 *(1520) CrossSection Zhiwen Zhao Physics 745

Λ BARYONS (S = − 1, I = 0) Λ 0 = u d s Λ(1520) D 03 I( J P ) = 0( 3/2 − ) Mass m = ± 1.0 MeV [a] Full width Γ = 15.6 ± 1.0 MeV [a] = ± 1.0 MeV [a] = 15.6 ± 1.0 MeV [a]

Physics Motivation  *(1520) production mechanism is still poorly understood due to the lack of experimental data Existing data from photo- and electro-production suggest dominance of t-channel processes and in particular of K* exchange Several model predictions for total and differential cross section available J. M. Laget V. Yu. Grishina et al. L. Roca et al. S. Nam et al.... Precise measurement of cross section and decay angular distribution can provide constraints on model prediction and insight on strangeness production  p K+K+ ** ?

Existing data Photoproduction Photoproduction measurement on Proton were performed at SLAC and Daresbury Daresbury measured differential, total cross section and decay angular distribution in the energy range GeV – First look at the decay angular distribution showed dominance of m z =±3/2 spin projection – Limited statistics No data on production on Neutron yet

Theoretical result S. Nam et al. Phy.Rev.D 71, (2005)

Existing data Electroproduction Electroproduction of  * has been studied at DESY and CLAS CLAS data (S. Barrow, e1c) showed – Dominance of t-channel process confirmed – Decay angular distribution showed significant contribution from m z =±1/2 spin projection

7 JLab accelerator CEBAF

8 CEBAF Large Acceptance Spectrometer Liquid D 2 (H 2 )target +  start counter; e minitorus Torus magnet 6 superconducting coils Drift chambers argon/CO 2 gas, 35,000 cells Time-of-flight counters plastic scintillators, 684 photomultipliers Gas Cherenkov counters e/  separation, 256 PMTs Electromagnetic calorimeters Lead/scintillator, 1296 photomultipliers

eg3 run ● Photon beam initial electron beam 5.77 GeV, 35 nA 5x10-4 radiator ● Target 40 cm upstream, LD2 ● Trigger Tagger bars 4.4 < E < 5.5 ST x TOF (3 out of 6 sectors, prescaled 2 out of 6) ● Torus field optimized to A, negative outbending ● Run Period 12/06/2004 – 01/31/ days of production on LD2 target ● Data 4.2 billion physics events 32 TB raw data average 2.7 tracks/event with good fit  p(n) → K +  *(p K - ) (n)  n(p) → K 0  *(p K - ) (p)

Particle identification (data)  p(n) → K +  *(p K - ) (n)

Particle identification (sim)  p(n) → K +  *(p K - ) (n)

Particle Distribution (data)  p(n) → K +  *(p K - ) (n)

Particle Distribution (sim)  p(n) → K +  *(p K - ) (n)

Neutron Missing Mass data sim  p(n) → K +  *(p K - ) (n)

Yield Extraction  p(n) → K +  *(p K - ) (n) the  * yield is extracted as a function of E  and t bin fitting the mass spectrum with BW function convoluted with a Gaussian + polynomial The width of the BW is fixed to the intrinsic width of the  * The peak of the BW is fixed to the PDG value of the  * the sigma of the Gaussian is one of the fit parameters

Yield Extraction (data)  p(n) → K +  *(p K - ) (n)

Yield Extraction (sim)  p(n) → K +  *(p K - ) (n)

Yield Extraction  p(n) → K +  *(p K - ) (n)

Luminosity  p(n) → K +  *(p K - ) (n)

CrossSection  p(n) → K +  *(p K - ) (n)

t slope  p(n) → K +  *(p K - ) (n)