Beijing, Sept 2nd 2004 Rachele Di Salvo Beam asymmetry in meson photoproduction on deuteron targets at GRAAL MENU2004 Meson-Nucleon Physics and the Structure of the Nucleon August 29th - Sep 4th 2004, Beijing (China) Rachele Di Salvo presented by Rachele Di Salvo On behalf of the GRAAL Collaboration I.N.F.N. – Sezione Roma2

Beijing, Sept 2nd 2004 Rachele Di Salvo Outline  The GRAAL experimental set-up  Physics motivations  Preliminary results for:  in ,  0 photoproduction on q.f. proton and q.f.neutron in deuteron  Update on search on pentaquark in:  n  n (P 11 )  d     Summary and Conclusions

Beijing, Sept 2nd 2004 Rachele Di Salvo The Graal facility is a backscattering photon facility located at the E.S.R.F. (Grenoble, France)

Beijing, Sept 2nd 2004 Rachele Di Salvo Main GRAAL features Production technique: Compton backscattering of laser light on electrons Energy range: 0.5  1.5 GeV e-e- e-e- E e,m e E ’ e, m e EE ELEL LL  Energy resolution: 1.1% (FWHM) High polarization degree (  100% for the higher energies)  Photon beam 1ch=50 ps  =147ps Monitoring of the flux

Beijing, Sept 2nd 2004 Rachele Di Salvo Photon detection (energy resolution 3% FWHM at 1 GeV) Charged particle identification and reconstruction (proton - pions) Energy measurement for protons Neutron detection (and energy measurement in forward direction)  Experimental Apparatus

Beijing, Sept 2nd 2004 Rachele Di Salvo The Graal detector: Lagran  e Large Acceptance Graal Apparatus for Nuclear  Experiments

Beijing, Sept 2nd 2004 Rachele Di Salvo Physics motivations In the resonance region perturbative QCD cannot be applied. The processes can be described in terms of effective theories based on a certain number of experimental constraints for the determination of static and dynamical properties of N* resonances: mass M, width , helicity amplitudes A 1/2 and A 3/2, partial decay widths   n,   n,  YK. 1) Precise measurements of differential cross sections and asymmetries in meson photoproduction on the nucleon are necessary 2) Measurements in neutron targets (deuteron) are necessary for a study of the isospin structure of photoexcitation amplitudes.

Beijing, Sept 2nd 2004 Rachele Di Salvo  +p+(n) ->  +  p+(n) To be compared with  photoproduction on free proton  +n+(p) ->  +  n+(p)  p ->  +  p  photo-production on quasi-free nucleons from Deuteron

Beijing, Sept 2nd 2004 Rachele Di Salvo  +p+(n)->  +p+(n) 2 2  Events selection (1) 1 neutron in central or forward direction NO charged particle (the proton is spectator) 1 proton in central or forward direction NO other neutral particle (the neutron is spectator) 2  in BGO (  invariant mass)  +n+(p)->  +n+(p) 2 2 

Beijing, Sept 2nd 2004 Rachele Di Salvo Invariant mass of 2  in BGO 0.45  M   0.65 GeV Bidimensional cut on  -nucleon coplanarity vs.    miss = Polar angle of the particle missing from  in 2-body kinematics  N = Nucleon polar angle    =  miss -  N Bidimensional cut on (M miss,  -M N ) vs. (M miss,N -M  ) M miss,  N  = Mass of missing particle from  (Nucleon) N.B. For the central neutron: M miss n obtained by the |p n | extracted by two body kinematics +  n and  n measured in the BGO detector Events selection (2)

Beijing, Sept 2nd 2004 Rachele Di Salvo Events selection (2): Two body reaction  Proton  miss -  p (deg)   -  p (deg)  miss -  n (deg)   -  n (deg) Neutron

