New experimental and simulated results on nuclear media effects in meson photoproduction off nuclei A.Ignatov, A.Mushkarenkov, V.Nedorezov for the GRAAL collaboration Institute for Nuclear Research RAS, Moscow

Motivations: Meson interaction with nuclear medium : -Unstable short living mesons; -Exotic nuclei (eta-mesic bound states etc); - New mechanisms of photo-nuclear interactions. -Intra-nuclear cascade

Break of the universal behavior of the total photoabsorption in heavy nuclei     N within 5% accuracy, except actinide nuclei: I.A. Pshenichnov, B.L.Berman, e.a. e-Print Archive: nucl- th/ First indication: A.A. Kazakov,e.a. JETP Lett.40: ,1984.

IDEA: correlation analysis of recoil nucleons [Moscow, EMIN-2001, p.170 ] M, MeV -Nucleus is the sum of quasi-free nucleons  detection + Complete kinematics -Low backgrounds  

Propagaion of mesons and nucleons in nuclear media: INC – Intra - Nuclear Cascade [Moscow, EMIN-2001, p.170 ] Probability of secondary interactions between meson and intra-nuclear nucleon : where  – cross section,  nuclear density ( 0.17 Fm -3 ), l – free mean pass.    el  in  Probability for zero and one interaction step within INC : The ratio = 6.7 for slow  –mesons (  =150 mb) Life time of unstable mesons depends on its velocity; for slow  – mesons the free mean pass l = 3 Fm.

INC prediction for different cascade steps [Moscow, EMIN-2001, p.170 ]

Simulations with LAGGEN+INC code for meson photoproduction on 14-N nucleus (  p = 2 0 – 10 0 ); multiple mesons (1-4) are included Correlations between energy of the recoil proton show that different meson regions are clearly separated [Moscow, EMIN-2001, p.170 ]

Correlations between momentum and angle of the primary INC proton show that different meson regions are clearly separated Simulations with LAGGEN+INC code for meson photoproduction on 14 N nucleus (E   1.5 GeV); multiple mesons (1-4) are included

GRAAL E  =600÷1500 МeV  E  =16 МeV P   100% NOT IN SCALE

LAGRAN  E Detector 1: Compton gamma beam, 2: Liquid H2/D2 target, 3: BGO Calorimeter 4: Cylindrical MWPC’s, 5: Plastic Barrel, 6: Plastic Wall, 7:Plane MWPCs, 8: Shower Wall Shower Wall neutron efficiency 20 %  / neutron PID

Deuteron target, E  = MeV,  =25 0, N charge tracks >= 1, SIMULATION EXPERIMENT (GRAAL DATA)

Deuteron target, E  = MeV,  >=25 0, N charge tracks >= 1, SIMULATION EXPERIMENT (GRAAL DATA)

gamma+p --> pi0+p gamma+n --> pi-+p gamma+p --> rho0+p gamma+n --> rho-+p gamma+p --> eta+p gamma+p --> omega+p Simulation: 2 D target Number of the charged tracks in forward >= 1 2<theta<1030<theta<402<theta<10

simulation Experiment Kinematics is not included Number of the charged tracks in forward = 1 Number of the neutral clusters in BGO = <theta<10 0

Number of the charged tracks in forward >= 1 gamma+d --> all channels gamma+p --> pi0+p gamma+n --> pi-+p gamma+p --> eta+p simulationexperiment

Number of the charged tracks in forward = 1 Number of the neutral clusters in BGO = 2 gamma+d --> all channels gamma+p --> pi0+p gamma+n --> pi-+p gamma+p --> eta+p simulationexperiment

Number of the charged tracks in forward >= 1 gamma+d --> all channels gamma+p --> pi0+p gamma+n --> pi-+p gamma+p --> eta+p simulationexperiment Egamma = MeV

Number of the charged tracks in forward = 1 Number of the neutral clusters in BGO = 2 gamma+d --> all channels gamma+p --> pi0+p gamma+n --> pi-+p gamma+p --> eta+p simulationexperiment Egamma = MeV

simulation gamma+p --> pi0+p gamma+n --> pi-+p gamma+p --> eta+p Number of the charged tracks in forward >= 1 Egamma = MeV

Number of the charged tracks in forward >= 1 simulationexperiment Egamma = MeV

Number of the charged tracks in forward = 1 Number of the neutral clusters in BGO = 2 simulationexperiment Egamma = MeV

Experiment on deutronSimulations done with INC code on 14 N nucleus Angle vs momentum correlation of primary recoil proton

GRAAL beam Low electromagnetic background Small low energy “tail”

GRAAL backgrounds Total yield after subtraction of the empty target contribution : Experiment & Simulation

Total photoabsorption cross section on the free proton (neutron) is the sum of the meson production cross sections (GRAAL data) subm.to Rus.J.N.P.

Simulations for 14 N (E  =0.8 GeV) (  p)    Correlation between momentums of the recoil proton and secondary particles. The region of meson photoproduction without final state interaction can be clearly seen at the bottom of each distribution. Other regions correspond to higher number of steps of the reaction.

Conclusion: GEANT-INC simulations show that modern facilities like GRAAL can be used to study meson (at least eta) photoproduction on nuclei using the Tagging meson method: Recoil protons from  and  photoproduction, measured in forward direction, can provide the identification of the reaction initial step. Preliminary analysis of the experimental GRAAL data for the deuteron confirms possibility to use the “tagging meson” method for heavier nuclei. The optimal candidate is 14 N.