Transcript Stepanyan ppt

Meson spectroscopy with CLAS [ CLAS12
CLAS/g6: gpnp+p+p-
Successful PWA of CLAS photoproduction data
showed a feasibility of meson spectroscopy
studies using the CLAS detector
a2
It also reviled importance of backgrounds from
D’s and N*’s
Background from s-channel processes
complicates PWA (need a high statistics
data), introduces ambiguities
Coherent production on nuclei can be used to eliminate s-channel background
Experiments with coherent production require:
 detection of A’ at ttmin (Ek>few MeV) - thin targets (~10-3 g/cm2)
 small size, high flux (virtual) photon beams
CLAS(12) with BoNuS RTPC and with available high precision, high intensity electron
beams opens a new avenue for meson spectroscopy using coherent production on nuclei
S. Stepanyan
Town Meeting, Rutgers Univ., January 12-14 2007
Coherent production of p0h and p0h’ on 4He (PR-07-009)
Coherent production on 4He eliminates s-channel
contribution
Scattering off of the spin and isospin zero
target works as a spin and parity filter for final
state mesons



Final states p0h and p0h’ have I=1, C=+1, G=-1, and P=(-1)l. Resonance in the Pwave will be an exotic - IGJPC = 1-1-+
Only C=-1 w-exchanges is allowed,
Natural Parity Exchange (NPE)
The helicity of the produced
state will be that of the incoming
photon, l=lg, production of p0h
(p0h’) in S-wave is forbidden
d
2
2
 A0  A  A
d C
A 
A 
L max
L
L 0
L max
1
1/ 2
2 L  1

l
1/ 2
 2 L  1
L1
A0  0; A  0;
2 Ll  ImDlL0 (,  ) 
2 L1 ImD10L (, ) 
2
d
5
 3 P1  5 D1 cos  
F1 (5 cos2   1) sin 2 
dC
2
S. Stepanyan
Town Meeting, Rutgers Univ., January 12-14 2007
CLAS12 with thin targets (3H, 3He, 4He) and with small angle tagger
Spectroscopy can be extended to the higher
masses (~3 GeV) and to the charged modes
Electroproduction at very small Q210-3,
scattering angles 1o-2o, is equivalent to
photoproduction with partially linearly
polarized photons, complimentary solution
to photon bremsstrahlung beams
1

(1   )

2


0

 1

    L (1   )1 / 2 
2

 

  1  2

Q
0
1
(1   )
2
0
 2 
 
tan 2 ( )
2
Q
2 
2
1
1

   L (1   )1 / 2  
2


0



L

L 
Q2
2
  103  0
S. Stepanyan
Town Meeting, Rutgers Univ., January 12-14 2007