1. Charmed Baryon Spectroscopy at BABAR
DPF Meeting – University of Hawai’i
A.J. Edwards - Stanford University
Oct. 30

2. But BABAR is also a charm factory σ(bb) = 1.1 nb σ(cc) = 1.3 nb
The BABAR Experiment
2.2 km circumference
BABAR is a “B-Factory” located a SLAC
Use the PEP-II storage rings to produce e+e-collisions at Υ(4S) resonance
Υ(4S) decays to BB pairs, which BaBar uses for precision measure-ments in B physics
But BABAR is also a charm factory σ(bb) = 1.1 nb σ(cc) = 1.3 nb 2

3. The BABAR Experiment e+ [3.1 GeV] e- [9 GeV] 3
Cherenkov Detector (DIRC)
144 fused silica bars
K,,p separation
Electromagnetic Calorimeter
6580 CsI crystals
e± ID,  and reco, KL detection
Drift Chamber
40 layers
Tracking + dE/dx
Instrumented Flux Return
19 layers of RPCs
 ID and KL detection
Silicon Vertex Tracker
5 layers of double-sided silicon strips
e+ [3.1 GeV]
e- [9 GeV] 3

4. The BABAR Experiment BABAR
Run 1-5
BABAR has recorded an enormous data sample with >390 million BB pairs + even more charm events
Data taking will restart early next year after some detector upgrades
Full data set is expected to reach >900 fb-1 in 2008
Results presented here are based on subsamples of the full dataset 4

5. Charmed Baryon Spectroscopy
Charmed baryon spectroscopy from the 2006 PDG 5

6. Charmed Baryon Spectroscopy
Λc(2940)+ is a new state seen along with Λc(2880)+ in a new type of excited Λc+ decay to D0p
Λc(2940)+
Λc(2880)+
D0p 6

7. Charmed Baryon Spectroscopy
Λc(2940)+ is a new state seen along with Λc(2880)+ in a new type of excited Λc+ decay to D0p
Λc(2940)+
Λc(2880)+
Ωc* is a newly observed state that corresponds to the last theoretically predicted charmed baryon ground state
Ωc*
D0p γ 7

8. Charmed Baryon Spectroscopy
Λc(2940)+ is a new state seen along with Λc(2880)+ in a new type of excited Λc+ decay to D0p
Λc(2940)+
Λc(2880)+ ?
Ωc* is a newly observed state that corresponds to the last theoretically predicted charmed baryon ground state
Ωc*
D0p ? γ
Do doubly charmed baryons exist? Are their production cross sections large enough to be seen?
Ξcc 8

9. Charmed Baryon Spectroscopy
Λc(2940)+ is a new state seen along with Λc(2880)+ in a new type of excited Λc+ decay to D0p
Ξc(3077)+
Two new excited Ξc states are found that are the first to decay into Σc++K- and Λc+K-π+
Ξc(2970)+
Λc(2940)+
Λc(2880)+
K-π+ ?
Ωc* is a newly observed state that corresponds to the last theoretically predicted charmed baryon ground state
Ωc*
D0p ? γ
Do doubly charmed baryons exist? Are their production cross-sections large enough to be seen?
Ξcc 9

10. Observation of Λc States Decaying to D0p
Searches for Doubly Charmed Baryons
Observation of Ξc(2970)+ and Ξc(3077)+ 10

11. Observation of Λc States Decaying to D0p
Submitted to PRL
With 287 fb-1 of data D0p invariant mass (D0 ® K-p+ or K-p+p+p-)
Lc(2880)+
Nsig = 2280 ± 310
Lc(2940)+
Λc(2880)+
A New Decay Mode
Improved mass measurement M=(2882±0.1±0.5) MeV/c2
The first width measurement Γ =(5.8±1.5±1.1) MeV
Λc(2940)+
New Charmed Baryon
M=(2939.8±1.3±1.0) MeV/c2
Γ=(17.5±5.2±5.9) MeV
D0p combination
D0 mass sidebands 11

12. Observation of Λc States Decaying to D0p
Are these states Λc+’s or Σc+’s ?
No signals implies both the 2880 and 2940 states are Λc’s, not Σc’s
D+p Invariant Mass with (D+→K-π+π+)
Establishes 2880 as a Λc+ for the first time
Signals if at same rate and efficiencies as D0p mode
Three different JP Λc states predicted at masses ~2940 MeV/c2 12
Sascha Migura et al. hep-ph/

13. Observation of Λc States Decaying to D0p
Searches for Doubly Charmed Baryons
Observation of Ξc(2970)+ and Ξc(3077)+ 13

14. Observation of Ωc* Ground state singly charmed baryons
~65 MeV/c2
~100 MeV/c2
~220 MeV/c2
Ground state singly charmed baryons
??? MeV/c2
Ωc* is the last ground state singly charmed baryon to be discovered
Ωc* is a JP = (3/2)+ css quark state
Predicted ΔM(Ωc*-Ωc0) 50 – 94 MeV/c2
Observed in only allowed decay: → Ωc0 γ 14

15. M(Ωc0) of ±2.5σ used for Ωc* search
Observation of Ωc*
Ωc0 Invariant Mass
Ωc0 is reconstructed in four different decay modes using 231fb-1 of data
156±15
92±26
23±10
Scaled momentum xp for Ωc0 is required to be above 0.5 to reduce combinatoric background
34±15
M(Ωc0) of ±2.5σ used for Ωc* search 15

16. Observation of Ωc* Measurements is most significant channel at 4.2σ
There is no signal found in the Ωc0 mass sidebands (grey histograms)
Measurements
Mass difference with Ωc0, yields, and significances measured in each channel
Cross sections are compared for xp>0.5 16

