Experimental results on the meson-nucleus optical potential and mesic states

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1 Experimental results on the meson-nucleus optical potential and mesic states Volker Metag II. Physikalisches Institut for the CBELSA/TAPS Collaboration Outline: theoretical predictions for meson-nucleus optical potentials exp. approaches and results on the imaginary part of the ω, η - nucleus potential exp. approaches and results on the real part of the ω, η - nucleus potential search for meson-nucleus bound states summary & outlook *funded by the DFG within SFB/TR16 International School of Nuclear Physics; 37th Course Probing Hadron Structure with Lepton and Hadron beams Erice, Sicily, Sept. 16-4, 15 1

2 deeply bound pionic states: Electromagnetic (+Strong) interaction meson-nucleus interactions; mesic states 5 4 Kenta Itahashi priv. com. 1 Sn(d, 3 He) θ < p s 1s a.u 3 charged pion nucleus 1 bound by superposition of attractive Coulomband repulsive strong interaction Q-value [MeV] excitation energy spectrum of π - 11 In system

3 meson-nucleus interactions; mesic states deeply bound pionic states: Electromagnetic (+Strong) interaction charged pion nucleus bound by superposition of attractive Coulomband repulsive strong interaction

4 meson-nucleus interactions; mesic states deeply bound pionic states: Electromagnetic (+Strong) interaction ω, η, η nucleus bound solely by the strong interaction charged pion nucleus? bound by superposition of attractive Coulomband repulsive strong interaction

5 symmetry breaking in the hadronic sector nonet of pseudoscalar mesons M=958 MeV/c MeV/c 1 75 η M=548 MeV/c K M=498 MeV/c 5 5 π M=14 MeV/c 3

6 symmetry breaking in the hadronic sector nonet of pseudoscalar mesons M=958 MeV/c MeV/c 1 75 η M=548 MeV/c K M=498 MeV/c 5 5 π M=14 MeV/c S. Klimt et al., Nucl. Phys. A 516 (199) 49 mass as a result of symmetry breaking Mass [GeV] π, K, η, η8 spontaneous! U(3)L x U(3)R! breaking! mi = The NJL Model η!!!! SU(3)L x SU(3)R! Goldstone!! bosons! π, K,! η8! U(1)A!! breaking mi = η η K π SU(3)F! breaking! mud 5 MeV! ms 13 MeV 3

7 symmetry breaking in the hadronic sector nonet of pseudoscalar mesons M=958 MeV/c MeV/c 1 75 η M=548 MeV/c K M=498 MeV/c 5 5 π M=14 MeV/c S. Klimt et al., Nucl. Phys. A 516 (199) 49 mass as a result of symmetry breaking partial restoration of chiral symmetry predicted in a nucleus impact on in-medium meson masses?? Mass [GeV] π, K, η, η8 spontaneous! U(3)L x U(3)R! breaking! mi = The NJL Model η!!!! SU(3)L x SU(3)R! Goldstone!! bosons! π, K,! η8! U(1)A!! breaking mi = η η K π SU(3)F! breaking! mud 5 MeV! ms 13 MeV 3

8 model predictions for the in-medium mass of the η meson H. Nagahiro, M. Takizawa and S. Hirenzaki, Phys. Rev. C 74 (6) 453 S. Sakai and D. Jido PRC 88 (13) 6496 SU(3) SU() Δm η (ρ) -8 MeV Δm η (ρ) -15 MeV Δm η (ρ) + MeV S. Bass and A. Thomas, PLB 634 (6) 368 Δm η (ρ) -4 MeV for θ ηη = - 4

9 model predictions for in-medium mass/width of the ω meson F. Klingl et al., NPA 61 (1997) 97; NPA 65 (1999) 99 M. Lutz et al., NPA 76 () 437 P. Mühlich et al., NPA 78 (6) 187 lowering of in-medium mass broadening of resonance with increasing nuclear density splitting into ω-like and N*N -1 mode due to coupling to nucleon resonances ω N* ω ρ" ρ" N spectral function for ω meson at rest: almost no mass shift; strong in-medium broadening Re(U) ; Im(U) large 5

