1. Latest results from GRAAL collaboration
Workshop on the Physics of Excited Nucleon – NSTAR 2009, Beijing
Latest results from GRAAL collaboration
presented by
Valentina Vegna
on behalf of the GRAAL Collaboration
Università degli Studi di Roma “Tor Vergata” and INFN Sezione di Roma Tor Vergata
the GRAAL experimental set-up;
 and 0 photoproduction on quasi-free neutron;
K+ and K+0 photoproduction on free proton;
in memoriam of Eid Hourany.

2. Meson Photoproduction at GRAAL
GRAAL/ESRF
Beam Asymmetry Measurements for accessible reactions:
polarized photon beam;
large acceptance apparatus;
tagged photon beam.
s (mb)
E (GeV)
’ threshold
K threshold
 threshold

3. GRAAL Polarized and Tagged Photon Beam
green line e-
Ee,me
E’e, me Eg EL gL g
UV line
Ee= 6 GeV
EL= 2.41 eV (green line, l = 514 nm)
EL= 3.53 eV (U.V. line, l = 351 nm)
Egmax= 1.1 GeV
Egmax= 1.5 GeV
Tagger
Energy Spectrum
Energy Resolution
16 MeV FWHM

4. GRAAL Detector Photon detection (energy resolution 3% FWHM at 1 GeV);
NOT IN SCALE
Photon detection (energy resolution 3% FWHM at 1 GeV);
Charged particle identification (protons - pions);
Energy measurement for protons;
Neutron detection (and energy measurement in forward direction).

5.  Measurement at GRAAL
Experimental Distribution at fixed E and mCM:

6.  Photoproduction on Quasi-Free Nucleon in Deuteron
A.Fantini et al., Phys.Rev.C 78, (2008) 1 3
Preselection:
2 neutral cluster detected in BGO (invariant mass  ( ) GeV/c2);
1 neutron or 1 proton (in the central or in the forward detectors);
no other particles.
Selection cuts: 2
Kinematic Analysis:
Two-body nature of each reaction step:

7.  in  Photoproduction on qfp and fp
A.Fantini et al., Phys.Rev.C 78, (2008)
qfp fp
MAID fp
reggeized model - qfp
MAID qfp
at low energies: dependence
with increasing energy: forward-backward asymmetry

8.  in  Photoproduction on qfn
A.Fantini et al., Phys.Rev.C 78, (2008)
qfn
reggeized model
MAID2001
: symmetric behaviour
: peak in forward direction
: symmetric behaviour

9.  in  Photoproduction on qfp and qfn
A.Fantini et al., Phys.Rev.C 78, (2008)
qfn
qfp
up to 1.05 GeV:
qfn quite close to qfn;
above 1.05 GeV:
P11(1670);
S11(1650)-P11(1710).

10. 0 Photoproduction on Quasi-Free Nucleon in Deuteron
R. Di Salvo, to be submitted 1 3
Pre-selection:
2 neutral cluster detected in BGO (invariant mass  ( ) GeV/c2);
1 neutron or 1 proton (in the central or in the forward detectors);
no other particles (quasi-free kine).
Selection cuts: 2
Kinematical Analysis:
Two-body nature of each reaction step:

11.  in 0 Photoproduction on qfp and fp
R. Di Salvo, to be submitted fp
qfp

12.  in 0 Photoproduction on qfn
R. Di Salvo, to be submitted
qfn
MAID2007
MAID2007 new

13. in 0 Photoproduction on qfn Multipole extraction in MAID2007
Immaginary part
Real part
MAID2007 qfn
mod MAID2007 qfn

14.  in 0 Photoproduction on qfp and qfn
R. Di Salvo, to be submitted
qfn
qfp
MAID2007 “new” for neutron
MAID2007 “new” for proton

15. K+ and K+0 Photoproduction on Free Proton
A.Lleres et al., EPJ A 31, (2007) 1 3
Preselection:
3 tracks + at most 1 neutral cluster detected in BGO (no neutral particle: K+; 1 neutral particle: K+0)
Selection cuts:
Energy balance;
Charged particles mass;
Missing mass ;
Energy of the  from  decay. 2 4
Check:  decay length
Kinematic Analysis:
Three-body kinematics;
Two-body nature of each reaction step;

16.  in K+ and K+0 Photoproduction
A.Lleres et al., EPJ A 31, (2007)
GRAAL
GRAAL
Ghent Isobar
Published Bonn coupled channel
Saclay
New Bonn coupled channel
Bonn coupled
channel

