1. Experiment (Jlab Exp 04-010: CLAS eg3)
Photoproduction of L*(1520) Zhiwen Zhao University of South Carolina, The CLAS Collaboration
Motivation
Theory
Experiment (Jlab Exp : CLAS eg3)
The study of strange baryons is essential to understand SU(3) symmetry.
L*(1520) production mechanism is still poorly understood due to the lack of experimental data.
Very few photoproduction measurement off the Proton,
No published data off the Neutron
Possible missing N* resonances decaying into strange channels.
Λ *(1520) D03     I( J P ) = 0( 3/2 −  ) 
29 days of photon beam, 40 cm long LD2 target upstream at -50 cm
Ee = 5.77 GeV, Ie = 30 nA
Photon energy range 1.5 < E < 5.5 GeV, only triggered above 4.5 GeV
Trigger: mainly 3-track trigger and partially pre-scaled 2-track trigger
4.2 billion physics events, 32 TB raw data g p K+ L* ? K0 L* g n ?
>> ?
Comparing between experiment and theory ( Proton )
 p(n) → K+ L* (n)
 n(p) → K0 L* (p)
(L* →p K- , K0 → Ks →  +  - )
Two exclusive channels studied
off Proton
off Neutron
D. P. Barber et al., Z. Phys. C 7, 17 (1980)
S. Nam et al. Phy. Rev. D 71, (2005)
Summary
Proton
Neutron
L*(1520) yield is obtained from fitting the peak in the invariant mass of pK- distributions
The total cross section on the Proton produced by integrated differential cross sections agrees with the result from g11 run group and extends to higher energies up to 5.5 GeV.
The total cross section on the Proton produced by fitting yields over E bins depends on the t slope input in the simulation. It could be tuned very close to the more accurate result in blue.
The total cross section on the Neutron is produced is obtained for the first time by fitting yields over E bins and it’s much larger than what the theory expected.
Study other inclusive channels (eg. K- not detected) with higher statistics to obtain differential cross section on the Neutron .
Look for possible missing N* resonances.
Data are binned by photon energy E and t*=-(t-t0).
The result for the Proton is shown below.
Cross sections obtained for Proton and Neutron are shown at the right.
Data Simulation
Preliminary
Preliminary Result
E, t* bin t* bin E bin
Outlook