10 meson-nucleus optical potential U(r) =V (r)+iw (r) 6

11 meson-nucleus optical potential U(r) =V (r)+iw (r) V (r) = m( ) (r) real part in-medium mass modification 6

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

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

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

15 The imaginary part W of the meson-nucleus optical potential 8

16 ω Photoproduction of ω and η mesons on nuclei experiments performed with the CBELSA/TAPS detector (Bonn) ω π γ 3γ M. Kotulla et al, PRL 1 (8) 193 T A = transparency ratio A A! X N! X counts / 1 MeV/c counts / 1 MeV/c C M = (956.1 ±.9) MeV/c σ = (8.8 ± 1.) MeV 384 counts M(π π η) [MeV/c ] Nb M = (955.6 ± 1.) MeV/c σ = (8.9 ±.6) MeV 385 counts M(π π η) [MeV/c ] η π π η 6γ M. Nanova et al., PLB 71 (1) 6 counts / 1 MeV/c counts / 1 MeV/c Ca Pb M = (955.3 ± 1.6) MeV/c σ = (9. ±.9) MeV 8 counts M(π π η) [MeV/c ] M = (956.4 ± 1.6) MeV/c σ = (9. ±.6) MeV 115 counts η M(π π η) [MeV/c ] 9

17 C ω C imaginary part of the ω- and η -nucleus optical potential M. Kotulla et al., PRL 1 (8) 193, PRL 114 (915) T C A = 1 A! X A C! X T A normalized to carbon M. Nanova et al., PLB 71 (1) E γ =1.7 GeV η low density approximation: Γ ω (<p ω > =1.1 GeV/c; ρ=ρ) MeV σ ω inel 6 mb A ω: W(ρ=ρ)= - Γ/ = -(7±5) MeV.7.6 η exp data Γ(ρ )=1 MeV Γ(ρ )=15 MeV Γ(ρ )= MeV Γ(ρ )=5 MeV Γ(ρ )=3 MeV Γ(ρ )=35 MeV Γ(ρ )=4 MeV 1 1 ( )=~c inel Γη (<pη > 1.5 GeV/c ) 15-5 MeV; A σ η inel 3-1 mb η : W(ρ=ρ)= - Γ/ = -(1±.5) MeV 1

18 what have we learned from transparency ratio measurements? transparency ratio measurements provide information on absorption of mesons in nuclei imaginary part W(ρ=ρ) 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(ρ) [MeV] < p >[GeV/c] W(ρ=ρ) [MeV] σinel [mb] ω , η , Φ 3-6,6-1, Φ 1,8 experiment CBELSA/ TAPS CBELSA/ TAPS ANKE@ COSY LEPS@ SPring-8 LEPS 11

19 Γ [MeV] momentum dependence of TA C, Γ and σinel for ω mesons S. Friedrich et al. M. Kotulla et al., PRL 1 (8) 193 Γ(ρ)= hc β ρ σinel C T A [MeV/c] VERY PRELIMINARY p [MeV/c] VERY PRELIMINARY p ω [mb] σ inel first information on momentum dependence of the imaginary part of the ω-nucleus optical potential ω χ / ndf 41.4 / 1 p ±.55 p1 5 ±.4 σ[mb]=5+33.7/p[gev/c] VERY PRELIMINARY [MeV/c] p ω 1

20 Γ [MeV] momentum dependence of TA C, Γ and σinel for ω mesons S. Friedrich et al. M. Kotulla et al., PRL 1 (8) 193 Γ(ρ)= hc β ρ σinel C T A p [MeV/c] VERY PRELIMINARY p [MeV/c] A. Ramos et al., EPJA49 VERY PRELIMINARY Cabrera & Rapp, PLB 79 (14) GiBU ω ω [mb] σ inel first information on momentum dependence of the imaginary part of the ω-nucleus optical potential ω χ / ndf 41.4 / 1 p ±.55 p1 5 ±.4 σ[mb]=5+33.7/p[gev/c] VERY PRELIMINARY [MeV/c] p ω 1