17. P in K+ Photoproduction
GRAAL
CLAS
Ghent Isobar
Saclay
Bonn coupled
channel
A.Lleres et al., EPJ A 31, (2007)
From  and P measurements:
Saclay Model:
Ghent Isobar Model:
Reggeized Model:
Bonn Coupled Channel Model:

18. Formalism for Recoil Observables in K+ Photoproduction
<Py’> S1 S2
lab=0°
lab=90°
<Px’,z’> S3 S4
lab=0°
lab=90°

19. Double Polarization Observables in K+ Photoproduction
A.Lleres et al., EPJ A 39, (2009)
GRAAL
GRAAL
GI RPR
GI RPR
Bonn Gatchina
Bonn Gatchina

20. T in K+ Photoproduction
A.Lleres et al., EPJ A 39, (2009)
From Ox, Oz and T extractions:
Ghent Isobar RPR Model:
Bonn Gatchina Model:
GRAAL
GI RPR
Bonn Gatchina

21. Comparison with CLAS
A.Lleres et al., EPJ A 39, (2009)

22. Conclusions  photoproduction on nucleon:
measurement of  in the energy range from 0.7 to 1.5 GeV;
qfp is similar to fp: it suggests that qfn is similar to fn;
the energy dependence of qfp and qfn is very similar up to 1.05 GeV;
above 1.05 GeV, qfp is forward peaked while qfn looks more symmetric around CM = 90°;
above 1.05 GeV and backward angles, qfn is substantially higher than qfp;
0 photoproduction on nucleon:
measurement of  in the energy range from 0.5 to 1.5 GeV;
qfpis similar to fp : it suggests that qfn is similar to fn;
qfp and qfn are very similar for low values of 0* but differ a lot with increasing of 0*;
K+ photoproduction:
systematic measurements of , P, Ox, Oz and T in the energy range from 0.9 to 1.5 GeV;
comparisons with 4 different models confirm the necessity to introduce new or poorly known resonances in the 1900 MeV mass region: P13and/or D13;
we need only one additional double-polarization observable to extract helicity amplitudes.

23. In memory of Dr. Eid Hourany
Dr Eid HOURANY died in October 2008 at the age of 67.
He had been involved as the leader of the Orsay team in the GRAAL venture since the beginning and constructed the scintillating wall of the GRAAL detection system.
He has been a talented experimentalist able to analyse complex data. In the last few years, he has analyzed almost alone, « exotic » final states as: Nπ0π0, Nπ0η, Nω and extracted from the GRAAL data very innovative information.
The quality of the GRAAL physics production is largely indebted to his constantly demanding attitude.

24. Double 0 photoproduction
...on the proton
...on the neutron
P.R.L. 90 (2003)
Phys.Lett.B 651 (2007)

25.  photoproduction on the proton
P.R.L. 96 (2006)

26. Simultaneous  and 0 photoproduction
3-body phase space
Döring, Oset,
Strottman (2006)
P.R.L. 100 (2008)

27. Thanks a lot for your attention

28. 0 Photoproduction: Re-calculation of 0 C.M.
R. Di Salvo, to be submitted
Deviation of the Lorentz Boost Axis
Re-calculation of 0 C.M.

29.  Photoproduction: Selected Events
Fantini et al., Phys.Rev.C 78, (2008)
proton
neutron
central region
forward region
Total exstimated background
Proton
Neutron
Centre
2.4%
3.9%
Forward
0.9%
1.4%

30.  Photoproduction: Check
Fantini et al., Phys.Rev.C 78, (2008)
Check on the validity of:
3-parameters fit:
Similiar results for  beam asymmetry;
Higer 2;
The quality of fits gets worse.

31. P0 in K+0 Photoproduction
u , unity vector along the direction of  emission in the 0 rest frame

32. K+ Photoproduction : Efficiency Dependence for N+ and N-
Lleres et al., EPJ A 31, (2007)
via Monte Carlo simulation
Detection efficiencies and correction factors depend on the input values of Ox , Oz and T: iterative method (3 iterations).

33. Internal Check
A.Lleres et al., EPJ A 39, (2009)

34.  Photoproduction: theoretical models for comparisons
Fantini et al., Phys.Rev.C 78, (2008)

35. Models in K photoproduction off free protons
SACLAY
G.I.
BCC
GRPR