We present a mini-review on charm spectroscopy at the BaBar experiment. We
first report on the $c\bar{s}$ meson spectrum, and present precise measurements
of the $D_{s1}(2536)$ meson as well as the properties of the many new states
discovered since 2003 ($D_{s0}^*(2317)$, $D_{s1}(2460)$, $D_{sJ}^*(2860)$, and
$D_{sJ}(2700)$ mesons). We then discuss about charmed baryons observed recently
in the BaBar experiment: $\Omega_c^0$ and $\Omega_c^{*0}$ $css$ baryons,
$\Lambda_c(2940)^+$ $udc$ baryon and the $\Xi_c$ $usc/dsc$ baryons.Comment: 8 pages, to be published in the proceedings of the XII International
  Conference on Hadron Spectroscopy held at INFN, Frascati, Italy between
  October 8-13, 200

Poireau, V.

English

arXiv

International audienceWe present a mini-review on charm spectroscopy at the BaBar experiment. We first report on the $c\bar{s}$ meson spectrum, and present precise measurements of the $D_{s1}(2536)$ meson as well as the properties of the many new states discovered since 2003 ($D_{s0}^*(2317)$, $D_{s1}(2460)$, $D_{sJ}^*(2860)$, and $D_{sJ}(2700)$ mesons). We then discuss about charmed baryons observed recently in the BaBar experiment: $\Omega_c^0$ and $\Omega_c^{*0}$ $css$ baryons, $\Lambda_c(2940)^+$ $udc$ baryon and the $\Xi_c$ $usc/dsc$ baryons

HAL Université de Savoie

Charm Spectroscopy at BaBar

HAL-IN2P3

We present a mini-review on charm spectroscopy at the BABAR experiment. We first report on the c{bar s} meson spectrum, and present precise measurements of the D{sub s1}(2536) meson as well as the properties of the many new states discovered since 2003 (D*{sub s0}(2317), D{sub s1}(2460), D*{sub sJ}(2860), and D{sub sJ}(2700) mesons). We then discuss about charmed baryons observed recently in the BABAR experiment: {Omega}{sub c}{sup 0} and {Omega}*{sub c}{sup 0} css baryons, {Lambda}{sub c}(2940){sup +} udc baryon and the {Xi}{sub c} usc/dsc baryons