21 - (Im U) Γ [MeV] momentum dependence of TA C, Γ and σinel for ω mesons S. Friedrich et al. M. Kotulla et al., PRL 1 (8) 193 Γ(ρ)= hc β ρ σinel C T A 1 8 Cabrera & Rapp, PLB 79 (14) 15 6 GiBU p [MeV/c] VERY PRELIMINARY p [MeV/c] A. Ramos et al., EPJA49 VERY PRELIMINARY VERY PRELIMINARY ω ω [mb] σ inel first information on momentum dependence of the imaginary part of the ω-nucleus optical potential ω χ / ndf 41.4 / 1 p ±.55 p1 5 ±.4 σ[mb]=5+33.7/p[gev/c] VERY PRELIMINARY [MeV/c] p ω 1

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

23 The real part of the ω-nucleus potential ω π γ sensitive to nuclear density at production point J. Weil, U. Mosel and V. Metag, PLB 73 (13 ) 1 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 γ excitation function E γ thr 14

24 The real part of the ω-nucleus potential ω π γ sensitive to nuclear density at production point J. Weil, U. Mosel and V. Metag, PLB 73 (13 ) 1 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 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 γ momentum distribution γ+ 93 Nb π γ+x E γ = GeV E γ thr 14

25 σ/a [µb] Carbon The real part of the ω-nucleus potential γa ω X MAMI V. Metag et al., PPNP, 67 (1) 53. ω M. Thiel et al., EPJA 49 (13) 13 E γ =9-13 MeV CB/TAPS@MAMI CBELSA/TAPS E γ thr GiBUU collisional broad. and mass shift V = MeV V = - MeV V = -4 MeV V = -55 MeV V = -94 MeV V = -15 MeV [GeV] E γ data not consistent with strong mass shift scenario (Δm/m -16%) V ω (ρ=ρ) = -(4±17(stat)±(syst)) MeV 15

26 The real part of the η -nucleus potential η σ η [µb] data: M. Nanova et al., PLB 77 (13) 417 calc.: E. Paryev, J. Phys. G 4 (13) 51 C data σ tot σ diff E γ thr V(ρ=ρ ) = MeV V(ρ=ρ ) = -5 MeV V(ρ=ρ ) = -5 MeV V(ρ=ρ ) = -75 MeV V(ρ=ρ ) = -1 MeV V(ρ=ρ ) = -15 MeV E γ [MeV] V η (ρ=ρ) = -(4±6(stat)±1(syst)) MeV data disfavour strong mass shifts dσ η /dp η [µb/gev/c] data: M. Nanova et al., PLB 77 (13) 417 calc.: E. Paryev, J. Phys. G 4 (13) 51 C data V(ρ=ρ ) = MeV E γ =15- MeV V(ρ=ρ ) = -5 MeV V(ρ=ρ ) = -5 MeV V(ρ=ρ ) = -75 MeV V(ρ=ρ ) = -1 MeV V(ρ=ρ ) = -15 MeV p η [GeV/c ] V η (ρ=ρ) = -(3±1(stat)±1(syst)) MeV <p η > 1.1 GeV/c 16

27 The real part of the η -nucleus potential η [µb] σ η' Mariana Nanova Nb γa η X data compared to calculations by E. Paryev (priv. com.) excitation function µb/gev/c] Nb data η momentum distribution = GeV E γ 1 /dp η [' dσ η' 1 η' thr E γ [GeV] VERY V = MeV V = -5 MeV V = -5 MeV V = -75 MeV V = -1 MeV V = -15 MeV E γ 1 V = MeV V = -5 MeV V = -5 MeV V = -75 MeV V = -1 MeV V = -15 MeV [GeV/c] VERY P η' V η (ρ=ρ) = -(±4(stat)±15(syst)) MeV V η (ρ=ρ) = -(38±5(stat)±15(syst)) MeV <p η > 1.1 GeV/c 17

