0
π electroproduction
Exclusive
in the resonance region.
Nikolay Markov, Maurizio Ungaro, Kyungseon Joo
University of Connecticut
Hadron spectroscopy meeting
September 26, 2009
Outline
 Motivation
 Experiment
 Analysis
 Results
 Conclusion
2
Motivation
3
• The experimental N* program has as
main component the accurate
measurements of transition form
factors (A3/2, A1/2, S1/2) of known states
as function of the photon virtuality
(Q2) to probe their internal structure
and confining mechanism
• Exclusive pion electroproduction from
protons is proven to be an especially
sensitive tool for the study of the
transition from the hadronic picture to
the quark-gluon picture of nucleon
resonance excitations.
e’
e
p, h, pp,..
γv
N*,△
N
N’
A3/2, A1/2, S1/2
Ml+/-, El+/-, Sl+/-
E1e run
4
Beam energy: 2.039 GeV
Beam polarization: ~ 70%
Current: 10nA
Target: Liquid Hydrogen, thickness 2 cm,
radius 0.2 – 0.6 cm
Torus current: 2250 A
Mini-torus current: 6000 A
Data taking period: 12.2002 – 1.2003
Number of triggers: 1.5*109
Data analysis: procedure
5
Particle ID
Electron ID
Proton ID
Good runs selection
Electron momentum correction
Proton momentum correction
π0 selection: BH subtraction
Cherenkov cut efficiency
Simulation and acceptance correction
Radiative and bin centering correction
Systematic studies
 Normalization
Elastic process
Inclusive process
Particle ID
Electron ID
 X versus Y cut
6
X, cm
Etot/P
Pel > 0.461 GeV
 Sampling fraction cut
 Number of photoelectrons
 E inner > 50MeV
Y, cm
 Minimum momentum cut
25
NPE
0.461
P, GeV
Particle ID
Electron fiducial cut
7
θ
 min
θ
Momentum and sector dependent
The regions of uniform acceptance:
50
50
40
40
30
30
20
20
C2
 C1 
p  C6
  C4 sin(    min )
-30 -15
TOF inefficiencies
θ
θ
P, GeV
φ
15 30
-30 -15
φ
15 30
Sector 5
φ
Particle ID
Proton ID
8
Based on the
ΔT =Tmeasured-Ttheoretical
-2ns < ΔT < 4ns
Timing correction
Tmeasured- Ttheoretical
for each scintillator
calculated
ΔT, ns
Pp,GeV
ΔT, s
M2,GeV2
For the loosely
identified protons
4
2
0
-2
-4
Pp,GeV
β
Resulting correction
is then applied
to the events.
M2,GeV2
P, GeV
Pp,GeV
Pp,GeV
Particle ID
Proton fiducial cut
9
8 bins in momentum
0.0 GeV < P < 0.4 GeV
0.4 GeV < P < 0.6 GeV
0.6 GeV < P < 0.8 GeV
0.8 GeV < P < 1.0 GeV
1.0 GeV < P < 1.2 GeV
1.2 GeV < P < 1.4 GeV
1.4 GeV < P < 1.6 GeV
1.6 GeV < P < 1.8 GeV
20 θ bins
0.4 < P < 0.6 GeV, Sector 1
Momentum correction
Electron momentum correction
10
Overview and reaction selection
Electron kinematics coverage in case of
Elastic events
BH events
π0 events
θ
P, GeV
Kinematical coverage of elastic events is quite
different from π0,while BH lies in similar region;
Since we have good statistics in
the elastic region, they will be
used as additional W bin with
its own kinematics.
BH selection, preand post-radiative
processes
Preradiative BH
selection, emitted
photon is aligned
with the beam
direction.
ep -> epX
all BH
pre-radiative
post-radiative
-0.02
0
0.02
0.04
mm2
Momentum correction
Electron momentum correction
11
Pdata  Ptheor
Pdata
is calculated for each event and stored in sector - W - θe - φe bins.
Gaussian fit to obtain a peak position is performed and peak positions
are fitted with 2nd order polynomial a + bx + cx2 as a function of φe.
Correction applied
Coefficients of the polynomial
fit are interpolated
as a function of W, giving as a
correction to be applied.
Elastic events
Peak position
σ
Data
Corrected
BH events
Peak position
Data
Corrected
σ
Data set selection
12
Based on the ratio of the number of events in the specific reaction in the run to the
faraday cup charge for this run, 4 runs were excluded from the further consideration.
Proton momentum correction
13
Energy loss
Based on the ep->epπ0 kinematics.
Based on the ratio of
generated and reconstructed
proton momentum.
Before correction
Uses electron momentum
and angles and proton
angles
Result, peak position
Before correction
ΔP/P
ΔP/P
Result, σ
-10
0
10
After correction
20 φ
ΔP/P
0.04
0.02
0
-0.02
-0.04
ΔP/P
After correction
P, GeV
0.04
0.02
0
-0.02
-0.04
-30 -20
-30 -20
P, GeV
-10
0
10
20
φ
Data | Corrected
BH separation
14
φe-φp
e –– φ
θφ2p
θpp
1p
All events
π0 events
θ2p – θp
φe-φp
mm2, GeV2
Θ1p – θp
φe-φp
Binning and kinematical coverage
15
Binning:
ΔW = 25 MeV
ΔQ2 = 0.1 GeV2
Δcosθ = 0.2
Δφ
= 300[15o]
Overview
Simulation
16
 Using MAID 2007 model with radiative effects, 130M
events were generated (10M data events)
 GSIM processing was based on e1e configuration
 GPP was used to include effects for:


