Cascade Physics at BaBar and GlueX

1
Cascade Physics at BaBar and GlueX with
Selected LASS-GlueX Comparisons Veronique
Ziegler (SLAC) GlueX Workshop Jefferson
Lab, March 6-8, 2008
2

• Overview
• Relevance of Cascades to Baryon Spectroscopy
• 2. Cascade Physics from Charm Baryon Decay ()
• BaBar as a Charm Baryon Factory
• Measurement of the W- spin PRL 97, 112001
  (2006)
• Motivation for quasi-two-body approach to Cascade
  Resonance study
• Application to Lc ? K X(1530)0, X(1530)0 ?
  X- p
• Measure X(1530) spin shortcomings of
  quasi-two-body approach need for understanding
  of entire Dalitz plot to be submitted to
  Phys.Rev.D
• Application to Lc ? K X(1690)0, X(1690)0 ? L
  K0
• Quasi-two-body approach again inadequate
  performed full Dalitz plot analysis Proceedings
  of MENU NSTAR conferences Phys.Rev.D article
  in preparation
• Comparison of Detector Characteristics Relevant
  to Cascade Physics
• BaBar - GlueX
• LASS - GlueX
• Possible Cascade Studies with GlueX
• Summary
• 
  
  
• Note The inclusion of charge conjugate states
  is implied for BaBar analyses.

()Ph.D. Thesis SLAC-R-868
3
Relevance of Cascades to Baryon Spectroscopy

• Quark content ( u or d, s, s )
• ? QCD calculations easier to handle
• ? Developments in fast algorithms raised
• expectations from Lattice QCD
• Narrow widths
• ? reduces potential overlap with
• neighboring states
• Predictions of mass, width, spin/parity
• rely on model-based calculations
• ? Experimental validations are essential
• ? Very little known about X states which
• might populate the 70, 1-1 and 56,
  22

X(1530)
3
4
Cascade Physics from Charm Baryon Decay
4
5
BaBar as a Charm Baryon Factory

• Present data sample contains (N s L)
• gt 490 M U(4S) ? BB events (s 1.05 nb)
• gt 1500 M ee- ? qq events (s 3.39 nb)
• gt 600 M ee- ? cc events (s 1.30 nb)
• Charm Baryon ( Meson)
• Factory

Excellent resolution High statistics charm ba
ryon production
?
Large Samples of Charm Baryon Two-body
Quasi-two-body Decays Rare Decay Modes
Accessible with Reasonable Statistics
?
Can Study Hyperon Hyperon Resonance propertie
s with high precision e.g. W- Spin PRL 97,
112001(2006)
?
Hyperon Hyperon Resonance Cottage Industry
?
5
6
Spin measurement of W- from Xc0 ? W- K, W- ?
L K- decays

• Helicity Formalism
• Examine implications of W- spin hypotheses
• for angular distribution of L from W- decay

density matrix element for W- spin projection
li density matrix element for charm
baryon parent
6
7
The X(1530)0 From Lc ? X- p K Decay
8
Reconstructed Lc ? X- p K, X- ? L p- Events
ct 7.9 cm
ct 4.9 cm
m(X- p) ? Lc mass-signal region ? m(X-
p) ? Lc mass-sideband region .



. m(X- p) ? (Lc)
mass-sideband-subtracted
ct 60 µm
Data 230 fb-1
(Lc)Mass-sideband-subtracted
Uncorrected
dominant
N 13800 events
? X(1530)0 ? X- p
HWHM 6 MeV/c2
? Lc ? X- p K
PDG mass
8
9
Resonant Structures in the Lc ? X- p K
Signal Region
Only obvious structure X (1530)0 ? X- p
Rectangular Dalitz plot
Note m2(X- K) depends linearly on cosqX
10
Using Legendre Polynomial Moments to Obtain
X(1530) Spin Information
Lc signal region
Efficiency-corrected P4 Moment Dist.
efficiency-corrected unweighted m(X- p)
distribution in data
wj (7/ v2) P4(cosq) from Lc signal region
? X(1530)0
Spin 5/2 Test

• PL moments (L 6) give no signal

? spin 3/2 clearly established ? spin 5/2
ruled out
Efficiency-corrected P2 Moment Dist.
wj v10 P2(cosq) from Lc signal region
Schlein et al. showed JP 3/2 or JP5/2-, and
claimed Jgt3/2 not required. Phys.Rev.Lett.11,
167 (1963), Phys.Rev.142,883 (1966)
Spin-parity 3/2 is favored by the data
PDG (2006)
Spin 3/2 Test
? Present analysis by establishing
J3/2 will also establish positive parity by
implication
i.e. P-wave resonance

• Other interesting aspects of Dalitz plot not
  as simple as it first appears !

