1. Electroproduction of φ Mesons in CLAS
Joe Santoro, Elton Smith
Exclusive Reactions
May 21, 2007

2. φ photoproduction
π, f2, P ω P   p 

3. Kinematics

4. Q2 (GeV2) W (GeV) Kinematic Coverage ep→epφ→epK+(K−)
e1a/e1b: E = 4.2 GeV,
Q2~ 0.7 ─ 2.2 GeV2
e1-6a: E = 5.75 GeV
Q2 ~ 1.7 ─ 3.8 GeV2
Q2 (GeV2) Q²
W (GeV)

5. e1-6 Experiment @ CLAS 5.75 GeV Beam Proton Target
21 mC integrated charge
ep →epφ→K+(K-)
Drift Chambers
TOF
Cherenkov
Electromagnetic Calorimeter

6. Electron Selection E/p vs P & EC energy Number of photoelectrons
in Cerenkov Counter
Electron Fiducial cuts

7. Hadron Identification
p and K+ selection
K- from missing mass
(2s selection cut) p
TOF Mass (GeV) K+
p+ contamination
Momentum (GeV)
Mx(epK+X) (GeV)

8. f yields ~4x number of φ’s as previous CLAS measurement in a
higher Q2 range
K+ K- Invariant Mass (GeV)

9. 6-D Acceptance Correction
Variable Q2 W t
cos(qH) y F
Nbins 5 4 7 8 6
33,600 bins, 108 events Q2 y W -t
cosqH F

10. Radiative Corrections
COS(q)CM=0.345, Q2= 2.47 GeV2
EXCLURAD was used to obtain
corrections in Q2,W,F, and COS(q)CM bins
W ranges from 1.9 GeV to 3.0 GeV

11. Total Cross Sections σ(Q2)
Laget Model
NP A581: , 1995
Phys. Lett. B. 489: , 2000
Preliminary
K+ K- Invariant Mass (GeV)

12. Differential Cross Section in t
Nuc. Phys. A581: , 1995
Phys. Lett. B. 489: , 2000
Q2=1.6 GeV2
Q2=2.1 GeV2
Q2=2.6 GeV2
Q2=3.8 GeV2
Q2=5.0 GeV2
Preliminary
K+ K- Invariant Mass (GeV)

13. Differential Cross Section in t’
Preliminary
K+ K- Invariant Mass (GeV)
Lukashin, et. al.

14. Differential Cross Section in Φ
c2const. = 1.9
SCHC Conserved
Preliminary

15. Angular Distributions
Preliminary
Preliminary

16. sL Extraction
Preliminary

17. Comparison to World Data
Filled previously unexplored
region of phase space
(low W, low-medium Q2)
Preliminary

18.  production summary Kinematic Range
1.6 ≤ Q2 ≤ 3.8, 0.0 ≤ t’≤ -3.6, 2.0 ≤ W ≤ 3.0
(Q2) ~ 1/(Q2+M2) 3 ± 1
F angular distribution consistent with SCHC
R=1.71 ± 0.30 , sL = 2.9 ± 0.8 nb integrated over Q2
t’ distribution slope bf=0.81 ± 0.18 GeV2
Interaction probes sizes ~ 1/3 fm.
Theoretical input welcome.