DC wire inefficiency
TOF smearing and DC smearing
 Same reconstruction code was used for both data and
simulation
 Same cuts applied to data and simulation
Simulation
GPP
17
TOF mass σ
simulation
TOF mass2, GeV2
TOF mass2, GeV2
simulation
mm2, GeV2
mm2, GeV2
Cherenkov cut efficiency
18
Problem:
400
E 
Electrons

f ( x ) dx
25
400

f ( x ) dx
0
Efficiency distribution for
Sector 2
Events with identifies
electron (no CC cut)
divided in the bins of
Pe, θe and φe,
Fit the npe spectrum with
the Poisson function.
←θ→
NPE
NPE
←φ→
Elastic
Normalization
19
-Elastic events with realistic radiative tail were generated
-Momentum correction was applied to the simulation;
-Electron or both electron and proton were detected in the final state.
Cross-sections comparison to
Cross-sections ratio to
Bosted parametereization
Bosted parameterization
Electron detection only
Electron and proton detection
Bosted parameterezation
Electron detection only
Electron and proton detection
Normalization
Inclusive
20
Radiative correction
Bin centering correction
Result
μB/GeV3
• Events were generated
using keppel_rad generator;
•Momentum correction,
which uses the generated
events as a precise
measurements, were applied
•Radiative correction based
on the ratio of
keppel_rad/keppel_norad
was applied;
•Bin centering correction
based on the keppel_rad
model was applied;
•Data is compared to the
Keppel and Brasse
parametrization
Data
Brasse
Keppel
Acceptance correction
Corrections
21
1.2 < W< 1.225 GeV, 0.4 < Q2 < 0.5 GeV2
1.2 < W< 1.225 GeV, 0.8 < Q2 < 0.9 GeV2
1.525 < W< 1.55 GeV, 0.5 < Q2 < 0.6 GeV2
1.725 < W< 1.75 GeV, 0.4 < Q2 < 0.5 GeV2
Acceptance
Radiative correction
Corrections
22
Radiative processes:
Bremmstrahlung
Vacuum polarization
exclurad code
MAID 07 model as an input
1.225 < W < 1.250 GeV
0.5 < Q2 < 0.6 GeV2
Vertex correction
Corrections
Bin centering correction
23
leave the value,
shift the point
Each W-Q2-θ-φ bin is
divided in 10 sub-bins
1.225 < W < 1.250 GeV
0.5 < Q2 < 0.6 GeV2
MAID 2007
leave the point,
shift the value
Cross-section
Results
μb
24
φ
Statistical error only
1.225 < W < 1.250 GeV
0.6 < Q2 < 0.7 GeV2
Data
MAID 03
MAID 07
Results
Structure functions extraction
μb
25
d
2Wp *p 0
2

(





sin
 cos 2   LT 2 (  1) sin  cos  )
T
L
TT
* 0
2
2
d p
W  mp
y  a  b cos   c cos 2
 T   L  a
 LT 
 TT 
Statistical error only
b
sin  2 (  1)
c
sin 2 
1.225 < W < 1.250 GeV
0.6 < Q2 < 0.7 GeV2
φ
Data
MAID 03
MAID 07
Structure functions
Results
μb
26
 T  L  LT
 TT
Statistical error only
1.225 < W < 1.250 GeV
0.6 < Q2 < 0.7 GeV2
Data
MAID 03
MAID 07
Overview
Systematics
27
Sampling fraction
Electron fiducial cut
Vertex cut
Proton timing
Proton fiducial cut
Missing mass cut
Electron fiducial cut
Systematics
φ
μb
28
θ
1.225 < W < 1.250 GeV
0.6 < Q2 < 0.7 GeV2
Data regilar cut
Dat strict Cut
Data strictest Cut
MAID 03
MAID 07
Missing mass cut
Systematics
μb
29
1.225 < W < 1.250 GeV
0.6 < Q2 < 0.7 GeV2
N. Markov
Data regular cut
Data strict Cut
Data strictest Cut
MAID 03
MAID 07
mm2, GeV2
Conclusions
30
 Preliminary cross-sections and structure functions
were obtained in wide kinematic range with high
statistics.
 Systematic studies are partially finished.
 Detailed partial wave analysis combined with other
channels using JANR will be performed.
More details
31
http://www.jlab.org/~markov/
31
N. Markov
Narrow φ* binning
32
μb/sr*GeV3
No BC and radiative corrections
φ bin size 15o
Statistical error only
1.225 < W < 1.250 GeV
0.6 < Q2 < 0.7 GeV2
Data
MAID 03
MAID 07
backup
33
Elastic generated events
Data
100% elastic events
90% elastics events