Overview over meson-nucleus interactions and mesic states

Transcription

1 Overview over meson-nucleus interactions and mesic states Volker Metag II. Physikalisches Institut and University of Bonn, Germany Outline: meson-nucleon interactions: ω, η meson-nucleus interactions: ω, η - A bound few body systems search for meson-nucleus bound states (π, η, ω, η ) summary & outlook *funded by the DFG within SFB/TR16 Symposium on Fundamental and Applied Subatomic Physics Cracow, Poland, June 8-12,

2 meson-nucleon interactions meson nucleon determination of the scattering length from near-threshold meson production 2

3 meson-nucleon interaction: for short-lived mesons (η, ω, η, Φ) no beams available; study of meson-nucleon interaction by final state interactions in elementary reactions, e.g. p + p p + p + η meson-nucleon interaction COSY11 p + p p + p + η η E. Czerwinski et al., PRL 113 (2014) problem: pp FSI very strong scattering length a (only modulus) - interaction attractive or repulsive? Re(a η p ) = (0 ± 0.43) fm; Im(a η p ) = -( ) fm

4 meson-nucleon interaction ω γp ωp near threshold photo production I. Strakowsky et al., PRC 91 (2015) Colin Wilkin information on scattering length from cross section near threshold σt = q k 4απ 2 γ 2 a ωp a ωp = (0.82 ± 0.03 ) fm consistent with scattering amplitude deduced from ω-nucleus optical potential (M. Kotulla et al., PRL 100 (2008) ; S. Friedrich et al., PLB 736 (2014) 26) a ωn = -((0.17±0.40) + i (0.79±0.11)) fm a ωn = (0.81±0.41) fm 4

5 meson-nucleus interactions: real and imaginary part of the meson-nucleus optical potential meson nucleus 5

6 meson-nucleus optical potential U(r) =V (r)+iw (r) V (r) = m( 0 ) (r) 0 (r) W (r) = 0/2 0 = 1 2 ~c (r) inel in-medium mass modification real part in-medium mass modification reduction of lifetime imaginary part in-medium width inelastic cross section 6

7 experimental approaches to determine the meson-nucleus optical potential U(r) =V (r)+iw (r) real part V (r) = m( 0 ) (r) 0 line shape analysis excitation function momentum distribution meson-nucleus bound states T A = A! 0 X A N! 0 X 7

8 experimental approaches to determine the meson-nucleus optical potential U(r) =V (r)+iw (r) V (r) = m( 0 ) real part (r) line shape analysis excitation function momentum distribution meson-nucleus bound states 0 imaginary part W (r) = 0/2 0 = 1 2 ~c (r) inel T A = (r) transparency ratio measurement T A = A A! A! 0 X 0 A N! 0 X N! 0 X 7

9 imaginary part of the optical potential from transparency ratio measurements 8

10 ω Photoproduction of ω and η mesons on nuclei experiments performed with the CBELSA/TAPS detector (Bonn) ω π 0 γ 3γ M. Kotulla et al, PRL 100 (2008) T A = transparency ratio A A! 0 X N! 0 X counts / 10 MeV/c 2 counts / 10 MeV/c C M = (956.1 ± 0.9) MeV/c 2 σ = (8.8 ± 1.0) MeV 384 counts M(π 0 π 0 η) [MeV/c 2 ] Nb M = (955.6 ± 1.0) MeV/c 2 σ = (8.9 ± 0.6) MeV 385 counts M(π 0 π 0 η) [MeV/c 2 ] η π 0 π 0 η 6γ M. Nanova et al., PLB 710 (2012) 600 counts / 10 MeV/c 2 counts / 10 MeV/c Ca Pb M = (955.3 ± 1.6) MeV/c 2 σ = (9.0 ± 0.9) MeV 208 counts M(π 0 π 0 η) [MeV/c 2 ] M = (956.4 ± 1.6) MeV/c 2 σ = (9.0 ± 0.6) MeV 115 counts η M(π 0 π 0 η) [MeV/c 2 ] 9

