Motivation

1
Light excited hyperon Production on a proton
target at CLAS
Lei Guo for CLAS Collaboration Thomas Jefferson
National Accelerator Facility, Newport News, VA

• Motivation
• Search for Missing hyperons such as S(1480)
• Accurate S(1385) Xsection measurement
• High stattistics CLAS data70/pb-1, E04 GeV
• Production mechanism?
• gp?K L(p0) analysis
• gp?K p-/(S-/) analysisS(1480)?Sp?
• L(1520) Xsection measurement

2
Motivation 1 measurement of S(1385) differential
cross section
Accurate Measurent of ds/dt needed to isolate the
double kaon component 1/(mK2 t)2
Information useful in constraining KN dynamics
at subthreshold energies
M. Lutz, M. Soyeur, Nucl.Phys.A748499 (2005)
3
Motivation 2 Is there a S(1480) state?
L polarization M2(Lp)
p p? K p L
M2(Lp)
???
JP ½ -1 Octet member? Y. Azimov, Phy. Rev.
C68(2003)
Y. Pan et al. Phys. Rev. D 2 (1970)
4
ZEUS result on Q
Is there a S(1480)?
hep-ex/0403051
S(1480)? Q(1540)?
5
CEBAF Large Acceptance Spectrometer_at_JLAB
6 Superconducting toroidal coils
Electromagnetic calorimeters
Beam line and the target
Drift chambers
TOF counters
Cherenkov counters
Tagger
CLAS Detector
6
gp?K L(p0) analysisEvent seleciton
MM2(KL)
M(pp-)
p0
L
gp0
h?
pp
Event selection Timing cuts and missing momentum
cuts at least one photon detected
7
gp?K L(p0) analysisBasic spectra
S0(1385)
K
K
KL/ KS(1385) interference? Need quantified study
8
Background gp?K L, L?S0p0, S0?(gL)
p0 side bankd events
p0 events
MM(K)
MM(K)
Bump around 1500MeV due to L(1520) bckground
9
gp?K L(p0) analysisS(1385) Xsection ds/dt(g?K
)
Eg 1.7GeV)
Eg 1.8GeV)
Eg 2.5GeV)
Eg 2.6GeV)
preliminary
Acceptance at low t region an issue Simulation
t slope tuned to the data
tslope (GeV/c2)-2
Eg (GeV)
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gp?K L(p0) analysisS(1385) Xsection
ds /dcos(qK )
s(mb)
Eg 2.2GeV)
Eg 3.6GeV)
preliminary
Eg (GeV)
Results consistent with scare
old data Extrapolation for s(total) an issue
11
gp?K p-p(n) analysis
Selecting S
Remove S- events
M(np)
S-
M(np-)
S(1385) L(1405)
M(Sp-)
M(Sp-)
L(1520)
Small bump around 1.48GeV appears when S- events
removed
12
gp?K p-/(S-/) analysis
M2(Sp-)
M2(S-p)
M2(pp-)
Bumps created by kinematics Removing Ks0 and S
13
Extracting L(1520) Xsection

• Three Groups worked independently
• Different Particle Identification Schemes used
• Cross section of L(1520) results consistent with
  SAPHIR
• Errors 30, mostly due to statistics

preliminary
-
14
Summary

• Multiple channels analyzed in search for S(1480)
• No obvious signal observed in Sp orLp decay
• Fake structure could be created by reflection or
  kinematical cuts
• Preliminary results of S0(1385) Xsection
  (Eg1.63.8 GeV) obtained
• Preliminary results of L(1520) (Eg1.93.8 GeV)
  Xsection
• KL/KL ratio to be determined, theoretical
  help needed
• Systematic study in progress

15
gp?K L(p0) analysis
S0 events removed by Pmissing cut
Missing momentum cuts for selecting p0
16
gp?K L(p0) analysis
MM2(LK)
MM2(LK)
Before Pmiss cut
after Pmiss cut
p0
Effects of missing momentum cuts
17
gp?K L(p0) analysis
Bump around 1.5GeV shifts with beam energy /w
18
gp?K L(p0) analysisS0(1385) yield extraction
Eg 2.5GeV
M(Lp0 )
19
gp?K p(S-) analysis
S
S-
Bump? around 1.48GeV when S events removed
20
gp?K0 p (L) analysis (40 g11 statistics)
Events dominated by K events and S (1385) No
S (1480) observed (50 background)
21
gp?K p- p (L) analysis5 g11 statistics
No obvious S(1480) in Lp spectra with high
Background