17. Observation of Ωc*
The data from all four Ωc0 decay channels are combined and fit
Combined data give a 5.2σ signal significance
ΔM = 70.8±1.4 MeV/c2
Theory Range: ΔM(Ωc*-Ωc0) 50 – 94 MeV/c2
Submitted to PRL 17

18. Observation of Λc States Decaying to D0p
Searches for Doubly Charmed Baryons
Observation of Ξc(2970)+ and Ξc(3077)+ 18

19. Searches for Doubly Charmed Baryons
In a u,d,s,c SU(4) scheme, the ground states occupy the top level of a 20'-plet.
Ξcc+ = ccd
I=1/2
JP=1/2+
Ξcc++ = ccu
Ωcc+ = ccs
I=0
Several experiments have searched for Ξcc+ and Ξcc++
There are many predictions for Ξcc+ and Ξcc++ properties
Masses: 3.5 to 3.8 GeV/c2 and a mass difference of ~1 MeV/c2 between the isodoublet members
Lifetimes: ps for Ξcc+ and ps for Ξcc++
e+e– cross sections: 1 to 250 fb at ~10.6 GeV 19

20. Searches for Doubly Charmed Baryons
SELEX has reported observations while FOCUS, Belle, and BABAR have reported upper limits
SELEX uses ~1,630 Λc+ candidates in their search
FOCUS uses ~19,500 Λc+ candidates in their search
BABAR uses ~600,000 Λc+ candidates in their search (232 fb-1)
Belle uses 461 fb-1 in their search
SELEX estimates that 20% of their Λc+ sample comes from decays of Ξcc+
SELEX
BABAR search uses ~600,000 Λc+→pK-π+ candidates 20 a

21. Searches for Doubly Charmed Baryons
Ξcc+→Λc+K-π+
Ξcc++→Λc+K-π+π+
p*(Ξcc) > 0.0 GeV/c
p*(Ξcc) > 2.3 GeV/c
At SELEX mass
Search in 210 MeV/c2 Range
p* > 0.0
Λc+ Sideband
p* > 2.3
232 fb-1 , Phys.Rev.D74:011103,2006 21

22. Searches for Doubly Charmed Baryons
p* > 0.0
Ξcc+→Ξc0π+
Ξcc++→ Ξc0π+π+
p*(Ξcc) > 0.0 GeV/c
p*(Ξcc) > 2.0 GeV/c
At SELEX mass
Search in 400 MeV/c2 Range
Ξc0 Sideband
p* > 2.0
232 fb-1 , Phys.Rev.D74:011103,2006 22

23. Searches for Doubly Charmed Baryons
No significant signals found
Upper limits calculated
With wide range & p* cut
Λc+K-π+(π+) σB
Ξc0π+(π+) σB
Ξcc+
4.4 fb
3.0 fb
Ξcc++
5.5 fb
3.1 fb
Assuming Ξcc branching fractions O(1%), there is no conflict with theoretical cross section predictions of fb
Decay modes with Λc+ are compared to σ(Λc+)B(pK-π+) and decay modes with Ξc0 can be compared to:
σB /σ(Λc+) for decay modes with Λc+ ≤ ~0.01
σB /σ(Λc+) for decay modes with Ξc0 ≤ ~1.0 23

24. Observation of Λc States Decaying to D0p
Searches for Doubly Charmed Baryons
Observation of Ξc(2970)+ and Ξc(3077)+ 24

25. Observation of Ξc(2970)+ and Ξc(3077)+
Belle observed two new Ξc+ states decaying to Λc+K-π+ (461 fb-1, hep-ex/ )
BABAR confirms these observations (316 fb-1, hep-ex/ )
Ξc(2970)+
Ξc(3077)+
Λc+K-π+
See evidence for decays through Σc++ resonances in Dalitz plots
Ξc(2970)+
Ξc(3077)+ 25

26. Observation of Ξc(2970)+ and Ξc(3077)+
Extract signal yield, mass, and width in 2D unbinned likelihood fit
Ξc(2970)+
Ξc(3077)+
Using mass difference gives better resolution
Σc(2520)++
M(Λc+π+)
Σc(2455)++
M(Λc+K-π+) 26

27. Observation of Ξc(2970)+ and Ξc(3077)+
Allow for Σc++ resonances and non-resonant components in both signal and background
Σc(2520)++
M(Λc+π+)
Ξc+ states fit with resolution-folded BW with an explicit phase-space factor
Ξc(2970)+
Ξc(3077)+
Σc++ contributions 27
M(Λc+K-π+)

28. Observation of Ξc(2970)+ and Ξc(3077)+
Results for Ξc(3077)+ are consistent. Babar mass and width values
for Ξc(2970)+ are significantly smaller than Belle's.
The phase space factor, included by Babar, has a significant effect
on Ξc(2970)+ parameters but not Ξc(3077)+ parameters 7 28

29. Conclusions
First observation of charmed baryon to charmed meson decays
New state Λc(2940)+
Λc(2880)+ observed in new decay mode to D0p. Established for first time as Λc, not Σc. First measurement of width and much improved mass value.
Ωc* discovered → all the ground state (L=0) singly charmed baryons have now been seen.
No significant doubly charmed baryon signals are found
Ξc(2970)+ is found to decay non-resonantly and resonantly through Σc(2455)++, while Ξc(3077)+ is found to decay resonantly through Σc(2455)++ and Σc(2520)++
BABAR mass and width values for Ξc(2970)+ are significantly smaller than those from Belle 29