11 C ω C imaginary part of the ω- and η -nucleus optical potential M. Kotulla et al., PRL 100 (2008) , PRL 114 (2915) T C A = 12 A! 0 X A C! 0 X T A normalized to carbon M. Nanova et al., PLB 710 (2012) E γ =1.7 GeV η low density approximation: Γ ω (<p ω > =1.1 GeV/c; ρ=ρ0) MeV σ ω inel 60 mb A ω: W(ρ=ρ0)= - Γ0/2 = -(70±5) MeV η exp data Γ(ρ 0 )=10 MeV Γ(ρ 0 )=15 MeV Γ(ρ 0 )=20 MeV Γ(ρ 0 )=25 MeV Γ(ρ 0 )=30 MeV Γ(ρ 0 )=35 MeV Γ(ρ 0 )=40 MeV ( 0 )=~c 0 inel Γη (<pη > 1.05 GeV/c ) MeV; A σ η inel 3-10 mb η : W(ρ=ρ0)= - Γ0/2 = -(10±2.5) MeV 10

12 Γ [MeV] momentum dependence of TA C, Γ and σinel for ω mesons S. Friedrich et al. M. Kotulla et al., PRL 100 (2008) PRL 115 (2015) Γ(ρ0)= hc β ρ0 σinel C T A VERY PRELIMINARY [MeV/c] VERY PRELIMINARY [mb] σ inel p ω VERY PRELIMINARY [MeV/c] p ω [MeV/c] p ω 11

13 Γ [MeV] momentum dependence of TA C, Γ and σinel for ω mesons S. Friedrich et al. M. Kotulla et al., PRL 100 (2008) PRL 115 (2015) Γ(ρ0)= hc β ρ0 σinel p [MeV/c] C T A A.Ramos et al.,epja 49(2013)148 D. Cabrera, R Rapp, PLB 729 (2014)67 VERY PRELIMINARY [MeV/c] GiBUU VERY PRELIMINARY VERY PRELIMINARY ωω [mb] σ inel [MeV/c] p ω VERY PRELIMINARY p ω 11

14 momentum dependence of TA C, Γ and σinel for ω mesons - (Im U) Γ [MeV] S. Friedrich et al. M. Kotulla et al., PRL 100 (2008) PRL 115 (2015) Γ(ρ0)= hc β ρ0 σinel A.Ramos et al.,epja 49(2013) D. Cabrera, R Rapp, 100 PLB 729 (2014) GiBUU p [MeV/c] C T A VERY PRELIMINARY [MeV/c] VERY PRELIMINARY VERY PRELIMINARY VERY PRELIMINARY ω [mb] σ inel [MeV/c] p ω VERY PRELIMINARY first information on momentum dependence of the imaginary part of the ω-nucleus optical potential; important for linking optical model parameters at high momenta to scattering length at production threshold p ω 11

15 what have we learned from transparency ratio measurements? transparency ratio measurements provide information on absorption of mesons in nuclei imaginary part W(ρ=ρ0) of meson-nucleus potential; applicable for any meson lifetime ω, η,φ mesons show broadening in nuclei; lifetime shortened (width increased) by inelastic processes Γ(ρ0) [MeV] < p >[GeV/c] W(ρ=ρ0) [MeV] σinel [mb] ω , η , Φ ,6-1, Φ 1,8 experiment CBELSA/ TAPS CBELSA/ TAPS ANKE@ COSY LEPS@ SPring-8 LEPS 12

16 real part of the optical potential from excitation functions and momentum distributions 13

17 The real part of the ω-nucleus potential ω π 0 γ sensitive to nuclear density at production point J. Weil, U. Mosel and V. Metag, PLB 723 (2013 ) 120 measurement of the excitation function of the meson in case of dropping mass - higher meson yield for given s because of increased phase space due to lowering of the production threshold cross section enhancement π 0 γ excitation function E γ thr 14

18 The real part of the ω-nucleus potential ω π 0 γ sensitive to nuclear density at production point J. Weil, U. Mosel and V. Metag, PLB 723 (2013 ) 120 measurement of the excitation function of the meson in case of dropping mass - higher meson yield for given s because of increased phase space due to lowering of the production threshold cross section enhancement π 0 γ excitation function momentum distribution of the meson: in case of dropping mass - when leaving the nucleus hadron has to become on-shell; mass generated at the expense of kinetic energy downward shift of momentum distribution π 0 γ momentum distribution γ+ 93 Nb π 0 γ+x E γ = GeV E γ thr 14