Poireau, Vincent

UNT Digital Library

Work supported in part by US Department of Energy contract DE-AC02-76SF00515Frascati Physics Series Vol. XLVI (2007), pp. 000-000HADRON07: XII Int. Conf. on Hadron Spectroscopy – Frascati, October 8-13, 2007Parallel SessionCHARM SPECTROSCOPY AT BABARVincent PoireauLAPP, IN2P3/CNRS et Universite´ de Savoie, Annecy-Le-Vieux, FranceAbstractWe present a mini-review on charm spectroscopy at the BABAR experiment.We first report on the cs¯ meson spectrum, and present precise measurementsof the Ds1(2536) meson as well as the properties of the many new states dis-covered since 2003 (D∗s0(2317), Ds1(2460), D∗sJ (2860), and DsJ (2700) mesons).We then discuss about charmed baryons observed recently in the BABAR ex-periment: Ω0c and Ω∗0c css baryons, Λc(2940)+ udc baryon and the Ξc usc/dscbaryons.1 IntroductionObservations of a long list of new meson and baryon resonances have beenrecently reported by the BABAR, Belle and CLEO experiments. We presenthere the new resonances observed in the cs¯ and charmed baryon sectors by theBABAR experiment.SLAC-PUB-13057arXiv:0711.3683v1[hep-ex]Contributed to 12th International Conference On Hadron Spectroscopy (Hadron 07) , 8-13 Oct 2007, Frascati, ItalyFor BaBar CollaborationIn this short review, we do not present results on cu¯ and cd¯ resonances(D, D∗, D∗∗ mesons) and on cc¯ states (charmonium or charmonium-like state).Analyzes presented here were performed using data collected at the Υ(4S)resonance with the BABAR detector 1), located at the PEP-II asymmetricenergy e+e− collider. From 1999 to 2007, the BABAR experiment recorded aluminosity of 432 fb−1 at the Υ(4S) peak and 45 fb−1 at 40 MeV below thepeak. This corresponds to about 475.106 BB¯ pairs and 620.106 cc¯ pairs. Theanalyzes presented here use only a subset of the total recorded luminosity.2 cs¯ mesonsBefore 2003, only four cs¯ mesons were known: two S-wave mesons, Ds (JP =0−) and D∗s (1−), and two P-wave mesons, Ds1(2536) (1+) and Ds2(2573) (2+).The masses predicted by the potential model 2) were in good agreement withthe measured masses. The potential model predicted also two other broadstates (width of a few hundred of MeV) at masses between 2.4 and 2.6 GeV/c2.2.1 Ds1(2536) mesonWith the discovery of additional cs¯ mesons, a comprehensive knowledge of allknown Ds mesons is mandatory. As of 2006, the properties of the Ds1(2536)meson were not perfectly known: the width was determined to be less than2.3 MeV at 90% confidence level, and the quantum numbers were only inferred.In Ref. 3), a high precision measurement of the mass and of the widthwas performed, using events in the cc¯ continuum. Reconstructing inclusivelythe decay Ds1(2536)→ D∗+K0S , with D∗+→ D0pi+ and D0 decaying either toK−pi+ or to K−pi+pi−pi+, one obtain a mass of (2534.85±0.02±0.40) MeV/c2(where the first error is statistical and the second is systematic). The error onthe mass is dominated by the uncertainty on the D∗+ mass. Furthermore, thewidth was measured at a value of (1.03 ± 0.05 ± 0.12) MeV. This is the firsttime that a direct measurement of the width is given, rather than just an upperlimit.Additionally, in another analysis 4), the Ds1(2536) meson was recon-structed exclusively in B decays, with B → D(∗)Ds1(2536) (8 modes in total)followed by Ds1(2536)→ D∗K. A total of 182± 19 events is seen, which givesan observation at the 12σ significance level (where σ is the 68% C.L. standarddeviation). With this method, a mass of (2534.78 ± 0.31 ± 0.40) MeV/c2 isobtained, in good agreement with the inclusive measurement. The exclusivereconstruction allows to determine the JP quantum number: fits to the helic-ity distribution in the data favor the quantum number J = 1 while J = 2 isdisfavored. More statistics is needed to conclude definitely and determine theparity P .2.2 D∗s0(2317) and