Experimental studies on the weak decay of Λ-hypernuclei. Alessandro Feliciello I.N.F.N. - Sezione di Torino

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1 Experimental studies on the weak decay of -hypernuclei Alessandro Feliciello I.N.F.N. - Sezione di Torino

2 Mission accomplished J π ( 15 N g.s. ) = 3/2 + 1 st, experimental assignment of J π ( 15 N )=3/2 + determination of the 2N 1 st, direct experimental evidence for 2N -induced NMWD π 2 1 st determination of p / or 8 Hypernuclei

3 Outline The FINUDA INFN/LNF DAΦNE: a detector designed for decay of hypernuclei study A revisited analysis of the proton spectra from NMWD of hypernuclei First determination of p / for 8 hypernuclei (A = 5-16) Determination of the full set of NMWD widths for 5 He and 11 B A look to the future 3

4 FINUDA in a nutshell energy 510 MeV luminosity cm -2 s -1 σ x (rms) σ y (rms) σ z (rms) bunch length crossing angle frequency (max) 2.11 mm mm 35 mm 30 mm 12.5 mrad MHz bunch/ring up to 120 part./bunch current/ring 5.2 A (max) A Z e Κ + e stop OSIM Be window beam pipe A + + ( Z ( A 2) ( A 3) φ Κ A Z ( Z ( Z A 1) + 1) + Z + 1) + π tofino Κ + + π ISIM targets p + n 4 p + n + n

5 FINUDA key features very thin nuclear targets ( g/cm 2 ) high resolution spectroscopy coincidence measurements with large acceptance (2π sr) decay mode study event by event K + tagging continuous energy and rate calibration irradiation of different targets in the same run systematic error reduction 5

6 Physics motivations lifetime of (light) -hypernuclei check of the validity of the ΔI=1/2 rule MWD decay exploited as indirect spectroscopic analysis tool the NMWD study provides the only practical means of exploring the four-fermion, strangeness changing N NN weak interaction n / p puzzle experimental evidence of 2N -induced process in medium modifications of hyperons weak decay 7

7 Alessandro Feliciello / HYP nd International Conference on Hypernuclaer and Strange Particle Physics, Sendai, Japan, September 7-12, 2015 Physics output (S = -1) M. Agnello et al., PLB 640 (2006) 145 M. Agnello et al., PRL 108 (2012) M. Agnello et al., NPA 881 (2012) 269 M. Agnello et al., PRC 86 (2012) B weak interaction nuclear models neutron-rich -hypernuclei n p p np n p n p p n spectroscopy M. Agnello et al., PLB 622 (2005) 35 M. Agnello et al., PLB 681 (2009) 139 M. Agnello et al., NPA 835 (2010) 414 M. Agnello et al., PLB 698 (2011) 219 (weak) decay medium effect low-energy N -Y interaction quark substructures deeply bound K states M. Agnello et al., PRL 94 (2005) M. Agnello et al., PLB 654 (2007) M. Agnello et al., NPA 804 (2008) 151 M. Agnello et al., PLB 681 (2009) 139 M. Agnello et al., NPA 835 (2010) 439 M. Agnello et al., PLB 685 (2010) 247 M. Agnello et al., PLB 701 (2011) 556 M. Agnello et al., NPA 881 (2012) 322 M. Agnello et al., PLB 738 (2014) 499 E. Botta et al., PLB 748 (2015) 86 8

8 Observables in Weak Decay of Hypernuclei A Z MWD + 0 π A A A A 0 Z (Z + 1) + π Z Z p + π π +π 0 n +π A ( A Z 2) ( Z 1) + T = 1N p + + p n + + n + p p + A Z τ ( A 2) hyp n Z + n + n + n n + n NMWD + 2 N + pp + np + nn ( A ( A A ( A + n + p + p Z 3) Z 3) Z + n + n + p Z + n + n + n ( 1) A A Z 3) ( Z 2) + p + p n + p + p + n + p n + n + p 11 + n + n n + n + n

9 Anatomy of NMWD p spectra p spectra background subtracted and acceptance corrected (*) (*) (*) 1N, 2N, FSI!!! (*) M. Agnello et al., NPA 804 (2008) 151. M. Agnello et al., PLB 685 (2010) MeV threshold! common features: structure at ~80 MeV low energy rise 12

10 Revisited analysis of the proton spectra Attempt of improving the fits by shifting down the lower edge for the fits to 50, 60 and 70 MeV: better value of χ 2 /n = 1.33 when choosing the starting point at 70 MeV

11 Refined determination of 2N the ratio 2N / p can be obtained (under the assumption that it is constant in the range A = 5 16). It was found (single particle spectra): 2N / p = 0.43 ± 0.25 ( 2N / NMWD = 0.24 ± 0.10) With the new values we find: / NMWD The central values of the fitting Gaussians (µ) were used to divide the full area of the proton spectra into two regions, A low and A high. It was shown that from the expression: R 1 ( A) = A low Alow( A) ( A) + A ( A) 2N / p = 0.50 ± 0.24 ( 2N / NMWD = 0.25 ± 0.12) high A low A high compatible with the previous one, within the errors.

