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

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

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

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

Charmed Baryon Spectroscopy Charmed baryon spectroscopy from the 2006 PDG 5

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

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

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

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

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

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

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/0602153

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

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

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

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

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

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

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: 0.1-0.2 ps for Ξcc+ and 0.5-1.5 ps for Ξcc++ e+e– cross sections: 1 to 250 fb at ~10.6 GeV 19

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

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

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

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 1-250 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

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

Observation of Ξc(2970)+ and Ξc(3077)+ Belle observed two new Ξc+ states decaying to Λc+K-π+ (461 fb-1, hep-ex/0606051) BABAR confirms these observations (316 fb-1, hep-ex/0607042) Ξc(2970)+ Ξc(3077)+ Λc+K-π+ See evidence for decays through Σc++ resonances in Dalitz plots Ξc(2970)+ Ξc(3077)+ 25

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

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+)

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

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