-nucleus optical potential and the search for mesic states in - PowerPoint PPT Presentation

η ’-nucleus optical potential and the search for η ’ mesic states in photo nuclear reactions Mariana Nanova II. Physikalisches Institut for CBELSA/TAPS Collaboration Outline: ◆ motivation ◆ experimental approaches for determining the η ’-nucleus optical potential: - imaginary part of the potential - transparency ratio measurement - real part of the potential: excitation function of the η ’-meson momentum distribution ◆ search for η ’-nucleus bound states ◆ summary *funded by the DFG within SFB/TR16 YITP Workshop on Hadron in Nucleus, 31st Oct.-2nd Nov. 2013, Kyoto, Japan 1

search for η ’-meson-nucleus bound states prediction of η ’- 12 C bound states and their width for different η ’ -meson nucleus potentials D. Jido et al., PRC 85 (2012) 032201 U( ρ ) = V( ρ ) + i W( ρ ) many states with width Γ << binding energy predicted more strongly bound states for deeper potentials W( ρ 0 ) ≈ -10 MeV from M. Nanova et al., PLB 710 (2012) 600 2

Experimental approaches to determine the meson-nucleus optical potential meson-nucleus optical potential U ( r ) = V ( r ) + iW ( r ) meson mass shift meson absorption V ( r ) = ∆ m ( ρ 0 ) · ρ ( r ) W ( r ) = − Γ 0 / 2 · ρ ( r ) ρ 0 ρ 0 = − 1 2 · ~ c · ρ ( r ) · σ inel · β line shape analysis: direct determination of Δ m Transparency ratio measurement excitation function: σ γ A ! η 0 X T A = provides information about the depth of V(r) A · σ γ N ! η 0 X experimental observable to extract meson momentum distribution: the in-medium width of the meson provides information about the depth of V(r) meson-nucleus-bound states: direct determination of E bin ( Δ m) 3

Crystal Barrel/TAPS@ELSA Experiment http://www.cb.uni-bonn.de photoproduction of η ’ meson beamtime 2003 beamtime 2009 E γ =0.7-3.1 GeV E γ =0.5-2.6 GeV MiniTAPS photon beam Forward Plug photon beam Crystal Barrel Crystal Barrel TAPS solid target: 12 C, 40 Ca, 93 Nb and 208 Pb solid target: 12 C 4 π photon detector: ideally suited for identification of multiphoton final states η ’ →π 0 π 0 η → 6 γ BR 8.1% 4

The imaginary part of the η ’-nucleus potential photoproduction of η ’ meson off 12 C, 40 Ca, 93 Nb and 208 Pb E γ = 1500 - 2200 MeV; 12 · σ γ A ! η 0 X normalized to carbon T C A = A · σ γ C ! η 0 X comparison with other mesons M. Nanova et al., PLB 710 (2012) 600 T A C T A E � =1.7 GeV 1 1 0.9 0.8 � ’ 0.9 0.7 0.6 0.8 � 0.5 � ’exp data � ( � 0 )=10 MeV 0.4 0.7 � ( � 0 )=15 MeV � � ( � 0 )=20 MeV � ( � 0 )=25 MeV � ( � 0 )=30 MeV 0.3 � ( � 0 )=35 MeV 0.6 � ( � 0 )=40 MeV 2 2 A 10 10 10 10 A η ’ interaction with nuclear matter at low density approximation: much weaker than for η , ω Γ ( ρ ) = Γ ( ρ 0 ) ρ Γ ( ρ ) = − Im Π ( ρ ) ∼ ρ v σ inel ; mesons ρ 0 E ➱ Γ η ’ (< ⎮ p η ’ ⎮ > ≈ 1.05 GeV/c ) ≈ 15-25 MeV; W( ρ = ρ 0 )= - Γ 0 /2 = - (7.5-12.5) MeV ρ 0 =0.17 fm -3 ; σ η ’inel ≈ 3 -10 mb 5

