DsJ and Charmed Baryons at BABAR

1
DsJ and Charmed Baryons at BABAR

• Outline
• Charmed Strange Mesons
• DsJ(2317), DsJ(2460), and DsJ(2860)
• Charmed Baryons
• ?c(2940), Xcc, Xcc, Wc0, and W-

• Amir Rahimi
• The Ohio State University
• For BABAR Collaboration
• Heavy Quarkonium Workshop
• June 27-30, 2006

2
Charmed Strange Mesons
3
Charmed Strange Mesons

• Picture for cs system is still incomplete
• The states DsJ(2317) and DsJ(2460) were first
  observed by BABAR and CLEO and confirmed by Belle
  (2003)
• Masses unexpectedly low
• Below DK and DK thresholds respectively
• Only electromagnetic and isospin-violating strong
  decays Kinematically allowed
• Narrow widths
• Decay pattern consistent with JP0 or JP1,
  respectively
• Possible candidates
• cs meson states
• Exotic particles such as four-quark states

Ds2
Ds1
DsJ(2460)
DsJ(2317)
Ds
Ds
4
Charmed Strange Mesons

• Comprehensive study of decays to Ds plus one or
  two p?, p0, or gs.
• Decay pattern if JP0 or JP1, respectively

BABAR 232 fb-1 Submitted to PRD
Ds?0 only decay mode observed for DsJ(2317)
5
DsJ(2317) ? Dsp0

• No Indication of neutral or doubly-charged
  partner near 2317 MeV ? I 0

N318080
(Ds(2112)?Dsg) g reflection
DsJ(2460)?Dsp0g reflection
Ds(2112) signal
Circles Ds sidebands
6
DsJ(2460)?Dsg / Ds(2112)p0 Dsg
DsJ(2460) ? Ds(2112)?0
DsJ(2460)?Ds ?
Open points Ds sidebands
N56040
Open points Ds sidebands
(DsJ(2317)?Dsp0)g reflection
(Ds(2112)?Dsg) gg reflection
N92060
BABAR 232 fb-1 Submitted to PRD hep-ex/0604030
7
DsJ(2460)?Dspp-
BABAR 232 fb-1
N63

• No indication of DsJ(2317)
• Also observe Ds1(2535)

N12315
N19322
DsJ(2317)
DsJ(2460)
Ds1(2536)
8
DsJ(2460) Absolute Branching Fractions

• BB sample with one B fully reconstructed ? Study
  decays of B?D(),0(Ds()-) X
• Observe DsJ(2460) signal in the recoil mass, mx
• Mass and momentum of X inferred from the
  kinematics of the two body B-decay

BABAR 210.5M BB
Submitted to PRD hep-ex/0605036
9
DsJ(2460) Absolute Branching Fractions, cont.

• First measurement of absolute BFs for
  B?D(),0DsJ(2460)- decays, e.g.
• B(B0? DDsJ(2460)-)(0.880.0.20.14)
• Combine with previously measured, exclusive
  product BFs
• B?D() DsJ (2460), DsJ(2460)?Ds? /
  Ds(2112)?0/Dspp- to obtain absolute BFs

Preliminary
B(DsJ(2460) ?Ds(2112)p0)0.560.130.09 (Ds
?Dsg) B(DsJ(2460) ?Dsg)0.160.040.03
B(DsJ(2460) ?Dspp-)0.04 0.01 Sum of BFs
for DsJ(2460) decaying to p0/g/pp- 7620
B(Ds ? fp) (4.620.360.51) as determined in
this analysis
10
Observation of a New Ds Meson Decaying to D0K,
D0? K- p
BABAR 240 fb-1

• New structure at 2.86GeV/c2
• Not observed in D0 sidebands
• Not observed in ee-?ccX MC
• Not due to D reflections
• Reflection from Ds1(2536)
• Ds1?D0K, D0?D0p0/g
• Narrow structure at threshold
• Ds2(2573) signal
• Broad structure at around 2.7 GeV/c2