12 Refined determination of 2N / NMWD By selecting (n,p) coincidence events we found: 2 N = 0.39 ± p stat 0.03sys With the new µ values, we got: 2 N = 0.36 ± p stat 0.04sys 2 N = ± stat 0.02sys NMWD 2 N = ± stat 0.02sys NMWD fully compatible with the previous one, within the errors. FINUDA Collaboration and G. Garbarino., PLB 701 (2011) 556. M. Kim et al., PRL 103 (2009) : 0.29 ± E. Bauer and G. Garbarino, PRC 81 (2010)

13 First determination of p / for 8 Hypernuclei Some information can be extracted by the proton spectra, but how it is possible to extract the true number of protons from NMWD. Spectra are severely distorted by several FSI effects At least 3 effects: a) number of primary protons from NMWD decreased by FSI b) in a given region of the spectrum increase due to the FSI not only of higher energy protons, but of neutrons as well c) quantum mechanical interference effect In the upper part of the experimental spectrum b) and c) are negligible How to calculate a) without resorting to any INC models, but only from experimental data?

14 First determination of p / for 8 Hypernuclei p = T 2(N p N2N ) + (N p N2N α 5 = 1.08 ± 0.16 α 12 = 2.58 ± 0.37 N α Hyp α 5 ( 5 He )= 1.15 ± 0.26 α 5 ( 12 C ) = 1.04 ± 0.19 ) T /, n / p, 2N / p π /, π0 / where α accounts for FSI: α 2 +α protons lost p / ( 5 He ) = 0.22 ± 0.03 p / ( 12 C ) = 0.49 ± 0.06 weighted average input: experimental results only J.J. Szymanski et al., PRC 43 (1991) 849: 0.21 ± 0.07 H. Noumi et al., PRC 52 (1995) 2936: 031 ± 0.07 H. Bhang et al., JKPS 59 (2011) 1461: 045± 0.10 assumption α scales linearly with A α(a) = (0.215 ± 0.031) A α 12 ( 12 C ) = 2.48 ± 0.46 α 12 ( 5 He )= 2.77 ± 0.63

15 First determination of p / for 8 Hypernuclei M. Agnello et al., PLB 738 (2014) 499. H. Noumi et al., PRC 534 (1995) K. Itonaga, T. Motoba, Progr. Theor. Phys. Suppl. 185 (2010) 252. J.J. Szymanski et al., PRC 43 (1991) 849. H. Bhang et al., JKPS 59 (2011) 1461.

16 First determination of p / for 8 Hypernuclei K. Itonaga, T. Motoba, Progr. Theor. Phys. Suppl. 185 (2010) 252.

17 First determination of p / for 8 Hypernuclei strong nuclear structure effects K. Itonaga, T. Motoba, Progr. Theor. Phys. Suppl. 185 (2010) 252.

18 Completion of decay pattern for 5 He and 11 B 43 / T / π 0 / π p / 2N / n / n / p 5 He 11 B 0.962± ± ± ± ± ± ± ± ± ± ± ± ± ± ± C 0.120± ± ±0.088 n / p K. Itonaga, T. Motoba, PTP 185 (2010) ± ± ± C 1.241± ± ± ± ± ± ± N / p = 0.36 ± stat 0.04sys

19 J-PARC K1.1 beam line old (2008) conservative (?) perspective E10 published data: > π + /spill one order of magnitude more efficient data collection expected with respect to K1.8 beam line H. Sugimura et al., PLB 729 (2014)

20 47 A possible apparatus concept layout Cylindrical Detector System (K1.8BR spectrometer) essential requirements (π +,K + ) magnetic analysis of decay products large detection solid angle (~2π) low detection threshold SKS magnet (K1.8 spectrometer)

21 49 A possible apparatus concept layout π + 7 Li 9 Be 12 C 16 O 5 He 7 Li 9 Be 11 B 12 C 15 N target thickness: ~ 0.7 gr/cm 2 along the beam: > 1.0 gr/cm 2 7 Li E15 E17 12 C E18 E31 9 Be 16 O ~400 mm 16 O

22 Expected rates (rough estimate) educated guess ~10 8 π + / spill H. Sugimura et al., PLB 729 (2014) 39. interspill: 3.5 s from previous experience KEK-PS: E336, E369, E419, E462, E508 ~1 12 C g.s. / 10 8 π + formation rate on 1 g/cm 2 target B.R. (0.5), Ω (0.5), ε riv/rec (0.5) E18 request: π + on target(s) ~10 12 π + / day ~ C g.s. / day ~ C g.s. / day > π + /spill required beam time: 10 days ~10 4 p from 1N 1% on p /, T / ~ p from 2N 2% on 2N / ~10 3 π - 3% on π -/ ~ π 0 5% on π 0/ 52

23 Conclusions First systematic determination of p / for p-shell Hypernuclei experimental data agree with the latest calculations by Itonaga & Motoba, (even though the errors are quite large ) First experimental verification of the complementary between MWD and NMWD, at least for charged channels Completion of 5 He and 11 B NMWD pattern Looking forward for new opportunities at J-PARC K. Itonaga, T. Motoba, Progr. Theor. Phys. Suppl. 185 (2010) 252.

24 Thank you! 有り難う 55