Transcript Nucleon Resonance Studies in π+ π

Nucleon resonance studies in π+ πelectroproduction off protons at high
photon virtualities
E. Isupov, EMIN-2009
Plan of the talk
– Major objectives for N* studies in
Nelectroproduction at high Q2
– Recent CLAS data on the π+ π- p electroproduction
– Evaluation of vNN* electrocouplings
– Preliminary data at high Q2
– Conclusions and outlook
Primary objectives in the studies of
N* structure in 2 electroproduction
• Our experimental program seeks to determine
– N-N* transition helicity amplitudes (electrocouplings) at photon virtualities
0.2< Q2<5.0 GeV2 for almost all excited proton states from analyzing
double-pion electroproduction.
– provide input for advanced coupled-channel approach developing by
EBAC.
• This comprehensive information on Q2 evolution of the N-N*
electrocouplings will allow us to:
– determine the active degrees of freedom in N* structure at various
distances;
– study the nonperturbative strong interactions which are responsible for
• the ground and excited nucleon state formation,
• and how they emerge from QCD.
How N* electrocouplings can be accessed
• Isolate the resonant part of production amplitudes by fitting the
measured observables within the framework of reaction models,
which are rigorously tested against data.
• N* electrocouplings can then be determined from resonant
amplitudes under minimal model assumptions.

e’
e

γv
N*,△
*
N’
N
A3/2, A1/2, S1/2
GM, GE, GC
+
γv
p
v
N
N
N’
p
Non-resonant
amplitudes.
Consistent results on N* electrocouplings obtained in analyses of various
meson channels (e.g. πN, ηp, ππN) with entirely different non-resonant
amplitudes will show that they are determined reliably
Advanced coupled-channel analysis methods are being developing at EBAC: B.Julia-Diaz,
T-S.H.Lee et al., PRC76, 065201 (2007);B.Julia-Diaz, et al., arXiv:0904.1918[nucl-th]
P11(1440) electrocouplings from the CLAS data on
N/N electroproduction
Npreliminary
N
Light front models:
I. Aznauryan
S. Capstick
hybrid P11(1440)
• Good agreement between the electrocouplings obtained from the N
and N channels: Reliable measure of the electrocouplings.
• The electrocouplings for Q2 > 2.0 GeV2 are consistent with P11(1440)
structure as a 3-quark radial excitation of the nucleon.
• Zero crossing for the A1/2 amplitude has been observed for the first
time, indicating the importance of light-front dynamics.
High lying resonance electrocouplings from N
CLAS data analysis
NCLAS
preliminary
Δ(1700)D33
Nworld
N(1720)P13
NCLAS
Q2=0
CLAS
Event Selection
• Electron ID
– Calorimeter cuts
– Cherenkov cut
– Fiducial cuts
– Zvertex cut
– Momentum corrections
– Zvertex corrections
EC sampling fraction before
and after electron ID cuts
Charged hadrons ID
•
•
•
•
•
•
Beta vs Momentum cuts
Fiducial cuts
Momentum corrections for positive pion
Energy loss corrections for proton
Zvertex corrections
Zvertex cut
Delta beta vs Momentum for
charged hadrons
Missing Mass of negative pion
3-body final state kinematics
variables
3-body final state kinematics
variables:
M+- , Mp+ are invariant masses
of the +- and p+ systems
respectively;
d- =d(cos-)d- is solid angle
for emitted -;
p+ is the angle between two
planes on the plot.
Cross-section extraction


7
d
1

N


2
2
dWdQ
dL
eff


W

Q


7-fold differential cross-section



d

d
M
d
M
d
c
o
s
()
d
d









p



p
L – luminosity, N – number of events inside multidimensional cell,
eff-efficiency determined from monte-carlo simulation. Then we
obtain virtual photon cross-section
5
7
d
1 d

2
d
 
dWdQ
d

v
Preliminary differential cross-sections at W=1.934 GeV
2
2
4
.
2

G
e
VQ
2
5
.
0

G
e
V
Cross-sections at higher Q2
Fully integrated 2 cross section
Q2=0.95 GeV2
Q2=2.2 GeV2
preliminary
Cross-sections at higher Q2
Fully integrated 2 cross section
preliminary
Q2=2.7 GeV2
Q2=3.3 GeV2
Q2=3.9 GeV2
Q2=4.6 GeV2
JLAB-MSU isobar model (JM) for N
electroproduction.
3-body processes:
Isobar channels included:
-++
• All well established N*s with  decays
and 3/2+(1720) candidate, seen in CLAS
2 data.
• Reggeized Born terms with effective FSI
& ISI treatment .
• Extra  contact term.
p
•All well established N*s with p decays and
3/2+(1720) candidate.
•Diffractive ansatz for non-resonant part and
-line shrinkage in N* region.
18
continued
3-body processes:
Isobar channels included:
(-)
(P++33(1640))
F015(1685)
(+)
• +D013(1520), +F015(1685), -P++33(1640)
isobar channels; observed for the first time
in the CLAS data at W > 1.5 GeV.
Direct 2 production
V. Mokeev, V .Burkert, J. Phys. 69, 012019 (2007);
V. Mokeev et al., arXiv:0809:4158[hep-ph]
Description of the CLAS N differential cross
sections within the framework of JM model
full JM calc.
-++
+0
2 direct
p
+D013(1520)
+F015(1685)
Resonant & non-resonant parts of N cross sections as
determined from the CLAS data fit within the framework of JM
model
full cross sections
resonant part
non-resonant part
Conclusions and outlook
• For the first time differential cross-sections of double pion
electroproduction were extracted in 2.0<Q2<5.0 GeV2
• It makes possible to use phenomenological model JM in order to
establish all essential mechanisms, contributing to double pion
electroproduction at this still unexplored kinematic area
• In near term prospect we expect to evaluate electrocouplings for
prominent resonances in 2.0<Q2<5.0 GeV2 region.