10
11
Further Investigation of X0(1530) Spin
Efficiency-corrected, Lc Mass-sideband-subtracte
d cos?X Spectrum
1.51 lt m(X-p) lt 1.56 GeV/c2
a (1 3 cos2?) for J3/2 hypothesis

• Assumption of single wave
• quadratic nature of
• distribution
• ? rule out spin 1/2
• Also rule out spin 5/2
• Best fit by far is with
• a (1 3 cos2?) but it is not
• a good fit!
• Strong interactions in the (X p) system ?
  possible X(1530) interference with other (X- p)
  amplitudes

Dominant 13cos2? structure
J5/2 hypothesis
12
Evidence for S-P wave interference in the (X- p)
system produced in the decay Lc ? X- p K
Efficiency-corrected m(X- p) distributions
weighted by P1(cosq)
Classic S-P wave interference pattern as a
function of m(X- p)
X(1530)0

• Oscillation due to rapid
• Breit-Wigner P-wave phase
• motion slowly varying
• S-wave phase.
• Eg. Kp scattering,
• D. Aston et al., Nucl.Phys.B296, 493 (1998)
• D0?K0 K K- for similar behaviour in f region
  Phys.Rev.D72, 052008(2005), BABAR

Lc signal region
Lc high mass sidebands
little evidence of structure

• First clear evidence of
• X(1530)0 Breit-Wigner phase motion

Lc low mass sidebands
13
Partial wave amplitude description of the (X-p)
system produced in the decay Lc ?? X- p K
Angular distribution of the X- produced in the
decay of the (X- p) system
? Total Intensity I
14
Helicity Formalism
Relationship between L, Sgt states helicity
states M. Jacob C.G. Wick On the General
Theory of Collisions for Particles with
Spin Annals of Physics 7, 401 (1959)
AJl in terms of S, P, D waves
?
J1/2
Interference
J3/2
(Assuming r1/2 r-1/2)
Cannot distinguish between (S1/2 P3/2) nor
between (P3/2 D3/2)
however strong P3/2 wave suggests term
containing S1/2, P3/2 amplitudes dominates
Minami ambiguity
Try simple model assuming only S1/2 and P3/2
amplitudes
15
Amplitude Analysis Assuming S and P Waves
-

Unphysical

• v10 P2(cosq) moment projects too much signal!!
• need more than S and P waves

16
Implication of Fits to the X(1530)0 Lineshape
Residuals
Residuals
Data - Fit
Data - Fit
Data - Fit
Data - Fit
Expected improvement in fit quality not realized

• Poor fit
• due to interference
• with other waves?

Effect should disappear in P0(cosq)
moment distribution
Structure in X- K i.e. another isobar ? Or
(Kp) I3/2 amplitude contribution?
17
Evidence for S-P wave interference in the (X- p)
system produced in the decay Lc ? X- p K
Efficiency-corrected P1(cosq) moment
Background-subtracted Efficiency-corrected
P0(cosq) moment
X(1690)0
X(1530)0
Im A

• S-wave accelerates catches up on the
  P-wave
• Dip (1680 MeV/c2) may be due to resonant
  X(1690)0 S-wave ? negative parity for
  X(1690)0

Speculation
non-resonant S-wave
Coherent superposition of resonant S-wave
i.e. slowly-varying amplitudes phase
X(1690)0
Does a small X(1690)0 ? X- p decay rate make
sense?
Re A
17
18
X(1690)0 Decay to X- p
345 GeV/c S- beam on Cu and C

• M 1686 4 MeV/c2
• G 10 6 MeV
• This X(1690) decay mode exists
• Product of the production cross
• section and branching fraction,
• s.BF, is small compared to that
• for X(1530)0

