005) 35 M. Agnello et al., PLB 81 (2009) 139 M. Agnello et al., NPA 835 (2010) 414 M. Agnello et al., PLB 98 (2011) 219 Physics output (S = -1) spectroscopy low-energy N -Y interaction neutron-rich Λ-hypernuclei medium effect n p p n n p p n Λ p p n deeply bound K states M. Agnello et al., PRL 94 (2005) B weak interaction (weak) decay quark substructures M. Agnello et al., NPA 804 (2008) 151 M. Agnello et al., PLB 81 (2009) 139 M. Agnello et al., NPA 835 (2010) 439 M. Agnello et al., PLB 85 (2010) 247 M. Agnello et al., PLB 701 (2011) 55 M. Agnello et al., NPA 881 (2012) 322 M. Agnello et al., PLB 739 (2014) 499

5 DAΦNE energy 510 MeV luminosity cm -2 s -1 σ x (rms) 2.11 mm σ y (rms) mm σ z (rms) 35 mm bunch length 30 mm crossing angle 12.5 mrad frequency (max) MHz bunch/ring up to 120 part./bunch current/ring 5.2 A (max) A Z e Κ e OSIM Be window beam pipe A ( Z ( A2) ( A3) Κ A Z ( Z ( Z A 1) 1) Z 1) tofino Κ ISIM targets p n 7 p n n

6 FINUDA key features very thin nuclear targets ( g/cm 2 ) high resolution spectroscopy coincidence measurement with large acceptance event by event K + tagging decay mode study indirect discovery tool continuous energy and rate calibration irradiation of different targets in the same run 9 systematic error reduction

7 Search for neutron-rich hypernuclei 11 central issue in hypernuclear physics historical paper: R.H. Dalitz and R. Levi Setti, Nuovo Cimento 30 (193) Pauli effect not effective for Λ 2. Λ extra binding energy existence of hypernuclei with core nucleus near (or even beyond) the neutron drip line unique opportunity to study: - effect of 3-body forces (ΛNN ) - ΛN- ΣN coupling contribution to binding en. - hyperon behaviour in n-rich environment w/o hyperons stiff EoS direct influence on neutron star EoS prediction of neutron star main parameters w/ hyperons soft EoS I. Vidaña et al., EPL 94 (2011) 11002

8 The status of the art (as of 2011) K A A Z Z A A (Z 2) ( Z 2) K K - + p 0 +, 0 + p + + n: 2-step (S-EX + C-EX) K - + p K 0 + n, K 0 + p + + : 2-step (C-EX + S-EX) K - + p + + -, - + p + n: 1-step (S-EX) experimental results theoretical predictions He ( Be) : u. l / Be ( C) : u. l..110 / C ( O) : u. l..210 / - + p 0 + n, 0 + p K + + : 2-step (C-EX + AP) - + p K 0 +, K 0 + p K + + n: 2-step (AP + C-EX) - + p K + + -, - + p + n: 1-step (AP) experimental results KEK KEK K K K INFN-LNF 5 H ( Li) : u. l. ( ) 10 / H ( Li) : u. l. ( ) 10 / ( C) : u. l. ( ) 10 Be / K K. Kubota et al., NPA 02 (199) 327 M. Agnello et al., PLB 40 (200) / K 7 T.Y. Tretyakova et al., NPA 91 (2001) 51c theoretical predictions K K 18 Li ( 10 B) : d / d nb / sr 10 P.K. Saha et al., PRL 94 (2005) T.Y. Tretyakova et al., PAT (2003) 181

9 The background issue m a i n b a c k g r o u n d K L int 220 pb -1 A Z A (Z 2) background subtraction 7 K Li H ( Li) : u. l. ( ) K Li 7 H ( Li) : u. l. ( ) 10 M. Agnello et al., PLB 40 (200) 145 H 5 H 5 / K 90% 90% 20 c. l. c. l.

10 Higher statistics was not enough L int 115 pb -1 K Li H 7 7 K Li H 22

11 The new NRH search strategy L int 115 pb -1 K Li H H He double C-EX p ~ 252 MeV/c n.m. decay p ~ 134 MeV/c apparatus capabilities: selective trigger (based on fast scintillator detectors) precise K - vertex identification < 1 mm 3 (PID + spatial resolution + K - tagging), K, p, d, separation (OSIM & LMDC de/dx) high momentum resolution 270 MeV/c % 110 MeV/c (tracker performance + He bag + thin target) 23

12 Analysis technique K Li H H He ( ( He) 801 ms) atomic mass tables M 2 ( He) p 2 ( ) M( He) MeV if H is a stable system 2 independent two-body reactions: decay at rest M M ( 2 ( H ) p ( MeV with B 0 2 ( ) M ( H ) 5 H ) M ( H ) M ( ) B( ) MeV) 24 cut on T ( ) T ( ) : MeV

