K* Photoproduction off the proton

1
NSTAR2005

Oct. 12, 2005

• K Photoproduction off the proton
• at CLAS
• via

2
OUTLINE

• Experiment and Physics Motivation
• Background and Analysis Cuts
• Results
• Cross sections
• Systematic Uncertainties
• Conclusion

3
Experiment and Motivation
E 3.115 GeV Target LH2 (L17.85 cm)
g1c data set
Motivation - K production mechanism -
Looking for N resonances Goal Measuring
Cross Sections - ds/dcos? vs.
E - ds/dcos? vs. cos?
N
4
Background

• 
  
• 
  (signal)
  
  
• 
  
  
• 
  ( b.g.)
• 
  
  
• 
  
  
• 
  

N
N
5
Analysis Cuts

• Particle identification
• - 2 detected particles
• - 3 timing cuts ?ß, (TOF-ST), and (TOF/Ttag )
• ?ß - lt 0.1
  
• TOF-ST TOF - (Start Counter) vtime lt
  1.0 ns
• TOF/Ttag TOF (Ttag zvertex/c) lt
  1.0 ns
• Kinematic cuts
• Kinematic coverage (cos vs. )
• zvertex R at vertex cuts
• Fiducial cuts
• Mass cuts
• missing mass
• K invariant mass

ToF-Ttag (K)
E
zvertex (K)
6
PID Timing cuts (kaons)
K
ß
P (before cuts)
P (after cuts)
P
K
M (after cuts)
M (before cuts)
7
MM(K)
K and S Peaks
K from IM( )
peak

From MM( )
from MM( ) for a cut on K peak
from MM( ) for a cut on K SBs
IM(K) vs. MM(K)
8
IM(K) vs. MM(K)
9
Kinematic Coverage

• K Cut
• Y Cut

cos(?)
E
10
Dalitz Plots
E2.00 GeV
E1.8125 GeV
E2.1625 GeV
2
IM( )
E2.300 GeV
E2.475 GeV
E2.600 GeV
E2.8125 GeV
E2.7125 GeV
E2.9125 GeV

2
IM( S )
11
Extracting Cross Sections
Normalized cross section
MH number of grams/mole of target ? and L
detectors density and length Na Avogadros
number A detectors acceptance
photon flux
12
Angular distribution of the diff. x-sec.
(E3.115 GeV)
ds/dcos?
(nb)
cos?
13
ds/d(cos?) for K photoproduction (E3.115GeV)
ds/dcos?
(nb)
E
14
ds/d(cos?) for K photoproduction (E3.115GeV)
ds/dcos?
(nb)
E
15
Cuts Uncertainty

• Systematic
• Uncertainties
• 6.65

2.51
3.11
2.17
2.0
3.0
16
Conclusion

• We have measured the differential cross sections
  for the
• K Photoproduction.
• Our results agree with theory at the "middle to
  backward" angles
• but disagree at forward angles.
• - Small angles forward-peaking
• strongly correlated to the
  t-channel kaon exchange
• - Large angle backward cross sections
• have less interferences from the
  t-channel meson exchange
• Our data are expected to play a role in
  constraining the
• quark-vector-meson couplings and in improving the
  model
• Q. Zhao, J. Al-Khalili, And C. Bennhold,
  Phys. Rev. C64(2001) 052210.

17
Appendix
Y background
18
Y b.g. contributions
19
Contribution from ?(1520)
From ?(1520) peak
From ?(1520) SBs


20
ds/dMM(K)
(nb)
21
ds/d(cos?) for K photoproduction (E3.115GeV)
ds/dcos?
(nb)
E
22
ds/d(cos?) for K photoproduction (E3.115GeV)
ds/dcos?
(nb)
E