Beijing, Sept 2nd 2004 Rachele Di Salvo M miss  (GeV) M miss N (GeV) Forward nucleon M miss N (GeV) M miss  (GeV) Proton Neutron Central nucleon Events selection (2)

Beijing, Sept 2nd 2004 Rachele Di Salvo  Invariant Mass Before cuts After cuts  Mass (GeV) Proton Neutron

Beijing, Sept 2nd 2004 Rachele Di Salvo Azimuthal Distribution:  Proton Neutron

Beijing, Sept 2nd 2004 Rachele Di Salvo  first  results on q.f.proton  +p+(n)->  +p+(n) Green Laser Line UV Laser Line Said- BO12 N.B. Error bars: statistical errors only Maid Preliminary

Beijing, Sept 2nd 2004 Rachele Di Salvo Preliminary Said- BO12 (free proton) Maid (free proton) Comparison  photoproduction on  + p ->  + p Free proton Quasi free proton  + p (n) ->  + p (n)

Beijing, Sept 2nd 2004 Rachele Di Salvo Maid (free proton) Maid (free neutron)  first  results on q.f.neutron  +n+(p)->  +n+(p) Green Line UV Line N.B. Error bars: statistical errors only Preliminary

Beijing, Sept 2nd 2004 Rachele Di Salvo Quasi free neutron Quasi free proton  + p (n) ->  + p (n)  + n (p) ->  + n (p) Comparison  photoproduction on Preliminary

Beijing, Sept 2nd 2004 Rachele Di Salvo  +p+(n) ->  0  +  p+(n) To be compared with  0 photoproduction on free proton  +n+(p) ->  0  +  n+(p)  p ->  0  +  p  0 photo-production on quasi-free nucleons from Deuteron

Beijing, Sept 2nd 2004 Rachele Di Salvo  +p+(n)->  0 +p+(n) 2 2  Events selection (1) 1 neutron in central or forward direction NO charged particle (the proton is spectator) 1 proton in central or forward direction NO other neutral particle (the neutron is spectator) 2  in BGO (  0 invariant mass)  +n+(p)->  0 +n+(p) 2 2 

Beijing, Sept 2nd 2004 Rachele Di Salvo Invariant mass of 2  in BGO M   0.25 GeV Bidimensional cut on  -nucleon coplanarity vs.   Bidimensional cut on (M miss,  -M N ) vs. (M miss,N -M  ) for forward nucleons Bidimensional cut on (E calc,N -E calc’,N ) vs. (M miss,  -M N ) for central nucleons E calc,N = Nucleon energy extracted from energy conservation E calc,N = E  + M N - E  E calc’,N = Nucleon energy extracted from 2-body kinematics E calc’,N (E  ,  N,  N ) Events selection (2)

Beijing, Sept 2nd 2004 Rachele Di Salvo Events selection (2): Two body kinematics  miss -  N (deg)   -  N (deg) Before cut After cut  miss -  N (deg)

Beijing, Sept 2nd 2004 Rachele Di Salvo Events selection (2) M miss N -M  ° GeV) M miss  ° -M N (Gev) Forward proton/neutron Before cut After cut M miss  ° -M N (Gev) M missN -M  ° GeV)

Beijing, Sept 2nd 2004 Rachele Di Salvo Events selection (2) Central proton/neutron Before cut After cut Ecalc N – Ecalc’ N (GeV) M miss  ° -M N (Gev) Ecalc N – Ecalc’ N (GeV) M miss  ° -M N (Gev)

Beijing, Sept 2nd 2004 Rachele Di Salvo Green Line Said- SM02 UV Line Maid Preliminary N.B. Error bars: statistical errors only Sistematic errors  1.5%  first  results on q.f.proton  +p+(n)->  0 +p+(n)

Beijing, Sept 2nd 2004 Rachele Di Salvo Said- FA01 (free proton) GRAAL data included up to 1.1 GeV Said - WI00 (free proton) GRAAL data NOT included Comparison  0 photoproduction on  + p ->  0 + p Free proton Quasi free proton  + p (n) ->  + p (n) (uv data) (green data) Preliminary