M.I. Adamovich et al. Eur.Phys.J. C5, 621 (1998)
consistent with BaBar values
X(1530)0
X(1690)0
X(1690)0

• Interesting to pursue the X- p S-P
• wave amplitude analysis
• Evidence for negative parity would
• contradict present theoretical
• expectations, except for

19
The X(1690)0 From Lc ? L K0 K Decay
20
Reconstructed Lc ? L KS K Events
Data 200 fb-1
N 2900 events
HWHM (3.1 0.5) MeV/c2
ct 7.9 cm
ct 2.7 cm
ct 60 µm
Selection Criteria
dE/dx Cherenkov info (DIRC)
21
The X(1690)0 from Lc ? (L KS) K Decay
Uncorrected
Uncorrected
(Lc)Mass-sideband-subtracted
? X(1690)0 ? L KS
N 2900 events
HWHM (3.1 0.5) MeV/c2
Lc Low-mass sideband limit
Note skewing
22
Using Legendre Polynomial Moments to Obtain
X(1690) Spin Information
Efficiency-corrected P4 Moment Dist.
Spin 5/2 Test
Suggest J(X1690) 1/2
efficiency-corrected, bckgr.-subtracted dist. in
data for 1.665ltm(L KS)lt1.705 GeV/c2
Efficiency-corrected P2 Moment Dist.
Spin 3/2 Test
however cosqL clearly not flat as expected for J
1/2 WHY?
22
23
Dalitz plot for Lc ? L KS K
Accumulation of events in KSK near threshold ?
evidence of a0(980)
a0(980)
23
X(1690)0
24
Isobar Model Description of the Lc ? L K0 K
Dalitz Plot
pL. ql
2l1
Fit for m0 G(m0) with L0, l0
gKK 473 49 MeV BaBar Exp.
25
Isobar Model Description of the Lc ? L K0 K
Dalitz Plot
Under the assumption of spin 1/2 for the X(1690)
relative strength
La0(980) - X(1690)0K Interference
Weak decay yields 4 terms with same structure
but different amplitude and phase Hence define
effective scale
effective phase

where p momentum of K in (L KS) rest-frame.
Individual Breit-Wigner Intensity Contributions
26
Comparison of Max. Likelihood Fit Result to the
Signal Projections
For J(X1690) 1/2
1.615 lt m(LKs) lt 1.765 GeV/c2

• Excellent reproduction of skewed lineshape and
  of cosqL distribution

• Background-subtracted, efficiency-corrected
  data
• ? Integrated signal function smeared by mass
• resolution Histogram
• ? Signal function with no resolution smearing
• ? A(a0(980)2 contribution
• ? A(X(1690)2 contribution
• ? Interference term contribution

c2/NDF 188.4/192 C. L. 56.4
27
Fit Results
For J(X1690) 1/2
X(1690)0 signal region

• Actual X(1690) signal significantly smaller
• (25) than apparent signal because of
  interference effects

27
28
Fit Results (different relative intensity scale)
Region of destructive interference
28
29
X(1690)0 Spin Study Conclusions

• Model based on coherent superposition of
• amplitudes describing Lc isobar modes
• JX(1690) 1/2 favored by the data (C.L.
  56.4)
• JX(1690) 3/2 (C.L. 1.9) 5/2 (C.L. 17.4)
  
• yield poorer fits and
• systematically fail to
  reproduce
• the skewed X(1690)0
  lineshape
• Discrimination should be improved with final
• BaBar statistics

30
Comparison of Detector Characteristics Relevant
to Cascade Physics
31
BaBar-GlueX Comparisons
Reminder X topology Diagram
() Would also like to reconstruct X0. Note 1st
W- event in BC was W- ? X0 p-

• Large acceptance, multi-pupose detector
• Acceptance -0.92 lt cosq lt 0.85 (q c.m.s.
  polar angle w.r.t. collision axis)
• Excellent charged particle tracking (SVT Drift
  Chamber) and P.I.D. ( DIRC)
• Excellent g measurement (i.e. p0 ? g g, h ? g g,
  etc.) in EMC

