Determination of the - and '-nucleus optical potential Mariana - PowerPoint PPT Presentation

Determination of the ω - and η '-nucleus optical potential Mariana Nanova for the CBELSA/TAPS Collaboration Outline: ◆ motivation ◆ exp. approaches to study the in-medium properties of mesons ◆ experimental results on the real and imaginary part of the ω - and η ’-nucleus optical potential ◆ summary & outlook MESON2016 Cracow, 2th - 7th June 2016 *funded by the DFG within SFB/TR16

baryons and mesons ◆ QCD vacuum as a Bose-Einstein condensate of qq − ◆ all states (particles) are created out of the vacuum state (“excitations of the QCD-vacuum”) ◆ the ground-state structure influences the particle properties if the QCD ground state changes in a medium ⇒ properties of hadrons (“excited states”) are also expected to change 2

hadrons in the medium how do the hadron properties (mass, width) change in a dense nuclear medium ?? pioneering papers: V. Bernard and U.-G. Meißner, NPA 489 (1988) 647 “Brown-Rho Scaling” m ≈ < ¯ m ? qq > ? G.E.Brown and M. Rho, ≈ 0 . 8( ρ ≈ ρ 0 ) < ¯ PRL 66 (1991) 2720 qq > 0 T.Hatsuda and S. Lee, m � = (1 − α ρ V ); α ≈ 0 . 18 PRC 46 (1992) R34 m V ρ 0 QCD sum rule approach: drop of ρ , ω mass by about 15% at ρ = ρ 0 widespread theoretical and experimental activities to search for in-medium modifications of hadrons 3

hadronic models: predictions for η ’ in-medium mass NJL-model NJL-model linear σ model H. Nagahiro et. al, V. Bernard and U.-G. Meissner, S. Sakai and D. Jido Phys. Rev. C 74 (2006) 045203 Phys. Rev.D 38 (1988) 1551 PRC 88 (2013) 064906 SU(3) SU(2) Δ m η ’ ( ρ 0 ) ≈ − 80 MeV QMC-model S. Bass and A. Thomas, almost no dependence of Δ m η ’ ( ρ 0 ) ≈ − 150 MeV PLB 634 (2006) 368 η ’ mass on density Δ m η ( ρ 0 ) ≈ +20 MeV Δ m η ’ ( ρ 0 ) ≈ − 40 MeV for θ ηη ’ = − 20 0 4

hadronic models: predictions for ω -spectral functions F. Klingl et al., M. Lutz et al., NPA 610 (1997) 297; NPA 706 (2002) 437 P . Mühlich et al., NPA 780 (2006) 187 NPA 650 (1999) 299 spectral function for ω meson splitting into ω -like ◆ lowering of in-medium mass at rest: and N*N -1 mode ◆ broadening of resonance almost no mass shift; due to coupling to with increasing nuclear density strong in-medium broadening nucleon resonances Re(U) ≠ 0; Im(U) ≠ 0 Re(U) ≈ 0; Im(U) large mass shift ? experimental task: search for { } broadening? of hadronic spectral functions structures? 5

meson-nucleus optical potential H. Nagahiro an S. Hirenzaki, U ( r ) = V ( r ) + iW ( r ) PRL 94 (2005) 232503 W ( r ) = − Γ 0 / 2 · ρ ( r ) V ( r ) = ∆ m ( ρ 0 ) · ρ ( r ) ρ 0 = − 1 2 · ~ c · ρ ( r ) · σ inel · β ρ 0 real part imaginary part ⬄ ⬄ lifetime shortened in-medium mass modification in-medium width, absorption inelastic cross section mass and lifetime (width) may be changed in the medium 6

experimental approaches to determine the meson-nucleus optical potential U ( r ) = V ( r ) + iW ( r ) imaginary part real part W ( r ) = − Γ 0 / 2 · ρ ( r ) V ( r ) = ∆ m ( ρ 0 ) · ρ ( r ) ρ 0 ρ 0 = − 1 2 · ~ c · ρ ( r ) · σ inel · β ◆ line shape analysis ◆ transparency ratio measurement ◆ excitation function ◆ momentum distribution σ γ A → η 0 X T A = ◆ meson-nucleus bound states A · σ γ N → η 0 X D. Cabrera et al., NPA 733 (2004)130 7