19 σ/a [µb] Carbon The real part of the ω-nucleus potential γa ω X MAMI V. Metag et al., PPNP, 67 (2012) 530. ω M. Thiel et al., EPJA 49 (2013) 132 E γ = MeV CB/TAPS@MAMI CBELSA/TAPS E γ thr GiBUU collisional broad. and mass shift V = 0 MeV V = -20 MeV V = -40 MeV V = -55 MeV V = -94 MeV V = -125 MeV [GeV] E γ data not consistent with strong mass shift scenario (Δm/m -16%) V ω (ρ=ρ0) = -(42±17(stat)±20(syst)) MeV 15

20 The real part of the η -nucleus potential η [µb] σ η' Mariana Nanova 10 1 Nb data γa η X data compared to calculations by E. Paryev (priv. com.) excitation function V = 0 MeV V = -25 MeV V = -50 MeV V = -75 MeV V = -100 MeV V = -150 MeV dσ η' /dp η' [µb/gev/c] 10 1 η momentum distribution Nb data V = 0 MeV V = -25 MeV V = -50 MeV V = -75 MeV V = -100 MeV V = -150 MeV = GeV E γ η' thr E γ VERY [GeV] V η (ρ=ρ0) = -(57±8(stat)±15(syst)) MeV E γ VERY [GeV/c] P η' V η (ρ=ρ0) = -(29±8(stat)±15(syst)) MeV <p η > 1.1 GeV/c 16

21 real part of η -nucleus potential from η kinetic energy η ELSA γ η E γ = GeV 1 0 θp 11 0 the higher the attraction the lower the kinetic energy of the η meson E. Paryev, arxiv: p d /de d [µb/gev sr] Carbon C p +X E = GeV 1<= p <=10 V=0 MeV V=-25 MeV V=-50 MeV V=-75 MeV V=-100 MeV V=-125 MeV V=-150 MeV PRELIMINARY peak position [MeV] 200 C data = GeV E PRELIMINARY T [GeV] potential depth [MeV] 17

22 real part of η -nucleus potential from η kinetic energy η ELSA γ η E γ = GeV 1 0 θp 11 0 the higher the attraction the lower the kinetic energy of the η meson E. Paryev, arxiv: p d /de d [µb/gev sr] Carbon C p +X E = GeV 1<= p <=10 V=0 MeV V=-25 MeV V=-50 MeV V=-75 MeV V=-100 MeV V=-125 MeV V=-150 MeV PRELIMINARY peak position [MeV] 200 C data = GeV E PRELIMINARY d /de d [µb/gev sr] C data = GeV E 3 2 1<= p <=10 fit to data PRELIMINARY (140 ± 17) MeV T [GeV] potential depth [MeV] T [GeV] 17

23 real part of η -nucleus potential from η kinetic energy η ELSA γ η E γ = GeV 1 0 θp 11 0 the higher the attraction the lower the kinetic energy of the η meson E. Paryev, arxiv: p d /de d [µb/gev sr] Carbon C p +X E = GeV 1<= p <=10 V=0 MeV V=-25 MeV V=-50 MeV V=-75 MeV V=-100 MeV V=-125 MeV V=-150 MeV PRELIMINARY peak position [MeV] C data E data = GeV GeV E PRELIMINARY d /de d [µb/gev sr] C data = GeV E 3 2 1<= p <=10 fit to data PRELIMINARY (140 ± 17) MeV T [GeV] potential -50 depth [MeV] 0 potential depth [MeV] V η (<p η > 500 MeV/c; ρ=ρ0) - (36±22) MeV T [GeV] 17

24 compilation of results for real and imaginary part of the ω, η -nucleus optical potential UωA(ρ=ρ0)= -((29±19(stat)±20(syst) + i(70±10)) MeV 100 Uη A(ρ=ρ0)= -((39±11(stat)±15(syst) + i(10±3)) MeV imaginary part [MeV] Im U > Re U Re U >> Im U potential depth [MeV] Im U > Re U ; ω not a good candidate to search for meson-nucleus bound states! Re U >> Im U ; η promising candidate to search for mesic states first (indirect) observation of in-medium mass shift of η at ρ=ρ0 and T=0 in good agreement with QMC model predictions (S. Bass et al., PLB 634 (2006) 368) 18