32
Excellent Vertex Reconstruction Capability (1)
233 fb-1 e e- data
SVT support tube
DCH inner wall
beampipe
33
Excellent Vertex Reconstruction Capability (2)
SVT Layer 1
Inner SVT r.f. shield
Ta foils
Beampipe
34
Excellent Vertex Reconstruction Capability (3)
(10 mm)
(10 mm)
Radial Vertex Resolution 90 mm
35
Very uniform Lc ? L K0 K Dalitz Plot
Acceptance Efficiency Parametrization as a
Function of m(LKS)
E0 Average Efficiency
E1
E3
E2
Smooth efficiency as a fcn of ( m, cosq )
E6
E5
E4
Ei fcn(mass) 2nd order polynomial
Weak dependence on cosqL
36
Very Good Invariant Mass Resolution e.g. for L K0
in Lc ? L K0 K
37
Very Good Particle I.D.
37
38
Q How do BaBar and GlueX Compare ?
BaBar
GlueX

• Multiple purpose Yes
• Acceptance 0.85 gt cosq gt -0.92
• Charged-particle tracking Excellent
• Photon detection Excellent
• Vertex resolution Excellent
• Mass resolution Excellent
• Particle ID Excellent
• Use Inclusive charm baryon production high
  multiplicity environment ? select large p
  events single production mechanism no initial
  polarization, etc

• Yes
• 4p problem with low polar angle charged
  tracks?
• Very good
• Very good
• Good (?)
• Very good
• Very good
• Inclusive AND Exclusive Production constrained
  kinematic fits improve substantially multiple
  production mechanisms polarization information.

For X Studies
A Very well Overall !
39
LASS-GlueX A More Direct Comparison

SLAC-R 298, (1986)
Innovations Solenoid (2.2 T) Dipole (30 kG
m) 4p Acceptance and Trigger Run in
"Interaction Mode Electronic Bubble
Chamber First use of microprocessor farm
in HEP 9 370 -168E processors built
by Paul Kunz 1 Tech. 2 3081E
processors later for MC and kinematic
fitting First use of a Solenoidal Vertex
magnet detector in a fixed target
experiment.

40
Example of Data QualityK- p ? K0S p- p at 11
GeV/c 100 k evts
Presented to Prof. Dalitz on his retirement (1990)
First use of colored scatter plots in HEP
(?) (Very primitive) No printer 35 mm slide of
IBM 5080 monitor off-site creation of
transparencies and prints
41
Chew-Low Plot Acceptance
K- p ? X L ( 11 GeV/c ) g p ? X p
( 9 GeV/c ) X pp-
K- p ? X L ( 11 GeV/c ) X
pp-
-u2(GeV/c)2
(34 k events) SLAC-R-421
Baryon exchange
Meson exchange
-t2(GeV/c)2
41
42
The Need to Reconstruct Tracks Backward-going in
the Lab
Peyrou Plot for p in K- p ? K- p n
pz 0
pT (GeV/c)
Backward in Lab Frame
pz (GeV/c)
43
Q How do LASS and GlueX Compare ?
LASS
GlueX

• Multiple purpose Somewhat
• Acceptance 4p dipole covers low q
• Charged-particle tracking O.K. (2mm
  wire-spacings P.C.s)
• Photon detection Non-existent
• Vertex resolution O.K.
• Mass resolution O.K
• Particle ID Very Limited
• Inclusive large flight length required (gt2 cm)
• Exclusive substantial gains from overall fits
  to topology and
  kinematics
• multiple production mechanisms polarization
  information

• Yes
• 4p problem with low polar angle charged
  tracks?
• Very good
• Very good
• Good (?)
• Very good
• Very good
• Inclusive AND Exclusive Production constrained
  kinematic fits improve substantially multiple
  production mechanisms polarization information.

no g detection
p0 from missing mass
For X Studies
A GlueX should do much better than LASS !
43
44
Effect of Constrained Kinematic Fits LASS K-
p ? L KS KS
Inclusive L and KS studies required flight length
gt 2 cm. For this exclusive reaction, after
kinematic and topological fit, no flight length
requirements necessary. Nucl.Phys.B 301, 525
(1988)
? f2(1525)
Low statistics, but very clean !
f0(980)
a2(1320)
45
Possible X Studies with GlueX