Beijing, Sept 2nd 2004 Rachele Di Salvo  first  results on q.f.neutron  +n+(p)->  0 +n+(p) Green Line UV Line Said (free neutron) Maid (free neutron) N.B. Error bars: statistical errors only Sistematic errors  1.5% Preliminary

Beijing, Sept 2nd 2004 Rachele Di Salvo Comparison  0 photoproduction on Quasi free proton  + p (n) ->  + p (n) Quasi free neutron  + p (n) ->  + p (n) Low energy bins Preliminary

Beijing, Sept 2nd 2004 Rachele Di Salvo Comparison  0 photoproduction on Quasi free proton  + p (n) ->  + p (n) Quasi free neutron  + p (n) ->  + p (n) High energy bins Preliminary

Beijing, Sept 2nd 2004 Rachele Di Salvo Conclusions (1)  First results have been obtained on the analysis of the  and  o photoproduction on the quasi-free proton and neutron on a deuteron target: Asymmetry results show:  photoproduction: qfp and free proton similar behavior qfn and qfp similar behavior  o photoproduction: qfp and free proton similar behavior qfn and qfp different behaviour at higher energy bins: NO change of sign for neutron

Beijing, Sept 2nd 2004 Rachele Di Salvo  + n    +    vs  + d    +  REACTION 1 Threshold 1738 MeV REACTION 2 Threshold 941 MeV ++ ++ ++ ++ ++ ++ It is accessible at lower incoming  energies

Beijing, Sept 2nd 2004 Rachele Di Salvo    Photo-production Decays  + d    +   K° p  - p       + d           p

Beijing, Sept 2nd 2004 Rachele Di Salvo  ° Invariant Masses  + d    +  VERY PRELIMINARY  ° 1 Invariant Mass GeV  ° 2 Invariant Mass GeV

Beijing, Sept 2nd 2004 Rachele Di Salvo X-Y Vertex  + d     VERY PRELIMINARY y (cm) x (cm)

Beijing, Sept 2nd 2004 Rachele Di Salvo VERY PRELIMINARY cm   Z Vertex  + d    

Beijing, Sept 2nd 2004 Rachele Di Salvo  theta vs. phi  + d     VERY PRELIMINARY

Beijing, Sept 2nd 2004 Rachele Di Salvo M  vs M K°  + d     VERY PRELIMINARY

Beijing, Sept 2nd 2004 Rachele Di Salvo VERY PRELIMINARY 1531 Mev   invariant mass from enlarged statistics Very Preliminary

Beijing, Sept 2nd 2004 Rachele Di Salvo N5(1710) or P11(1710) From a recent paper of Polyakov “On photoexcitation of baryon antidecuplet” HEP-PH/ ; Eur. Phys.J. A18, (2003)) the photoexcitation of the P11 in the  -channel should be much more strongly pronounced on the neutron than on the proton:  + n (p) ->  + n (p)  + p (n) ->  + p (n)

Beijing, Sept 2nd 2004 Rachele Di Salvo The  -nucleon invariant mass in the final state of the reactions:  + d ->  + n + (p)  + d ->  + p + (n) Data Simulation The N 5 (1715) dduuu Final State VERY PRELIMINARY Do not quote Very Preliminary

Beijing, Sept 2nd 2004 Rachele Di Salvo The  -nucleon invariant mass calculated from the energy of the incoming gamma ray:  + d ->  + n + (p)  + d ->  + p + (n) Data Simulation The N 5 (1715) dduuu Initial State VERY PRELIMINARY Do not quote Very Preliminary

Beijing, Sept 2nd 2004 Rachele Di Salvo Conclusions WORK IN PROGRESS on the two promising channels:  + d      + n (p)  N 5   n (p) More results are expected in the near future from new data taking Future: Data taking with a polarized HD target