28 real part of ω-nucleus potential from ω kinetic energy ELSA γ ω E γ = GeV 1 θp 11 the higher the attraction the lower the kinetic energy of the ω meson p 18

29 real part of ω-nucleus potential from ω kinetic energy ELSA γ ω E γ = GeV 1 θp 11 the higher the attraction the lower the kinetic energy of the ω meson H. Nagahiro, priv. com. p dω [nb/mev/sr] σ π γ /de kin d , W ) (V - (156,7) MeV - (1,7) MeV - ( 5,7) MeV - (,7) MeV - (-,7) MeV - (-5,7) MeV [MeV] E π γ 18

30 real part of ω-nucleus potential from ω kinetic energy ELSA γ ω E γ = GeV p 1 θp 11 the higher the attraction the lower the kinetic energy of the ω meson H. Nagahiro, priv. com. S. Friedrich, PLB 736 (14) 6 dω [nb/mev/sr] σ π γ /de kin d d [nb/mev/sr] /de kin d Carbon , W ) (V - (156,7) MeV - (1,7) MeV - ( 5,7) MeV - (,7) MeV - (-,7) MeV - (-5,7) MeV [MeV] E π γ -.5 Ekin=(6.5±7)MeV [MeV] E 18

31 real part of ω-nucleus potential from ω kinetic energy ELSA γ ω E γ = GeV dω [nb/mev/sr] σ π γ /de kin d θp 11 the higher the attraction the lower the kinetic energy of the ω meson H. Nagahiro, priv. com., W ) (V - (156,7) MeV - (1,7) MeV - ( 5,7) MeV - (,7) MeV - (-,7) MeV - (-5,7) MeV [MeV] E π γ peak position [MeV] d) S. Friedrich, PLB 736 (14) potential depth [MeV] d [nb/mev/sr] /de kin d Carbon V ω (p ω 3 MeV/c; ρ=ρ) = -(15±35) MeV p Ekin=(6.5±7)MeV [MeV] E 18

32 real part of η -nucleus potential from η kinetic energy η ELSA γ η E γ = GeV 1 θp 11 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 <=1 V= MeV V=-5 MeV V=-5 MeV V=-75 MeV V=-1 MeV V=-15 MeV V=-15 MeV PRELIMINARY peak position [MeV] C data = GeV E PRELIMINARY T [GeV] potential depth [MeV] 19

33 real part of η -nucleus potential from η kinetic energy η ELSA γ η E γ = GeV 1 θp 11 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 <=1 V= MeV V=-5 MeV V=-5 MeV V=-75 MeV V=-1 MeV V=-15 MeV V=-15 MeV PRELIMINARY peak position [MeV] C data = GeV E PRELIMINARY d /de d [µb/gev sr] C data = GeV E 3 1<= p <=1 fit to data PRELIMINARY (14 ± 17) MeV T [GeV] potential depth [MeV] T [GeV] 19

34 real part of η -nucleus potential from η kinetic energy η ELSA γ η E γ = GeV 1 θp 11 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 <=1 V= MeV V=-5 MeV V=-5 MeV V=-75 MeV V=-1 MeV V=-15 MeV V=-15 MeV PRELIMINARY peak position [MeV] C data E data = GeV -.6 GeV E PRELIMINARY d /de d [µb/gev sr] C data = GeV E 3 1<= p <=1 fit to data PRELIMINARY (14 ± 17) MeV T [GeV] potential -5 depth [MeV] potential depth [MeV] V η (<p η > 5 MeV/c; ρ=ρ) - (36±) MeV T [GeV] 19

35 ω compilation of results for real and imaginary part of the ω, η -nucleus optical potential imaginary part: η WωA(ρ=ρ)= -Γ/ = - (65-75) MeV Wη A(ρ=ρ) = -Γ/ = - ( ) MeV syst real part: excitation function syst C Nb excitation function mom. distribution peak E kin peak E kin V C [MeV] cross section fit V η'a [MeV] VωA(ρ=ρ) = -(9±19(stat)±(syst))MeV Vη A(ρ=ρ) = -(3±3(stat)±15(syst))MeV