The real part of the η ’-nucleus potential J. Weil, U. Mosel and V. Metag, PLB 723 (2013 ) 120 E. Paryev, J. Phys. G: Nucl. Part. Phys. 40 (2013) 025201 based on γ p → η ’p and γ n → η ’n exp. data - measurement of the momentum distribution - measurement of the excitation function of of the meson: 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 10 100 10 100 12 C-> η ’X 93 Nb-> η ’X γ 1 10 γ 12 C-> η ’X d σ γ Nb-> η ’X /dp η ’ [ µ b/(GeV/c)] γ d σ γ C-> η ’X /dp η ’ [ µ b/(GeV/c)] 93 Nb-> η ’X γ E γ =1.5-2.2 GeV σ γ C-> η ’X [ µ b] σ γ Nb-> η ’X [ µ b] E γ =1.5-2.2 GeV 1 10 0.1 1 Coll. Broadening Coll. Broadening ( σ η ’N =8 mb) ( σ η ’N =8 mb) Coll. Broadening Coll. Broadening Coll. Broadening + ( σ η ’N =8 mb) ( σ η ’N =8 mb) Coll. Broadening + 0.01 0.1 Mass Shift (-5%) Mass Shift (-5%) Coll. Broadening + Coll. Broadening + Mass Shift (-5%) Mass Shift (-5%) E thr E thr γ N γ N 0.1 1 1E-3 0.01 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 1.0 1.2 1.4 1.6 1.8 2.0 2.2 1.0 1.2 1.4 1.6 1.8 2.0 2.2 p η ’ [GeV/c] E γ [GeV] p η ’ [GeV/c] E γ [GeV] 6

excitation function for η ’ photoproduction off C comparison of CBELSA/TAPS data with calculations by E. Paryev, J. Phys. G: Nucl. Part. Phys. 40 (2013) 025201 and priv. communication decay mode: η ’ → π 0 π 0 η exp. data and the 5 scenarios divided by the excitation function V( ρ = ρ 0 )=0 MeV calculation for scenario 10 � � ’ [ µ b] � � ’ [ µ b] C data � tot ratio � diff 5 V( � = � 0 ) = 0 MeV V( � = � 0 ) = -25 MeV 4 V( � = � 0 ) = -50 MeV 1 V( � = � 0 ) = 0 MeV V( � = � 0 ) = -75 MeV V( � = � 0 ) = -100 MeV V( � = � 0 ) = -25 MeV 3 V( � = � 0 ) = -50 MeV V( � = � 0 ) = -150 MeV V( � = � 0 ) = -75 MeV V( � = � 0 ) = -100 MeV 2 V( � = � 0 ) = -150 MeV -1 10 E � thr 1 E � thr 1000 1500 2000 2500 1500 2000 2500 E � [MeV] E � [MeV] E � [MeV] strong mass shift not supported by data calculations normalized to data for E γ = 2000-2500 MeV; downscaled by 1.2 7

estimation of the real part of the η ’-nucleus potential from the η ’ excitation function M. N. et al., paper accepted for publication in PLB significance test excitation function � 2 /f 10 30 � � ’ [ µ b] � � ’ [ µ b] C data � tot � diff 25 20 1 V( � = � 0 ) = 0 MeV 15 V( � = � 0 ) = -25 MeV V( � = � 0 ) = -50 MeV V( � = � 0 ) = -75 MeV 10 V( � = � 0 ) = -100 MeV V( � = � 0 ) = -150 MeV σ η ’N =11mb -1 5 10 E � thr 0 1000 1500 2000 2500 -150 -100 -50 0 potential depth [MeV] E � [MeV] E � [MeV] χ 2 -fit of the data with the calculated excitation functions V( ρ = ρ 0 ) = -40±6 MeV for the 6 scenarios 8