CBELSA/TAPS experiment ω→π 0 γ→ 3 γ E γ =0.7-3.1 GeV E γ =0.7 - 3.1 GeV MiniTAPS )] 2 [1/(4 MeV/c 2 m=792.5 ± 0.4 MeV/c Forward Plug C photon beam 216 BaF 2 2 σ =25.8 ± 0.3 MeV/c 4 10 γ 0 π N σ m σ m ≈ 3% m ≈ 3% m 64456 counts 64456 counts 3 10 600 650 700 750 800 850 900 950 2 M [MeV/c ] Crystal Barrel 0 π γ η ’ →π 0 π 0 η→ 6 γ 1320 CsI )] 2 1800 [1/(6 MeV/c 2 Nb m=957.6 0.5 MeV/c ± 2 1600 =11.8 0.3 MeV/c σ ± 1400 η 0 solid target: 12 C and 93 Nb π 0 1200 3177 counts π N 1000 4 π photon detector: ideally suited for 800 identification of multi-photon final states 600 σ m ω→π 0 γ→ 3 γ BR 8.2 % 400 3177 counts ≈ 1% m 200 η ’ →π 0 π 0 η→ 6 γ BR 8.5% 0 850 900 950 1000 1050 1100 1150 8 2 M [MeV/c ] 0 0 π π η

The real part of the meson-nucleus optical potential 9

the real part of the ω -nucleus potential ω→π 0 γ J. Weil, U. Mosel and V. Metag, PLB 723 (2013 ) 120 sensitive to nuclear density at production point and not at decay point ◆ measurement of the excitation function ◆ momentum distribution of the meson: of the meson in case of dropping mass - when leaving the in case of dropping mass - nucleus hadron has to become on-shell; higher meson yield for given √ s mass generated at the expense of kinetic because of increased phase space energy due to lowering of the production threshold ➯ downward shift of momentum distribution ➯ cross section enhancement π 0 γ momentum distribution π 0 γ excitation function γ + 93 Nb →π 0 γ +X E γ =0.9-1.3 GeV E γ thr 10

excitation function for ω photoproduction off C comparison with GiBUU calculation CB/TAPS @ MAMI V. Metag et al., PPNP , 67 (2012) 530 M. Thiel et al., EPJA 49 (2013) 132 excitation function momentum distribution b] Carbon Carbon µ /A [ σ -1 ★ CB/TAPS@MAMI 10 ● CBELSA/TAPS GiBUU collisional broad. vacuum and mass shift collisional broadening(CB) V = 0 MeV CB+mass shift (-16%) V = -20 MeV -2 mass shift (-16%) V = -40 MeV 10 V = -55 MeV V = -94 MeV E γ thr V = -125 MeV 0.9 1 1.1 1.2 1.3 1.4 E [GeV] γ V( ρ = ρ 0 ) = − (42±17(stat)±20(syst)) MeV data not consistent with strong mass shift scenario ( Δ m/m ≈ -16%) 11

excitation function and momentum distribution for η ' photoproduction off C CBELSA/TAPS @ ELSA data: M. Nanova et al., PLB 727 (2013) 417 γ C →η ’X calc.: E. Paryev, J. Phys. G 40 (2013) 025201 10 d σ η ’ /dp η ’ [ µ b/GeV/c] σ η ’ [ µ b] σ η ’ [ µ b] C data C data E γ =1500-2200 MeV σ tot σ diff 1 1 V( ρ = ρ 0 ) = 0 MeV σ η ’N =11 mb V( ρ = ρ 0 ) = -25 MeV V( ρ = ρ 0 ) = 0 MeV V( ρ = ρ 0 ) = -50 MeV V( ρ = ρ 0 ) = -25 MeV V( ρ = ρ 0 ) = -75 MeV V( ρ = ρ 0 ) = -100 MeV V( ρ = ρ 0 ) = -50 MeV V( ρ = ρ 0 ) = -150 MeV V( ρ = ρ 0 ) = -75 MeV -1 V( ρ = ρ 0 ) = -100 MeV -1 10 σ η ’N =11 mb 10 V( ρ = ρ 0 ) = -150 MeV E γ thr 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 1000 1500 2000 2500 p η ’ [GeV/c ] E γ [MeV] E γ [MeV] V η ’ (p η ’ ≈ 1.1 GeV/c; ρ = ρ 0 ) = − (32±11) MeV V η ’ ( ρ = ρ 0 ) = − (40±6) MeV data disfavour strong mass shifts 12

