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) presented by Rachele Di Rachele Di Salvo Salvo On behalf of the GRAAL Collaboration
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Beijing, Sept 2nd 2004 Rachele Di Salvo Beam asymmetry in meson photoproduction on deuteron targets at GRAAL MENU2004 Meson-Nucleon Physics and the Structure.
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Beijing, Sept 2nd 2004 Rachele Di Salvo
Beam asymmetry in meson photoproduction on deuteron targets at
GRAAL
MENU2004Meson-Nucleon Physics and the Structure of the Nucleon
August 29th - Sep 4th 2004, Beijing (China)
presented by
Rachele Di SalvoRachele Di SalvoOn 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 (P11) 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-Ee,me
E’e, me
E
EL
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: Lagrane
Large Acceptance Graal Apparatus for Nuclear Experiments
Beijing, Sept 2nd 2004 Rachele Di Salvo
Physics motivationsIn 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 A1/2 and A3/2 ,
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
Events selection (1)
•1 neutron incentral or forward direction
•NO charged particle (the proton is spectator)
•1 proton incentral or forward direction
•NO other neutral particle (the neutron is spectator)
•2 in BGO ( invariant mass)
+n+(p)->+n+(p) 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 kinematicsN = Nucleon polar angle
= miss-N
Bidimensional cut on (Mmiss,-MN ) vs. (Mmiss,N-M )
Mmiss,N= Mass of missing particle from
(Nucleon)
N.B. For the central neutron: Mmiss n obtained by the |pn| 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
Mmiss (GeV)
Mmiss N (GeV)
Forward nucleon
Mmiss N (GeV) Mmiss (G
eV)
Proton
Neutron
Central nucleon
Events selection (2)
Beijing, Sept 2nd 2004 Rachele Di Salvo
Invariant Mass
Before cuts
After cuts
Mass (GeV) Mass (GeV)
Proton
Neutron
Beijing, Sept 2nd 2004 Rachele Di Salvo
Azimuthal Distribution: ))cos(2P(121
/KN/KN/KN
2211
11
Proton
Neutron
Beijing, Sept 2nd 2004 Rachele Di Salvo
firstresults on q.f.proton+p+(n)->+p+(n) Green Laser LineUV Laser Line
Said- BO12
N.B. Error bars: statistical errors only
Maid
Preliminary
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)
firstresults on q.f.neutron+n+(p)->+n+(p) Green LineUV Line
N.B. Error bars: statistical errors only
Preliminary
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
Events selection (1)
•1 neutron incentral or forward direction
•NO charged particle (the proton is spectator)
•1 proton incentral or forward direction
•NO other neutral particle (the neutron is spectator)
•2 in BGO (0 invariant mass)
+n+(p)->0+n+(p)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 (Mmiss,-MN ) vs. (Mmiss,N-M )
for forward nucleons
• Bidimensional cut on (Ecalc,N-Ecalc’,N ) vs. (Mmiss,-MN
)
for central nucleons
Ecalc,N = Nucleon energy extracted from energy
conservation
Ecalc,N = E + MN - E
Ecalc’,N = Nucleon energy extracted from 2-body kinematics
Conclusions (1)First results have been obtained on the analysis of the ando 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