Dsj (2536) reflection
11
Other observations of DsJ(2860)

• Similar structure were observed in
• D0K, D0? K- pp0
• DK0S, D? K-pp
• Need extra structure around 2.7 GeV/c2 (fits
  better with a Gaussian).
• Activity in this region seen in the D0 sidebands
  at very low p

872139 events (6.3 s)
1099214 events (5.1 s)
585212 events (2.8 s)
D? K-pp
Removing the DsJ(2860) from the fit Dc2108 for
DNDF5
No evidence for DsJ(2860) to DK decays ?
implies natrual spin-parity JP 0, 1-, 2, 3-
12
Charmed Baryons
7-foot Bubble Chamber
Discovery of the Charmed Baryon (BNL, 1975)
Discovery of W- Particle (BNL, 1964)
13
New Charmed Baryon ?c(2940)
First evidence for bare charm including Lc and
Sc came from BNL group

• Observed in cc continuum events in the decay
  mode D0p (D0?K-?, K-???-)
• New state ( 7s)
• First observation of
  
  ?c(2880)?D0p
  
• No structure in Dp
• No doubly-charged
  partner for either state
• No isospin partners

BABAR 287 fb-1 Submitted to PRL
Preliminary
N2280310 (7 s)
?c(2880)
N3020 220
?c(2940)
D0 sidebands
D0p
14
Doubly Charmed Baryons
In a u,d,s,c SU(4) scheme, the ground states
occupy the top level of a 20'-plet.
Double-charm baryons Six ground states three
with JP ½ three with JP 3/2

• Bjorken has estimated several branching
  fractions.
• B(?cc ? D0 ? p) 7.0
• B(?cc ? D0 ? p p) 5.0
• B(?cc ? ?c K- p p) 5.0
• B(?cc ? ?c0 p p) 4.5
• B(?cc ? ?c K- p) 3.0
• B(?cc ? ?c0 p) 1.5
• Many theories predicted masses (3.5-3.8) GeV/c2
• M(?cc - ?cc) 1 MeV/c2
• Predicted lifetimes (0.1-1.0) ps

15
Doubly Charmed Baryons

• No significant signals in this analysis for
• Xcc ? Lc K- p p
• Xcc ? Xc0 p p
• Xcc ? Lc K- p
• Xcc ? Xc0 p
• SELEX reports signal for five double charmed
  baryons
• Xcc ? Lc K- p
• Xcc ? D-pK-
• at m35191 MeV/c2
• also sees Xcc
• Null results also reported by Belle and FOCUS

95 C.L.
?c Sidebands
?cKpp p2.3 GeV/c
?c?pKp 232 fb1
?c0??p 232 fb1
95 C.L.
95 C.L.

95 C.L.

95 C.L.
16
Study of Wc0 Production and Decay
Line Shape Triple Gaussian (same mean) Linear
background function
hep-ex/0507011

• Properties of Wc0 baryon not well know (few
  observations of its production decay)
• Observation of Wc0 ? W- p at 5-s level
• Large uncertainties in previous measurements of
  ratio of B.F.
• high lumi ? improved measurements using larger
  sample
• First measurement of this ratio of Branching
  Fractions

Yield 138.5 14.8 HWHM 7 MeV/c2
225 fb-1 Data
W-p
Yield 29.9 13.6 HWHM 5 MeV/c2
Ratios of Efficiency Corrected Yields
X-K-pp
Yield 11.8 7.5 HWHM 5 MeV/c2
W-pp-p
17
PRODUCTION OF Wc0 CANDIDATES
Wc0 ? W-p

• Clear evidence of Wc0 production from B decays is
  visible at low p
• Absent in off peak data

All Data
First significant evidence for Wc0 production
from B decay
(GeV/c)
Off-Peak Data
? data ? ee- ? cc signal MC
(GeV/c)
18
The W- Spin Measurement
W- was discovered at BNL