Ds1(2460) mesonsIn 2003, two new resonances were discovered by the BABAR and CLEO experi-ments: the D∗s0(2317) and Ds1(2460) mesons5). These two resonances are verynarrow, and have masses well below what was predicted by the potential model(the D∗s0(2317) and Ds1(2460) mesons were predicted to lie above the DK andD∗K threshold, respectively, but have been observed below these thresholds).These states are very well known experimentally: masses are measured withan error below 2 MeV/c2, 95% confidence level upper limits on widths areabout 4 MeV ; JP quantum numbers (0+ and 1+ for D∗s0(2317) and Ds1(2460)respectively), decay modes and branching fractions are also well measured. De-spite a good knowledge of these states, their theoretical interpretation is stillunclear. One obvious possibility is to identify these two resonances with the0+ and 1+ cs¯ states, although it is difficult to fit these resonances within thepotential model. Other interpretations have been proposed: four quark states,DK molecules or Dpi atoms 6).2.3 D∗sJ(2860) mesonThe D∗sJ (2860) resonance was discovered by BABAR in 20067), looking in thecc¯ continuum: e+e− → D0K+X and e+e− → D+K0sX , where we considerthe decays D0 → K−pi+,K−pi+pi0 and D+ → K−pi+pi+ and where X couldbe anything. A clear peak is observed in the DK invariant mass for the sumof these 3 modes, with a mass of (2856.6 ± 1.5 ± 5.0) MeV/c2 and a widthof (47 ± 7 ± 10) MeV. This signal is seen with a statistical significance above8σ. Although this resonance is observed with a high significance, no otherexperiments have yet confirmed this state. Given that this resonance decaysto two pseudoscalars, the JP quantum number should be 0+, 1−, 2+, etc.Different interpretations have been proposed, inside the cs¯ scheme: this statecould be a radial excitation of the D∗s0(2317), but other possibilities are notruled out 8).2.4 DsJ(2700) mesonIn the same analysis, BABAR reported a broad enhancement, named X(2690),at a mass of (2688± 4± 3) MeV/c2 and a width of (112± 7± 36) MeV. A newstate, the DsJ (2700), was reported independently by Belle at a similar mass,with a JP quantum number equal to 1−, looking at B+ → D¯0D0K+ events 9).Since the X(2690) and DsJ (2700) mesons have the same decay modes and thatthe mass and width are consistent with each other, it is reasonable to thinkthat they are indeed the same state.BABAR performed an exclusive analysis 9), looking at events where Bdecays to D¯(∗)D(∗)K. Thanks to the many final states studied, this analy-sis has the advantage to be able to look at four D0K+ invariant mass dis-tributions as well as four D+K0s invariant mass distributions. Adding thesefinal states together, a clear resonant enhancement is seen around a mass of2700 MeV/c2. Furthermore, adding the four D∗0K+ and four D∗+K0s invari-ant mass distributions together, a similar enhancement is observed around amass of 2700 MeV/c2. No precise measurement was given by this preliminaryanalysis yet.The potential model predicts the 23S1 cs¯ state at a mass of 2720 MeV/c2.Also, from chiral symmetry considerations, a 1+−1− doublet of states has beenpredicted. If the 1+ state is identified as the Ds1(2536), the mass predicted forthe 1− state is (2721± 10) MeV/c2 10).3 Charmed baryonsThe production and decay of singly-charmed baryons are largely unexploredand provide an interesting environment to study the dynamics of quark-gluoninteractions. All nine ground states with JP = 1/2+ and all six ground stateswith JP = 3/2+ are now observed (the last missing state, Ω∗0c , was discoveredby BABAR in 2006). Several orbitally excited states have already been seenas well. The spin and parity of each of these excited single-charm baryons areassigned based on a comparison of the measured masses and natural widthswith predictions of theoretical models.3.1 Ω0c and