excitation function and momentum distribution for η ' photoproduction off Nb CBELSA/TAPS @ ELSA γ Nb →η ’X M. Nanova et al., submitted to PRC for publication b] b/GeV/c] Nb Nb E =1.3 - 2.6 GeV µ γ [ σ ' η tot σ σ diff µ 10 / [ ' η P R E L I M I N A R Y /dp 10 σ ' η d ' η = 14 mb σ = 14 mb σ inel inel P R E L I M I N A R Y V( = ) = 0 MeV ρ ρ V( = ) = 0 MeV ρ ρ 0 0 V( = ) = - 25 MeV V( = ) = - 25 MeV ρ ρ ρ ρ 0 0 V( = ) = - 50 MeV ρ ρ V( = ) = - 50 MeV ρ ρ 0 0 V( = ) = - 75 MeV ρ ρ V( = ) = - 75 MeV ρ ρ 0 0 V( = ) = -100 MeV 1 ρ ρ V( = ) = -100 MeV ρ ρ 0 0 V( = ) = -150 MeV ρ ρ ' thr η 1 E V( = ) = -150 MeV ρ ρ 0 γ 0 1 1.5 2 2.5 0.5 1 1.5 2 2.5 p [GeV/c] E [GeV] γ ' η V η ' (p η ' ≈ 1.14 GeV/c; ρ = ρ 0 ) = − (41±22) MeV V η ' ( ρ = ρ 0 ) = − (46±15) MeV data disfavour strong mass shifts 13

real part of ω -nucleus potential from ω kinetic energy ω CBELSA/TAPS @ ELSA γ E γ =1.25-3.1 GeV p 1 0 ≤θ p ≤ 11 0 the higher the attraction the lower the kinetic energy of the ω meson H. Nagahiro, priv. com. S. Friedrich et al., PLB 736 (2014) 26 [nb/MeV/sr] 90 1.5 [nb/MeV/sr] peak position [MeV] 2.2 Carbon d) 80 2.1 � � d � kin 1 2 Ω /dE 70 d kin � 1.9 0 � � /dE � � 2 � d 60 γ 1.8 0 π 0.5 σ 2 d 1.7 50 (V , W ) 1.6 0 0 - (156,70) MeV 0 - (100,70) MeV 40 1.5 - ( 50,70) MeV - ( 0,70) MeV - (-20,70) MeV 1.4 - (-50,70) MeV E kin =(60.5±7)MeV 30 -0.5 20 30 40 50 60 70 80 90 -150 -100 -50 0 50 E -782 [MeV] 0 potential depth [MeV] π γ -300 -200 -100 0 100 200 300 400 E -782 [MeV] 0 � � � � V ω (p ω ≈ 300 MeV/c; ρ = ρ 0 ) = − (15 ±35 ) MeV 14

compilation of results for the real part of the ω - and η ’-nucleus optical potential ω η ’ C C excitation function excitation function Nb mom. distribution peak E kin average weighted average 80 60 40 20 0 20 − − − − 80 60 40 20 0 − − − − V [MeV] V [MeV] η 'A 'A η V ω A ( ρ = ρ 0 ) = V η ’A ( ρ = ρ 0 ) = − (29±19(stat)±20(syst)) MeV − (40±8(stat)±15(syst)) MeV 15

The imaginary part of the meson-nucleus optical potential: momentum dependence 16

momentum differential cross section for ω , η ’ produced off C, Nb E γ = 1.2- 2.9 GeV η ’ ω γ C,Nb → ω X γ C,Nb →η ’X 2.5 b/(GeV/c)] 0.25 b/(GeV/c)] C C Nb 2 Nb 0.2 µ µ /A [ /A [ ω /dp ' η /dp 1.5 0.15 σ σ d d P R E L I M I N A R Y P R E L I M I N A R Y 1 0.1 0.5 0.05 0 0 0 500 1000 1500 2000 2500 0 500 1000 1500 2000 2500 p [MeV/c] p [MeV/c] ω ' η T Nb/C (p m ) = 12 ⦁ σ γ Nb → mX (p m ) m momentum differential cross sections ⇒ 93 ⦁ σ γ C → mX (p m ) 17