36 compilation of results for real and imaginary part of the ω, η -nucleus optical potential UωA(ρ=ρ)= -((9±19(stat)±(syst) + i(7±1)) MeV imaginary part [MeV] Im U > Re U ω Uη A(ρ=ρ)= -((3±3(stat)±15(syst) + i(1±3)) MeV V. Metag Hyp.Int. 34 (15) Re U >> Im U η' Im U > Re U ; ω not a good candidate to search for meson-nucleus bound states! potential depth [MeV] Re U >> Im U ; η promising candidate to search for mesic states first (indirect) observation of in-medium mass shift of η at ρ=ρ and T= in good agreement with QMC model predictions (S. Bass et al., PLB 634 (6) 368) 1

37 summary of theoretical predictions and experimental results on U η (ρ)=vreal(ρ)+i Wimag(ρ) Vreal[MeV]= m η (ρ)-m η chiral unitary CBELSA/TAPS p η 1GeV/c M. Nanova et al., PLB 77 (13) COSY11 at threshold E. Czerwinksi et al., PRL 113 (14) 64-6 NJL linear σ QMC Wimag[MeV] Satoru Hirnezaki Steven Bass

38 search for η -mesic states in hadronic reactions 1 C(p,d)η 11 C K. Itahashi et al., PETP 18 (1) 61 H. Nagahiro et al., PRC 87 (13) 451 Kenta Itahashi particle identification by time-of-flight analysis ongoing.5 GeV protons 1 C target missing mass spectrometry: Δmm =1.6 MeV/c S aerogel Cerenkov.7-.9 GeV/c deuterons (protons) MWDC S4 p/d separation by aerogel Cerenkov TOF S-S4 (diff. ns) plastic scintillators aerogel Cerenkov 3

39 outlook: search for η -mesic states in photo-nuclear reactions 1 C(γ,p) η GeV p η γ formation and decay of η -mesic state Δp/p 1- % BGO-OD ideally suited for exclusive measurement approved proposal: ELSA/3-1-BGO 4

40 outlook: search for η -mesic states in photo-nuclear reactions 1 C(γ,p) η GeV p η N γ η formation and decay of η -mesic state Δp/p 1- % BGO-OD ideally suited for exclusive measurement approved proposal: ELSA/3-1-BGO 4

41 outlook: search for η -mesic states in photo-nuclear reactions 1 1 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- % BGO-OD ideally suited for exclusive measurement approved proposal: ELSA/3-1-BGO 4

42 summary real and imaginary part of the ω and η -nucleus potential have been determined first (indirect) observation of an in-medium mass shift of the pseudo-scalar η meson by Δm(ρ=ρ) -3 MeV only weak attraction between ω, η mesons and nuclei ω: Im U > Re U not a good candidate for the search for mesic states η : Re U >> Im U good candidate for the search for mesic states first results on momentum dependence of the ω- and η -nucleus optical potential The run for η mesic states has started: photo-nuclear experiments: LEPS, BGO-OD: 1 C(γ, p) η 11 B N. Muaramtsu,T. Nakano hadronic pick-up reaction: FRS@GSI: 1 C(p,d) η 11 C K.Itahashi, H. Fujioka,Y. Tanaka 5

43 The real part of the η -nucleus potential η [µb] σ η' Mariana Nanova 35 Nb γa η X data compared to calculations by E. Paryev (priv. com.) excitation function VERY η' thr E γ V = MeV V = -5 MeV V = -5 MeV V = -75 MeV V = -1 MeV V = -15 MeV [GeV] V η (ρ=ρ) = -(±4(stat)±15(syst)) MeV E γ µb/gev/c] /dp η [' dσ η' η momentum distribution 5 Nb data E γ = GeV VERY V = MeV V = -5 MeV V = -5 MeV V = -75 MeV V = -1 MeV V = -15 MeV [GeV/c] V η (ρ=ρ) = -(38±5(stat)±15(syst)) MeV <p η > 1.1 GeV/c P η' 6