Ω∗0c baryonsThe Ω0c baryon, a css state with JP = 1/2+, was observed by BABAR 11)decaying to four hadronic modes: Ω0c → Ω−pi+ (with a significance of 18σ),Ω0c → Ω−pi+pi0 (5.1σ), Ω0c → Ω−pi+pi+pi− (4.2σ) and Ω0c → Ξ−K−pi+pi+ (4.3σ).The ratios of branching fractions were measured, significantly improving uponthe previous values. The p∗ spectrum of Ω0c was also measured in order tostudy the production rates in both cc¯ and BB¯ events, using only the Ω−pi+final state. This analysis find comparable production rates of Ω0c baryons fromthe continuum and from B meson decays. This is the first observation of thisbaryon in B decays.Recently, BABAR discovered 12) the css ground state with JP = 3/2+,the Ω∗0c baryon. This baryon was observed with a significance of 5.2σ in thedecay to Ω0cγ, combining the four decay modes of the Ω0c cited in the previousparagraph. The difference of mass between Ω∗0c and Ω0c was measured to be(70.8± 1.0± 1.1) MeV/c2. A non-relativistic QCD effective field theory calcu-lation predicts the mass difference to be in the range 50-73 MeV/c2, while alattice calculation gives a mass difference equal to (94± 10) MeV/c2 13).The ratio of inclusive production cross-section was determined to beσ(e+e− → Ω∗0c X,xp(Ω∗0c ) > 0.5)σ(e+e− → Ω0cX,xp(Ω0c) > 0.5)= 1.01± 0.23± 0.11, (1)where the scaled momentum xp = p∗/p∗max of the Ω∗0c (Ω0c) is required to begreater than 0.5 in the numerator (denominator) cross-section.3.2 Λc(2940)+ baryonA search for charmed baryons decaying to D0p was performed 14) and re-vealed two states: the Λc(2880)+ baryon and a previously unobserved state,the Λc(2940)+. This is the first observation of charmed baryons decaying to aD meson and a light baryon.The Λc(2880)+ baryon was previously observed 15) by the CLEO exper-iment in the Λcpi+pi− decay mode, with a mass of (2880.9± 2.3) MeV/c2 anda width less than 8 MeV at 90% confidence level. Using BABAR data in theD0p channel leads to much more precise values, in particular with the firstmeasurement of the width of the Λc(2880)+: m = (2881.9± 0.1± 0.5) MeV/c2and Γ = (5.8 ± 1.5 ± 1.1) MeV. The existence of the decay D0p rules outvarious interpretations of this baryon 16).The new baryon Λc(2940)+ is observed with a significance above 7σ, witha mass of (2939.8± 1.3± 1.0) MeV/c2 and an intrinsic width of (17.5± 5.2±5.9) MeV. This new state could be interpreted as a udc baryon. To determineif this new state belongs to an isotriplet (analogous to Σ0c and Σ++c ), a searchfor doubly-charged partner was performed, looking at the decay mode D+p.No signal corresponding to either the Λc(2880)+ or Λc(2940)+ baryon wasobserved, which shows that both states are isoscalar.3.3 Ξc(2980)+, Ξc(3077)+/0, Ξc(3055)+ and Ξc(3123)+ baryonsThe BABAR experiment searched 17) for the excited charm-strange baryonsΞc(2980)+ and Ξc(3077)+/0, discovered previously by the Belle collaboration 18).BABAR confirms the states Ξc(2980)+, Ξc(3077)+/0, looking at the Λ+c K−pi+and Λ+c K0Spi− final states, with Λ+c → pK−pi+, pK0S, pK0Spi−pi+, Λpi+, Λpi+pi−pi+.The Ξc(2980)+ baryon is observed at a mass of (2969.3 ± 2.2 ± 1.7) MeV/c2with a width of (27±8±2) MeV. The Ξc(3077)+ is seen at a mass of (3077.0±0.4 ± 0.2) MeV/c2 with an intrinsic width of (5.5 ± 1.3 ± 0.6) MeV. BABARconfirmed also the Ξc(3077)0 state at a mass of (3079.3 ± 1.1 ± 0.2) MeV/c2with a width of (5.9±2.3±1.5) MeV. These results are in good agreement withthe values given by Belle, except for the Ξc(2980)+ baryon where the differencecould be explained by the fact that BABAR incorporates phase space effectnear the threshold and takes into account decays to Σc(2455)++K−.In addition to these confirmations, BABAR discovered a new baryon, theΞc(3055)+, and found an evidence for the Ξc(3123)+ baryon. The Ξc(3055)+and Ξc(3123)+ signals are observed only in Σc(2455)+K− and