• Measure spin of W- from Xc0?W-K and Wc0?W-p
• W-?L0 K-
• Present analysis assume that the Xc0, Wc0, and L0
  have spin 1/2
• The L angular distribution obtained for spin
  hypothesis JW 1/2, 3/2, and 5/2

Xc0
J1/2
Wc0
J3/2
J5/2
b maybe non-zero as a consequence of parity
violation in charm baryon and W- weak decay
19
The W- Spin Measurement

• Using Xc0?W-K, W-?L0 K
• Negligible Decay Asymmetry Parameter for JO3/2
• b 0.04 0.06
• Verify using Wc0?W-p
• Fit prob 0.69
• Consistent with result from Xc0?W-K result of
  J(W-) 3/2

Background-Subtracted Efficiency-Corrected
Xc0?W-K,
Data 116 fb-1
W0?W- p
Conclusion J(W-) 3/2 Assuming J(Xc0)
J(Wc0) 1/2
20
Summary

• Did a comprehensive study of DsJ(2317) and
  DsJ(2460) decays
• Masses unexpectedly low
• Measured DsJ(2460) absolute branching ratio
• Observed new strange meson decaying to DK system,
  DsJ(2860)
• Observed new charmed Baryon, ?c(2940)
• Observed ?c(2880)?D0p
• Studied Wc0 production and decay mechanism
• First significant evidence for Wc0 production
  from B decay
• Measured W- spin

21
Backup Slides
22
Production of hidden and open charm states
charmonium

• Production in B decays
• 380x106 BB events
• provides access to
• inclusive measurements
• of absolute branching fractions
• ee-!cc fragmentation
• 455x106 events
• spectroscopy of open charm
• states with high precision
• Initial state radiation (ISR) ee-!?ISR(cc)
• J/? sample 1.1x106 events
• resonance production in the
• energy range
• only production of JPC1-- states)

open charm
c
q
q
q
q
c
Babar offers excellent options for charm /
charmonium spectroscopy
23
Reconstruction
K-
?
?0
K

• Clean sample
• well identified K und ? candidates
• common vertex required
• Momentum pCM(Ds)2.2 GeV/c
• 400.000 reconstructed
• Ds!?(KK-)? and
• Ds ! K(K-?)K decays
• Combination of Ds candidates
• with further ?,?0,? of same event
• Momentum pCM(DsJ)3.2 GeV/c

?
?
Ds
e
e-
24
Reflections in Ds?0
Data
MC
Efficiency / resolution
25
Reflections in Ds?0?
Upper sideband
Fraction of reflection underlaying
signal estimated from upper and lower Ds
sidebands
Signal region
Lower sideband
26
Exclusive study of the DK system
949k entries

• Exlusive study of the DK system
• in ee-!cc processes
• Good kaon / pion identification
• Clean KS!??- and ?0!?? selection
• Kinematic fit to common vertex
• CMS momentum p(DK)3.5 GeV

791k entries
432k entries
Babar 240 fb-1 preliminary
27
Spin measurement of W- from Xc0 ? W- K, W- ?
L0 K- decays
Angular Distribution Parametrizations for JO3/2
hypothesis
Data 116 fb-1
Background-Subtracted Efficiency-Corrected
Negligible Decay Asymmetry Parameter
b 0.04 0.06
No Asymmetry
b 0
Asymmetry
Fit for b ? b 0.04 0.06
7
28
UPPER LIMIT ON RATIO OF BRANCHING FRACTIONS
For Wc0 ? W- p p p- no significant signal
events over bkgr ? 90 C.L. on ratio ? Toy Monte
Carlo inputs for each mode ? measured yields
? statistical uncertainties (Gaussian) ?
systematic uncertainties (Gaussian)
Toy Monte Carlo
90 C.L.
Wc0 B.R.
hep-ex/0507011