experimental data on η ’ photoproduction off 12 C η ’ →π 0 π 0 η → 6 γ E γ = 1250 - 2600 MeV BR: 8.1% sensitivity to different scenarios E. Ya. Paryev, priv. communication below threshold at threshold above threshold 1250-1350 MeV 1550-1600 MeV 1800-1900 MeV 4 4 V = 0 MeV 1 V = -25 MeV; 2 2 V = -50 MeV 0 V = -75 MeV 0 0 d � /d(cos � � ’ ) [ µ b] d � /d(cos � � ’ ) [ µ b] d � /d(cos � � ’ ) [ µ b] 1600-1700 MeV 1900-2000 MeV 1350-1450 MeV 5 5 V = -100 MeV; 2 V = -150 MeV 2.5 2.5 0 0 0 1450-1550 MeV 1700-1800 MeV 2100-2200 MeV 5 5 2 2.5 2.5 0 0 0 -1 -0.5 0 0.5 1 -1 -0.5 0 0.5 1 -1 -0.5 0 0.5 1 cos( � � ’ ) cm cos( � � ’ ) cm cos( � � ’ ) cm high sensitivity to different scenarios at threshold strong mass shift not supported by data 9

η ’ momentum distribution off C comparison of CBELSA/TAPS data with calculations by E. Paryev, J. Phys. G: Nucl. Part. Phys. 40 (2013) 025201 and priv. communication exp. data and the 5 scenarios divided by the momentum distribution V( ρ = ρ 0 )=0 MeV calculation for scenario d � � ’ /dp � ’ [ µ b/GeV/c] 10 C data E � =1500-2200 MeV ratio E � =1500-2200 MeV 8 1 C data 6 V( � = � 0 ) = 0 MeV V( � = � 0 ) = -25 MeV V( � = � 0 ) = 0 MeV V( � = � 0 ) = -50 MeV V( � = � 0 ) = -75 MeV V( � = � 0 ) = -25 MeV 4 V( � = � 0 ) = -100 MeV V( � = � 0 ) = -50 MeV V( � = � 0 ) = -150 MeV V( � = � 0 ) = -75 MeV -1 V( � = � 0 ) = -100 MeV 10 2 V( � = � 0 ) = -150 MeV 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 0 0.5 1 1.5 p � ’ [GeV/c ] p � ’ [GeV/c ] calculation normalized to data in p = 1.5-1.8 GeV/c, downscaled by 1.2 V( ρ = ρ 0 ) ≈ -50 MeV ➯ attractive! data favour 10

estimation of the of η ’-nucleus potential depth from the η ’ momentum distribution � 2 /f d � � ’ /dp � ’ [ µ b/GeV/c] C data E � =1500-2200 MeV 10 8 1 6 V( � = � 0 ) = 0 MeV 4 V( � = � 0 ) = -25 MeV V( � = � 0 ) = -50 MeV V( � = � 0 ) = -75 MeV -1 V( � = � 0 ) = -100 MeV 2 10 V( � = � 0 ) = -150 MeV 0 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 -150 -100 -50 0 potential depth [MeV] p � ’ [GeV/c ] V( ρ = ρ 0 ) = -32±11 MeV consistent with predictions by: S. Bass and A.W.Thomas, Acta Phys. Pol. B 41 (2010) 2239 H. Nagahiro et al., PLB 709 (2012) 87. W( ρ = ρ 0 ) = -10±2.5 MeV, M. Nanova et al., PLB 710 (2012) 600. ⎮ V ⎮ >> ⎮ W ⎮ ! ➯ search for η ’ mesic states promising 11

excitation function for η ’ photoproduction off Nb data will be taken with CB/TAPS detector system at ELSA Nov. 2013 / Jan. 2014 E. Paryev, private communication excitation function momentum distribution 10 2 d � � ’ /dp � ’ [ µ b/GeV/c] � � ’ [ µ b] Nb E � =1500-2200 MeV Nb 10 10 V( � = � 0 ) = 0 MeV V( � = � 0 ) = -25 MeV V( � = � 0 ) = 0 MeV 1 V( � = � 0 ) = -50 MeV V( � = � 0 ) = -25 MeV V( � = � 0 ) = -75 MeV V( � = � 0 ) = -50 MeV V( � = � 0 ) = -100 MeV V( � = � 0 ) = -75 MeV V( � = � 0 ) = -150 MeV 1 V( � = � 0 ) = -100 MeV σ η ’N =11mb V( � = � 0 ) = -150 MeV -1 10 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 1 1.5 2 2.5 3 p � ’ [GeV/c ] E � [MeV] 12