*(1520) CrossSection

Zhiwen ZhaoPhysics 745

Λ BARYONS (S = − 1, I = 0) Λ0 = u d s

• Λ(1520) D03 I( J P ) = 0( 3/2 − )

• Mass m = 1519.5 ± 1.0 MeV[a] Full width Γ = 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+

*

?

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 2.8-4.8 GeV

– First look at the decay angular distribution showed dominance of mz=±3/2 spin projection

– Limited statistics

• No data on production on Neutron yet

Theoretical result

S. Nam et al. Phy.Rev.D 71,114012 (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 mz=±1/2 spin projection

7

JLab accelerator CEBAFJLab accelerator CEBAF

8

CEBAF Large Acceptance Spectrometer

Liquid D2 (H2)target +

start counter; e minitorus

Torus magnet6 superconducting coils

Drift chambersargon/CO2 gas, 35,000 cells

Time-of-flight countersplastic scintillators, 684 photomultipliers

Gas Cherenkov counterse/ separation, 256 PMTs

Electromagnetic calorimetersLead/scintillator, 1296 photomultipliers

eg3 run

● Photon beaminitial electron beam 5.77 GeV, 35 nA 5x10-4 radiator

● Target 40 cm upstream, LD2

● TriggerTagger bars 4.4 < E < 5.5ST x TOF (3 out of 6 sectors, prescaled 2 out of 6)

● Torus fieldoptimized to -1980 A, negative outbending

● Run Period 12/06/2004 – 01/31/200529 days of production on LD2 target

● Data4.2 billion physics events32 TB raw dataaverage 2.7 tracks/event with good fit

p(n) → K+ *(p K-) (n) n(p) → K0 *(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)