Overview: Cascade physics provides a window to baryon spectroscopy

1
Cascade Spectroscopy at CLAS
Lei Guo, JLAB for CLAS Collaboration

• Overview Cascade physics provides a window to
  baryon spectroscopy
• Ground state X(1320) gp?K K(X-)
• Few photon data existed. New CLAS g11
  data70/pb-1, E04.0186 GeV
• Cross section measurement
• Production mechanism probe (Y?X K?)
• Search for excited X states in X- ? X0p-
• gp?K K p-(X0) analysis
• Summary

2
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
3
X(1620) andSearch for X- ?X 0p-
Excited cascades Mass (GeV/c2) Width (MeV/c2) BR
X-0(1530) 1.535 9.1 100
X0(1620) () 1.6-1.63 22 Xp
X-0(1690) () 1.69 lt30 seen

• Fewer excited cascade states observed
• X(1620)s exotic nature
• Does it exist?
• Is the mass too low
• N partner? (Azimov et al)
• (nucl-th/0307088)
• Dynamicaally generated? member of JP1/2
  octet?
• Ramos et.al (nuclth/0204044 )
• CLAS ideal for X- in exclusive reaction gp?K
  K p-(X0)

p-
X0
4
Is there a X(1620) state? New Very high
statistics results
X 103
Inclusive reaction S- (C, Cu) ? (X-p) X M(X-
p ) 345GeV/c
No mention of X0(1620) X0 (1690) claimed
Adamovich et al. W89 Collaboration Eur. Phys. J.
C5(1998) 621
After backgroud subtraction
5
g11 KK missing mass spectrain reaction gp?K
K(X-)
X- (1320)
X-
Events/2MeV/c2
Events/2MeV/c2
X- (1530)
MM(KK) (GeV/c2)
MM(KK) (GeV/c2)
Loose PID cuts Eg gt2.6 GeV
Tighter PID cuts TOF_Vtime RFVtimelt 1ns
6
Data Simulation comparison
Cos(q)_K1,2
Cosq(X)
M(K K )
M(X- K1,2 )
Y input M 1.96GeV/c2 width 220 MeV/c2
Simulation t channel process gp?K Y, Y?KX-
7
g11 X- Cross section extraction
g
K
K-
K
p
Y
s(nb)
X-
Preliminary
Y Mass (GeV) Width (MeV) BR?XK
S(1940) 1.94 200 N/A
S(2030) 2.03 180 lt2
L(2100) 2.10 200 lt3
Eg(GeV)
s extracted from ds/dcos(qK ) and
ds /dcos(qX )
8
X- differential Cross section extraction ds
/dcos(qX )
Eg 3.09 GeV
Eg 3.29 GeV
Eg 3.19 GeV
Eg 3.59 GeV
Eg 3.49 GeV
Eg 3.39 GeV
Eg 3.69 GeV
Eg 3.79 GeV
Data consistent with t channel process
9
X- differential Cross section extraction ds
/dcos(qK )
Eg 3.09 GeV
Eg 3.29 GeV
Eg 3.19 GeV
Eg 3.59 GeV
Eg 3.49 GeV
Eg 3.39 GeV
Eg 3.69 GeV
Eg 3.79 GeV
Yield extracted when either K falls in dcos(qK
)
10
X- differential Cross section extraction
ds/dt(g?Kfast )
Eg 3.09 GeV
Eg 3.29 GeV
Eg 3.19 GeV
Eg 3.59 GeV
Eg 3.49 GeV
Eg 3.39 GeV
Eg 3.69 GeV
Eg 3.79 GeV
Acceptance at very low t an issue Two identical
bosons!
11
Is X coming from Y decay?gp?K Y, Y?nK0 /pK
-/ KX-
Eggt 3.4GeV gp?K Y
Eggt 3.4GeV gp?K KX-
M(nK0 )
/10MeV/c2
Events/10MeV/c2
M(pK- )
/5MeV/c2
M(X-K)
Information from ds/dM(KK),ds /dM(KX), ds
/dcos(qX ) and ds /dcos(qK ) could be used to
determine properties of Y
12
Is X coming from Y decay?gp?K Y, Y?nK0 /pK
-/ KX-

• Statitics insufficient to be conclusive
• Not inconsistent with multiple Y?XK
• ds strength independent of Eg at low M(XK)
  Diffractive process?

ds/dM(XK)
ds(nb/GeV)
M(XK) (GeV/c2)
13
gp?K KX-, X- ? p-X0
MM(KKp-)
M(X0p-)
Preliminary
Shaded events Background from out of target
events
M(X0p-)
Background subtracted
14
Simulated pion background
Preliminary
p
p
g
X
Events/4MeV/c2
p-
p0
N
p
n
MM(KKp-)
M1.675GeV, G0.153GeV (to be tuned)
X(1620)?
Events/10MeV/c2
Background with only one p ---gt K to be added
M(X0p-)
X(1530)
15
Angular distributions
CosHELqp VS M(X0p-)
CosHELqp
Around X(1530)
Preliminary
Cosq(Xp) VS M(X0p-)
Around X(1620)?
Produced in background angles in CM frame
Interesting structures
16
Summary and outlook

• CLAS good instrument for Cascade photoproduction
• X-(1320) cross section obtained for Eg 2.743.84
  GeV ( s(Eg) ?Eg ?)
• Data consistent with t channel production of Y?
  X- K
• New way to study Y through possible XK decay
• Observation of X-(1620)?? in g p? p- K K(X0 )
  ?
• Angular distributions to be interpreted
• Future high energy experiment desirable!

17
X0p- invariant mass spectrain different Eg ranges
Eglt 3.75GeV
Eggt 3.75GeV
Events/4MeV/c2
M(X0p-) (GeV/c2)
M(X0p-) (GeV/c2)
If the peak is due to reflection it will migrate
when Eg /(w) changes
18
gp?K K0(X0) or gp?K KX-, X- ? p-(X0)
X0
X0
gp?K K0(X0) unlikely
19
Do we see it in MM(KK) without detecting p-?
MM(KK)
M(K)_TOF
TOFvtime-vtime lt1ns
X- (1530)
?
TOFvtime-vtime lt200ps
More pion background in gp?K K(X-)