25 summary of theoretical predictions and experimental results on U η (ρ0)=vreal(ρ0)+i Wimag(ρ0) Vreal[MeV]= m η (ρ0)-m η chiral unitary CBELSA/TAPS p η 1GeV/c M. Nanova et al., PLB 727 (2013) COSY11 at threshold E. Czerwinksi et al., PRL 113 (2014) NJL linear σ QMC Wimag[MeV] Satoru Hirnezaki Steven Bass 19

26 bound few body systems 20

27 Mikhail Baskanov: The dibaryon d*(2380) ; (deltaron) WASA@COSY: P. Adlarson et al, PRL 106 (2011) first observation in pn d*(2380) ΔΔ dπ 0 π 0 p Δ π d n Δ π M=2.38 GeV/c2; Γ= 70 MeV I(J π )=0(3 + ) J π =1 + J π =3 + Avraham Gal: pion assisted dibaryons; also d*(2150) (NΔ)bound quantitatively described by long range interaction among N, π, Δ 21

28 The dibaryon d*(2380) established in various decay channels dπ 0 π 0 dπ+ π - pn# #d*(2380) # pn ppπ - π 0 pnπ 0 π 0 pnπ + π - 22

29 Search for kaonic clusters SIDDHARTA: x-ray spectroscopy of kaonic hydrogen: strong K - N attraction in I=0 channel FINUDA, DISTO: evidence for K - pp cluster Laura Fabbietti: HADES@GSI pp pλk 3.5 GeV G. Agakishiev et al., PLB 742 (2015) 242 PWA analysis, using known sources: no evidence for K - pp cluster in mass range GeV/c 2 23

30 using low energy K - from Φ decay Search for kaonic clusters K - +C Σ 0 +p+x; looking for ppk - Σ 0 +p statistical analysis including kaonic bound state with BE = 45MeV/c 2 and Γ= 30 MeV gives better χ 2 but only slightly better local p value 24

31 using low energy K - from Φ decay Search for kaonic clusters K - +C Σ 0 +p+x; looking for ppk - Σ 0 +p statistical analysis including kaonic bound state with BE = 45MeV/c 2 and Γ= 30 MeV gives better χ 2 but only slightly better local p value Slawomir Wycech: importance of multi-nucleon clusters in K - capture 24

32 Search for kaonic clusters Y. Ichikawa et al., Prog.Theor. Exp. Phys.(2015) 021D01 missing mass spectrum for d(π +,K + ) in coincidence with protons at 39 0 <θp lab <122 0 B( K - pp ) = ( (stat) +30 (syst)) MeV; evidence for K - pp - like structure Γ( K - pp ) = ( (stat) +66 (syst)) MeV

33 search for and study of meson-nucleus bound states 26

34 meson-nucleus interactions; Electromagnetic (+Strong) interaction mesic states charged pion nucleus bound by superposition of attractive Coulomband repulsive strong interaction Kenta Itahashi 27

35 meson-nucleus interactions; mesic states Electromagnetic (+Strong) interaction ω, η, η nucleus charged pion nucleus bound by superposition of attractive Coulomband repulsive strong interaction Kenta Itahashi bound solely by the strong interaction? talks by Kenta Itahashi Magdalena Skurzok Mariana Nanova 27

36 deeply bound pionic states halo-like π - distribution around nucleus 119 Sn: B1s = (3.82±0.01) MeV; Γ1s= (0.33±0.05) MeV Suzuki et al., PRL 92 (2004) optical potential parameters (real and imaginary part) determined from binding energy and width of bound states Kenta Itahashi RIBF@RIKEN (2010) Sn(d, 3 He) θ < a.u π threshold PRELIMINARY Q-value [MeV] 28

37 theoretical predictions for η-nucleus bound states C. Garcia-Recio et al., PLB 550 (2002) 47 E. Friedman, A. Gal, J.Mares PLB 725 (2013) 334 for most nuclei B η Γ η most states predicted to have tails into the continuum, allowing for η decays of bound states 29