Σc(2520)+K−intermediate-resonant decays, respectively. The Ξc(3055)+ is seen with a 6.4σsignificance, with a mass of (3054.2± 1.2± 0.5) MeV/c2 and a width of (17±6±11) MeV, while the Ξc(3123)+ is observed with a 3.6σ significance at a massof (3122.9± 1.3± 0.3) MeV/c2 and with a width of (4.4± 3.4± 1.7) MeV.These baryons have same or similar decay channels as the double-charmbaryon, but are identified as single-charm based on the measured masses, nat-ural widths and charges of the members of the isospin doublet. In the currentstate of knowledge, it is difficult to assign a spin-parity to these baryons. Moretheoretical and experimental work is needed to clarify the properties of thesestates.4 ConclusionAlthough no new resonances were discovered in many years, BABAR gave animpressive list of new results since 1999. In the cs¯ sector, the D∗s0(2317)and Ds1(2460) mesons are now very well known experimentally, but no def-inite interpretation was given theoretically. The D∗sJ (2860) and DsJ (2700)mesons were discovered recently and need more experimental inputs. Manynew charmed baryon states were observed by BABAR. Thanks to the discoveryof the Ω∗0c , all ground states are now established. A lot of excited states havebeen observed, and probably many of them have yet to be discovered. The pro-duction rate, the decay channels and the measured properties (masses, widths)of these excited states will help to understand the internal quark dynamics.A lot of analyzes are still in progress with the current data set in BABAR:more decay modes for the resonances presented here are being investigated.BABAR is taking data until the end of 2008, which is the promise of moresurprises to arise.5 AcknowledgementsThe author is very grateful to the organizers of the HADRON 2007 conferencefor their support and all efforts in making this venue successful.We are also grateful for the excellent luminosity and machine conditionsprovided by our PEP-II colleagues, and for the substantial dedicated effortfrom the computing organizations that support BABAR.References1. B. Aubert et al. (BABAR Collaboration), Nucl. Instrum. Meth. A 479 1(2002).2. S. Godfrey and N. Isgur, Phys. Rev. D 32 189 (1985).3. B. Aubert et al. (BABAR Collaboration), arXiv:hep-ex/0607084 (2006).4. B. Aubert et al. (BABAR Collaboration), arXiv:0708.1565 (2007).5. S.K. Choi et al. (Belle Collaboration), Phys. Rev. Lett. 91 262001(2003) ;B. Aubert et al. (BABAR Collaboration), Phys. Rev. D74 032007 (2006).6. H-Y Cheng and W-S Hou, Phys. Lett. B566 193 (2003) ; T. Barnes, F. E.Close, and H. J. Lipkin, Phys. Rev. D68 054006 (2003) ; A. Szczepaniak,Phys. Lett. B567 23 (2003).7. B. Aubert et al. (BABAR Collaboration), Phys. Rev. Lett. 97 222001(2006).8. E. van Beveren, and G. Rupp, Phys. Rev. Lett. 97 202001 (2006) ; P.Colangelo, F. De Fazio, and S. Nicotri, Phys. Lett. B642 48 (2006).9. J. Brodzicka et al. (Belle Collaboration), arXiv:0707.3491 (2007) ; B.Aubert et al. (BABAR Collaboration), preliminary (2007).10. M. A. Nowak, M. Rho, and I. Zahed, Phys. Polon. B 35, 2377 (2004).11. B. Aubert et al. (BABAR Collaboration), Phys. Rev. Lett. 99 062001(2007).12. B. Aubert et al. (BABAR Collaboration), Phys. Rev. Lett. 97 232001(2006).13. N. Mathur et al., Phys. Rev. Lett. B592, 1 (2004) ; R. M. Woloshyn, Nucl.Phys. Proc. Suppl. 93, 38 (2001).14. B. Aubert et al. (BABAR Collaboration), Phys. Rev. Lett. 98, 012001(2007).15. M. Artuso et al. (CLEO), Phys. Rev. Lett. 86, 4479 (2001).16. A. E. Blechman, A. F. Falk, D. Pirjol, and J. M. Yelton, Phys. Rev. D67,074033 (2003).17. B. Aubert et al. (BABAR Collaboration), arXiv:hep-ex/0607042 (2006) ;B. Aubert et al. (BABAR Collaboration), preliminary (2007).18. R. Chistov et al. (Belle Collaboration), arXiv:hep-ex/0606051 (2006).

Charm Spectroscopy at BaBar

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