• Survey Processes to Provide an Overview of X()
  Photoproduction
• Inclusive X- (X0 ?) Production
• Feynman x and pT2 distributions
• Chew-Low plot(s)
• Polarization measurements
• Etc
• Similar Studies for Cascade Resonance Production
  (e.g. X(1530)?X-p) and Associated Spectra
• Note In the LASS search for W- states, the
  inclusive mass distribution for (X-pK-) showed
  nothing however when the (X-p) was selected
  to correspond to the X(1530)0, a signal for the
  W(2250)- was observed.

46
Possible X Studies with GlueX (ctd.)

• Exclusive t-channel (i.e. meson exchange)
  Processes
• Production of two-body systems with a X
• e.g. g p. ? K (X- K)
• ? K (X0 K0)
• ? K0 (X0 K)
• would enable the study
• of high mass L and S
• states decaying via these
• X modes.

47
Possible X Studies with GlueX (ctd.)

• Production of three-body systems with a X, or a
  X system with two-body decay
• with a forward K0
• e.g. g p. ? K0 (X- p) K, K0 (X0 p0) K, K0 (X0
  K0) p
• ? K0 (L K0) K
• with a forward K
• e.g. g p. ? K (X- p) K0, K (X- p0) K
• ? K (X0 p-) K, K (X0 p0) K0
• ? K (L K-) K
• Interesting four-body possibilities
• when add pion
• e.g. g p. ? K (L K- p) K,
• accessible at BaBar via Xc0? LK-p, complicated
  Dalitz plot

S, L
States analyzed in Lc decay
- can observe in a totally different context
m(Lc)
48
Possible X Studies with GlueX (ctd.)

• Exclusive u-channel (i.e. baryon exchange)
  Processes
• All of the t-channel processes discussed have
  corresponding u-channel counterparts in which the
  bachelor K or K0 is attached to the proton vertex

• At 9 GeV/c, such processes should have small
  cross section values however with very large
  statistics and an interaction trigger,
  interesting results may be obtained. E.g. in
  LASS, the forward-produced KK- system in
  K-p ? L(KK-) was studied, but when K-p ?(L
  K-)fwd K was examined, a nice X(1820) signal was
  observed. So in g p ? (X- K)fwd K may see
  some interesting L/S distributions!

K-p ? (L K-)fwd K _at_ 11GeV/c (4c fits)
? X(1820)
49
SUMMARY

• Three-body systems involving two-body Cascade
  resonance decays require analysis of the entire
  Dalitz plot when the statistical level is such
  that the shortcomings of a quasi-two-body
  approach become apparent. GlueX should be in
  this statistical situation.
• In terms of acceptance, track and vertex
  reconstruction (after kinematic fits), and
  particle identification capability, GlueX should
  be able to perform Cascade studies of the kind
  suggested in section 4) provided the relevant
  cross section values are large enough.

50
BACKUP SLIDES
51
MIGRAD FIT PARAMETER VALUES
Fit c2/NDF 188.4/192 Prob.. 56.4
SLAC-R-868
52
Fit Results (K KS) (L KS) Mass Projections
m(L KS) mass cut-off 1.62 lt m(L KS) lt1.765
GeV/c2 introduces a kink because of restricted
range of (L K) helicity cosine
52
53
Comparison of Max. Likelihood Fit Result to the
Signal Projections
Under the assumption of spin 3/2 for the X(1690)
c2/NDF 234.3/192 C. L. 1.9
Interference term very small ? Equiv. to
incoherent superposition of amplitudes
Lineshape skewing not reproduced!
54
Comparison of Max. Likelihood Fit Result to the
Signal Projections
Under the assumption of spin 5/2 for the X(1690)
c2/NDF 210.3/192 C. L. 17.4
Net interference term very small ? Equiv. to
incoherent superposition of amplitudes
Lineshape skewing not reproduced!
55
Summary of Results Systematic Uncertainties
Spin 1/2
Spin 1/2 favored
Poor C.L.
Accept. C.L.
Fail to reproduce skewed lineshape fit mass
value moves higher in attempt to compensate
55