13 Data selection absolute energy scale: + (235. MeV/c) from K 2 p < 0.12 MeV/c - (132.8 MeV/c) from 4 H p < 0.2 MeV/c systematic errors T sys = 0.17 MeV T( + ) = 0.9 MeV, T( - ) = 0.84 MeV T exp = 1.3 MeV T = 1.3 MeV T ( ) T ( ) : MeV 25 FINUDA Coll. And A. Gal, NPA 881 (2012) 29

14 Data selection 5 H + 3 H + 2n MeV/c ( p =1.1 MeV/c) MeV/c ( p =1.2 MeV/c) 0.0 MeV -1.7 MeV selection range fixed by including H lowest particle stability threshold p + = MeV/c p - = 135. MeV/c B = 1.5 MeV (out of ped K - events) 2 4 H + 2n MeV

15 H Λ production rate 28 background sources accidentals: + ( MeV/c) and - ( MeV/c) 0.27 ± 0.27 ev. - He n n K Li K 4 Li production rate H n n + 4 He + - total background on Li: end point ~190 MeV/c end point ~282 MeV/c end point ~252 MeV/c p( - ) = 133 MeV/c BGD1 + BGD2 = 0.43 ± 0.28 ev. 0.1 ± 0.07 ev. negligible Poisson statistics: 3 events DO NOT belong to pure C.L. = 99% assumption BR( ) 4 H 0.49 H. Tamura et al., PRC 40 (1989) R479 R BR( ) (3 BGD1 BGD2) /[ ( ) ( )( n. R BR( ) ( ) 10 / R ( ) 10 / K FINUDA Coll. and A. Gal, PRL 108 (2012) K ( K ) 10 5 on / K Li)] M. Agnello et al., PLB 40 (200) 145

16 Kinematics and binding energy 8 ( N Y ) / Z( H ) 5 N / Z( He) 3 theoretical predictions B = 4.2 MeV R.H. Dalitz and R. Levi Setti, NC 30 (193) 489 B = 4.2 MeV L. Majling, NPA 585 (1995) 211c formation mass values systematically higher than the ones from decay Akaishi M = ( ± 1.1) MeV B = (4.0 ± 1.1) MeV ( 5 H + ) (0.98 ± 0.74) MeV excited states production E. Hiyama et al., NPA 908 (2013) 29 A. Gal, D.J. Millener, PLB 725 (2013) MeV MeV B.F. Gibson, I.R. Afnan, FBS 55 (2014) 913 nrh prod. rate: ~10-2 hyp. prod. rate in (K -, - ) B = 5.8 MeV ( 5 H + ) NN force 1.4 MeV FINUDA Coll. and A. Gal, PRL 108 (2012) FINUDA Coll. and A. Gal, NPA 881 (2012) 29

17 Kinematics compatibility: visual scan

18 9 He Λ production rate 34 0 observed events ( - ), ( + ) n. ped K - on 9 Be = ev. R R BR( ) ( ) 10 BR( ) / K M. Agnello et al., PLB 81 (2009) He 4 spectator 5 (90% C. L.) neutrons /( n. 4 upper limit evaluation / K K M. Agnello et al., PRC 8 (2012) on 9 Be) R 1.10 (90% C.L.) 9 9 ( He g. s. Lig. s. ) / K A. Gal, NPA 828 (2009) 72 (90% C. L.) K. Kubota et al., NPA 02 (199) 327

19 Neutron-rich hypernucley summary Glue-like role of : observation of n-rich hyperfragments in emulsions He, 8 He, 9 Li N = Z Z 4 He H Be 5.1 Li He H Be.84 7 Li 5.58 He 4.18 xxx 5 H 3.1 xxx 9 Be.71 8 Li.80 7 He 5.23 n halo H 4.2 xxx 10 Be Li He 7.1 xxx 7 H 5.2 xxx 11 Be 10.2 xxx 9 He 8.5 n halo 12 Be 11.4 n halo B (MeV) xxx = unstable core N observed not observed FINUDA JLab 35 from: Nuclear Wallet Cards 2001, NNDC, BNL L. Majling, NPA 585 (1995) 211c

20 n-rich (K -, + ) production rate vs A K. Kubota et al., NPA 02 (199) 327 M. Agnello et al., PLB 40 (200) 145 FINUDA Coll. and A. Gal, PRL 108 (2012) M. Agnello et al., PRC 8 (2012) theoretical interest: D.J. Millener, NPA 881 (2012) 298 E. Hiyama et al., NPA 908 (2013) 29 A. Gal, D.J. Millener, PLB 725 (2013) 445

21 E10: no evidence!?! J-PARC E10 Li H K H. Sugimura et al., PLB 729 (2014) 39.) d / d 1.2 nb / sr (90% C. L one order of magnitude lower than 10 B 10 Li K g.s. B = 2.5 MeV (FWHM) d / d nb / sr B = 0 KEK-E521 P.K. Saha et al., PRL 94 (2005)

22 Summary and outlook Last but not least results from FINUDA: first experimental evidence for the heavy hyperhydrogen H Λ limited number of candidates (3) powerful but not universal method negative results from J-PARC E10 theoretical predictions not in agreement further investigations needed both experimental and theoretical 42

23 43 Thank you! 非常感謝