38 η-nucleus or N*-nucleus bound states? Neelima Kelkar N*-nucleus bound states may exist, however very broad: Γ several 10 MeV 30

39 search for η-mesic states coherent η photo production on 3 He M. Pfeiffer et al., PRL 92 (2004) F. Pheron et al., PLB 709 (2012) 21 γ 3 He η 3 He T.Mersmann et al., PRL 98 (2007) dp η 3 He very strong rise of cross section directly at threshold in contrast to phase-space expectations strong 3 He-η FSI; quasi bound state close to threshold?? 31

40 Magdalena Skurzok W. Krzemien search for η-mesic states: η 4 He dd η 4 He 3 He pπ -, 3 He nπ 0 dd 3 He nπ 0 dd 3 He pπ - upper limit for bound state signal few nb 32

41 η bound state formation in d+d fusion Satoru Hirenzaki dd α η search for η-mesic states d+d η 4 He d+d η 4 He 3 He π - p; ( 3 He π 0 n) formation of η 4 He bound states with σ 80 nb 33

42 ω-nucleus bound states ω- mesic states 12 C(γ,p)ω 11 B CBELSA/TAPS E. Marco and W. Weise, PLB 502 (2001) 59 S. Friedrich et al., PLB 736 (2014) 26 quasi-free dω [nb/mev/sr] σ π 0 γ /de kin 2 d Carbon [MeV] E π 0 γ cross section in bound state region compatible with theoretical predictions, but no pronounced structure observed; consistent with tails extending into bound state region due to large imaginary part of the ω-nucleus optical potential 34

43 theoretical predictions for η -nucleus bound states η - mesic states: η 12 C D. Jido et al., PRC 85 (2012) H. Nagahiro et al., PRC 87 (2013) most states with Γ η B η excitation energy spectrum of the η 12 C system 35

44 theoretical predictions for η -nucleus bound states η - mesic states: η 12 C D. Jido et al., PRC 85 (2012) H. Nagahiro et al., PRC 87 (2013) most states with Γ η B η Moeki Miyatani: γ + 6 Li d +α η recoilless η production off quasi deuteron in 6 Li ; excitation energy spectrum of the η 12 C system d 2 σ de dω 10 pb/(mev sr) 35

45 search for η -mesic states in hadronic reactions 12 C(p,d)η 11 C K. Itahashi et al., PETP 128 (2012) 601 H. Nagahiro et al., PRC 87 (2013) Kenta Itahashi particle identification by time-of-flight analysis ongoing 2.5 GeV protons 12 C target missing mass spectrometry: Δmm =1.6 MeV/c 2 S2 aerogel Cerenkov GeV/c deuterons (protons) MWDC S4 p/d separation by aerogel Cerenkov TOF S2-S4 (diff. 20 ns) plastic scintillators aerogel Cerenkov 36

46 outlook: search for η -mesic states in photo-nuclear reactions 12 C(γ,p) η GeV p η γ formation and decay of η -mesic state Δp/p 1-2 % BGO-OD ideally suited for exclusive measurement approved proposal: ELSA/ BGO 37

47 outlook: search for η -mesic states in photo-nuclear reactions 12 C(γ,p) η GeV p η N γ η formation and decay of η -mesic state Δp/p 1-2 % BGO-OD ideally suited for exclusive measurement approved proposal: ELSA/ BGO 37

48 outlook: search for η -mesic states in photo-nuclear reactions C(γ,p) η GeV p η N C(γ,p) η GeV γ η formation and decay of η -mesic state Δp/p 1-2 % BGO-OD ideally suited for exclusive measurement approved proposal: ELSA/ BGO 37

49 meson-nucleus optical potential: summary ω: weak attraction; strong absorption; Vreal << Vimag η : weak attraction, small absorption; Vreal > Vimag measure momentum dependence of potential parameters to provide link to scattering length at production threshold few body systems: d*(2380) well established in various reactions and decay channels existence of K - pp clusters still controversial search for mesic states: π: deeply bound pionic states well established η: indication for bound η 4 He state with large width?? ω: no evidence for bound state due to large in-medium width η : promising candidate for meson-nucleus bound state: search ongoing at FRS@GSI, BGO-OD@ELSA, LEPS2@Spring8 38